THE EVOLUTION OF THE MAMMALIAN FEMUR

Comparison of the femora of advanced cynodonts, tritylodonts and monotremes shows that the antero‐ventral trochanter of the cynodonts is the mammalian trochanter minor and not the reptilian trochanter internus as has been held. Consideration of the form of the pelvis supports this conclusion. The femora and pelves of anomodonts indicate that an essentially mammalian musculature was developed and that, though no trochanter minor is known in the group, an iliacus muscle must be presumed to have been developed. Among Theriodontia, the gorgonopsids are considered to have retained a largely reptilian thigh musculature, but the therocephalia and scaloposaurid bauriamorphs appear to have achieved a condition intermediate between those of reptiles and mammals. It is claimed that the femora of primitive Theria are very similar to those of advanced cynodonts and could have been derived directly from one of this type. The femora of tritylodonts and monotremes, and two of the three supposed mammalian femora from the Jurassic, are considered to be specialized.