Skull and Hyoid 231 



of the body, and the other two molars below the region of the malar prominence and 

 the postero-external surface. The inner alveolar wall, behind the premaxillary 

 region, is in the plane of the inner surface of the body, while its outer wall is confluent 

 with the superficial surface of the body, so that the alveolar process can be said to form 

 the floor of the maxillary sinus or antrum : the fangs of the teeth, particularly of the 

 first molar, may occasionally project into the cavity, covered by its lining mucous 

 membrane. 



The complete alveolar arcade made by the two maxillae forms a semi-ellipse, 

 contrasting with the parabolic curve of the mandibular alveolus ; as a result of 

 this difference the back upper molars are somewhat out-turned to oppose the lower teeth. 



The palatine or horizontal process is on the level of the lower part of the body and 

 thus projects inwards above the alveolar level. It has a rough median border articu- 

 lating with its fellow and forming with it a raised septal crest that supports the vomer; 

 also a rough but thin posterior border articulating with the horizontal plate of the 

 palate bone. It is thicker in front where it joins the premaxillary part of the alveolus, 

 and at the junction on the inner articular surface, the anterior palatine foramen or canal 

 is visible on the bone. The anterior palatine canal (naso-palatine) lies centrally 

 between the premaxilla and the palate proper, and each maxilla has the half-impression 

 of the canal ; the common lower opening of the canal leads to four smaller canals which 

 form the upper part of the foramen, and these are : two antero-posterior for the naso- 

 palatine nerves and two side by side for the terminal parts of the posterior palatine 

 vessels. 



The upper surface of the palatine process is concave between the septal crest and 

 the outer wall of the nose and rises slightly in front on to the premaxilla. The lower 

 surface is roughened by the mucous membrane and grooved by the posterior palatine 

 nerve and vessels running forward. 



The malar process has a smooth concave facial surface, a smooth posterior aspect 

 looking toward the zygomatic fossa, a lower bracket-like ridge that extends to the 

 alveolus between the first two molars, and a rough upper and outer surface, continuous 

 with the orbital surface, that carries the malar and enables this bone to complete 

 the outer part of the floor of the orbit. 



The antrum has the alveolus as its floor, and is often irregularly ridged in this 

 situation. The cavity may extend into the malar process and even a short way into 

 the premaxilla. It may be partly or completely subdivided by bony septa. The 

 infraorbital canal causes a ridge in its front and upper part, and other ridges may be 

 seen running from this and containing the middle and anterior dental nerves ; the 

 last nerve, going to the incisors, runs close to the anterior nasal margin. 



This bone is further considered in association with the palate (p. 235), spheno- 

 maxillary fossa (p. 23^), nose (p. 244), and orbit (p. 253). 



Development. 



The bone is developed in membrane, laid down in the maxillary process of the 

 mandibular arch and in the fronto-nasal process with which this fuses. Ossification 

 commences in the sixth week on the outer side of the dental groove, in the future canine 

 region, and extends from this forward into the incisor region and backwards towards 

 the molars. The body of the bone and its nasal and malar processes are extensions 

 upwards from this primary centre. 



This "single" centre is apparently made by the rapid fusion of two distinct ossifications, which 

 appear, in the body and premaxillary regions respectively, at the same time. 



