THE HEAD AND NECK. 



141 



the third, fourth, sixth, and the three divisions of the ophthalmic branch of the 

 fifth nerve, the ophthalmic vein, and some minor structures. 



3. The inferior external angle. In this is the spheno-maxillary fissure. This 

 fissure transmits the superior maxillary nerve and its orbital branches, the ascend- 

 ing branches from Meckel's ganglion, the infraorbital branch of the internal max- 

 illary artery and its vein. 



4. The inferior internal angle contains the beginning of the osseous part of 

 the lachrymal apparatus that conveys tears to the nasal fossae. This apparatus 

 will be considered under the head of orbital contents. (Fig. 104.) 



The periosteum of the orbit (Fig. 95) lines the walls of the cavity, 

 delaminates at the orbital margin of the base, one layer uniting with the peri- 

 osteum externally, the other layer forming the tarsal ligaments and tarsal 

 cartilages above and below. The orbital fascia is to the contents of the orbit, 

 other things equal, what the deep fascia of the thigh is to the structures of the 

 thigh. Keep this in mind, for here, as in the thigh, you will find sheaths, 

 capsules, and septa derived from this fascia. 



In your dissection you will find the following structures 



1. The optic nerve the special nerve of the sense of sight. (Fig. 100.) 



2. The motor oculi nerve, or third nerve. (Fig. 98.) 



OPTIC FORAMEN 



DELAMINATION OF THE ORBITAL 

 PERIOSTEUM 



arsal ligament 



Tarsal cartilage 



PALPEBRAL FISSURE 



ORBITAL PERIOSTEUM 



OHBITAL PERIOSTEUM 



FIG. 95. SCHEMATIC REPRESENTATION TO Snow RELATION OF PERIOSTEUM TO TARSAL CARTI- 

 LAGES AND TARSAL LIGAMENTS. 



3. The patheticus, or fourth nerve. (Fig. 98.) 



4. The abducens, or sixth nerve. (Fig. 98.) 



5. Ophthalmic branch of the fifth nerve. (Fig. 98.) 



6. The lachrymal gland and its capsule. (Fig. 103.) 



7. The ophthalmic artery and its branches. (Fig. 103.) 



8. The ophthalmic vein and its branches. (Fig. 103.) 



9. The ciliary ganglion and its branches. (Fig. 98.) 



10. The orbital connective tissue and fat. 



11. The levator palpebrae muscle. (Fig. 100.) 



12. The superior rectus muscle. (Fig. 100.) 



13. The external rectus muscle. (Fig. 99.) 



14. The inferior rectus muscle. (Fig. 99.) 



15. The internal rectus muscle. (Fig. 99.) 



1 6. The superior oblique muscle. (Fig. 100.) 



17. The inferior oblique muscle. (Fig. 100.) 



1 8. The capsule of Tenon. 



19. The eyeball with sclerotica and iris. (Fig. 99.) 

 Dissection of the Orbital Contents Steps : 



I. Remove the orbital plate and supraorbital arch by cutting through the 



