DISSECTION OF THE HEAD AND NECK. 175 



muscle — the levator palpebi-pe superioris. Of these, the skin and con- 

 junctiva have already been sufficiently noticed. 



The Orbicularis Palpebrarum (Fig. 19, page 161). This muscle will 

 be exposed by removing the layer of skin from the eyelids, and from 

 around the orbital rim for the breadth of an inch. The fibres of the 

 muscle are closely adherent to the skin of the eyelids, and have a 

 circular or elliptical disposition around the palpebral fissure. Below the 

 nasal canthus a number of the fibres are inserted by a slender tendon 

 into the lachr^-mal tubei'cle on the bone of the same name, but for the 

 most part the fibres are without bony attachment. Above the orbit the 

 muscle is confounded witli some thin fibres — the corrugator su2yercilii — 

 which wrinkle the overlying skin. 



Action. — The orbiculai-is muscle closes the eye by approximating the 

 free edge of the eyelids, and in this action the upper lid has a much 

 wider range of movement than the lower. 



The Palpebral Tendon. This is a fibrous layer which w'ill be 

 exposed by removing the orbicularis muscle. At the free edge of the 

 eyelid it is margined by the tarsal cartilage, while by its opposite border 

 it is fixed to the rim of the orbit. 



The Tarsal Cartilage. This is a slender rod of elastic cartilage 

 imbedded in the free edge of each eyelid. The meibomian glands lie in 

 grooves on its ocular surface. It prevents the margins of the lids from 

 being drawn, or puckered, when the ox'bicular muscle contracts. 



The Levator Palpebr.e Superioris. This muscle is found in the 

 upper eyelid only. The fleshy portion of the muscle is a slender flat 

 fasciculus which takes origin at the back of the orbit (Fig. 22, page 209) 

 above the optic foramen, where it will subsequently be exposed along 

 with the other contents of the cavity. Passing along the eyeball and 

 beneath the lachrymal gland, it is succeeded by a thin flat tendon which 

 in the lid is placed beneath the palpebral tendon, and joins the tarsal 

 cartilage. 



Action. — To open the eye by raising the upper lid. In this move- 

 V- rri^it the muscle plays over the eyeball like a rope over a pulley. The 

 lower lid, it is to be observed, has no analogous muscle, because, in the 

 first place, it is raised but slightly under the action of the orbicularis, 

 and, secondly, because its own weight and elasticity are sufficient to 

 depress it. 



Vessels. The arteries of the eyelids are derived from the supra- 

 orbital and lachrymal arteries, and from the orbital branch of the 

 superior dental artery. 



The Supra-Orbital Artery will be found emerging from the orbit 

 by the supra-orbital foramen. It is a branch of the ophthalmic 

 artery. 



The Lachrymal Artery is also a branch of the ophthalmic, and is 



