CORNEA CHORD ID. 



61? 



posterior elastic lamina. It consists of a single layer of polygonal transparent 

 nucleated cells, similar to those found lining other serous cavities. 



Arteries and Nerves. The cornea is a non-vascular structure, the capillary 

 vessels terminating in loops at its circumference. Lymphatic vessels have not 

 as yet been demonstrated in it. The nerves are numerous, twenty or thirty in 

 number : they are derived from the ciliary nerves, and enter the laminated sub- 

 stance of the cornea. They ramify throughout its substance in a delicate net- 

 work. 



Dissection. 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 having been pinched up, an operation not easily performed from the ex- 

 treme 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 blowpipe 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, and may be 

 removed in separate portions. The front segment being then drawn forwards, the handle of the 

 scalpel should be pressed gently against it at its connection with the iris, and, these being sepa- 

 rated, a quantity of perfectly transparent fluid will escape ; this is the aqueous humor. In the 

 course of the 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. 



Fig. 304. The Choroid and Iris. (Enlarged.) 



CHOROID, IRIS, AND CILIARY PROCESSES. 



The second tunic is formed by the choroid behind ; the iris and ciliary pro- 

 cesses in front ; and by the ciliary ligament, and Ciliary muscle, at the point of 

 junction of the sclerotic and cornea. 



The Choroid is the vascular and pigmentary tunic of the eyeball, investing the 

 posterior five- sixths of the globe, and extending as far forwards as the cornea ; 

 the Ciliary Processes being appendages of the choroid developed from its inner 

 surface in front. The Iris is the circular-shaped muscular septum, which hangs 

 vertically behind the cornea, presenting in its centre a large circular aperture, 

 the pupil. The ciliary ligament and Ciliary muscle form the white ring observed 

 at the point where the choroid and iris join with each other, and with the sclerotic 

 and cornea. 



