466 PHYSIOLOGICAL SERIES. 



memory, would enable it to acquire the cunning and skill to evade 

 danger and yet adequately attend to its needs. In many of the 

 Eocene Mammalia (cf. the cranial cast of Dlnoceras) the neopullium 

 is reduced to such diminutive proportions that the brain resembles 

 the reptilian type ; and in each successive generation the neopallium 

 becomes larger or the creature, in self-defence, is compelled to adopt 

 some safe form of life. The Hippopotamus and the Sirenia are 

 examples of mammals which have not kept pace in the fierce race 

 for neopallial supremacy but survive by adopting habits of life which 

 are eminently safe. The condition of the human brain represents the 

 other extreme. Here the neopallium has attained its maximum 

 development, and its possessor has not had to seek refuge either in 

 a retired mode of life or by any protective specialisations of structure 

 either for offence or defence, but has attained the dominant position in 

 the animal kingdom, whilst retaining much of the generalised structural 

 features of a primitive mammal. 



This expansion of the neopallium is general and not restricted to 

 any localised areas. Thus we cannot say that the greatness of the 

 human neopallium is to be wholly attributed to a growth of the frontal 

 or of the parietal or of the occipital areas, as various writers have 

 maintained ; because all parts exhibit distinct evidences of extension. 

 But some regions exhibit the effects of this general expansion more 

 decisively than others, and many writers have assumed (quite 

 erroneously, 1 believe) that such effects are to be attributed to localised 

 growth *. Thus there are very noteworthy evidences of growth in the 

 region around the insula in the human brain, but this is probably for 

 the most part an expression of the general extension in a region 

 which lends itself to a clear demonstration of any increase. 



In the early mammals the olfactory areas form by far the greater 

 part of the cerebral hemisphere, which is not surprising when it is 

 recalled that the forebrain is in the primitive brain essentially an 

 appendage, so to speak, of the smell-apparatus. When the ceivbral 

 hemisphere comes to occupy such a dominant position in the brain it 

 is perhaps not unnatural to find that the sense of smell is the moM 

 influential and the chief source of information to the animal ; or 

 perhaps it would be more accurate to say that the olfactory sense, 

 which conveys general information to the animal such as no other 

 sense can bring concerning its prey (whether near or far, hidden or 



* There is no doubt that localised hypertrophies do occur, but the fumla- 

 mental distinction of the human brain is the general expansion of \\\<- 

 neopallium. 



