STRUCTURAL ARRANGEMENTS OF CEREBRUM 433 



In the visuo-sensory area the granular layer is the thickest, and is 

 divided into two layers by the band of tangential fibres forming the line 

 of Gennari. In the association areas, both those, such as the intermediate 

 precentral and visuo-psychic, which are normally associated with motor 

 or sensory processes, as well as the higher association centres of Flechsig, 

 i.e. the frontal, parietal and temporal lobes, the most marked feature in the 

 section is the great development of and the large number of cells observed 

 in the outer cell lamina or pyramidal cell layer. It will be noticed, too, that 

 the audito-sensory area is but small in extent and lies almost entirely within 

 the lips of the fissure of Sylvius, while the greater part of the superior 

 temporal convolution, which on the left side is associated with the auditory 

 images and associations necessary for the comprehension of speech, partakes 

 of the character of an intermediate or psychic sensory area. 



The same method may be applied to a comparison of the relative develop- 

 ment of the cerebral functions in different types of animals. A comparison of 

 the brain of the dog, ape, and man shows that while the absolute amount of 

 brain substance devoted to the elementary functions of movement and 

 sensation remains practically the same throughout, in man these~ areas are, 

 relatively to the whole brain, very much diminished in size, the greater part 

 of the brain surface being taken up with the nervous material of the type 

 which is connected with the functions of association involved in the higher 

 processes of reflection, intelligence, and volition. 



If we draw still lower animals into the sphere of our observations we are 

 enabled to form some idea as to the relative significance of the various 

 elements of the cortex. Thus in an animal, such as the rabbit, the poly- 

 morphous layer is three times the thickness of the pyramidal layer ; whereas 

 in man, with an infinitely greater range of reaction, it is only one-third of the 

 thickness of this layer. If we may roughly assign a function to each of the 

 types of cells found in the cortex, we may say that the pyramidal cell layer 

 is generally associative in functions. The large pyramidal cells of Betz are 

 motor ; the granular layer is sensory, while the polymorphous layer presides 

 over the lowest cortical functions, such as those concerned in the getting of 

 food, the sexual instincts, and so on. 



The description given above applies to the whole of the neopallium. 

 In the more primitive part of the brain, the archipallium, represented 

 by the hippocampus, we find only two cell laminae which are homologous 

 with the middle (granule) and the inner polymorphous cell layers of the 

 neopallium. 



