CH. XLVIIL] 



STRUCTURE OF THE CORTEX 



697 



5. The inner cell lamina or polymorphic layer. These are small 

 scattered cells, many of a fusiform shape. In the Island of Eeil this 

 layer is hypertrophied, and is separated from the rest of the grey 

 matter by a stratum of white fibres; it is known then as the 

 claustrum. 



The G-olgi method of staining has proved conspicuously useful for 

 studying the shapes and dispositions of the cells (figs. 433, 434, 435). 



Nerve-fibres pass in vertical streaks through the deeper layers of 

 the grey matter ; some of these are axons conveying impulses down- 

 wards, others are sensory in function and carry impulses upwards. 

 Some strands lie parallel to the surface of the cortex; this is 

 specially noticeable in the layers we have numbered 1 and 4. In 



FIG 435. II tman cerebral cortex, showing a Betz cell or giant pyramid : Golgi's method. 

 High power. (Mott.) 



the portion of the occipital lobe which is the visual sphere, the 

 granule layer (No. 3), which is so specially characteristic of sensory 

 function, is of great depth and is divided into two by optic radiations 

 running horizontally, which constitute the white line of Gennari. 



Bolton regards the fifth lamina as the fundamental cell layer, the 

 others being formed from it from within outwards, both in embryonic 

 and historical development. Defect of development of the outer layers 

 leads to various forms of amentia (inborn lack of mental develop- 

 ment, or idiocy) ; in dementia (degenerative mental change coming 

 on later in life) there are retrograde changes in the upper layers of 

 cells. The fifth or inner cell layer is probably concerned with the 

 performance of organic and instinctive activities, and there is but 



