76 Lachrymal Apparatus 



have a characteristic, hour-glass shape, on account of its bulging above 

 and below the tendo oculi, while its middle is constricted by the un- 

 yielding tendon. 



A lachrymal fistula may follow its evacuation ; stricture of the 

 nasal duct, the result of chronic inflammatory thickening, is generally 

 associated with the fistula. The treatment of the stricture consists 

 in slitting up the inferior lachrymal canal, and thus finding an entrance 

 for a special probe into the sac. Before slitting up the canal, the 

 lower lid should be drawn firmly outwards so that the canal may be 

 made straight and direct. False passages may be made by the unscien- 

 tific use of the probe, through the lachrymal bone and into the ethmoid, 

 or between the cheek and the maxilla. 



The nasal duct, in. long, descends in the groove in the maxillary 

 and the lachrymal bones, and against the inferior turbinated, to open 

 into the inferior meatus. Its direction is downwards, with a slight in- 

 clination outwards and backwards ; it is the unobliterated part of the 

 orbital fissure (v. p. 123) which ran from the side of the fronto-nasal 

 process through the mouth and into the orbit. 



The sac and the duct are composed of fibrous tissue, and have a 

 mucous lining which is carpeted with columnar ciliated epithelium, like 

 that of the nose. 



THE ORBIT 



The long axes of the orbits diverge considerably, so that the field 

 of vision may be extended laterally. The inner wall is straight from 

 before backwards, but the outer wall runs outwards as well as forwards ; 

 this slope is taken advantage of in enucleation of the eye-ball, the curved 

 scissors being passed along the outer wall so as more easily to divide 

 the optic nerve. 



Boundaries. The floor is formed of the superior maxilla and the 

 malar and palate bones ; the roof by the frontal and the lesser wing 

 of the sphenoid. 



The inner wall is composed of the nasal process of the maxilla, 

 the internal angular process of the frontal, lachrymal, os planum of 

 ethmoid, and body of sphenoid ; and the outer wall of the malar, the 

 external angular process of the frontal, and the great wing of the 

 sphenoid. 



The roof is extremely thin, and if a child fall with a pencil upright 

 in his hand the point may be driven through into the anterior lobe of 

 the brain. In chronic hydrocephalus (p. 56) the fluid within the lateral 

 ventricles pushes down the frontal lobes and the roofs of the orbits 

 until they bulge into the orbits and thrust forwards the eye-balls. The 

 inner wall is also thin, and in roughly attempting to introduce a style 

 into the nasal duct a clumsy manipulator may thrust it into the ethmoid 



