58 



DISSECTION OF THE ORBIT. 



Between the heads of origin of the external rectus, the different nerves 

 before mentioned are transmitted into the orbit, viz., the third, the nasal 

 branch of the fifth, and the sixth, together with the ophthalmic vein. 



Action. The four recti muscles, attached to the eyeball at opposite 

 sides in front of the transverse diameter, are able to turn the pupil in 

 opposite directions. 



The inner and outer recti move the ball horizontally around a vertical 

 axis, the former directing the pupil towards the nose and the latter towards 

 the temple. 



Fi". 12. 



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THIRD VIEW OF THK OKBIT (Illustrations of Dissections). 

 Nerves : 



Mustcles : 



a.. Upper rectus and levator palpebrse thrown 

 back together. 



b. External rectus. 



c. Inferior rectus. 



d. Internal rectns. 



/. Upper oblique cut, showing the insertion. 

 h. Insertion of inferior oblique. 



1. Upper branch of the hird. 



2. Sixth nerve. 



3. Inferior oblique branch of the third. 



4. Branch of third to inferior rectus. 



5. Brunch of third to internal rectus. 



The upper and lower recti elevate and depress the fore part of the ball 

 around a transverse axis ; but as their fibres are directed obliquely out- 

 wards, the upper muscle turns the pupil up and in, and the lower muscle 

 turns it down and in. 



By the simultaneous action of two contiguous recti, the ball will be 

 moved to a point intermediate to that to which it would be directed by 

 either muscle singly. 



Dissection. By opening the optic foramen, the attachment of the recti 

 muscles will be more fully laid bare. To dissect out the inferior oblique 

 muscle, let the eyeball be replaced in its natural position ; then by taking 



