598 THE TISSUES. 



firmly at their union, with the sclerotica. (Figs. 427-8.) The choroid 

 itself is essentially a thin lamina of capillaries, with arteries and 

 veins external to it, and lined on its internal surface by a single 

 layer of nucleated pigment-cells of a pentagonal or hexagonal shape. 

 (Fig. 69.) Between the capillary network and the arteries and 

 veins, as well as among the veins themselves, there is also an abun- 

 dance of pigment-cells. The internal plexus of capillaries is termed 

 the tunica Ituyttchiana. (Fig. 429.) The veins of the choroid are 

 arranged in beautiful curves, and are termed vasa vorticosa. For 

 J- of an inch behind the ciliary ligament, the choroid coat is sepa- 

 rated from the sclerotic by the ciliary muscle, consisting of smooth 

 muscular fibres. (Fig. 428.) The last is covered externally by the 

 ciliary processes, which are projecting folds of the choroid, lodged 

 in similar folds upon the vitreous body the ciliary zone. They 

 also are very vascular (Fig. 430), and contain an abundance of ir- 

 regular pigment-cells. The ciliary nerves are seen on their way to 

 the iris in Fig. 427. 



Fig. 427. 



Choroid and iris exposed by turning aside the sclerotica. c, c. Ciliary nerves branching in tl." 

 iris. d. Smaller ciliary nerve, e, e. Vasa vorticosa. h. Ciliary ligament and muscle, ft. Con- 

 verging fibres of the greater circle of the iris. I. Looped and knotted form of these near the pupil, 

 with the converging fibres of the lesser circle of the iris within them. o. The optic nerve. (From 

 Zinn.) 



3. The retina has already been described (pp. 450-3, and Figs. 

 295 to 299). The relations of the crystalline lens and the vitreous 

 body are shown by Fig. 431. 



4. The cornea has already been described at length (pp. 280-1, 

 and Figs. 178 to 180). 



