CHAI". VII.] 



GENERA L CHAR A C TERS. 



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 



ma 



Fig. 31. — Human stenuim and sternal ribs, \. ps presternum; ms mesosternum; 

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

 sternal ribs. 



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 embryo, traces of this original median 

 division are generally seen in very young sterna, and are 



