LACHRYMAL SAC AND DUCT. 405 



The orifices in the puncta are sufficiently large to admit 

 readily a small bristle or probe. The ducts which lead from 

 the puncta to the lachrymal sac, are called canalicula lack- 

 rymalia. They are not straight ; they commence by ascend- 

 ing perpendicularly in the upper, and by descending in the 

 lower lid, for a line and a half; they are then turned at 

 a right angle upon themselves, and pursue a course nearly 

 horizontal to the lachrymal sac. Where the ducts turn 

 to form the angle, a sensible dilatation takes place, in which are 

 found one or two minute mucous cryptse,* which sometimes 

 embarrass the surgeon in operating through the ducts, the end 

 of the probe or tube becoming entangled in the lower folds. 



About one-fourth part of the lachrymal sac is situated above 

 the junction of the two eyelids, or the tendon of the orbicu- 

 laris muscle ; and the remainder below. After it descends 

 below the orbit of the eye, it contracts and takes the name of 

 the Lachrymal or Nasal Duct. 



The lachrymal sac is ovoidal in its form, and closed at 

 top ; it rises about two lines above the round tendon of the 

 orbicularis muscle, which is immediately in front of it, and 

 feels like a grain of rice. Its diameter is about equal to that 

 of a common goosequill. Anteriorly it is covered by the 

 integuments, the tendon above alluded to, and the orbicularis 

 muscle. Externally it is bounded by the caruncle, and con- 

 junctiva. 



The sac and duct have some resemblance to the Schneiderian 

 membrane in structure ; and are defended with a similar 

 mucus. The membrane of which they are composed, adheres 

 to the periosteum of the bony canal. 



Their walls are composed of two membranes, a mucous 

 and fibrous ; or rather of a mucous facing on a fibrous basis. 

 The mucous membrane, is internal, contains a number of t 

 follicles, which secrete a lubrifying mucus, as in the urethra, 

 and as in the latter organ are apt, when inflamed, to produce 

 strictures or obstructions in the passage, and thus become one 

 of the causes of fistula lachrymalis. 



* Dalrymple, Anat. of Human Eye, p. 277. Lond. 1834. p. 



