236 



Dr. B. Lewis. On the 



[June 19, 



ships through, their branches, the latter being far more numerous in 

 the swollen irregular cells of higher Mammals. 



6th. The pyramidal cells of this layer closely approach in their 

 dimensions and contour the larger pyramidal cells of the third layer 

 in man and the ape, and may be assumed to work upon the same 

 physiological level. 



7th. The ganglionic series in these members of the Ungulata, 

 assumes the clustered arrangement which is seen most highly de- 

 veloped in the motor area of the brain of the higher Mammalia. 

 These clusters, or nests of Betz, are in the pig and sheep more densely 

 packed with cells than in higher animals, cover oblong or oval areas 

 of some depth, and in the most highly developed region of this 

 lamination are so closely approximated that they tend to become con- 

 fluent and assume most distinctive features. 



8th. The regions over which the five-laminated cortex, with its 

 nested cells, spreads, are for the Ungulata the anterior half of the great 

 limbic lobe (superior arc), the whole of the frontal lobe, and the 

 lower parietal gyri. 



9th. The chief point of interest as regards the five-laminated cortex, 

 is the fact that the whole ganglionic series throughout this extensive 

 area maintains a remarkable uniformity of the magnitude of its ele- 

 ments, and in the complexity of their relationships. 



10th. This fact is highly significant, since, upon localising the 

 corresponding stratum in the cat and the ocelot, we find its grand 

 development limited to the immediate neighbourhood of the crucial 

 sulcus. On the other hand, in the ape and in man we find over 

 a wide area of the cortex the same type of formation, but, far from 

 there being general uniformity in the size and complexity of its cells, 

 there is exhibited here an exceedingly rich development of this layer 

 in the paracentral lobule of Betz, and the centre for the movements 

 of the hand and arm, whilst other portions of the motor area are less 

 conspicuously developed the more distant they are from these areas. 



11th. These anatomical facts enable us to conclude : — 



(a.) That in the Carnivora the motor centres are concentrated, so to 

 speak, upon the limited area occupied by the limbic and parietal 

 boundaries of the crucial sulcus. 



(&.) That in the Quadrumana and Man they are more widely 

 scattered and betray great divergence in developmental complexity at 

 different sites. 



(c.) That in the Ungulata they are still more widely scattered, but 

 exhibit at all points a most noteworthy uniformity in their structural 

 details and groupings, assuming, at the same time, a great resem- 

 blance to the elements of the third layer of the cortex in the higher 

 orders of Mammalia. 



12th. It is, therefore, inferred, that dissociation of centres plays an 



