PRACTICAL CONSIDERATIONS : LACHRYMAL APPARATUS. 1479 



The sac is about 15 mm. long, and 5-6 mm. in diameter when distended. It is 

 situated near the inner canthus and lies within the deep lachrymal groove between 

 the superior maxillary and the lachrymal bone. Its closed upper end, or fundus, 

 extends beneath the internal tarsal ligament and some of the fibres of the orbicularis 

 palpebrarum, whilst its orbital surface is covered by the fibres of the latter muscle, 

 which spring from the lachrymal bone and are known as the tensor tarsi or Horncr' s 

 muscle. The lower end of the sac narrows where it passes into the nasal duct. The 

 wall is lined with a double layer of columnar epithelial cells, which in part are 

 provided with cilia. It is composed of fibro-elastic tissue and is loosely connected with 

 the periosteum. 



The nasal or naso-lachrymal duct, the lower portion of the tear-passage, is 

 situated within the bony canal formed by the superior maxillary, lachrymal and infe- 

 rior turbinate bones. It varies in length from 1 2-24 mm. , according to the position 

 of the lower opening, and is from 34 mm. in diameter. Its 

 direction is also subject to individual variation, but is slightly FIG. 



backward, as well as downward, and is usually indicated by 

 a line drawn from the inner canthus to the anterior edge of 

 the first upper molar tooth. The duct opens into the lower 

 nasal meatus, at a point from 30-35 mm. behind the poste- 

 rior margin of the anterior nares. The aperture may be 

 imperfectly closed by a fold of mucous membrane, the so- 

 called valve of Hasncr (plica lacrimalis). The structure 

 of the duct includes a lining of mucous membrane which is 

 clothed with columnar epithelium and may contain glandular 

 tissue in the lower portion. The mucous membrane is sep- D 



arated from the periosteum by areolar tissue and a venous 

 plexus; it may present additional folds, resembling valves, c of tear . passages . c 



the best marked of which is situated at the junction of the canaik-uii; s, lachrymal sac; 



j,ii .D, naso-lachrvmal duct ; nat- 



sac and the duct. uraisize. (Dwight.) 



The arteries supplying the lachrymal duct are from the 



nasal and the inferior palpebral. The large and numerous veins mostly join the 

 nasal plexus and empty into the ophthalmic and facial. The nerves are derived from 

 the infratrochlear division of the nasal branch of the ophthalmic.. 



Practical Considerations. The most frequent congenital error of develop- 

 ment in the lachrymal apparatus is found in connection with the canaliculus. It 

 may be entirely absent, or, what is more common, may appear only as a groove, 

 the edges having failed to unite. This union of the edges may occur only in part, 

 so that the canaliculus may have two or more openings. 



The lachrymal gland is rarely the seat of inflammation. Hypertrophy or 

 enlargement may be congenital or syphilitic. Prolapse or dislocation forward may 

 occur so that the gland can be seen or felt below the upper outer margin of the orbit ; 

 it has been excised in extreme cases. Cysts are due to occlusion of one or more ducts. 



The ducts of the gland open into the outer third of the upper conjunctival 

 fornix, and the tears sweep over the front of the eye towards the puncta under the 

 influence of gravity and the contractions of the orbicularis muscle. The lower 

 punctum is frequently everted so that it no longer dips into the lacus lacrimalis, and 

 the tears, instead of finding their way into the normal passage, flow over the lower 

 lid on to the cheek (epiphora). This is usually the first step in the development of 

 ectropion or turning out of the lid (vide stipra). When the eversion cannot be cor- 

 rected, the canaliculus is usually slit up on its posterior side so as to form a groove 

 dipping into the lacus, from which the tears may again be taken up by the natural 

 passages. The most common cause of epiphora is obstruction of the lachrymal 

 passages. This occurs most frequently at the junction of the lachrymal sac and 

 nasal duct, which is the narrowest part of the duct. The method of correcting such 

 an obstruction is by the use of sounds, which are passed from the punctum with or 

 without first slitting the canaliculus. The rule is to slit the canaliculus when the sound- 

 ing is to be kept up for any length of time, but if it is performed for diagnosis only, 

 the slitting is not done. The upper canaliculus is shorter but narrower than the lower, 



