NASAL CAVITIES 393 



A few nasal branches from the spheno-palatine ganglion, and 

 also from the nerve of the pterygoid canal, reach the muco- 

 periosteum over the superior and posterior part of the septum. 

 They are very minute, and it is questionable if the dissector 

 will be able to discover any trace of them in an ordinary part. 



The medial nasal branches of the anterior ethnwidal nerve 

 will be found descending over the anterior part of the nasal 

 septum. They may be traced as far as the vestibule. 



The arteries which convey blood to the septum nasi are : 

 (i) the posterior nasal septal, which accompanies the naso- 

 palatine nerve; (2) a branch of the anterior ethmoidal accom- 

 panying the medial branches of the anterior ethmoidal nerve ; 

 (3) some minute twigs to the upper part of the septum from 

 the posterior ethmoidal artery ; (4) the septal branch of the 

 superior labial artery, which is distributed upon the columna 

 nasi. 



Dissection. The muco- periosteum of the septum may now be divided, 

 by the scissors, along the roof of the nasal cavity. Before doing this, 

 disengage from its surface the naso- palatine nerve and the medial branches 

 of the anterior ethmoidal nerve, in order that they may be afterwards traced 

 to their origins. When the layer of muco-periosteum, thus detached from 

 the roof of the nose, is thrown down the nasal cavity is exposed. 



Cava Nasi. The nasal cavities are two chambers placed 

 one on each side of the septum nasi. They are narrow, but 

 the vertical depth and antero-posterior length of each cavity 

 is very considerable. The width increases somewhat from 

 above downwards; thus, in the upper part, the superior 

 concha is separated from the septum by an interval of only 

 2 mm., whilst lower down a space of 4 or 5 mm. intervenes 

 between the inferior concha and the septum. Each nasal 

 cavity presents a medial wall formed by the septum, a lateral 

 wall, a roof, a floor, and an anterior and a posterior aperture. 



The anterior apertures of the nasal cavities, or nostrils, are 

 two oval orifices which open upon the face and look down- 

 wards. The posterior apertures, or choance, open into the naso- 

 pharynx and look posteriorly and downwards. 



The narrow roof of the nasal cavity consists of an inter- 

 mediate horizontal portion formed by the cribriform plate of 

 the ethmoid bone, and of an anterior and a posterior sloping 

 part. The anterior part is formed by the narrow grooved 

 nasal surface of the frontal spine of the frontal bone, the 

 nasal bone, and the angle between the lateral cartilage and 



