STRUCTUKE OF THE GREY SUBSTANCE OF THE SPINAL CORD. 357 



the fourth ventricle, and in Man, as Stilling* has shown, extends 

 into the conus medullaris, where it becomes progressively 

 more posterior, ultimately terminating in the posterior longi- 

 tudinal fissure. It is only completely filled with cerebro-spinal 

 fluid in children and young people ; at a later period of life it 

 becomes contracted, and frequently, especially in the cervical 

 region, obliterated or rather plugged up by the proliferation of 

 epithelial cells, which begins to occur even at the age of 

 puberty ; at least, I found indications of it in the body of a man 

 eighteen years of age. The innermost layer of tissue immediately 

 surrounding the central canal is composed of columnar epithe- 

 lial cells (fig. 227, 6), which in children have a ciliated border, 



Fig. 227. 



Fig. 227. Epithelium of the central canal of Man. Magnified 500 

 diameters, a, Fibrous connective tissue with a cellular element ; 

 b, ciliated columnar cells with fibrous appendages ; c, ciliated cell in 

 process of development ; d, finely granular substance between the 

 fibrous appendages of the ciliated cells. 



though this is subsequently lost. In specimens prepared with 

 chromic acid a thread-like process is given off from the pointed 

 extremity of each cell, that may sometimes be traced into the 

 fibrous connective tissue. The intervals between these append- 

 ages are occupied by a very finely granular material (fig. 

 227, d), which I consider to be a kind of connective tissue, in 

 which there are no fine elastic-tissue plexuses. In this substance, 

 and between the attached extremities of the columnar cells, are 



* Neue Untermchungen uber den Bau des Riickenmarks. " Further In- 

 vestigations into the Structure of the Spinal Cord." Cassel, 1867. 



