CHAP. VIII.] ORIGIN OF NERVES. 217 



Origin. The fibres of nerves may be traced into the nervous 

 centres, the white or fibrous part of which they contribute to 

 form. As they enter the centre, the fibres diverge slightly either 

 singly or in separate bundles, and pass on to form a connexion with 

 vesicular matter, in the immediate vicinity of the point of immer- 

 gence or at a more remote situation. How the fibres comport 

 themselves with respect to the elements of the vesicular matter is 

 not exactly known. It is certain, however, that nerve-tubes fre- 

 quently adhere to the sheaths of nerve- vesicles, and that many of 

 them pass between the nerve- vesicles, probably to form a connexion 

 with more distant ones. This may be well seen in the vesicular 

 matter of any of the centres. It is very distinct in the ganglions, 

 and also sufficiently manifest in the spinal cord or brain. In the 

 last-named centres some of the tubes which are found in the vesi- 

 cular matter are reduced to an extremely minute size (figs. 56, /; 

 57, A, b' and B, b) } and exhibit small varicosities, sometimes at 

 very regular distances from each other. 



Valentin describes a looped and plexiform arrangement of the 

 fibres in the vesicular matter of the centres. Hitherto, such an 

 arrangement has eluded our observation so completely, that, but for 

 the high authority on which this statement rests, we should not 

 have deemed it necessary to allude to it. The only confirmation 

 of this view with which we have met is derived from a highly inter- 

 esting dissection, by Mr. Lonsdale of Edinburgh, of a monstrosity, 

 in which the spinal cord, medulla oblongata, and cerebellum were 

 absent, but the hemispheres of the brain were present. Several of 

 the encephalic and spinal nerves hung as " loose threads " in the 

 cavity of the cranium or spine. On examining the free or central 

 extremities of these nerves, their constituent fibres were found to 

 form distinct loops, convex towards the cranial or spinal cavity. 

 These loops were imbedded in granular matter, supposed to be ve- 

 sicular matter in an early stage of formation. Similar loops were 

 observed by the same anatomist in the cranial nerves of an anen- 

 cephalous foetus which had been preserved in spirits."* 



Branching. As a nerve passes from centre to periphery, it breaks 

 up into a number of small bundles, which form so many branches 

 destined for the organs or tissues among which they are placed. 

 These branches generally separate from the parent trunk at an 

 acute angle, and soon plunge into the muscles or other parts to 

 which they tend, dividing and subdividing among them. Some 



* Dr. Lunsdale's case of Monstrosity. Ed. Med. and Surg. Journ., No. 157. 



