This apparatus is somewhat complex, but its chief features are as follows: A superior interdigital ligament is attached on either side to the third phalanges of the small digits, while centrally it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal joints of the chief digits. Two bands (central longitudinal interdigital ligaments) arise on the bases of the small digits, cross the flexor tendons obliquely downward and inward, pass through the superior interdigital ligament, and blend below with the inferior interdigital ligament. Two lateral bands (lateral longitudinal interdigital ligaments) are attached in common with the superior interdigital ligaments to the third phalanges of the small digits, and blend below with the outer part of the inferior interdigital ligament. =Dog.=—Each joint has a capsule and two lateral ligaments. The distal joints have also two elastic =dorsal ligaments= (Ligamenta dorsalia), which extend from the proximal end of the second phalanx to the ridge at the base of the third phalanx (Fig. 133). They produce dorsal flexion of the joint, and thus raise or retract the claws when the flexor muscles relax. The distal sesamoids are represented by complementary cartilages attached to the volar margins of the articular surfaces of the third phalanges. Three interdigital ligaments restrict the spreading apart of the digits. Two of these cross the volar surface of the proximal parts of the chief digits, _i. e._, one for the second and third, the other for the fourth and fifth; they blend with the annular ligaments on either side. The third ligament is attached on either side to the foregoing ligaments and the annular ligaments of the third and fourth digits, and curves downward centrally, ending in the large pad on the paw. ARTICULATIONS OF THE PELVIC LIMB SACRO-ILIAC JOINT This joint and the pelvic ligaments present no very striking differences in the other animals. The sacro-sciatic ligament in the dog is a narrow but strong band which extends from the posterior part of the lateral margin of the sacrum to the tuber ischii; it is the homologue of the ligamentum sacro-tuberosum of man. HIP JOINT =Ox.=—The shallowness of the acetabulum is compensated by the greater size of the marginal cartilage. The head of the femur has a smaller radius of curvature than that of the horse, and the articular surface extends a considerable distance outward on the upper surface of the neck. The round ligament is entirely intraarticular; it is small, and sometimes absent. The pubo-femoral or accessory ligament is absent. There are no important differences in the other animals. STIFLE JOINT