LACHRYMAL APPARATUS 



869 



and duct and at the lower end of the duct. That at the top of the duct is the most 

 important, as it sometmies mterferes with the proper fiow of tears onT of fW 

 The total length of the lachrymal canal is roughly ^t'4ntv-foLmmimetr^ h.lf f 

 this being sac, and half nasal duct. If, howe^yer ::1^JZ^Tc!te ollue 

 passage through the nasal mucous membrane, this measurement may occastnaHy 

 be mcreased by eight or ten millimetres. The lachrymal sac, whin dfstended 

 measures about six milhmetres from before backwards, by four millimetlis Trans' 

 versely. The nasal duct is practically circular, and has a^ diamete Ja out th?'; 

 milhme res, rather less at its junction witli the sac, where we find the narrowest 

 part of the whole lachrymal canal. me narro\\est 



