868 



ORGANS OF SPECIAL SENSE 



j)ressed. antero-posteriorly; the lumen of the lower ])unetuiu is somewhat larger 

 than that of the upper. As the lower papilla is a little further from the inner 

 canthus than the upper, the corresponding canaliculus is longer. 



On tracing either canaliculus from its origin, we tind that at first it runs nearly 

 vertically for a short distance, then bends sharply toAvards the nose, and finally 

 courses more or less horizontally, converging slightly towards its fellow, and not 

 infrequently joining it before opening into the sac. The calibre varies considerabh' 

 in this course, being narrowest a short distance from the punctum, and widest at 

 the bend, from which point it again narrows very gradually as it nears the sac. 

 The wall of the canaliculus consists mainly of elastic and white fibrous tissue, 

 lined internally by epithelium, and covered externally by striated muscle (part of 

 the orbicularis). The muscle-fibres run parallel to the canaliculus in the horizontal 

 part of its course; but they are placed, some in front and some behind, around the 

 vertical part, acting here as a kind of sphincter. .Just before their termination, the 

 canaliculi pierce the periosteal thickening that constitutes the posterior limb of the 

 inner palpebral ligament. 



The lachrymal sac lies in a depression in the bone at the inner angle of the 

 orbit (the lachrymal fossa). It is vertically elongated, and narrows at its upper 

 and lower ends; the upper extremity or fundus is closed, Avhile the low^er is contin- 

 uous directly with the nasal duct. Laterally, the sac is somewhat compressed, so 

 that its antero-posterior is greater than its transverse diameter. The canaliculi, 



Fig. 492. — Lachrymal Apparatus. i^After Sebwalbe.) 



SUPERIOR LACHRYMAL GLAND 

 INFERIOR LACHRYMAL GLAND 



DUCT FROM SUPERIOR GLANC 



UPPER EYELID PARTIALLY 

 DIVESTED OF SKIN 



UPPER PUNCTUM 



LACHRYMAL SAC, NEAR ITS FUNDUS 



COMMON DUCT FORMED BY JUNC- 

 TION OF CANALICULI 



UPPER AND LOWER CANALICULI 

 LOWER PUNCTUM 



either separately or by a short common tube, open into a bulging on the outer sur- 

 face of the sac near the fundus. As has previously been mentioned, the sac is 

 surrounded by periosteum, but between this and the mucous membrane forming 

 the true sac-wall there is a loose connective tissue, so that the cavity is capable 

 of considerable distension. The relations of the inner palpebral ligament have 

 already been described; it is to be noted that the fundus of the sac extends above 

 this ligament. 



The nasal duct reaches from the lower end of the sac to the top of the inferior 

 meatus of the nose, opening into the latter just beneath the adherent border of the 

 inferior turbinated bone. Traced from above, its main direction is downwards, but 

 it has also a slight inclination backwards and outwards. It lies in a bony canal, 

 whose periosteum forms its outer covering. Between this and the mucous mem- 

 brane of the duct there is a little intermediate tissue, in which run veins of consid- 

 erable size connected with the plexus of the inferior turlnnated bone. The duct 

 does not usually open directly into the nasal cavity at the lower end of the bony 

 canal, l)ut pierces the nasal mucous membrane very ol)liciuely, so that a fap of 

 mucous membrane covers the lower border of the opening in the bone, ujion which 

 tlap the tears first trickle after escaping from tlie duct proper. 



The sac and nasal duct together constitute the lachrymal canal, lined through- 

 out by a continuous mucous membrane. This membrane presents folds in some 

 situations, especially near the opening of the canaliculi, at the junction of the sac 



