110 



HISTOLOGY. 



the latter surrounds only single axis cylinders, and not 

 bundles. 



Histogenesis of the Neurone. 



The following description is based on the account of the 

 development of the neurone given by Barker, who, in turn, has 

 used as a foundation the writings of His. As is well known, 

 the medullary plate of the nervous system is derived from the 

 ectoblast, by the turning in of a single layer of epithelium 

 (Fig. 82). The neural tube is formed from this, its inner sur- 



Fio. 82. 



Section through the medullary plate of a rabbit. Among the epithelial cells a large round 

 germinal cell with clear protoplasm is visible. (Barker, after His.) 



face corresponding with the outer surface of the ectoblast. The 

 cells increase in length and the nuclei come to lie at different 

 levels (Fig. 83). There are formed three zones, however, the 



FIG. 83. 



Section through a rabbit's neural tube which is beginning to close, 

 epithelial nuclei is increased. (Barker, after His.) 



The number of 



inner and outer of which are made up of the protoplasmic ends 

 of the cells, while the middle zone contains the nuclei. The 

 distal ends of the cells i. e., the ends toward the lumen of the 



