THE BRAIN^ IN THE EDENTATA. 339 



In the Dog the brain is, ronghly speaking, more than 10 \ of the body-weight heavier 

 tlian in the Ant-eater, taking into consideration only animals of approximately the same 

 size. 



"We find upon examination that tlie difference in size of the brain in Mijrmecopliaga 

 and Cants (in animals of approximately the same size) is almost wholly a question of 

 the extent of the cerebral cortex. 



Now in IJijrmecopluuja the rhinencephalon is both relatively and absolutely very much 

 more extensive than it is in Canis, and hence the disproportion between the size of the 

 pallium in the two brains is even greater than a comparison of the brain-weights 

 might lead us to imagine. It becomes an interesting question to determine what effect 

 this increase in extent has upon the configuration of the paUium. 



I have already explained the effect of local hypertrophy of the excitable cortex in 

 the production of the crucial sulcus and the lateral displacement of tlie anterior ead of 

 tlie coronal sulcus (7). I have also shown how two definite opercula form around the 

 fossa Sylvii and ultimately expand so as to cover up that depressed area. In addition to 

 this the homologues of the sulci which the pallium of Myrmecophaga presents become 

 deeper and more extensive in the Dog, and large numbers of new^ sulci make their 

 appearance to enable the more extensive pallium to accommodate itself in a minimum 

 space. 



Let us notice also some general results of the larger pallium. In the Ant-eater the 

 posterior border of the hemisphere is vertical, and the hemisphere itself entirely in front 

 of the cerebellum. In the Dog the general expansion of the cortex is relieved by the 

 caudal extension of the postero-superior part of the hemisphere over the cereliellum, 

 so that the posterior border becomes oblique. This l)ackward or occipital extension has 

 obvious effects upon the mesial surface, which need not be specifically detailed. 



This occipital extension of the pallivtm in the Carnivores is analogous to the much 

 more pronounced growth in the caudal direction which we find in the Primates. 



I have discussed at some length the points of resemblance and of contrast in these 

 two brains in order to explain more clearly the salient characters of the brain in the 

 Ant-eater. "\Ve have thus been able to estimate those features wiiich constitute the 

 superiority of the Dog's brain over that of the Ant-eater, and have been impressed 

 with the important conclusion that the two brains are built upon essentially the same 

 plan, or, in other words, that the same factors wliich are at work in mouldin"" 

 the pallium in the Carnivora are fashioning the homologous part of the brain of 

 Myrmecophaga in the same likeness. 



The significance of these facts will be considered later. At present I merely note 

 the resemblance. The records of any observations which have hitherto been made upon 

 the brain of Tamandua are of the scantiest nature. Gervais gives a figure representing 

 the dor.«al aspect of a cranial cast *, and Pouchet gives figures of the dorsal and lateral 

 aspect of the cerebral hemispheres t, but these figures are very unsatisfactory, because 

 they lack all detail. Even a landmark so well-defined as the rhinal fissure is repre- 

 sented only in a small ])art of its course. 



* P. Gervais, op. cit. pi. ii. fig. 2. f G. Pouchet, op. cit. pi. v. figs. 1 & 2. 



