MUSCLES OF THE EYE. 519 



the postorbital process of the frontal (Fig. 56, Pro. po.). To demon- 

 strate these bands, draw the eyeball laterad and pull upon the 

 fibro-cartilaginous pulley. The tense lines show the direction of 

 the bands and serve as guides in isolating them. Continue to draw 

 the ball laterad and isolate the tendon of the M. trochlearis after it 

 passes the pulley. Draw it taut and it will be seen to pass directly 

 laterad toward the eyeball. It passes entad of the M. levator pal- 

 pebrse and then expands into a thin sheet which is inserted into the 

 eyeball at right angles to the insertion of the dorsal rectus, as the 

 ventral oblique is inserted into the ball at right angles to the lateral 

 rectus ( 1406). 



1412. MM. choanoidei, s. M. choanoideus, s. MM. recti 

 xninores, s. MM. recti posteriores, s. M. suspensor oculi. These 

 are four straight muscles like the recti proper, but smaller. They 

 may be demonstrated by separating the recti muscles. They will 

 be seen to alternate with the recti as they extend along the eyeball 

 to their insertion, which is by a broad, thin tendon near the middle 

 of the eyeball. This is true of all but the ventral (inferior) one, 

 whose tendon, like those of the recti, is inserted into the edge of the 

 white zone of the sclerotic (Fig. 126). 



1413. Origin of the Muscles of the Eye. All of the muscles 

 of the eye described above, except the ofbicularis palpebrarum 

 ( 1404) and the obliquus ventralis ( 1406), arise in a circle sur- 

 rounding the optic nerve at its exit from the skull, thus forming for 

 it a muscular sheath. 



The levator palpebrce dorsalis arises near the sutura fronto- 

 orbito-sphenoidea, dorsad of the origin of the dorsal rectus, which 

 arises very near the foramen opticum. 



The trochlearis is in like manner ectad of the mesal rectus. 



The lateral rectus passes between the tendon of the ventral rec- 

 tus and the combined tendon of the choanoid muscles to be inserted 

 into the septum between the optic and anterior lacerated foramina. 



The ventral rectus arises from the lateral and ventral aspects of 

 the foramen lacerum anterius, and just ectad of its origin is the 

 common tendon of the four choanoid muscles (Fig. 126). 



In determining the origin of the muscles, the connections of the 

 eyeball should be so far separated from the socket that one may 

 work in any part of the orbital fossa without difficulty. 



1414. Action of the Muscles of the Eye. With the recti this is probably as in 

 man, viz. , that they move the eye in the direction of the four cardinal points according to 



