Warm-blooded Vertebrates (p. 16), usually covered with hair, and
bringing forth living young, that suck for some time after birth. The
female is provided with milk-glands on the thorax or abdomen, or both
those regions.
Speaking quite broadly, the skeleton is like that of man, described on
pp. 4–8. There are, however, great differences in detail. The cranium is
relatively much smaller, and the bones of the face (especially of the
jaws) are usually much larger than in the human skull. The number of the
cervical vertebræ is seven in all Mammals, as in man; but the other
kinds of vertebræ vary in number in the different species. The number of
caudal vertebræ, for example, is very variable. As most Mammals go on
all fours, their fore and hind limbs are much more similar than is the
case in man. In many the thigh and upper-arm bones are drawn closely up
to the body (horse, ox, pig). Mammals never have more than five fingers
or toes, but may have fewer. The thumb or great toe is the first to
disappear (hind foot of dog, fore and hind foot of pig). There may be
only three (rhinoceros), two (ox, sheep), or one (horse) digit
developed. In addition to fully developed digits, there are in many
Mammals very small stunted ones (“dew-claws” of the stag).
[Illustration:
FIG. 12.—Vertical Section of a Human Grinding Tooth.
]
[Illustration:
FIG. 13.—Crown of a Grinder of the Ox. _a_, cement; _b_, enamel; _c_,
dentine; _d_, enamel; _e_, cement.
]
There are also great differences in the way of resting the feet on the
ground. Man and bear tread on the soles of the feet (plantigrade); dog
and cat walk on the under side of the toes (digitigrade), not on the
other parts of the feet. Ox, pig, horse, etc., rest while walking only
on the tips of the toes, which are sheathed in hoofs (unguligrade).
The teeth of mammals are wedged into special sockets in the jaw-bones.
The structure of a mammalian tooth is made clear by Fig. 12. We first
distinguish a pulp-cavity (_p_), which in the living animal is filled
with a substance supplied by a bloodvessel and nerve. This cavity is
surrounded by the dentine (_d_), a hard substance which makes up the
greater part of the tooth. Hard enamel (_s_) covers the whole of the
crown in man and many animals, while in certain other forms it is found
only on part of the crown. The root of the tooth is covered with cement
(_z_), a bone-like substance.
All teeth in which the entire surface of the crown is covered by enamel
only are known as _simple teeth_, while those into which the enamel only
penetrates in more or less deep folds, leaving the rest of the crown
uncovered, are known as _compound teeth_ (Fig. 13). The structure of the
teeth is related to the nature of the food. We distinguish three kinds
of teeth in the same animal, which, however, are not all present in
every species; these are the _incisors_, _canines_, and _grinders_. The
first two kinds are changed; but only the anterior grinders, known as
the _premolars_, are changed, while the hinder ones, the _true molars_,
do not first appear as “milk” teeth, but rather later on with the other
“permanent” teeth.
The following orders of Mammals are distinguished: I. Bimana (Man), II.
Quadrumana (Apes), III. Carnivora (Beasts of prey), IV. Insectivora
(Insect-eaters), V. Cheiroptera (Bats), VI. Rodentia (Gnawers), VII.
Ruminantia, VIII. Solidungula, IX. Pachydermata, X. Cetacea, XI.
Edentata, XII. Marsupialia (Pouched animals), XIII. Monotremata.
I shall deal here only with those orders which are of agricultural
importance.
ORDER: =Carnivora= (BEASTS OF PREY).
In each jaw there are six relatively small incisor teeth; and, on each
side of these, a large projecting canine, by which the flesh is torn
from the body of the prey (Fig. 14). The premolars and the first of the
true molars (the carnassials[2]) are strongly compressed, and have a
cutting crown; their outer surface is completely covered with hard
enamel. As the lower jaw is smaller than the upper jaw, and is only able
to move up and down, not from side to side, the sharp crowns of the
premolars, and especially those of the large carnassials, cut along one
another, and divide anything coming between them as if with shears. The
small molars which are usually found behind the carnassials have broad
tuberculated crowns. The temporal (_i.e._ chewing) muscles are strongly
developed, the general result of which is that the head is broad. The
claws are very sharp in some of the families. The Carnivora are powerful
animals, move very quickly, and are endowed with keen smell and sight.
Footnote 2:
The upper carnassials = last premolars.
The lower „ = first molars.—TR.
The wild Carnivora living in Britain belong to the families of cats,
dogs, and weasels.
Family: =Felidæ= (_Cat Family_).
Typical Carnivora with very large canines and carnassials, two premolars
in each half of each jaw, one of the upper molars, but none of the lower
ones, small and tuberculated. Tongue rough. Fore and hind feet
five-toed. When not in use, the claws are drawn back (retracted). The
Felidæ are digitigrade. Backbone very flexible, and with free power of
movement. The Felidæ are bloodthirsty, nocturnal animals, many of which
climb well, and spring upon their prey.
The group is specially exemplified by the =Domestic Cat=, the parent
stock of which is the Nubian cat (_Felis maniculata_), a native of Nubia
and the Soudan. The =Wild Cat= (_Felis catus_) is larger than the common
kind, and has a thicker tail. Formerly it was tolerably common in
Britain, but now only occurs in a few thinly populated districts.
[Illustration:
FIG. 14.—Skull of Domestic Cat.
]
The =Lynx= (_Felis Lynx_), found at one time in Germany, still lives
in the Carpathians, and in Switzerland, but occurs more commonly in
Scandinavia, Denmark, and Russia.
Family: =Canidæ= (_Dog Family_).
Head longer than in cats; canines and carnassials relatively less
developed. Two tuberculated molars on each side of each jaw. Claws not
so sharp as those of cats, and cannot be drawn back (_i.e._ are
nonretractile). Fore-foot five, hind-foot four toes. Tongue smooth.
The various races of the =Domestic Dog= belong here.
The wolf (_Canis lupus_) is no longer an inhabitant of Britain or
Germany, but sometimes crosses the German frontier from Russia,
Galicia, Hungary, the Alps, and the Ardennes, especially in winter,
and preys upon the larger domestic animals.