CONJUNCTIVAL MUCOUS MEMBRANE. 725 



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, closely attached to 

 the skin, surrounding the free margin of the lids, and extending a short dis- 

 tance 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 angular 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. 



The levator palpebrae 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 cartilage. 

 Its action is to raise the upper lid. This muscle and its relations are shown 

 in Fig. 259 (9, 10, 10), page 718. 



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 ; although when the will ceases to act the lids are closed. Never- 

 theless there is hardly a conscious effort usually in keeping the eyes open, 

 and an effort is required to close the eyes. During sleep the eyes are closed 

 and the globes are turned upward. The contractions of the orbicular mus- 

 cles which take place in winking usually are involuntary. This act occurs at 

 short intervals, and it is useful in spreading the lachrymal secretion over the 

 exposed portions of the globes. The action of both sets of muscles usually is 

 simultaneous, although they may be educated so as to close one eye while the 

 other is kept open. The action of the orbicularis is so far removed from the 

 control of the will, that when the surface of the globe is touched or irritated 

 or when the impression of light produces intense pain, it is impossible to keep 

 the eye open. 



Conjunctival Mucous Membrane. The entire inner surface of the upper 

 and lower eyelids is lined by a mucous membrane, which is reflected forward, 

 from the inner periphery of the lids, over the eyeball. The membrane lining 

 the lids is called the palpebral conjunctiva, and that covering the eyeball, the 

 ocular conjunctiva. The latter presents a sclerotic and a corneal portion. 

 The conjunctiva presents a superior and an inferior fold, where it is reflected 

 upon the globe. In the superior conjunctival fold, are glandular follicles, or 

 accessory lachrymal glands, which secrete a certain portion of the fluid which 

 moistens the surface of the eyeball. These are generally described as form- 

 ing a part of the lachrymal gland. At the inner can thus there is a vertical 

 fold, the plica semilunaris, with a reddish, spongy elevation at its inner por- 

 tion, called the caruncula lacrymalis. The caruncula presents a collection of 



