SENSE OEGANS. 



83 



blood vessels and viscera, which there form a complicated network 

 of nervous fibres 

 containing here and 



there ganglion cells. 



The 



nervous sys- 



tem possesses further 

 peripheral apparatus, 

 the sense organs, the 

 function of which is 

 to bring about the 

 perception of certain 

 conditions of the 

 outer world as im- 

 pressions of a definite 

 mode of sensation 

 (specific energy of 

 nerves* Joh. Miiller). 

 These peripheral 

 organs usually have 

 the form of peculiarly 

 arranged aggrega- 

 tions of hair-shaped 

 or rod-shaped nerve 

 terminations (hair- 

 cells, rod-cells of sen- 

 sory epithelium) con- 

 nected by fibrilhie 

 with ganglion cells, 

 through which under 

 the action of external 

 influences a move- 

 ment of the nervous 

 substance is set up, 

 which travels to the 

 central organ and 

 there affects con- 



: In opposition to the 

 differences in the quali- 

 ties of the sensations 

 produced by each indi- 

 vidual sense organ 

 (colour, tone). 



FIG. 80. Nervous system of the frog (after Ecker). Ol 

 olfactory nerves ; O, eye ; Op, optic nerve ; Vy, Gasseriau 

 ganglion ; Xg, ganglion of vagus ; Spn 1, first spinal nerve ; 

 Sr, brachial nerve ; Sql-W, the ten ganglia of the sym- 

 pathetic system. Ji, ischial nerve. 



