THE PALPEBRAL REGION 367 



ellipses. The upper fibres of this portion blend with the Occipitofrontalis and 

 Corrugator supercilii. 



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Relations. By its superficial surface, with the integument. By its deep surface, above, with 

 the Occipitofrontalis and Corrugator supercilii, with which it is intimately blended, and with 

 the supraorbital vessels and nerve; below, it covers the lacrimal sac, and the origin of the Levator 

 labii superioris alaeque nasi, the Levator labii superioris, and the Zygomaticus minor muscles. 

 Internally, it is occasionally blended with the Pyramidalis nasi. Externally, it lies on the tem- 

 poral fascia. On the eyelids it is separated from the conjunctiva by the Levator palpebrae, 

 the tarsal ligaments, the tarsal plates, and the Meibomian glands. 



The tendo oculi or internal tarsal ligament (ligamentum palpebrale mediale) is a 

 short tendon, about one-sixth of an inch in length and half as much in breadth, 

 attached to the frontal process of the maxilla in front of the lacrimal groove. 

 Crossing the lacrimal sac, it divides into two parts, each division being attached 

 to the inner extremity of the corresponding tarsal plate. As the tendon crosses 

 the lacrimal sac, a strong aponeurotic lamina is given off from the posterior surface, 

 which expands over the sac, and is attached to the ridge on the lacrimal bone. 

 This is the reflected aponeurosis of the tendo oculi. 



The external tarsal ligament (raphe palpebralis lateralis) is a much weaker struc- 

 ture than the tendo oculi. It is attached to the margin of the frontal process of 

 the malar bone, and passes inward to the outer commissure of the eyelid, where 

 it divides into two slips, which are attached to the margins of the two tarsal plates. 



USE OF TENDO OCULI. Besides giving attachment to part of the Orbicularis 

 palpebrarum and to the tarsal plates, it serves to suck the tears into the lacrimal 

 sac, by its attachment to the sac. Thus, each time the eyelids are closed, the 

 tendo oculi becomes tightened, through the action of the Orbicularis, and draws 

 the wall of the lacrimal sac outward and forward, so that a vacuum is made in 

 the sac, and the tears are sucked along the lacrimal canals into it. 



The Corrugator supercilii (Figs. 288 and 289) is a small, narrow, pyramidal 

 muscle, placed at the inner extremity of the eyebrow, beneath the Occipito- 

 frontalis and Orbicularis palpebrarum muscles. It arises from the inner .extrem- 

 ity of the superciliary ridge, from whence its fibres pass upward and outward 

 between the palpebral and orbital portions of the Orbicularis palpebrarum, 

 and are inserted into the deep surface of the skin, opposite the middle of the 

 orbital arch. 



Relations. By its superficial surface with the Occipitofrontalis and Orbicularis palpebrarum 

 muscles; by its deep surface, with the frontal bone and supratrochlear nerve. 



The Tensor tarsi or Horner's muscle (pars lacrimalis m. orbicularis pal- 

 pebrarum) (Fig. 290) is a small thin muscle about a quarter of an inch in breadth 

 and half an inch in length, situated at the inner side of the orbit, behind the tendo 

 oculi and lacrimal sac. It arises from the crest and adjacent part of the orbital 

 surface of the lacrimal bone, and, passing across the lacrimal sac, divides into two 

 slips, which cover the lacrimal canals and are inserted into the tarsal plates internal 

 to the puncta lacrimal ia. Its fibres appear to be continuous with those of the 

 palpebral portion of the Orbicularis palpebrarum; it is occasionally very indis- 

 tinct. 



Nerves. The Orbicularis palpebrarum, Corrugator supercilii, and Tensor tarsi are supplied 

 by the facial nerve. 



Actions. The Orbicularis palpebrarum is the sphincter muscle of the eyelids. The palpebral 

 portion acts involuntarily, closing the lids gently, as in sleep, or in blinking; the orbicular por- 

 tion is subject to the will. When the entire muscle is brought into action, the skin of the fore- 

 head, temple, and cheek is drawn inward toward the inner angle of the orbit, and the eyelids 

 are firmly closed as in photophobia. When the skin of the forehead, temple, and cheek is thus 

 drawn inward by the action of the muscle it is thrown into folds, especially radiating from the 



