MOTOR CORTICAL CENTRES. 



687 



ft 



^ 



t 



I 



IK 



4ir 



Fig. 474. 

 Cortex of motor area 

 of brain of monkey 

 ( x 150). 1, super- 

 ficial layer ; 2, small 

 angular cells ; 3, py- 

 ramidal cells ; 4, gan- 

 glionic cells and cell- 

 clusters ; 5, fusiform 

 cells (Ferrier, after Bevan 

 Lewis). 



which are larger in the deeper than in 

 the more superficial layers. They are 

 not so closely packed together, as many 

 granules lie between them. At the 

 lowest part of this layer, the cells are 

 larger than elsewhere, presenting some 

 resemblance to the cells of the anterior 

 cornu of the grey matter of the spinal 

 cord. By some it is described as a 

 special layer, and termed the ganglion- 

 cell layer. This layer is specially well 

 marked in those convolutions which 

 are described as containing motor 

 centres. Amongst the large cells are a 

 few small angular-looking cells, which 

 become more numerous lower down, 

 and from (4) a narrow layer of numer- 

 ous small, branched, irregular, gangli- 

 onic cells the " granular formation" 

 of Meynert. In the motor areas mixed 

 with these are large pyramidal cells, 

 disposed in groups called "cell-clus- 

 ters." (5) A layer of spindle-shaped 

 fusiform branched cells the claustral 

 formation of Meynert lying for the 

 most part parallel to the surface of the 

 convolution. No layer is composed 

 exclusively of one form of cell. The 

 above represents the motor type. Then 

 follows the white matter (m), consisting 

 of medullated nerve-fibres, which run 

 in groups into the grey matter, where 

 they lose their myelin. The fibres are 

 somewhat smaller than in the other 

 parts of the nervous system (diameter 

 1^5-^ inch), and between them lie a few 

 nuclear elements.] 



[In the sensory type, as in the occi- 

 pital lobe (fig. 475), the first and second 

 layers are not unlike the corresponding 

 layers in the motor type, and the fusi- 

 form cells in the seventh layer also 

 resemble the latter. The layer of pyra- 

 midal cells (3) is not so large, while its 

 deeper part, sometimes called the "gan- 

 glion-cell layer," contains no large 

 cells. (5) Between the two is (4) a 

 layer with numerous angular granule- 

 like bodies or cells, called the " granule- 

 layer."] 



[The hippocampus major contains, 

 besides a layer of neuroglia and some 

 white matter on the surface, a regular- 

 series of pyramidal cells, which give it 

 a characteristic appearance. This is the 

 part which varies most. It is to be re- 

 membered that the transition from one 

 type to the other takes place gradually. ] 



[Pyramidal Cells of the Cortex. 

 Each cell is more or less pyramidal in 

 shape, giving off several processes (a) 

 an apical process, which is often very 

 long, and runs towards the surface of 

 the cerebrum, where it is said to ter- 

 minate in an ovoid corpuscle, closely 

 resembling those in which the ultimate 

 branches of Purkinje's cells of the cere- 



as? 



Cortex of occipital lobe. 1, 

 superficial layer ; 2, small 

 angular cells ; 3, 5, pyra- 

 midal cells ; 4, granule 

 layer ; 6, granules and 

 ganglionic layer ; 7, 

 spindle-cells (Ferrier, 

 after Bevan Lewis). 



