CEKEBRO-SPIXAL NEEVES. cxlv 



nenrilemma has been heretofore applied. The use of the term perineurium 

 is unobjectionable and may sometimes be convenient, but the proposed new 

 and restricted application of the term neurilemma will, I think, lead to am- 

 biguity, and is of doubtful propriety. 



The funiculi of a nerve are not all of one size, but all are sufficiently 

 large to be readily seen with the naked eye, and easily dissected out from 

 each other. lu a nerve so dissected into its component funiculi, it is seen 

 that these do not run along the nerve as parallel insulated cords, but join 

 together obliquely at short distances as they proceed in their course, the 

 cords resulting from such union dividing in their further progress to form 

 junctions again with collateral cords ; so that in fact the funiculi composing 

 a single nervous trunk have an arrangement with respect to each other 

 similar to that which we shall presently find to hold in a plexus formed by 

 the branches of different nerves. It must be distinctly understood, how- 

 ever, that iu these communications the proper nerve-fibres do not join to- 

 gether or coalesce. They pass off from one nervous cord to enter another, 

 with whose fibres they become intermixed, and part of them thus inter- 

 mixed may again pass off to a third funiculus, or go through a series of 

 funiculi and undergo still further intermixture ; but throughout all these 

 successive associations (until near the termination of the nerve) the fibres 

 remain, as far as known, individually distinct, like the threads in a rope. 



The fibres of the cerebro-spinal nerves are chiefly, in some cases perhaps 

 exclusively, of the white or medullated kind, but in most instances there 

 are also grey fibres in greater or less number. Moreover, it has often 

 appeared to me as if there were filaments of extreme tenuity, like the white 

 filaments of connective tissue, but of doubtful nature, mixed up with well- 

 characterised nerve-fibres within the sheaths of the funiculi. Lying along- 

 side each other, the fibres of a fuuiculns form a little skein or bundle, which 

 runs in a waving or serpentine manner within its sheath ; and the alternate 

 lights and shadows caused by the successive bendings being seen through 

 the sheath, give rise to the appearance of alternate light and dark cross 

 stripes on the funiculi, or even on larger cords consisting of several fuuiculi. 

 On stretching the nerve, the fibres are straightened and the striped appear- 

 ance is lust. 



Vessels. The blood-vessels of a nerve supported by the sheath divide 

 into very fine capillaries, said by Heule to measure in the empty state not 

 more than ^'^th. f an i ncn i" diameter. These, which are numerous, run 

 parallel with the fibre.-*, many of them within the funicular sheaths, but are 

 connected at intervals by short transverse branches, so as in fact to form 

 a network with long narrow meshes. 



Branching and conjunction of Nerves. Nerves in their progress very 

 commonly divide into branches, and the branches of different nerves not 

 unfrequently join with each other. As regards the arrangement of the 

 fibres in these cases, it is to be observed, that, in the branching of a nerve, 

 collections of its fibres successively leave the trunk and form branches ; and 

 that, when different nerves or their branches intercommunicate, fibres pass 

 from one nerve to become associated with those of the other in their further 

 progress ; but in neither case (unless towards their peripheral terminations) 

 is there any such thing as a division or splitting of an elementary nerve- 

 fibre into two, or an actual junction or coalescence of two such fibres 

 together. 



A communication between two nerves is sometimes effected by one or 

 two connecting branches. In such comparatively simple modes of connec- 



