i62 THE OSTEOLOGY OF THE REPTILES 



entepicondylar foramen. This foramen is reported for Cochleosaurus, 

 a rhachitomous temnospondyl, and is known in Diplocaulus of the 

 LepospondyU, but is known in no other amphibian. An ectepicon- 

 dylar foramen is quite unknown in the class. 



Femur. The thigh-bone, or femur {e. g., Figs. 129 b, 135), like the 

 humerus, is variable in shape. Its articulation in the acetabulum is 

 by a more or less convex head. The femur of most reptiles is turned 

 outward from the long axis of the body in locomotion, with the artic- 

 ulation at the extremity; or if the bone is directed more or less up- 

 ward, as well as outward, the convexity is more on the dorsal side, as 

 in the Chelonia. . The two femora of a lizard, for instance, cannot be 

 brought parallel with each other in the same direction without dis- 

 location from the socket. There is, consequently, in such reptiles, no 

 real neck, so characteristic of birds and mammals. The dinosaurs 

 (Fig. 132) and pterodactyls (Fig. 155) only, because of the more or 

 less vertical or antero-posterior position of the femora, have the head 

 set off from the shaft of the bone by a more or less well-marked neck, 

 most noticeable in the bipedal types of dinosaurs, but also apparent 

 in the quadrupedal. The absence, then, of a neck to the femur is 

 indicative of crawling or aquatic habits. Many of the Therapsida 

 (Fig. 132), though without a diiferentiated neck, have the proximal 

 preaxial border of the femur more or less curved, with the articula- 

 tion more on the preaxial side, giving evidence of a more upright, 

 mammal-Hke mode of progression. Pariasaurus of the Cotylosauria 

 has also been restored in a more upright posture, but its femur is 

 quite like that of the earlier cotylosaurs,^ and like them it probably 

 never was brought below a horizontal position in walking, though, as 

 in Diadectes, the mode of locomotion was probably more like that of 

 the turtles, accounting, perhaps, for the reduction of the phalangeal 

 formula in that genus. So also, the propodials of Lystrosaurus and 

 doubtless of other Anomodontia were directed horizontally in loco- 

 motion. 



On the preaxial ventral side, usually on the upper third of the 

 bone, but sometimes, as in the short-limbed Cotylosauria, descend- 



1 [ButRomer {Bulletin, Amer. Mus. Nat. Hist., 1922, vol. XLVi, plate xlvi) shows 

 that the pariasaur femur (Propappus) differs in significant features from the femora of 

 cotylosaurs, while Amalitzky, Broom, and Romer are agreed that the femur of paria- 

 saurs was directed obliquely downward. — Ed.] 



