i86 



HISTORY OF THE HUMAN BODY 



thus forming a uniserial form, as in the selachians ; in another 

 the hind limb of the salamander Ranodon was used as a basis, 



Radius 



Radius 



Ulna 



[Ulna] 



[Radius] 



FIG. 51. Two theories of derivation of the chiridium (cheiroptery- 

 gium) from the fin (ichthyopterygium). The figures represent the ante- 

 rior limb in all cases, [a-c, after HUXLEY; d-f, after POLLARD.] 



(a) Cestracion, a primitive selachian, (b) Ichthyosaurus, an extinct lizard. (c) 

 Necturus, a primitive salamander, (d) Chlamydoselachus, a primitive selachian, (e) 

 Polypterus, a ganoid, (f) Ranodon, a slamander. 



In the three upper figures the ulna is dotted, the radius designated by a diagonal 

 striping; in the three lower the reverse is the case. 



and femur, fibula, intermedium, the two centralia, carpale II 

 and the second digit were taken as the central axis, leaving one 



