470 STRUCTURE OP 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 hyoid 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 Trunk, 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 vertebra (fig. 224), 

 which are arranged under five divisions ; r. The 

 Cervical vertebrae c, or vertebrae of the neck, of 

 which there are 7 \ n. The dorsal vertebrae d, or 

 vertebrae of the back, of which there are 12 ; 

 in. The lumbar vertebrae I, or vertebrae of the 

 loins, of which there are 5 ; iv. The sacral ver- 

 tebrae s, of which also there are 5 ; and v. The 

 coccygeal vertebrae co, of which there are 4. All 

 these vertebrae are separate at the time of birth ; 

 but the 5 sacral vertebrae are soon afterwards united 

 into one piece, forming the bone which is termed 

 \ s the sacrum : and the coccygeal vertebrae 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 

 VERTEBRAL lumbar vertebrae to be united together by bony 



COLUMN. ma ^. e r deposited in their cartilages and ligaments. 



627. The dorsal vertebrae 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 vertebrae 



