ANATOMICAL STRUCTURE OF ANTHROPOID APES. 131 



tail, present the points of unlikeness with the human 

 skeleton in this part of the skeleton of these animals 

 in the strongest light (comp. Figs. 40 and 41). 



The bony thorax of anthropoids is distinguished 

 from the human thorax in normal cases by the 

 abrupt way in which it widens outwards. The 

 thorax of the gorilla, and the widely diverging 

 pelvic bones, which enclose the belly and give it a 

 tun-shaped form, contrast with the graceful moulding 

 of the corresponding parts of the human form. 



Certain peculiarities in the structure of the bones 

 of the shoulder-girdle and of the extremities of 

 anthropoids, in which they differ from corresponding 

 parts in the human structure, have been already 

 mentioned. 



With reference to the humerus of the gorilla, Aeby 

 asserts that the head of the bone forms a cycloid, 

 placed transversely, while in man its shape is that 

 of the segment of a sphere. But I have pointed 

 out in my treatise on the gorilla that there is a not 

 inconsiderable variation in the form of the head of 

 the humerus in these animals, and it is sometimes 

 cycloidal or vertically-cycloidal, sometimes a seg- 

 ment of a true sphere. In the chimpanzee, orang, 

 and gibbon this part of the humerus is always a 

 segment of a sphere, while in man its form is 

 not equally invariable. Aeby further observes that 

 the transverse-cycloidal form of the head of the 

 humerus in the gorilla justifies the inference that 

 this animal, in the use of its fore-limbs, is accus- 

 tomed to turn them transversely on their axis. But 

 the direct observation of a living anthropoid, as 



