864 THE SENSE ORGANS AND SKIN OF THE HORSE 
bundles are arranged chiefly in meridional and equatorial layers. The very limited 
blood-supply is derived from the ciliary arteries, and the veins open into the ven 
vorticos and ciliary veins. The lymphatics are represented by intereommunicat- 
ing cell spaces. The nerves are derived from the ciliary nerves. 
2. The cornea forms the anterior fifth of the fibrous tunic. It is transparent, 
colorless, and non-vascular. Viewed from in front it is oval in outline, the long 
axis being transverse and the broad end medial; it appears more uearly circular 
when viewed from behind. Its anterior surface (Facies anterior) is convex and is 
more strongly curved than the sclera; its central part is termed the vertex cornez. 
The posterior surface (Facies posterior) is concave; it forms the anterior boundary 
of the anterior chamber, and is in contact with the aqueous humor. The margin 
(Limbus corneze) joins the sclera; the latter overlaps the cornea more in front than 
behind, and more above and below than at the sides, thus explaining the apparent 
Sclera 
Reflection of conjunctiva 
Cornea 
Optic papilla 
Retrobulbar fat — Lens 
Anterior chamber 
Rectus oculi inferior Keen 
Ciliary processes 
Chorioid 
Fic. 694.—VerticaL Section oF EYEBALL OF Horse, ABour 3. 
The contour of the erystalline lens is dotted. 
difference in outline of the two surfaces. The cornea is thinnest at the vertex. 
The cornea consists, from before backward, of the following layers (1) The epi- 
thelium cornee is continuous with that of the conjunctiva sclera, and is of the 
stratified squamous type. (2) The lamina limitans anterior is merely a condensa- 
tion of the next layer. (3) The substantia propria forms the bulk of the cornea 
and is composed of interlacing bundles of connective tissue, arranged in part in 
lamellze disposed parallel with the surface. In the amorphous cement substance 
between the lamelle are flattened connective-tissue cells, the corneal corpuscles. 
These have branching processes which unite with those of other cells, thus form- 
ing a protoplasmic network.! (4) The lamina elastica posterior’ is a thin and 
1 According to Piersol, the system of spaces and canaliculi in the substantia propria is com- 
pletely filled by the cells and their processes, upon which the nutrition of the cornea largely de- 
pends. The lamina elastica anterior (Bowman’s membrane), formerly described as a distinct 
layer between the corneal epithelium and the substantia propria, does not exist as such, but there 
is a condensation of the superficial part of the latter, which Rollett termed the anterior limiting 
layer; it is not elastic. 
2 Also known as the membrane of Descemet or Demours 
