SUPERIOR MAXILLARY BONES. 47 



strong ascending plate of the nasal process, marked inferiorly by a 

 rough horizontal ridge, which gives attachment to the inferior tur- 

 binated bone. The concave depression immediately above this 

 ridge corresponds with the middle meatus of the nose, and that below 

 the ridge with the inferior meatus. Between the nasal process and 

 the opening of the antrum, is a deep groove, which is converted 

 into a canal by the lachrymal bone, and constitutes the nasal duct 

 or ductus ad nasum. The superior border of the nasal surface is 

 irregularly cellular, and articulates with the lachrymal and ethmoid 

 bone ; the posterior border is rough, and articulates with the palate 

 bone ; the anterior border is sharp, and forms the free margin of the 

 opening of the nose; and from the inferior border projects inwards 

 a strong horizontal plate, the palate process. 



The posterior surface may be called zyg'omatic, from forming part of 

 the zygomatic fossa ; it is bounded externally by the malar process, 

 and internally by a rough and rounded border, the tuberosity, 

 which is pierced by a number of small foramina, giving passage to 

 the posterior dental nerves and branches of the superior dental 

 artery. The lower part of this tuberosity presents a rough oval 

 surface, to articulate with the palate bone, and immediately above 

 and to the inner side of this articular surface a smooth groove, 

 which forms part of the posterior palatine canal. The superior 

 border is smooth and rounaed to form the lower boundary of the 

 spheno-maxillary fissure, and is marked by a notch, the commence- 

 ment of the infra-orbital canal. The inferior boundary is the 

 alveolar process, containing the two last molar teeth. 



The orbital surface is triangular and thin, and constitutes the 

 floor of the orbit. It is bounded internally by an irregular edge, 

 which articulates with the palate, ethmoid, and lachrymal bone ; 

 posteriorly, by the smooth border which enters into the formation 

 of the spheno-maxillary fissure; and anteriorly, by a convex 

 margin, partly smooth and partly rough, the smooth portion forming 

 part of the lower border of the orbit, and the rough articulating 

 with the malar bone. The middle of this surface is channelled by 

 a deep groove and canal, the infra-orbital, which terminates at the 

 infra-orbital foramen. 



The four processes of this bone are, the nasal, malar, alveolar, 

 and palate. 



The nasal process ascends by the side of the nose, to which it 

 forms the lateral boundary, and articulates with the frontal and 

 nasal bone. 



By its external surface it gives attachment to the levator labii 

 superioris ala3que nasi, and to the orbicularis palpebrarum muscle ; 

 its internal surface contributes to form the inner wall of the nares, 

 and the posterior border is thick and hollowed into a groove for the 

 nasal duct. The margin of the nasal process, which is continuous 

 with the lower border of the orbit, is sharp and marked by a small 

 tubercle which serves as a guide to the introduction of the knife in 

 the operation for fistula lachrymalis. 



The malar process, large and irregular, is situated at the angle 



