1422 



HUMAN ANATOMY. 



of life, but also often on the two sides of the same individual ; their communications 

 with the nasal fossae, however, are fairly constant. 



The Maxillary Sinus. — This space, (sinus maxillaris), or the antr7im of 

 Highmorc, the largest of the pneumatic cavities, lies to the outer side of the nasal 

 fossa and resembles in its general form a three-sided pyramid (Fig. 1184). It 

 occupies the greater part of the superior maxillary bone, so that its walls, with the 

 exception of the postero-inferior ore, are very thin and often in places of papery 

 delicacy (Fig. 256). The median waJl, ox base, is directed toward the nasal fossa, from 

 which it is separated by a thin osseous partition in the formation of which the vertical 

 plate of the palate bone, the uncinate process of the ethmoid, the maxillary process 

 of the inferior turbinate and a small part of the lachrymal bone assist. The apex lies 

 at the zygomatic process of the maxilla. The upper or orbital wall is thin and often 



Fig. I 184. 



Vestibule 



Anterior ethmoidal cells 



Left inaxillarv sinus 



inferior meatus 

 Place where frontal sinus was attached 



\nterior ethmoidal cells 



Maxillary sinus 

 Posterior ethmoidal cells 



Left sphenoidal cell 



Right sphenoidal cell 



Naso-pharynx 



Cast of nasal fossae and accessory air-spaces, viewed from above; casts of frontal sinuses have been removed; 



natural size. (Kallitts.) 



modelled by the ridge containing the infraorbital canal. The anterior wall presents 

 towards the face and is varyingly impressed by the canine fossa. The postero- 

 inferior wall is normally the thickest, but is sometimes reduced by extension of the 

 sinus into the adjacent alveolar border. The sinuses are often so modified by local 

 enlargements that the typical pyramidal form is lost and their dimensions materially 

 influenced. As an indication of the size of the average sinus, a sagittal diameter of 

 35 mm. (i^ in.), and a vertical and frontal one of 27 mm. (about i in.) each 

 (Kallius), may be taken as approximate measurements. Not infrequently, however, 

 considerable asymmetry exists even to the extent of one antrum being almost twice as 

 large as the other. The usual capacity of the antrum is between 12-18 cc. (3^-4^ 

 fi. dr.) with an average of approximately 15 cc. , or 4 fi. dr. (Braune and Clasen). 



The antrum communicates indirectly with the middle meatus by means of an 

 aperture (ostium maxillare) that pierces the upper and anterior part of the base to 

 open into the infundibulum, and thence by way of the hiatus semilunaris, into the 



