SECT. 225.] TIGMENT OF THE CHOROID. 547 



ciliaris s. tensor chorioulca, was recognised as being of a muscular 

 nature, almost simultaneously by JBrucke and Bowman : it is a 

 tolerably thick lamina, of radiating, smooth muscular fasciculi, 

 which pass from the most anterior border of the sclerotic to the 

 corpus ciliare, and are lost in the anterior half of that body, at 

 the spot corresponding to the situation of the ciliary processes 

 internally. More accurately described, the ciliary muscle arises 

 at that part of the sclerotic where it is furrowed for the formation 

 of the venous sinus of Schlemm ; indeed it is from a special dense, 

 smooth tract, which forms the inner wall of the above-mentioned 

 canal, and coalesces with the sclerotic, receiving a part of the 

 fibrous networks prolonged from the membrane of Demours ; the 

 last-mentioned fibres coalesce perfectly with the similar elements 

 of the special tract, which are, however, finer, anastomose more 

 densely, and have a circular direction. The termination of the 

 ciliary muscle is at the attached part of the ciliary processes, but 

 not in these structures themselves. The muscular elements are 

 somewhat shorter (o , 02"') and broader (0-003'" to 0-004'") than 

 the ordinary fibre cells, and are finely granular and very delicate; 

 they are, indeed, so perishable, that they cannot easily be isolated 

 in the human subject. Very lately, H. Midler has discovered a 

 circular muscular layer, quite anteriorly beneath the radiating 

 fibres of the ciliary muscle ; and this may be called the ' circular 

 muscle of Muller? 



The black pigment completely lines the inner surface of the 

 choroid membrane, as a connected purely cellular lamina, which 

 consists, as far forwards as the ora serrata, of a single layer of 

 beautiful cells, almost regularly hexagonal, o'oo6'" to 0008'" in 

 diameter, and 0-004'" in thickness, dis- Fig. 220. 



posed in the manner of a mosaic ; the « 



large quantity of pigment in them AAA 



as a clear spot in the interior ; but this 



V 



nucleus is seen on a lateral view to be 9W 

 situated in the outer half of the cells, 

 where they are poorer in pigment 



<rrunnlf>e "EVnrn flip nra «prrnrn nn. Cells of the black pigment of man. 



giailUlCS. JUOni tne Oia Seriata On- „ seen from the surface, 6. from the 



wards, the pigment-cells are arranged side ; c - pigmeut grannle& 

 in two or more layers, becoming roundish, smaller, and quite 

 filled with pigment, so that even the nuclei are scarcely visible. 

 All the pigment-cells have very delicate walls, and are very readily 

 ruptured by pressure ; their pigment consists of extremely small, 



N N 2 



