262 The Cerebral Cortex in Felis Domesticus 



I will now offer a detailed account of the structural characters and distribution of all these 

 areas, as they appear in the different brains. 



FELIS DOMESTICUS. 

 l or Jlotor Area. 



We are indebted to the experimental physiologist for the information that the motor cortex 

 of the common members of the Carnivore family is deposited in relation to the sulcus cruciatus. 

 Acting on this knowledge, the histologist has already paid attention to this region, and found an 

 arrangement of elements, akin to that present in the "precentral or motor" cortex of man, and, 

 in particular, he has observed that a field can be mapped out, distinguishable in possessing the 

 equivalents of "giant" cells of Betz or "ganglionic" cells of Dr Sevan Lewis'. 



Cell Lamination. 



A plexiform layer is present but calls for no special remarks. 



The small pyramidal cells are more stunted, and do not form such a distinct layer, as in man. 



A layer of mixed medium-sized and small pyramidal cells follows, and, for reasons appearing 

 later, it is important to notice that this layer does not harbour cells of outstanding size. 



As to the "giant" cells, I hasten to mention that a most careful histological account of these 

 elements, as they appear in the cat, was written as long ago as the year 1879, by Dr Bevan 

 Lewis, and in regard to their size, number and distribution there is nothing for me to add to 

 that description. The cells are the largest in the whole brain, and immediately remind one of 

 the human precentral "giants"; plump and of oval or pear shape, they issue numerous dendrites 

 radiating downwards and outwards, while their body is well stocked with chromophilic elements. 

 I have not measured many cells, but they vary considerably in size, and, according to Dr Bevan 

 Lewis, range in diameter from 26 x 14/x to 106 x 32/x, the largest occurring round the lateral end 

 of the crucial sulcus, the next in size on the posterior wall and bank, and the smallest on the 

 anterior wall and bank of the same fissure. Another human peculiarity which we find repeated 

 is the tendency for the cells to be arranged in nests or clusters. 



The next layer containing fusiform cells is not of special interest. 



Fibre Arrangement. 



In the cat the motor area cannot be mapped out with such ease from an examination of 

 the fibres only as in the human being or ape, for, although rich in fibres of medium size, its 

 cortex is wanting in those of large calibre, and does not stain so intensely as some placed further 

 back (postcrucial area). 



Briefly stated the composition is as follows : 



1. A deep and dense zonal layer, made up for the most part of fine varicose elements, but 

 containing in addition a few medium-sized and some large medullated fibres. 



2. A supraradiary layer which seems shallow compared with that of other regions, but which is 

 interesting in showing numerous fibres of Martinotti arching up to join the zonal layer, at a tangent. 



3. A deep and well-stained radiary zone, in which the radiary fasciculi are voluminous and 

 compact, but lacking in gross fibres ; the same defect applies to the interradiary plexus, whose 

 real fibre wealth is not appreciated until it is examined under a high power lens. 



1 To explain references made hereafter to the comparative sizes of cells, I must state that the term "giant" 

 applies to the great cells of the cruciate cortex ; the term " large " to the equivalents of the " large external " and 

 "large internal" pyramidal cells of man; and the terms "medium-sized" and "small" to the cells corresponding 

 with the elements known by those significations in man. In the same way, among nerve fibres, we will find 

 medullated fibres of "large" and "medium" size, varicose fibres, and varicose fibrils. 



