NEUROLOGY. 105 



tion. The two are closely related to each other, and the influence of the 

 former on the latter is not to be mistaken. 



Each nervous system has a central and a peripherical portion. The 

 central portion of the animal system is the brain and spinal marraw, the 

 peripherical the white thread-like nerves which proceed from these to the 

 various organs and back again. In the sympathetic system, the central 

 portion is constituted by two cords, one on each side of the median line of 

 the body, with ganglia or knots placed at intervals all along. 



There are two kinds of structure visible in the nervous system, the white 

 or fibrous and the grey or cineritious. The white matter, with the neuri- 

 lema or nerve sheath and the areolar tissue which it incloses, constitutes 

 the whole of the nervous trunks, wherever they occur, and forms a large 

 part of the central masses with which they are connected. It consists of 

 tubes of great minuteness, which are composed of an interlacement of 

 extremely delicate fibres. When examined immediately after death, the 

 contents of these tubes appear pellucid and homogeneous, and of a fluid 

 consistence ; subsequently, however, this contained substance coagulates, 

 and is seen distinct from its investment. The diameter of the cylindrical 

 nervous tubuli varies from l-2000th to l-6000th of an inch; the fibres 

 decrease, however, as they approach the brain. The nerve matter in the 

 tubes originally consists of nucleated cells. 



The other elementary form of nervous structure is the cineritious or 

 reddish grey matter. It appears to consist principally of a plexus of blood- 

 vessels into which the fibres of the first form may be traced, and amongst 

 these lie a number of nucleated globules without any very definite arrange- 

 ment. This substance is usually disposed in the interior of the larger 

 masses with which the nervous trunks are connected. It occupies part of 

 the interior of the spinal cord and of the ganglia, but in the brain it is 

 disposed externally, forming a coating to the subjacent mass, which consists 

 almost entirely of fibrous structure ; hence it is called sometimes the cortical 

 substance, as distinguished from the medullary, or the fibrous portion. 

 The ganglion globules are from l-300th to l-1250th of an inch in diameter, 

 possessing a spherical or oval form, more or less flattened, and having a 

 reddish color. Each contains one or more nuclei with subordinate nucleoli, 

 and is inclosed in a very fine filamentous investment, in which it is com- 

 monly found to be loosely suspended. The sheaths of the several globules 

 are connected with each other by prolonged filaments or peduncles, and 

 these form a kind of network, which occupies the interstices of the fine 

 vascular plexus by which every part of the grey matter is traversed. 



If we examine one of the cerebro-spinal nerves, we shall find it to be 

 invested by a sheath of membrane already referred to under the name of 

 neurilema. Its office is chiefly mechanical, namely, that of binding together 

 the constituent fibrillas and fascicles of the nerve, so as to protect them, 

 and support the delicate plexus of capillary blood-vessels from which they 

 derive their nutriment. To the naked eye the neurilema exhibits the ap- 

 pearance of a white and almost silvery membrane. 



After the external part of the neurilema has been removed, the nerve 



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