KYI;. 



EYE. 



cellular tissue there is a broad layer of muscular fibres arranged 

 elliptically round the transverse fissure of the eyelids, the disposi- 

 tion of which is well shown in fiy. 12. The office of this muscle, 

 which is called the orbicularis, is to close the lids; and it is 

 capable of acting under certain circumstances with great force. It 

 ia collected at the inner angle or canthus of the eye into a round 

 short tendon, which is attached in that situation to the bone. Else- 

 where it is connected with the skin and aponeurotio expansions of 

 the face and forehead. It is also connected with the occipito-frontalis 

 muscle, which elevates the eye-brows and with the corrugator 

 supercilii, which wrinkles and knits them in the act of frowning. A 



View of the left eyebrow and lids, showing their tarsal margins. 



a, lower punctum lachrymale ; 6, tarsal edge of the upper lid ; r, orifices of 

 the ducts of the Meibomiun glands (those on the upper lid are similar) ; 

 (/, caruncle, situated at the inner canthus, or corner of the eye. 



The double line of points external to the Mcibomian orifices marks the 

 situation of the eyelashes, which are removed. 



Fig. 12. 



View of the orbicular muscle of the left eyelid, as it appears when denuded 

 of the integuments. 



a, the tendon at the inner angle, or canthus of the eye ; >>, the outer canthus 

 drawn in by the ligamcntous attachment of the tarsal cartilage to the temporal 

 tide of the orbit. 



Fig. 13. 



View of the internal surface of the right eyelid and lachrymal gland. 

 a, conjunctiva propria, or mucous lining of the lid. The edges of the fold 

 which passes to the sclerotic are seen loose and floating ; b, lachrymal gland ; 

 f, orifice* of the lachrymal ducts ; <l, tendon of the elevator muscle of the upper 

 lid ; e t, parallel rows or clusters of the Meibomian glands ; /, the semilunar 

 fold of the conjunctiva at the inner canthus, which is the rudiment of the third 

 eyelid of birds and other animals. Near /, on the right, are seen the two 

 puncta lachrymalia. 



person acquainted with mechanics will have no difficulty in perceiving 

 the advantage derived from the oblique, or, as it might almost be 

 called, the incidental action of the orbicularis in closing the lids, to 

 the edges of which its fibres are parallel. A more direct application 

 of muscular force would have been more powerful ; but the actual 

 arrangement secures a rapidity incomparably more conducive to the 

 function of the eyelids, which is to cleanse and moisten the surface 

 of the eye. 



Levator Palpebrse Superioris. Below the orbicularis, in the upper 

 lid, is the broad tendon of the muscle which elevates the upper lid. 

 (Fiys. 13, d ; 10, y.) This muscle arises from the edge of the optic 

 foramen, just above the rectus superior, aud passing over it along the 

 roof of the orbit, forms the thin tendon we have mentioned, which 

 is inserted into the inner surface or rather the thiu upper edge of 

 the taraal cartilage. There is no such provision for depressing the 

 lower lid, which is rendered unnecessary by its inferior extent. 

 Moreover the muscle we have just described sufficiently answers the 

 purpose, by pressing down the globe, and causing it to slide a little 

 forwards ; as may be easily felt if a finger be placed against the lower 

 lid when the eye is close, and suffered to remain while the upper lid 

 is slowly raised. 



Meibomian Glands. (Fig. 13, e, e). Between the tarsus of either 

 lid and the conjunctiva are disposed numerous vertical rows ol 

 minute whitish grains, which appear through the semi-transparent 

 mucous membrane, and occupy an elliptic space, taking both lids 

 together, of about half an inch in width, exactly in front of the 

 globe. These are called the Meibomian glands, from their discoverer. 

 They secrete an unctuous matter which passes into tubes centrally 

 placed in each row, and exudes from as many minute orifices on 

 the ciliary margin of the lid. (Fig. 11, c). There are about forty of 

 these parallel clusters in the upper lid : in the lower there are not 

 so many, nor are they individually so long. We need not dilate 

 upon the use of this secretion, which often collects in a sensible 

 quantity upon the edges of the lids during sleep, especially when 

 the glandular action is excited by slight inflammatory irritation of 

 the part. The palpebral conjunctiva, already described, immediately 

 covers these glandular corpuscles. The caruncle, a small red 

 prominence at the inner angle of the eye (fir/. 11, d) consists of a 

 number of similar bodies. 



Lachrymal Apparatus. (Figs. 13, 14). At the upper and outer 

 part of the interior of the eyelid are several minute orifices (jiy. 13, 

 c), generally seven in number, arranged in a half circle, which lead 

 into the secretory ducts of the. lachrymal gland. (Figs. 13, b; 14, e.) 

 This is a white flattened lobulated body, of the size of a large bean, 

 lodged in a depression just within the margin of the orbit, and 

 covered externally by the orbicular muscle. The function of this 

 gland is to secrete the tears ; and is probably always going on, 

 although not in a degree sufficient to be remarked, except in weeping, 

 or when some foreign body or acrid vapour stimulates the surface or 

 the eye, and by sympathy excites the gland to unusual secretion. 



Fi K . H. 



a, the two puncta feading into the lachrymal ducts ; b, the common entrance 

 of these ducts into the lachrymal sac ; c, the head of the lachrymal sac ; rf, the 

 narrow portion of the sac, or membranous lachrymal canal passing downwards 

 to the nose ; e, the lachrymal gland. 



The involuntary actions of the rectus externus and inferior oblique 

 muscles, to which we have alluded, are supposed to have a relation 

 to the lachrymal secretion. In the act of winking, the eye-ball is 

 thrown up in an outward direction, as it would be by the action of 

 these muscles, which not only brings the cornea into the vicinity of 

 the ducts, but makes pressure upon the gland, while it relatively 

 increases the rapidity with which the lids, drawn in winking towards 

 the fixed nasal tendon are swept over the surface of the globe. That 

 there is such a movement however produced is certain : the motion 

 of the prominent cornea may be felt by the finger gently pressed 

 upon the half-shut lid if it be completely and suddenly closed. The 

 approximation of the lids towards the nose in winking is one of 

 several provisions by which offending particles or superfluous fluids 

 are brought to the inner canthus of the eye to be protruded or 



