1-BRAIN OR PROSENC 



the terminations of the projection, Commissural, or association fibers, ascend to end in the cortex. 

 The axons of the cells of Martinotti are also ascending fibers. 



Special Types of Cerebral Cortex. It has been already pointed out that the minute structure 

 of the cortex differs in different regions of the hemisphere; and A. W. Campbell 1 has endeavored 

 to prove, as the result of an exhaustive examination of a series of human and anthropoid brains, 

 "that there exists a direct correlation between physiological function and histological structure." 

 The principal regions where the "typical" structure is departed from will now be referred to. 



1. In the calcarine fissure and the gyri bounding it, the internal band of Baillarger is absent, 

 while the band of Gennari is of considerable thickness, and forms a characteristic feature of this 

 region of the cortex. If a section be examined microscopically, an additional layer of cells is 

 seen to be interpolated between the molecular layer and the layer of small pyramidal cells. This 

 extra layer consists of two or three strata of fusiform cells, the long axes of which are at right 

 angles to the surface; each cell gives off two dendrites, external and internal, from the latter of 

 which the axon arises and passes into the white central substance. In the layer of small pyramidal 

 cells, fusiform cells, identical with the above, are seen, as well as ovoid or star-like cells with 

 ascending axons (cells of Martinotti). This is the visual area of the cortex, and it has been shown 

 by J. S. Bolton 2 that in old-standing cases of optic atrophy the thickness of Gennari's band is 

 reduced by nearly 50 per cent. 



White substance dorsal part) 



Neuroglia 





White substance (ventral 

 part) 



-Medullary layer 



.^Mitral cells 



Molecular 

 layer 



Glomerular layer 



Layer of olfactory nerve fibers 

 FIG. 755. Coronal section of olfactory bulb. (Schwalbe.) 



A. W. Campbell says: " Histologically, two distinct types of cortex can be made out in the 

 occipital lobe. The first of these coats the walls and bounding convolutions of the calcarine 

 fissure, and is distinguished by the well-known line of Gennari or Vicq d'Azyr; the second area 

 forms an investing zone a centimetre or more broad around the first, and is characterized by a 

 remarkable wealth of fibers, as well as by curious pyriform cells of large size richly stocked with 

 chromophilic elements cells which seem to have escaped the observation of Ramon y Cajal, 

 Bolton, and others who have worked at this region. As to the functions of these two regions 

 there is abundant evidence, anatomical, embryological, and pathological, to show that the first 

 or calcarine area is that to which visual sensations primarily pass, and we are gradually obtain- 

 ing proof to the effect that the second investing area is constituted for the interpretation and 

 further elaboration of these sensations. These areas therefore deserve the names visuo-sensory 

 and visuo-psychic." 



2. The anterior central gyrus is characterized by the presence of the giant cells of Betz and 

 by "a wealth of nerve fibers immeasurably superior to that of any other part" (Campbell), and 

 in these respects differs from the posterior central gyrus. These two gyri, together with the 

 paracentral lobule, were long regarded as constituting the "motor areas" of the hemisphere; 

 but Sherrington and Grunbaum have shown 3 that in the chimpanzee the motor area never extends 

 on to the free face of the posterior central gyrus, but occupies the entire length of the anterior 

 central gyrus, and in most cases the greater part or the whole of its width. It extends into the 

 depth of the central sulcus, occupying the anterior wall, and in some places the floor, and in 

 some extending even into the deeper part of the posterior wall of the sulcus. 



1 Histological Studies on the Localization of Cerebral Function, Cambridge University Press. 



2 Philosophical Transactions of Royal Society, Series B, cxciii, 165. 



3 Transactions of the Pathological Society of London, vol. liii. 



