352 THE NERVES OF THE MUSCLES OF THE EYE. 



brarum, and its nasal portion is described as adhering 

 closely to the lachrymal sac. 



Function. According to Homer, it dilates the lach- 

 rymal sac, thus producing a vacuum by which, through 

 atmospheric pressure, the tears are constantly propelled 

 into it. Another use is also assigned it, i. e., of keeping 

 the eyelids in contact with the ball. 



Fascia of Muscles. The muscles of the orbit are sur- 

 rounded by a distinct fascia, called the ocular fascia, which 

 separates them from the ball of the eye. It is loose upon 

 the ball, and represented by Mr. Ferrall as having six 

 openings for the passage of the^ tendons of the several 

 muscles, which play through it as so many pulleys. Its 

 use is supposed to be to protect the ball of the eye from 

 the action of the muscles, and to connect and retain all 

 these muscles in their proper relations. 



Combined action of Muscles. When the recti muscles act 

 in pairs, the eye is rolled in the diagonal of their action, 

 as upward and inward, downward and inward, upward 

 and outward, downward and outward. The two oblique, 

 acting conjointly, draw the eye forward-. 



THE NERVES OF THE MUSCLES OF THE EYE. (Fig. 101.) 



These comprise the third, fourth, and sixth, which are 

 motor nerves, with the first or ophthalmic division of the 

 fifth, which is a nerve of sensation. 



These nerves, entering the orbit through the foramen 

 lacerum superius, as described under the head of cerebral 

 nerves, are distributed as follows : The third pair, or mo- 

 tores oculorum, divides. into a superior and inferior branch. 

 The superior is the smaller of the two, and, going between 

 the two heads of the rectus externus muscle, over the optic 

 and nasal nerves, is distributed to the rectus superior, and 

 levator palpebrce muscle. The inferior or larger branch 

 passes to the outside and below the optic nerve, then sep- 

 arating into three branches, is distributed to the inferior 

 rectus, the rectus internus, and inferior oblique muscle. 



