FOOTNOTE:

[1] Malthus himself said, "It is probable that, having found the bow

bent too much one way, I was induced to bend it too much the other in

order to make it straight."

MALTON, a market town in the Thirsk and Malton parliamentary division of

Yorkshire, England, 21 m. N.E. of York by a branch of the North Eastern

railway. The town comprises Old Malton and New Malton in the North

Riding, and Norton on the opposite side of the river Derwent, in the

East Riding. Pop. of urban district of Malton (1901), 4758; of urban

district of Norton 3842. The situation, on the wooded hills rising from

the narrow valley, is very picturesque. The church of St Michael is a

fine late Norman building with perpendicular tower; the church of St

Leonard, of mixed architecture, with square tower and spire, has three

Norman arches and a Norman font. The church of St Mary at Old Malton was

attached to a Gilbertine priory founded in 1150; it is transitional

Norman and Early English, with later insertions. Remains of the priory

are scanty, but include a crypt under a modern house. In the

neighbourhood of Malton are the slight but beautiful fragments of

Kirkham Abbey, an Early English Augustinian foundation of Walter l'Espec

(1131); and the fine mansion of Castle Howard, a massive building by

Vanbrugh, the seat of the earls of Carlisle, containing a noteworthy

collection of pictures. Malton possesses a town-hall, a corn exchange, a

museum, and a grammar-school founded in 1547. There are iron and brass

foundries, agricultural implement works, corn mills, tanneries and

breweries. In the neighbourhood are lime and whinstone quarries.

Traces of a Romano-British village exist on the east side of the town,

but there appears to be no history of Malton before the Norman Conquest.

The greater part of Malton belonged to the crown in 1086 and was

evidently retained until Henry I. gave the castle and its appurtenances

to Eustace son of John, whose descendants took the name of Vescy.

Eustace meditated the deliverance of Malton Castle to King David of

Scotland in 1138, but his plans were altered owing to the battle of the

Standard. The "burgh" of Malton is mentioned in 1187, and in 1295 the

town returned two members to parliament. It was not represented again,

however, until 1640, when an act was passed to restore its ancient

privileges. In 1867 the number of members was reduced to one, and in

1885 the town was disfranchised. Until the 17th century the burgesses

had all the privileges of a borough by prescriptive right, and were

governed by two bailiffs and two under-bailiffs, but these liberties

were taken from them in 1684 and have never been revived. From that time

a bailiff and two constables were appointed at the court leet of the

lord of the manor until a local board was formed in 1854. In the 13th

century Agnes de Vescy, then lady of the manor, held a market in Malton

by prescription, and Camden writing about 1586 says that the lord of the

manor then held two weekly markets, on Tuesday and Saturday, the last

being the best cattle market in the county. The markets are now held on

Saturdays and alternate Tuesdays, and still belong to the lord of the

manor.

MALTZAN, HEINRICH VON, BARON ZU WARTENBURG UND PENZLIN (1826-1874),

German traveller, was born on the 6th of September 1826 near Dresden. He

studied law at Heidelberg, but on account of ill health spent much of

his time from 1850 in travel. Succeeding to his father's property in

1852, he extended the range of his journeys to Morocco and other parts

of Barbary, and before his return home in 1854 had also visited Egypt,

Palestine and other countries of the Levant. In 1856-1857 he was again

in Algeria; in 1858 he reached the city of Morocco; and in 1860 he

succeeded in performing the pilgrimage to Mecca, which he afterwards

described in _Meine Wallfahrt nach Mecca_ (Leipzig, 1865), but had to

flee for his life to Jidda without visiting Medina. He then visited Aden

and Bombay, and after some two years of study in Europe again began to

wander through the coasts and islands of the Mediterranean, repeatedly

visiting Algeria. His first book of travel, _Drei Jahre im Nordwesten

von Afrika_ (Leipzig), appeared in 1863, and was followed by a variety

of works and essays, popular and scientific. Maltzan's last book, _Reise

nach Südarabien_ (Brunswick, 1873), is chiefly valuable as a digest of

much information about little-known parts of south Arabia collected from

natives during a residence at Aden in 1870-1871. Among his other

services to science must be noticed his collection of Punic inscriptions

(_Reise in Tunis und Tripolis_, Leipzig, 1870), and the editing of

Adolph von Wrede's remarkable journey in Hadramut (_Reise in Hadramaut_,

&c., Brunswick, 1870). After long suffering from neuralgia, Maltzan died

by his own hand at Pisa on the 23rd of February 1874.

MALUS, ÉTIENNE LOUIS (1775-1812), French physicist, was born at Paris on

the 23rd of June 1775. He entered the military engineering school at

Mezières; but, being regarded as a suspected person, he was dismissed

without receiving a commission, and obliged to enter the army as a

private soldier. Being employed upon the fortifications of Dunkirk, he

attracted the notice of the director of the works, and was selected as a

member of the École polytechnique then to be established under G. Monge.

After three years at the École he was admitted into the corps of

engineers, and served in the army of the Sambre and Meuse; he was

present at the passage of the Rhine in 1797, and at the affairs of

Ukratz and Altenkirch. In 1798 he joined the Egyptian expedition and

remained in the East till 1801. On his return he held official posts

successively at Antwerp, Strassburg and Paris, and devoted himself to

optical research. A paper published in 1809 ("Sur une propriété de la

lumière réfléchie par les corps diaphanes") contained the discovery of

the polarization of light by reflection, which is specially associated

with his name, and in the following year he won a prize from the

Institute with his memoir, "Théorie de la double refraction de la

lumière dans les substances cristallines." He died of phthisis in Paris

on the 23rd of February 1812.

MALVACEAE, in botany, an order of Dicotyledons belonging to the series

Columniferae, to which belong also the orders Tiliaceae (containing

_Tilia_, the lime-tree), Bombaceae (containing _Adansonia_, the baobab),

Sterculiaceae (containing _Theobroma_, cocoa, and _Colo_, cola-nut). It

contains 39 genera with about 300 species, and occurs in all regions

except the coldest, the number of species increasing as we approach the

tropics. It is represented in Britain by three genera: _Malva_, mallow;

_Althaea_, marsh-mallow; and _Lavatera_, tree-mallow. The plants are

herbs, as in the British mallows, or, in the warmer parts of the earth,

shrubs or trees. The leaves are alternate and often palmately lobed or

divided; the stipules generally fall early. The leaves and young shoots

often bear stellate hairs and the tissues contain mucilage-sacs. The

regular, hermaphrodite, often showy flowers are borne in the leaf-axils,

solitary or in fasicles, or form more or less complicated cymose

arrangements. An epicalyx (see MALLOW, figs. 3, 4), formed by a whorl of

three or more bracteoles is generally present just beneath the calyx;

sometimes, as in _Abutilon_, it is absent. The parts of the flowers are

typically in fives (fig. 1); the five sepals, which have a valvate

aestivation, are succeeded by five often large showy petals which are

twisted in the bud; they are free to the base, where they are attached

to the staminal tube and fall with it when the flower withers. The very

numerous stamens are regarded as arising from the branching of a whorl

of five opposite the petals; they are united into a tube at the base,

and bear kidney-shaped one-celled anthers which open by a slit across

the top (fig. 2). The large spherical pollen-grains are covered with

spines. The carpels are one to numerous; when five in number, as in

_Abutilon_, they are opposite the petals, or, as in _Hibiscus_, opposite

the sepals. In the British genera and many others they are numerous,

forming a whorl round the top of the axis in the centre of the flower,

the united styles rising from the centre and bearing a corresponding

number of stigmatic branches. In _Malope_ the numerous carpels are

arranged one above the other in vertical rows. One or more anatropous

ovules are attached to the inner angle of each carpel; they are

generally ascending but sometimes pendulous or horizontal; the position

may vary, as in _Abutilon_, in one and the same carpel.

[Illustration: FIG. 1.--Floral Diagram of Hollyhock (_Althaea rosea_).

a, Stamens.

b, Bract.

g, Pistil of carpels.

i, Epicalyx, formed from an involucre of bracteoles.

p, Petals.

s, Sepals.]

[Illustration: FIG. 2.

1, Anther.

2, Pollen grain of Hollyhock (_Althaea rosea_) enlarged. The pollen

grain bears numerous spines, the dark spots indicate thin places in

the extine.]

The flowers are proterandrous; when the flower opens the unripe stigmas

are hidden in the staminal tube and the anthers occupy the centre of the

flower; as the anthers dehisce the filaments bend backwards and finally

the ripe stigmas spread in the centre. Pollination is effected by

insects which visit the flower for the honey, which is secreted in pits

one between the base of each petal and is protected from rain by hairs

on the lower margin of the petals. In small pale-flowered forms, like

_Malva rotundifolia_, which attract few insects, self-pollination has

been observed, the style-arms twisting to bring the stigmatic surfaces

into contact with the anthers.

Except in _Malvaviscus_ which has a berry, the fruits are dry. In

_Malva_ (see MALLOW) and allied genera they form one-seeded schizocarps

separating from the persistent central column and from each other. In

_Hibiscus_ and _Gossypium_ (cotton-plant, q.v.), the fruit is a capsule

splitting loculicidally. Distribution of the seeds is sometimes aided by

hooked outgrowths on the wall of the schizocarp, or by a hairy covering

on the seed, an extreme case of which is the cotton-plant where the seed

is buried in a mass of long tangled hairs--the cotton. The embryo is

generally large with much-folded cotyledons and a small amount of

endosperm.

The largest genus, _Hibiscus_, contains 150 species, which are widely

distributed chiefly in the tropics; _H. rosasinensis_ is a well-known

greenhouse plant. _Abutilon_ (q.v.) contains 80 species, mainly

tropical; _Lavatera_, with 20 species, is chiefly Mediterranean;

_Althaea_ has about 15 species in temperate and warm regions, _A.

rosea_ being the hollyhock (q.v.); _Malva_ has about 30 species in the

north-temperate zone. Several genera are largely or exclusively

American.

MALVASIA (Gr. _Monemvasia_, i.e. the "city of the single approach or

entrance"; Ital. _Napoli di Malvasia_; Turk. _Mengeshe_ or _Beneshe_),

one of the principal fortresses and commercial centres of the Levant

during the middle ages, still represented by a considerable mass of

ruins and a town of about 550 inhabitants. It stood on the east coast of

the Morea, contiguous to the site of the ancient Epidaurus Limera, of

which it took the place. So extensive was its trade in wine that the

name of the place became familiar throughout Europe as the distinctive

appellation of a special kind--Ital. _Malvasia_; Span. _Malvagia_; Fr.

_Malvoisie_; Eng. _Malvesie_ or _Malmsey_. The wine was not of local

growth, but came for the most part from Tenos and others of the

Cyclades.

As a fortress Malvasia played an important part in the struggles

between Byzantium, Venice and Turkey. The Byzantine emperors

considered it one of their most valuable posts in the Morea, and

rewarded its inhabitants for their fidelity by unusual privileges.

Phrantzes (Lib. IV. cap. xvi.) tells how the emperor Maurice made the

city (previously dependent in ecclesiastical matters on Corinth) a

metropolis or archbishop's see, and how Alexius Comnenus, and more

especially Andronicus II. (Palaeologus) gave the Monembasiotes freedom

from all sorts of exactions throughout the empire. It was captured

after a three years' siege by Guillaume de Villehardouin in 1248, but

the citizens retained their liberties and privileges, and the town was

restored to the Byzantine emperors in 1262. After many changes, it

placed itself under Venice from 1463 to 1540, when it was ceded to the

Turks. In 1689 it was the only town of the Morea which held out

against Morosini, and Cornaro his successor only succeeded in reducing

it by famine. In 1715 it capitulated to the Turks, and on the failure

of the insurrection of 1770 the leading families were scattered

abroad. As the first fortress which fell into the hands of the Greeks

in 1821, it became in the following year the seat of the first

national assembly.

See Curtius, _Peloponnesos_, ii. 293 and 328; Castellan, _Lettres sur

la Morée_ (1808), for a plan; Valiero, _Hist. della guerra di Candia_

(Venice, 1679), for details as to the fortress; W. Miller in _Journal

of Hellenic Studies_ (1907).

MALVERN, an inland watering-place in the Bewdley parliamentary division

of Worcestershire, England, 128 m. W.N.W. from London by the Great

Western railway, served also by a branch of the Midland railway from

Ashchurch on the Bristol-Birmingham line. Pop. of urban district(1901),

16,449. It is beautifully situated on the eastern slopes of the Malvern

Hills, which rise abruptly from the flat valley of the Severn to a

height of 1395 ft. in the Worcestershire Beacon. The district still

bears the name of Malvern Chase, originally a Crown-land and forest,

though it was granted to the earldom of Gloucester by Edward I. A ditch

along the summit of the hills determined the ancient boundary. Becoming

a notorious haunt of criminals, the tract was disafforested by Charles

I., with the exception of a portion known as the King's Chase, part of

which is included in the present common-land formed under the Malvern

Hills Act of 1884.

Malvern was in early times an important ecclesiastical settlement, but

its modern fame rests on its fine situation, pure air, and chalybeate

and bituminous springs. The open-air cure for consumptive patients is

here extensively practised.

The name Malvern is collectively applied to a line of small towns and

villages, extending along the foot of the hills for 5 m. The principal

is GREAT MALVERN, lying beneath the Worcestershire Beacon. It has a

joint station of the Great Western and Midland railways. Here was the

Benedictine priory which arose in 1083 out of a hermitage endowed by

Edward the Confessor. The priory church of SS. Mary and Michael is a

fine cruciform Perpendicular building, with an ornate central tower,

embodying the original Norman nave, and containing much early glass and

carved choir-stalls. The abbey gate and the refectory also remain.

There are here several hydropathic establishments, and beautiful

pleasure gardens. Malvern College, founded in 1862, is an important

English public school. A museum is attached to it. Mineral waters are

manufactured. At MALVERN WELLS, 2½ m. S., are the principal medicinal

springs, also the celebrated Holy Well, the water of which is of perfect

purity. There are extensive fishponds and hatcheries; and golf-links.

The Great Western railway has a station, and the Midland one at Hanley

Road. LITTLE MALVERN lies at the foot of the Herefordshire Beacon, which

is crowned by a British camp, 1½ m. S. of Malvern Wells. There was a

Benedictine priory here, of which traces remain in the church. MALVERN

LINK, 1 m. N.E. of Great Malvern, of which it forms a suburb, has a

station on the Great Western railway. WEST MALVERN and NORTH MALVERN,

named from their position relative to Great Malvern, are pleasant

residential quarters on the higher slopes of the hills.

MALWA, an historic province of India, which has given its name to one of

the political agencies into which Central India is divided. Strictly,

the name is confined to the hilly table-land, bounded S. by the Vindhyan

range, which drains N. into the river Chambal; but it has been extended

to include the Nerbudda valley farther south. Its derivation is from the

ancient tribe of Malavas about whom very little is known, except that

they founded the Vikrama Samvat, an era dating from 57 B.C., which is

popularly associated with a mythical king Vikramaditya. The earliest

name of the tract seems to have been Avanti, from its capital the modern

Ujjain. The position of the Malwa or Moholo mentioned by Hsuan Tsang

(7th century) is plausibly assigned to Gujarat. The first records of a

local dynasty are those of the Paramaras, a famous Rajput clan, who

ruled for about four centuries (800-1200), with their capital at Ujjain

and afterwards at Dhar. The Mahommedans invaded Malwa in 1235; and in

1401 Dilawar Khan Ghori founded an independent kingdom, which lasted

till 1531. The greatest ruler of this dynasty was Hoshang Shah

(1405-1435), who made Mandu (q.v.) his capital and embellished it with

magnificent buildings. In 1562 Malwa was annexed to the Mogul empire by

Akbar. On the break-up of that empire, Malwa was one of the first

provinces to be conquered by the Mahrattas. About 1743 the Mahratta

peshwa obtained from Delhi the title of governor, and deputed his

authority to three of his generals--Sindhia of Gwalior, Holkar of

Indore, and the Ponwar of Dhar who claims descent from the ancient

Paramaras. At the end of the 18th century Malwa became a cockpit for

fighting between the rival Mahratta powers, and the headquarters of the

Pindaris or irregular plunderers. The Pindaris were extirpated by the

campaign of Lord Hastings in 1817, and the country was reduced to order

by the energetic rule of Sir John Malcolm. Malwa is traditionally the

land of plenty, in which sufferers from famine in the neighbouring

tracts always take refuge. But in 1899-1900 it was itself visited by a

severe drought, which seriously diminished the population, and has since

been followed by plague. The most valuable product is opium.

The Malwa agency has an area of 8919 sq. m. with a population (1901) of

1,054,753. It comprises the states of Dewas (senior and junior branch),

Jaora, Ratlam, Sitamau and Sailana, together with a large portion of

Gwalior, parts of Indore and Tonk, and about 35 petty estates and

holdings. The headquarters of the political agent are at Nimach.

Malwa is also the name of a large tract in the Punjab, south of the

river Sutlej, which is one of the two chief homes of the Sikhs, the

other being known as Manjha. It includes the British districts of

Ferozpore and Ludhiana, together with the native states of Patiala,

Jind, Nabha and Maler Kotla.

See J. Malcolm, _Central India_ (1823); C. E. Luard, _Bibliography of

Central India_ (1908), and _The Paramars of Dhar and Malwa_ (1908).

MAMARONECK, a township of Westchester county, New York, U.S.A., on Long

Island Sound, about 20 m. N.E. of New York City and a short distance

N.E. of New Rochelle. Pop. (1890), 2385; (1900) 3849; (1905) 5655;

(1910) 5602. Mamaroneck is served by the New York, New Haven & Hartford

railway. The township includes the village of Larchmont (pop. in 1910,

1958), incorporated in 1891, and part of the village of Mamaroneck (pop.

in 1910, including the part in Rye township, 5699), incorporated in

1895. Larchmont is the headquarters of the Larchmont Yacht Club. The

site of Mamaroneck township was bought in 1660 from the Indians by John

Richbell, an Englishman, who obtained an English patent to the tract in

1668. The first settlement was made by relatives of his on the site of

Mamaroneck village in 1676, and the township was erected in 1788. On the

28th of August 1776, near Mamaroneck, a force of American militiamen

under Capt. John Flood attacked a body of Loyalist recruits under

William Lounsbury, killing the latter and taking several prisoners. Soon

afterwards Mamaroneck was occupied by the Queen's Rangers under Colonel

Robert Rogers. On the night of the 21st of October an attempt of a force

of Americans under Colonel John Haslet to surprise the Rangers failed,

and the Americans, after a hand-to-hand fight, withdrew with 36

prisoners. Mamaroneck was the home of John Peter DeLancey (1753-1828), a

Loyalist soldier in the War of Independence, and was the birthplace of

his son William Heathcote DeLancey (1797-1865), a well-known Protestant

Episcopal clergyman, provost of the University of Pennsylvania in

1827-1832 and bishop of western New York from 1839 until his death.

James Fenimore Cooper, the novelist, married (1811) a daughter of John

Peter DeLancey; lived in Mamaroneck for several years, and here wrote

his first novel, _Precaution_, and planned _The Spy_.

MAMELI, GOFFREDO (1827-1849), Italian poet and patriot, was born at

Genoa of a noble Sardinian family. He received a sound classical

education at the Scolopi College, and later studied law and philosophy

at the university of Genoa. When nineteen years old he corresponded with

Mazzini, to whom he became whole-heartedly devoted; among other

patriotic poems he wrote a hymn to the Bandiera brothers, and in the

autumn of 1847 a song called "Fratelli d'Italia," which as Carducci

wrote, "resounded through every district and on every battlefield of the

peninsula in 1848 and 1849." Mameli served in the National Guard at

Genoa, and then joined the volunteers in the Lombard campaign of 1848,

but after the collapse of the movement in Lombardy he went to Rome,

where the republic was proclaimed and whence he sent the famous despatch

to Mazzini: "Roma! Repubblica! Venite!" At first he wrote political

articles in the newspapers, but when the French army approached the city

with hostile intentions he joined the fighting ranks and soon won

Garibaldi's esteem by his bravery. Although wounded in the engagement of

the 30th of April, he at once resumed his place in the ranks, but on the

3rd of June he was again wounded much more severely, and died in the

Pellegrini hospital on the 6th of July 1849. Besides the poems mentioned

above, he wrote hymns to Dante, to the Apostles, "Dio e popolo," &c. The

chief merit of his work lies in the spontaneity and enthusiasm for the

Italian cause which rendered it famous, in spite of certain technical

imperfections, and he well deserved the epithet of "The Tyrtaeus of the

Italian revolution."

See A. G. Barrili, "G. Mameli nella vita e nell' arte," in _Nuova

Antologia_ (June 1, 1902); the same writer's edition of the _Scritti

editi ed inediti di G. Mameli_ (Genoa, 1902); Countess Martinengo

Cesaresco, _Italian Characters_ (London, 1901); A. Luzio, _Profili

Biografici_ (Milan, 1906); G. Trevelyan, _Garibaldi's Defence of the

Roman Republic_ (London, 1907).

MAMELUKE (anglicized through the French, from the Arabic _mamluk_, a

slave), the name given to a series of Egyptian sultans, originating

(1250) in the usurpation of supreme power by the bodyguard of Turkish

slaves first formed in Egypt under the successors of Saladin. See EGYPT:

_History_ (Moslem period).

MAMERTINI, or "children of Mars," the name taken by a band of Campanian

(or Samnite) freebooters who about 289 B.C. seized the Greek colony of

Messana at the north-east corner of Sicily, after having been hired by

Agathocles to defend it (Polyb. 1. 7. 2). The adventure is explained by

tradition (e.g. Festus 158, Müller) as the outcome of a _ver sacrum_;

the members of the expedition are said to have been the male children

born in a particular spring of which the produce had been vowed to

Apollo (cf. SAMNITES), and to have settled first in Sicily near

Tauromenium. An inscription survives (R. S. Conway, _Italic Dialects_,

1) which shows that they took with them the Oscan language as it was

spoken in Capua or Nola at that date, and the constitution usual in

Italic towns of a free community (_touta_ =) governed by two annual

magistrates (_meddices_). The inscription dedicated some large building

(possibly a fortification) to Apollo, which so far confirms the

tradition just noticed. Though in the Oscan language, the inscription is

written in the Greek alphabet common to south Italy from the 4th century

B.C. onwards, viz. the Tarentine Ionic, and so are the legends of two

coins of much the same date as the inscription (Conway, ib. 4). From 282

onwards (B. V. Head, _Historia numorum_, 136) the legend itself is

Graecized ([Greek: MAMERTINON] instead of [Greek: MAAMERTINOUM]) which

shows how quickly here, as everywhere, "Graecia capta ferum victorem

cepit." On the Roman conquest of Sicily the town secured an independence

under treaty (Cicero, _Verr._ 3. 6. 13). The inhabitants were still

called Mamertines in the time of Strabo (vi. 2. 3).

See further Mommsen, _C.I.L._ x. sub loc., and the references already

given. (R. S. C.)

MAMERTINUS, CLAUDIUS (4th century A.D.), one of the Latin panegyrists.

After the death of Julian, by whom he was evidently regarded with

special favour, he was praefect of Italy (365) under Valens and

Valentinian, but was subsequently (368) deprived of his office for

embezzlement. He was the author of an extant speech of thanks to Julian

for raising him to the consulship, delivered on the 1st of January 362

at Constantinople. Two panegyrical addresses (also extant) to Maximian

(emperor A.D. 286-305) are attributed to an older _magister_ Mamertinus,

but it is probable that the corrupt MS. superscription contains the word

_memoriae_, and that they are by an unknown _magister memoriae_ (an

official whose duty consisted in communicating imperial rescripts and

decisions to the public). The first of these was delivered on the

birthday of Rome (April 21, 289), probably at Maximian's palace at

Augusta Trevirorum (Trèves), the second in 290 or 291, on the birthday

of the emperor. By some they are attributed to Eumenius (q.v.) who was a

_magister memoriae_ and the author of at least one (if not more)

panegyrics.

The three speeches will be found in E. Bahrens, _Panegyrici latini_

(1874); see also Teuffel-Schwabe, _Hist. of Roman Literature_ (Eng.

trans.), § 417. 7.

MAMIANI DELLA ROVERE, TERENZIO, COUNT (1802-1885), Italian writer and

statesman, was born at Pesaro in 1799. Taking part in the outbreaks at

Bologna arising out of the accession of Pope Gregory XVI., he was

elected deputy for Pesaro to the assembly, and subsequently appointed

minister of the interior; but on the collapse of the revolutionary

movement he was exiled. He returned to Italy after the amnesty of 1846,

and in 1848 he was entrusted with the task of forming a ministry. He

remained prime minister, however, only for a few months, his political

views being anything but in harmony with those of the pope. He

subsequently retired to Genoa where he worked for Italian unity, was

elected deputy in 1856, and in 1860 became minister of education under

Cavour. In 1863 he was made minister to Greece, and in 1865 to

Switzerland, and later senator and councillor of state. Meanwhile, he

had founded at Genoa in 1849 the Academy of Philosophy, and in 1855 had

been appointed professor of the history of philosophy at Turin; and he

published several volumes, not only on philosophical and social

subjects, but of poetry, among them _Rinnovamente della filosofia antica

italiana_ (1836), _Teoria della Religione e dello stato_ (1869), _Kant e

l'ontologia_ (1879), _Religione dell' avenire_ (1880), _Di un nuovo

diritto europeo_ (1843, 1857). He died at Rome on the 21st of May, 1885.

See _Indice delle opere di Terenzio Mamiani_ (Pesaro, 1887); Gaspare,

_Vita di Terenzio Mamiani_ (Ancona, 1887); Barzellotti, _Studii e

ritratti_ (Bologna, 1893).

MAMMALIA (from Lat. _mamma_, a teat or breast), the name proposed by the

Swedish naturalist Linnaeus for one of the classes, or primary

divisions, of vertebrated animals, the members of which are collectively

characterized by the presence in the females of special glands secreting

milk for the nourishment of the young. With the exception of the lowest

group, such glands always communicate with the exterior by means of the

teats, nipples or mammae, from which the class derives its name. The

class-name (modified by the French into _Mammifères_, and replaced in

German by the practically equivalent term _Säugethiere_) has been

anglicized into "Mammals" (mammal, in the singular). Of recent years,

and more especially in America, it has become a custom to designate the

study of mammals by the term "mammalogy." Etymologically, however, that

designation cannot be justified; for it is of hybrid (Latin and Greek)

origin, and is equivalent to "mastology," the science which deals with

the mammary gland (Gr. [Greek: mastos], woman's breast), a totally

different signification. As regards existing forms of life, the

limitations of the class are perfectly well defined and easy of

recognition; for although certain groups (not, by the way, whales,

which, although excluded in popular estimation from the class, are in

all essential respects typical mammals) are exceedingly aberrant, and

present structural features connecting them with the lower vertebrate

classes, yet they are by common consent retained in the class to which

they are obviously most nearly affiliated by their preponderating

characteristics. There is thus at the present day a great interval,

unbridged by any connecting links, between mammals and the other classes

of vertebrates.

Not so, however, when the extinct forms of vertebrate life are taken

into consideration, for there is a group of reptiles from the early part

of the Secondary, or Mesozoic period, some of whose members must have

been so intimately related to mammals that, were the whole group fully

known, it would clearly be impossible to draw a distinction between

Mammalia on the one hand and Reptilia on the other. Indeed, as it is, we

are already partially acquainted with one of these early intermediate

creatures (_Tritylodon_), which forms a kind of zoological shuttlecock,

being, so to speak, hit from one group to another, and back again, by

the various zoologists by whom its scanty remains have been studied.

Considered collectively, mammals, which did not make their appearance on

the earth for some time after reptiles had existed, are certainly the

highest group of the whole vertebrate sub-kingdom. This expression must

not, however, be considered in too restricted a sense. In mammals, as in

other classes, there are low as well as high forms; but by any tests

that can be applied, especially those based on the state of development

of the central nervous system, it will be seen that the average exceeds

that of any other class, that many species of this class far excel those

of any other in perfection of structure, and that it contains one form

which is unquestionably the culminating point amongst organized beings.

Mammals, then, are vertebrated animals, possessing the normal

characteristics of the members of that primary division of the animal

kingdom. They are separated from fishes and batrachians (Pisces and

Batrachians) on the one hand, and agree with reptiles, and birds

(Reptilia and Aves) on the other, in the possession during intra-uterine

life of the membranous vascular structures respectively known as the

amnion and the allantois, and likewise in the absence at this or any

other period of external gills. A four-chambered heart, with a complete

double circulation, and warm blood (less markedly so in the lowest group

than in the rest of the class), distinguish mammals from existing

reptiles, although not from birds. From both birds and reptiles the

class is distinguished, so far at any rate as existing forms are

concerned, by the following features: the absence of a nucleus in the

red corpuscles of the blood, which are nearly always circular in

outline; the free suspension of the lungs in a thoracic cavity,

separated from the abdominal cavity by a muscular partition, or

diaphragm, which is the chief agent in inflating the lungs in

respiration; the aorta, or main artery, forming but a single arch after

leaving the heart, which curves over the left terminal division of the

windpipe, or bronchus; the presence of more or fewer hairs on the skin

and the absence of feathers; the greater development of the bridge, or

commissure, connecting the two halves of the brain, which usually forms

a complete corpus callosum, or displays an unusually large size of its

anterior portion; the presence of a fully developed larynx at the upper

end of the trachea or windpipe, accompanied by the absence of a syrinx,

or expansion, near the lower end of the same; the circumstance that each

half of the lower jaw (except perhaps at a very early stage of

development) consists of a single piece articulating posteriorly with

the squamosal element of the skull without the intervention of a

separate quadrate bone; the absence of prefrontal bones in the skull;

the presence of a pair of lateral knobs, or condyles (in place of a

single median one), on the occipital aspect of the skull for

articulation with the first vertebra; and, lastly, the very obvious

character of the female being provided with milk-glands, by the

secretion of which the young (produced, except in the very lowest group,

alive and not by means of externally hatched eggs) are nourished for

some time after birth.

In the majority of mammals both pairs of limbs are well developed and

adapted for walking or running. The fore-limbs may, however, be

modified, as in moles, for burrowing, or, as in bats, for flight, or

finally, as in whales and dolphins, for swimming, with the assumption in

this latter instance of a flipper-like form and the complete

disappearance of the hind-limbs. Special adaptations for climbing are

exhibited by both pairs of limbs in opossums, and for hanging to boughs

in sloths. In no instance are the fore-limbs wanting.

In the great majority of mammals the hind extremity of the axis of the

body is prolonged into a tail. Very generally the tail has distinctly

the appearance of an appendage, but in some of the lower mammals, such

as the thylacine among marsupials, and the aard-vark or ant-bear among

the edentates, it is much thickened at the root, and passes insensibly

into the body, after the fashion common among reptiles. As regards

function, the tail may be a mere pendent appendage, or may be adapted to

grasp boughs in climbing, or even to collect food or materials for a

nest or sleeping place, as in the spider-monkeys, opossums and

rat-kangaroos. Among jumping animals it may serve as a balance, as in

the case of jerboas and kangaroos, while in the latter it is also used

as a support when resting; among many hoofed mammals it is used as a

fly-whisk; and in whales and dolphins, as well as in the African

_Potamogale_ and the North American musquash, it plays an important part

in swimming. Its supposed use as a trowel by the beaver is, however, not

supported by the actual facts of the case.

As already indicated, the limbs of different mammals are specially

modified for various modes of life; and in many cases analogous

modifications occur, in greater or less degree, throughout the entire

body. Those modifications most noticeable in the case of cursorial types

may be briefly mentioned as examples. In this case, as might be

expected, the greatest modifications occur in the limbs, but correlated

with this is also an elongation of the head and neck in long-legged

types. Adaptation for speed is further exhibited in the moulding of the

shape of the body so as to present the minimum amount of resistance to

the air, as well as in increase in heart and lung capacity to meet the

extra expenditure of energy. Finally, in the jumping forms we meet with

an increase in the length and weight of the tail, which has to act as a

counterpoise. As regards the feet, a reduction in the number of digits

from the typical five is a frequent feature, more especially among the

hoofed mammals, where the culmination in this respect is attained by the

existing members of the horse tribe and certain representatives of the

extinct South American _Proterotheriidae_, both of which are

monodactyle. Brief reference may also be made to the morphological

importance of extraordinary length or shortness in the skulls of

mammals--dolichocephalism and brachycephalism; both these features being

apparently characteristic of specialized types, the former condition

being (as in the horse) often, although not invariably, connected with

length of limb and neck, and adaptation to speed, while brachycephalism

may be correlated with short limbs and an abbreviated neck. Exceptions

to this rule, as exemplified by the cats, are due to special adaptive

causes. In point of bodily size mammals present a greater range of

variation than is exhibited by any other living terrestrial animals, the

extremes in this respect being displayed by the African elephant on the

one hand and certain species of shrew-mice (whose head and body scarcely

exceed an inch and a half in length) on the other. When the aquatic

members of the class are taken into consideration, the maximum

dimensions are vastly greater, Sibbald's rorqual attaining a length of

fully 80 ft., and being probably the bulkiest and heaviest animal that

has ever existed. Within the limits of individual groups, it may be

accepted as a general rule that increase in bulk or stature implies

increased specialization; and, further, that the largest representatives

of any particular group are also approximately the latest. The latter

dictum must not, however, be pushed to an extreme, since the African

elephant, which is the largest living land mammal, attaining in

exceptional cases a height approaching 12 ft., was largely exceeded in

this respect by an extinct Indian species, whose height has been

estimated at between 15 and 16 ft.

In regard to sense-organs, ophthalmoscopic observations on the eyes of

living mammals (other than man) have revealed the existence of great

variation in the arrangement of the blood-vessels, as well as in the

colour of the retina; blue and violet seem to be unknown, while red,

yellow and green form the predominating shades. In the main, the various

types of minute ocular structure correspond very closely to the

different groups into which mammals are divided, this correspondence

affording important testimony in the favour of the general correctness

of the classification. Among the exceptions are the South American

squirrel-monkeys, whose eyes approximate in structure to those of the

lemurs. Man and monkeys alone possess parallel and convergent vision of

the two eyes, while a divergent, and consequently a very widely

extended, vision is a prerogative of the lower mammals; squirrels, for

instance, and probably also hares and rabbits, being able to see an

object approaching them directly from behind without turning their

heads.

An osteological question which has been much discussed is the fate of

the reptilian quadrate bone in the mammalian skull. In the opinion of F.

W. Thyng, who has carefully reviewed all the other theories, the balance

of evidence tends to show that the quadrate has been taken up into the

inner ear, where it is represented among the auditory ossicles by the

incus.

Although the present article does not discuss mammalian osteology in

general (for which see VERTEBRATA), it is interesting to notice in this

connexion that the primitive condition of the mammalian tympanum

apparently consisted merely of a small and incomplete bony ring, with,

at most, an imperfect ventral wall to the tympanic cavity, and that a

close approximation to this original condition still persists in the

monotremes, especially _Ornithorhynchus_. The tympano-hyal is the

characteristic mammalian element in this region; but the entotympanic

likewise appears to be peculiar to the class, and to be unrepresented

among the lower vertebrates. The tympanum itself has been regarded as

representing one of the elements--probably the supra-angular--of the

compound reptilian lower jaw. The presence of only seven vertebrae in

the neck is a very constant feature among mammals; the exceptions being

very few.

Two other points in connexion with mammalian osteology may be noticed. A

large number of mammals possess a perforation, or foramen, on the inner

side of the lower end of the humerus, and also a projection on the shaft

of the femur known as the third trochanter. From its occurrence in so

many of the lower vertebrates, the entepicondylar foramen of the

humerus, as it is called, is regarded by Dr E. Stromer as a primitive

structure, of which the original object was to protect certain nerves

and blood-vessels. It is remarkable that it should persist in the

spectacled bear of the Andes, although it has disappeared in all other

living members of the group. The third trochanter of the femur, on the

other hand, can scarcely be regarded as primitive, seeing that it is

absent in several of the lower groups of mammals. Neither can its

presence be attributed, as Professor A. Gaudry suggests, to the

reduction in the number of the toes, as otherwise it should not be found

in the rhinoceros. Its general absence in man forbids the idea of its

having any connexion with the upright posture.

_Hair._--In the greater number of mammals the skin is more or less

densely clothed with a peculiarly modified form of epidermis known as

hair. This consists of hard, elongated, slender, cylindrical or

tapering, thread-like masses of epidermic tissue, each of which grows,

without branching, from a short prominence, or papilla, sunk at the

bottom of a pit, or follicle, in the true skin, or dermis. Such hairs,

either upon different parts of the skin of the same species, or in

different species, assume very diverse forms and are of various sizes

and degrees of rigidity--as seen in the fur of the mole, the bristles

of the pig, and the spines of the hedgehog and porcupine, which are

all modifications of the same structures. These differences arise

mainly from the different arrangement of the constituent elements into

which the epidermal cells are modified. Each hair is composed usually

of a cellular pithy internal portion, containing much air, and a

denser or more horny external or cortical part. In some mammals, as

deer, the substance of the hair is almost entirely composed of the

central medullary or cellular substance, and is consequently very

easily broken; in others the horny part prevails almost exclusively,

as in the bristles of the wild boar. In the three-toed sloth

(_Bradypus_) the hairs have a central horny axis and a pithy exterior.

Though generally nearly smooth, or but slightly scaly, the surface of

some hairs is imbricated; that is to say, shows projecting scale-like

processes, as in some bats, while in the two-toed sloth (_Choloepus_)

they are longitudinally grooved or fluted. Though usually more or less

cylindrical or circular in section, hairs are often elliptical or

flattened, as in the curly-haired races of men, the terminal portion

of the hair of moles and shrews, and conspicuously in the spines of

the spiny squirrels of the genus _Xerus_ and those of the mouse-like

_Platacanthomys_. Hair having a property of mutual cohesion or

"felting," which depends upon a roughened scaly surface and a tendency

to curl, as in domestic sheep, is called "wool."

It has been shown by J. C. H. de Meijere that the insertion of the

individual hairs in the skin displays a definite arrangement, constant

for each species, but varying in different groups. In jerboas, for

example, a bunch of twelve or thirteen hairs springs from the same

point, while in the polar bear a single stout hair and several slender

ones arise together, and in the marmosets three equal-sized hairs form

regular groups. These tufts or groups likewise display an orderly and

definite grouping in different mammals, which suggests the origin of

such groups from the existence in primitive mammals of a scaly coat

comparable to that of reptiles, and indeed directly inherited

therefrom.

In a large proportion of mammals there exist hairs of two distinct

types: the one long, stiff, and alone appearing on the surface, and

the other shorter, finer and softer, constituting the under-fur, which

may be compared to the down of birds. A well-known example is

furnished by the fur-bearing seals, in which the outer fur is removed

in the manufacture of commercial "seal-skin," leaving only the soft

and fine under-fur.

Remarkable differences in the direction or slope of the hair are

noticeable on different parts of the body and limbs of many mammals,

especially in certain apes, where the hair of the fore-limbs is

inclined towards the elbow from above and from below. More remarkable

still is the fact that the direction of the slope often differs in

closely allied groups, as, for instance, in African and Asiatic

buffaloes, in which the hair of the middle line of the back has

opposite directions. Whorls of hair, as on the face of the horse and

the South American deer known as brockets, occur where the different

hair-slopes meet. In this connexion reference may be made to patches

or lines of long and generally white hairs situated on the back of

certain ruminants, which are capable of erection during periods of

excitement, and serve, apparently, as "flags" to guide the members of

a herd in flight. Such are the white chrysanthemum-like patches on the

rump of the Japanese deer and of the American prong-buck

(_Antilocapra_), and the line of hairs situated in a groove on the

loins of the African spring-buck. The white underside of the tail of

the rabbit and the yellow rump-patch of many deer are analogous.

The eye-lashes, or _ciliae_, are familiar examples of a special local

development of hair. Special tufts of stout stiff hairs, sometimes

termed _vibrissae_, and connected with nerves, and in certain cases

with glands, occur in various regions. They are most common on the

head, while they constitute the "whiskers," or "feelers," of the cats

and many rodents. In other instances, notably in the lemurs, but also

in certain carnivora, rodents and marsupials, they occupy a position

on the fore-arm near the wrist, in connexion with glands, and receive

sensory powers from the radial nerve. In some mammals the hairy

covering is partial and limited to particular regions; in others, as

the hippopotamus and the sea-cows, or Sirenia, though scattered over

the whole surface, it is extremely short and scanty; but in none is

it reduced to so great an extent as in the Cetacea, in which it is

limited to a few small bristles confined to the neighbourhood of the

lips and nostrils, and often present only in the young, or even the

foetal condition.

Some kinds of hairs, as those of the mane and tail of the horse,

persist throughout life, but more generally, as in the case of the

body-hair of the same animal, they are shed and renewed periodically,

generally annually. Many mammals have a longer hairy coat in winter,

which is shed as summer comes on; and some few, which inhabit

countries covered in winter with snow, as the Arctic fox, variable

hare and ermine, undergo a complete change of colour in the two

seasons, being white in winter and grey or brown in summer. There has

been much discussion as to whether this winter whitening is due to a

change in the colour of the individual hairs or to a change of coat.

It has, however, been demonstrated that the senile whitening of human

hair is due to the presence of phagocytes, which devour the

pigment-bodies; and from microscopic observations recently made by the

French naturalist Dr E. Trouessart, it appears that much the same kind

of action takes place in the hairs of mammals that turn white in

winter. Cold, by some means or other, causes the pigment-bodies to

shift from the normal positions, and to transfer themselves to other

layers of the hair, where they are attacked and devoured by

phagocytes. The winter whitening of mammals is, therefore, precisely

similar to the senile bleaching of human hair, no shift of the coat

taking place. Under the influence of exposure to intense cold a small

mammal has been observed to turn white in a single night, just as the

human hair has been known to blanch suddenly under the influence of

intense emotion, and in both cases extreme activity of the phagocytes

is apparently the inducing cause. The African golden-moles

(_Chrysochloris_), the desmans or water-moles (_Myogale_), and the

West African _Potamogale velox_, are remarkable as being the only

mammals whose hair reflects those iridescent tints so common in the

feathers of tropical birds.

The principal and most obvious purpose of the hairy covering is to

protect the skin. Its function in the hairless Cetacea is discharged

by the specially modified and thickened layer of fatty tissue beneath

the skin known as "blubber."

_Scales, &c._--True scales, or flat imbricated plates of horny

material, covering the greater part of the body, are found in one

family only of mammals, the pangolins or _Manidae_; but these are also

associated with hairs growing from the intervals between the scales or

on the parts of the skin not covered by them. Similarly imbricated

epidermic productions form the covering of the under-surface of the

tail of the African flying rodents of the family _Anomaluridae_; and

flat scutes, with the edges in apposition, and not overlaid, clothe

both surfaces of the tail of the beaver, rats and certain other

members of the rodent order, and also of some insectivora and

marsupials. Armadillos alone possess an external bony skeleton,

composed of plates of bony tissue, developed in the skin and covered

with scutes of horny epidermis. Other epidermic appendages are the

horns of ruminants and rhinoceroses--the former being elongated,

tapering, hollow caps of hardened epidermis of fibrous structure,

fitting on and growing from conical projections of the frontal bones

and always arranged in pairs, while the latter are of similar

structure, but without any internal bony support, and situated in the

middle line. Callosities, or bare patches covered with hardened and

thickened epidermis, are found on the buttocks of many apes, the

breast of camels, the inner side of the limbs of _Equidae_, the

grasping under-surface of the tail of prehensile-tailed monkeys,

opossums, &c. The greater part of the skin of the one-horned Asiatic

rhinoceros is immensely thickened and stiffened by an increase of the

tissue of both the skin and epidermis, constituting the well-known

jointed "armour-plated" hide of those animals.

_Nails, Claws and Hoofs._--With few exceptions, the terminal

extremities of the digits of both limbs of mammals are more or less

protected or armed by epidermic plates or sheaths, constituting the

various forms of nails, claws or hoofs. These are absent in the

Cetacea alone. A perforated spur, with a special secreting gland in

connexion with it, is found attached to each hind-leg of the males of

the existing species of Monotremata.

_Scent-glands, &c._--Besides the universally distributed sweat-glands

connected with the hair-system, most mammals have special glands in

modified portions of the skin, often involuted to form a shallow

recess or a deep sac with a narrow opening, situated in various parts

of the surface of the body, and secreting odorous substances, by the

aid of which individuals recognize one another. These probably afford

the principal means by which wild animals are able to become aware of

the presence of other members of the species, even at great distances.

To this group of structures belong the suborbital face-gland,

"larmier," or "crumen," of antelopes and deer, the frontal gland of

the muntjak and of bats of the genus _Phyllorhina_, the chin-gland of

the chevrotains and of _Taphozous_ and certain other bats, the

glandular patch behind the ear of the chamois and the reed-buck, the

glands on the lower parts of the legs of most deer and a few antelopes

(the position of which is indicated by tufts of long and often

specially coloured hair), the interdigital foot-glands of goats,

sheep, and many other ruminants, the temporal gland of elephants, the

lateral glands of the musk-shrew, the gland on the back of the hyrax

and the peccary (from the presence of which the latter animal takes

the name _Dicotyles_), the gland on the tails of the members of the

dog-tribe, the preputial glands of the musk-deer and beaver (both well

known for the use made of their powerfully odorous secretion in

perfumery), and also of the swine and hare, the anal glands of

Carnivora, the perineal gland of the civet (also of commercial value),

the caudal glands of the fox and goat, the gland on the wing-membrane

of bats of the genus _Saccopteryx_, the post-digital gland of the

rhinoceros, &c. Very generally these glands are common to both sexes,

and it is in such cases that their function as a means of mutual

recognition is most evident. It has been suggested that the

above-mentioned callosities or "chestnuts" on the limbs of horses are

vestigial scent-glands; and it is noteworthy that scrapings or

shavings from their surface have a powerful attraction for other

horses, and are also used by poachers and burglars to keep dogs

silent. The position of such glands on the lower portions of the limbs

is plainly favourable to a recognition-taint being left in the tracks

of terrestrial animals; and antelopes have been observed deliberately

to rub the secretion from their face-glands on tree-trunks. When

glands are confined to the male, their function is no doubt sexual;

the secretion forming part of the attraction, or stimulus, to the

other sex.

[Illustration: FIG. 1.--Upper and Lower Teeth of one side of the Mouth

of a Dolphin (_Lagenorhynchus_), as an example of the homoeodont type

of dentition. The bone covering the outer side of the roots of the

teeth has been removed to show their simple character.]

_Dentition._--In the great majority of mammals the teeth form a

definite series, of which the hinder elements are of a more or less

complex type, while those in front are simpler. With the exception of

the marsupials, a set of deciduous, or milk, teeth is developed in

most mammals with a complicated type of dentition; these milk-teeth

being shed at a comparatively early period (occasionally even _in

utero_), when they are succeeded by the larger permanent series, which

is the only other ever developed. This double series of teeth thus

forms a very characteristic feature of mammals generally. Both the

milk and the permanent dentition display the aforesaid complexity of

the hinder teeth as compared with those in front, and since the number

of milk-teeth is always considerably less than that of the permanent

set, it follows that the hinder milk-teeth are usually more complex

than the teeth of which they are the predecessors in the permanent

series, and represent functionally, not their immediate successors,

but those more posterior permanent teeth which have no direct

predecessors. This character is clearly seen in those animals in which

the various members of the lateral or cheek series are well

differentiated from each other in form, as the Carnivora, and also in

man.

In mammals with two sets of teeth the number of those of the permanent

series preceded by milk-teeth varies greatly, being sometimes, as in

marsupials and some rodents, as few as one on each side of each jaw,

and in other cases including the larger portion of the series. As a

rule, the teeth of the two sides of the jaws are alike in number and

character, except in cases of accidental or abnormal variation, and in

the tusks of the narwhal, in which the left is of immense size, and

the right rudimentary. In mammals, such as dolphins and some

armadillos, which have a large series of similar teeth, not always

constant in number in different individuals, there may indeed be

differences in the two sides; but, apart from these in describing the

dentition of any mammal, it is generally sufficient to give the number

and characters of the teeth of one side only. As the teeth of the

upper and the lower jaws work against each other in masticating, there

is a general correspondence or harmony between them, the projections

of one series, when the mouth is closed, fitting into corresponding

depressions of the other. There is also a general resemblance in the

number, characters and mode of succession of both series; so that,

although individual teeth of the upper and lower jaws may not be in

the strict sense of the term homologous parts, there is a great

convenience in applying the same descriptive terms to the one which

are used for the other.

The simplest dentition is that of many species of dolphin (fig. 1), in

which the crowns are single-pointed, slightly curved cones, and the

roots also single and tapering; so that all the teeth are alike in

form from the anterior to the posterior end of the series, though it

may be with some slight difference in size, those at the two

extremities being rather smaller than the others. Such a dentition is

called "homoeodont" (Gr. [Greek: homoios], like, [Greek: odous],

tooth), and in the case cited, as the teeth are never changed, it is

also monophyodont (Gr. [Greek: monos], alone, single, [Greek: phyein],

to generate, [Greek: odous], tooth). Such teeth are adapted only for

catching slippery living prey, like fish.

In a very large number of mammals the teeth of different parts of the

series are more or less differentiated in character; and, accordingly,

have different functions to perform. The front teeth are simple and

one-rooted, and are adapted for cutting and seizing. They are called

"incisors." The back, lateral or cheek teeth, on the other hand, have

broader and more complex crowns, tuberculated or ridged, and supported

on two or more roots. They crush or grind the food, and are hence

called "molars." Many mammals have, between these two sets, a tooth at

each corner of the mouth, longer and more pointed than the others,

adapted for tearing or stabbing, or for fixing struggling prey. From

the conspicuous development of such teeth in the Carnivora, especially

the dogs, they have received the name of "canines." A dentition with

its component parts so differently formed that these distinctive terms

are applicable to them is called heterodont (Gr. [Greek: heteros],

different). In most cases, though by no means invariably, mammals with

a heterodont dentition are also diphyodont (Gr. [Greek: diphyês], of

double form).

[Illustration: FIG. 2.--Milk and Permanent Dentitions of Upper (I.)

and Lower (II.) Jaws of the Dog (_Canis_), with the symbols by which

the different teeth are designated. The third upper molar (_m_ 3) is

the only tooth wanting to complete the typical heterodont mammalian

dentition.]

This general arrangement is obvious in a considerable number of

mammals; and examination shows that, under great modifications in

detail, there is a remarkable uniformity of essential characters in

the dentition of a large number of members of the class belonging to

different orders and not otherwise closely allied, so much that it is

possible to formulate a common plan of dentition from which the others

have been derived by the alteration of some and the suppression of

other members of the series, and occasionally, but very rarely, by

addition. In this generalized form of mammalian dentition the total

number of teeth present is 44, or 11 above and 11 below on each side.

Those of each jaw are placed in continuous series without intervals

between them; and, although the anterior teeth are simple and

single-rooted, and the posterior teeth complex and with several roots,

the transition between the two kinds is gradual.

In dividing and grouping such teeth for the purpose of description and

comparison more definite characters are required than those derived

merely from form or function. The first step towards a classification

rests on the fact that the upper jaw is composed of two bones, the

premaxilla and the maxilla, and that the division or suture between

these bones separates the three front teeth from the rest. These three

teeth, which are implanted in the premaxilla, form a distinct group,

to which the name of "incisor" is applied. This distinction is,

however, not so important as it appears at first sight, for their

connexion with the bone is only of a secondary nature, and, although

it happens conveniently that in the great majority of cases the

division between the bones coincides with the interspace between the

third and fourth tooth of the series, still, when it does not, as in

the mole, too much weight must not be given to this fact, if it

contravenes other reasons for determining the homologies of the teeth.

The eight remaining teeth of the upper jaw offer a natural division,

inasmuch as the three hindmost never have milk-predecessors; and,

although some of the anterior teeth may be in the same case, the

particular one preceding these three always has such a predecessor.

These three, then, are grouped as the "molars." Of the five teeth

between the incisors and molars the most anterior, or the one usually

situated close behind the pre-maxillary suture, very generally assumes

a lengthened and pointed form, and constitutes the "canine" of the

Carnivora, the tusk of the boar, &c. It is customary, therefore, to

call this tooth, whatever its size or form, the "canine." The

remaining four are the "premolars." This system has been objected to

as artificial, and in many cases not descriptive, the distinction

between premolars and canine especially being sometimes not obvious;

but the terms are now in such general use, and also so convenient,

that it is not likely they will be superseded. It is frequently

convenient to refer to all the teeth behind the canine as the

"cheek-teeth."

With regard to the lower teeth the difficulties are greater, owing to

the absence of any suture corresponding to that which defines the

incisors above; but since the number of the teeth is the same, since

the corresponding teeth are preceded by milk-teeth, and since in the

large majority of cases it is the fourth tooth of the series which is

modified in the same way as the canine (or fourth tooth) of the upper

jaw, it is reasonable to adopt the same divisions as with the upper

series, and to call the first three, which are implanted in the part

of the mandible opposite to the premaxilla, the incisors, the next the

canine, the next four the premolars, and the last three the molars.

It may be observed that when the mouth is closed, especially when the

opposed surfaces of the teeth present an irregular outline, the

corresponding upper and lower teeth are not exactly opposite,

otherwise the two series could not fit into one another, but as a rule

the points of the lower teeth shut into the interspaces in front of

the corresponding teeth of the upper jaw. This is very distinct in the

canine teeth of the Carnivora, and is a useful guide in determining

the homologies of the teeth of the two jaws.

For the sake of brevity the complete dentition is described by the

following formula, the numbers above the line representing the teeth

of the upper, those below the line those of the lower jaw: incisors

(3--3)/(3--3), canines (1--1)/(1--1), premolars (4--4)/(4--4), molars,

(3--3)/(3--3) = (11--11)/(11--11) total 44. As, however, initial

letters may be substituted for the names of each group, and it is

unnecessary to give more than the numbers of the teeth on one side of

the mouth, the formula may be abbreviated into:

_i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3; total 44.

The individual teeth of each group are enumerated from before

backwards, and by such a formula as the following:--

_i_ 1, _i_ 2, _i_ 3, _c_, _p_ 1, _p_ 2, _p_ 3, _p_ 4, _m_ 1, _m_ 2, _m_ 3

-------------------------------------------------------------------------

_i_ 1, _i_ 2, _i_ 3, _c_, _p_ 1, _p_ 2, _p_ 3, _p_ 4, _m_ 1, _m_ 2, _m_ 3

a special numerical designation is given by which each one can be

indicated. In mentioning any single tooth, such a sign as m1 will mean

the first upper molar, m1 the first lower molar, and so on.

When, as is the case among nearly all existing mammals with the

exception of the members of the genera _Sus_ (pigs), _Gymnura_

(rat-shrew), _Talpa_ (moles) and _Myogale_ (desmans) the number of

teeth is reduced below the typical forty-four, it appears to be an

almost universal rule that if one of the incisors is missing it is the

second, or middle one, while the premolars commence to disappear from

the front end of the series and the molars from the hinder end.

The milk-dentition is expressed by a similar formula, _d_ for

deciduous, being added before the letter expressive of the nature of

the tooth. As the three molars and (almost invariably) the first

premolar of the permanent series have no predecessors, the typical

milk-dentition would be expressed as follows: _di_ 3/3, _dc_ 1/1, _dm_

3/3 = 28. The teeth which precede the premolars of the permanent

series are called either milk-molar or milk-premolar. When there is a

marked difference between the premolars and molars of the permanent

dentition, the first milk-molar resembles a premolar, while the last

has the characters of the posterior molar. It is sometimes convenient

to refer to all the seven cheek-teeth as members of a single

continuous series (which they undoubtedly are), and for this purpose

the following nomenclature has been proposed:--

Upper Jaw. Lower Jaw.

Cheek-tooth 1 Protus. Protid.

" 2 Deuterus. Deuterid.

" 3 Tritus. Tritid.

" 4 Tetartus. Tetartid.

" 5 Pemptus. Pemptid.

" 6 Hectus. Hectid.

" 7 Hebdomus. Hebdomid.

With the exception of the Cetacea, most of the Edentata, and the

Sirenia, in which the teeth, when present, have been specialized in a

retrograde or aberrant manner, the placental mammals as a whole have a

dentition conforming more or less closely to the foregoing type.

With the marsupials the case is, however, somewhat different; the

whole number not being limited to 44, owing largely to the fact that

the number of upper incisors may exceed three pairs, reaching indeed

in some instances to as many as five. Moreover, with the exception of

the wombats, the number of pairs of incisors in the upper always

exceeds those in the lower. When fully developed, the number of

cheek-teeth is, however, seven; and it is probable that, as in

placentals, the first four of these are premolars and the remaining

three molars, although it was long held that these numbers should be

transposed. The most remarkable feature about the marsupial dentition

is that, at most, only a single pair of teeth is replaced in each jaw;

this pair, on the assumption that there are four premolars,

representing the third of that series. With the exception of this

replacing pair of teeth in each jaw, it is considered by many

authorities that the marsupial dentition corresponds to the deciduous,

or milk, dentition of placentals. If this be really the case, the

rudiments of an earlier set of teeth which have been detected in the

jaws of some members of the order, represent, not the milk-series, but

a prelacteal dentition. On the assumption that these functional teeth

correspond to the milk-series of placentals, marsupials in this

respect agree exactly with modern elephants, in which the same

peculiarity exists.

In very few mammals are teeth entirely absent. Even in the whalebone

whales their germs are formed in the same manner and at the same

period of life as in other mammals, and even become partially

calcified, although they never rise above the gums, and completely

disappear before birth. In the American anteaters and the pangolins

among the Edentata no traces of teeth have been found at any age.

Adult monotremes are in like case, although the duck-billed platypus

(_Ornithorhynchus_) has teeth when young on the sides of the jaws. The

northern sea-cow (_Rhytina_), now extinct, appears to have been

toothless throughout life.

In different groups of mammals the dentition is variously specialized

in accordance with the nature of the food on which the members of

these groups subsist. From this point of view the various adaptive

modifications of mammalian dentition may be roughly grouped under the

headings of piscivorous, carnivorous, insectivorous, omnivorous and

herbivorous.

The fish-eating, or piscivorous, type of dentition is exemplified

under two phases in the dolphins and in the seals (being in the latter

instance a kind of retrograde modification from the carnivorous type).

In the dolphins, and in a somewhat less marked degree among the seals,

this type of dentition consists of an extensive series of conical,

nearly equal-sized, sharp-pointed teeth, implanted in an elongated and

rather narrow mouth (fig. 1), and adapted to seize slippery prey

without either tearing or masticating. In the dolphins the teeth form

simple cones, but in the seals they are often trident-like; while in

the otters the dentition differs but little from the ordinary

carnivorous type.

This carnivorous adaptation, in which the function is to hold and kill

struggling animals, often of large size, attains its highest

development in the cats (_Felidae_). The canines are in consequence

greatly developed, of a cutting and piercing type, and from their wide

separation in the mouth give a firm hold; the jaws being as short as

is consistent with the free action of the canines, or tusks, so that

no power is lost. The incisors are small, so as not to interfere with

the penetrating action of the tusks; and the crowns of some of the

teeth of the cheek-series are modified into scissor-like blades, in

order to rasp off the flesh from the bones, or to crack the bones

themselves, while the later teeth of this series tend to disappear.

In the insectivorous type, as exemplified in moles and shrew-mice, the

middle pair of incisors in each jaw are long and pointed so as to have

a forceps-like action for seizing insects, the hard coats of which are

broken up by the numerous sharp cusps surmounting the cheek-teeth.

In the omnivorous type, as exemplified in man and monkeys, and to a

less specialized degree in swine, the incisors are of moderate and

nearly equal size; the canines, if enlarged, serve for other purposes

than holding prey, and such enlargement is usually confined to those

of the males; while the cheek-teeth have broad flattened crowns

surmounted by rounded bosses, or tubercles.

In the herbivorous modification, as seen in three distinct phases in

the horse, the kangaroo, and in ruminants, the incisors are generally

well developed in one or both jaws, and have a nipping action, either

against one another or against a toothless hard pad in the upper jaw;

while the canines are usually small or absent, at least in the upper

jaw, but in the lower jaw may be approximated and assimilated to the

incisors. The cheek-teeth are large, with broad flattened crowns

surmounted either by simple transverse ridges, or complicated by

elevations and infoldings. In the specialized forms the premolars tend

to become more or less completely like the molars; and, contrary to

what obtains among the Carnivora, the whole series of cheek-teeth

(with the occasional exception of the first) is very strongly

developed.

Opinions differ as to the mode in which the more complicated

cheek-teeth of mammals have been evolved from a simpler type of tooth.

According to one theory, this has been brought about by the fusion of

two or more teeth of a simple conical type to form a compound tooth. A

more generally accepted view--especially among palaeontologists--is

the tritubercular theory, according to which the most generalized type

of tooth consists of three cusps arranged in a triangle, with the apex

pointing inwards in the teeth of the upper jaw. Additions of extra

cusps form teeth of a more complicated type. Each cusp of the

primitive triangle has received a separate name, both in the teeth of

the upper and of the lower jaw, while names have also been assigned to

super-added cusps. Molar teeth of the simple tritubercular type

persist in the golden moles (_Chrysochloris_) among the Insectivora

and also in the marsupial mole (_Notoryctes_) among the marsupials.

The type is, moreover, common among the mammals of the early Eocene,

and still more so in those of the Jurassic epoch; this forming one of

the strongest arguments in favour of the tritubercular theory. (See

Professor H. F. Osborn, "Palaeontological Evidence for the Original

Tritubercular Theory," in vol. xvii. (new series) of the _American

Journal of Science_, 1904.)

_Digestive System._--As already mentioned, mammals are specially

characterized by the division of the body-cavity into two main

chambers, by means of the horizontal muscular partition known as the

diaphragm, which is perforated by the great blood-vessels and the

alimentary tube. The mouth of the great majority of mammals is

peculiar for being guarded by thick fleshy lips, which are, however,

absent in the Cetacea; their principal function being to seize the

food, for which purpose they are endowed, as a rule, with more or less

strongly marked prehensile power. The roof of the mouth is formed by

the palate, terminating behind by a muscular, contractile arch, having

in man and a few other species a median projection called the uvula,

beneath which the mouth communicates with the pharynx. The anterior

part of the palate is composed of mucous membrane tightly stretched

over the flat or slightly concave bony layer which separates the mouth

from the nasal passages, and is generally raised into a series of

transverse ridges, which sometimes, as in ruminants, attain a

considerable development. In the floor of the mouth, between the two

branches of the lower jaw, and supported behind by the hyoid

apparatus, lies the tongue, an organ the free surface of which,

especially in its posterior part, is devoted to the sense of taste,

but which by reason of its great mobility (being composed almost

entirely of muscular fibres) performs important mechanical functions

connected with masticating and procuring food. Its modifications of

form in different mammals are numerous. Between the long, extensile,

worm-like tongue of the anteaters, essential to the peculiar mode of

feeding of those animals, and the short, immovable and almost

functionless tongue of the porpoise, every intermediate condition is

found. Whatever the form, the upper surface is, however, covered with

numerous fine papillae, in which the terminal filaments of the

taste-nerve are distributed. In some mammals, notably lemurs, occurs a

hard structure known as the sublingua, which may terminate in a free

horny tip. If, as has been suggested, this organ represents the tongue

of reptiles, the mammalian tongue will obviously be a super-added

organ distinctive of the class.

[Illustration: FIG. 3.--Diagrammatic Plan of the general arrangement

of the Alimentary Canal in a typical Mammal.

o, oesophagus;

st, stomach;

p, pylorus;

ss, small intestine (abbreviated);

c, caecum;

ll, large intestine or

colon, ending in

r, the rectum.]

Salivary glands, of which the most constant are the parotid and the

submaxillary, are always present in terrestrial mammals. Next in

constancy are the "sublingual," closely associated with the

last-named, at all events in the locality in which the secretion is

poured out; and the "zygomatic," found only in some mammals in the

cheek, just under cover of the anterior part of the zygomatic arch,

the duct entering the mouth-cavity near that of the parotid.

The alimentary, or intestinal, canal varies greatly in relative length

and capacity in different mammals, and also offers manifold

peculiarities of form, being sometimes a simple cylindrical tube of

nearly uniform calibre throughout, but more often subject to

alterations of form and capacity in different portions of its

course--the most characteristic and constant being the division into

an upper and narrower and a lower and wider portion, called

respectively the small and the large intestine; the former being

arbitrarily divided into duodenum, jejunum and ileum, and the latter

into colon and rectum. One of the most striking peculiarities of this

part of the canal is the frequent presence of a blind pouch, "caecum,"

situated at the junction of the large and the small intestine. Their

structure presents an immense variety of development, from the

smallest bulging of a portion of the side-wall of the tube to a huge

and complex sac, greatly exceeding in capacity the remainder of the

alimentary canal. It is only in herbivorous mammals that the caecum is

developed to this great extent, and among these there is a

complementary relationship between the size and complexity of the

organ and that of the stomach. Where the latter is simple the caecum

is generally the largest, and vice versa. In vol. xvii. (1905) of the

_Transactions_ of the Zoological Society of London, Dr P. Chalmers

Mitchell has identified the paired caeca, or blind appendages, of the

intestine of birds with the usually single caecum of mammals. These

caeca occur in birds (as in mammals) at the junction of the small with

the large intestine; and while in ordinary perching-birds they are

reduced to small nipple-like buds of no functional importance, in many

other birds--owls for instance--they form quite long receptacles.

Among mammals, the horse and the dog may be cited as instances where

the single caecum is of large size, this being especially the case of

the former, where it is of enormous dimensions; in human beings, on

the other hand, the caecum is rudimentary, and best known in connexion

with "appendicitis." The existence of paired caeca was previously

known in a few armadillos and anteaters, but Dr Mitchell has shown

that they are common in these groups, while he has also recorded their

occurrence in the hyrax and the manati. With the aid of these

instances of paired caeca, coupled with the frequent existence of a

rudiment of its missing fellow when only one is functional, the author

has been enabled to demonstrate conclusively that these double organs

in birds correspond in relations with their normally single

representative in mammals.

In mammals both caecum and colon are often sacculated, a disposition

caused by the arrangement of the longitudinal bands of muscular tissue

in their walls; but the small intestine is always smooth and

simple-walled externally, though its lining membrane often exhibits

contrivances for increasing the absorbing surface without adding to

the general bulk of the organ, such as the numerous small tags, or

"villi," by which it is everywhere beset, and the more obvious

transverse, longitudinal, or reticulating folds projecting into the

interior, met with in many animals, of which the "valvulae

conniventes" of man form well-known examples. Besides the crypts of

Lieberkühn found throughout the intestinal canal, and the glands of

Brunner confined to the duodenum, there are other structures in the

mucous membrane, about the nature of which there is still much

uncertainty, called "solitary" and "agminated" glands, the latter more

commonly known by the name of "Peyer's patches." Of the liver little

need be said, except that in all living mammals it has been divided

into a number of distinct lobes, which have received separate names.

It has, indeed, been suggested that in the earlier mammals the liver

was a simple undivided organ. This, however, is denied by G. Ruge

(vol. xxix. of Gegenbaur's _Morphologisches Jahrbuch_).

_Origin of Mammals._--That mammals have become differentiated from a

lower type of vertebrates at least as early as the commencement of the

Jurassic period is abundantly testified by the occurrence of the remains

of small species in strata of that epoch, some of which are mentioned in

the articles MARSUPIALIA and MONOTREMATA (q.v.). Possibly mammalian

remains also occur in the antecedent Triassic epoch, some

palaeontologists regarding the South African _Tritylodon_ as a mammal,

while others consider that it was probably a reptile. Whatever may be

the true state of the case with regard to that animal probably also

holds good in the case of the approximately contemporaneous European

_Microlestes_. Of the European Jurassic (or Oolitic) mammals our

knowledge is unfortunately very imperfect; and from the scarcity of

their remains it is quite probable that they are merely stragglers from

the region (possibly Africa) where the class was first differentiated.

It is not till the early Eocene that mammals become a dominant type in

the northern hemisphere.

It is now practically certain that mammals are descended from reptiles.

Dr H. Gadow, in a paper on the origin of mammals contributed to the

_Zeitschrift für Morphologie_, sums up as follows: "Mammals are

descendants of reptiles as surely as they [the latter] have been evolved

from Amphibia. This does not mean that any of the living groups of

reptiles can claim their honour of ancestry, but it means that the

mammals have branched where the principal reptilian groups meet, and

that is a long way back. The Theromorpha, especially small Theriodontia,

alone show us what these creatures were like." It may be explained that

the Theromorpha, or Anomodontia, are those extinct reptiles so common in

the early Secondary (Triassic) deposits of South Africa, some of which

present a remarkable resemblance in their dentition and skeleton to

mammals, while others come equally near amphibians. A difficulty

naturally arises with regard to the fact that in reptiles the occipital

condyle by which the skull articulates with the vertebral column is

single, although composed of three elements, whereas in amphibians and

mammals the articulation is formed by a pair of condyles. Nevertheless,

according to Professor H. F. Osborn, the tripartite reptilian condyle,

by the loss of its median element, has given rise to the paired

mammalian condyles; so that this difficulty disappears. The fate of the

reptilian quadrate bone (which is reduced to very small dimensions in

the Anomodontia) has been referred to in an earlier section of the

present article, where some mention has also been made of the

disappearance in mammals of the hinder elements of the reptilian lower

jaw, so as to leave the single bone (dentary) of each half of this part

of the skeleton in mammals.

Most of the earliest known mammals appear to be related to the

Marsupialia and Insectivora. Others however (inclusive of _Tritylodon_

and _Microlestes_, if they be really mammals), seem nearer to the

Monotremata; and the question has yet to be decided whether placentals

and marsupials on the one hand, and monotremes on the other are not

independently derived from reptilian ancestors.

With regard to the evolution of marsupials and placentals, it has been

pointed out that the majority of modern marsupials exhibit in the

structure of their feet traces of the former opposability of the thumb

and great toe to the other digits; and it has accordingly been argued

that all marsupials are descended from arboreal ancestors. This doctrine

is now receiving widespread acceptation among anatomical naturalists;

and in the _American Naturalist_ for 1904, Dr W. D. Matthew, an American

palaeontologist, considers himself provisionally justified in so

extending it as to include all mammals. That is to say, he believes

that, with the exception of the duckbill and the echidna, the mammalian

class as a whole can lay claim to descent from small arboreal forms.

This view is, of course, almost entirely based upon palaeontological

considerations; and these, in the author's opinion, admit of the

conclusion that all modern placental and marsupial mammals are descended

from a common ancestral stock, of which the members were small in bodily

size. These ancestral mammals, in addition to their small size, were

characterized by the presence of five toes to each foot, of which the

first was more or less completely opposable to the other four. The

evidence in favour of this primitive opposability is considerable. In

all the groups which are at present arboreal, the palaeontological

evidence goes to show that their ancestors were likewise so; while

since, in the case of modern terrestrial forms, the structure of the

wrist and ankle joints tends to approximate to the arboreal type, as we

recede in time, the available evidence, so far as it goes, is in favour

of Dr Matthew's contention.

The same author also discusses the proposition from another standpoint,

namely, the condition of the earth's surface in Cretaceous times. His

theory is that in the early Cretaceous epoch the animals of the world

were mostly aerial, amphibious, aquatic or arboreal; the flora of the

land being undeveloped as compared with its present state. On the other

hand, towards the close of the Cretaceous epoch (when the Chalk was in

course of deposition), the spread of a great upland flora vastly

extended the territory available for mammalian life. Accordingly, it was

at this epoch that the small ancestral insectivorous mammals first

forsook their arboreal habitat to try a life on the open plains, where

their descendants developed on the one hand into the carnivorous and

other groups, in which the toes are armed with nails or claws, and on

the other into the hoofed group, inclusive of such monsters as the

elephant and the giraffe. The hypothesis is not free from certain

difficulties, one of which will be noticed later.

_Classification._--Existing mammals may be primarily divided into three

main groups, or subclasses, of which the second and third are much more

closely related to one another than is either of them to the first.

These three classes are the Monotremata (or Prototheria), the

Marsupialia (Didelphia, or Metatheria), and the Placentalia

(Monodelphia, or Eutheria); the distinctive characters of each being

given in separate articles (see MONOTREMATA, MARSUPIALIA and

MONODELPHIA.)

The existing monotremes and marsupials are each represented only by a

single order; but the placentals are divided into the following

ordinal and subordinal groups, those which are extinct being marked

with an asterisk (*):--

1. Insectivora (Moles, Hedgehogs, &c.).

2. Chiroptera (Bats).

3. Dermoptera (Colugo, or Flying Lemur).

4. Edentata:--

a. Xenarthra (Anteaters, Sloths and Armadillos).

b. Pholidota (Pangolins).

c. Tubulidentata (Ant-bears, or Aard-varks).

5. Rodentia (Gnawing Mammals):--

a. Duplicidentata (Hares and Picas).

b. Simplicidentata (Rats, Beavers, &c.).

6. *Tillodontia (_Tillotherium_).

7. Carnivora:--

a. Fissipedia (Cats, Dogs, Bears, &c.).

b. Pinnipedia (Seals and Walruses).

c. *Creodonta (_Hyaenodon_, &c.).

8. Cetacea (Whales and Dolphins):--

a. *Archaeoceti (_Zeuglodon_, &c.).

b. Odontoceti (Spermwhales and Dolphins).

c. Mystacoceti (Whalebone Whales).

9. Sirenia (Dugongs and Manatis).

10. Ungulata (Hoofed Mammals):--

a. Proboscidea (Elephants and Mastodons).

b. Hyracoidea (Hyraxes).

c. *Barypoda (_Arsinöitherium_).

d. *Toxodontia (_Toxodon_, &c.).

e. *Amblypoda (_Uintatherium_, &c.).

f. *Litopterna (_Macrauchenia_, &c.).

g. *Ancylopoda (_Chalicotherium_, &c.).

h. *Condylarthra (_Phenacodus_, &c.).

i. Perissodactyla (Tapirs, Horses, &c.).

j. Artiodactyla (Ruminants, Swine, &c.).

11. Primates:--

a. Prosimiae (Lemurs and Galagos).

b. Anthropoidea (Monkeys, Apes and Man).

Separate articles are devoted to each of these orders, where

references will be found to other articles dealing with some of the

minor groups and a number of the more representative species.

_Relationships of the Groups._--As we recede in time we find the

extinct representatives of many of these orders approximating more and

more closely to a common generalized type, so that in a large number

of early Eocene forms it is often difficult to decide to which group

they should be assigned.

The Insectivora are certainly the lowest group of existing placental

mammals, and exhibit many signs of affinity with marsupials; they may

even be a more generalized group than the latter. From the Insectivora

the bats, or Chiroptera, are evidently a specialized lateral offshoot;

while the Dermoptera may be another branch from the same stock. As to

the Edentata, it is still a matter of uncertainty whether the

pangolins (Pholidota) and the ant-bears (Tubulidentata) are rightly

referred to an order typically represented by the sloths, anteaters,

and armadillos of South and Central America, or whether the two

first-named groups have any close relationship with one another. Much

uncertainty prevails with regard to the ancestry of the group as a

whole, although some of the earlier South American forms have a

comparatively full series of teeth, which are also of a less

degenerate type than those of their modern representatives.

An almost equal degree of doubt obtains with regard to the ancestry of

that very compact and well-defined group the Rodentia. If, however,

the so-called Proglires of the lower Eocene are really ancestral

rodents, the order is brought into comparatively close connexion with

the early generalized types of clawed, or unguiculate mammals. Whether

the extinct Tillodontia are most nearly allied to the Rodentia, the

Carnivore or the Ungulata, and whether they are really entitled to

constitute an ordinal group by themselves, must remain for the present

open questions.

The Carnivora, as represented by the (mainly) Eocene Creodonta, are

evidently an ancient and generalized type. As regards the number and

form of their permanent teeth, at any rate, creodonts present such a

marked similarity to carnivorous marsupials, that it is difficult to

believe the two groups are not allied, although the nature of the

relationship is not yet understood, and the minute internal structure

of the teeth is unlike that of marsupials and similar to that of

modern Carnivora. There is the further possibility that creodonts may

be directly descended from the carnivorous reptiles; a descent which

if proved might introduce some difficulty with regard to the

above-mentioned theory as to the arboreal ancestry of mammals

generally. Be this as it may, there can be little doubt that the

creodonts are related to the Insectivora, which, as stated above, show

decided signs of kinship with the marsupials.

A much more interesting relationship of the creodont carnivora has,

however, been established on the evidence of recent discoveries in

Egypt. From remains of Eocene age in that country Dr E. Fraas, of

Stuttgart, has demonstrated the derivation of the whale-like

_Zeuglodon_ from the creodonts. Dr C. E. Andrews has, moreover, not

only brought forward additional evidence in favour of this most

remarkable line of descent, but is confident--which Professor Fraas

was not--that _Zeuglodon_ itself is an ancestral cetacean, and

consequently that whales are the highly modified descendants of

creodonts. It must be admitted, however, that the links between

_Zeuglodon_ and typical cetaceans are at present unknown; but it may

be hoped that these will be eventually brought to light from the

deposits of the Mokattam Range, near Cairo. Whales and dolphins being

thus demonstrated to be nothing more than highly modified Carnivora,

might almost be included in the same ordinal group.

An analogous statement may be made with regard to the sea-cows, or

Sirenia, which appear to be derivates from the great herbivorous order

of Ungulata, and might consequently be included in that group, as

indeed has been already done in Dr Max Weber's classification. It is

with the proboscidean suborder of the Ungulata to which the Sirenia

are most nearly related; the nature of this relationship being

described by Dr Andrews as follows:--

"In the first place, the occurrence of the most primitive Sirenians

with which we are acquainted in the same region as the most

generalized proboscidean, _Moeritherium_, is in favour of such a view,

and this is further supported by the similarity of the brain-structure

and, to some extent, of the pelvis in the earliest-known members of

the two groups. Moreover, in the anatomy of the soft-parts of the

recent forms there are a number of remarkable points of resemblance.

Among the common characters may be noted the possession of: (1)

pectoral mammae; (2) abdominal testes; (3) a bifid apex of the heart;

(4) bilophodont molars with a tendency to the formation of an

additional lobe from the posterior part of the cingulum. The peculiar

mode of displacement of the teeth from behind forwards in some members

of both groups may perhaps indicate a relationship, although in the

case of the Sirenia the replacement takes place by means of a

succession of similar molars, while in the Proboscidea the molars

remain the same numerically, but increase greatly in size and number

of transverse ridges."

These and certain other facts referred to by the same author point to

the conclusion that not only are the Sirenia and the Proboscidea

derived from a single ancestral stock, but that the Hyracoidea--and so

_Arsinöitherium_--are also derivatives from the same stock, which must

necessarily have been Ethiopian.

Of the other suborders of ungulates, the Toxodontia and Litopterna are

exclusively South American, and while the former may possibly be

related to the Hyracoidea and Barypoda, the latter is perhaps more

nearly akin to the Perissodactyla. The Amblypoda, on the other hand,

are perhaps not far removed from the ancestral Proboscidea, which

depart comparatively little from the generalized ungulate type. The

latter is represented by the Eocene Condylarthra, which undoubtedly

gave rise to the Perissodactyla and Artiodactyla, and probably to

most, if not all, of the other groups. The Condylarthra, in their

turn, approximate closely to the ancestral Carnivora, as they also do

in some degree to the ancestral Primates. As regards the latter order,

although we are at present unacquainted with all the connecting links

between the lemurs and the monkeys, there is little doubt that the

ancestors of the former represent the stock from which the latter have

originated. C. D. Earle, in the _American Naturalist_ for 1897,

observes that "so far as the palaeontological evidence goes it is

decidedly in favour of the view that apes and lemurs are closely

related. Beginning with the earliest known lemur, _Anaptomorphus_,

this genus shows tendencies towards the anthropoids, and, when we pass

up into the Oligocene of the Old World, _Adapis_ is a decidedly mixed

type, and probably not far from the common stem-form which gave origin

to both suborders of the Primates. In regard to _Tarsius_, it is

evidently a type nearly between the lemurs and apes, but with many

essential characters belonging to the former group."

_Distribution._--For an account of the "realms" and "regions" into which

the surface of the globe has been divided by those who have made a

special study of the geographical distribution of animals, see

ZOOLOGICAL DISTRIBUTION. For the purposes of such zoo-geographical

divisions, mammals are much better adapted than birds, owing to their

much more limited powers of dispersal; most of them (exclusive of the

purely aquatic forms, such as seals, whales, dolphins and sea-cows)

being unable to cross anything more than a very narrow arm of the sea.

Consequently, the presence of nearly allied groups of mammals in areas

now separated by considerable stretches of sea proves that at no very

distant date such tracts must have had a land-connexion. In the case of

the southern continents the difficulty is, however, to determine whether

allied groups of mammals (and other animals) have reached their present

isolated habitats by dispersal from the north along widely sundered

longitudinal lines, or whether such a distribution implies the former

existence of equatorial land-connexions. It may be added that even bats

are unable to cross large tracts of sea; and the fact that fruit-bats of

the genus _Pteropus_ are found in Madagascar and the Seychelles, as well

as in India, while they are absent from Africa, is held to be an

important link in the chain of evidence demonstrating a former

land-connexion between Madagascar and India.

There is another point of view from which mammals are of especial

importance in regard to geographical distribution, namely their

comparatively late rise and dispersal, or "radiation," as compared with

reptiles.

As regards terrestrial mammals (with which alone we are at present

concerned), one of the most striking features in their distribution is

their practical absence from oceanic islands; the only species found in

such localities being either small forms which might have been carried

on floating timber, or such as have been introduced by human agency.

This absence of mammalian life in oceanic islands extends even to New

Zealand, where the indigenous mammals comprise only two peculiar species

of bats, the so-called Maori rat having been introduced by man.

One of the leading features in mammalian distribution is the fact that

the Monotremata, or egg-laying mammals, are exclusively confined to

Australia and Papua, with the adjacent islands. The marsupials also

attain their maximum development in Australia ("Notogaea" of the

distributionists), extending, however, as far west as Celebes and the

Moluccas, although in these islands they form an insignificant

minority among an extensive placental fauna, being represented only by

the cuscuses (_Phalanger_), a group unknown in either Papua or

Australia. Very different, on the other hand, is the condition of

things in Australia and Papua, where marsupials (and monotremes) are

the dominant forms of mammalian life, the placentals being represented

(apart from bats, which are mainly of an Asiatic type) only by a

number of more or less aberrant rodents belonging to the mouse-tribe,

and in Australia by the dingo, or native dog, and in New Guinea by a

wild pig. The dingo was, however, almost certainly brought from Asia

by the ancestors of the modern natives; while the Papuan pig is also

in all probability a human introduction, very likely of much later

date. The origin of the Australasian fauna is a question pertaining to

the article ZOOLOGICAL DISTRIBUTION. The remaining marsupials (namely

the families _Didelphyidae_ and _Epanorthidae_) are American, and

mainly South and Central American at the present day; although during

the early part of the Tertiary period representatives of the

first-named family ranged all over the northern hemisphere.

The Insectivora (except a few shrews which have entered from the

north) are absent from South America, and appear to have been mainly

an Old World group, the only forms which have entered North America

being the shrew-mice (_Soricidae_) and moles (_Talpidae_). The

occurrence of one aberrant group (_Solenodon_) in the West Indies is,

however, noteworthy. The family with the widest distribution is the

_Soricidae_, the _Talpidae_ being unknown in Africa. The tree-shrews

(_Tupaiidae_) are exclusively Asiatic, whereas the jumping-shrews

(_Macroscelididae_) are equally characteristic of the African

continent. Madagascar is the sole habitat of the tenrecs

(_Centetidae_), as is Southern Africa of the golden moles

(_Chrysochloridae_). It is, however, important to mention that an

extinct South American insectivore, _Necrolestes_, has been referred

to the family last mentioned; and even if this reference should not be

confirmed in the future, the occurrence of a representative of the

order in Patagonia is a fact of considerable importance in

distribution.

The Rodentia have a wider geographical range than any other order of

terrestrial mammals, being, as already mentioned, represented by

numerous members of the mouse-tribe (_Muridae_) even in Australasia.

With the remarkable exception of Madagascar, where it is represented

by the _Nesomyidae_, that family has thus a cosmopolitan distribution.

Very noteworthy is the fact that, with the exception of Madagascar

(and of course Australia) the squirrel family (_Sciuridae_) is also

found in all parts of the world. Precisely the same may be said of the

hares, which, however, become scarce in South America. On the other

hand, the scaly-tailed squirrels (_Anomaluridae_), the jumping-hares

(_Pedetidae_), and the strand-moles (_Bathyergidae_) are exclusively

African; while the sewellels (_Haplodontidae_) and the pocket-gophers

(_Geomyidae_) are as characteristically North American, although a few

members of the latter have reached Central America. The beavers

(_Castoridae_) are restricted to the northern hemisphere, whereas the

dormice (_Gliridae_) and the mole-rats (_Spalacidae_) are exclusively

Old World forms, the latter only entering the north of Africa, in

which continent the former are largely developed. The jerboa group

(_Dipodidae_, or _Jaculidae_) is also mainly an Old World type,

although its aberrant representatives the jumping-mice (_Zapus_) have

effected an entrance into Arctic North America. Porcupines enjoy a

very wide range, being represented throughout the warmer parts of the

Old World, with the exception of Madagascar (and of course

Australasia), by the _Hystricidae_, and in the New World by the

_Erethizontidae_. Of the remaining families of the Simplicidentata,

all are southern, the cavies (_Caviidae_), chinchillas

(_Chinchillidae_), and degus (_Octodontidae_) being Central and South

American, while the _Capromyidae_ are common to southern America and

Africa, and the _Ctenodactylidae_ are exclusively African. The near

alliance of all these southern families, and the absence of so many

Old World families from Madagascar form two of the most striking

features in the distribution of the order. Lastly, among the

Duplicidentata, the picas (_Ochotonidae_ or _Lagomyidae_) form a group

confined to the colder or mountainous regions of the northern

hemisphere.

Among the existing land Carnivora (of which no representatives except

the introduced dingo are found in Australasia) the cat-tribe

(_Felidae_) has now an almost cosmopolitan range, although it only

reached South America at a comparatively recent date. Its original

home was probably in the northern hemisphere; and it has no

representatives in Madagascar. The civet-tribe (_Viverridae_), on the

other hand, which is exclusively an Old World group, is abundant in

Madagascar, where it is represented by peculiar and aberrant types.

The hyenas (_Hyaenidae_), at any rate at the present day, to which

consideration is mainly limited, are likewise Old World. The dog-tribe

(_Canidae_), on the other hand, are, with the exception of Madagascar,

an almost cosmopolitan group. Their place of origin was, however,

almost entirely in the northern hemisphere, and not improbably in some

part of the Old World, where they gave rise to the bears (_Ursidae_).

The latter are abundant throughout the northern hemisphere, and have

even succeeded in penetrating into South America, but, with the

exception of the Mediterranean zone, have never succeeded in entering

Africa, and are therefore of course unknown in Madagascar. The raccoon

group (_Procyonidae_) is mainly American, being represented in the Old

World only by the pandas (_Aelurus_ and _Aeluropus_), of which the

latter apparently exhibits some affinity to the bears. The birthplace

of the group was evidently in the northern hemisphere--possibly in

east Central Asia. The weasel-tribe (_Mustelidae_) is clearly a

northern group, which has, however, succeeded in penetrating into

South America and Africa, although it has never reached Madagascar.

The extinct creodonts, especially if they be the direct descendants of

the anomodont reptiles, may have originated in Africa, although they

are at present known in that continent only from the Fayum district.

Elsewhere they occur in South America and throughout a large part of

the northern hemisphere, where they appear to have survived in India

to the later Oligocene or Miocene.

In the case of the great order, or assemblage, of Ungulata it is

necessary to pay somewhat more attention to fossil forms, since a

considerable number of groups are either altogether extinct or largely

on the wane.

So far as is at present known, the earliest and most primitive group,

the Condylarthra, is a northern one, but whether first developed in

the eastern or the western hemisphere there is no sufficient evidence.

The more or less specialized Litopterna and Toxodontia, as severally

typified by the macrauchenia and the toxodon, are, on the other hand,

exclusively South American. With the primitive five-toed Amblypoda, as

represented by the coryphodon, we again reach a northern group, common

to the two hemispheres; but there is not improbably some connexion

between this group and the much more specialized Barypoda, as

represented by _Arsinöitherium_, of Africa. The Ancylopoda, again,

typified by _Chalicotherium_, and characterized by the claw-like

character of the digits, are probably another northern group, common

to the eastern and western hemispheres.

Recent discoveries have demonstrated the African origin of the

elephants (Proboscidea) and hyraxes (Hyracoidea), the latter group

being still indeed mainly African, and in past times also limited to

Africa and the Mediterranean countries. As regards the elephants (now

restricted to Africa and tropical Asia), there appears to be evidence

that the ancestral mastodons, after having developed from African

forms probably not very far removed from the Amblypoda, migrated into

Asia, where they gave rise to the true elephants. Thence both

elephants and mastodons reached North America by the Bering Sea route;

while the former, which arrived earlier than the latter, eventually

penetrated into South America.

The now waning group of Perissodactyla would appear to have originally

been a northern one, as all the three existing families, rhinoceroses

(_Rhinocerotidae_), tapirs (_Tapiridae_), and horses (_Equidae_), are

well represented in the Tertiaries of both halves of the northern

hemisphere. If eastern Central Asia were tentatively given as the

centre of radiation of the group, this might perhaps best accord with

the nature of the case. Rhinoceroses disappeared comparatively early

from the New World, and never reached South America. In Siberia and

northern Europe species of an African type survived till a

comparatively late epoch, so that the present relegation of the group

to tropical Asia and Africa may be regarded as a modern feature in

distribution. Horses, now unknown in a wild state in the New World,

although still widely spread in the Old, attained a more extensive

range in past times, having successfully invaded South America. On the

other hand, in common with the rest of the Perissodactyla, they never

reached Madagascar. In addition to the occurrence of their fossil

remains almost throughout the world, the former wide range of the

tapirs is attested by the fact of their living representatives being

confined to such widely sundered areas as Malaysia and tropical

America.

The Artiodactyla are the only group of ungulates known to have been

represented in Madagascar; but since both these Malagasy forms--namely

two hippopotamuses (now extinct) and a river-hog--are capable of

swimming, it is most probable that they reached the island by crossing

the Mozambique Channel. As regards the deer-family (_Cervidae_), which

is unknown in Africa south of the Sahara, it is quite evident that it

originated in the northern half of the Old World, whence it reached

North America by the Bering Sea route, and eventually travelled into

South America. More light is required with regard to the past history

of the giraffe-family (_Giraffidae_), which includes the African okapi

and the extinct Indian _Sivatherium_, and is unknown in the New World.

Possibly, however, its birthplace may prove to be Africa; if so, we

shall have a case analogous to that of the African elephant, namely

that while giraffes flourished during the Pliocene in Asia (where

they may have originated), they survive only in Africa. An African

origin has also been suggested for the hollow-horned ruminants

(_Bovidae_); and if this were substantiated it would explain the

abundance of that family in Africa and the absence from the heart of

that continent of the deer-tribe. Some confirmation of this theory is

afforded by the fact that whereas we can recognize ancestral deer in

the Tertiaries of Europe we cannot point with certainty to the

forerunners of the _Bovidae_. Whether its birthplace was in Africa or

to the north, it is, however, clear that the hollow-horned ruminants

are essentially an Old World group, which only effected an entrance

into North America at a comparatively recent date, and never succeeded

in reaching South America. So far as it goes, this fact is also in

favour of the African ancestry of the group.

The _Antilocapridae_ (prongbuck), whose relationships appear to be

rather with the _Cervidae_ than with the _Bovidae_, are on the other

hand apparently a North American group. The chevrotains

(_Tragulidae_), now surviving only in West and Central Africa and

tropical Asia, are conversely a purely Old World group.

The camels (_Tylopoda_) certainly originated in the northern

hemisphere, but although their birthplace has been confidently claimed

for North America, an equal, if not stronger, claim may be made on the

part of Central Asia. From the latter area, where wild camels still

exist, the group may be assumed to have made its way at an early

period into North America; whence, at a much later date, it finally

penetrated into South America. In the Old World it seems to have

reached the fringe of the African continent, where its wanderings in a

wild state were stayed.

The pigs (_Suidae_) and the hippopotamuses (_Hippopotamidae_) are

essentially Old World groups, the former of which has alone succeeded

in reaching America, where it is represented by the collateral branch

of the peccaries (_Dicotylinae_). An African origin would well explain

the present distribution of both groups, but further evidence on this

point is required before anything decisive can be affirmed, although

it is noteworthy that the earliest known pig (_Geniohyus_) is African.

The Suinae are at present spread all over the Old World, although the

African forms (other than the one from the north) are markedly

distinct from those inhabiting Europe and Asia. Hippopotamuses, on the

contrary, are now exclusively African, although they were represented

in tropical Asia during the Pliocene and over the greater part of

Europe at a later epoch.

A brief notice with regard to the distribution of the Primates must

suffice, as their past history is too imperfectly known to admit of

generalizations being drawn. The main facts at the present day are,

firstly, the restriction of the Prosimiae, or lemurs, to the warmer

parts of the Old World, and their special abundance in Madagascar

(where other Primates are wanting); and, secondly, the wide structural

distinction between the monkeys of tropical America (Platyrrhina), and

the Old World monkeys and apes, or Catarrhina. It is, however,

noteworthy that extinct lemurs occur in the Tertiary deposits of both

halves of the northern hemisphere--a fact which has induced Dr J. L.

Wortman to suggest a polar origin for the entire group--a view we are

not yet prepared to endorse. For the distribution of the various

families and genera the reader may be referred to the article

PRIMATES; and it will suffice to mention here that while chimpanzees

and baboons are now restricted to Africa and (in the case of the

latter group) Arabia, they formerly occurred in India.

As regards aquatic mammals, the greater number of the Cetacea, or

whales and dolphins, have, as might be expected, a very wide

distribution in the ocean. A few, on the other hand, have a very

restricted range, the Greenland right whale (_Balaena mysticetus_)

being, for instance, limited to the zone of the northern circumpolar

ice, while no corresponding species occurs in the southern hemisphere.

In this case, not only temperature, but also the peculiar mode of

feeding, may be the cause. The narwhal and the beluga have a very

similar distribution, though the latter occasionally ranges farther

south. The bottle-noses (_Hyperöodon_) are restricted to the North

Atlantic, never entering, so far as known, the tropical seas. Other

species are exclusively tropical or austral in their range. The pigmy

whale (_Neobalaena marginata_), for instance, has only been met with

in the seas round Australia, New Zealand and South America, while a

beaked whale (_Berardius arnouxi_) appears to be confined to the New

Zealand seas.

The Cetacea, however, are by no means limited to the ocean, or even to

salt water, some entering large rivers for considerable distances, and

others being exclusively fluviatile. The susu (_Platanista_) is, for

instance, extensively distributed throughout nearly the whole of the

river systems of the Ganges, Brahmaputra and Indus, ascending as high

as there is water enough to swim in, but apparently never passing out

to sea. The individuals inhabiting the Indus and the Ganges must

therefore have been for long ages isolated without developing any

distinctive anatomical characters, those by which _P. indi_ was

separated from _P. gangetica_ having been shown to be of no constant

value. _Orcella fluminalis_, again, appears to be limited to the

Irrawaddy; and at least two distinct species of dolphin, belonging to

different genera, are found in the Amazon. It is remarkable that none

of the great lakes or inland seas of the world is inhabited by

cetaceans.

The great difference in the manner of life of the sea-cows, or

Sirenia, as compared with that of the Cetacea, causes a corresponding

difference in their geographical distribution. Slow in their

movements, and feeding on vegetable substances, they are confined to

the neighbourhood of rivers, estuaries or coasts, although there is a

possibility of accidental transport by currents across considerable

distances. Of the three genera existing within historic times, one

(_Manatus_) is exclusively confined to the shores of the tropical

Atlantic and the rivers entering into it, individuals scarcely

specifically distinguishable being found both on the American and the

African. The dugong (_Halicore_) is distributed in different colonies,

at present isolated, throughout the Indian Ocean from Arabia to North

Australia; while the _Rhytina_ or northern sea-cow was, for some time

before its extinction, limited to a single island in the extreme north

of the Pacific Ocean.

The seals (_Pinnipedia_) although capable of traversing long reaches

of ocean, are less truly aquatic than the last two groups, always

resorting to the land or to ice-floes for breeding. The geographical

range of each species is generally more or less restricted, usually

according to climate, as they are mostly inhabitants either of the

Arctic or Antarctic seas and adjacent temperate regions, few being

found within the tropics. For this reason the northern and the

southern species are for the most part quite distinct. In fact, the

only known exception is the case of a colony of elephant-seals

(_Macrorhinus leoninus_), whose general range is in the southern

hemisphere, inhabiting the coast of California. In this case a

different specific name has been given to the northern form, but the

characters by which it is distinguished are of little importance, and

probably, except for the abnormal geographical distribution, would

never have been discovered. The most remarkable circumstance connected

with the distribution of seals is the presence of members of the order

in the three isolated great lakes or inland seas of Central Asia--the

Caspian, Aral and Baikal--which, notwithstanding their long isolation,

have varied but slightly from species now inhabiting the Polar Ocean.

AUTHORITIES.--The above article is partly based on that of Sir W. H.

Flower in the 9th edition of this work. The literature connected with

mammals is so extensive that all that can be attempted here is to

refer the reader to a few textbooks, with the aid of which, combined

with that of the annual volumes of the _Zoological Record_, he may

obtain such information on the subject as he may require: F. E.

Beddard, "Mammals," _The Cambridge Natural History_, vol. x. (1902);

W. H. Flower and R. Lydekker, _The Study of Mammals_ (London, 1891);

Max Weber, _Die Säugethiere_ (Jena, 1904); W. T. Blanford, _The Fauna

of British India--Mammalia_ (1888-1891); D. G. Elliot, _Synopsis of

the Mammals of North America_ (Chicago, 1901) and _The Mammals of

Middle America and the West Indies_ (Chicago, 1904); W. L. Sclater,

_The Fauna of South Africa--Mammals_ (Cape Town, 1901-1902); W. K.

Parker, _Mammalian Descent_ (London, 1885); E. Trouessart, _Catalogus

mammalium, tam viventium quam fossilium_ (Paris, 1898-1899); and

supplement, 1904-1905; T. S. Palmer, _Index generum mammalium_

(Washington, 1904); W. L. and P. L. Sclater, _The Geography of

Mammals_ (London, 1899); R. Lydekker, _A Geographical History of

Mammals_ (Cambridge, 1896). (W. H. F.; R. L.)

MAMMARY GLAND (Lat. _mamma_), or female breast, the organ by means of

which the young are suckled, and the possession of which, in some region

of the trunk, entitles the animal bearing it to a place in the order of

Mammalia.

_Anatomy._--In the human female the gland extends vertically from the

second to the sixth rib, and transversely from the edge of the sternum

to the mid axillary line; it is embedded in the fat superficial to the

pectoralis major muscle, and a process which extends toward the arm-pit

is sometimes called the axillary tail. A little below the centre of the

glandular swelling is the _nipple_, surrounding which is a pigmented

circular patch called the areola; this is studded with slight nodules,

which are the openings of areolar glands secreting an oily fluid to

protect the skin during suckling. During the second or third month of

pregnancy the areola becomes more or less deeply pigmented, but this to

a large extent passes off after lactation ceases. In structure the gland

consists of some fifteen to twenty lobules, each of which has a

_lactiferous duct_ opening at the summit of the nipple, and branching in

the substance of the gland to form secondary lobules, the walls of which

are lined by cubical epithelium in which the milk is secreted. These

secondary lobules project into the surrounding fat, so that it is

difficult to dissect out the gland cleanly. Before opening at the nipple

each lactiferous duct has a fusiform dilatation called the _ampulla_.

After the child-bearing period of life the breasts atrophy and tend to

become pendulous, while in some African races they are pendulous

throughout life. Variations in the mammary glands are common; often

the left breast is larger than the right, and in those rare cases in

which one breast is suppressed it is usually the right, though

suppression of the breast does not necessarily include absence of the

nipple.

[Illustration: (From A. F. Dixon, Cunningham's _Text Book of Anatomy_.)