THE SEXSE3. 591 



Pig. 396, A. The nervous elements of the retina are represented in Fig. 

 396, B, and consist of delicate fibres passing up from the nerve-fibre 

 layer to the rods and cones, and connected with the ganglionic corpus- 

 cles and granules of the internal and external layer. 



Blood-vessels of the Eye-ball. The eye is very richly supplied 

 with blood-vessels. In addition to the conjunctival vessels which are 

 derived from the palpebral and lachrymal arteries, there are at least two 

 other distinct sets of vessels supplying the tunics of the eyeball. (1) 

 The vessels of the sclerotic, choroid, and iris, and (2) The vessels of the 

 retina. 



(1) These are the short and long posterior ciliary arteries which pierce 

 the sclerotic in the posterior half of the eyeball, and the anterior ciliary 

 which enter near the insertions of the recti. These vessels anastomose 

 and form a very rich choroidal plexus; they also supply the iris and 



FIG. 399. Section through the eye carried through the ciliary processes. 1, Cornea; 2, mem- 

 brane of Descemet; 3. sclerotic; 3', corneo-scleral junction; 4, canal of Schlemm; 5, vein; 6, nucle- 

 ated network on inner wall of canal of Schlemm; 7, lig. pectinatum iridis, abc; 8, iris stroina; 9, 

 pigment of iris; 10, ciliary processes; 11, ciliary muscle; 12, choroid tissue; 13, meridional and 14, 

 radiating fibres of ciliary muscle; 15, ring-muscle of Muller; 16, circular or angular bundles of cili- 

 ary muscle. (Schwalbe.) 



ciliary processes, forming a very highly vascular circle round the outer 

 margin of the iris and adjoining portion of the sclerotic. 



The distinctness of these vessels from those of the conjunctiva is well 

 seen in the diiference between the bright red of blood-shot eyes (con- 

 junctival congestion), and the pink zone surrounding the cornea which 

 indicates deep-seated ciliary congestion. 



(2) The retinal vessels are derived from the arteria centralis retina, 

 which enters the eyeball along the centre of the optic nerve. They 

 ramify all over the retina, chiefly in its inner layers. They can be seen 

 by direct ophthalmoscopic examination. 



The Crystalline Lens. Structure. The lens is made up of a series 

 of concentric laminae (Fig. 403), which when it has been hardened, can 

 be peeled off like the leaves of an onion. The laminae consist of long rib- 

 bon-shaped fibres, which in the course of development are derived from 

 cells. The fibres, therefore, when young contain oval nuclei, but these 



