THE LACHRYMAL APPARATUS. 567 



The lachrymal canals (canaliculi ; fig. 207, 'and 3 ) lead from the Canals for 

 puiicta, and convey the tears to the lachrymal sac. From the the tears - 

 margin of the lid, each canal is directed vertically for about one- 

 sixteenth of an inch, and then bends inwards following the course 

 of the internal tarsal ligament. Internally the two canals converge, 

 and they open into the lachrymal sac, rather above its middle, 

 either separately or by a common orifice. 



The lachrymal sac and nasal duct extends from the inner side of Receptacle 

 the orbit to the nose, and convey the tears into the latter cavity. of the tears> 

 They form one tube, of which the upper dilated end is the sac, and 

 the lower part the duct. 



The sac ( 5 ) is placed in the hollow formed by the nasal process of Situation of 

 the superior maxillary and the lachrymal bones. In front, it is diiated'part. 

 crossed by the internal tarsal ligament of the eyelids ; and behind, 

 it is> covered by an expansion 

 derived from that band, which is 

 fixed to the lachrymal crest. If 

 the aponeurotic covering be re- 

 moved, the mucous lining will 

 appear. Into the outer side of 

 the sac the lachrymal canals open. 



The duct ( 6 ) is the narrower 

 part of the tube, and is about 

 half an inch long. It is entirely 

 surrounded by bone, and inclines 



slightly outwards and backwards FIG. 207. THE ETKLIDS AXD 

 as it 'd^scmds. In the nasal LACHRYMAL APPARATUS. 



cavity it opens into the fore part l. Puncta lachrymalia. 

 of the inferior meativs, where its 2. Upper, and 3, lower lachrymal 



opening is guarded by a small wa ' f . 



4. Caruncula lachrymalis. 

 fold of the mucous membrane. 5 Lachrymal sac. opening. 



Within the bone, the duct has t>! Nasal duct.^ S KV ct ^ re * 



' of the duct. 



a fibrous coat lined by mucous 



membrane, which is continuous with that of the nose below, and, 

 through the canals, with the conjunctiva above. 



STRUCTURE OF THE EYELIDS. Each lid consists fundamentally Different 

 of a fibrous plate attached to the bone by ligaments. Superficial eyelids 11 

 to this framework are the integuments with a layer of fibres of the 

 orbicularis palpebrarum, and beneath it the mucous lining of the 

 conjunctiva. The upper lid includes also the tendon of the levator 

 palpebrae. Vessels and nerves are contained in the lids. 



Dissection. The student should now examine the structure of Dissect lids. 

 the lids. The bit of tow or wool may remain beneath the lids ; 

 and the palpebral part of the orbicularis muscle is to be thrown 

 inwards by an incision around the margin of the orbit. In raising 

 the muscle care must be taken of the thin membranous palpebral 

 fatcia beneath, and of the vessels and nerves of the lid. 



Orbicularis palpcbrarum. The palpebral fibres of this muscle form Layer of 

 a pale layer which reaches the free edge of the eyelids, and a thin 

 stratum of areolar tissue without fat unites the muscle with the skin. 



