VERTEBRATE ANIIiIALS. 
2 
called the shoulder-blades, which lie upon the ribs, 
and are kept in their proper position partly by the 
action of powerful muscles, and partly by the support 
afforded them by one or two pairs of bones which spring 
from the front of the breast-bone ; these bones are often 
wanting. The hinder extremities, on the contrary, 
are usually articulated to a strong bony ring or basin 
(the pelvis) which is firmly attached to the vertebral 
column below the loins; the vertebrae of this part of the 
spine being also completely united to each other, so as 
to form a single bony piece (the sacrum). 
In the essential structure of the limbs there is a 
wonderful uniformity' throughout the whole of this 
great group of animals. Each limb consists of four 
distinct parts, which correspond exactly in the anterior 
and hinder extremities, although, in conformity with 
the usages of human anatomists, they have received 
different names in the two pairs. In the fore-limb 
the bones are the arm-bone, the two bones of the 
fore-arm, the bones of the wrist, and those of the 
hand; in the hind-limb they are the thigh-bone, the 
two bones of the shank, the heel-bones, and those of 
the foot. The arm-hone and thigh-bone {humerus and 
femur) articulate respectively with the shoulder-blade 
and pelvis ; they are single bones, usually of a cylin- 
drical form. The fore-arm and the shank include two 
parallel bones (called the ulna and radius in the arm, 
the tibia and fibula in the leg), one of which, in each 
member (the ulna and the tibia), is united by a hinge- 
like joint with the lower extremity of the arm or 
thigh-bone, forming the elbow or the knee. The 
other bones {radius vradi fibula) are scarcely, if at all, 
attached at this joint ; they are consequently capable 
of rotating to a certain extent, and thus enable the 
hand or foot to he turned in various directions. It 
is to the broad extremity of these latter bones that 
those of the wrist and heel {carpal and tarsal bones) 
are attached; these are numerous short bones, packed 
closely together, but still capable of a greater . or less 
freedom of motion. They are followed by the bones of 
the hand and foot {metacarpal, metatarsal, and digital 
hones), which frequently form five rays of three or 
four joints in each, starting from the wrist or heel. 
Of these the metacarpal and the metatarsal bones 
constitute the palm of the hand and the sole of the 
foot in man; the digital bones, which are also called 
phalanges, form the fingers and toes. 
It is not to be supposed, however, that all these 
parts present themselves to our notice with equal 
distinctness in every creature formed upon what is 
called by naturalists the vertebrate type; in fact, we 
meet with an almost endless variety of modifications in 
the different regions of the body, but especially in the 
limbs ; and the study of these modifications, of the 
wonderful series of changes, by which the Creator of 
all things, submitting himself, as it were, to a self- 
imposed law, has adapted the same general type of 
structure to the most dissimilar purposes, is not only 
one of the most interesting branches of zoology, but 
also one of the most striking proofs furnished by 
natural theology of the prevalence of an intelligent 
design in Animated Nature. 
It is the business of the philosophical anatomist to 
investigate these marvellous modifications of structure; 
to trace the plan by which the same organs have been 
adapted to the most different offices, and to endeavour, 
by deducing therefrom the abstract or ideal form from 
which all the special structures presented to our obser- 
vation may be derived by variations in the degree of 
development of the different parts, to obtain a type 
with which things, apparently the most dissimilar, may 
be compared : and thus to enter, as it were, into the 
mind of the great Designer of the universe. It is, how- 
ever, unnecessary here to dwell at any length upon this 
most interesting branch of science, and we shall there- 
fore content ourselves with giving a very brici abstract 
of the general results which have been obtained by 
much earnest thought on the part of some of the great- 
est minds of the present century. 
According to the generally received views, the 
skeleton of a vertebrate animal is composed of 
numerous segments or vertebrae (the latter term being 
used in an ideal sense). Even the skull itself is proved 
to consist of several vertebrae developed in a remark- 
able manner — the bones of the face holding the same 
relation to those of the true skull, that the ribs do to 
the superior arch of the dorsal vertebrae through which 
the spinal cord passes. The four limbs are appendages 
of two particidar vertebral segments; and similar appen- 
dages are met with in a rudimentary form upon other 
segments in some animals. 
Eegarding the skeleton in accordance with these 
views, as consisting ideally of a series of similar seg- 
ments, we find that it is by the suppression of certain 
parts of some of these, and the greater or less develop- 
ment of others, that the varied forms of vertebrate 
animals are produced. The appendages constituting 
the limbs are, as already stated, usually suppressed 
completely in all but two segments, and the ribs often 
share the same fate in the neck, loins, and tail. In 
other cases the bones of one or both pairs of limbs are 
wanting, and in some of the lowest forms we find nothing 
left but the vertebral column itself, which sometimes 
is not even ossified, but consists of a gelatinous or car- 
tilaginous cord, running, with little or no trace of any 
division into vertebrm, from the head to the extremity 
of the tail. 
Yet throughout all these variations the intelligent 
observer traces one uniform plan : the great centre of 
the nervous system always consists of a brain and 
spinal cord, supported in all but one instance, by a 
structure which may he recognized as a vertebral 
column; the jaws are always supported by bones or 
cartilage beneath the skull, and their opening is alwaj's 
horizontal; the limbs are never more than four in 
number ; the heart is always muscular, and connected 
with a distinct system of vessels, through which courses 
a blood, coloured red by innumerable globules; and 
the organs of the four special senses (sight, hearing, 
smell, and taste) are almost always highly developed, 
and invariably placed in cavities of the face and head. 
The viscera are very similar in their nature throughout 
the entire group, and the animals are always male or 
female, never hermaphrodite. 
