TEE GLOBE OF THE EYE. 



927 



The Membranes of the Eye. 



A. FiBKOus Membranes. 

 1. The Sclerotic (Fig. 502, h). 



The sclerotic is a white, very solid membrane, forming in itself about four- 

 fifths of the external shell of the eye. 



Its external face., in relation with the recti muscles and adipose tissue, receives 

 posteriorly — though lower than the middle — the insertion of the optic nerve, 



Fig. 502. 



THEORETICAL SECTION OF THE HORSE S EYE 



1, Orbital arch ; 2, lachrymal gland, a, Optic nerve ; 6, sclerotic ; c, choroid ; d, rptina; e, cornea, 

 / /, iris ; ^, A, ciliary ligament and processes given off by the choroid, though represented as 

 isolated from it, in order to indicate their limits more clearly; i, insertion of the ciliary processes 

 on the capsule of the crystalline lens ; jy crystalline lens ; k, crystalline capsule ; I, vitreous 

 humour ; ?«, n, anterior and posterior chambers ; o, theoretical indication of the membrane of 

 the aqueous humour ; p, p, tarsi ; q q, fibrous membrane of the eyelids ; r, elevator muscle of 

 the upper eyelid; s s, orbicularis muscle of the eyelids; t t, skin of the eyelids; u, conjunctiva; 

 V, epidermic layer of this membrane covering the cornea ; x, posterior rectus muscle ; y, superior 

 rectus muscle; z, inferior rectus muscle; w, fibrous sheath of the orbit (or orbital membrane). 



which passes through it and the choroid to form the retina. Its internal face is 

 loosely united to the choroid by vessels, nerves, and connective tissue. 



In front, the sclerotic shows an elliptical opening, the greatest diameter of 

 which is transversal, while its border — bevelled on the inner side — is closely 

 united to the circumference of the cornea. The substance of this membrane is 

 traversed by numerous vessels ^and nerves, and is not of the same thickness 

 throughout ; at the back, around the entrance of the optic nerve, it is thickest ; 

 it then diminishes gradually towards the larger axis of the organ, and afterwards 

 increases until it meets the cornea. 



Structure. — The sclerotic is wholly composed of fasciculi of connective 



