STRUCTURE OF MEDULLARY NEURINE. 545 



ceeded in isolating these tooth-like processes to an extent of 

 many times their diameter, so as to be enabled to observe their 

 similarity to the primitive gray fibres of the ganglionic nerves. 

 There is therefore some reason to believe that this is the mode 

 of origin of many of the ganglionic nerves — that is, those which 

 exclusively belong to the organic functions, — and that many of 

 the cerebro-spinal nervous filaments originate in the same way, 

 especially those which have latterly been denominated by Mr. 

 Marshall Hall the excito-motory, or with more propriety, the 

 reflex system of nerves. 



Of the Medullary Neurine. 



— The medullary neurine, substantia medullaris, forms a large 

 portion of the interior of the cerebrum and cerebellum, and has 

 received its name from its central position in these parts, like 

 that of the medulla or marrow within the cavity of a bone. 

 But this term is far from being generally appropriate, for the 

 medullary nervous substance, is found forming the exterior of 

 the crura cerebri and cerebelli, the pons varolii, medulla oblongata 

 and spinal marrow, and constitutes very nearly the entire 

 structure of the nervous cords. But the term, introduced at an 

 early period, has become so hallowed by usage, as to be con- 

 sidered classical and is very generally employed. The medulla- 

 ry nervous substance in its natural state is every where of a 

 white or cream color. Unlike the cineritious substance of the 

 brain, the medullary is apparently placed no where in detached 

 masses ; the nervous cords are continuous with the medullary 

 portion of the spinal marrow and this again with the medullary 

 masses of the encephalon. The ganglia themselves being no 

 interruption to the course of the nervous cords. 

 — Unlike the cineritious matter also, the medullary is every 

 where found to be fibrous ; a fact that was first demonstrated 

 by Vieussens in 1684,* and which is now as generally admitted 

 as any other truth in anatomy and physiology, and may be shown 

 convincingly on a hardened brain to the most sceptical inquirer. 

 — The mode adopted by Vieussens in order to display these 

 medullary fibres, was that of scraping its surface in the recent 

 * Vieussens, Neurographia Universalis. 



46* 



