136 



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 





[After WIEDERSHEIM.] 



(e) Polypterus (a spe- 



FIG. 35. Morphology of ribs. 



(a) Ganoid, (b) Dipnoan. (c) Teleost. (d) Selachian, 

 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 



