THE SINUS MAXILLARIS 129 



being thicker than the central area. The medial portion of 

 the wall forms the anterior boundary of the fossa pterygo- 

 palatina (Fig. 33). 



The anterior or facial wall of the sinus maxillaris varies 

 from 2 to 5 mm. in thickness, and is, with the exception of 

 that portion of the floor which is formed by the alveolar 

 process, the thickest and the strongest of all the walls. It 

 faces in an anterolateral direction, with a varying antero- 

 inferior obliquity. This obliquity, which depends upon the 

 degree of approximation of the inferior portion of the wall 

 toward the posterior wall, produces the variations in the 

 number of teeth which are in relation to the sinus floor, and 

 greatly influences the capacity of the sinus. The anterior 

 surface presents, below the infra-orbital margin, the foramen 

 infraorbitale, beneath which is a variable depression, the 

 fossa canina (Fig. 55). 



The inferior wall of the pyramid, the floor of the sinus 

 maxillaris, is formed near the medial wall by the processus 

 alveolaris, and, more laterally, by the well-rounded angle 

 produced by the approximation of the inferior portions of 

 the anterior and posterior walls. 



The floor of the sinus maxillaris, in all stages of its de- 

 velopment, is in close relation to the teeth (Figs. 17, 21, 28, 

 30, and 33), and the increase in the vertical diameter of 

 the sinus is found to be much more of a process of expansion 

 as the body of the maxilla increases in size, than it is one 

 of resorption of cancellous bone previously occupying the 

 area. 



The number of teeth, the roots of which are in close rela- 

 tion to the floor of the sinus, shows marked variations (Figs. 

 45, 47, 50, 54, and 55). However, the typical floor may be 

 9 



