324 MANUAL OF HISTOLOGY. 



rected toward the periphery and often drawn out into a slen- 

 der axis-cylinder process, while from their base several delicate 

 processes are given off. These cells all have large nuclei and 

 nucleoli. Here and there are seen larger conical cells, which 

 will be described with the next layer. The characteristic fea- 

 ture of the second layer, however, is the presence of a great 

 number of small, round cells and free nuclei similar to those in 

 the third layer of the cerebellar cortex. 



In the third layer the matrix is still more dense, and con- 

 tains, besides a few small triangular cells, round cells, and free 

 nuclei, a large number of large conical corpuscles, the so-called 

 u giant cells" of the cortex, the distinguishing feature of this 

 layer. When isolated from their surroundings these cells ap- 

 pear like cones which taper gradually from a broad base to a 

 very slender apex, which, when it attains the size of an axis- 

 cylinder, can be traced for a long distance without showing a 

 division. This undoubtedly terminates in a myelinic nerve- 

 fibre. The base of the cell is not square, but crenated and 

 notched by the giving off of numerous delicate basal processes 

 which are lost in the granular matrix. 



The cells all have nuclei and nucleoli, most of which are 

 round, but some of which seem also to have a triangular shape 

 corresponding to the cell-body. The cells average 25 /*. in 

 diameter. A great difference is made in the apparent shape of 

 the cell by obliquity of the section. If the line of section is 

 moderately oblique, it shortens the cells ; if still more oblique, 

 it makes them very short and blunt ; while if the section is at 

 right angles to their axis, all the cells appear round and of 

 various sizes. In the deepest parts of this layer the giant-cells 

 gradually disappear, and the gray matter of the cortex merges 

 into the white matter. In the two inner layers of the cortex 

 there are seen many fibres and bundles of fibres having a ver- 

 tical direction, which, with the blood-vessels (the largest of 

 which being perpendicular to the surface), give the cortex a 

 somewhat striated appearance. 



We see, then, that the only difference between the second 

 and third layers of the cortex is the greater number of small 

 cells in the second and the greater number of large cells in the 

 third, while the division of the third layer into three, as is 

 accepted by most authors, seems purely arbitrary, there being 

 a gradual gradation into the white substance. 



