ANATOMICAL STRUCTURE OF ANTHROPOID APES. 139 



a male gorilla in the College of Surgeons Museum 

 has an index width of 68'1, that of a female of 65"0, 

 while the index of the chimpanzee's tibia is 61"1, 

 which is about the average of the tibias of Perthi- 

 chwareu. It is unnecessary to indicate the other 

 marked distinctions between the tibiae of men and 

 apes ; if platycnemy is to be regarded as genetic, it 

 must be admitted that man has in this particular 

 far exceeded afpes.* Neither the gorilla, the chim- 

 panzee, the orang-utan, nor even the baboon pos- 

 sesses a tibia which is flattened in its upper or middle 

 part. In all these apes the middle of the bone is 

 more or less rounded, almost as if it had been rounded 

 by a turning-lathe. According to my experience,' 

 the degree of platycnemy in anthropoids is subject 

 to certain variations. It appears to me to be least 

 marked in the aged male gorilla (Fig. 41), and in 

 the gibbon {Hylobates agilis, syndactijlus), in which 

 latter animal the transverse section of the tibia 

 represents an almost equilateral triangle. The 

 platycnemy was more marked in an almost adult 

 female gorilla, still more decided in an aged male 

 chimpanzee, which came from the river Kiulu, and 

 again in an aged female chimpanzee. On the other 

 hand, the centre of the shaft of the tibia in another 

 aged male chimpanzee which came from Loango, 

 was rounded, and not platycnemic. In the tibia of 

 an adult orang-utan which I examined, the platyc- 

 nemy was very marked. But I agree with Boyd- 

 Dawkins in never having met with an anthropoid in 

 which the platycnemy is so considerable as it is, 



* See Spengel's Caves and Primitive Inhabitants of Europe. 



