NASAL CHAMBERS. 325 



nostrils is very thin, containing a quantity of pigment, or 

 colouring material. It is continuous with the mucous membrane 

 of the interior, and adheres to the muscles by dense fibro-cellular 

 tissue. 



The blood-vessels are the superior coronary, nasal, and palato- 

 labial arteries and veins. The nerves are derived from the fifth 

 and seventh pairs. 



In the horse the power of dilating the nostril attains its 

 maximum. The use of the nostril is to give passage to the air 

 in inspiration and expiration. 



NASAL CHAMBERS. 



These are cavities extending from the cribriform plates of the 

 ethmoid bone to the nostrils, in a direction parallel to the long 

 axis of the face, and are separated from each other by the cartila- 

 ginous septum nasi, which in age undergoes partial ossification^ 

 and is attached postero-inferiorly to the groove of the vomer. 

 Being continuous with the perpendicular plate of the ethmoid, 

 superiorly it rests in a groove formed by the union of the nasal 

 bones, thus preventing any communication between the chambers. 

 Anteriorly, it is expanded and attached to the alar cartilages of 

 the nostrils. The interval wall of the chambers is smooth, and 

 formed by the septum nasi ; the external, which is irregular, is 

 chiefly formed by the superior maxilla. The roof is formed by 

 the nasal and part of the frontal bones. The floor, broader and 

 shorter than the roof, is completed by the palatine process of the 

 superior maxilla and the palatine bones, and is concave from 

 wall to wall. The anterior extremity contains the nasal 

 openings. The posterior is occupied above by the cells of the 

 ethmoid ; below is the oval opening common to the posterior 

 nares, which communicate with the pharynx. Each chamber is 

 divided by the turbinated bones into three passages, or meati ; 

 the superior lies between nasal and frontal bones above, and the 

 superior turbinated bone below ; the middle between the two 

 turbinated bones, reaching to the cribriform plates of the ethmoid 

 bone ; while the inferior is between the inferior turbinated bone 

 and the floor of the chamber. 



The nasal chambers are lined by a delicate, pale rose-coloured 

 mucous membrane, the pituitary or Schneiderian membrane, 

 which is continuous with the skin at the nostrils, the mucous 



