NERVE3. 



[ 540 ] 



NERVES. 



Doubtless many nerve -fibres originate from 

 very small cells imbedded in tlie grey sub- 

 stauce, and which are usually destroyed by 

 the processes of preparation. 



The ganglia (fig. 516) consist of nerve- 

 tubes either separate or united into bundles, 

 intermingled vsdth nerve-cells, from which 

 some of the nerve-tubes arise. The tubes 

 and cells are imbedded in or supported by a 

 stroma of connective tissue, sometimes 

 homogeneous, at others more or less di- 

 stinctly fibrous, forming an apparent sheath 

 to the ganglia, and ending in numerous 



septa, rarely but occasionally forming a di- 

 stinct envelope to the individual cells ; some- 

 times it consists of elongated, triangular, or 

 spindle-shaped nucleated cells — in short, 

 corresponding to connective tissue in various 

 stages of development. 



The finer nerve-fibres are often with difii- 

 culty distinguished fi'om fibres of connective 

 tissue; but the frequent occiu'reuce of nuclei 

 will often serve to distinguish them. 



The nerves are developed from the ele-. 

 mentary embryonic cells, which at first 

 appear rounded or slightly elongated and 



Fig. 516. 



Fig. 617. 



Fig. 518. 



Fie ."iie. Sixth thoracic sympathetic ganglion of the left side of a rabbit. Been from behind, after treatment with 

 soda r.2. trunk of sympathetic; Jt. c, conmnmicating branches, each bifurcating; .S'p^sphmehnic branch. *, gan- 

 glial'braneh, with large and smaU branches probably going to vessels ; 5-, ganglion-globules and ganghal hbres. 



MacniCed 40 diameters. , ,. • . ,1 i_ /■ » 1  n ? 



he. r,17. 1. Ganglion-globules from a spinal ganglion of a four-months human io-tus: », nueleus in the pale 

 process of the cell? 2. Nerye-tubea in development, from a two-months human ioDtus. A. Cells from the ciueri- 

 tious cerebral substance of the same fcctus. ,,^^ o-xt iir 1 



Fie 518 1 Two nerre-libres from the ischiatic nerve of a four-months foetus. 2. Nerve-tubes from a newly- 

 born rabbit: a, sheath ; h, nucleus; c, white substance. 3. Nei-ve-Ubrc from the tail of a tadpole: a, 6, c, as above; 

 at d the fibre has still the embryonic character. 



somewhat flattened. In their further gi-owth 

 they either retain their primitive shape (fig. 

 617), or send out persistent lateral pro- 

 cesses, so forming nerve-cells or ganghou- 



globules ; or the processes of adjacent cells 

 unite into nucleated fibres, much resembling 

 those of the sympathetic system, in which 

 the white substance and axial fibre of the 



