THE CINERITIOUS AND MEDULLARY NEURINE. 543 



the origin of the nerves. Though thus diversified in its mode o 

 disposition about the body, the nervous substance, or neurine, as. 

 it is now more appropriately called, is susceptible of being divided 

 from its physical qualities and difference of functions, into two 

 kinds, the cineritious and medullary. 



Of the Cineritious Neurine. 



The cineritious neurine, substantia cinerea, has as the term 

 imports, derived its name from its gray or ash color, and is 

 soft and pulpy. It is found only in the brain and spinal mar- 

 row, and in the ganglia of the nerves.* It forms the central 

 part of the medulla spinalis, and the portion of it lodged in that 

 position, has received the name of the nucleus of the spinal 

 marrow. It is found also, in the central parts of the cerebrum, 

 the cerebellum, the crura cerebri, the pons varolii and the 

 medulla oblongata. It forms, besides, the whole of the outer 

 covering of the cerebrum and cerebellum, existing there in the 

 form of a layer, a line to a line and a half in thickness, dipping 

 down between and covering the bases and sides of the convo- 

 lutions of the cerebrum, as well as the horizontal layers of the 

 cerebellum, and thus amplifying the superficies of those organs 

 to three or four times that of the interior surface of the walls 

 of the cranium. From the external position it occupies in 

 these organs, it has been called, though very inappropriately, 

 the cortical substance of the brain. It is very abundantly 

 supplied with blood-vessels, which exist in it in the form of 

 meshes of capillary vessels conveying red blood, and pervade 

 its whole substance, so as to render it, if not the most, one of 

 the most, vascular portions of the body. This great vascularity 

 appears to be the cause of the grayish brown color from which 

 the name of cineritious has been derived. It is of a darker 

 color in man than any other animal, and is found gradually 

 to become paler, as we descend in our investigations, along 

 the animal scale. Some of the central deposits of cineritious 



* The microscopical observations of Remak and Mailer, have shown it to 

 exist occasionally in the nerves of the sympathetic, and in some of the enceph- 

 alic nerves of the cerebro-spinal system. But in such cases, the nerves con- 

 taining' it are devoted wholly to the organic functions, and may be considered 

 rather as elongated funicular ganglia. 



