206 A Consideration of Function [CHAP. 



But we are still far from being out of the wood, for not only is the proof which we 

 are able to provide on the above-mentioned preliminaiy point quite inadequate to the sup- 

 pression of speculation, but also we have to bear in mind that the physiological process 

 composing sensation does not end with the mere reception and interpretation of the stimulus ; 

 we still have to reckon with the higher faculty of which sensations are the essential basis, 

 consciousness. 



Now, however, we reach a particularly thorny part, one where speculation completely 

 masters proof and one which I must refrain from entering because my only weapon, the 

 microscope, is of little service as an aid to argument. I will indicate only that, reasoning 

 on lines suggested by Hughlings Jackson's master mind, it may be contended that common 

 sensation is first represented in the cortex of the " postcentral " area proper, and that after 

 being re-represented in the " intermediate postcentral " area it has a still further representa- 

 tion in the physical basis of consciousness, and this may be situated in the " parietal " 

 area. In this connection it is interesting to observe that the area designated " parietal " 

 lies wholly within the field mapped out by Flechsig from studies on myelogenesis and called 

 by him on hypothetical grounds the " great posterior association centre." 



I will close this chapter with a reference to the parietal region in animals lower than 

 man in the vertebrate scale ; for although studies in comparative anatomy do not assist us 

 in determining its function it will still be interesting to obtain a view of the part from 

 the standpoint of homology. 



Taking the phylogenetic history of the principal fissures hereabouts, there seems to be 

 no doubt that the ansate fissure in lower animals becomes the postcentral in primates, while 

 the lateral and post-lateral fissures become the ram us horizontals and ramus occipitalis of the 

 intraparietal fissure, respectively (Elliot Smith). Then on the mesial surface, part of the 

 intercalary sulcus may become the post-limbic. Between these different fissures, therefore, 

 exists the homology of the superior parietal lobe. 



Histologically it has been found by Professor and Madame Vogt in a developmental study 

 of the brains of the domestic cat and dog, that the surface can be subdivided into three 

 different areas, in accordance with the period at which the cortical fibres receive their myelinic 

 investment, viz. precocious, intermediate, and late regions (regiones precoces, intermediae et 

 tardivae). Two chief precocious areas are found, one anteriorly in the region of the cruciate 

 sulcus, the other towards and on the occipital pole ; between these precocious regions, bounded 

 internally by the splenial or intercalary sulcus and externally by the suprasylvian sulcus, 

 lies the intermediate region. The rest of the cortex, that which would correspond to the 

 common temporal and common limbic areas of man, is late in maturing. 



Now in the anterior precocious region Professor and Madame Vogt do not. so far as 

 I am aware, make any subdivision, but from an examination of the brain of the adult cat, 

 dog, and pig, carried out in my laboratory, I am of opinion that the field can be broken 

 up into two, representing the primate " precentral " and " postcentral " areas respectively. 

 Concerning the posterior precocious region there seems little doubt that it represents the 

 visual area. 



Therefore, just as in man and the manlike ape the " parietal " area is neatly intercalated 

 between the central and visual fields, so it is also in the case of these lower animals. 



