MUSCLES AND PARTS CONNECTED WITH THE EYE 177 



extent as the animal might wish or require ; therefore 

 the eye is furnished with two other muscles, whose 

 entire office is to turn it. They are placed obliquely, 

 and in consequence are called the oblique muscles. 

 The upper one, a b, is curiously constructed. It 

 emanates from the back part of the orbit, and follows 

 a direction upwards and towards the inner side, and 

 there, immediately under the ridge of the orbit, it 

 passes through a perfect mechanical pulley, and 

 turning round takes a direction across the eye, and is 

 inserted a little beyond the middle of the eye, and 

 towards the outer side. Thus the globe of the eye 

 is evidently directed inward and upward. This is 

 not all which is accomplished by this remarkable 

 mechanism. That the eye may be completely de- 

 fended, it is sunk deep in the orbit, but it may be 

 occasionally requisite to bring the eye forward and 

 enlarge the field of vision. Under the influence of 

 fear the eye is positively protruded, and it is not only 

 forced more forward, but the lids are opened more 

 widely. It may be asked, how can this be possibly 

 accomplished ? The remarkable pully-muscle, or 

 trochlearis, at b c, readily effects this, while the 

 straight muscles at the same time do not oppose it, 

 or only regulate the direction of the eye, it is really 

 brought forward. The lower oblique muscle has its 

 insertion just within the lachrymal-bone, n, and pro- 

 ceeding across the eye is fixed into part of the sclero- 

 tica, opposite to the other oblique muscle, and turns 

 the eye in an opposite direction, and also assisting the 

 upper oblique muscle in bringing the eye forward 

 from its socket. 



There is another beautiful provision preventing 

 impurities or insects from being carried to and lodging 

 in the corner of the eye, which would, if allowed to 



M 



