290 General Reflections 



pallium which marks the superiority of Man, and is the last to appear in the phylogeuic progress 

 of cerebral growth. Interest centres mainly on its extent, and although the subject has been freely 

 discussed by others with a riper experience than mine, I have no compunction in reopening the 

 question, because I am sure it will be conceded by all that microscopic examination is the most 

 accurate gauge we can employ for the exact determination of the areal limitations about which we 

 are doubtful. 



Beginning with the frontal lobe, we at once notice that the lobe in Man has undergone great 

 expansion, evident enough on the mesial surface, plainer on the orbital face, and more pronounced 

 still on the convexity ; further, we learn from the microscope, that this expansion, this new 

 formation, is associated with the deposition of fresh types of cortex, types we failed to recognise in 

 the lower animal. Just along the anterior margin of the Carnivore motor area, it is true, there 

 does exist a fringe of cortex bearing a slight resemblance, a very slight one, to that of the extensive 

 " intermediate precentral " area of Man ; in front of this, however, it is impossible to see any 

 similarity between the undeveloped-looking grey mantle of the lower animal and the definitely 

 constituted, but perhaps still incomplete, " frontal " and " prefrontal " cortex of both Man and the 

 Anthropoid. 



Passing on to the parietal lobe we again find evidence of superior development ; and perhaps 

 the clearest conception of this is obtained by viewing the dorsal surface, and noticing the space 

 intervening between the combined motor and sensory areas in front, and the visual area behind. 

 In Man, the visual area is drawn backwards and downwards, and almost pushed oft' the horizon : 

 in the lower animal, on the contrary, the same area is not only mainly resident on the dorsal 

 surface, but is separated by a short interval only from the sensory and motor fields. In anatomical 

 terms, the precuneus, and the superior and posterior parietal lobules sutler in the comparison. And 

 it is of further interest to observe that in Sus this space is distinctly less than it is in either Felis 

 or Canis. From the structural aspect, the differences are less pronounced than they were in the 

 case of the frontal lobe: the "intermediate precentral" and "parietal" types of Homo are not 

 repeated, but nevertheless the existing cortex is well constructed. This discloses a comparative 

 distinction between parietal and frontal cortex which might be dilated upon, but as space forbids, I 

 will merely express the opinion that it suggests an earlier phylogenesis for the former than the 

 latter. 



The truth that the visual area occupies virtually the whole of the occipital lobe, roughly 

 estimated at about one-sixth of the entire cortex, sufficiently emphasises the value of this sense to 

 the lower animal. But in a comparative examination it is interesting to notice that the investing 

 zone of cortex we saw in Man, and to which we assigned a psychic function, is almost wholly 

 unrepresented in the lower mammal ; only in Canis was a trace of homologous cortex observed. 



In the temporal lobe, again, the brain of Man shows to enormous advantage, indeed, the 

 homologue of the second, third, and fourth temporal gyri is undefinable in the lower animal. 

 Further, I have failed to differentiate a specialised field of cortex to compare with the "audito- 

 psychic " area. 



Others have written in thoughtful detail of the changes leading to the operculation of the 

 Insula ; I can only add that histology j'ields proof of the stability of the covering cortex through 

 the phylogenetic series, an attribute which indirectly confirms the opinion I have given elsewhere, 

 that the insular cortex may deal with the elaboration of gustatory impressions. 



From what is written in the foregoing paragraphs it is plain that I share the opinion of those 

 who maintain, that while the human brain shows signs of having expanded more decisively in some 

 parts than in others, yet that expansion, if we except the olfactory and visuo-sensory areas, has 

 been general in kind. 



