NERVOUS CENTRES. (THEIR MICROSCOPICAL ANATOMV.; 



707 



delirium which succeed to haemorrhages, large 

 bleedings, or the sudden lighting up of inflam- 

 mation in the pericardium or within the heart. 

 In nearly all these cases, however, it is important 

 to notice that the blood is more or less damaged 

 in quality, deficient in some of its staminal 

 principles, or charged with some morbid matter; 

 and this vitiated state of the vital fluid has no 

 doubt a considerable share in the production of 

 the morbid phenomena.* 



Of the encephalic nerves. There are no com- 

 mon characters possessed by these nerves, such 

 as have been enumerated at a preceding page 

 for the spinal nerves. They are, however, dis- 

 posed in pairs, and are quite symmetrical. 

 With the exception of the olfactory, optic, and 

 third pair, they are all connected with the 

 mesocephale or medulla oblongata. 



The arrangement of these nerves originally 

 proposed by Willis has been so long adopted 

 in this country and on the continent that no 

 advantage would arise from abandoning it, un- 

 less some other of an unexceptionable nature 

 could be substituted for it. It has, therefore, 

 been followed in this work, and the anatomy 

 and physiology of the encephalic nerves have 

 been described in articles prefixed by their 

 numerical titles, in all cases except the olfactory 

 and optic, and the eighth pair of nerves, t 



Twelve pairs of nerves are found in con- 

 nection with the base of the encephalon. Five 

 pairs have been so classed by Willis as to form 

 two in his arrangement, three pairs being al- 

 lotted to his eighth pair of nerves, and two to 

 his seventh. Willis's arrangement, therefore, 

 comprises nine pairs of nerves, which he 

 enumerates, beginning at the anterior and pas- 

 sing to the posterior part of the base of the 

 brain. These are the first pair or olfactory 

 nerves ; the second pair or optic ; the third 

 pair, motores oculorum ; the fourth pair, pa- 

 thetici ; the fifth pair; the sixth pair, ubdu- 

 centes oculi; the seventh pair, including the 

 portio mollis or auditory nerve, and the portio 

 dura or facial nerve; the eighth pair, including 

 the glosso-pharyngeal, the pneumo-gastric, and 

 the spinal accessory ; the ninth pair or hypo- 

 glossal. The first cervical nerve or the sub-occi- 

 pital was considered by Willis as an encephalic 

 nerve and counted as the tenth pair. 



As the cranium may be shewn to be com- 

 posed of the elements of three vertebrae, it 

 has been attempted to prove that among these 

 nerves some may be classed with the vertebral 

 or spinal nerves. The fifth is obviously of this 

 kind from its anatomical characters, namely, 

 two roots; one, small, ganglionless ; the other 

 large, ganglionic; but with the former, which 

 is analogous to the anterior root of a spinal 

 nerve, the third, fourth, and sixth nerves may 

 be conjoined from their similarity in structure 

 and distribution. Thus one crania-vertebral 



* The subject of the circulation in the cranium 

 has been very ably discussed by Dr. G. Burrows in 

 the Lumleian Lectures for 1843, Lond. Med. Ga- 

 zette, vol. xxxii. 



t The olfactory nerve is described in the atricle 

 NOSE, the optic in OPTIC NERVES, and the eighth 

 pair under the titles of its three portions. 



nerve is formed, the anterior root of which 

 consists of the small portion of the fifth, the 

 third, fourth, and sixth nerves; and the pos- 

 terior or sensitive root, of the large portion of 

 the fifth. A second cranio-vertebral nerve 

 consists of the eighth pair, to which might be 

 added the facial contributing to its motor por- 

 tion ; and a third is formed by the hypoglossal. 

 The analogy, especially in the latter case, is far 

 from being very obvious. 



Sketch of the microscopical anatomy of the 

 spinal cord and brain. We conclude our ac- 

 count of the anatomy of the spinal cord and 

 brain with a rapid glance at the present state 

 of our knowledge of their minute anatomy as 

 revealed by microscopical observation. 



The elements of the two kinds of nervous 

 matter, fibrous and vesicular, have been al- 

 ready sufficiently described. We shall only 

 remark here that the great object of the ana- 

 tomist's research should be to find out the 

 precise manner in which the nerve-fibres are 

 united with the nerve-vesicles. Of their in- 

 timate connection there can be no doubt, 

 much less of the influence which they are 

 capable of exerting mutually upon each other.* 

 Among the peculiarities of the fibrous mat- 

 ter in the centres it may be here stated that 

 the fibres pass through a much greater range of 

 size than in the nerves; that here we meet with 

 nerve-tubes of the largest size, and, on the other 

 hand, with minute fibres which seem to be con- 

 tinuous with the branching processes of the 

 caudate nerve-vesicles. These fibres are per- 

 fectly transparent and differ from the nerve-tubes 

 in the absence of any of the white substance of 

 Schwann, and of the tubular membrane. 



Some idea of the relation of the vesicular 

 and fibrous matter in different parts of the cere- 

 bro-spinal centre may be formed by examining 

 thin sections of the several portions of them 

 made in various directions. It is impossible 

 to make these sections sufficiently thin to enable 

 us to explore a large surface with a high power, 

 for which great transparency is necessary. Such 

 sections, however, may be examined with low 

 powers, as Stilling and Wallach have done. It 

 is important, however, to notice that the ap- 

 pearances observed in this way afford no certain 

 indication of the course and direction of the 

 nerve-fibres, nor of the situation of the finer 

 elements of the vesicular matter. The nerve- 

 tubes are too minute to admit of being followed 

 with an object-glass which magnifies less than 

 from two hundred to three hundred diameters; 

 yet Stilling's researches have been made with a 

 power of no more than ten or twelve diameters. 

 The fibrous matter of the spinal cord consists 

 of some fibres which pass either in a vertical 

 direction, or obliquely, taking a long course, 

 and deviatingbut slightly from the parallel to the 

 axis of the cord. The fibres of the posterior 

 columns are the most obviously longitudinal, 

 and those which lie quite on the surface of the 

 antero-lateral columns follow very much the 

 same direction. Among the elements of the 

 grey matter, fibres are found in great numbers, 



* See the article NEKVE, and pp. 646, 7, et seqq. 



