THE HEAD AND NECK I191 



Superiorly it presents a round, closed extremity, and inferiorly it 

 opens into the nasal duct. Externally it receives the lachrymal 

 canaliculi, separately or conjointly, and anteriorly it is crossed by 

 the tendo palpebrarum or internal tarsal ligament, which furnishes 

 an offset round it. Posteriorly it is related to the tensor tarsi 

 muscle. 



The guide to the lachrymal sac is the lachrymal tubercle or spine 

 of the superior maxilla, which is situated at the point of continuity 

 of the infra-orbital margin of the bone and the crista lacrimalis 

 anterior on the outer surface of the nasal process. The lachr^-mal 

 sac lies immediately intemaUto this tubercle. In many cases, 

 however, the tubercle or spine is very rudimentar}'. 



The nasal duct extends from the lower end of the lachr^inal sac 

 to the anterior part of the inferior meatus of the nose, under cover 

 of the front part of the inferior concha. Its length is about | inch, 



Lachrymal Gland • ?''<» Semilunaris 



Ladirymal Ducts^ Xfx jt^ ^ „i Superior Punctum Lacrimale 



" ' ' ' ' Caruncula Lacrimalis 



Superior Lachrymal Canal 



A' 



y^^ Lachrymal Sac 



^~ Inferior Lacbrynal 

 Canal 



_ Nasal Duct 



Inferior Punctum Lacrimale . 



Fig. 483. — The Lachrymal Apparatus of the Right Eye. 

 (The Meibomian Glands of the Upper Eyelid are also shown.) 



and its diameter about ^ inch. It is directed downwards, outwards, 

 and backwards, and its opening into the anterior part of the inferior 

 meatus of the nose is usually guarded by an imperfect mucous fold, 

 kno\\'n as the valve of Hasner. The nasal orifice of the duct is about 

 i\ inches from the anterior nasal aperture. 



Structure of the Lachrymal Sac and Nasal Duct. — The wall is composed of 

 fibro-elastic tissue, which adheres closely to the periosteum of the bones, 

 and is covered by mucous membrane. The epithelial hning is of the columnar 

 variety, and at intervals the cells are furnished with ciUa. The mucous 

 membrane is continuous superiorly with the conjunctiva through the lach- 

 r>'mal canaUculi and puncta, and inferiorly it is continuous with the nasal 

 mucous membrane. In the nasal duct it may present one or f:s"o folds. 



Development of the Nasal Duct and its Appendages. — The efferent lachrymal 

 apparatus consists of (i) the lachr>'mal canaliculi, (2) the lachrymal sac, and 

 (3) the na-sal duct. 



In the course of the development of the face, the maxillary' process and the 

 lateral nasal process, of either side, are separated by a groove which extends 



