LACHRYMAL GLAND, CANALS AND SAC. 449 



its excretory ducts ; the puncta lachrymalia, and lachrymal canals ; 

 the lachrymal sac and nasal duct. 



The Lachrymal gland is situated at the upper and outer angle of 

 the orbit, and consists of two portions, orbital and palpebral. The 

 orbital portion, about three quarters of an inch in length, is flattened 

 and oval in shape, and occupies the lachrymal fossa in the orbital 

 plate of the frontal bone ; being in contact with the periosteum, to 

 which it is closely connected by its upper and convex surface ; being 

 in relation with the globe of the eye, and with the superior and ex- 

 ternal rectus by its inferior or concave surface ; and with the broad 

 tarsal ligament by its anterior border. By its posterior border it 

 receives its vessels and nerves. The palpebral portion, smaller than 

 the preceding, is situated in the upper eyelid, extending downwards 

 to the superior margin of the tarsal cartilage. It is continuous with 

 the orbital portion above, and is enclosed in an investment of dense 

 fibrous membrane. The secretion of the lachrymal gland is con- 

 veyed away by ten or twelve small ducts which run for a short 

 distance beneath the conjunctiva, and open upon its surface by a 

 series of pores about one-twentieth of an inch apart, situated in a 

 curved line a little above the upper border of the tarsal cartilage. 



Lachrymal canals. The lachrymal canals commence at the 

 minute openings, puncta lachrymalia, seen upon the lachrymal 

 papillae of the lids at the outer extremity of the lacus lachrymalis, 

 and proceed inwards to the lachrymal sac, where they terminate 

 beneath a valvular semilunar fold of the lining membrane of the 

 sac. The superior duct at first ascends, and then turns suddenly 

 inwards towards the sac, forming an abrupt angle. The inferior 

 duct forms the same kind of angle, by descending at first, and then 

 turning abruptly inwards. They are dense and elastic in structure, 

 and remain constantly open, so that they act like capillary tubes in 

 absorbing the tears from the surface of the eye. The two fasciculi 

 of the tensor tarsi muscle are inserted into these ducts, and serve 

 to draw them inwards. 



The Lachrymal sac is the upper extremity of the nasal duct, and 

 is scarcely more dilated than, the rest of the canal. It is lodged in 

 the groove of the lachrymal bone, and is often distinguished inter- 

 nally from the nasal duct by a semilunar or circular valve.. It con- 

 sists of mucous membrane, but is covered in and retained in its place 

 by a fibrous expansion, derived from the tendon of the orbicularis, 

 which is inserted into the ridge on the lachrymal bone: it is also 

 covered by the tensor tarsi muscle, which arises from the same ridge, 

 and in its action upon the lachrymal canals may serve to compress 

 the lachrymal sac. 



The Nasal duct is a short canal about three quarters of an inch 

 in length, directed downwards, backwards, and a little outwards to 

 the inferior meatus of the nose, where it terminates by an expanded 

 orifice. It is lined by mucous membrane, which is continuous with 

 the conjunctiva above, and with the pituitary membrane of the nose 



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