i6o 



THE OSTEOLOGY OF THE REPTILES 



radial or lateral tuberosity or process. On the opposite side, nearer 

 the head, and often not well marked, is the ulnar or medial tuberosity 

 (Figs. 129, 130). Between the two, on the ventral side, is the bicipi- 

 tal fossa (Fig. 131). Immediately below the lateral tuberosity the 

 shaft is usually round or oval in cross-section. Among all reptiles 

 the lateral process is most developed in the pterodactyls (Fig. 141). 

 It is also largely developed in the Cotylosauria (Figs. 128, 130, 133), 



Fig. 131. Ophiacodon mirus Marsh (Theromorpha). A, left humerus, ventral side, one half natural size. 

 B, left humerus, distal end, one half natural size. C, left ulna, radius and carpus, ventral side, one half 

 natural size. D, left carpus, dorsal side, three fourths natural size. 



Theromorpha (Figs. 129, 131, 134), and Anomodontia, sometimes 

 descending below the middle of the bone. 



The expanded extremities of the humerus are in divergent planes, 

 the angle sometimes slight, at other times approximating or even 

 exceeding a right angle, the bicipital fossa in such cases looking more 

 dorsad than ventrad. The width of the more expanded distal ex- 

 tremity may be less than an eighth of the length of the bone, or may 

 nearly equal it in stout-limbed reptiles like the Cotylosauria (Figs. 

 130, 133). The distal expansion is always great in the Cotylosauria 

 and Anomodontia, as also in some Theromorpha (Figs. 129, 131). 

 Doubtless in these animals, or some of them at least, the peculiar 

 humerus is to be correlated with the screw-like motion in the glenoid 



