THE LIMBS 



Epipodials 



165 



Radius and Ulna. The two bones of the forearm or antihrachium 

 are always complete in reptiles and movable upon each other, freely 

 in most terrestrial reptiles, flexibly in the aquatic types, that is, with- 

 out rotation of the radius; they may be more or less fixed in the 



Fig. 133. Cotylosaur limb: Lim- 

 noscelis, left foreleg, ventral side. 

 One fourth natural size. 



Fig. 134. Ophiacodon: Anterior extremity, as 

 mounted. One half natural size. 



chelonians (Fig. 145 a), though not crossed. The forearm in this 

 order has a peculiar twist on the humerus by which the dorsal sur- 

 face of the forearm, wrist, and hand is turned forward at right angles 

 to the humerus without pronation or rotation of the radius (Fig. 

 145 a). 



