308 HEAD AND NECK 



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

 part. 



The medial nasal branches of the anterior ethmoidal 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 branch of the spheno-palatine 

 artery, which accompanies the naso-palatine nerve; (2) a 

 branch of the anterior ethmoidal, accompanying 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 to the lower and front part of the 

 septum. 



Dissection. Disengage the naso-palatine nerve and the 

 medial branches of the anterior ethmoidal nerve from the surface 

 of the muco-periosteum of the septum, in order that, afterwards, 

 they may be traced to their origins. Then, with scissors, divide 

 the muco-periosteum along the roof ot the nasal cavity and 

 turn it down. When that is done, the opposite nasal cavity 

 will be 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 choancz, open into the naso- 

 pharynx and look backwards and downwards. 



The narrow roof of the nasal cavity consists of a 

 middle, 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, by the 

 nasal bone, and by the angle between the lateral cartilage and 

 the septal cartilage. The posterior part of the roof is com- 

 posed of the anterior and inferior surfaces of the body of the 



