MEDULLA OBLONGATA OF THE RABBIT. 



5 



between them. This space corresponds to the anterior 

 fissure of the adult cord. (Fig. 2.) 



Thus, in a general way, the morphology of the spinal 

 •cord is explained. 



The medullary wall may be divided into three layers, 

 the ependymal or inner neuroglia layer, the Randschleier or 

 outer neuroglia layer, and between the two the gray or 

 mantel layer. 



The ependymal layer in the adult is represented by the 

 epitlieliod cells lining the central canal of the cord. 



The Randschleier corresponds to the white substance of 

 the adult cord, and is deficient in nerve cells. 



The gray or mantel layer is that which lies between 

 the other two, and it is only in this layer that nerve cells 

 are to be found. 



There are two principal types of nerve cells, and these 

 differ materially from each other: 1. The Golgi type. 

 2. The Deiter type. 



The Golgi are found chiefly in the posterior horns of 

 the gray matter, and their neuraxons, or axis cylinders, do 

 not leave the nervous system, but act within it as commis- 

 sural fibres. 



I here use the term Golgi type in its broadest sense. 



The Deiter tyj^e, on the other hand, is only present in 

 the anterior horns of the gray matter, and their neuraxons 

 leave the nervous system, and invariably by way of the ven- 

 tral zones. After their exit from the medullary wall, they 

 form the anterior nerve roots, or, as they were formerly 

 called, the motor roots of the spinal nerves. So we see that 

 an anterior nerve root is composed of fibres derived from 

 Deiter' s cells, which leave the medullary wall by means of 

 the ventral zone. 



