SEGMENTATION OF SKELETON. 67 



The remaining processes are the transverse, Pt, which 

 run outwards and a little dorsally. Each of these has a 

 smooth articular surface, Ft, near its outer end. 



On the "body" are seen two articular surfaces on each 

 side: one, Fes, at its anterior, the other, Fci, at its poste- 

 rior end, and both close to the attachment of the neural 

 arch. Each of these surfaces forms with corresponding 

 areas on the vertebrae in front and behind a pit into which 

 the end of a rib fits and the rib attached in this way to 

 the anterior part of the "body" also fitted on, a little way 

 from its dorsal end, to the articular surface at the end of 

 the transverse process. 



The Segments of the Axial Skeleton. If a dorsal verte- 

 bra, say the first (Fig. 17), be detached with the pair of ribs, 

 Cv, belonging to it and the 

 bit of the sternum, S, to 

 which these ribs are fixed 

 ventral ly, we would find a 

 bony partition formed by 

 the body of the vertebra, 

 lying between two arches 

 which surround cavities. 

 The dorsal cavity inclosed 

 by the " body" and "neural . 



* '. . FIG. 17. Diagrammatic representation 



arch Contained Originally of a segment of the axial skeleton. F, a 



, v mi vertebra; C. Ct',*ribs articulating above 



part Of the Spinal COrd. The with the body and transverse process of 



,, -, TIT the vertebra; S, the breast-bone. The 



Other ring, made Up by trie lighter-shaded part between S and C is 



body of the vertebra dor- the rib cartilage " 

 sally, the sternum ventrally, and the ribs on the sides, sur- 

 rounds the chest cavity with its contents. All of these 

 parts together form a typical segment cf the axial skeleton, 

 which, however, only attains this completeness in the 

 thoracic region of the trunk. In the skull it is greatly 

 modified; and in the neck and the lower part of the trunk 

 the ribs are either absent or very small, appearing only as 

 processes of the vertebrae; and the sternal portion is wanting 

 altogether. 



Nevertheless we may regard the whole axial skeleton as 

 made up of a series of such segments placed one in front of 



