MUSCLES OF THE EYEBALL. 303 



cause the skin of the forehead to descend, the lower ones elevate 

 the integuments of the cheek. Like the other sphincters, this 

 is a mixed muscle. The fibres which are supposed te be the 

 proper voluntary portion, are those which correspond to the 

 margin of the orbit, and are of a red color. The involuntary 

 fibres, form the thin portion which covers the lids, (musculus 

 ciliaris of Albinus,) and are of a pale color, like the muscles 

 of organic life. They contract involuntarily while we are awake, 

 in the action of winking, and during sleep in maintaining the 

 lids closed. 



The ciliaris of some authors is only a part of this muscle 

 covering the cartilages of the eyelids, called cilia or tarsi. 



There is often a small fleshy strip, which runs down from 

 the outer and inferior part of this muscle above the zygomati- 

 cus minor, and joints with the levator labii superioris alaeque 

 nasi. 



2. Levator Palpebrce Superioris, 



Arises from the upper part of the foramen opticum of the 

 sphenoid bone, through which the optic nerve passes, above the 

 levator oculi, near the trochlearis muscle. 



Inserted, by a broad thin tendon, into the cartilage that sup- 

 ports the upper eyelid, named tarsus. 



Use. To open the eye, by drawing the eyelid upwards ; 

 which it does completely, by being fixed to the tarsus, pulling 

 it below the eyebrow, and within the orbit.*' 



Muscles of the Eyeball 



The muscles which move the globe of the eye are six, viz : 

 four straight, and two oblique. 



The four straight muscles very much resemble each other : all 



Arising by a narrow beginning, a little tendinous and fleshy, 



from the bottom of the orbit around the foramen opticum of 



the sphenoid bone, where the optic nerve enters, so that they 



* There is no antagonist muscles provided especially to depress the lower lid. 

 Its depression is effected, according to the suggestion of Sir C. Bell, by the pro- 

 trusion of the eyeball. p. 



