546 



THE VASCULAR CHOROID. 



[sect. 225. 



and with the hyaloid membrane {zonula Zinnii), so that it can 

 never be completely detached from these spots. 



The choroid consists essentially of two parts, of a thicker ex- 

 ternal vascular lamina, the proper choroid, and of an inner dis- 

 tinctly-coloured layer, the Hack pigment of the eye. The former, 

 however, can be divided into three strata, of course not sharply 

 separated from each other; they are, 1, an outer brown, soft 

 lamella, which supports the ciliary nerves and long ciliary vessels, 

 and contains anteriorly the musculus ciliaris ; this is named the 

 ( external pigment lamina' {lam. fusca et supra-chor'widea of 

 authors) ; 2, the less-coloured proper vascular layer, with the 

 larger arteries and veins ; and, 3, a colourless delicate inner layer, 

 containing an extremely rich capillary network, the menibrana 

 Fi s- 219 - choriocapillaris, which, however, does not 



extend further forwards than the ora ser- 

 rata. With regard to the tissue forming 

 the proper choroid, a great portion is made 

 up of vessels and nerves, and of the ciliary 

 muscle; but beyond these there is found 

 a peculiar tissue, which I classify with the 

 elastic tissue. In the outer parts of the 

 tunic, this basement tissue or stroma is 

 formed by nucleated cells, of an irregular, fusi- 

 form, or stellate shape, and either quite pale, 

 or containing some brown pigment. They 

 measure crooS'" to O'oi!" in length, and ana- 

 stomose irregularly with each other by shorter 

 and longer processes, which are mostly very 

 delicate (measuring 0'0005"' H1 breadth), but somewhat rigid and 

 pale; by the large number of these anastomoses a loose mem- 

 branous tissue results, which resembles in many respects the 

 fine-fibred elastic membranes. In the inner layers of the choroid, 

 and especially in the membrana choriocapillaris, these cellular 

 networks, which I class with the networks of plasmatic cells, 

 gradually pass into a homogeneous nucleated tissue, at first with 

 a little pigment, but afterwards colourless, which is distinguished 

 from connective tissue by its resistance to acids and alkalies. This 

 tissue terminates close upon the black pigment, by a delicate 

 membrane without structure, or finely fibrous, which may be 

 exhibited separately, and is o , ooo6'" thick; this I have named the 

 1 elastic lamella of the choroid/ 



The ligamentum ciliare of anatomists, called also, musculus 



Cells from the stroma of 

 the choroid, a. pigmen- 

 tated cells ; 6. pigmentless 

 fusiform ones ; c. anasto- 

 moses of the former ; mag- 

 nified 350 times. Of man. 



