386 SENSITIVE SYSTEM. 



we reckon a very small one indeed, which is generally found be- 

 side it. Along the lower edge there are likewise three, sometimes 

 four of them : but these are comparatively inconsiderable, not 

 being larger than pins' heads. The corpora nigra superiora 

 hang more or less over the pupillary opening in front: the cor- 

 pora inferiora project just enough to interrupt the regularity of 

 the pupillary line. I am inclined to regard these bodies as pro- 

 ductions of the black pigment: they have similar fringed or 

 velvety surfaces, and appear to be resolvable into the same mu- 

 cous substance, and to be continued from the uvea — to be, in fact, 

 uveal excrescences. Professor Coleman has seen them as large 

 as the largest garden peas, without their seeming to interfere at 

 all with vision. 



Choroid Coat. 



The tunica choroides is the black, soft, delicate texture 

 immediately covered by the scleiotica. It extends from around 

 the termination of the optic nerve, by which it is perforated, in 

 intimate contact with the internal surface of the sclerotica, as far 

 forward as the edge of the cornea, where it ends in the ciliary 

 circle : it being connected to the sclerotica by a very fine 

 cellular web, by intercurrent bloodvessels, and by the ciliary 

 nerves. 



Ciliary Circle. — If that part of the sclerotica in union with 

 the cornea be removed, we shall expose, immediately behind the 

 vanishing edge of the latter, a whitish cellular belt about two 

 lines in breadth : this is named the orbicularis ciliaris, ciliary 

 circle, or ciliary ligamoit. It forms the medium of union or 

 line of demarcation between the choroides and iris ; it is also the 

 place where the sclerotica has the firmest connexion with the 

 choroides, and through that connexion likewise an intermediate 

 one with the iris. The basis of the ciliary circle is nothing but 

 condensed cellular membrane ; but the ciliary vessels and nerves 

 in their course pervade it, forming a sort of vascular and nervous 

 plexus : a circumstance that has given rise to other names for it. 

 This part may be stripped off altogether with the forceps; and 

 in doing so it will be found to adhere with most tenacity to the 

 choroides. Fontana has described in the human eye a triangular 

 canal in the cellular tissue between the sclerotica and this circle; 

 but, for my own part, I cannot find any such cavity in the eye 

 of the horse. 



Structure. —The inner surface of the choroides is accurately 

 applied in every point to the internal tunic — the retina ; though 

 so closely applied, however, they nowhere adhere, either by vas- 

 cular or cellular connexion. Externally, the choroides presents 



