THE CENTRAL NERVOUS SYSTEM. 2IQ 



like the outer layer of the cerebral cortex, of a deli- 

 cate connective-tissue framework, which supports 

 fine nerve-fibres and small spindle-shaped and 

 branching nerve-cells ; the middle, cellular layer, is 

 formed by an irregular row of large ganglion-cells, 

 Purkinje s cells, whose branching processes extend 

 into and ramify in the outer layer, while the axis- 

 cylinder process passes inward through the inner 

 layer ; the inner, granular layer, contains a great 

 number of small spheroidal cells whose nature is un- 

 determined. The granular layer merges gradually 

 into the white substance and is thickest at the sum- 

 mit of the convolutions, where also Purkinje's cells 

 are most abundant. 



The blood-vessels penetrate the cortex of both 

 cerebrum and cerebellum, in the form of small 

 arterial twigs from the pia, and form an abundant 

 net-work in the gray substance, being somewhat 

 differently distributed in different parts of the 

 organ, and less abundant in the white than in the 

 gray matter. 



The Dura Mater of the brain is a dense connective- 

 tissue membrane containing numerous elastic fibres 

 and lined within by endothelial cells. Where it is 

 attached to the bones of the skull, to whose inner 

 surface it acts as periosteum, the tissue on the at- 

 tached surface is looser in texture and abundantly 

 supplied with blood-vessels. It contains the ordi- 

 nary flattened connective-tissue cells, and usually a 



