CONJUNCTIVITIS. 457 



either separately or after joining, into the lachrymal sac, situated 

 at the side of the nose in a groove on the lachrymal bone, 

 behind the tendo-oculi and in front of the tensor tarsi muscle. 

 The lachrymal sac opens into the nasal duct, which passes 

 downwards, somewhat backwards and outwards, to terminate in 

 the nose under cover of the anterior part of the inferior turbinate 

 bone. This duct contains as a rule two small valves of mucous 

 membrane. Generally, however, air can be blown from the nose 

 through the lachrymal channels and out through the puncta. 

 Obstruction to any part of the lachrymal drainage system may 

 induce epiphora. 



THE CONJUNCTIVA. 



The exposed position of the conjunctiva readily explains the 

 frequency with which it becomes infected, conjunctivitis result- 

 ing. Eeflex irritation of the orbicularis palpebrarum muscle 

 in conjunctivitis, is a cause of the blepharospasm. The loose 

 cellular tissue of the conjunction may become greatly infil- 

 trated by inflammatory products leading to chemosis. Blood 

 effused beneath the conjunctiva is not infrequently seen in cases 

 of fracture of the anterior fossa of the base of the skull. 



THE CORNEA. 



Normally the cornea is partially covered by the upper eyelid 

 even when the eyes are open, and wholly covered by the approxi- 

 mation of the lids during their closure. For this reason, as well 

 as owing to the lachrymal secretion, it is well protected and 

 cleansed, and therefore guarded from injury and infection. Its 

 want of blood vessels, however, may be a predisposing cause of 

 keratitis, and it is interesting to see how the surrounding con- 

 junctival blood vessels frequently invade the corneal area for the 

 purpose of absorbing inflammatory products. Thus a leash of 

 vessels can often be seen extending from the conjunctiva to 

 vascularise an ulcer of the cornea. 



In the case of interstitial keratitis the vessels are derived 



