404 PUNCTA LACHRYMALIA. 



colored with indigo, ink, or blood, the orifices become visible, 

 and the ducts may be filled with mercury up to the gland. 

 The ducts are three or four lines in length. 



The fluid secreted by this gland, (viz. the tears,) is transpa- 

 rent, but is always salt to the taste. When evaporated, by 

 exposure to the air, some cubic crystals, and a small quantity 

 of mucilaginous matter remain. Chemistry has ascertained that 

 these crystals contain muriate of soda, and soda uncombined, and 

 that phosphate of lime and phosphate of soda may be obtained 

 by burning inspissated tears ; but the whole of the saline matter 

 does not amount to one-hundredth part of the tears in which 

 they are dissolved. The tears, therefore, jconsist of these salts, 

 and of mucus, dissolved in a large proportion of water. 



The tears are carried from the eye by two small canals, which 

 commence, one on each eyelid, at the internal extremities of the 

 cartilages, opposite to each other.* 



The orifices of these canals, being in small cartilages, (but not 

 in those called the tarsi,) are always open, and are called the 

 Puncta Lachrymalia. 



Each of these canals run, within the edge of each eyelid, 

 from the place of its commencement to the lachrymal sac, which 

 is a larger membranous canal situated in the depression formed 

 by the anterior portion of the os unguis and the corresponding 

 portion of the upper maxillary bone ; and extending thence 

 along the bony canal is the nasal duct, which continues from 

 this depression into the nose, and terminates under the inferior 

 spongy bone near its anterior extremity. 



These canals are very small at their commencement at the 

 puncta lachrymalia ; but this small portion is very short ; it 

 forms an angle with the remainder of the canal, which is con- 

 siderably larger.f 



The canals gradually approach each other as they proceed 

 towards the lachrymal sac, into which they enter, in contact 

 with each other, but by distinct orifices. 



* The little hollow at the internal canthus, in front of the caruncle, and 

 where the tears collect before entering the puncta, is called the lacus lachry- 

 mails. P. 



f These canals were known to Galen, and were particularly described by 

 Fallopius in 1584. H. 



