INTERNAL STEUCTUEE. 



559 



according as its very numerous vessels contain much or little blood. 

 Then folloTv, 3. Another thin whitish layer ; and 4. A thin grey 



Fig. 390.— Section op Fig. 390. 



THE Cortical Sub- 

 stance OF A Cerebral 

 Convolution (from 

 Remak). 



In A, the parts are 

 nearly of the natural 

 size. To the right of the 

 figure, a and e are two 

 white, and h and/ two 

 grey strata ; to the left 

 of the figure, an addi- 

 tional white layer, e, di- 

 vides the first grey into 

 two, h and d. In B, a 

 small jjart of the cortical 

 substance of aconvolution 

 is represented, magnified 

 to show more clearly the 



relative position of the strata ; a, superficial white layer ; i, reddish grey layer ; c , inter- 

 mediate white layer ; d, inner part of the outer grey layer ; e, thin white layer ; /, inner 

 grey layer ; g, radiating white fibres from the medullary substance of the convolution 

 passing into the layers of the cortical substance. 



stratum. This last lies next to the central white matter of the hemispnere, 

 In some convolutions, especially in the occipital region, a paler layer 

 (fig. 390, B) divides the outer grey layer into two {h and d). 



This cortical grey substance of the convolations contains cells and 

 fibres embedded in a matrix. In this matrix most observers (Ehrenberg, 

 Henle, Boll) have found only a granular structure, while others (as Max 

 Schultze) believe that it consists of a network of fibres. It contains 

 nuclei, and is probably of the nature of connective tissue (neuroglia), 

 similar to that which supports the elements in other parts of the nerve 

 centres (p. 136), and later researches have traced in it a similar cor- 

 puscular structure. 



The cells are of various forms and sizes, — spherical, angular, fusiform, 

 pyramidal, stellate, — many of them with numerous processes. Some of 

 these branching cells are irregular in form and position, others are 

 more regularly pyramidal in shape, and have the apex of the pyramid 

 turned towards the surface of the convolution. The average size of the 

 larger pyramidal cells is y-j-^y^th of an inch in diameter at the base, and 

 each contains a rounded nucleus having an average diameter of v-^rrcfth 

 of an inch. They commonly contain & little yellowish pigment. The 

 process from the apex may be traced for some distance towards the sur- 

 face of the convolution, and is then lost. The mode of its termination 

 is unknown. Several fine branching processes pass from the angles afc 

 the base of these cells and run outwards or towards the medullary centre. 

 Some of these divide and ramify, the branches forming a network of 

 fine anastomosing fibres, while others have been traced inwards undi- 

 vided, and are supposed to be continuous with the axis-cylinder of a 

 nerve fibre. The undivided axis-cylinder process, according to some 

 observers, arises from the centre of the base of the cell, as in some 

 other parts of the nervous system. The processes of these cells, as 

 \Yell as the body of the cell itself, are said to possess a distinct longi- 



