NASAL CHAMBERS. 325 



by the dilatator naris transversalis. The inferior part is 

 prolonged by a blunt point to the external ala, to which the 

 orbicularis oris, dilatator naris lateralis, and levator labii 

 superioris alseque nasi are attached. The skin which covers the 

 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 fibre-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 internal 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 open- 

 ings. 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. 



