THE SUPERIOR MAXILLARY BONES. 



87 



These cavities are eight in number, and vary in size and depth according to the 

 teeth they contain. That for the canine tooth is the deepest ; those for the molars 

 are the widest, and subdivided into minor cavities ; those for the incisors are single, 

 but deep and narrow. The Buccinator muscle arises from the outer surface of this 

 process, as far forward as the first molar tooth. 



The Palate Process, thick and strong, projects horizontally inward from the 

 inner surface of the bone. It is much thicker in front than behind, and forms a 

 considerable part of the floor of the nostril and the roof of the mouth. 



Its inferior surface (Fig. 51) is concave, rough and uneven, and forms part of 

 the roof of the mouth. This surface is perforated by numerous foramina for the 

 passage of the nutrient vessels, channelled at the back part of its alveolar border 

 by a longitudinal groove, sometimes a canal, for the transmission of the posterior 

 palatine vessels, and the anterior and external palatine nerves from Meckel's gan- 

 glion, and presents little depressions for the lodgement of the palatine glands. 

 When the two superior maxillary bones are articulated together, a large orifice 

 may be seen in the middle line, immediately behind the incisor teeth. This is 

 the anterior palatine canal or fossa. On examining the bottom of this fossa four 

 canals are seen : two branch off laterally to the right and left nasal fossae, and 

 two, one in front and one behind, lie in the middle line. The former pair of 

 these canals are named the foramina of Stenson, and through them passes the 

 anterior or terminal branch of the descending or posterior palatine arteries, 

 which ascend from the mouth to the nasal fossae. The canals in the middle line 

 are termed the foramina of Scarpa, and transmit the naso-palatine nerves, the 

 left passing through the anterior, and the right through the posterior, canal. 

 On the palatal surface of the process a delicate linear suture may sometimes be 

 seen extending from the anterior palatine fossa to the interval between the lateral 

 incisor and the canine tooth. This marks out the intermaxillary or incisive bone, 

 which in some animals exists permanently as a separate piece. It includes the 

 whole thickness of the alveolus, the corresponding part of the floor of the nose, 

 and the anterior nasal spine, and contains the sockets of the incisor teeth. The 

 i<l>[>t'r surface is concave from side to side, smooth, and forms part of the floor of 

 the nose. It presents the upper orifices of the foramina of Stenson and Scarpa, 

 the former being on each side of the middle line, the latter being situated in the 

 intermaxillary suture, and therefore not visible unless 

 the two bones are placed in apposition. The outer border 

 of the palate process is incorporated with the rest of the 

 bone. The inner border is thicker in front than behind, 

 and is raised above into a ridge, the nasal crest, which, 

 with the corresponding ridge in the opposite bone, forms 

 a groove for the reception of the vonier. In front this 

 crest rises to a considerable height, and this portion is 

 named the incisor crest. The anterior margin is bounded 

 by the thin, concave border of the opening of the nose, 

 prolonged forward internally into a sharp process, form- 

 ing, with a similar process of the opposite bone, the 

 <utt<>r!>- nasal spine. The posterior border is serrated for 

 articulation with the horizontal plate of the palate bone. 



Development. This bone commences to ossify at a 

 very early period, and ossification proceeds in it with 

 great rapidity, so that it is difficult to ascertain with 

 certainty its precise number of centres. It appears, 

 however, probable that it is ossified from four centres, 

 which are deposited in membrane. 1. One which forms 

 that portion of the body of the bone which lies internal 

 to the infra-orbital canal, including the floor of the orbit, 

 the outer wall of the .nasal fossa, and the nasal process; 2. A second which gives 

 origin to that portion of the bone which lies external to the infra-orbital canal 



Inferior Surface. 



FIG. 52. Development of 

 superior maxillary bone. At 

 birth. 



