158 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



enlargement; it probably, however, extends high up into the 

 medulla oblongata. 



At the tip of the posterior horn there is found a glassy, 

 semi-transparent body, the substantia gelatinosa Rolandi. As 

 has been shown by Corning, this is the remains of a tissue which 

 was present throughout the spinal cord during the embryonal 

 period. Its cells strongly resemble ganglion-cells, but their 

 nature is still unknown. Many fibres of the posterior root pass 

 through it (Fig. 93). 



At several points in the gray matter there can be seen but 

 few nervt>fibres, and scarcely any ganglion-cells. At these 

 points the neuroglia is the only constituent, and they therefore 



present a pale-grayish, translucent 

 appearance to the naked eye. A 

 very plentiful deposit of neuroglia 

 is situated around the central canal , 

 and is called the substantia gelati- 

 nosa centralis. The whole periph- 

 ery of the spinal cord is also cov- 

 ered with a thin mantle of almost 



FIG. 95. 



Part of cross-section of the white pure neUl'Oglia, tile gelatlllOUS C01'- 



subst an ce of one of the lateral-columns. 



The transversely-divided nerve-fibres, tlCal laver. 



in the centre of each of which is an ' J 



axis-cylinder, are surrounded by neu- Tlip \vliifp <jnh<5fiTirr> snvvrmml 



roglia containing Deiters' cells. (After 



ing the gray matter consists prin- 

 cipally of fibres running lengthwise of the spinal cord, of the 

 obliquely-ascending roots of the nerves, and of fibres which 

 run more or less perpendicular to the long axis of the cord, 

 from the gray matter into the white substance. The nerve-fibres 

 have an axis-cylinder and a medullary sheath. The width of 

 the latter varies greatly. The sheath of Schwann is wanting. 

 Between the fibres lies the neuroglia, which at many points is 

 continuous with a fibrous connective tissue. In this connective 

 tissue, which is continuous externally with the neuroglia and 

 with the pia mater, are situated blood-vessels which have a some- 

 what radial arrangement. The neuroglia consists here, as in the 



