820 THE ORGANS OF SPECIAL SENSE. 



Nasal Fossae. 



The nasal fossae are two irregular cavities situated in the middle of the face, 

 and extending from before backward. They open in front by the two anterior 

 nares, and terminate, behind, by the posterior nares in the naso-pharynx. The 

 anterior nares are somewhat pear-shaped apertures, each measuring about one inch 

 antero-posteriorly and half an inch transversely at their widest part. The posterior 

 nares 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 in the vertical, and half an inch in the transverse direction in a 

 well-developed adult skull. 



For the description of the bony boundaries of the nasal fossae see section on 

 Osteology. 



Inside the aperture of the nostril is a slight dilatation, the vestibule, which 

 extends as a small pouch, the ventricle, toward the point of the nose. The fossa, 

 above and behind the vestibule, has been divided into two parts: an olfactory 

 portion, consisting of the upper and central part of the septum and probably the 

 superior turbinated bone, and a respiratory portion, which comprises the rest of 

 the fossa. 



Outer Wall. The sphenoidal air sinus opens into the spJieno-ethmoidal recess, 

 a narrow recess above the superior turbinated bone. The posterior ethmoidal 

 cells open into the front and upper part of the superior meatus. On raising or 

 cutting away the middle turbinated bone the outer wall of the middle meatus is 

 fully exposed, and presents (1) a rounded elevation, termed the bulla ethmoidalis, 

 opening on or immediately 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 Avhich the anterior ethmoidal cells and the antrum of 

 Highmore open, the orifice of the latter being placed near the level of its roof. 

 The middle meatus is prolonged, above and in front, into the infundibulum, which 

 leads into the frontal sinus. The anterior extremity of the meatus is continued 

 into a depressed area, which lies above the vestibule and is named the atrium. 

 The nasal duct opens into the anterior part of the inferior meatus, the opening 

 being frequently overlapped by a fold of mucous membrane. 



The inner wall or septum is frequently more or less deflected from the mesial 

 plane, thus limiting the size of one fossa and increasing that of the other. Ridges 

 or spurs of bone growing outward from the septum are also sometimes present. 

 Immediately over the incisive foramen at the lower edge of the cartilage of the 

 septum a depression, the naso-palatine recess, may be seen. In the septum close 

 to this recess a minute orifice may be discerned : it leads into a blind pouch, the 

 rudimentary organ of Jacobson, which is well developed in some of the lower ani- 

 mals, and is supported by a plate of cartilage, the cartilage of Jacobson. 



The mucous membrane lining the nasal fossae is called the pituitary, from the 

 nature of its secretion ; or Schn eider ian, from Schneider, the first anatomist who 

 showed that the secretion proceeded from the mucous membrane, and not, as was 

 formerly imagined, from the brain. It is intimately adherent to the periosteum 

 or perichondrium, over which it lies. It is continuous externally with the skin 

 through the anterior nares, and with the mucous membrane of the naso-pharynx 

 through the posterior nares. From the nasal fossse its continuity may be traced 

 with the conjunctiva through the nasal duct and lachrymal canals; with the 

 lining membrane of the tympanum and mastoid cells through the Eustachian 

 tube ; and with the frontal, ethmoidal, and sphenoidal sinuses, and the antrum of 

 Highmore through the several openings in the meatuses. The mucous membrane 

 is thickest and most vascular over the turbinated bones. It is also thick over the 

 septum, but in the intervals between the spongy bones and on the floor of the 

 nasal fossae it is very thin. Where it lines the various sinuses and the antrum of 

 Highmore it is thin and pale. 



Owing to the great thickness of this membrane, the nasal fossae are much 



