THE ACCESSORY ORGANS OF VISION. 945 



The lachrymal gland belongs to the category of conglomerate glands ; con- 

 sequently, it IS analogous to the salivary glands. (The gland is maintained in 

 situ by a capsule formed by the fascia of the orbit.) 



The hygrophthalmic canals have a thin fibrous membrane for their walls ; 

 .this is covered by cyUndrical epithelium. 



Caruncula lachrymalis. — This name is given to a small round (or fusiform) 

 body, frequently entirely, or partially black (or brown), slightly uneven, and 

 situated in the nasal angle of the eye ; it is nothing more than a small fold of 

 conjunctiva covering some agglomerated follicles, and the bulbs of several fine 

 hairs, which are readily seen on its surface. It may be regarded as designed to 

 •direct the tears towards the puncta, or to separate any extraneous particles that 

 this fluid may carry towards it. 



It has for its base a small mass of connective tissue, in the midst of which 

 are some hair-roots, and some rather large glandules, lined by an epithelium 

 ■charged with fat-granules. Nerve-tubes ramify around the hair-bulbs. 



Puncta lachrymalia. — These are two little openings, situated one in each 

 eyelid, a short distance from the nasal commissure, by which the tears pass from 

 the oculo-palpebral surface into the lachrymal 'ducts. 



Lachrymal ducts. — These are continuations of the last, and, like them, are 

 very narrow ; they carry the tears into the lachrymal sac. The superior is 

 longer than the inferior duct, and arrives at the sac behind it. The mucous 

 membrane lining these ducts is thin, and covered by a stratified pavement 

 epithelium, similar to that of the conjunctiva. 



Lachrymal sac. — This little reservoir— lodged in the indifundibulum that 

 precedes the lachrymal foramen in the bone of that name — receives the tears 

 from the two ducts, and passes them into the lachrymal canal. Its mucous 

 membrane only differs from that of the ducts in being covered with ciliated 

 epithelium. 



Lachrymal canal (nasal duct). — The tears accumulated in the sac flow into 

 this long duct, which extends to the lower aperture of the nostril. About one- 

 half of its course is in the canal of the lachrymal bone, which protects it, and 

 which terminates between the two turbinated bones. The remainder of the canal 

 is beneath the nasal mucous membrane, whence it passes to the inner surface of 

 the outer wing of the nostril ; there it terminates by an orifice — sometimes two 

 — that looks as if punched out of the membrane, towards the lower commissure, 

 near the point where there is a line of demarcation between the dark colour of 

 the skin and the rosy tint of the mucous lining. 



This aperture constitutes the " nasal outlet." 



The epithelium of the membrane lining the canal is ciKated in its bony, 

 ■stratified in its nasal, portion. On the surface of the membrane are to be seen 

 the openings of the secretory ducts of some racemose glands, which are lodged 

 in the walls of the canal. Throughout its extent, the canal is lined by a con- 

 tinuation of the mucous membrane of the lachrymal sac. In Solipeds, this canal 

 •opens on the cutaneous surface at the entrance to the nostrils ; it therefore 

 happens that in these animals the conjunctiva, with it prolongations, forms a 

 particular mucous membrane, independent of the great gastro-pulmonary 

 membrane. 



In the Ass and Mule, the orifice of the lachrymal canal is situated at the 

 inner face of the outer wing of the nostril, and not near the inferior conmiissure, 

 as in the Horse. 



