General, Characters. MAMMALIA. General Characters. 5 
of the human subject, and the enormously long one of 
the giraffe, each contain seven vertebrae, although the 
one constitutes only one-seventh and the other three- 
sevenths of the entire vertebral column. In the whales 
the vertebrae of this region of the body are completely 
united together, to form a single bone. Except in the 
sloths, all the cervical vertebrae are destitute of ribs, 
and the spinous processes gradually increase in height 
as we recede from the head. The first two vertebrae, 
however, in the Mammalia, present peculiarities of 
structure which have obtained them distinct names in 
all systems of anatomy. The first, called the atlas, 
forms a bony ring, bearing on its upper surface a pair 
of cuplike depressions for the reception of the promi- 
nent condjdes or articulating tubercles of the base of 
the skull (see p. 3) ; by means of this articulation the 
head is enabled to move up and down. The second 
vertebra is called the axis, from its possessing a peculiar 
process which projects forward into the ring of the first, 
and articulates with a flat surface on the inside of its 
anterior part. By this arrangement the rotatory move- 
ment of the head is effected. 
The dorsal vertebrae are usually thirteen in number ; 
but this general rule is liable to many exceptions. The 
foremost dorsal vertebrae usually have their upper 
spinous processes greatly developed, especially in ani- 
mals possessing long necks or heavy heads ; these 
processes and those of the posterior cervical vertebrae 
give attachment to a strong ligament (the nuchal liga- 
ment), which powerfully aids in supporting the head, 
and in some animals is continued backward as far as 
tlie loins. The dorsal vertebrae are distinguished from 
the rest by their bearing the articulating surfaces for 
the ribs, which are confined to this region of the bod 3 ^ 
The ribs are long, usually slender, curved bones, which 
articulate by their heads with the bodies of two verte- 
brae, and are nearly always supported by a tubercle 
against the transverse processes of the hinder of these. 
The anterior or true ribs are united by cartilaginous 
pieces with the sternum or breast-bone, which occupies 
the centre of the anterior or lower part of the chest. 
Behind these are some shorter ribs, commonly known 
as false or floating ribs, which are never united directly 
with the sternum, but only by the intermediation of a 
common cartilaginous band. 
Of the lumbar vertebrae there are usually six or 
seven, but the number varies from two to nine. They 
are usually larger in the body than the dorsal vertebrae, 
and the lateral processes are often greatly developed ; 
they are distinguished from the dorsal vertebrae by the 
absence of ribs, and of the surfaces for the attachment 
of the latter. Behind the lumbar region comes the 
sacrum, a single bony piece, which sometimes con- 
sists of only one vertebra, but is usually composed 
of three or four amalgamated together, bearing traces 
of its compound nature in the apertures which indicate 
the original points of separation of the distinct vertebrae. 
This bone gives a firm attachment to the pelvis, or 
supporting arch of the hinder limbs, which will be 
described in treating of those members. Tire caudal 
vertebrae are usually numerous, amounting to as many 
as forty-six in the long-tailed manis. The smallest 
number of distinct joints is four; but in the human 
species, and in some others, the caudal region of the 
vertebral column is reduced to a mere rudiment. 
The structure of the limbs is nearly identical with 
the description of the typical conformation of the 
extremities of the vertebrata already given. The 
anterior limbs are always present in mammals ; the 
posterior are sometimes deficient. The former are 
articulated to a shoulder-blade or scapula, Q, a flat 
and somewhat triangular bone, usually provided with 
a strong ridge on its upper surface, which lies amongst 
the muscles upon the anterior ribs. The shoulder- 
blades are frequently supported in their position by 
collar-bones or clavicles, which spring from the fore 
part of the sternum, and at the opposite extremity 
articulate with the lower part of the shoulder-blade. 
These, however, are sometimes wanting, or imperfectly 
developed. The coracoid bones, which form an im- 
portant part of the supporting arch of the anterior 
members in Birds and Reptiles, constituting, in fact, a 
second and even more powerful pair of collar-bones, 
only occurs in its full development in one small group 
of mammals ; in the rest it is reduced to a rudimentary 
condition and amalgamated with the shoulder-blade, 
of which it forms a small process. 
The anterior limb Itself usually consists, as previously 
stated, of the arm-bone or humerus, k ; the radius and 
ulna, s, T ; the carpus or wrist, u ; the metacarpus or 
hand, v ; and the fingers, w. These parts all undergo 
great modifications, not only as regards their form and 
comparative size, but also by the amalgamation, or 
total suppression of some of their subordinate consti- 
tuents. Thus, in the monkeys, Plate 34, fig. Ill, we 
generally find all the parts fully developed, and almost 
equal in perfection to the same parts in man ; in the 
carnivorous beasts, Plate 33, fig. 105, the various por- 
tions of the apparatus are still very distinct, but the 
great mobility they possess in man and the monkeys is 
already considerably diminished, to adapt the limbs to 
the purposes of terrestrial progression ; in the seals, 
Plate 34, fig. 114, and the cetacea, Plate 34, fig. 109, we 
still recognize the same parts, but with their mutual 
powers of motion still further limited, to fit them to act 
as paddles in the water. The ant-eater and the sloth, 
Plate 33, fig. 107, and Plate 34, fig. 112, also exhibit the 
same structure, modified in its details to suit particular 
purposes, and in the latter case displaying a diminution 
in the number of fingers. With the exception of the 
aquatic seal and dugong, all the animals to which we 
have hitherto referred are either terrestrial or arboreal 
in their habits; but in the bats, Plate 34, fig. 110, we 
find the anterior limbs adapted for the purpose of flight. 
In these the arm-bone, R, is not very disproportionately 
elongated, but the bones of the fore-arm, s, the meta- 
carpal bones, v, and the phalanges or finger-bones, w, 
are of immense length, and these, by stretching a 
leathery membrane which unites them, enable the bats 
to raise themselves into the air, and to fly through that 
element with great swiftness. 
In the terrestrial animals to which we have already 
referred, the radius and ulna were still capable of a 
certain amount of rotatory motion, although not to the 
extent presented by the monkeys. In the herbivorous 
terrestrial mammals, the toes are terminated by hoofs, 
