88 NORMAL HISTOLOGY. 



roglia, and medullated fibres. The cells give rise to axis cylinders 

 which produce the cranial nerves. The white matter of the ven- 

 tricles consists of medullated fibres and neuroglia. 



THE SYMPATHETIC NERVOUS SYSTEM. 



The sympathetic system consists of a double chain of ganglia 

 (about twenty-four pairs) extending along the anterior portion of 

 the spinal column and connected together by intervening cords, 

 three great plexuses (cardiac in cervical region, epigastric in ab- 

 dominal region, and hypogastric in pelvic region), smaller ganglia, 

 and many non-medullated nerve fibres. The nerve fibres are of two 

 kinds communicating and distributory. They are non-medullated, 

 and by some authorities are supposed to be without a neurilemma. 



TERMINAL NERVOUS SYSTEM. 



The peculiar modifications of nerve endings may appropriately 

 be considered as constituting a third nervous system, the terminal 

 system, often styled the peripheral system. 



Every nerve has central and peripheral terminations. The cen- 

 tral ending is in the cell with which it originates. There are three 

 important varieties of peripheral endings for sensory nerve fibres 

 viz., free nerve endings, terminal corpuscles, and neuro-epithelial 

 cells. 



1. Free nerve endings occur in the skin, mouth, cornea, and 

 spinal cord. By this method the nerve fibre loses its neurilemma 

 and medullary sheath, and the axis cylinder breaks up into deli- 

 cate fibrils, which sometimes anastomose with each other. In the 

 skin the fibrils are confined to the stratum Malpighii. 



2. Terminal corpuscles occur in the skin. Stirling and Piersol 

 give four kinds of peripheral corpuscles (1) simple tactile cells, 

 (2) compound tactile cells, (3) end bulbs, (4) touch corpuscles. 



Simple tactile cells occur in the stratum Malpighii. The fibre 

 breaks up into fibrils by the usual method, but each fibril terminates 

 in a tactile disk, above which lies the tactile cell. 



In compound tactile cells, the tactile disk forming the termination 

 of the axis cylinder lies between two tactile cells. 



End bulbs occur in mucous membranes, the cutis, and other 



