190 



THE SKELETON. 



of the upper jaw. Each bone assists in the formation of three cavities, the roof of 

 the mouth, the floor and outer wall of the nasal fossae, and the floor of the 

 orbit, and also enters into the formation of two fossae, the zygomatic and spheno- 

 maxillary, and two fissures, the spheno-maxillary and pterygo-maxillary. 



The bone presents for examination a body and four processes malar, nasal, 

 alveolar, and palate. 



The body is somewhat cuboid, and is hollowed out in its interior to form a large 

 cavity, the antrum of Highmore. Its surfaces are four an external or facial, a 

 posterior or zygomatic, a superior or orbital, and an internal. 



The external or facial surface (Fig. 154) is directed forward and outward. 

 Just above the incisor teeth is a depression, the incisive or myrtiform fossa, which 

 gives origin to the Depressor alae nasi ; and below it to the alveolar border is 

 attached a slip of the Orbicularis oris. Above and a little external to it the 

 Compressor nasi arises. More external is another depression, the canine fossa, 



Outer Surface. 



TENOO OCULI 



Incisive fossa. 



Posterior dental 

 canals. 



MaxiUary tuberosity. 



FIG. 154. Left superior maxillary bone. Outer surface. 



larger and deeper than the incisive fossa, from which it is separated by a vertical 

 ridge, the canine eminence, corresponding to the socket of the canine tooth. The 

 canine fossa gives origin to the Levator anguli oris. Above the canine fossa is the 

 infraorbital foramen, the termination of the infraorbital canal ; it transmits the 

 infraorbital vessels and nerve. Above the infraorbital foramen is the margin of 

 the orbit, which affords partial attachment to the Levator labii superioris proprius. 

 To the sharp margin of bone which bounds this surface in front and separates it 

 from the internal surface is attached the Dilator naris posterior. 



The posterior or zygomatic surface is convex, directed backward and outward, 

 and forms part of the zygomatic fossa. It presents about its centre several aper- 

 tures leading to canals in the substance of the bone ; they are termed the posterior 

 dental canals, and transmit the posterior dental vessels and nerves. At the lower 

 part of this surface is a rounded eminence, the maxillary tuberosity, especially 

 prominent after the growth of the wisdom-tooth, rough on its inner side for artic- 

 ulation with the tuberosity of the palate bone, and sometimes with the external 

 pterygoid plate. It gives attachment to a few fibres of origin of the Internal 



