THE NERVOUS TISSUES. 



1007 



lemma nuclei are occasionally seen as deeply stained crescentic figures that partially 

 embrace the nerve-fibre, lying beneath the neurilemma within depressions in the 

 medullary substance. 



FIG. 850. 



Perineurium 



Endoneuriutn 



Nerve-fibre 



FIG. 85 r. 



Epineurium 



Blood-vessel 



Transverse section of funiculus composed of nerve-fibres held together by endoneurium and 

 surrounded by perineurium. X 175. 



Viewed in cross-section, the nonmedullated fibres appear as small irregularly 

 round figures arranged in groups that correspond to bundles (Fig. 851). When 

 numerous, the latter are aggregated 

 into secondary bundles between 

 which extend delicate connective- 

 tissue septa, continuous with the 

 general envelope investing the nerve- 

 trunk. The medullary substance 

 being wanting, the pale fibres are 

 of small size and often possess a 

 diameter of less than .001 mm. 



The Ganglia. The cell- 

 bodies of the neurones that consti- 

 tute the sensory pathways within the 

 peripheral nerves and of the neu- 

 rones of the sympathetic system 

 are collected at various points into 

 aggregations known as ganglia. 

 Familiar examples of the latter are 

 the spinal ganglia on the posterior 

 roots of the spinal nerves, certain 

 cranial ganglia (as the Gasserian 

 connected with the fifth nerve, the 



acoustic with the eighth, and those on the trunks of the seventh, ninth and tenth 

 cranial nerves), and the sympathetic ganglia along the gangliated cords and within 

 various plexuses of the sympathetic. 



A longitudinal section of a spinal ganglion (Fig. 852), which may be taken 

 as a type of such collections, shows the entire ovoid mass to be enclosed by a fibrous 

 capsule continuous with that ensheathing the nerves. Immediately beneath the 

 capsule the ganglion-cells are arranged in a fairly continuous layer of varying thick- 

 ness, while the cells, more deeply placed, are broken up into groups by the tracts of 



iter-fascicular 

 septum 



Transverse section of small splenic nerve consisting chiefly ol 

 nonmedullated fibres. X 200. 



