ELEMENTS OF NERVOUS TISSUE. 67 



nerve fibres of the spinal cord are of the smaller 

 varieties. 



The grey matter of the cord forms a quadrangular Grey matter, 

 prism with hollowed sides, or rather, a fluted column. 

 In its centre is a canal, sometimes closed in the adult, 

 and of greater diameter at either extremity of the 

 cord, than in its middle. Its walls are formed by a 

 layer of connecting tissue of varied thickness, rich in 

 plasm atic cells, and lined internally by a stratum of 

 cylindrical ciliated epithelium. Virchow, Kolliker, 

 and Ley dig* have particularly directed the attention 

 of microscopists to this cylinder of connecting tissue 

 which is thus inclosed in the grey matter of the cord, 

 as the plasmatic cells which it contains are often the 

 origin of morbid formations which occasionally in- 

 volve its substance. 



The grey matter itself is made up of blood-vessels. Eeiation be- 



17 . * 1 tween nerve cells 



fine nerve fibres, and caudate nerve cells, the largest of r d d f breB ' in the 

 which are found towards the extremities of the ante- 

 rior horns. In man the connexions of the caudate 

 cells have not as yet been clearly demonstrated. 

 This is not true, however, of some of the lower ani- 

 mals ; thus, in accordance with the researches of 

 Owsjannikow, in fishes, each cell has five prolonga- 

 tions, which are disposed as follows: The most internal 

 process, after it leaves the cell, enters the white com- 

 missure of the cord, and traversing it, reaches the 

 white substance of the opposite side, where it loses 

 itself in another similar cell (PL XII. fig. V. 7) ; this 

 is the branch which establishes a route of connexion 



Professor of Comparative Anatomy in the University of Wiirzburg. 



