Volume 3

Quain's elements of anatomy / edited by Edward Albert Schäfer and George Dancer Thane.

Date:
1895-1898
Catalogue details

Licence: Public Domain Mark

Credit: Quain's elements of anatomy / edited by Edward Albert Schäfer and George Dancer Thane. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    is directed inwards and slightly downwards for 6 to 7 mm. to join the lachrymal sac |fig. The lower canal descends, from the corresponding punctum andjhen takes a nearly horizontal course inwards. Both canals are smallest at the punctum, Fig. 10.—Section op the eyklids, passing along THE LACURYMAL CANALS, ((jerlftcli.) Magiiilied. c, inner caiithus of eye ; s.c, i.e., superior ami inferior canals respectively; l.s., lachrymal sac; orb., fibres of orbicularis muMle. r S M St-' and here they are a little wider at the njouth than at the base of the papilla lacrimalis, where they only measure Q-l mm. in diameter ; they then become enlarged and present a further enlarge- ment at the bend, where each has a marked dilatation, enlargiiig_ta, LfflHi- diameter or more (fig. 10). The bend is sharper m the embryo than in later life. From this the horizontal limb passes off as a neai;]j cylindrical tube of about 0;6..uun. diameter, gradually naiTowing to half that size. A part of the orbicularis palpebrarum (mrs lacrmalis, iet^sx 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. Tig, 11. —Section showing THK COURSE AND RELA- TIONS OP THE NASAL SAC ASD DUCT. (Slightly modified from Merkel.) Zcicht-ffntat ocinods ^ JfoiscU- •sac- pifiei'jiaZflebra.Z Corzeha. Concha^ 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 lachxmialsat: (fig.!), 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_enibeddcd.in a deep gi'oove in the lachrymal and superior maxillary bones, from which it is separated by athin 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^lo.gg, and about^ 5_or.iLiaia. wide, and is sometimes narrower below where it passes into the nasal duct. Its