NERVES. 



[ 540 ] 



NERVES. 



Doubtless many nerve -fibres originate from 

 very small cells imbedded in the grey sub- 

 stance, 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 with 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 



Fig. 516. 



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 diffi- 

 culty distinguished from fibres of connective 

 tissue; but the frequent occurrence 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. 617. 



Pic 516. Sixth thoracic sympathetic ganglion of the left side of a rabbit, seen from behind, after treatment with 

 soda T. 2, trunk of sympathetic ; E. c, communicating branches, each bifurcating; Spl. splanchnic branch. S, gan- 

 glial branch, with large and small branches probably going to vessels; g, ganglion-globules and ganghal fibres. 



* 517 1 ^nolfon-elobules from a spinal ganglion of a four-months human foetus: a, nucleus in the pale 

 process of the cell? 2. Nerve-tubes in development, from a two-months human foetus. 3. Cells from the cineri- 

 tious cerebral substance of the same foetus. 



Fig. 518. 1. Two nerve-fibres from the ischiatic nerve of a four-months foetus. 2. Nerve-tubes from a newly- 

 born rabbit: a, sheath; 6, nucleus; c, white substance. 3. Nerve-fibre from the tail of a tadpole: a, b, c, as above; 

 at d the fibre has still the embryonic character. 



somewhat flattened. In their further growth 

 they either retain their primitive shape (fig. 

 517), or send out persistent lateral pro- 

 cesses, so forming nerve-cells or ganglion- 



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 



