2G THE CILIARY ZONE. [BOOK in. 



epithelium transparent. Between the epithelium and the under- 

 lying connective tissue body which corresponds to the dermis, lies 

 a thin cuticular sheet or basement membrane, the anterior clastic 

 lamina or membrane of Bowman ; and from the under surface 

 of this, prolongations in the form of fibres arch downward into the 

 substance of the cornea. 



The concave hind surface of the body of the cornea is bounded 

 by a conspicuous cuticular membrane possessing elastic properties. 

 This, which is sufficiently thick to give in section an easily recog- 

 nised double outline, is called the posterior elastic lamina or mem- 

 brane of Descemet or of Desmours. Upon this lies a single layer of 

 flat polygonal epithelioid plates, which, like the similar but less 

 conspicuous cells covering the front surface of the iris, may be 

 regarded as the lymphatic epithelium of the anterior chamber. 



In the body of the cornea neither blood vessels nor lymphatic 

 vessels are present. At the circumference are a few capillary loops 

 and the beginnings of a few lymphatics ; but within this circle the 

 nutrition of the cornea is effected through the branched spaces in 

 which the corneal corpuscles lie. These, communicating freely with 

 each other by means of their branched prolongations, and being 

 only partially filled by the substance of the cells, form a labyrinth 

 of lymphatic spaces, along which a flow of lymph is continually 

 taking place. We shall deal with the nerves of the cornea in con- 

 nection with those of the skin in treating of touch. 



717. The Ciliary Zone. The region in the front part of the 

 eye at which the sclerotic changes into the cornea is of great 

 importance since here the choroid, represented by the outer parts of 

 the ciliary processes and the outer margin of the iris, becomes 

 joined to the sclerotic, and to the junction are attached the plain 

 muscular fibres forming the ciliary muscle. This region which 

 we may call " the ciliary zone " deserves especial attention. 



When the transparent body of the cornea changes into the 

 opaque sclerotic, the epithelium of the former becomes separated 

 from the latter by the intercalation of ordinary loose connective 

 tissue, which serves as a dermis to the epithelium and so forms the 

 delicate skin covering the eyeball known as the conjunctiva; 

 the epithelium of the cornea leaves the cornea to become the 

 epithelium or epidermis of the conjunctiva (Fig. 140 e.cj.) This 

 takes place on the outside of the ciliary zone. 



On the inside the curved circumferential portion of the cornea 

 makes a blunt angle, " iridic angle," with the outer edge of the more 

 or less horizontal iris ; and here several peculiar structures make 

 their appearance. The thick membrane of Descemet with its epi- 

 thelioid covering is in part continued on, greatly reduced in thick- 

 ness, over the front surface of the iris to form the anterior basement 

 membrane and overlying epithelioid layer of that structure. But 

 in part only. At the angle the compact substance of the cornea 

 is on its inner surface frayed out into a loose network of bundles of 



