PHYSIOLOGY, AND PATHOLOGY OF THE CHIMPANZEE. 421 



If some object is held above the animal's head one can see that 

 there is a considerable upward movement of the eyeballs, but the 

 head does not move much. And the greater vipward movement 

 of the eyes compared with that in Man is eiSected by a more 

 posterior attachment of the inferior oblique muscle. 



The Chimpanzee uses its arms as hook-like suspenders, but the 

 diminutive thumb is of no great use for suspension. The new- 

 born child can, it is well known, support the weight of its body 

 for a half to two minutes in a similar manner. Its fingers 

 reflexly assume this position if one places his index finger in its 

 palm. 



Much has been written about the attitude of the Chimpanzee, 

 but the conclusions, in several instances, have been drawn fiom 

 the study of dead material, or from the observation of sluggish 

 animals moving clumsily across the floors of their cages. Those 

 who have observed Chimpanzees in their natural haunts testify 

 t© their activity and agility ; and I have been fortunate in being 

 able to examine a male XJganda Chimpanzee, lately arrived at 

 the Gardens, which still exhibits much of its original activity. 

 It runs about actively, using its arms and legs almost equally ; it 

 occasionally uses its foot as a spring-board ; and it swings about 

 on the branches in its cage very actively. 



Anatomical descriptions state that the Chimpanzee keeps its 

 knees semi-flexed and give that as one of the factors which 

 prevent the animal from assuming the erect attitude. And 

 Humphry (26) states that one cannot fully extend the knee 

 without doing violence to the muscles. If, however, the living 

 animal is examined a different state of aflfairs can be observed ; 

 but the observations must be long and frequent. I observed the 

 active animal mentioned above extending its joints fully, 

 both during active progression and while standing up and 

 holding on to the bars of its cage. Two young animals were then 

 examined during their active movements, and the same conditions 

 were observed. After studying the active range of movement I 

 examined the passive movements in two other young animals, 

 and I found that I could easily extend the knees; but the 

 curvature of the upper end of the tibia gave the leg an appai^ent 

 slight flexion even when the knee is lightly extended. It is, 

 therefore, evident, from the results obtained on these five living 

 animals that the knee-joint can be fully extended. The position 

 of semi-flexion is, however, more comfortable in the Chimpanzee, 

 as it is in Man, and an animal which becomes sluggish in 

 captivity will develop stifi' joints, so full extension of the knee 

 will then become impossible, either actively or passively. And I 

 believe that some anatomical accounts have been based on the 

 examination of limbs so affected. 



If the animal were deprived of its arms it could not stand 

 upright like Man, but it can under momentum be erect for a 

 short period ; I have observed the active animal mentioned above 

 Peoc. Zool. Soc— 1923, No. XXVIII. 28 



