538 ^STHESIOLOGY. 



The Superior Oblique muscle is situated at the side of the 

 internal and superior recti. It arises from near the optic 

 foramen, and is directed forwards against the internal wall of 

 the cavity, passing through a cartilaginous loop at the base of 

 the orbital process of the frontal bone, near the inner canthus, 

 whence it is directed backwai:ds, and under the terminal extremity 

 of the superior rectus, to become inserted to the sclerotic, between 

 the superior and external recti. The action of this muscle is to 

 elevate and rotate the eyeball. 



The Inferior or Lesser Oblique arises from the lachrymal 

 fossa, is carried obliquely outwards, and is inserted to the sclerotic 

 between the external and inferior recti muscles. Its action being 

 to depress and turn the eye inwards, is antagonistic to that of 

 the superior oblique muscle. 



Professor Turner has described a non-striated mass of muscular 

 fibres connected with the periosteum of the orbit. (See Appen- 

 dix III.) 



appendages of the eye. 



The accessory parts or appendages of the eye, are the eyebrows, 

 eyelids, membrana nictitans, conjunctiva, caruncula lachry- 

 malis, lachrymal apparatus, and ocular sheath. 



The Eyebrows, very rudimentary in the horse, are the emin- 

 ences formed by the orbital processes of the frontal bone. They 

 are furnished with a few long hairs, and serve to interrupt the 

 too vivid rays of light, and prevent foreign bodies from descending 

 into the eyes. 



The Eyelids are the two moveable curtains, superior and 

 inferior, which protect the eye. Both are capable of expansion 

 and contraction, though the superior is the larger and more 

 movable of the two. When drawn apart, they form an elliptical 

 opening, the angles of which are termed the canthi. The outer 

 canthus, or temporal angle, is acute ; the inner canthus, or nasal 

 angle, is more obtuse or rounded, and it contains the caruncula 

 lachrymalis. The external surface of the eyelids is covered with 

 fine short hairs ; the internal surface is smooth, lined by the 

 conjunctiva, a continuation of the skin modified, and is in contact 

 with the globe of the eye. Their free borders are thick, and on 

 their margins are rows of long hairs, the eyelashes, or cilia,. 

 which serve to prevent the intrusion of foreign bodies. The 

 ciliary borders of the lids also present a series of minute openings^ 

 ■which are the ducts of the Meibomian glands. 



