HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL. 153 



grey matter into two main groups, an anterior and a posterior. Just beneath the 

 superficial white matter several well-defined groups of nerve-cells may be seen (n.), and 

 posteriorly a group is also to be distinguished. Many small nerve-cells are scattered 

 throughout the masses of grey matter. 



VI. THE HISTOLOGY OF THE CONVOLUTIONS OF THE PRECENTRAL GYEUS. 



(Text-fig. 5.) 



The cortex of the motor area presents a fairly typical structure, except that large 

 mnltipolar nerve-cells occur at a relatively deep level, forming a deeply staining layer 





FIG. 5. Semidiagrammstic vertical section f a part of the motor cortex cerebri (preoentral convolution), x 6. 



1. Plexiform layer. 



2. Layer of small nerve-cells (grannies). 



3. Layer of large Mask-shapi-il nerve-cells, \\w a\mi> passing centrally, dcndrons peripherally. 



4. Lay.r of large pyramidal cells (comp. to Bett's cells of human motor cm \, . 



5. Deep layer .>f larye ]iyraniiils, lyin.i,' next, t" the white centre : there is much dcnsi' ncurnfjlia in this layer. 



lying next the fibres of the white centre; in all, about four layers of ner\ r-crlU ni,-iy 

 be distinguished. The following layers are quite distinct : 



(n) \ superficial l.-iycr fonned of interwoven fibres (plexiform layer). 



(6) A second layer of small nerve cells, the axons of which are not very obvious. 



(c) A third layer of large flask-shaped cells not unlike the Purkinje cells of the 



cerebellum, with axons passing centrally and dendrons peripherally. 

 (il) A fourth layer of rather large pyramidal cells, the axons passing centrally, 

 (c) A fifth layer of large multipolar cells, the axons passing in many dim-linns : 

 this layer contains much deeply staining neuroglia. 



(ROT. SOC. EDIN. TRANS., VOL. XI, VIII., SCI.) 



