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TEXT-BOOK OF PHYSIOLOGY. 



present a variety of shapes, for which reason the layer was at 

 one time termed the ambiguous layer. The apical process of the 

 pyramidal cells is broad at the base, but narrows rapidly as it 

 passes upward. It ^frequently divides into several branches, 



each of which develops club- 

 shaped processes or gemmules, 

 which give to it a feathery appear- 

 ance. Dendrites are also given 

 off from the sides and base of 

 the cell-body. From the base 

 a single axon descends which ulti- 

 mately becomes the axis-cylinder 

 of a medullated nerve. 

 The Layer of Large Pyramidal 

 Cells. The nerve-cells of this 

 layer, as the name implies, are 

 also pyramidal in shape, but of 

 large size. Each cell presents the 

 same features as the cells of the 

 preceding layer, with the exception 

 that the apical process is larger, 

 better developed, and branches 

 more freely. All the dendrites 

 are extensively provided with 

 gemmules. The axon is well 

 developed, sharply defined, and 

 smooth . After giving off collateral 

 branches, the axon descends into 

 the cerebrum and becomes a 

 medullated nerve-fiber. 

 The Layer of Polymorphous Cells. 

 In this layer the nerve-cells pre- 

 sent a variety of forms: e. g., 

 spindle, polygonal, pyramidal, etc. 

 The spindle form is the most 

 common. From either end of the 

 spindle a large dendrite emerges 

 which soon branches and becomes 

 gemmulated. The axon is well 

 defined and it soon descends into 

 the white matter. 

 The Number of Cortical Cells. Attempts have been made by 

 various histologists to estimate the total number of functional nerve- 

 cells in the cerebral cortex of man. Though the estimates are widely 

 different, the lowest presents numbers which are beyond compre- 



, 222. SECTION OF THE CERE- 

 BRAL CORTEX (MOTOR AREA) 

 OF CHILD, STAINED BY 

 GOLGI'S SILVER METHOD. 



A. Layer of neuroglia cells. 



B. Layer of small pyramidal 

 ganglion cells. C. Layer of 

 large pyramidal cells. D. 

 Layer of irregular smaller 

 cells. (Piersol.) 



