80 LABORATORY METHODS OF 



closing membranes, the horns of the cord in the gray 

 matter, the different .shaped and sized nerve cells in the 

 anterior horn, central canal, anterior and posterior 

 roots, the different commissures, and the entrance of 

 the blood vessels in the pia mater. 



CEREBRUM. 



The cerebrum is composed of five layers of nerve 

 cells, which merge imperceptibly into each other. 

 They are : 



1. The molecular layer. This is the first layer, and 

 is composed of a number of finely granular cells, with 

 medullated fibers and neuroglia. The cells of Cajal 

 are found in this layer. 



2. l^he layer of small pyramidal cells. This is located 

 under the first layer and the processes that leave the 

 cells form a net work. The axis-cylinders leave the 

 basal ends of the cells and send collaterals in the me- 

 dulla. The dendrites enter the molecular layer. 



3. The layer of large pyramidal cells. This differs 

 from the second only in size of the cells, and in this 

 layer there is no network sent to the layer above. 



4. The layer of irregular cells. This layer is com- 

 posed of oval or polygonal cells, which have no special 

 dendrites. Each axis-cylinder sends out collaterals, 

 and enters the medulla to become one or two nerve 

 fibers. 



