140 SPECIAL SENSES. 



sidering this as a distinct muscle, it consists of two delicate 

 slips, which pass from either eyelid behind the lachrymal sac, 

 uniting here to go to its attachment at the posterior portion 

 of the lachrymal bone. When this acts with the orbicularis, 

 it compresses the lachrymal sac. 



The orbicularis palpebrarum is a broad, thin muscle, close- 

 ly attached to the skin, surrounding the free margin of the 

 lids, and extending a short distance over the bones, beyond 

 the margin of the orbit. This muscle may be described as 

 arising from the tendo palpebrarum, the surface of the nasal 

 process of the superior maxillary bone, and the internal an- 

 gular process of the os frontis. From this origin at the inner 

 angle of the eye, its fibres pass elliptically around the fissure 

 of the lids, as above indicated. Its action is to close the lids. 

 In the ordinary, moderate contraction of this muscle, only 

 the upper lid is moved ; but, in forcible contraction, the lower 

 lid moves slightly and the lids are drawn toward the nose. 

 In facial palsy, or when the temporo-facial branch of the 

 portio dura of the seventh nerve is paralyzed, this muscle 

 cannot act, and it is impossible to close the eye. 



The levator palpebrse superioris is situated within the 

 orbit. It arises from a point a little above and in front of 

 the optic foramen at the apex of the orbit, passes forward 

 above the eyeball, and spreads into a thin tendon, which is 

 inserted into the anterior surface of the superior tarsal carti- 

 lage. Its evident action is to raise the upper lid. It is ani- 

 mated by filaments from the third pair of cranial nerves ; 

 and, when this nerve is paralyzed, we have permanent falling 

 of the upper lid, or blepharoptosis. This muscle and its re- 

 lations are shown in Fig. 8, page 131. 



In the act of opening the eyes, the levator muscles alone 

 are brought into play. Closing of the lids is accomplished 

 by the orbicular muscles. Both of these sets of muscles act 

 to a great extent without the intervention of the will. The 

 eyes are kept open almost involuntarily, except in extreme 

 fatigue; though, when the will ceases to act, the lids are 



