THE LACHRYMAL APPARATUS. 



is directed inwards and slightly downwards for 6 to 7 mm. to join the lachrymal sac 

 (fig. 11). The lower canal descends from the corresponding punctum and then 

 takes a nearly horizontal course inwards. Both canals are smallest at the punctum, 



Fig. 10. SECTION OF THE EYRLIDS, PASSING ALONG 

 THE LACHRYMAL CANALS. (Grerlach. ) Magnified. 



c., inner canthus of eye ; s.c., i.e., superior anil 

 inferior canals respectively ; l.s. , lachrymal sac ; 

 orb., fibres of orbicularis muscle. 



and here they are a little wider at the 

 mouth than at the base of the papilla 

 lacrimalis, where they only measure 

 O'l mm. in diameter ; they then become 

 enlarged and present a further enlarge- 

 ment at the bend, where each has a 

 marked dilatation, enlarging to 1 mm. 

 diameter or more (fig. 10). The bend is 

 sharper in the embryo than in later life. 

 From this the horizontal limb passes off 



as a nearly cylindrical tube of about 0*6 mm. diameter, gradually narrowing to 

 half that size. A part of the orbicularis palpebrarum (pars lacrimalis, tensor 

 tarsi) runs parallel to the horizontal limbs, which are embraced by some of the 

 muscular fibres, and when the orbicularis contracts the canals may be compressed by 

 these fibres (Merkel). The canals either unite near their end, or they open 

 separately, but close together, into a diverticulum of the nasal sac which is known 

 as the sinus of Maier. 



Fig. 11. SECTION SHOWING 



THE COURSE AND RELA- 

 TIONS OF THE NASAL SAC 

 AND DUCT. (E. A. S., 



slightly modified from 

 Merkel.) 



Zcichrr/mal canals ;/'" 



^ 





The mucous mem- 

 brane in the canaliculi 

 is lined by a stratified 

 scaly epithelium set on 

 a corium rich in elastic 

 fibres. 



The lachrymal sac 

 and nasal duct con- 

 stitute together the 

 passage by which the 

 tears are conveyed from 

 the lachrymal canals to 

 the cavity of the nose. 

 The lachrymal sac (fig. 9, 



2 ; fig. 11), the slightly dilated upper or orbital portion of the passage, is situated at 

 the side of the nose, near the inner canthus of the eye, and lies embedded in a deep 

 groove in the lachrymal and superior maxillary bones, from which it is separated by 

 a thin layer of the orbital periosteum. When distended with tears it forms a distinct 

 swelling here at the side of the nose. It is about 15 mm. long, and about 5 or 6 mm. 

 wide, and is sometimes narrower below where it passes into the nasal dnct. Its 



