38 



WATER REPTILES OF THE PAST AND PRESENT 



swimming reptiles. The humerus of flying reptiles has an enor- 

 mous process on the side, corresponding to the attachment of the 

 deltoid muscle. The head of the humerus, for articulation with the 

 glenoid cavity of the scapula, is rounded in all reptiles, except the 

 pterodactyls, and the articulation is always at the extremity. At 



the lower extrem- 

 ity the protuber- 

 ance at the outer or 

 radial side is called 

 the ectocondyle; 

 that on the inner 

 or ulnar side, the 

 entocondyle. Be- 

 tween the two at 

 the end are the 

 articular surfaces for the radius and ulna, 

 the capitellum and trochlea. A little above 

 each of these condyles there is usually, on 

 one side or the other or on both, a foramen 

 or hole for the passage of arteries or nerves. 

 That on the inner side, which is character- 

 istic of all early reptiles and of many 

 mammals, is called the entepicondylar 

 foramen; that on the outer side, the ectepi- 

 condylar foramen; the latter is present in 

 the lizards, and both are found in the 

 tuatera and some of the early reptiles. 

 The radius and ulna are always distinct 

 bones in reptiles, and always freely mov- 

 able on each other; they are usually shorter 

 than the humerus, but in some springing 

 and climbing reptiles they are quite as long. 



The carpus or wrist of reptiles consists primitively of eleven 

 distinct, irregularly shaped bones, which articulate more or less 

 closely with each other in three rows. Those of the first row, all 

 true carpals, are known usually as the radiale, intermedium, ulnare, 

 and pisiform, corresponding quite with the bones of the human wrist 



Fig. 21. — Anterior ex- 

 tremity of Ophiacodon. 



