The lacrimal apparatus. Right side.
The lacrimal canaliculi, (sing. canaliculus), also known as the lacrimal canals or lacrimal ducts, are the small channels in each eyelid that commence at minute orifices, termed puncta lacrimalia, on the summits of the papillae lacrimales, seen on the margins of the lids at the lateral extremity of the lacus lacrimalis.
- The superior duct, the smaller and shorter of the two, at first ascends, then bends at an acute angle, and passes medialward and downward to the lacrimal sac.
- The inferior duct at first descends, then runs almost horizontally to the lacrimal sac.
At the angles they are dilated into ampullæ. Able to be seen under a microscope, they are lined by nonkeratinizing stratified squamous epithelium surrounded by fibrous tissue.
Outside the latter is a layer of striped muscle, continuous with the lacrimal part of the Orbicularis oculi; at the base of each lacrimal papilla, the muscular fibers are circularly arranged and form a kind of sphincter.