The lacrimal part ( tensor tarsi ) is a small, thin muscle, about 6 mm in breadth and 12 mm in length, situated behind the medial palpebral ligament and lacrimal sac.
12.
As the ligament crosses the lacrimal sac, a strong aponeurotic lamina is given off from its posterior surface; this expands over the sac, and is attached to the posterior lacrimal crest.
13.
On the cheek it distributes branches which anastomose with the infraorbital; after supplying the lacrimal sac and Orbicularis oculi, it ends by anastomosing with the dorsal nasal branch of the ophthalmic artery.
14.
The lacrimal part of the Orbicularis oculi draws the eyelids and the ends of the lacrimal canals medialward and compresses them against the surface of the globe of the eye, thus placing them in the most favorable situation for receiving the tears; it also compresses the lacrimal sac.
15.
The lateral margin of the groove is named the anterior lacrimal crest, and is continuous below with the orbital margin; at its junction with the orbital surface is a small tubercle, the lacrimal tubercle, which serves as a guide to the position of the lacrimal sac.
16.
Each time the eyelids are closed through the action of the Orbicularis, the medial palpebral ligament is tightened, the wall of the lacrimal sac is thus drawn lateralward and forward, so that a vacuum is made in it and the tears are sucked along the lacrimal canals into it.
17.
It arises from the posterior crest and adjacent part of the orbital surface of the lacrimal bone, and passing behind the lacrimal sac, divides into two slips, upper and lower, which are inserted into the superior and inferior tarsi medial to the puncta lacrimalia; occasionally it is very indistinct.
18.
On the face, some branches pass upward to the medial angle of the orbit and the lacrimal sac, anastomosing with the angular artery, a branch of the facial artery; others run toward the nose, anastomosing with the dorsal nasal branch of the ophthalmic artery; and others descend between the levator labii superioris and the levator anguli oris, and anastomose with the facial artery, transverse facial artery, and buccal artery.
19.
The " upper border " articulates with the frontal bone and the " anterior " with the nasal; the " posterior border " is thick, and hollowed into a groove, which is continuous below with the lacrimal groove on the nasal surface of the body : by the articulation of the medial margin of the groove with the anterior border of the lacrimal a corresponding groove on the lacrimal is brought into continuity, and together they form the lacrimal fossa for the lodgement of the lacrimal sac.
