470 STRUCTURE OF THE VERTEBRAL COLUMN, 
mouth and draws together the lips. The antagonists to these 
are several small muscles which form the fleshy part of the 
face, and produce the various changes by which its expression 
is given. These muscles are more numerous in Man and the 
Monkey tribe than in any other animals. 
625. Besides the twenty-two bones of which the skull is 
properly composed, we may reckon as belonging to it the four 
small bones which form part of the apparatus of hearing 
(§ 516); and also the hyvid bone, which lies at the root of 
the tongue and at the top of the larynx (fig. 107). This last 
bone, in Man and the Mammalia generally, is connected with 
other parts of the skeleton by ligaments and muscles only ; 
but in Birds it is connected with the temporal bone on each 
side by a set of bony pieces jointed together like links in 
a chain. 
626. The most important part of the Zrunk, and even of 
the whole skeleton,—that which serves to sustain the rest, 
and which varies the least in the different classes of Verte- 
brated animals,—is the spinal or vertebral column. The 
general conformation of this has been already described (§ 71). 
In Man it consists of 33 vertebre (fig. 224), 
which are arranged under five divisions ;—1. The 
Cervical vertebre c, or vertebre of the neck, of 
which there are 7; mu. The dorsal vertebre d, or 
vertebrae of the back, of which there are 12; 
—i. The lumbar vertebra J, or vertebrae of the 
loins, of which there are 5 ;—1v. The sacral ver- 
tebree s, of which also there are 5 ;—and v. The 
coceygeal vertebree co, of which there are 4. All 
these vertebrae are separate at the time of birth ; 
but the 5 sacral vertebre are soon afterwards united 
into one piece, forming the bone which is termed 
the sacrum: and the coccygeal vertebree are also 
commonly united into one piece, the coccyx, which — 
is not unfrequently united in old age to the sacrum. 
Fig. 224, In old persons, too, it is not uncommon for the 
Vertesnat lumbar vertebre to be united together by bony 
Cows. matter deposited in their cartilages and ligaments. 
627. The dorsal vertebre are distinguished from the cervi- 
cal and lumbar, as being those to which the ribs are attached. 
It is remarkable that the number of the cervical vertebra 
