THE ENTIKE SKULL 473 



THE ORBITS. 



The Orbits (Figs. 387, 388) lie at the sides of the skull in front 

 under the middle of the cranial cavity and separated from each other 

 by the nasal cavity and by the anterior part of the cranial cavity. 



Each orbit is a conical cavity pointing from in front inward, back- 

 ward, and downward, so that the inner ends of the two if continued 

 into the cranial cavity would meet over the sella turcica. The base 

 of the cone is at the plane of the large anterior opening and limited 

 by the orbital rim ; it faces forward, outward, and upward. The apex 

 is at the side of the skull, behind the middle, near the optic foramen, 

 and points backward, inward, and downward. The antero-posterior 

 diameter of the cone is one-fifth greater than the widest diameter of 

 its base in front. At their posterior ends the orbits are separated 

 only by the presphenoid, but at their anterior ends by the greatest 

 width of the nasal cavity. 



The orbital rim is formed in front by the posterior edge of the 

 nasal process of the maxillary and the upper edge of the malar, the 

 junction of the two lying at the anterior end of the long diameter. It 

 is bounded below by the same edge of the malar, above by the internal 

 angular process, the orbital border, and the postorbital process of the 

 frontal. The opening of the orbit, surrounded by the orbital rim, is 

 oval, and is a fifth wider than high. The wider diameter is not trans- 

 verse; from within, it points upward as well as outward. The vertical 

 diameter, at right angles to this, is not really vertical, but runs from 

 below inward and upward. The orbits are not wholly enclosed by 

 bony walls, but large openings are left, which are in the natural state, 

 however, filled by muscles arid fascia. Of the walls, the inner wall 

 alone is complete ; the lower wall, or floor, is limited to the orbital 

 plate of the maxillary in the inner part of the anterior third and to a 

 strip of the palatine along the inner side. The outer wall is present 

 only in front, in the form of a bony ring, which is furnished by the 

 malar bone and the frontal postorbital process. The upper wall, or 

 roof, is formed by the orbital plate of the frontal and part of the 

 orbital surface of the sphenoid. It is limited on the outside by a line 

 drawn between the root of the frontal postorbital process above and 

 the front of the foramen rotimdum below along a marked convexity 

 situated on the frontal and alisphenoid bones. A plane directed from 

 this convexity outward and forward in such a manner as to pass 



