IXTEENAL STRUCTURE. 



561 



separation into groups more 

 distinct, has been described as 

 a separate layer by Lockhart 

 Claike. 



Fig. 391. — Section op Cerebral 

 CoNVOLCTiox (MejTiert). 



1, Superficial layer of scattered 

 corpiiscles ; 2, dense layer of .small 

 angular corpuscles ; 3, broader layer 

 of ijyramidal corpuscles, separated 

 into columns by the radiating nerve- 

 fibres ; 4, narrow layer of small ir- 

 regular corpuscles ; 5, layer of fusi- 

 form and irregular cells in medullary 

 centre. 



4. The fourth layer is nar- 

 rower, and contains many 

 small, irregnlarly-shaped, often 

 " grannie-like," corpuscles, 

 round or angular, with fine 

 processes, placed irregularly 

 and less distinctly separated 

 into groups. 



5. The fifth layer, of greater 

 width than the last, is com- 

 posed of fusiform and ir- 

 regular cells. The fusiform 

 corpuscles have a definite ar- 

 rangement, being placed for 

 the most part vertically at the 

 summit of a gyrus, but parallel 

 to the surface of a sulcus, 

 where they correspond in di- 

 rection to the arcifonn fibres 

 passing from one convolution 

 to another, with which they 

 are said to be connected. 



Beneath the last layer is 

 the medullary centre, with 

 ■which it gradually blends. 

 The fibres of the white sub- 

 stance, as they radiate into 

 the grey matter, become finer, 

 in consequence, it is thought, 

 of dividing or branching. 



The chief deviations from 

 this type are due to varia- 

 tions in the large pyramidal 

 cells, which in places lose their 

 characteristic size and distri- 

 bution. The most conspicuous 

 variation occurs in some parts 

 of the occipital region, especi- 

 ally near the sulcus hippo- 



Fig. 301. 



rf'rTT 





