Paleontology. 



179 



plantigrade into a highly digitigrade type the 

 curved lines of connexion serving to indicate the 

 homologous bones (Figs. 76, 77). 



I will now proceed to detail the history of mammalian 

 limbs, as this has been recorded for us in fossil remains. 



The most generalized or primitive types of limb 

 hitherto discovered in any vertebrated animal above 



IV 



B 



FIG. 78. A, posterior limb of Baptanodon discus. (After Marsh.) F, 

 thigh-bone ; I to VI, undifferentiated bones of the leg and foot. B, 

 anterior limb of Chelydra serfentina. (After Gcgenbanr.) U and R, 

 bones of the fore-arm ; I to V, fully differentiated bones of the haud, 

 following those of the wrist. 



the class of fishes, are those which are met with in 

 some of the extinct aquatic reptiles. Here, for 

 instance, is a diagram of the left hind limb of 

 Baptanodon discus (Fig. 78). It has six rows of little 

 symmetrical bones springing from a leg-like origin. 



N 2 



