6T6 



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 foetal 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 



-> is 13 ip ^ u^BBfcp 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. 

 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). , ,. , 



1, optic nerve ; 2, 2, 2, 2, 3, 3. 3, 4, sclerotic coat, divided and turned OCCUplGS tliat portion OI the 

 back to show the choroid ; 5, 5, 5, 5, the cornea, divided into pvfi Ko|l nr>T-rpnrmrHno- + n thp 

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



Tf io v^yfvvi'a-f-arl 



KIT- fVio rvn+ir> 

 Y me 



nerve and is connected in 

 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 -fa 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- 





, , 



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 ; 

 11, 11, ciliary nerves ; 12, long ciliary artery ; 13, 13, 13. 13, 



14 ' iris; 15 ' 15 ' vascularcircleofthe 



