THE SKULL AS A WHOLE 65 



THE EXTERNAL SURFACE OF THE SKULL 



The external surface may be divided into superior or vertex, 

 inferior, or base, anterior, or face, and lateral regions. 



The superior region, or vertex, extends from the supra- 

 orbital margins to the superior curved line of the occiput, 

 bounded laterally by the temporal lines. It is a smooth, 

 convex surface covered by muscle and aponeurosis. The 

 greatest transverse diameter of the skull is at the junction 

 of the posterior and middle thirds, viz., 5f inches (140 mm.); 

 the greatest longitudinal diameter from the under margin 

 of the frontal bone to the external occipital protuberance is 

 6f inches (170 mm.). 



The anterior region, or face, presents the openings of the 

 orbits, the bridge of the nose, below that the anterior nasal 

 aperture (apertura pyriformis), presenting the anterior nasal 

 spine below. Below the aperture are the incisor fossae of the 

 upper jaw, below the orbits the canine fossae, and external 

 to them the malar prominences. The lower jaw completes 

 the skeleton of the face with its incisor fossae, mental promi- 

 nence, etc. 



In a nearly vertical line on either side are three foramina 

 for the exit of some part of the three divisions of the fifth 

 cranial nerve, viz., the supraorbital, infraorbital, and mental. 

 There are also the malar foramina on the malar bone. 



The orbits are pyramidal fossse, somewhat quadrihedral, 

 with their bases turned forward and out; their inner w r alls 

 are nearly parallel, and their outer walls diverge at nearly 

 right angles to each other. Each is formed of seven bones, 

 or eleven for the two the frontal, sphenoid, malar, superior 

 maxillary, lacrymal, ethmoid, and palate. The roof of each 

 is formed by the orbital plate of the frontal and small wing 

 of the sphenoid ; the floor by the malar, superior maxilla, and 

 orbital plate of the palate; the inner wall by the nasal process 

 of the superior maxilla, the lacrymal, ethmoid, and body of 

 the sphenoid; the outer wall by the malar and great wing of the 

 sphenoid. The xplicnoida] fuwwc at its inner part occupies 

 the apex of the orbit; its outer extremity lies between the 

 roof and outer wall. 



The optic foramen is internal to and above the fissure. In 

 5 



