L.t 





♦ . r_S,-\ >L.Il 



>•■;■ t 



'• : * 



Tv '.: 



f] L.IU 



LIV&v 





VL.IVtV 



(i) Man. (2) Dog. (3) Pig. 



x 74 diameters. x 89 diameters. x 109 diameters. 



Fig. 154. — Cortex of the Betz Cell Area of Man and of the Corresponding 

 Areas in the Dog and Pig (Watson). 



The magnification of (1) is less than that of (2) and (3). The depth of the 

 different layers of the cortex is approximately indicated by the markings to 

 the right of the figure. 



In man, L.II. — the pyramidal lamina — is much the best developed layer of the 

 cortex, being considerably deeper than the conjoined layers III. to V. It is 

 the lamina of ' psychic, associative, and educative significance.' In the dog and 

 pig, L.II. is comparatively poorly developed, having a depth of only one- 

 ihird to one-half of the conjoined layers III. to V. The conjoined layers 

 IV. and V., which are of ' organic and instinctive significance,' are of more 

 nearly equal depth in all three specimens. In this region L.III. — the granule 

 or receptive lamina — is reduced to a minimal depth and distinctness in all 

 the cortices. L.I. — the outer fibre lamina — is relatively deep in the pig, 

 possibly owing to a failure of development, in the upward direction of the 

 pyramidal layer. 



The larger cells of L.IV. in the ' motor ' area of the pig have not the characteristic 

 shape and appearance of the Betz cells of the human motor cortex ; the cor- 

 responding cells in the cortex of the dog more nearly approximate to the 

 human type. 



In the cortex of the pig the individual nerve cells, though fewer in number than 

 jn the dog, have a less embryonic appearance. 



