250 COMPARATIVE ARTHROLOGY 



ment of ligaments which connect the small digits with each other and with the 

 chief digits (Fig. 258). 



This apparatus is somewhat complex, but its chief features are as follows : A proximal inter- 

 digital 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 hgaments) arise on the 

 bases of the small digits, cross the flexor tendons obhquely downward and centrally, pass through 

 the proximal interdigital hgament, and blend below with the distal interdigital ligament. Two 

 collateral bands (collateral longitudinal interdigital ligaments) are attached in common with the 

 proximal interdigital hgaments to the third phalanges of the small digits, and blend below with 

 the outer part of the distal interdigital hgament. 



Dog. — Each joint has a capsule and two collateral ligaments. The dista} 

 joints have also two elastic dorsal ligaments (Ligg. dorsalia), which extend from 

 the proximal end of the second phalanx to the ridge at the base of the third 

 phalanx. 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 (Fig. 259) . 

 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 flfth; they blend with the 

 annular ligaments on either side. The third ligament is attached on either side to 

 the foregoing ligaments and the annular hgaments of the third and fourth digits, 

 and curves downward centrally, ending in the large pad on the paw. 



Articulations of the Pelvic Limb 



SACRO-ILUC joint 



This joint and the pelvic ligaments present no very striking differences in the 

 other animals except that 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, which is specially large laterally. 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 intra-articular; it is small, and sometimes absent. The 

 accessory ligament is absent. 



There are no important differences in the other animals. 



STIFLE JOINT 



Ox. — There is a considerable communication between the femoro-patellar 

 and medial femoro-tibial joint cavities; this is situated as in the horse, but is wider. 

 A small communication with the lateral femoro-tibial capsule sometimes occurs. 

 The two femoro-tibial capsules usually communicate. The middle patellar liga- 

 ment is not sunken, as there is no groove on the tuberosity of the tibia where it is 

 attached. The lateral patellar ligament fuses completely with the tendon of in- 

 sertion of the biceps femoris, and a large synovial bursa is interposed between them 

 and the lateral condyle of the femur. 



Pig. — The femoro-patellar capsule is strongly reinforced on both sides by bands 



