NASAL CAVITIES 391 



In favourable cases a minute orifice may be detected in the mucous 

 membrane, on the lower and anterior part of the nasal septum, immediately 

 posterior ,to the vestibular area. It is placed above the anterior end of a 

 well-marked elongated projection which passes obliquely posteriorly and 

 upwards, and corresponds to the thickened lower margin of the septal 

 cartilage. This aperture varies in diameter from ^ mm. to i^ mm. 

 (Schwalbe). It leads into a narrow canal, which passes posteriorly for 

 a short distance, and then ends blindly. It is of interest because it 

 represents in the human subject the rudiment of the voniero-nasal organ 

 (O.T. organ of Jacobsoii], a tubular structure which is highly developed in 

 some of the lower animals. 



Construction of the Nasal Septum. Strip the muco- 

 periosteum from the exposed surface of the septum nasi and 

 the parts forming the septum will be rendered visible. The 

 bulk of the partition is composed of the perpendicular lamina 

 of the ethmoid and the vomer posteriorly, and of the septal 

 cartilage anteriorly. Small portions of other bones take a 

 minor part in its construction. Thus, above and posteriorly 

 there are the crest and rostrum of the sphenoid ; above and 

 anteriorly is the nasal spine of the frontal bone ; whilst below 

 there is the crest of bone formed by the apposition of the 

 palatal processes of the palate and maxillary bones of opposite 

 sides. 



Cartilago Septi Nasi. The septal cartilage fills up the 

 wide angular gap which intervenes between the perpendicular 

 lamina of the ethmoid and the vomer, and it projects anteriorly 

 towards the point of the nose. It is a broad irregularly 

 quadrilateral plate. Its upper and posterior border is in ap- 

 position with the anterior border of the perpendicular lamina 

 of the ethmoid ; its lower and posterior border, much thickened, 

 is received into the groove in the anterior border of the vomer 

 and the nasal crest of the maxillae. The angle between these 

 two borders is prolonged posteriorly, for a varying distance, 

 in the form of a tongue-shaped cartilaginous process, which 

 occupies the interval between the two plates of the vomer. 

 The upper and anterior border of the septal cartilage is in 

 contact above with the suture between the two nasal bones ; 

 below this it is related to the two lateral cartilages of the 

 nose, whilst still lower down it is seen in the interval between 

 the two larger alar cartilages. 



Its connection with the lateral cartilage on each side is a very intimate 

 one ; indeed, below the nasal bones, the three cartilages are directly 

 continuous, but lower down they are separated by a fissure which runs 

 upwards for some distance on each side. The lower and anterior border is 

 very short ; it is free, and extends posteriorly to the anterior nasal spine. 



