THE VASCULAR TUNIC 



865 



practically homogeneous membrane which is less intimately attached to the sub- 

 stantia propria than the anterior lamina. It is clear, glistening, and elastic. At 

 the periphery the lamina divides into three sets of fibers. The anterior fibers join 

 the sclera, the middle give attachment to the ciliary muscle, while the posterior 

 pass into the ins and form the Ugamentum pectinatum iridis. (5) The endotheUum 

 of the anterior chamber (Endothelium camera anterioris) consists of a layer of 

 flattened polygonal cells, and is reflacted on to the anterior surface of the iris. The 

 cornea is non-vascular except at its periphery, where the terminal twigs of the vessels 

 of the sclera and conjunctiva form loops. The nerves are derived from the ciliary 

 nerves. They form a plexus around the periphery (Plexus annularis), from which 

 fibers pass into the substantia propria, become non-medullated, and form the funda- 

 mental or stroma plexus. From this perforating branches go through the anterior 

 limiting layer and form a subepithelial plexus, from which filaments pass between 

 the epithelial cells. Other branches from the plexuses in the substantia propria 

 end as fibrils which are in close relation with the corneal corpuscles. 



The Vascular Tunic 



The vascular tunic (Tunica vasculosa oculi) lies internal to the fibrous coat; 

 it comprises three parts — the chorioid, the ciliary body, and the iris. 



1. The chorioid (Chorioidea) is a thin membrane which lies between the sclera 

 and retina. It is in general rather loosely attached to 

 the sclera by the lamina fusca, but is intimately adherent 

 at the point of entrance of the optic nerve and less closely 

 in places where the ciliary vessels and nerves pass through. 

 The inner surface is in contact with the layer of pigmented 

 cells of the retina, which adhere so closely to the chorioid 

 that they were formerly regarded as a part of the latter. 

 The general color of the chorioid is dark brown, but an 

 extensive semilunar area a little above the level of the 

 optic papilla has a remarkable metallic luster, and is 

 termed the tapetum of the chorioid (Tapetum chorioidese) . 

 The appearance here varies in different individuals, but 

 the prevailing colors in most cases are iridescent blue 

 and green in various nuances shading into yellow. Pos- 

 teriorly the chorioid is perforated by the optic nerve, 

 and anteriorly it is continuous with the ciliary body. 



The chorioid consists of four layers, which from without inward are as follows: 

 (1) The lamina suprachorioidea consists of interlacing fine lamellae of fibrous tissue, 

 each containing a network of elastic tissue. Among these are large, branched, pig- 

 mented, connective-tissue cells. The spaces between the lamellae are lined with 

 endothelium, and form a system of lymph-clefts which together form the pericho- 

 rioid space (Spatium perichorioideale) . (2) The lamina vasculosa is the outer part 

 of the proper tissue of the chorioid. It contains the larger blood-vessels, which 

 are supported by areolar tissue. (3) The lamina choriocapillaris consists of an 

 extremely rich network of capillaries embedded in an almost homogeneous matrix. 

 Between it and the lamina vasculosa is a layer of fibro-elastic tissue, the tapetum 

 fibrosum, which causes the metallic luster mentioned above. (4) The lamina 

 basalis is very thin and transparent. It is composed of an inner homogeneous part 

 and an outer elastic part. 



2. The ciliary body (Corpus ciliare), the middle part of the vascular coat, con- 

 nects the chorioid with the periphery of the iris. In meridional section it has the 

 form of a narrow triangle, the base of which is next to the iris. On its inner side 

 are the ciliary processes and on its outer side is the ciliary muscle. It consists of 

 three parts — the ciliary ring, ciliary processes, and ciliary muscle. The ciliary 

 55 



Fig. 695. — Tapetum of Horse. 

 a, Optic papilla; 6, lower bor- 

 der of tapetum. {After EUea- 

 berger, in Leisering's Atlas.) 



