174 THE EVOLUTION OF MAN. 



Old World have exactly this human structure of the teeth, — 

 all Apes which have as yet been found, either living or as 

 fossils, in Africa, Asia, and Europe. All Apes of the New 

 World, on the contrary, all American Apes, have an extra 

 tooth on both sides of each jaw ; this is a biscupid tooth. 

 Thus they have six back-teeth on both sides of each jaw, — 

 in all, thirty-six teeth. This characteristic difference be- 

 tween the Eastern and Western Apes has been so constantly 

 transmitted within the two groups, that it is of the greatest 

 value to us. A small family of South American Apes does, 

 indeed, appear to form an exception in this respect. The 

 pretty little Silk Apes, or Marmosets (ITapalida), namely, to 

 which the Brush-monkey (Midas) and the tufted Marmoset 

 (Jacchus) belong, have but five back-teeth in each half of 

 the jaw, instead of six, and, accordingly, seem to approach 

 nearer the Eastern Apes. But on closer observation it 

 is found that, like all the Western Apes, they have the 

 three biscupids, and that the hindmost grinder has been 

 lost. Thus this apparent exception confirms the value of 

 the distinction. 



Among the other marks by which the two main groups 

 of the Apes are distinguished, the structure of the nose is 

 specially important and prominent. In all Old World Apes 

 the structure of the nose is the same as in Man ; namely, a 

 comparatively narrow partition of the two halves, so that 

 the nostrils are directed downwards. In a few Eastern Apes, 

 the nose projects as prominently and is as characteristically 

 formed as in Man. We have already called attention, 

 in this respect, to the remarkable Nose-ape (Semno- 

 pithecus nasicus), which has a well-curved and long nose 

 (Fig. 202). Most of the Eastern Apes have, it is true, a 



