THE NERVOUS SYSTEM 1443 



the tangential fibres. The base of the pyramidal cell is directed 

 towards the medullary centre of the gyrus, and from its centre an 

 axon is given off, which enters the medullary centre, giving off 

 collaterals in its course. From each side of the body of the cell, as 

 well as from each lateral angle of its base, dendrites are given off. 



The polymorphous layer is the deepest layer, and is composed of 

 cells which have different shapes. Each cell gives off several den- 

 drites, which pass towards, but do not enter, the molecular layer. 

 The axon of each cell enters the medidlary centre as a nerve-fibre. 



In addition to the foregoing cells of the cerebral cortex, two 

 other kinds of cells are met with amongst the pyramidal and poly- 

 morphous cells, namely, the cells of Golgi and the cells of Martin- 

 otti. The cells of Golgi are characterized by the fact that the 

 axon of each almost immediately divides into several branches, 

 which pass towards the surface, but soon terminate without entering 

 the molecular layer. The cells of Martinotti are chiefly met with 

 in the poljTnorphous layer. The axon of each cell passes towards 

 the surface, and enters the molecular layer, where it divides into 

 terminal branches, which form part of the tangential fibres of this 

 layer. 



Nerve-fibres of the Cortex. — These are arranged in two groups — 

 vertical and tangential. 



The vertical (radial) fibres are disposed in radiating bundles, 

 which issue from the medullary centre, and traverse the poly- 

 morphous and large pyramidal layers, after which they become 

 indistinguishable. The pol^Tuorphous and large pjrramidal cells 

 lie in the spaces between these bundles, and assume a columnar 

 arrangement. The fibres of the radiating bundles gradually 

 become less nmnerous, some of them becoming the axons of the 

 polymorphous cells, but most of them becoming the axons of the 

 large pyramidal cells. The radiating bundles contain centripetal 

 cortical fibres, which pass into the molecular layer and end in 

 terminal ramifications, forming part of its tangential fibres. 



The tangential fibres are disposed horizontally at different levels, 

 and form the following strata: (i) the superficial tangential fibres 

 (plexus of Exner), which occupy the superficial part of the mole- 

 cular layer; (2) the band of Bechterew, which is situated in the 

 superficial part of the small pyramidal layer; (3) the outer band 

 of Baillarger {band of Vicq d'Azyr), which intersects the large 

 pyramidal layer; (4) the inner band of Baillarger, which is situated 

 between the large pyramidal and polymorphous layers; and 

 (5) the deep tangential fibres [intra-cortical association fibres), yihich 

 are situated in the deep part of the polymorphous layer. 



The tangential fibres are formed by (i) the collaterals of the 

 polymorphous and pyramidal cells and of the cells of Martinotti; 

 (2) the ramifications of the axons of the cells of Golgi; and (3) asso- 

 ciation fibres. 



Medullary Centre of Cerebral Hemisphere. — The white matter of 

 the medullary centre consists of medullated nerve-fibres, which 



