PHYSIOLOGICAL ANATOMY OF THE EYEBALL 



6 5 I 



parent. The corneal substance is very tough and will resist a pressure 

 sufficient to rupture the sclerotic. 



On the posterior, or concave surface of the cornea, is the membrane 

 of Descemet or of Demours. This is elastic, transparent, structureless, 

 rather loosely attached, and covered with a single layer of regularly 

 polygonal, nucleated epithelium. At the circumference of the cornea a 

 portion of this membrane passes to the anterior surface of the iris, in 

 the form of a number of processes which constitute the ligamentum iridis 

 pectinatum, a portion passes into the substance of the ciliary muscle and 

 a portion is continuous 

 with the fibrous structure 

 of the sclerotic. 



In the adult the cornea 

 is almost without blood- 

 vessels, but in foetal life 

 it presents a rich plexus 

 extending nearly to the 

 centre. These disappear, 

 however, before birth, 

 leaving a very few deli- 

 cate looped vessels at the 

 extreme edge. 



In the cornea, fine 

 nerve-fibres terminate in 

 the nuclei of the posterior 

 layer of the epithelium of 

 its convex surface. The 

 cornea also contains 

 lymph-spaces and the so- 

 called " wandering cells." 

 The surface of the cornea 

 is exquisitely sensitive. 



Choroid Coat. Calling the sclerotic and the cornea the first coat of 

 the eyeball, the second is the choroid, with the ciliary processes, the 

 ciliary muscle and the iris. This was called by the older anatomists the 

 uvea, a name which was later applied, sometimes to the entire iris and 

 sometimes to its posterior, or pigmentary layer. The choroid and 

 ciliary processes will be described together as the second coat. The 

 ciliary muscle and the iris will be described separately. 



The choroid is distinguished from the other coats by its dark color and 

 its great vascularity. It occupies that portion of the eyeball correspond- 

 ing to the sclerotic. It is perforated posteriorly by the optic nerve and is 



Fig. 166. Choroid coat of the eye (Sappey). 



I, optic nerve ; 2, 2, 2, 2, 3, 3, 3, 4, sclerotic coat, divided and 

 turned back to show the choroid ; 5, 5, 5, 5, the cornea, divided 

 into four portions and turned back ; 6, 6, canal of Schlemm ; 7, 

 external surface of the choroid, traversed by the ciliary nerves 

 and one of the long ciliary arteries; 8, central vessel, into 

 which open the vasa vorticosa ; 9, 9, 10, 10, choroid zone; u, 

 ii, ciliary nerves; 12, long ciliary artery; 13, 13, 13, 13, ante- 

 rior ciliary arteries ; 14, iris ; 15, 15, vascular circle of the iris ; 

 16, pupil. 



