THE EYE 211 



reflected on to the anterior surface of the eyeball. The lines 

 along which this reflection takes place are known as the 

 fornices of the conjunctiva. Modified sweat glands open on 

 the margins of the lids just behind the eyelashes. They may 

 become obstructed and inflamed, giving rise to styes. The 

 tarsal (Meibomiari) glands, which are embedded in the tarsi, 

 form thin reddish streaks, visible when the lid is everted. 

 They open on the margin of the lid and are liable to become 

 obstructed, causing tarsal cysts. 



3. The EYEBALL consists of segments of two spheres, which 

 differ in the size of their diameters, the anterior or corneal 

 segment being much smaller and more sharply curved than the 

 posterior or scleral segment. As a result, entering rays of light 

 undergo a greater amount of refraction than they would if the 

 eyeball were a perfect sphere. 



The ocular conjunctiva is thin and translucent, so that the 

 white appearance of the fibrous sclerotic coat of the eyeball is 

 rendered visible. It forms a very thin layer over the cornea. 

 Subconjunctival hcemorrhage may arise after rupture of the 

 episcleral vessels, and it is then most profuse around the cir- 

 cumference of the cornea ; or, it may be due to the spread of 

 haemorrhage from the orbit (p. 210). In the latter case, the 

 haemorrhage is most marked at the periphery of the conjunc- 

 tiva and it is scanty in the neighbourhood of the cornea. 



The Sclera covers the posterior five-sixths of the eye. 

 Anteriorly, it becomes continuous with the cornea, which 

 covers the remaining sixth. The sclera is composed of strong 

 fibrous tissue and it receives the insertions of the various 

 ocular muscles (p. 57). It is pierced a little below and 

 medial to its posterior pole by the optic nerve (p. 50), and 

 around the point of entrance of the nerve it is pierced by the 

 ciliary nerves and arteries. The anterior ciliary arteries run 

 forwards on the outer surface of the sclera until they almost 

 reach the corneo-scleral junction, and, before they pass through 

 the sclera, they form anastomoses with one another. In this 

 way an arterial ring is formed around the corneo-scleral 



