148 OCULAR GROUP. 



The roof of the orbit may then be comminuted by a few light blows 

 with the hammer ; a process easily accomplished, on account of the 

 thinness of the orbital plate of the frontal bone and lesser wing of 

 the sphenoid. The superciliary portion of the orbit may now be 

 driven forwards by a smart blow, and the broken fragments of the 

 roof of the orbit removed. The periosteum will then be exposed 

 unbroken and undisturbed. Remove the periosteum from the whole 

 of the upper surface of the exposed orbit, and the muscles may then 

 be examined. 



The levator palpebrce is a long, thin, and triangular muscle ; it 



arises from the upper margin of 

 Fig. 69.* the optic foramen, and from the 



fibrous sheath of the Optic nerve, 

 and is inserted into the upper 

 border of the superior tarsal 

 cartilage. 



Relations. By its upper surface 

 with the fourth nerve the supra- 

 orbital nerve and artery, the peri- 

 osteum of the orbit, and in front 

 with the broad tarsal ligament. By 

 its under surface it rests upon the superior rectus muscle, and the 

 globe of the eye ; it receives its nerve and artery by this aspect, 

 and in front is lined for a short distance by the conjunctiva. 



The rectus superior (attollens) arises from the upper margin of the 

 optic foramen, and from the fibrous sheath of the optic nerve, and is 

 inserted into the upper surface of the globe of the eye at a point 

 somewhat more than three lines from the margin of the cornea. 



Relations. By its upper surfacewiih the levator palpebraj muscle; 

 and by the under surface with the optic nerve, the ophthalmic artery 

 and nasal nerve, from which it is separated by a layer of fascia and 

 by the adipose tissue of the orbit, and in front with the globe of the 

 eye, the tendon of the superior oblique muscle being interposed. 



The rectus inferior (depressor) arises from the inferior margin 

 of the optic foramen by a tendon (ligament of Zinn) which is 

 common to it, the internal and the external rectus, and from the 

 fibrous sheath of the optic nerve ; it is inserted into the inferior sur- 

 face of the globe of the eye at a little more than two lines from the 

 margin of the cornea. 



Relations. By its upper surface with the optic nerve, the infe- 



* The muscles of the eyeball ; the view is taken from the outer side of the right 

 orbit. 1. A small fragment of the sphenoid bone around the entrance of the optic 

 nerve into the orbit. 2. The optic nerve. 3. The globe of the eye. 4. The levator 

 palpebrra muscle. 5. The superior oblique muscle. 6. Its cartilaginous pulley. 7. Its 

 reflected tendon. 8. The interior oblique muscle, the small square knob at its com- 

 mencement is a piece of its bony origin broken off. 9. The superior rectus. 10. The 

 internal rectus almost concealed by the optic nerve. 11. Part of the external rectus, 

 showing its two heads of origin. 12. The extremity of the external rectus at its in- 

 sertion ; the intermediate portion of the muscle having been removed. 13. The inferior 

 rectus. 14. The tunica albuginea, formed by the expansion of the tendons of the four 

 recti. 



