THE SKULL THE CRANIUM 



277 



the outside, to receive the eye. From the inner edge of the horizontal 

 plate there descends a second, much smaller, vertical plate, called the 

 median plate, which forms, behind, the inner wall of the cavity which 

 lies in the centre of the frontal bone, known as the frontal sinus, and 

 in front articulates with the nasal bone and the upper border of the 

 median plate of the ethmoid. The median plate thus contributes one- 

 half of the upper part of the median partition which divides the nasal 

 cavity into two halves. The inner flat surface of the median plate 

 joins the corresponding part of the opposite frontal bone. 



Nasal Pmces 



FIG. 200. 



Entrance to Left Frontal Sinus. 



Frontal (Orbital Plate). 



Postorbital Process. - 



Internal Angular 



Process. 



Opening Closed by Ethmoid. 



Entrance to Right Sphe- 

 noidal Sinus. 



Temporal (Zygoma- 

 tic Process). 



( Presphenoid. 



SPHENOID. { Pterygoid Process. 



I Basisphenoid. 



Temporal (Squamous). 



Sphenoid (Alisphenoid. Orbito- 

 sphenoidjust in front). 



Ltjt Auditory Bulla. 



Temporal (Tympanic). - 



Occipital (Basi-occipital). 

 THE CRANIUM VIEWED FROM IN FRONT, BELOW, AND THE LEFT SIDE. (Natural size.) 



The Horizontal Plate presents a superior or outer surface (Fig. 

 201) which is somewhat triangular, pointed in front and wider behind. 

 For most of its extent it is smooth arid flat, but in front and behind 

 and at the outer side it slopes downward. The inner border is straight, 

 except at its anterior end, which turns slightly outward and as the 

 inner border of the pointed nasal process joins the upper part of the 

 outer border of the nasal bone. The other side of the process is con- 

 tinued backward and outward into the anterior border of the frontal, 

 which is deeply emarginate, so as to receive the ascending process of 

 the maxillary, and ends in a distinct internal angular process, from 

 the side of which the lateral border, or orbital arch, begins. The 

 lateral border divides the horizontal from the vertical or orbital plate, 

 and forms the upper rim of the orbital opening. It is sharp, arched, 

 and ends behind in the anterior border of the external angular or 



