BRANCHING AND CONJUNCTION OF NERVES. 141 



The tissue here described as investing each funiculus and enclosing 

 its proper fibres is named the neurilemma.'^ It is covered quite exter- 

 nally by a layer of large thin flattened cells, the outlines of which are 

 brought into view by the silver treatment (as in fig. 83). 



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. In 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 fi-om 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 arrange- 

 ment 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, however, that in these communications 

 the proper nerve-fibres do not join together or coalesce. They pass off 

 from one nervous cord to enter another, with whose fibres they become 

 intermixed, and part of them thus intermixed may again pass off to a 

 third funiculus, or go through a scries 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 per- 

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

 there are also grey fibres in greater or less number. Moreover, fila- 

 ments of extreme tenuity, like the white filaments of connective tissue, 

 occur, mixed up with well-characterised nerve-fibres within the sheaths 

 of the funiculi. Lying alongside each other, the fibres of a funiculus 

 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 funiculi. On stretching 

 the nerve, the fibres are straightened and the striped appearance is lost. 



Vessels. — The Nood-vesseh of a nerve, supported by the sheath, 

 divide into very fine capillaries. These, which are numerous, run 

 parallel with the fibres, 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. Lijmjihatics are found in the 

 uniting connective tissue or perineurium. Little is known of their mode 

 of commencement, but it is probable that, as in other parts, they take 

 origin in the connective tissue. Spaces which appear to be lymphatic 

 are met with between the layers of the neurilemma. 



Branching and conjunction of Herves. — Nerves in their pro- 

 gress very commonly divide into branches, and the branches of different 

 nerves not unfrequently join with each other. As regards the arrange- 



* Some recent ■m-iters believing that the primitive sheath of the nerve-fibre cor- 

 responds to the sarcolemma of muscle, have proposed to designate it as the neurilemma, 

 and to use the term perineurium for the coarser sheathing of the nerves and nervous 

 cords, to which the term neurilemma has been usually 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 would lead to ambiguity, and is of 

 doubtful propriety. The general external covering of the nervous trunks has been 

 named ' ' cellular sheath " {vai/ina ccUulosa). 



