374 SENSITIVE SYSTEM. 



Lachri/mal Puncta and Conduits. 



The lachrymal puncta are two small circular holes, 

 large enough to admit the end of a common silver probe, more 

 distinct in the living than in the dead subject, piercing the inward 

 margins of the two lids near the root of the caruncle. The supe- 

 rior punctum is ordinarily smaller than the inferior, and the 

 latter is nearer to the caruncle. They are the openings of two 

 little canals, named 



The lachrymal co7iditits, which are formed within the sub- 

 stance of the lids. The superior conduit is somewhat longer 

 than the inferior. 



These canals are both lined with conjunctiva, and the mem- 

 brane assumes a finer texture at the entrance of the puncta. 

 They take an oblique direction inward to terminate in the 

 lachrymal sac; the superior one slanting downward, the inferior 

 likewise inclining a little downward, but at the same time bending 

 forward. 



Lachrymal Sac. 



The lachrymal sac is a small membranous bag lodged 

 within the funnel-shaped bony hollow that leads into the canal 

 in the lachrymal bone, behind and rather below the little emi- 

 nence upon the orbital ridge of that bone, which forms a very 

 convenient guide to find it. Our English veterinarians have de- 

 nied the existence of a sac : the best argument I can offer of its 

 presence is dissection — the same that has convinced myself. The 

 front of the sac is crossed by the fibres of the orbicularis, which 

 operate in discharging its contents; it has also a connexion 

 with the tendon of that muscle. The posterior part of the sac 

 adheres firmly to the lachrymal bone. It is composed of a dense, 

 white, fibrous membrane, and this is furnished with a lining 

 from the conjunctiva. The sac corresponds nearly in figure to 

 the funnel-shaped hollow in which it lies : it is broad and capa- 

 cious above, where it is perforated by the lachrymal conduits ; 

 but contracted below, where it is joined to the ductus ad nasum. 

 The internal surface is uneven, and is lubricated by a mucous 

 secretion. This sac is the reservoir into which the tears flow 

 from the lachrymal conduits; and from which they are pressed, 

 in the action of winking, into the ductus ad nasum. Gravita- 

 tion also, in the ordinary position of the head, may assist their 

 defluxion. 



believe it is merely mechanical — merely placed there to prevent the tears 

 from going beyond the puncta. In some animals — I allude to the horse — 

 it is covered by cuticle, and therefore it cannot be a secretory organ. — 

 Ahernethifs Lectures. 



