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 joi 
the sclera, the middle give attachment to the ciliary muscle, while the posterior 
pass into the iris and form the ligamentum pectinatum iridis. (5) The endothelium 
of the anterior chamber (Endothelium camer anterioris) consists of a layer of 
flattened polygonal cells, and is reflected 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 chorioidex). 
The appearance here varies in different individuals, but 
= Fic. 695.—Tarrtum oF Horse. 
the prevailing colors in most cases are iridescent blue a, Optic papilla; b, lower bor- 
and green in various nuances shading into yellow. Pos- der of tapetum. (After Ellen- 
berger, in Leisering’s Atlas.) 
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 lamellze of fibrous tissue, 
each containing a network of elastic tissue. Among these are large, branched, pig- 
mented, connective-tissue cells. The spaces between the lamellz 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 
vo 
