82 



OSTEOLOGY. 



surfaces, an external or facial, a posterior or zygomatic, a superior or orbital, 

 and an internal. 



The external or facial surface (fig. 45) is directed forwards and outwards. In 

 the median line of the bone, just above the incisor teeth, is a depression, the 

 incisive or myrtiform fossa, which gives' origin to the Depressor alas nasi. Above 

 and a little external to it, the Compressor naris arises. More external, is another 

 depression, the canine fossa, 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 infra-orbital foramen, the termination of the 

 infra-orbital canal ; it transmits the infra-orbital nerve and artery. Above the 

 infra-orbital foramen is the margin of the orbit, which affords partial attachment 

 to the Levator labii superioris proprius. 



The posterior or zygomatic surface is convex, directed backwards and outwards, 

 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 



Fig. 45. Left Superior Maxillary Bone, Outer Surface. 

 Outer Surface. 



rele. 



Incisive- foss. 



rior Dental CctncJs 



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 

 articulation with the tuberosity of the palate bone. Immediately above the rough 

 surface is a groove, which, running 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 

 articulates, in front, with the lachrymal ; in the middle, with the os planum of 

 the ethmoid ; behind, with the orbital process of the palate bone ; externally, by 

 a smooth rounded edge which enters into the formation of the spheno-maxillary 

 fissure, and which sometimes articulates at its anterior extremity with the orbital 

 plate of the sphenoid ; and in front, by part of the circumference of the orbit, 



