676 



SPECIAL SENSES. 



cleated 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 foatal life 

 it presents a rich plexus extending nearly to the centre. These disappear, 

 however, before birth, leaving a very few delicate, looped vessels at the ex- 

 treme 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 cor- 

 nea 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 mus- 

 cle and the iris. This was 

 called by the older anato- 

 mists the uvea, a name 

 which was later applied, 

 sometimes to the entire iris, 

 and sometimes to its pos- 

 terior, or pigmentary layer. 

 The choroid and ciliary 

 processes will be described 

 together as the second coat. 



'UP-- -:-..Jp The ciliary muscle and the 



iris will be described sepa- 

 rately. 



The choroid is distin- 

 guished from the other coats 

 of the eye by its dark color 

 and its great vascularity. It 



FIG. 244. Choroid coat of the eye (Sappey). **. *. ru 



1, optic nerve ; 2, 2, 2, 2, 3, 3. 3, 4, sclerotic coat, divided and turned OCCUpieS that portion Of the 



back to show the choroid ; 5, 5, 5, 5, the cornea, divided into pvp V, a ll pnrrprnnrlino- fr tViP 



four portions and turned back ; 6, 6, canal of Schlemm ; 7, ^yvL mg IL 



external surface of the choroid, traversed by the ciliary oplprnfin Tf i rprfnrafpd 



nerves and one of the long ciliary arteries ; 8, central vessel, k AG ' 



into which open the vasa vorticosa ; 9, 9, 10, 10, choroid zone ; nnsfprinrlv hv thp rvntio 



11, 11, ciliary nerves ; 12, long ciliary artery ; 13, 13, 13, 13, P 0> )r V D J 



anterior ciliary arteries ; 14, iris ; 15, 15, vascular circle of the nerve and is Connected in 

 iris ; 16, pupil. 



front with the iris. It is 



very delicate in its structure and is composed of two or three distinct layers. 

 Its thickness is -fa to ^ of an inch (0-3 to 1 mm.) Its thinnest portion is 

 at about the middle of the eye. Posteriorly it is a little thicker. Its thick- 

 est portion is at its anterior border. 



The external surface of the choroid is connected with the sclerotic by 

 vessels and nerves (the long ciliary arteries and the ciliary nerves), and very 

 loose, connective tissue. This is sometimes called the membrana fusca, al- 

 though it can hardly be regarded as a distinct layer. It contains, in addi- 





