THE NERVES. 65 



and sends numerous processes into the interior of the ganglia, which support 

 the bloodvessels supplying its substance. 



In structure, all ganglia are essentially similar ; consisting of the same struc- 

 tural elements as the other nervous centres, viz., a collection of vesicular nervous 

 matter, traversed by tubular and gelatinous nerve-fibres. The vesicular nervous 

 matter consists of nerve-cells or ganglion globules, most of which appear free, 

 and of a round or oval form : these are more especially seated near the surface 

 of the ganglion ; others have caudate processes, and give origin to nerve-fibres. 

 In the ganglia, the nerve-cells are usually inclosed in a capsule of granular 

 corpuscles and fibres. The tubular nerve-fibres run through the ganglion, 

 some being collected into bundles, while others, separating from each other, 

 take a circuitous course among the nerve-cells before leaving the ganglia. 



The Nerves are round or flattened cords, which are connected at one end with 

 the cerebro-spinal centre or the ganglia, and are distributed, at the other, to 

 the various textures of the body : they are subdivided into two great classes, 

 the Cerebro-spinal, which proceed from the cerebro-spinal axis, and the Sym- 

 pathetic or Ganglionic nerves, which proceed from the ganglia of the sympa- 

 thetic. 



The cerebro-spinal nerves consist of numerous nerve-fibres, collected together 

 and inclosed in a membranous sheath. A small bundle of primitive fibres, 

 inclosed in a tubular sheath, is called afuniculus: if the nerve is of small size, 

 it may consist only of a single funiculus, but if large, the funiculi are collected 

 together into larger bundles or fasciculi ; and are bound together in a common 

 membranous investment, termed the sheath. In structure, the common sheath 

 investing the whole nerve, as well as the septa given off from the sheath, and 

 which separate the fasciculi, consist of areolar tissue, composed of white and 

 yellow elastic fibres, the latter existing in greatest abundance. The tubular 

 sheath of the fuuiculi, or neririlemma, consists of a fine, smooth, transparent 

 membrane, which may be easily separated, in the form of a tube, from the 

 fibres it incloses; in structure, it is, for the most part, a simple and homo- 

 geneous transparent film, occasionally composed of numerous minute reticular 

 fibres. 



The cerebro-spinal nerves consist almost exclusively of the tubular nerve- 

 fibres, the gelatinous fibres existing in very small proportion. 



The bloodvessels supplying a nerve terminate in a minute capillary plexus, 

 the vessels composing which run, for the most part, parallel with the funiculi; 

 they are connected together by short transverse vessels, forming narrow oblong 

 meshes, similar to the capillary system of muscle. 



The nerve-fibres, as far as is at present known, do not coalesce, but pursue 

 an uninterrupted course from the centre to the periphery. In separating a 

 nerve, however, into its component funiculi, it may be seen that they do not 

 pursue a perfectly insulated course, but occasionally join at a very acute angle 

 with other funiculi proceeding in the same direction ; from which, again, 

 branches are given off, to join again in like manner with other funiculi. It 

 must be remembered, however, that in these communications the nerve-fibres 

 do not coalesce, but merely pass into the sheath of the adjacent nerve, become 

 intermixed with its nerve-fibres, and again pass on to become blended with the 

 nerve-fibres in some adjoining fasciculus. 



Nerves, in their course, subdivide into branches, and these frequently com- 

 municate with branches of a neighboring nerve. In the subdivision of a nerve, 

 the filaments of which it is composed are continued from the trunk into the 

 branches, and at their junction with the branches or neighboring nerves, the 

 filaments pass to become intermixed with those of the other nerve in their fur- 

 ther progress; in no instance, however, have the separate nerve-fibres been 

 shown to inosculate. 



The communications which take place between two or more nerves, form 

 5 



