74 



APPLIED ANATOMY. 



orbital plate of the superior maxilla. In operations involving the floor of the 

 orbit, care is necessary to avoid breaking through into the maxillary sinus (antrum) 

 beneath. 



At the edge of the junction of the outer and lower walls lies the inferior orbital 

 {sphenomaxillary*} fissure. It runs forward to within 1.5 cm. of the edge of the 

 orbit and extends back to the apex of the orbit, where it unites with the siiperior 

 orbital {sphenoidal} fissure, which lies between the roof and outer wall and extends 

 forward about one-third of the distance to the edge of the orbit. The optic foramen 

 enters the apex of the orbit at its upper and inner portion. 



At the lower inner edge of the orbit is the lachrymal groove for the lachrymo- 

 nasal duct, leading from the eye to the inferior meatus of the nose. At the junction of 

 the middle and inner thirds of the upper edge is the supra-orbital notch. This can 

 be felt through the skin. It transmits the supra-orbital artery and nerve. If a 

 complete foramen is present instead of a notch, its location cannot be so readily 

 determined. 



Contents of the Orbit. The orbit is lined with a periosteum, and contains 

 the eyeball, the muscles which move it, the veins, arteries, and nerves which go to 



Capsule of Tenon 



Superior oblique muscle 



Superior orbitotarsal 

 ligament 



Levator palpebrae 

 superior muscle 



Superior rectus muscle 



Tarsal cartilage 



Inferior rectus muscle 

 Inferior oblique muscle 



Inferior orbito- 

 tarsal ligament 



FIG. 88. Sagittal section through the eye and orbit. 



it together with some which traverse the orbit to go to the face, and the lachrymal 

 gland. These structures are more or less surrounded with a fascia which is continu- 

 ous with the periosteum. 



Periosteum. The periosteum of the orbit is not tightly attached and in cases 

 of disease can readily be raised from the bone beneath. Anteriorly, it is continuous 

 at the orbital rim with the periosteum of the bones of the face. Posteriorly, it is con- 

 tinuous through the optic foramen and sphenoidal fissure with the dura mater. 

 It sends prolongations inward, covering all the separate structures in the orbit. 

 From the edge of the orbit it stretches over to the tarsal cartilages, forming the 

 superior and inferior orbilotarsal ligaments. These form a barrier (called the sep- 

 tum orbitale} to the exit of pus from within the orbit, and for that reason it is advised 

 that orbital abscesses should be opened early. The lower portion, as it reaches 

 the lachrymal groove, splits to cover the lachrymal sac. Another extension 

 from above splits to enclose the lachrymal gland, which is seen to lie comparatively 

 loose in the upper outer portion of the orbit, sustained by its suspensory ligament. 

 It then sends thin fibrous layers which cover the muscles, arteries, veins, nerves, fat 

 pellicles, and finally the eyeball posterior to the insertion of the muscles and optic 

 nerve. This last portion, called the capsule of Tenon, begins as far forward as the 



