HISTORY OF THE HUMAN BODY 



of the later development in birds and mammals. In these 

 latter a typical rib possesses two well-marked segments, a 

 dorsal and a ventral, often bent at an angle to each other ; both 



^ A 





FIG. 35. Morphology of ribs. [After WIEDERSHEIM.] 



(a) Ganoid, (b) Dipnoan. (c) Teleost. (d) Selachian, (e) Polypterus (a spe- 

 cial case among ganoids), (f) Urodele. 



In the three first the condition in both trunk and tail is given. In all the figures 

 the " fish rib " is striped, the myocommatous rib is black, and the basal stumps are 

 outlined. 



may be fully ossified, as in birds, or the ventral segments 

 may remain cartilaginous, forming the so-called " costal car- 

 tilages," characteristic of mammals. In birds the dorsal seg- 

 ments possess flat uncinate processes, which extend backwards 

 from their posterior edges and overlap the succeeding rib, thus 



