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 fibrillse 

 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 ; Vg, Gasserian 

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

 Br, brachial nerve ; 5^1-10, the ten ganglia of the sym- 

 pathetic system. Js, ischial nerve. 



