.".urtace of tho sclerotic is coated by a thin layer of areolar tissue stained 

 with black pigment the lamina futon.) 



The tirtiries of tho sclerotic are derived from tho anterior and posterior 

 ciliary arteries; the veins pass into trunks lying parallel to tlie ciliary 

 s. Nerves have been found in the sclerotic of the llabbit, but in none 

 other of the domesticated animals. " It is frequently found that in tho Ass, 

 particularly when it is old, the back part of the sclerotic is encrusted with 

 an unmistakable layer of bony matter. This fact was unknown to Carus, 

 wlio states that in none of the mammalia does this membrane become 

 ossified." Lecoq. (In Birds, bony plates are found in this region, and 

 some reptiles also have them.) 



2. The Cornea. (Fig. 383, e.) 



(Preparation. The cornea should be removed with the sclerotic coat, by immersing the 

 eye under water, and making a circular incision with scissors about a quarter of an inch 

 from the margin of the membrane). 



The cornea is a transparent membrane forming the anterior part of the 

 eye, to whose interior it allows the light to pass. It closes up the anterior 

 oj. ciiin^ i 'f the sclerotic, and thus completes the external envelope or shell 

 of the globe, of which it forms about a fifth part. 



Elliptical, like the opening it closes, the cornea presents: 1, Two faces, 

 perfectly smooth one external, convex, the other internal, concave form the 

 i xt.-rnal wall of the anterior chamber; 2, A circumference, bevelled on its 

 outer edge, and received into the similar bevel around the sclerotic opening, 

 like the glass of a watch into its case. 



STRUCTUKE. Three layers enter into the composition of the cornea: an 

 '/. internal^ and middle. 



Mliltlli- lnye-r. This, the proper cornea, is remarkable for its thickness. 

 "When pressed between the fingers, its two faces can be easily made to glide 

 over each other, a proof that its tissue is disposed in superposed and parallel 

 plan.-s; it is indeed possible to decompose the cornea into several lamina- 

 and laniellic. but as their number varies with the amount of skill employed 

 in their >.-paration, they should be considered as an artificial production of 

 tion. Microscopically examined, it is found to be formed by bundles 

 of exccs>ively fine eonjuntival fibrillte, slightly undulating, and arranged 

 parallel to the surface of the cornea. These wavy fasciculi, when placed 

 each other, leave numerous spaces which are oval in a transverse 

 secti.'ii; til- sr communicate by means of fine canaliculi, and contain round 

 cellular elements which may move from one space to another. 



Between the fasciculi of the cornea is found a fluid amorphous substance, 



" a kind of transparent serosity like tho cornea itself, which maintains its 



flexibility, and which, like it, also loses its transparency under tho influence of 



different causes. It is only necessary, in a fresh eye, to squeeze tho globe in 



i.rder to produce a degree of opacity in tho comea which will bo more or 



<^reat in proportion to the amount of prt-ssure exercised. Is a similar 



produced by tho swelling of the eyo when tho cornea becomes opaque 



in ophthalmia?" Lecoq. 



The i.rli ntal layer is only the conjunct ival epithelium spread over tho 

 ant> rior face of tho cornea. This epithelium in stratified, flattened on its 

 MM faer, but cylindrical below, whore it rests on tho middle layer, and from 

 which it i- n.. t .-. -parated. as in many species of animals, by a proper 

 l.mitary membrane. 



The tniii-i- ///<) is a portion of the membrane of the aqueous humour. 



3 (s '2 





