ON THE ESSENTIAL OEGANS OF SIGHT. 



747 



Fig. 53S. —Theoretical Section of the Horse's Eye. 



a.— Optic nerve. 6.— Sclerotic, c— Choroid.— rf.—Eetina. e —Cornea. /.— Iris.— 

 <7ft.— Ciliary circle lor ligament) and processes given oft by the choroid, though repre- 

 sented as isolated from it, In order to indicate their limits more clearly, i. — Insertion 

 o£ the ciliary processes on the crystalline lens. j. —Crystalline lens. k. — Crystalline 

 capsule. I. — Vitreous hody. ■«i?i.— Anterior and posterior chambers, o.— Theoretical 

 indication of the membrane of the aqueous humor, pp. — Tarsi. <?g— Fibrous mem- 

 brane of the eyelids, r. — Elevator muscle of the upper eyelid, ss.— Orbicularis muscle 

 of the eyelids. (.-Skin of the eyelids, v- —Conjunctiva. ».— Epidermic layer of this 

 membrane covering the cornea, x — Posterior rectus muscle. 2/.— Superior rectus 

 muscle, z —Inferior rectus muscle, w —Fibrous sheath of the orbit (or orbital mem- 

 brane). 



To this essential organ are added as accessories, first, a mus- 

 cular apparatus, constituted by seven muscles — d^posterior straight 

 or retractor, four others, also straight, the superior, inferior, ex- 

 ternal and internal; and two oblique, or rotators, the great and 

 small, or external and inter?ial oblique/ second, an adipose pad; 

 third, au ai?paratus of lubrication, composed of the lachrymal 

 gland and its means of conducting the tears, the product of its 

 secretion, viz., the hygr ophthalmic canals, the 2:>un.cta lachrymalis, 

 the caruncula, lachrymalis, the lachrymal ducts, the lachrymal 

 sac, and the lachrymal canal. 



The whole mass of this apparatus is enclosed in a conical 

 fibrous sac, the ocular sheath, which forms a membranous lining, 

 as it were, to the orbital cavity, or bony bos, which is anteriorly 

 open, except when closed by the eyelids. 



Our desio-n in the present chapter is to confine our considera- 

 tion entirely to such portions of surgical ophthalmology as are 

 likely to demand the careful and practical attention of the vet- 

 erinarian. 



