THE SUPERIOR MAXILLARY BONES. 



191 



pterygoid muscle. Immediately above the rough surface is a groove which, run- 

 nin<* obliquely down on the inner surface of the bone,, is converted into a canal 

 by articulation with the palate-bone forming the posterior palatine canal. 



The superior or orbital surface is thin, smooth, triangular, and forms part of 

 the floor of the orbit. It is bounded internally by an irregular margin which 

 in front presents a notch, the lachrymal notch, which receives the lachrymal bone ; 

 in the middle articulates with the os planum of the ethmoid, and behind with the 

 orbital process of the palate bone ; -bounded externally by a smooth, rounded edge 

 which enters into the formation of the spheno-maxillary fissure, and which some- 

 times articulates at its anterior extremity with the orbital plate of the sphenoid ; 

 bounded in front by part of the circumference of the orbit, which is continuous 

 on the inner side with the nasal, on the outer side with the malar, process. Along 

 the middle line of the orbital surface is a deep groove, the infraorbital, for the 

 passage of the infraorbital vessels and nerve. The groove commences at the mid- 

 dle of the outer border of this surface, and. passing forward, terminates in a canal, 

 which subdivides into two branches. One of the canals, the infraorbital, opens 

 just below the margin of the orbit; the other, which is smaller, runs in the sub- 

 stance of the anterior wall of the antrum : it is called the anterior dental canal, 

 ami transmits the anterior dental vessels and nerve to the front teeth of the upper 

 jaw. From the back part of the infraorbital canal a second small canal is some- 

 times given off", which runs in the substance of the bone, and conveys the middle 

 dental nerve to the bicuspid teeth. Occasionally, this canal is derived from the 

 anterior dental. At the inner and fore part of the orbital surface, just external 

 to the lachrymal groove for the nasal duct, is a depression which gives origin to 

 the Inferior oblique muscle of the eye. 



The internal surface (Fig. loo) is unequally divided into two parts by a hori- 

 zontal projection of bone, the palate process : the portion above the palate process 



Bone-' partially dosing orifice of antrnm 

 marked in outline. 



Ethmoid.. 



Inferior turbinated. 

 Palate. 



Anterior nasal spine. 



Bristle passed 

 through anterior 

 palatine canal. 



FIG. 155. Left superior maxillary bone. Internal surface. 



forms part of the outer wall of the nasal fossae ; that below it forms part of the 

 cavity of the mouth. The superior division of this surface presents a large, irreg- 

 ular opening leading into the antrum <>f Hiahmore. At the upper border of this 

 aperture are numerous broken cellular cavities, which in the articulated skull are 

 closed in by the ethmoid and lachrymal bones. Below the aperture is a smooth 



