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 venae 

 vorticosae and ciliary veins. The lymphatics are represented by intercommunicat- 

 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 nearly 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 comeae. 

 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 corneae) joins the sclera; the latter overlaps the cornea more in front than 

 behind, and more above and below than a''j the sides, thus explaining the apparent 



Sclera 



Optic nerve 



Optic papilla 

 Retrobulbar fat 



Rectus oculi inferior 



Reflection of conjunctiva 



Granula iridis 



Cornea 



Lens 

 y' Anterior chamber 



Ciliary processes 



Chorioid 



Fig. 694. — Vertical Sectiow of Etebaix of Horse, about t 

 The contour of the crystalline Lena ia 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 corneae is continuous with that of the conjunctiva scleras, 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 

 lamellae disposed parallel with the surface. In the amorphous cement substance 

 between the lamellae 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 



' 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 epithehum and the substantia propria, does not exist as such, but there 

 is a condensation of the superficial part of the latter, which RoUett termed the anterior limiting 

 layer; it is not elastic. 



2 Also known as the membrane of Descemet or Demours 



