Page:The Osteology of the Reptiles.pdf/182

164 below the middle, there is, especially in crawling forms, a rugosity or eminence, the lesser trochanter, from which usually a more or less pronounced ridge or roughening descends toward, or nearly to, the postaxial condyle (Figs. 129, 132). It corresponds to the linea aspera of mammals and may be called the adductor ridge or crest.

On the opposite side, and nearer the head, obsolete or even absent in ordinary crawling reptiles but well developed in the Chelonia (Fig. 154) [and in certain Therapsida, Fig. 132], is the great trochanter. Between the two there is a depression or fossa [intertrochanteric], at the upper extremity in turtles (Fig. 154), but broadly ventral in most other forms.

The femora of the dinosaurs (Fig. 132 bis), especially the bipedal Predentata, but also indicated in the Sauropoda, have near the middle on the ventral preaxial side a rugosity or prominence, the fourth trochanter, sometimes, as in Camptosaurus, long and pendent.

The condyles, at the distal extremity of the femur, are separated by a groove in front and another behind (Fig. 129 ). The preaxial condyle, usually the smaller, gives articulation to the tibia; the postaxial condyle, to the fibula, and in part to the tibia behind. The shaft of the femur is sometimes markedly curved (Figs. 155, 157), sigmoidally in the more slender kinds. It is always longer and more slender than the humerus, its distal width seldom if ever equal to more than half the length of the bone.

The femur of the temnospondylous amphibians (Fig. 151 ) is sometimes indistinguishable from that of the cotylosaurs, but usually the adductor ridge is more strongly developed, and the articular ends are less well ossified.