40 SURGICAL ANATOMY OF 



through the frontal bone, first in a line with the inner 

 angle and the optic foramen, and again in a line with 

 the outer angle and sphenoidal fissure ; a few taps on 

 the orbital plate with a hammer will break it through, 

 and the triangle of bone can be readily tilted forwards 

 by a blow on the margin of the skttll ; the ring round 

 the optic foramen should be retained, as the muscles are 

 attached to it. 



Boundaries. The bony walls of the orbit are formed 

 as follows : 



The roof, concave, directed downwards and forwards, 

 by the orbital plate of the frontal bone in front, and by 

 the lesser wing of the sphenoid behind. The floor, nearly 

 flat, by the malar, superior maxillary, and orbital plate 

 of palate. Outer watt, concave, by the greater wing of 

 sphenoid and malar bone. Inner wall, flat, by the lach- 

 rymal, os planum of ethmoid, and sphenoid. Regarding 

 the shape of the orbit as nearly conical, its base is nearly 

 quadrilateral, and at its several angles are found the su- 

 tures of its component bones. At its external, that of 

 the external orbital process of the frontal with the malar ; 

 at its internal, that of the frontal with the lachrymal 

 and nasal process of superior maxilla ; below, that of the 

 malar with the superior maxilla. 



Its apex corresponds to the optic foramen and sphe- 

 noidal fissure. 



The spheno-maxillary fissure is found on the floor of 

 the orbit. The continuity of this fissure with the 

 spheno-maxillary fossa explains the protrusion of the 

 eyeball from processes of tumors passing through it 

 from the spheno-maxillary region. 



Contents. The periosteum of the orbit is formed by 

 the dura mater, and enters the cavity by the optic fora- 



