II76 



HUMAN ANATOMY. 



Subpial layer 

 Tangential fibres 



Stratum zoriale ;=; 



Layer of small 

 pyramidal cells 



stratum — four layers being more or less clearly recognizable. In certain localities, 

 as in the precentral convolution, the inner gray lamina is subdivided by an 

 additional white line, the inner stripe of Baillarger. In the vicinity of the 

 calcarine fissure, particularly in the adjacent part of the cuneus, the outer stripe of 

 Baillarger, whilst narrow, is unusually distinct and confers, therefore, a character- 

 istic appearance upon the cortex of this region (Fig. 1013). The band in this 

 location receives the name of the stripe of Gennari, or the stripe of Vicg d' Azyr. 

 In recognition of the priority of description, Gennari's name is sometimes applied 

 to the external stripe of Baillarger wherever found. The significance of these 

 light colored strata will be pointed out in connection with the intimate structure 

 of the cortex, suffice it here to note that the stripes of Baillarger correspond to 

 zones in which the felt-work of horizontal cell-processes is unusually dense, the 

 stratum zonale corresponding to a compact layer of fibres running parallel with 

 the surface. Occasionally a condensation of tangential fibres immediately beneath 

 the stratum zonale produces the appearance of an additional light line, which in 

 honor of its discoverer, is known as the stripe of Bechterew. 



The essential histological elements of the cerebral cortex are the nerve-cells and 

 the nerve-fibres. The importance of the former is evident when their three-fold 



activity is recalled — (i)-as receptors of 

 Fig. 1014. corticipetal impulses, (2) as distributors 



of the impressions so received to other 

 parts of the brain, and (3) as originators 

 of corticifugal impulses which control 

 the nuclei from which immediately arise 

 the motor nerves. No single method 

 of preparation suffices to display satis- 

 factorily both groups of structural 

 elements, for when stains are employed 

 which best bring out the cells, the 

 fibres are inadequately shown ; and, 

 conversely, when methods adapted for 

 the demonstration of the fibres are 

 followed, the cells are but imperfectly 

 displayed. It is advantageous, there- 

 fore, to study the histological details 

 of the brain by more than a single 

 method, combining the results ob- 

 tained by the use of cellular stains 

 with those yielded by procedures ex- 

 hibiting the fibres. Among the latter, 

 the well known method of Weigert, or 

 its modifications, has been of great 

 service in extending our knowledge 

 concerning the various fibre-tracts. 

 The methods of silver impregnation 

 introduced by Golgi, although not 

 producing true staining but only in- 

 crustations on the cell and its pro- 

 cesses, have materially advanced our 

 knowledge concerning the form of the 

 cell-bodies and the number and extent 

 of the processes of the neurones. _ 



Whilst varying as to details in 

 different regions, the cerebral cortex 

 presents a general plan of structure which may be considered : (^a) in relation to 

 the nerve-cells and {b^ in relation to the nerve-fibres. 



The Nerve-Cells of the Cortex.— When sections cut perpendicular to the 

 surface of the convolution are stained with basic stains (Fig. 191 5) ^i' prepared 

 after silver impregnation (Fig. 1016), the cerebral cortex exhibits four layers, 



Outer stripe of 

 Baillarger 



Layer of large 

 pyramidal cells 



Layer of poly- 

 morphic cells 



Medullary fibres 



Diagram showing constituents of cerebral cortex ; 

 cells in the right half, fibres in left half of figure; A, B, 

 large and small pyramidal cells ; C polymorphic cells ; 

 /?, cell of Martinotti ; ii. cell of type II; F, association 

 cell; /, /, corticipetal fibres; 2. 2, corticifugal fibres 

 (axones of pyramidal cells) ; N, TV, neuroglia cells. 



