The anatomy and diseases of the lachrymal passages / by W. Spencer Watson.

  • Watson, W. Spencer (William Spencer), 1836-1906.
Date:
1892
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Licence: Public Domain Mark

Credit: The anatomy and diseases of the lachrymal passages / by W. Spencer Watson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    The functions of the orbicularis and tensor tarsi (Horner's muscle) in relation to the lachrymal passages. The circumferential or orbital division of the orbicularis has no relations to the lachrymal sac, and can only in extreme and forcible closing of the eyes have any influence in directing the tears towards it. In the ordinary automatic winking movements of the eyelids its two other divisions play an important part. The automatic movements, though ordinarily unnoticed, are constantly going on at short intervals. Their chief object is that of clearing the surface of the eye from the tears which would otherwise accumulate or overflow. While the edges of the closing lids (chiefly the upper) sweep the tears downwards and inwards, the movement of the inner end of the tarsus to- wards the nose and the lifting forwards of the tendo patyebarum cause a dilatation of the lachrymal sac. At the same moment the puncta are drawn inwards and immersed in the fluid in the lacus lachrymalis. The result is that the tears pass into the canaliculi and thence into the sac. The capillarity of the cana- liculi and the suction power of the dilating sac are the two forces which induce the downward flow of the tears. (See Dia- grams on Plate figs. 2 and 3). The anterior lachrymal muscle has the chief influence in closing the lids and drawing them towards the inner canthus. The act of closing them also brings them forwards, and with them the tendo palpebrarum. This movement necessitates the ad- vance of the anterior and inner wall of the lachrymal sac, and is the source of its dilatation and consequent suction powers, which can produce only a downward flow. An upward flow from the nasal fosses is prevented by the valvular folds in the sac and duct, and especially by the valvular termination of the nasal duct in the inferior meatus. It has been proved experimentally that neither water nor air can be forced upwards from the nose through the normal nasal duct into the lachrymal sac. The opening of the eyelids restores the tendo palpebrarum to its naturally depressed position be- tween the inner canthus and the nasal process of the superior maxillary bone, and with it the exterior wall of the sac recedes. These movements are brought about by the contraction of the tensor tarsi which also compresses the sac, when it is distended, and forces its contents downwards.