286 The Homolofjies of the Temporal Lobe 



that in endowing the Ungulate brain with a crucial fissure, I place myself at variance with, at any 

 rate, most comparative anatomists, but, at the same time, I see no other way of explaining these 

 findings. 



PARIETAL AREA. 



In Primates I have given the name parietal to the field of cortex intercalated between the 

 postcentral or sensory and the visual areas, and I believe that a corresponding area is definable in 

 the brains of lower animals. In the case of Felis, Canis, and Sus it is similarly interposed between 

 the above-mentioned areas, it occupies the middle portion of the marginal gyrus (vide diagrams), it 

 comes in contact with limbic cortex on the mesial surface, and in the outward direction tends to 

 spread beyond the sulcus lateralis. In Man similar anatomical relations have been observed and a 

 resemblance of special interest is that the ramus horizontalis of the intraparietal fissure, like the 

 sulcus lateralis, does not form a constant boundary ; there is a tendency to overlap. 



Considered spatially, there is little doubt that the area in Man is proportionately much greater 

 than in the lower animals ; further, it appears that the field is somewhat more extensive in both 

 Felis and Canis than in Sus. The disparity is perhaps best demonstrated by comparing the space 

 intervening between the sensory or, better still, the motor and the visual areas in the different 

 animals. But it must be added that although spatially inferior in Sus the structural components 

 by which the same cortex is recognised are just as well if not better developed than in the 

 Carnivorae. 



From the point of view of homology, the distribution of this area is entirely favourable to the 

 commonly accepted deduction that the lateral sulcus of lower orders is the equivalent of the Primate 

 ramus horizontalis of the intraparietal fissure. 



Further, in the cerebrum of the pig the distribution favours the suggestion, hinted at in an 

 earlier section, that the fissure usually called suprasylvian (I have labelled it suprasylvian with a 

 note of interrogation in my diagrams), and not that lying in the midst of the visual area, is the 

 true sulcus lateralis. This construction also fits in with what has been written on the homologies 

 of the sulcus coronalis. 



The function of the parietal area, even in Homo, is very imperfectly understood, and unfor- 

 tunately the present research, so far as I can see, does not add to our knowledge of the subject. 

 Let us hope it may be of help in the future. 



ECTOSYLVIAN REGION. 



Though the steps in such a metamorphosis are by no means easy to trace, there exist good 

 reasons for upholding, that out of the ectosylvian region of lower mammals is developed the Sylvian 

 region, including the Insula, and much of the temporal lobe of Homo. Before setting down 

 my own histological deductions it will be useful to employ a few words in pointing out the local 

 homologies which have been formulated for us by the comparative anatomist. 



We are told that in Man alone the Sylvian fissure is seen in its complete form. In the 

 animals with which I am dealing the fissure called "Sylvius" is so named merely for descriptive 

 convenience ; in reality it is but a shallow kink in the hemisphere produced by the downward 

 expansion of pallium placed more posteriorly. The human fissure is evolved from the operculation 

 of the outer walls of three sulci, each having a distinct phylogenic origin. The contributing sulci 

 in the process are the suprasylvian, the so-called " Sylviau," and the Primate fronto-orbital ' ; 



1 It must be explained, in reference to the fronto-orbital sulcus, that its equivalent in the lower animal brain, 

 unless it be the sulcus iliagoualis of Felidae, is undetermined. 



