122 PEOF. G. ELLIOT SMITH OX THE 



isiualler in the arboreal Cycloturiis tlian in tlie terrestrial Ilyrmecopharia, two Edentates 

 of the same family; but it is the peculiarity of the Apes that they have become 

 extremely microsmatic for no apparent reason, the dirnimition of their olfactory organs 

 being much more pronounced than it is in any other arboreal animal. This phenomenon 

 is undoubtedly to be mainly attributed to the increasing efficacy of the neopallium as an 

 " organ of mind," and its consequent usurpation of the rule of guiding the creature, 

 i\ hicli elsewhere among mammals is fulfilled chiefly by the sense of smell. 



It is a very significant fact that the Lemur which exhibits evidence of being the 

 most primitive — Tarsias — possesses the most extensive occipital prolongation, and is 

 more microsmatic than any other of the Prosimioe. Thus the olfactory bull) of Tarsius 

 is only half as large as that oi llicrocebus; and yet the former is appreciably greater 

 than that of Ilidas. 



The importance \vhieh has been attached to the amount of cerebellum covered by the 

 cerebral hemisphere as an index of the degree of brain-development is altogether 

 disproportionate to its true significance. By this I do not moan to imply that the degree 

 of caudal prolongation of the hemisphere is not a very important indication of the size 

 of the cerebral hemisphere, but it must not be forgotten that it is merely one of several 

 indications of the degree of cerebral expansion. The failure of the cerebral hemispheres 

 to completely overlap the cerebellum is an obvious point of distinction between the 

 brain of the Lemurs and most Apes. In the Lemurs the extent of the backward 

 pi'olongation of tlie hemisphei'e varies considerably. In Nycticebus, for example, there 

 is only a very narrow strip of cerebellum uncovered. In the Galagiufie and in Tarsius 

 the extent of the caudal prolongation of the hemisphere is perhaps greater than in any 

 other Lemur; /. e., if its dimensions are estimated in relation to the position of the 

 corpus callosum and by the size of the calcar, rather than by the situation of the caudal 

 pole of the bemisjihere with relation to the cerebellimi. The relative greatness of 

 the occipital extension of the hemisj)here in these particular forms is all the more 

 significant, because Tarsius and Galago are the Lemurs which have probably become 

 least changed (so far as the brain is concerned) from the early Prosimian type. It is 

 hence probable that the immediate ancestors of the Lemurs possessed brains of a more 

 pithecoid form. There are many other suggestive facts which point in the same 

 direction. 



In most mammals the calcarine and intercalary (? paracalcarine) sulci become 

 continuous (probably for purely mechanical reasons), and it is hardly conceivable that 

 tlie small caudal extension of the hemisphere in the recent Lemurs is sufficient to 

 so completely dissociate the calcarine from the intercalary sulcus, and to lead to its 

 confluence with the retrocalcarine sulcus, or in fact to supply the mechanical factors 

 which call the latter sulcus into being. It is difficult to conceive of the present relations 

 of the three sulci of the calcarine group having been produced except in a brain with a 

 mxich more pronounced extension of the hemisphere than at present exists. 



It has been shown by Prof. A. Milne-Edwards, and emphasized by Dr. Eorsyth Mnjor*, 



* ' Xovilates Zoologicie,' vol. i. lyjk p. 33, 



