Alfftl'lH/HIII -7-") 



characterising sensory cortex in other animals. Furthermore, there is an absence of those large 

 cells which we saw in the motor area. 



PARIETAL AREA. 



The area I have now to describe possesses such distinctive cortex that it is defined with the 

 _MV, -it. 'M readiness; it is not so easy to determine, however, to what part it corresponds in other 

 animals. 



It is the field placed mesial to the motor area, confined to the marginal gyrus, and shown by 

 short horizontal lines in the diagrams. 



By its cell lamination the area is :nost readily mapped out ; I shall, therefore, describe this 

 first. Following on an uninteresting plexiform layer is a layer of polymorphs, more prominent than 

 in the surrounding fields. Then follows a deep layer of medium-sized pyramidal cells, of which the 

 individual members are neither numerous, nor well-stained, and this layer leads without break or 

 interval into a stratum of large pyramidal cells calling for special consideration. These cells, 

 although not nearly equal in diameter to the "motor" cells, must still be classed as of large size, 

 they have the form of elongated pears, a dozen or more can be found in a single low power field, 

 they stand erect and in line, and being distinctly chromophilous (it is not so with the "motor" 

 cells) they constitute the most prominent feature in the section, and afford a ready guide to the 

 definition of the area. This layer is directly followed by one containing well-stained fusiform cells. 



Now when I first saw the cells to which I have just made special reference, and took note of 

 the part over which they are distributed, I imagined I had located the motor area, but an 

 examination of the sections stained for nerve fibres at once dispelled this idea. For in such 

 specimens the cortex appeared quite pallid, betraying a degree of fibre, poverty inconsistent with 

 motor cortex. Then, under a high power, I found that the radiations were long and attenuated, and 

 contained only a few fibres of medium size, and that the interradiary plexus was very deficient in 

 density ; in short, it presented an arrangement like that in the area labelled "parietal" in Canis and 

 1'Vlis, and as in these animals, large, deep-seated, chromophilous elements are the principal cell 

 representatives of the area, one is forced to believe that the chromophilous cells, distinguishing the 

 same area in Sus, are the homologues of these, but for some reason better developed. 



LIMBIC AREA. 



The limbic area presents no difficulties, but, in Sus, the pregenual and postsplenial variations 

 cover a greater extent of the limbic gyrus; especially does this apply to the posterior field. 



As in the brains of other animals, the cortex is weakly supplied with nerve fibres, there is a 

 total absence of those of large calibre, and similarly, the cells are all of small size. The field 

 investing the genu is only interesting in accommodating a well-marked, deep layer of small chro- 

 mophilous lanceolate cells, very like those to be found in the same area in Homo ; and, in regard 

 to the postsplenial area, care must be exercised not to confound it with the visual, for in sections 

 stained for nerve fibres, a linear arrangement occurs, which a superficial observer might mistake for 

 a line of Gennari. 



ECTOSYLVIAN REGION. 



Just behind the long Sylvian fissure, a considerable collection of large fibres is seen in the 

 depths of the cortex, and the cell lamination is slightly different from that of the neighbouring 

 parts, so that it probably represents the Ectosylvian Area A of Canis and Felis, but it obviously 

 deviates in respect to its small extent. One point of special interest, to be commented upon later, 

 is that the area stops short of the " sulcus ectosylvius," and another is that similar cortex is 

 found concealed in the upper half of the well-developed "Sylvian" fissure. 



352 



