HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL. 861 
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. Tue Histotocy oF THE CONVOLUTIONS OF THE PRECENTRAL GYRUS. 
(Text-fig. 5.) 
The cortex of the motor area presents a fairly typical structure, except that large 
‘multipolar nerve-cells occur at a relatively deep level, forming a deeply staining layer 
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Fic. 5.—Semidiagrammatic vertical section of a part of the motor cortex cerebri (precentral convolution). <6. 
Plexiform layer. 
. Layer of small nerve-cells (granules). 
. Layer of large flask-shaped nerve-cells, the axons passing centrally, dendrons peripherally. 
. Layer of large pyramidal cells (comp. to Bett’s cells of human motor cortex). 
. Deep layer of large pyramids, lying next to the white centre : there is much dense neuroglia in this layer. 
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lying next the fibres of the white centre ; in all, about four layers of nerve-cells may 
be distinguished. The following layers are quite distinct :— 
(a) A superficial layer formed of interwoven fibres (plexiform layer). 
(b) 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. 
(d) A fourth layer of rather large pyramidal cells, the axons passing centrally. 
(e) A fifth layer of large multipolar cells, the axons passing in many directions ; : 
this layer contains much deeply staining neuroglia. 
