Lacrimal canaliculi

The lacrimal canaliculi, also known as the lacrimal canals or lacrimal ducts, are the small channels in each eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...

 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, and then bends at an acute angle, and passes medialward and downward to the lacrimal sac
  Lacrimal sac
  The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...
  
  .

• The inferior duct at first descends, and then runs almost horizontally to the lacrimal sac
  Lacrimal sac
  The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...
  
  .

At the angles they are dilated into ampullæ.

The lacrimal canaliculi, also known as the lacrimal canals or lacrimal ducts, are the small channels in each eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...

 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, and then bends at an acute angle, and passes medialward and downward to the lacrimal sac
  Lacrimal sac
  The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...
  
  .

• The inferior duct at first descends, and then runs almost horizontally to the lacrimal sac
  Lacrimal sac
  The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...
  
  .

At the angles they are dilated into ampullæ. Microscopically, they are lined by nonkeratinizing stratified squamous epithelium

Stratified squamous epithelium

A stratified squamous epithelium consists of squamous epithelial cells arranged in layers upon a basement membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity...

 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

Sphincter

A sphincter is a structure, usually a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning...

.