220 ELEMENTS OF SCIENCE 



certain special nerves pass from the brain to the eye, the 

 ear and nose, and the tongue. 



That to the eye expands into a delicate membrane of 

 nervous tissue (of wonderfully complex construction) 

 called the retina, upon which an image of external things 

 is projected according to the laws of light,* as in a 

 camera obscura, owing to the various different trans- 





H 



VERTICAL SECTION OF A LION'S EYE. 



Aq Aqueous humour. 



Ch Choroid coat. 



Cm Ciliary muscle. 



On Cornea. 



Cp Ciliary processes. 



Cr Crystalline lens. 



Ir Iris. 



Op Optic nerve. 



R Muscle of the eyeball. 



Rt Eetina. 



Scl Sclerotic coat. 



parent media placed in front of the retina and forming 

 the bulk of the eye -ball. 



The true organ of hearing, or internal ear, is a com- 

 plexly-shaped, membranous bag (containing, and floating 

 in, fluid) on which the auditory nerve ramifies. 



The organ of smell consists of minute branches of 

 nerves which proceed from two forward prolongations of 



* See ante, p. 107. 



