348 Jacob Parsons Schaeffer. 
median walls of the sinus are closely approximated, that the 
sinus capacity is markedly lessened, These sinuses may have 
marked infraorbital recesses and the processus alveolaris may be 
hollowed out towards its dorsal termination. In this manner com- 
pensation may be made for the marked bulging toward the cavity 
of the ventral and median walls of the sinus. It, however, 
remains that in the vast majority of cases, where these walls are 
simultaneously bulging into the cavity, the sinus 1s correspond- 
ingly reduced in size and the canine and premolar teeth not in 
direct relation to the sinus. 
Fic. 25 (* 1). Composite chart showing how anatomical variations in the 
extent of the recesses and the approximation of the walls of the sinus maxillaris 
affect the shape and size of its median wall or base. 
1 to 6, = outlines of different bases; V. D., S. I., V.S. D.,D.S. D., = ventrodorsal, 
superoinferior, ventrosuperior diagonal, and dorsosuperior diagonal, respectively. 
These variations in the approximation of the sinus walls, and 
the great difference in the extent of the various recesses, have 
a marked effect on the shape of the base of the cavity. <A refer- 
ence to figure 25 will show various shapes and sizes. Note espec- 
ially case 4 in which the ventrosuperior diagonal is very short, 
and the dorsosuperior, because of a marked infraorbital recess, 
comparatively long. The great difference in the two diagonals 
produces a peculiarly shaped base. 
