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NERVOUS SYSTEM. (NERVE.) 



nerves both kinds of fibres may be found, but 

 in the latter these peculiar fibres are enormously 

 predominant, so that $ 9 ths of their elements, or 

 even a larger proportion, are composed of them ; 

 in passing into neighbouring trunks they run as 

 often centrad as to the periphery. When the 

 sympathetic fibres occur in cerebro-spinal 

 nerves, they are collected into separate bun- 

 dles. The nervous branches which go to the 

 involuntary muscles contain almost exclusively 

 the smaller or sympathetic fibres. Mucous 

 membranes are almost exclusively supplied by 

 these fibres. The viscera of the chest and ab- 

 domen receive nerves which are made up 

 almost exclusively of sympathetic fibres. 



[These statements are quite at variance with 



sheath, and the faintness and indistinctness of 

 the margins of the nerve-tubes contained within 

 it, this arrangement in the smaller nerves lias 

 very much the appearance of a bifurcation of the 

 nerve-tubes themselves. There seems, however, 

 no reason to believe that the nerve-tubes of In- 

 vertebrata follow a different law from that which 

 regulates their disposition in the Vertebrate 

 series. It is likewise highly probable that the 

 relations of these nerve-tubes to both periphery 

 and centre are essentially the same as in Ver- 

 tebrata. Plexuses occur much more rarely, 

 according to Valentin, in the nerves of Inver- 

 tebrata. 



Of the developement of nerve. We can add 

 nothing to the account given by Schwann of 



the results of my observations, as well as of the developement of nerve. The following is 



those of Henle and Valentin.] 



The authors remark a considerable difference 

 as regards the relation which these peculiar 

 fibres bear to the cerebro-spinal centres in 

 Frogs, Mammalia, Birds, and Fishes. In 

 frogs the fine fibres originate in greatest part 



quoted from Wagner's Physiology. 



" The nerves appear to be formed after 

 the same manner as the muscles, viz. by the 

 fusion of a number of primary cells arranged 

 in rows into a secondary cell. The pri- 

 mary nervous cell, however, has not yet been 



from the ganglions on the posterior roots of seen with perfect precision, by reason of the 



spinal nerves and from those of the sympa- 

 thetic. In Mammalia the brain and spinal 

 cord are not the only sources of the sympathetic 

 fibres. The ganglia also probably give off some. 



difficulty of distinguishing nervous cells whilst 

 yet in their primary state, from the indifferent 

 cells out of which entire organs are evolved. 

 When first a nerve can be distinguished as such, 



In birds the ganglion of the vagus is a pro- it presents itself as a pale cord with a longitu- 

 bable source of sympathetic fibres ; and in dinal fibrillation, and in this cord a multitude 

 fishes the great thickness of the branches of the of nuclei are apparent. (Fig. 335, a.) It is 

 vagus, which are very rich in the fine fibres com- easy to detach individual filaments from a cord 

 pared with the small size of its roots which are -p. 



deficient in them, indicates that the &' 



ganglion of that nerve is a source of tt d 



very numerous sympathetic fibres. ~ "^ J 



The anatomical statements of these 

 writers would, if founded in fact, go 

 far to confirm the opinions of those 

 physiologists who uphold the inde- 

 pendence of the sympathetic system, 

 and to prove the ganglia to be distinct 

 centres of nervous influence. It is 

 impossible to enter further upon the 

 discussion of this question at present, 

 without introducing physiological ar- 

 guments. In a subsequent part of the 

 article we shall return to the subject.* 



of this kind, as the figure just referred to 



Nerves of Invertebrata. In those Inverte- shows, in the interior of which many nuclei 

 brata in which a definite arrangement of the are included, similar to those of the primitive 



muscular fasciculus, but at a greater distance 

 from one another. The filaments are pale, 

 granulated, and (as appears by their farther 

 developement) hollow. At this period, as in 

 muscle, a secondary deposit takes place upon 

 the inner aspect of the cell-membrane of the 

 secondary nervous cell. This secondary de- 

 posit is a fatty white-coloured substance, and 

 it is through this that the nerve acquires its 

 opacity (fig. 335, 6). Superiorly the fibril is 

 still pale; inferiorly, the deposition of the 



nervous system has been made out, the same 

 elements of the nervous matter are to be found 

 as in the Vertebrata. The grey matter consists 

 of globules with nuclei and riucleoli precisely 

 like those of the human brain. From the gan- 

 glia the nerves radiate ; the nerve-tubes, which 

 are very delicate and transparent in the recent 

 state, contain a soft pulpy matter easily altered 

 by re-agents. They are themselves collected 

 into bundles which are surrounded by a clear 

 transparent membrane, of the same kind as 



the sarcolemma of muscle, which accompa- white substance has occurred, and its effect in 



nies and surrounds the branches of the nerves, rendering the fibril dark is obvious. With the 



As the nerve-tubes separate from the primary advance of the secondary deposit, the fibrils 



trunk into smaller fascicles, these sheaths bi- become so thick, that the double outline of 



furcate, so as to adapt themselves to the new tne ' r parietes comes into view and they ac- 



brancl.es. From the clear outline of the 



f Die Selbstandigkfit des sympatheschen Ner- 

 vonsystems, &c. von. Jiiduer uud Volkmann. 



q inre a tubular appearance (r). On the oc- 

 currence of this secondary deposit the nuclei 

 ^ tne ce " s are generally absorbed; yet a few 

 may still be found to remain for some time 



