entepicondylar foramen. This foramen is reported for Cochleosaurus, a rhachitomous temnospondyl, and is known in Diplocaulus of the Lepospondyli, but is known in no other amphibian. An ectepicondylar 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 articulation at the extremity; or if the bone is directed more or less upward, 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 dislocation 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 differentiated neck, have the proximal preaxial border of the femur more or less curved, with the articulation more on the preaxial side, giving evidence of a more upright, mammal-like 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,[1] 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 locomotion.
On the preaxial ventral side, usually on the upper third of the bone, but sometimes, as in the short-limbed Cotylosauria, descend-
- ↑ [But Romer (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 pariasaurs was directed obliquely downward.—Ed.]
