222 



Organ of Vision. 



Anterior pole 

 Puyil Cornea 



300. Horizontal Section through both Eyeballs. 



After Ferdinand A r 1 1 sen. 



The eyeball, Bulbus oculi, consists of three concentric coats; 

 these coats are : a) the white sclerotic coat, Sclerotica s. Sclera, 

 and the transparent Cornea; b) the chore id, Choriokka, and the 7m; 

 c) the Retina. The cavity of the eyeball is filled out by the aqueous 

 humor, Humor aqiteus, the cry st aline lens, Lens crystalline^ and the 

 vitreous body, Corpus vitreum. 



The sclerotica is an opaque, fibrous coat, whose most anterior 

 segment is joined with the cornea, and whose posterior part is pierced 

 for the passage of the optic nerve ; this perforation is not in the axis 

 of the eye, but about a line internal to it. At the point where the 

 optic nerve passes through the sclerotica, this membrane forms a thin, 

 cribriform lamina, Lamina crlbrosa. The inner surface of the sclerotic is 

 covered with delicate pigmented bundles of connective tissue, the Lamina fusca. 



The cornea projects forwards beyond the sclerotic ; it is nearly 

 circular, but a little broader in the transverse direction ; the anterior 

 surface is encroached upon by the sclerotic. Near the junction of the 

 sclerotic and cornea is a venous, cavernous sinus, the canal of Schlemm 

 (see Fig. 302, 303). The substance of the cornea consists of transparent 

 connective tissue bundles, which cross one another at right angles in the 

 alternate layers ; the epithelium which covers the front of the cornea, con- 

 sists of several layers of epithelial cells ; beneath this is the structure- 

 less anterior elastic lamina of Bow man; the posterior surface consists 

 of a single layer of epithelial cells, above which is the Membrana Descemetii. 



