VISION. 



75 



of pectinate ligament. The fifth layer of the cornea is the posterior 

 epithelial layer, composed of low, hexagonal cells. The epithelium 

 is deficient at the circumference in the interval between the pillars 

 of the iris. The openings formed are mouths of cavernous spaces 

 (the spaces of Fontana), which lead into the circumferential channel 

 (canal of Schlemm), through the intervention of which the aqueous 

 chamber is placed in connection with the canal of Schlemm, which 

 is a lymphatic channel. The cornea contains no blood-vessels. The 

 corneal nerves enter into the substantia propria of the cornea, where 



Fig. 325. Corneal Nerves of the Pig. (ROLLET.) 



1, 1, Larger nerves. 2, Plexus beneath Bowman's layer. 3, 3, Terminal twigs 

 ascending through the epithelium. 4, Sub-epithelial plexus. 



they lose their medullary sheaths and form four plexuses at different 

 levels: 



1. The ground plexus, in the deep layer of the substantia 

 propria. 



2. -The subbasal plexus. 



3. The subepithelial plexus. 



4. The intraepithelial plexus, which consists of fine fibers run- 

 ning between the epithelial cells, ending in knoblike terminations. 



CHOKOID. The dark-brown choroid coat is the vascular coat 

 of the eye. It consists of two parts, which are continuous with one 

 another 'the choroid and the iris. The choroid is composed of sev- 

 eral layers. Externally it is bounded by a nonvascular membrane, 

 the lamina supra choroidea. The arteries groove the sclerotic coat 



