THE NASAL CAVITIES. . 443 



bone : it is the narrowest. The middle, comprised between the two tur- 

 binated bones, presents, on arriving near the ethmoidal cells, the orifice 

 which brings all the sinuses into communication with the nasal fossa. This 

 orifice is ordinarily narrow and curved; but we have seen it sometimes 

 converted into a foramen sufficiently wide to permit the introduction of a 

 finger end. It is also by this meatus that the inferior compartment of the 

 turbinated bones opens into the nasal fossa, these two bones being each 

 rolled in a contrary direction. The inferior meatus, situated under the 

 maxillary turbinated bone, is not distinct from the floor of the nasal cavity. 

 See figure 224 for the arrangement of the turbinated bones and the meatuses 

 on the external wall of the nose. 



Hoof or arch. This is formed by the nasal bone, and is only a narrow 

 channel, confounded, as has been said, with the superior meatus. 



Floor. Wider, but not so long as the roof, which is opposite to it, but 

 from which it is distant by the height of the cartilaginous septum, the floor 

 is concave from side to side, and rests on the palatine arch, which separates 

 the mouth from the nasal cavities. 



In front of this nasal region is remarked the canal or organ of Jacobson : 

 a short duct terminating in a cul-de-sac in the middle of the cartilaginous 



Fig. 224. 



LONGITUDINAL MEDIAN SECTION OF THE HEAD AND UPPER PART OF NECK. 



1, 1, Atlas; 2, 2, Dentata ; 3, Trachea; 4, Right stylo-thyroideus ; 5, Guttural 

 pouch; 6, Stylo-pharyngeus ; 8, Palato-pharyngeus ; 9, Sphenoidal sinus; 10, 

 Cranial cavity; 11, Occiput; 12, Parietal protuberance; 13, Frontal sinus; 

 14, Ethmoidal turbinated bone; 15, Maxillary turbinated bone; 16, Entrance to 

 nostril, 18, Pharyngeal cavity; 19, Inferior maxilla; 20, Premaxilla; 21, 

 Hard palate. 



substance which closes the incisive foramen. At the bottom of this cul-de- 

 sac opens a second canal, longer, wider, and more remarkable, but which 

 has not yet been described. (It has been described by Stenson, and is named 

 " Stenson's duct.") It has sometimes the diameter of a writing quill, 

 commences by a cul-de-sac on a level with the second molar tooth, accom- 

 panies the inferior border of the vomer from behind to before, where it is 

 enveloped in a kind of cartilaginous sheath a dependency of the nasal 

 septum ; it terminates, as we have said, after a course of about 5 inches, 



