CHAP. VII.] 



GENERAL CHARACTERS. 



The ribs are attached to the sides of the sternum : the 

 first pair to the presternum ; the second to the presternum 

 and the mesosternum at their point of junction ; the 

 remainder to the mesosternum, opposite the interspaces 

 between each segment, though two or more pairs are often 

 clustered round the last segment. The xiphisternum bears 

 no ribs. 



Development. The osseous sternum is preceded by a 

 continuous or non-segmented piece of cartilage ; and as the 



FIG. 31 Human sternum and sternal ribs, ^. ps presternum ; Jiis mesosternum ; 

 xs xiphisternum ; c point of attachment of clavicle ; i to 10 the cartilaginous 

 sternal rids. 



portion of the body in which this is developed is formed by 

 the union in the middle line of the two " ventral laminae '' of 

 the embyro, traces of this original median division are generally 

 seen in very young sterna, and are often persistent through 



