1204 



THE RESPIRATORY SYSTEM 



cation with the pharynx is established through the paired choanae. Furthermore 

 accessory nasal cavities, the paranasal sinuses, open into the cavum nasi. The 

 walls of the nasal cavit}^ are covered with periosteum and mucosa, the latter pre- 

 senting important differences in the .respiratory and olfactory regions. The 

 organ of smell, included in the nasal cavity, is described on p. 1049. 



The cavum nasi is divided into right and left symmetrical parts, called the nasal 

 fossse, by the septum of the nose [septum nasi]. The latter is supported by a 

 framework composed of the osseous septum [septum nasi osseum] posteriorly, and 

 the cartilaginous septum [septum cartilagineum] anteriorly. Antero-inferiorly, 

 the small movable part of the septum is also called the membranous septu7n 

 [septum membranaceum]. 



The nasal septum is almost always straight in primitive races and Caucasian 

 children; but in a large proportion of Caucasian adults it is deflected to one side or 

 the other. 



Fig. 966. — Sagittal Section through the Facial Part of the Head and the Bodies 

 OF the upper three Cervical Vertebrae. The section lies to the right of the median 

 plane. The nasal septum has been removed. (Rauber-Kopsch.) 



Cribriform plate 



Spheno-ethmoidal , 



Hypophysis recess ' 



Dorsum sellse 



Choanal arch - - jtr.\ 



Nasopharyngeal -^,' 



meatus l''t''J'^- 



Pharyngeal tonsil ■■ ''" - 



Torus tubarius 

 Levator cushion ...- y 

 Anterior lip ' 

 of tubal aperture ■ r f f> - V 

 Salpingopharyn- ■i\vi'»r \ j 

 gealfold " \,';1' *' 



Uvula ■ -*^ ^ • ' 



Foramen csecum 

 Palatopharyngeal fold 



Epiglottis 



,/ 1 Incisive canal 



— Upper lip 



i, .. .. Vestibulum oris 



.,.. - .. Mouth cavity proper 



^,; , - Lower lip 



■^ — Sublingual mucosa 



Hyoid bone 



In the septum, upon each side, just superior to the nasal spines of the maxilla;, there is 

 frequently a minute opening loading superiorly and posteriorly and ending blindly. This cavity 

 is closely related to the vomero-nasal cartilage and is a rudimentary representative of the vomero- 

 nasal organ (of Jacobson) [organon vomero-nasale|, which in some animals is well developed 

 and receives a branch of the olfactory nerve. On the floor of the nasal cavity about 2 cm. from 

 the posterior margin of the naris and near the nasal septum a small depression, the nasopalatine 

 recess, is often seen. This is the mouth of the incisive duct [ductus incisivus] which leads into 

 the incisive canal for a greater or less distance and may even extend to the mouth, where its 

 termination is marked by the incisive pajjilla. 'I'ho incisive duct indicates the jiosition of a 

 foramen which in the embryo connected tlie mouth and nose. 



The naris leads upward into the vestibule of the nose [vestibulum nasi], the 

 small cavity within tlio compass of the greater alar cartilage. Its walls are lined 

 with skin Ix'set with tiie large hairs called vibrissas and containing many seba- 

 ceous glands. I'he vibrisste serve to protect the nasal cavity from the entrance of 

 foreign matter. On tiie lateral wall, the vestibule is marked off from the rest of 

 the nasal cavity by a distinct ridge, the limen nasi, corresponding to the superior 

 margin of the greater alar (cartilage. On the lateral wall of the cavity within the 

 limen nasi are three antero-posterior ridges, tin; superior, middle, and inferior 



