CHAP. IV.] 



THE SKELETON. 



39 



The vertebrse in the upper three portions of the spine are 

 separate throughout the whole of life ; but those found in the 

 sacral and coccygeal regions are, in the adult, firmly united, so 

 as to form two bones, five entering into the upper bone or 

 sacrum, and four into the terminal bone of the spine, or coccyx. 



Each vertebra consists of two essential parts, an anterior 

 solid portion or body, and a posterior portion or arch. The 

 bodies of the vertebrse 

 are piled one upon 

 another, forming a 

 solid, strong pillar, 

 for the support of the 

 cranium and trunk, 

 the arches forming a 

 hollow cylinder be- 

 hind for the protec- 

 tion of the spinal 

 cord. Each arch has 

 seven processes: four 



articular, two trans- FIG. 41. A CERVICAL VERTEBRA. Inferior sur- 



Verse and One SDi- ^ ace - *> spinous process, slightly bifid ; 4, transverse 



** process ; 5, articular process, inferior surface. Below 



nOUS process. The the arch, or hollow portion, is seen the solid portion, 



different vertebrae are or bod y- 



connected together by means of the articular processes, and by 

 disks of intervertebral nbro-eartilage placed between the ver- 

 tebral bodies, while the transverse and spinous processes serve 

 for the attachment of muscles which move the different parts of 

 the spine. In the cervical region of the vertebral column the 

 bodies of the vertebrse are smaller than in the dorsal, but the 

 arches, are larger; the spinous processes are short, and are often 

 cleft in two, or bifid. The first and second cervical vertebrae 

 differ considerably from the rest. The first, or atlas, so named 

 from supporting the head, has practically no body, and may be 

 described as a bony ring divided into two sections by a trans- 

 verse ligament. The dorsal section of this ring contains the 

 spinal cord, and the ventral or front section contains the bony 

 projection which arises from the front of the second cervical ver- 

 tebra, or axis. This bony projection, or odontoid process, is 

 really the body of the atlas, which in early life separates from its 

 own vertebra and grows on the axis. Around this peg the atlas 



