10S4 



THE ORGANS OF SPECIAL SENSE 



versely at their widest part. The nasal fossae in the dry skull open in front by 

 the anterior nasal aperture (apertura pyriformis). 



The posterior nares (choanae) are two oval openings, which are smaller in the 

 living or recent subject than in the skeleton, because they are narrowed by the 

 mucous membrane. Each measures an inch (2.5 cm.) in the vertical and half 

 an inch (1.2 cm.) in the transverse direction in a well-developed adult skull. 



For the description of the bony boundaries of the nasal fossse see page 138. 



Inside the aperture of the nostril is a slight dilatation, the vestibule (vestibulum 

 //f/.y/), which extends as a small pouch, the ventricle, toward the point of the nose. 

 Above and behind the vestibule is surrounded by a prominence (limen nasi). 

 Below the prominence the vestibule is lined with skin; above and behind it the 

 fossa is lined with mucous membrane. The fossa, above and behind the vesti- 

 bule, has been divided into two parts an olfactory portion (regio olfactoria), a slit- 



PROBC 

 SINUS TH ft *-4> 



OPENINGS OF POSTERIOR 

 ETHMOIDAL CELLS 



SPHENOIDAL 

 SINUS 



FIG. 791. External wall of right nasal fossa, parts of the turbinates having been cut away to show the 

 orifices of the sinuses which open into the meatuses. (Testut.) 



like cavity, comprising the upper and central part of the septum and the superior 

 turbinated process, and a respiratory portion (regio respiratoria), which comprises 

 the rest of the fossa. 



The Outer Wall (Figs.^790 and 791). The superior, middle, and inferior meatus 

 (meatus nasi superior, medius, and inferior] are described on page 141. The 

 sphenoidal air sinus opens into the sphenoethmoidal recess (recessus xpheno- 

 ethmoidalis), a narrow recess above the superior turbinated process (Fig. 791). 

 The posterior ethmoidal cells open into the front and upper part of the superior 

 meatus (Fig. 790). On raising or cutting away the middle turbinated process 

 the outer wall of the middle meatus is fuily exposed (Figs. 791 and 792) and pre- 

 sents (1) a rounded elevation, termed the bulla ethmoidalis, opening on or immedi- 

 ately above which are the orifices of the middle ethmoidal cells; (2) a deep, narrow, 

 curved groove, in front of the bulla ethmoidalis, termed the hiatus semilunaris, 

 into which the anterior ethmoidal cells and the maxillary sinus open, the orifice 

 of the latter being placed near the level of its roof. The middle meatus is pro- 



