Dissection of Eye of the Ox. 261 



anteriorly, i.e. like a watch-glass, and, at the circumference, 

 blended with the Sclerotic coat by continuity of tissue ; and 

 will be found to be smooth and firm, though soft to the touch. 



On looking into the eye, there will be seen behind the 

 transparent Cornea, a coloured membrane which gives the 

 tint to the eye ; it is the Iris, and the central aperture by 

 which it is perforated is the Pujnl. The small bodies situated 

 on the pupillary margin of the Iris are called Corpora nigra. 

 The pupillary opening is entirely filled by a portion of the 

 anterior surface of the Capsule of the Crystalline Lens. The 

 space, between the Cornea in front and the Lens behind, in 

 which the Iris is suspended, contains a clear watery fluid, 

 named the Aqueous Humor. These several parts act as 

 follows : the Cornea transmits, but also deflects (refracts, or 

 bends towards the axis of the cone) the rays of light trans- 

 mitted ; the movements of the Iris regulate the quantity of 

 light admitted to the Lens ; the Lens has the power of 

 refracting and causing the convergence of the rays of the cone 

 of light, not only on their entrance from a rarer medium 

 (aqueous humor) into its anterior convex surface, but also at 

 their exit from its posterior convex surface into the rarer 

 medium (vitreous humor).* 



Removal of Cornea.! The Student should now cut with 



Kirke's Phys., Ed. 7, p. 647. 



t The following mode of operation is suggested in "Gray's Anatomy." In 

 order to separate the Sclerotic and Cornea, so as to expose the second tunic, the 

 eyeball should be immersed in water contained in a small vessel. A fold of the 

 Sclerotic near its anterior part being then pinched up, an operation not easily 

 performed from the extreme tension of the membrane, it should be divided with 

 a pair of blunt-pointed scissors. As soon as the Choroid is exposed, the end of 

 a blow-pipe should be introduced into the orifice, and a stream of air forced into 

 it, so as to separate the slight cellular connection between the Sclerotic and 

 Choroid. The Sclerotic should now be divided around its entire circumference 

 {i.e. midway between the Cornea and Optic nerve), and may be removed in 

 separate portions. The front segment being now drawn forwards, the handle 

 of the scalpel should be pressed gently against it at its connection witb 

 the Iris, and, these being separated, a quantity of perfectly transparent fluid 

 will escape ; this is the aqueous humor. In the course of this dissection, the 

 Ciliary nerves may be seen lying in the loose cellular tissue between the Choroid 

 and Sclerotic, or contained in delicate grooves on the inner surface of the latter 

 membrane. P. bbQ (Ed. 1858). 



