TUNICS OF THE EYEBALL. 



533 



Fig. 206. 



Globe of the eye— Antero-lateral 

 view, a, Sclerotic ; 6, Optic nerve ; 

 c, c, Cornea ; d, d, Eliptic opening in 

 the cornea. 



connection with the cellular and adipose tissue, and with the 

 muscles of the eyeball, the tendons of the four recti expanding 

 ■over it and forming a thin tendinous 

 layer, the tunica alhuginea, which is 

 pa.rtly covered by the conjunctiva, and 

 forms the "white of the eye." Its 

 internal surface is in contact with the 

 choroid coat, from which it receives a 

 stain, and to which it is united by 

 very delicate cellular tissue, and by 

 minute nerve filaments and vascular 

 ramifications. Its anterior opening is 

 elliptical, and presents a bevelled edge, 

 which receives the cornea in a manner 

 similar to that in which a watch-glass 

 is received by the groove in its case. 

 Posteriorly it is pierced for the passage 

 of the optic and ciliary nerves, and 

 ciliary arteries, the optic nerve fila- 

 ments passing through numerous minute openings in the portion 

 called the lamina crihrosa, the larger opening in the centre, the 

 forus opticus, being for the passage 

 of the arteria centralis retinas. 



The Cornea is transparent, ellip- 

 tical in shape, and fitted into the 

 bevelled edge of the sclerotic, to 

 which it is firmly adherent. Its 

 anterior surface is convex, and 

 covered by a continuation of the 

 conjunctiva, while its inner surface 

 is concave, and covered by the 

 lining membrane of the anterior 

 chamber of the eyeball. 



The cornea is composed of two 

 layers ; the cornia propria and the 

 cornea elastica. The former con- 

 sists of several thin lamellae, held 

 together by extremely fine areolar 

 tissue ; the latter is a fine, elastic, 

 and exquisitely transparent membrane, closely applied to the inner 

 surface of the propria. It retains its transparency long after the 



Fio. 207. 



Globe of the eye— part of the sclerotic 



reflected away, a, Sclerotic ; b, Mem- 



brana f usca ; c. Choroid, with ciliary 



nerves. 



