812 SPECIAL SENSES. 



which is regarded by some anatomists as a deep portion of the orbicularis. Considering 

 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, closely 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 maxiliary 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. 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 impos- 

 sible to close the eye. 



The levator palpebraB 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 evident action is to raise the upper lid. It is 

 animated 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 relations are shown in Fig. 254 (9, 10, 10), page 808. 



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 mus- 

 cles 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. Nevertheless, we are hardly conscious of an effort in keeping the 

 eyes open, in our waking moments, and we require an effort to close the eyes. During 

 sleep, the eyes are closed and the globes are turned upward. The contractions of the 

 orbicular muscles which take place in winking are usually 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 is usually simultaneous, although 

 we may educate them 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. 



Oonjunctival 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 periph- 

 ery 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 membrane presents a superior and an inferior 

 fold, where it is reflected upon the globe. In the superior conjunctival fold, are numer- 

 ous 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 

 forming a part of the lachrymal gland. At the inner canthus, there is a vertical fold 

 (the plica semilunaris) with a reddish, spongy elevation at its inner portion, called the 

 caruncula lacrymalis. The caruncula presents a collection of follicular glands, with a 

 few delicate hairs on its surface. The conjunctiva is continuous with the membrane of 

 the Jachrymal ducts, of the puncta lacrymalia, and of the Meibomian glands. Beneath the 

 conjunctiva, except in the corneal portion, is a loose connective tissue. 



The palpebral conjunctiva is reddish, thicker than the ocular portion, furrowed, and 

 presents small, isolated papilla near the borders of the lids, which increase in number 



