THE ORBITAL REGION. 



303 



The palpebral portion acts involuntarily, closing the lids gently, as in sleep or in 

 blinking ; the orbicular portion is subject to the will. When the entire muscle is 

 brought into action, the skin of the forehead, 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 outer 

 angle of the eyelids, which give rise in old age to the so-called " crow's feet." The 

 Levator palpebrse is the direct antagonist of this muscle ; it raises the upper eyelid 

 and exposes the globe. The Corrugator supercilii draws the eyebrow downward 

 and inward, producing the vertical wrinkles of the forehead. It is the " frowning " 

 muscle, and may be regarded as the principal agent in the expression of suffering. 

 The Tensor tarsi draws the eyelids and the extremities of the lachrymal canals 

 inward 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 serves, 

 also, to compress the lachrymal sac. 



4. Orbital Region (Fig. 197). 



Levator palpebrae superioris. Rectus internus. 



Rectus superior. Rectus externus. 



Rectus inferior. Obliquus oculi superior. 



Obliquus oculi inferior. 



Dissection. To open the cavity of the orbit, remove the skull-cap and brain ; then saw 

 through the frontal bone at the inner extremity of the supraorbital ridge, and externally at its 



FIG. 197. Muscles of the right orbit. 



junction with the malar. Break in pieces the thin roof of the orbit by a few slight blows 

 of the hammer, and take it away; drive forward the superciliary portion of the frontal bone by 

 a smart stroke, but do not remove it, as that would destroy the pulley of the Obliquus 

 superior. When the fragments are cleared away, the periosteum of the orbit will be exposed ; 

 this being removed, together with the fat which fills the cavity of the orbit, the several muscles 

 of this region can be examined. The dissection will be facilitated by distending the globe 

 of the eye. In order to effect this, puncture the optic nerve near the eyeball with a curved 

 needle, and push the needle onward into the globe ; insert the point of a blowpipe through 

 this aperture, and force a little air into the cavity of the eyeball ; then apply a ligature round 

 the nerve so as to prevent the air escaping. The globe being now drawn forward, the muscles 

 will be put upon the stretch. 



The Levator palpebrae superioris is thin, flat, and triangular in shape. It 

 arises from the under surface of the lesser wing of the sphenoid, above and in 

 front of the optic foramen, from which it is separated by the origin of the Superior 

 rectus. At its origin it is narrow and tendinous, but soon becomes broad and 



