58 THE SKELETON 



till' antrum is, as a rulr, very uneven, due to prominences corresponding to the 

 roots of the molar teeth. In most cases the bone separating the teeth from tlie 

 antrum is very thin, and not rarely the roots project uncovered into it. The 

 teeth which come into closest relationship with the antrum are the first and second 

 molars, but the sockets of any of the teeth lodged in the maxilla may, under 

 diseased conditions, communicate with it. Although, as a rule, the cavity of the 

 antrum is single, yet specimens occasionally come to hand in which it is divided 

 l)y bony sei)ta into chambers, and it is far from uncommon to find it divided into 

 recesses l>y bony processes. In many maxilhe, the roof of the antrum presents 

 near its anterior aspect Avhat appears to be a thick rib of bone; this is hollow and 

 corresponds to the infraorl)ital canal. 



The most satisfactory method of studying the relation of the bones closing in 

 the base of the antrum is to cut away the outer wall of the cavity (see fig. 80). 



Articulations. — The maxilla articulates with its felloAV, and with the fronted, 

 nasal, laclu-ymal, ethmoid, palate, vomer, malar and inferior turbinal bones. Occa- 

 sionally it articulates with the greater wing, and less frequently with the pterygoid 

 })rocess of the sphenoid bone. 



The muscles attached to it are mainly those known as muscles of expression: — 



Compressor naris. Levator anguli oris. 



Orbicularis palpebrarum. Inferior oblique. 



Orbicularis oris. Depressor alae nasi. 



Levator labii superioris. Buccinator. 



Levator labii superioris alaeque nasi. Internal pterygoid. 



Masseter. 



Blood-supply. — The maxilla is a very vascular bone, and its arteries are nume- 

 rous and large. They are derived from the infraorbital, alveolar, descending palatine, 

 naso-])alatine. ethmoidal, frontal, nasal, and facial vessels. 



Ossification. — The maxilla arises from four centres Avliich are deposited in 

 membrane. 



The various centres may be termed premaxillary, maxillary, malar, and pre- 

 palatine. They arise about the eighth week of embryonic life, and fuse very 

 raj) idly. 



(rt) The premaxillary nucleus gives rise to that portion of the bone which 

 lodges the incisor teeth. It sends a narrow process upwards which forms part of 

 the outer boundary of the anterior narial aperture. On the palatine aspect it 

 furnishes a spiculum which surrounds the anterior and mesial aspect of Stenson's 

 (tanal. The posterior limit is indicated up to the end of the first dentition by the 

 maxillo-premaxillarv suture. The greater part of this centre is formed in mem- 

 brane, but the inner part subsequently invades the ethmo-vomerine cartilage. 



(ft) The maxillary nucleus forms the nasal process, and the greater part of the 

 body of the maxilla. 



(c) The malar centre gives origin to that portion of the bone lying external to 

 the infraorbital groove. 



{d) The prepalatine centre gives rise to the nasal surface of the maxilla and 

 the palatine process posterior to Stenson's canal. This i)ortion is in shape similar 

 to the j)alate bone. 



THE PALATE BONE 



The palate bone is R'ctangular in shape, and wedged between the maxilla and 

 the pterygoid processes of the sphenoid. It has a horizontal and a vertical plate, 

 a tuberosity, and two processes. 



The horizontal plate is smaller than the vertical; it is (luadrilaternl in shape. 

 The ui)])er surface forms the posterior part of the floor of the nasal fossa; the 

 inferior surface completes the hard jjalate posteriorly, and presents near its pos- 

 terior border a transverse ridge, which gives attachment to the temor pahiti muscle. 

 The anterior l)order is rough for articulation with the palatine process of the 

 maxilla. The posterior border is free, curved, and sharp; it gives attachment to 



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