THE PALATE BONE 



91 



Ossification. — The maxilla is developed from several centres which are deposited in mem- 

 brane during the second month of intrauterine life. Several pieces are formed which speedily 

 fuse, so that at birth, with the exception of the incisor fissure separating the maxilla from the 

 premaxiUa, there is no trace of the composite character of the bone. The centres of ossification 

 comprise — -(Ij the malar, which gives rise to the portion of bone outside the infra-orbital canal; 



(2) the maxillary, from which the greater part of the body and the frontal process are developed; 



(3) the palatine, forming the hinder three-fourths of the palatal process and adjoining part 

 of the nasal wall; (4) the premaxillary, giving rise to the independent premaxillary bone (os 

 incisivum), which lodges the incisor teeth and completes the anterior fourth of the hard palate. 

 In the early stages of growth the premaxiUa may consist of two pieces arising from two centres 

 of ossification which Albrecht has named as follows: — the endognathion, or mecUal division for 



Fig. 114. — jM.\xill.e at the end of the First Dentition in both of which the Sutures 



BETWEEN ^L\XILLA AND PrEM.\XILLA, AND BETWEEN THE TWO PaRTS OF THE PrEMAXILLA, 



ARE SEEN. 



Gubernacular canal 



Gubernacular canal with tooth 

 visible 



Endognathion 

 Mesognathion 



£ndo-mesognathic suture 

 Meso-exognathic suture 



the central incisor, and the mesognathion, or lateral division for the lateral incisor; the rest 

 of the maxilla is named the exognathion; (5) the prepalatine, corresponding to the infra-vomerine 

 centre of Rambaud and Renault, forms a portion of bone interposed between the premaxillary 

 in front and the palatine process behind. It gives rise to a part of the nasal surface and com- 

 pletes the medial wall of the incisive canal. 



At birth the sinus is narrow from side to side and does not extend laterally to any appre- 

 ciable extent between the orbit and the alveoli of the teeth. Dm-ing the early years of life it 

 gradually enlarges, but does not attain its full growth until after the period of the second 

 dentition. 



THE PALATE 



The palate bone [os palatinum] (figs. 115, 116) forms the posterior part of the 

 hard palate, the medial wall of the nasal fossa between the maxilla and the 

 medial pterygoid plate, and, by its orbital process, the hinder part of the floor 

 of the orbit. It is somewhat L-shaped and presents for examination a horizontal 

 part and a perpendicular part; at their point of junction is the pyramidal process, 

 and surmounting the top of the vertical plate are the orbital and sphenoidal 

 processes, separated by the spheno -palatine notch. 



The horizontal part resembles the palatine process ofthe maxilla, but is much 

 shorter. The superior surface is smooth, concave from side to side, and forms 

 the back part of the floor of the nasal fossa; the inferior surface completes the 

 hard palate behind and presents near its prosterior border a transverse ridge 

 which gives attachment to the tensor veil 'palatini muscle. 



The anterior border is rough for articulation with the palatine process of the maxilla; the 

 posterior is free, curved, and sharp, giving attachment to the soft palate. Medially it is thick 

 and broad for articulation with its fellow of the opposite side, forming a continuation of the 

 crest of the palatal processes of the maxillae and supporting the vomer. The posterior extremity 

 of the crest is the posterior nasal spine, from which the azygos uvulce arises. Laterally, at its 

 junction with the perpendicular part, it is grooved by the lower end of the pterygo-palatine 

 canal. 



lateral 



The perpendicular part is longer and thinner than the horizontal plate. The 

 sral surface is in relation with the maxilla and is divided into two parts by 



