202 



HUMAN ANATOMY. 



accord with the larger size of the sinuses in man. The internal surface is largely 

 smooth. Bony ridges springing from various parts tend to subdivide the cavity. 

 They sometimes form litde pockets above the teeth. According to Gruber/ it 

 may in rare cases be completely subdivided into a smaller posterior chamber and a 

 larger front one, both of which open into the nasal cavity. The lowest part of the 

 antrum is indented by the roots of the molars and of the second bicuspid, at least 

 very frequently. The first and second molars always indent it, but the bicuspid and 

 the wisdom-tooth may not. (For further details, see Teeth, page 1556.) 



Articulations. — All the bones of the face, except the lower jaw and the hyoid, 

 touch the superior maxilla. It has been described as the key to the architecture 

 of the face. The palate bone both completes the palate and lies between this bone 

 and the pterygoids, closing the posterior part of the opening into the antrum. The 

 malar, joining the process of that name, makes the prominence of the cheek and 

 helps to bound the orbit. The nasals complete the anterior nasal aperture. The 

 lachrymals and ethmoid touch the inner side of the orbital plate, and the ethmoid 

 the inner surface of the nasal process. The frontal rests on the nasal process, the 



Fig. 225. 



Nasal process 



Ethmoidal crest 

 Middle meatus 



Inferior turbinate crest 

 Inferior meatus 

 Incisor crest 

 Anterior nasal spine 



.interior palatine canal 

 Alveolar procesi 



Completes ethmoidal 

 cells 



Antrum 



Posterior palatine canal 

 Nasal crest 

 Palatal process 



Tuberosity 



Right superior maxillary bone, inner surface. 



inferior turbinate rests on the inner surface of the maxilla, and the vomer on the crest 

 made by the union of the palate processes. 



Development and Changes. — There are certainly four chief centres, all of 

 which appear at about the end of the sixth week of fcetal life. Three of them fuse 

 very rapidly. There is one on either side of the infra-orbital groove, a }?ialar and 

 an orbito -facial, and below and internally di palatine. The fourth, the intermaxillary, 

 stays distinct longer. It comprises the front of the palate as far back as the anterior 

 palatine canal, and represents a very constant separate ossification in vertebrates, 

 the premaxilla, in front of the maxilla, except in certain mammals in which it is 

 between them. It bears the incisor teeth, and at the third foetal month fuses with 

 the maxilla. As the intermaxillary grows, the suture in the roof of the mouth per- 

 sists for a time. It is very plain at birth and often for a year or two later. Some- 

 times it is seen in the adult. At first the posterior suture is very close to the 

 incisors, but as it grows the intermaxillary forms a large part of the palate. If 

 detached, it is seen notched behind, so as to form the inner wall of the upper part of 



' Virchow's Archiv, Bd. Ixiii. 



