950 



EVOLUTIONAL MODIFICATIONS 



a progressive evolutional development. In other words, does each one of 

 these features \\:[\v its sinijilest morphological expression in the lowest of 

 the primatts, and pass progressi\"ely through graded intermediate stages, 

 to a euhnination of its greatest complexity in the highest member of the 

 order? 



E\oLi rioNAL Significance of Brain Indices. In the matter of the 

 brain indices it is certain that the primates show a steady and progressive 

 advance. There are scune incidental lluctuations, however, which may be 

 allributi'd to \anations m the degree ol specialization. Thus the lemur, the 

 tarsier and tlu' marmoset stand at the lower end of the series in so far as 

 the forebrain index is concerned, each of these genera being slightly above 80 

 per cent in this respect. The intermediate group is next in position. The 

 great anthropoids, although they show a dchnite increase m their lorebrain 

 index, are still considerabl\ below man. The accompanying tabulation indi- 

 cates the tendency toward expansion as witnessed by this index among the 

 primates. 



Encephalic Indices 



Animal 



Encephalic index (per cent) 



Forebrain ; Midbrain 1 Hindbrain 



Myc etes 



Baboon 



Macacus 



Gibbon 



Oiang-Outaiij: 



CInmpaii/ee 



Gorilla 



I lunian 



81.6 



83 

 84 



83 



_84 



86-89 



4.8 



_i4 



J4 



_i6 



12 



la 



J4 



10-13 



