NERVOUS CENTRES. (HITMAN ANATOMY. THE MENINGES.) 



627 



The ganglions are small masses occupying 

 certain situations in the body. They are ex- 

 tremely numerous in the human body, and very 

 variable in shape and size. One great sub- 

 division of them, in man and the mammalia, 

 is connected with the posterior roots of the 

 spinal, and with certain encephalic nerves. 

 Another class belongs to the sympathetic sys- 

 tem. In the Invertebrata the nervous system 

 is made up of a series of them variously dis- 

 posed, with their afferent, efferent, and con- 

 necting nerves. 



The spinal cord and the brain are peculiar 

 to the great class of vertebrated animals. They 

 may be regarded as compound ganglions, being 

 physiologically resolvable into a series of smaller 

 centres, which are, to a certain extent, inde- 

 pendent of each other. Viewed anatomically, 

 they are not so obviously divisible: in the 

 spinal cord, in which the independent influence 

 of separate segments may be most easily 

 demonstrated, no anatomical subdivision is 

 obvious, for the segments are fused together 

 into a cylindroid body, which has a certain 

 relation to the length and muscular activity of 

 the animal. Indications, however, of this 

 composite form of the spinal cord are afforded, 

 in the marked difference of dimensions which 

 certain parts of it present when compared with 

 others, there being always a manifest corres- 

 pondence between the size of any segment of 

 the cord and the motor or sensitive endowment 

 of that segment of the body which receives its 

 nerves from it. And the case of the common 

 gurnard ( Trigla Lyra) may be here quoted as 

 a remarkarble instance of the developement of 

 distinct gangliform bodies on a portion of the 

 cord, in accordance with a particular exaltation 

 of tactile sensibility. 



The brain is much more evidently made up 

 of a series of separate centres or smaller masses, 

 exhibiting sufficiently distinct boundaries on 

 their surfaces, but so intimately connected by 

 what are called commhsural or uniting fibres, 

 as to manifest the same kind of fusion (although 

 to a less degree) as that noticed in the spinal 

 cord. These gangliform bodies are so readily 

 distinguishable from one another, that from the 

 earliest periods of anatomical investigation each 

 of them has been designated by a distinct name, 

 which is generally derived from some prominent 

 feature of the body itself, or from the name of 

 some familiar object which it has been sup- 

 posed (often fancifully) to resemble. The 

 aggregate of these bodies is known in popular 

 language by the name of Brain, (a word of 

 Saxon origin, sometimes used in the plural); 

 this word, however, anatomically speaking, is 

 applicable only to the great hemispheric lobes 

 which form the largest portion of the whole 

 mass ; and the term Encephalon may be more 

 correctly used to denote the whole of the intra- 

 cranial contents. 



It is proposed in the present article to con- 

 sider the general and descriptive anatomy of 

 these nervous centres severally, beginning with 

 an examination of their coverings. 



COVERINGS OF THE NERVOUS CENTRES. 



COVERINGS or THE GANGLIONS. Every 



ganglion is covered by a more or less dense 

 layer of white fibrous tissue, similar to that 

 which forms the neurilemma of nerves. It per- 

 forms precisely the same office for the elements 

 of the ganglions that the neurilemma does for 

 those of nerves ; that is, it gives them a me- 

 chanical support, and is the medium through 

 which bloodvessels are conveyed to their ner- 

 vous matter. It is continuous with the neu- 

 rilemma of the nerves which are connected 

 with the ganglions. It is found in all forms and 

 classes of ganglions, presenting the same essen- 

 tial characters. These bodies are generally 

 surrounded by and imbedded in a considerable 

 quantity of fat, which also involves more or less 

 the nerves that proceed from them. 



COVERINGS OF THE SPINAL COED AND BRAIN. 



- These are also called the membranes of these 

 centres, or the meninges (prtviy%, membrana). 

 They are three in number. Those of the brain 

 are continuous with those of the spinal cord, 

 but, as there are certain distinctive characters 

 proper to each, it will be convenient to describe 

 the cerebral and spinal meninges separately. 

 They are, enumerating them from without in- 

 wards, the dura mater, the arachnoid mem- 

 brane, and the pia mater. 



The term, mater, pir-rig, originated with the 

 Arabian anatomists, who regarded these mem- 

 branes as the parents of all others in the body. 

 Galen adopted the word pjnyf, and distin- 

 guished the first and last of the membranes 

 above enumerated by the adjectives wptmgj 

 and hiKTYi. The Germans use the word hunt, 

 and designate these membranes as hautige 

 Hullen des Gehirns und des Rue kenmarkes ; 

 die harte Hirnhaut, die harte Ruckenmark- 

 haut, the dura mater of the brain and spinal 

 cord ; die Spinnwebenhaut, the arachnoid ; and 

 die weiche Hunt, the pia mater. 



Dura mater. The dura mater is a dense 

 membrane composed almost exclusively of 

 white fibrous tissue. It has all the characters, 

 physical and vital, of that texture, possessing 

 great strength and flexibility with but little 

 elasticity. It is freely supplied by blood- 

 vessels, and at certain situations, which will 

 be more particularly described by-and-bye, 

 it separates into two laminae, which inclose 

 prolongations of the lining membrane of the 

 venous system, forming peculiar sanguiferous 

 channels, which are commonly known by the 

 name of sinunes. It has an apparent lamellar 

 disposition, from the fact of its fibres being 

 arranged in different planes. In the child a 

 subdivision into two layers may sometimes be 

 easily effected. Some nerves have been de- 

 monstrated in the dura mater; a branch of the 

 fifth nerve has been particularly described and 

 delineated by Arnold, as passing in a recur- 

 rent course between the laminae of the tento- 

 rium, and Pappenheim has found nervous 

 fibres in the cerebral dura mater derived from 

 the superior maxillary division of the fifth, 

 from the fourth nerve, from the vidian, and 

 probably also from the frontal branch of the 

 ophthalmic.* 



* Valentin Rcpcrtorium, vol. v. p. 87. 



2 s -2 



