226 



HUMAN ANATOMY. 



These arrangements are about equally common. It receives also the openings of 

 the anterior- ethmoidal cells, the aperture of the antrum into the infundibulum, and 

 a larger opening from the antrum behind the infundibulum. The lachrymal catial 

 opens into the inferior meatus under the fore part of the turbinate. External to the 

 outer wall are the orbit, the antrum, and farther back the spheno-maxillary fossa 

 with the posterior palatine canal below it. 



The Accessory Pneumatic Cavities. — These include the frojital sinuses, 

 the maxillary antra, the etlwioidal cells, and the sphotoidal siiiuses. They have 

 already been described with the separate bones, but may be here further briefly con- 

 sidered in their mutual relations to the nasal fossae and the skull. All of these spaces 

 open into the nasal chambers above the inferior meatus, — the sphenoidal cells into 

 the roof, the posterior ethmoidal cells into the superior meatus, the anterior eth- 

 moidals, the antra, and the frontal sinuses into the middle meatus. 



Fig. 258. 



Infratemporal crest Spheno-maxillary fissure 

 Spheno-palatine foramen 



Glenoid fossa 



Malar 

 bone 



Infra- 

 orbital 

 foramen 



Mastoid process 

 External auditory meatus 



Styloid process Zygoma 

 Inner wall of zygomatic fossa (external ptery' 

 goid plate) 



Spheno-maxillary fossa seen through ptervgo- 

 maxillary fissure 



Posterior dental canal 

 Hamular process 



Lateral view of skull with zygomatic arch removed. 



The sphenoidal sinuses (Fig. 257) are almost invariably unequal, the sep- 

 tum being much to one side. The large openings in the front of the body of the 

 sphenoid are much reduced when the cornua sphenoidalia are in place. The open- 

 ings of the posterior ethmoidal cells are small and irregular. The anterior 

 cells make a part of the floor of the frontal sinuses. They open either into the 

 infundibulum or under the middle turbinate. 



The frontal sinuses (Figs. 255. 257), when exposed from the front, have 

 a vaguely triangular outline. One side is against the septum, separating it from 

 its fellow, which is rarely symmetrical. The upper border runs from the top of 

 this downward and outward. The lower border bends downward at the inner end, 

 where the cavity runs down to the nose at the inner angle of the orbit. The innei 

 part extends back for a varying distance over the orbit. In about half the cases 

 the cavity opens directly into the middle meatus; in the rest it opens into the top of 



