PHYSIOLOGY, AND PATHOLOGY OF THE CHIMPANZEE. 369 



The Hip Joint : — The capsule is attached as in Man. The 

 ilio-femoral ligament consists of one band, which arises under 

 cover of the rectus f emoris and is strengthened by its tendon. It 

 runs as does the anterior band of the Y-shaped ligament in Man. 

 No other ligaments are formed from the capsule. The gluteus 

 minimus strengthens the capsule at the proximo-anterior part of 

 the great trochanter. The ligamentum teres, cotyloid ligament, 

 and transverse ligament are as in Man. The joint contains a 

 pad of fat. 



The Knee Joint : — The ligamentum patellce is broad and strong, 

 and has a more extensive insertion than in Man (see page 358). 

 The internal lateral ligament is not inserted into the internal 

 condyle of the tibia, but is fixed to the upper third of the shaft. 

 The external lateral ligament is as in Man. The oblique popliteal 

 ligament is absent, but a strong femoral intercondylar ligament 

 is attached to the posterior aspects of the two condyles. The 

 ligamentitm mucosum is just as in Man. The anterior cruciate 

 ligament is attached to the tibia as in Man, but its femoral in- 

 sertion is into the upper half of the mesial aspect of the external 

 condyle. It is smaller than the posterior cruciate ligament ; the 

 latter is attached to the tibia farther back than in Man, and it 

 receives a slip from the external semilunar cartilage (text- 

 fig. 36 F). Two semilunar cartilages are present. The internal 

 one is larger than the external, and is crescentic in shape. It is 

 attached in front of the anterior cruciate ligament. Its posterior 

 horn is inserted as in Man. The external cartilage forms a 

 small, complete circle. Internally it is attached by a broad liga- 

 ment to the external side of the tubercles and spine of the tibia. 

 Postero-mesially it is united by a ligament to the outer surface 

 of the internal condyle of the femur. It is also connected to the 

 posterior cruciate ligament. The joint dijffers in many ways 

 from that in Man, and its construction is such that it is one of 

 the factors which prevent the animal assuming a firm, erect 

 attitude. Humphry (26), who has made a thorough study of this 

 joint, points out that the femur in Man is broad and compara- 

 tively flat on the distal end of the external condyle ; and the 

 attachments of the lateral ligaments are nearer the posterior 

 parts of the bone. So the joint is firm and locked when it is 

 fully extended. In the Chimpanzee, on the other hand, the 

 distal end of the external condyle is rounded, and the lateral 

 ligament is not attached far back. He also shows that the 

 lateral, cruciate, and posterior ligaments are all tight when the 

 human knee is fully extended, but they never become simul- 

 taneously tight in the Chimpanzee ; to olDtain tightness of each 

 ligament it is necessary to divide all the others. Finally, the 

 attachment of the gracilis and hamstring muscles to the fascia 

 of the leg, and the laxity of the ligaments of the joint, are con- 

 tributory factors which prevent the animal assuming the erect 

 attitude *. 



* See the observations on living specimens recorded on page 420. 



