NERVOUS CENTRES. (HUMAN ANATOMY. THE GANGLIONS.) 



649 



only by the movement of the nucleus, which is 

 the consequence of it. * * * In proportion as 

 the granular mass contracts itself within certain 

 limits, (sich immer mehr abgrenzt,) a cell-mem- 

 brane probably becomes developed around it, 

 so that the vesicle gradually acquires its precise 

 form and size, and its contents their proper 

 characters, which belong to a fully formed cen- 

 tral nervous corpuscule.* Valentin compares 

 the developement of these vesicles to that of 

 the ovum. The nucleolus of the nerve-vesicle 

 is always first formed, then around it the primi- 

 tive cell, and around this the outer cell. This 

 process resembles exactly that which takes 

 place during the formation of the ovum, for the 

 germ corresponds to the nucleolus, the germinal 

 vesicle to the nucleus, the yolk to the contents 

 of the outer enveloping cell, and the vitelline 

 membrane to the delicate wall of this cell, sup- 

 posing that this latter membrane always exists, f 



The great simplicity in the form of the ele- 

 ments of the grey nervous matter is one of its 

 most remarkable characteristics. That a tissue, 

 which, as will be shown by-and-bye, plays so 

 prominent a part in the nervous actions, whether 

 they are prompted by mental change, or are 

 purely corporeal, should exhibit scarcely any 

 more complexity of structure than that which 

 is found in the simplest animal or vegetable 

 textures, or in structures that have not passed 

 their earliest phase of developement, is an ana- 

 tomical fact pregnant with great physiological 

 interest. Have this simplicity of form and de- 

 licacy of structure reference to the celerity of 

 the nervous actions ? or to that proneness to 

 change which must be induced by the constant 

 and unceasing round of impressions which the 

 grey matter must receive from the ordinary nu- 

 trient actions that are going on in the body, as 

 well as from the continual action of thought ? 

 If, according to common acceptation, we ad- 

 mit that the mind is in immediate connexion 

 with the cerebral convolutions, it may well be 

 imagined that no part of the frame can be the 

 seat of such active change, from its being on the 

 one hand the recipient of impressions from the 

 body, and, on the other, from an association with 

 the psychical principle so intimate that probably, 

 under ordinary circumstances, an affection of 

 the one cannot occur without being communi- 

 cated to and producing a change in the other. 



Another curious fact, in connexion with the 

 intimate structure of the grey nervous matter, 

 is the large quantity of pigment or colouring 

 matter which exists in it, and which appears 

 to form one of its essential constituents, more 

 abundant in some situations than in others, 

 but present in all. We are utterly ignorant 

 of the design of this peculiarity of structure. 

 If this pigment bear any resemblance of che- 

 mical composition to the colouring matter of the 

 blood, /Hematosine, and it is not improbable 

 that it does, an increased interest attaches to 

 the practical importance of minute attention, 

 on the part of practitioners, to avail themselves 



* Valentin, in Soemmering vom Baue. &c. t. iv. 

 24. 

 t Loc. cit. 25. 



of all the means which are capable of impro- 

 ving that important element of the nutrient 

 fluid both in quantity and quality, for it is 

 most reasonable to presume that the pigment 

 of the nervous matter would derive its nou- 

 rishment from that of the blood. 



It may be further remarked that pigment oc- 

 curs in connexion with the nervous system in 

 another form besides that of incorporation with 

 its elementary particles, that is, upon the exte- 

 rior of parts of the nervous centres or of parti- 

 cular nerves. Examples of this may be re- 

 ferred to in the case of the olfactory nerve of 

 the sheep and of other Mammalia, the bulb 

 of which is surrounded by black pigment con- 

 nected with the pia mater. It is also found 

 sometimes on the pia mater of the spinal cord 

 of the human subject. Valentin, who deli- 

 neates a magnified view of this pigment, states 

 that it occurs chiefly in the cervical region. In 

 frogs, the whole spinal cord and encephalon 

 are covered with a silvery pigment interspersed 

 with black. The same occurs in fishes. The 

 black pigment in connexion with the retina has 

 an obvious use. On the choroid gland of fishes, 

 which lies immediately contiguous to the re- 

 tina and surrounds the optic nerve, there is a 

 silvery membrane which contains a quantity of 

 the same kind of pigment as that alluded to 

 upon their nervous centres. On some of the 

 ganglia of the invertebrata particles of pig- 

 ment are likewise found. 



Of the structure of ganglions. The descrip- 

 tion of the minute anatomy of ganglions as 

 well as of all other nervous centres may be 

 regarded as the solution of the following pro- 

 blem : to determine the relation which the 

 white substance of these centres bears to the 

 grey matter on the one hand, and to the nervous 

 trunks connected with them on the other hand. 



The white substance of the ganglions con- 

 sists of a series of minute nerve-tubes, as well 

 as of some gelatinous fibres, which are conti- 

 nuous with those which exist in the nerves 

 themselves. If we trace a nerve into a gan- 

 glion, it is found to break up into its com- 

 ponent nerve-tubes, and it does so by a se- 

 paration of the tubules within into smaller 

 bundles, or single tubes. Sometimes adjoining 

 bundles interlace, each yielding to its neigh- 

 bour one or more tubes. The nerves which 

 emerge from the ganglia derive their component 

 nerve-tubes from different bundles, so that the 

 same kind of interchange of tubules, which we 

 have noticed as taking place in plexuses, occurs 

 also in ganglia. The emerging nerves result 

 from a further subdivision and greater inter- 

 mixture of the bundles of nerve-tubes which 

 enter the ganglions. The arrangement is well 

 shown in jig. 373, where the nerve (</), which 

 enters the ganglion, may be seen breaking up 

 into a plexus, from which three branches (b, b, 

 b) emerge, and it may be observed that these 

 emerging nerves derive nerve-lubes from very 

 different and opposite parts of the ganglionic 

 plexus. In the meshes, which are left be- 

 tween the interlacing nerve-tubes, the gangli- 

 onic globules or nerve-vesicles are situate (figs. 

 373, 374). Certain fibres, according to Valen- 



