Of the varied forms of animal life that people the globe, those that
possess a back-bone and two pairs of limbs (the VERTEBRATA) are considered
the highest in the scale. Of the _Vertebrata_, those are held to be of
superior organisation which possess warm red blood and suckle their young
with milk from the breast (_i.e._, MAMMALIA). Our present volume deals with
the highest and most specialised group of the Mammalia, and, therefore, of
the whole Animal Kingdom.
Man, in respect of his mental endowments, stands alone and unapproachable
among living creatures. Considered as to his "place in nature," however, he
must be described as an erect-walking Mammal, possessing anterior
extremities developed into hands of great perfection, for exclusive use as
tactile and grasping organs, and posterior limbs, on which his body is
perfectly balanced and entirely supported, exclusively devoted to
locomotion, as well as highly specialised cerebral characters. These
attributes in part constitute the standard by which we estimate superiority
in animal structure, and fitness of adaptation.
Notwithstanding the numerous varieties and races of {2}mankind distributed
over every region of the globe, each exhibiting differences in habits,
customs and superficial complexion, Man forms but one species, _Homo
sapiens_, the sole representative of the unique genus of his family. Though
the genus _Homo_ is thus far apparently zoologically isolated, there is a
remarkable group of animals, which we designate "Apes," and which,
possessing many of the same structural characters more or less modified,
stand apart from all the other Mammalia, and make a distinct approach to
Man. Between Man, however, and the Apes, even the untrained eye at once
perceives, amid obvious marks of inferiority, unmistakable resemblances,
while anatomical investigations reveal that "the points in which Man
differs from the Apes most nearly resembling him, are not of greater
importance than those in which the Ape differs from other and universally
acknowledged members of the group." (_Flower_ and _Lydekker_.) The Apes, on
the other hand, are so nearly related to the Monkeys, the Baboons and the
Marmosets, by characters which insensibly merge into each other that they,
along with Man, must logically be embraced in the same zoological division.
The animals known to us as Lemurs, called by the Germans "Half-Apes" and by
the French "False-Monkeys," are the nearest to the Apes and Man of all the
remaining Mammals, though there are many points of divergence from the
above-named groups. The Lemurs, in fact, exhibit considerable affinity to
lower forms of Mammalia, especially to the Insectivora, but in internal
structure and habit they approach the Anthropiform[1] group just referred
to--in the flattened form of the digits, the opposable great toe, with its
ankle-bone (the ento-cuneiform) rounded for its articulation, as in the
higher Apes and Man.
{3}The Lemurs have, by many distinguished naturalists, been relegated to a
distinct Order quite separate from the latter; but by such pre-eminent
authorities as Linnæus, Lesson, Huxley, Broca and Flower, they have been
assigned a subordinate position within that great Order, on which has been
conferred the rank of the Primates of the Animal Kingdom.
The Order PRIMATES, therefore, comprises two very homogeneous
sub-orders--(1) The Lemur-like animals (LEMUROIDEA) including the Aye-Aye,
the Tarsier, and the True Lemurs; and (2) the Man-like animals (the
ANTHROPOIDEA), which embrace the Marmosets, the Baboons, the great Apes,
and Man.
In common with all other Mammals, the Primates are furnished with an
epidermal covering, which, except in Man, consists of a woolly or hairy
fur. They possess four limbs and a tail, which may be long, short, or
concealed, and which is often used as a prehensile organ. The young are
born in a condition of greater or less helplessness, with their eyes, as a
rule, unopened, and the framework of their bodies incompletely ossified,
and consequently requiring protective care and entire nourishment from the
mother, for a considerable period. At maturity this skeleton consists of a
skull, a breast- and a back-bone of many pieces, ribs, jointed limbs, and a
pair of collar-bones. As a knowledge of many of these bones and some of the
more prominent organs of the body are necessary for an accurate
comprehension of the description and classification of the animals
discussed in this volume, a few of the more important must be briefly
referred to.
The _cranium_, formed of many bones firmly united together, consists of a
cerebral region, or box, containing and guarding the brain, and a facial
region, in which are situated, besides the mouth, the organs of sight and
smell. The bones connected with the {4}mouth are the two maxillæ, along the
margins of which are placed the grinding- or cheek-teeth; the two
pre-maxillæ, in which are set the cutting- and the eye-teeth; and lastly,
the palatine bones which form the roof of the mouth. Hinged on to the sides
of the cranium is the toothed mandible, or lower jaw, composed of two
halves, which may be solidly or loosely joined together in the mid-line, or
symphysis. Along the under surface of the skull, there are, besides the
great (often posterior) orifice for the entrance of the spinal cord,
numerous _foramina_, or openings, for the passage of blood-vessels for the
nourishment of the brain, and of nerves which bring all parts of the body
into relation with the supreme directing centre. Conspicuous near its
posterior part, on each side, is an ivory-like capsule, the periotic bone,
containing the essential organ of hearing. Lying beneath the lower jaw is
the hyoid arch, a slender framework of bones, supporting the tongue and the
upper end of the windpipe with the organ of voice. In a few of the Monkeys
and Apes certain of the bones of this arch are much enlarged and hollowed
for increasing the volume of sound emitted by them. On either side of the
great opening which is so conspicuous at the hinder part of the skull, for
the reception of the spinal cord, is a smooth kidney-shaped surface, called
a "condyle." These two condyles serve for the articulation of the first
segment of the back-bone to the cranium, and by the possession of this pair
of condyles the Mammalian skull can always be distinguished from that of
Birds and Reptiles. The pieces of which the back-bone are composed are
named the _vertebræ_. Those of the neck, the "cervical" vertebræ, are
recognised by having no true ribs attached to them, and are, in all
Primates, seven in number. Those of the back, or "dorsal" vertebræ, may be
distinguished by having articulated to them, on each side, {5}a movable
rib, the other end of which is attached to the breast-bone; they follow
next to the cervical vertebræ, while to them succeed the "lumbar" vertebræ
which carry no complete ribs. The dorsal and lumbar segments vary in
number, but together they rarely exceed seventeen. Behind these extend the
"sacral" vertebræ--completely ossified together, and lastly, the bones of
the tail or "caudal" vertebræ, which may be many or few, according to the
length of that appendage.
The fore-limb is composed of three segments, the arm, fore-arm, and hand,
together with a block by which it is attached to the side of the body. To
this block--the blade-bone or _scapula_--is articulated the arm-bone, or
_humerus_, which at its elbow-joint hinges with the two bones, the _ulna_
and the _radius_, of the fore-arm, on which in turn the hand is rotated.
The hand is made up of three parts, the wrist-bones, or _carpus_, closely
united together in two transverse rows with a central bone intervening
between them; next the elongated bones of the palm of the hand, or
_metacarpus_, one to each finger, and lastly the _phalanges_, or
finger-bones, three to each digit, except in the thumb, where there are but
two. The hind-limb is formed on exactly the same plan. It has a connecting
block--the pelvis; giving suspension to the thigh, with its single bone,
the _femur_, to which articulates the leg, with two bones (_tibia_ and
_fibula_), and the tripartite foot, composed of _tarsus_, _metatarsus_, and
_phalanges_.
Of the digestive organs of the Primates the teeth present very important
characters, from the point of view of the classification of the Order. They
differ in form and number, and have distinct functions to perform. The
teeth situated in front are the _incisors_ and _canines_, sharp and
pointed, for seizing, cutting, and holding the food. Behind them come the
{6}_pre-molars_, and still further back the _molars_, both with broad
crowns of complicated tubercles and ridges for milling the hard portions
contained in the food. Animals provided--as all the Primates are--with
these different sorts of teeth, are said to be _Heterodont_,[2] in
contradistinction to forms like the Dolphins and Whales, which are termed
_Homodont_,[3] because the whole of these teeth are of the same pattern.
The Primates are _Diphyodont_[4] as well, because many of their permanent
teeth are preceded by another set, commonly known as the _milk-teeth_. In
order to present to the eye at a glance the number of each sort that any
species possesses, a _dental formula_ has been adopted by naturalists. Such
a formula as I2/2, C1/1, P3/3, M3/3 = 36, indicates that in _one half of
the mouth_, above and below, there are 2 incisors, 1 canine, 3 pre-molars,
and 3 molars = 18; and therefore in the _two halves_ of the mouth together
there are 36 teeth in all.
The masticated food, partially digested by the saliva of the mouth,
descends the gullet by the muscular contractions of its walls to the
simple, sac-like, stomach, and thence to the intestines. These latter
consist of two portions, one smaller and narrower, nearer to the stomach,
and a second portion further down, larger and wider; the junction of the
two portions being marked by a process of varying length, the _cæcum_. The
stomach and intestines, with other important structures, such as the liver,
kidneys and generative organs, are contained in a lower cavity, separated
by a muscular midriff, the diaphragm, from the upper part or thorax,
containing the blood-purifying and pumping organs, the lungs and the heart.
{7}The upper part of the windpipe is, in all Primates, modified to form the
larynx, or organ of voice, constituted by fibrous strings stretched across
its orifice, where they may be set in vibration by the air, in its passage
to and from the lungs.
The brain is relatively large in proportion to the body, and attains in the
higher of the two sub-orders its most perfect development. The main brain
(or cerebral hemispheres), when viewed from above, in size preponderates
over, and conceals (except in the Lemurs) all the other parts of that
organ. The surface of its lateral halves, which are connected by transverse
bands so as to insure harmony of action between them, is marked by fissures
and foldings, or convolutions, which vary in number and complexity,
evidently in relation to the intelligence of the animal. The brain within
the skull gives origin to the nerves for the chief organs of sense; while
from its posterior part it is continued along the back--within a canal
formed by the neural arches of the vertebræ--as the spinal column, from
which arise the rest of the nerves for the body.
The young of all the Primates are nourished in the mother's womb by the
passage of material from the blood-vessels of the parent through an organ
known as the _placenta_. They are all born in a helpless condition, and
remain unable to look after themselves for a considerable period, during
which they are dependent on the milk secreted on the ventral surface of the
mother by two or four glands, the teats or _mammæ_--those characteristic
organs from which the "Mammalia" have derived their name. These glands are
present in both sexes, but are functional only in the female.
We shall now proceed to describe more minutely the first of the two
sub-orders of the Primates--the Lemur-like animals.
{8}I. THE LEMURS--SUB-ORDER LEMUROIDEA.
The Aye-Aye, the Tarsier, and the True Lemurs constitute this first
sub-order. They are characterised by having the muzzle long and narrow,
more or less Dog-like in shape, and the upper lip often divided into two by
the nose-pad. The external ears (Fig. 1) are enlarged, with flattened
margins, but have no "hem" as in the higher Anthropoids. (Fig. 2.)
[Illustration: Fig. 1. Lemuroid Ear.]
[Illustration: Fig. 2. Anthropoid Ear.]
The trunk is relatively long and compressed, and the tail when long is
never truly prehensile. Of the limbs, the posterior are longer than the
anterior, and all have five digits, each bearing a flat nail except the
second toe, which has invariably a long pointed claw, their tips ending in
prominent discoidal tactile pads. (Fig. 3.)
Of the digits, the index is sometimes quite rudimentary, while the thumb is
large, and the great toe especially so, both being opposable. Teats occur
on the breast, on the abdomen, or on both.
Of the skeleton, the eye-sockets, or orbits, are directed forward, and have
complete bony margins, which, however, are not {9}closed in by bone behind
(as in Monkeys), but freely communicating beneath the post-orbital process
(except in _Tarsius_) with the temporal hollow behind. In the young of some
species the orbit is more enclosed than it is in the adult: the orifice for
the lachrymal duct of the eye is placed external to the margin of the
orbit: the hollow for the olfactory lobes of the brain is always large.
[Illustration: Fig. 3. Foot of _Chirogale trichotis_, Günther.
(P. Z. S., 1875, p. 79.)]
Having four kinds of teeth, and a set in succession to the milk-teeth, they
are Heterodont and Diphyodont. The dental formula is I2/2, C1/1, P3/3, M3/3
= 36 (_vide_ anteà, p. 6), and the upper jaw has a toothless space in the
centre (except in the Aye-Aye). Of the upper teeth, the _incisors_ are
sometimes absent, but generally present; if unequal in size the inner one
is the larger of the two. The canines are prominent; the pre-molars all
have a _cingulum_, or girdle, round the base, more or less enlarged
backwards into a process ("talon" or "heel"); the anterior pre-molar
vertically long and canine-shaped; the median and posterior with three main
points (tubercles or cusps) and one or two smaller ones on the crown, and
having a bar or ridge uniting the front inner with the hind outer cusp. The
anterior and median _molars_ have three or four main cusps, and one {10}or
two smaller or subsidiary ones on the crown; the cingulum is well
developed. The posterior molars have generally three cusps.
In the lower jaw the _incisors_ are close-set and comb-like, remarkable for
protruding in front, like the teeth of a Rat or a Rabbit. The _canines_
also protrude horizontally, and, being placed alongside of the incisors,
are difficult to distinguish from the latter excepting that they are
broader and thicker.
[Illustration: Fig. 4. Skull of Lemuroid.