There is a slight ridge on the femur in the place of a third trochanter.
Iv.), and the pelvis and another femur (vii.
This, when fully developed, consists of two parts, but inserted by a single ribbon-like tendon upon the hinder surface of the femur, near the end of its first third; the caudal part, femoro-caudalis, expressed by Garrod by the symbol A, arises from transverse processes of the tail; the iliac part (accessorofemoro-caudal of Garrod, with the symbol B), arises mostly from the outer surface of the postacetabular ilium.
The most generalized type is Coryphodon, representing the family Goryphodontidae, from the lower Eocene of Europe and North America, in which there were 44 teeth, and no horn-like excrescences on the long skull, while the femur had a third trochanter.
It may also be noticed that in mammals and birds which hop on two legs, such as jerboas, kangaroos, thrushes and finches, the proportionate length of the thigh-bone or femur to the tibia and foot (metatarsus and toes) is constant, being 2 to 5; in animals, on the other hand, such as hares, horses and frogs, which use all four feet, the corresponding lengths are 4 to 7.
It is remarkable that it should persist in the spectacled bear of the Andes, although it has disappeared in all other living members of the group. The third trochanter of the femur, on the other hand, can scarcely be regarded as primitive, seeing that it is absent in several of the lower groups of mammals.
The vertebrae of the neck unite by nearly flat surfaces, the humerus has lost the foramen, or perforation, at the lower end, and the third trochanter to the femur may also be wanting.
Femur without third trochanter.
In many birds the insertion is shifted from the femur to the neck of the tibia, in which case the " accessory head " is said to be absent, a condition expressed by Garrod by the symbol X.
In the hinder limb the femur is marked, as in other perissodactyles, by the presence of a " third trochanter," a flattened process, curving forwards and arising from the outer side of the bone, about one-third of the distance from the upper end.
In most insects the leg is built up of nine segments: (1) a broad triangular, sub-globular, conical or cylindrical haunch (coxa); (2) a small trochanter; (3) an elongate stout thigh (femur); (4) a more slender shin (tibia); and (5-9) a foot consisting of five tarsal segments.
The hind limbs are very strong; the massive femur has a large pneumatic foramen; the tibia has a bony bridge on the anterior surface of the lower portion, a character in which the moas agree only with Apteryx amongst the other Ratitae.
There were three toes to each foot, and the femur lacked a third trochanter.
A large number of mammals possess a perforation, or foramen, on the inner side of the lower end of the humerus, and also a projection on the shaft of the femur known as the third trochanter.
The joint between the femur and tibia, corresponding to the knee of man, is called the " stifle-joint "; that between the tibia and tarsus, corresponding to the ankle of man, the " hock."
The femur often possesses a well visible pneumatic foramen on the median side of the proximal end of its shaft.
Femur with a third trochanter.
The femur varies considerably in form, but generally has a welldefined third trochanter.
The hinder part of the body is much contracted, and the femur long and vertically placed, so that the knee-joint is lower in position, and the thigh altogether more detached from the abdomen than in most mammals.
In the young jerboa the proportion of the femur to the rest of the leg is the same as in ordinary running animals.
The femur is short, and the tibia and fibula of great length, as is the foot, the whole of which is applied to the ground when the animal is at rest in the upright position.
The femur has a small third trochanter, the radius and ulna and tibia and fibula are respectively separate, at least in the young, and the fibula articulates with the astragalus.