FEMUR, the thigh-bone in human anatomy. In general terms, it consists of a shaft very slightly curved, and two extremities. The upper extremity bears two projections, called the greater and lesser trochanters, for the attachment of muscles, and a short neck, nearly at right angles to the shaft, terminated by a hemispherical head, which being received into a cavity of the pelvis called the acetabulum, forms the hip-joint, a ball-and socket joint. The lower extremity of the femur has on each side an enlargement called a condyle, or knuckle. The articular surface of the condyles is hemicylindrical, as also is the somewhat depressed space between them, called the trochela, and with the large bone of the leg, called the tibia, forms a hinge joint. The femur is attached to the pelvis by two ligaments—a capsular ligament, which incloses the head and neck, and the liga mentura teres, a sharp ligament which joins the head with the bottom of the acetabulum. It is attached to the tibia by several ligaments, placed in different positions, to combine strength with freedom of motion, the most important of which are the lateral ligaments and the crucial ligaments. The crucial ligaments cross from one member of the joint
to the other in oblique directions. Powerful extensor and flexor muscles, besides per forming their ordinary functions, aid in keeping the parts in opposition. The femur has a wide range of distribution 'in the animal kingdom, and is not the exclusive property of warm-blooded animals. In man, it is the strongest, longest, and largest bone. In the whale, it is only rudimentary. In fishes, it is not represented, hut has a varying importance in mammals, birds, reptiles, and amphibians. It is a short bone in the rumi nants and horse family. In the tortoises, the curve is considerable, while it is almost straight in carnivora, bats, etc. In many reptiles it is slightly rudimentary.