CAPSULE OF TENON. ] 1 



Except when directed towards near objects, the axes of the eyes are nearly 

 parallel ; the optic nerves, on the contrary, diverge considerably. Each nerve 

 enters the corresponding eye about 2 to 8 mm. to the inner or nasal side of the 

 axis of the eyeball. 



The eyeball consists of three concentric coats, and of certain fluid and solid 

 parts enclosed by them. The coats are (1) an external fibrous covering, forming 

 the sclerotic (tunica sclera) and cornea, (2) a middle vascular, pigmented, and in part 

 also muscular membrane, the cJioroid and iris (tunica uvea), and (3) an internal 

 nervous and epithelial stratum, the retina. The enclosed refracting media, three 

 in number, are the aqueous humour, the vitreous lody, and the lens. 



Around the posterior two-thirds of the eyeball there is a tunic of fascia, tunica 

 vaginalis oculi, or capsule of Tenon, which is perforated by the tendons of the recti 



Tcwsi 



Outer palpebrctl 

 tiqatnent. 



tocUl of muscle 

 orbit 



Fig. 12. HORIZONTAL SECTION OF ORBIT. (After Gerlach.) Magnified. 



and obliqui muscles, along which it sends sheaths which blend with the perimysium 

 of the muscles (figs. 12 and 13). It is connected with the sclerotic by delicate con- 

 nective tissue (adventilia oculi, Lockwood), except posteriorly, at the entrance of the 

 ciliary vessels and nerves, where it blends with the sclerotic. Anteriorly the capsule 

 of Tenon is continued into the conjunctiva. This capsule is lined by flattened 

 endothelial cells, and encloses a lymph-space, which separates the eyeball from the 

 orbital fat. It is strengthened just behind the places where the recti muscles 

 perforate it, by bands of fibrous tissue (figs. 12 and 13,), and it is attached on 

 either side to the malar and lachrymal bones by elastic ligamentous structures, which 

 also receive fibrous slips from the internal and external recti. These structures 

 serve as check-ligaments (fig. 12) to these muscles. They are stated by Sappey to 

 contain plain muscular fibres. Fibrous slips also pass from the sheaths of the 

 superior and inferior rectus, and are attached to the conjunctiva palpebrarum and 



