406 CARUNCULA LACHRYMALIS. 



The length of the nasal duct is from four to six lines ; about 

 equal to that of the sac. The direction of the duct in its bony 

 canal, is downwards, backwards, and slightly inwards. At 

 its termination in the inferior meatus of the nose, (about seven 

 lines from the root of the nasal process of the upper maxillary 

 bone,) the mucous lining membrane is thrown into a sort of 

 valvular fold, which sometimes obstructs the introduction of a 

 probe into it, from the nostril. The swelling of this valve, in 

 coryza, measles, &c., is said to be one of the causes of the 

 accompanying epiphora. 



The tears appear to enter the puncta lachrymalia upon the 

 principle of capillary attraction ; and to be propelled forwards 

 by the motion of the eyelids and the pressure of the orbicularis 

 muscle. 



Between the puncta lachrymalia and the termination of the 

 eyelids, at their junction with each other, is a small angular 

 space, which is occupied by a body called the Caruncula 

 Lachrymalis ; which is of a reddish color, with a few small 

 hairs growing out of it : it is supposed to be glandular, and to 

 secrete a sebaceous substance. It has an effect in directing the 

 tears to the puncta lachrymalia. 



The caruncula lachrymalis, consists of a collection of 

 small mucous glands seven in number substitutes for the 

 Meibomian glands which are deficient in the internal canthus. 

 Six of these glands are placed upon a common level, and the 

 seventh is seated upon the top of the rest near their centre, 

 making the caruncle conoidal in shape, and about the size of a 

 grain of wheat. 



The conjunctiva is spread over them, and is pierced by a 

 number of small apertures, which are the orifices of the excre- 

 tory tubes of these glands. Each duct is garnished with a 

 small hair placed close to its orifice. 



Between the caruncula lachrymalis and the cornea, the 

 tunica conjunctiva, in many persons, forms a plait or fold, 

 which is very obvious when the eye is directed inwards ; 

 this has some analogy with the membrana nictitans, or third 

 eyelid of certain animals, and has been called the Valvula 



