324 



^LANCHNOLOGY. 



extremity of the nasal chambers, and disposed obliquely from 

 above downwards, and without inwards, being slightly curved so 

 as to present their concavities externally. The nostrils consist 

 of an incomplete cartilaginous skeleton covered by muscles, and 

 lined internally by mucous membrane. They are bounded by 

 movable wings, or alee, which are covered within and without by 

 a thin delicate skin, clothed with fine soft hairs. The external 

 wing is concave on its free border, the internal being convex, 

 the commissures of the alse are a superior and an inferior. The 

 finger introduced into the superior commissure does not enter the 



nasal cavity, but a conical cul-de- 

 sac, the false nostril, a diverticulum 

 of the nose. This cavity is formed 

 by the skin, and lies in the * space 

 between the nasal peak and the 

 external process of the premaxillary 

 bone. The false nostrils communi- 

 cate freely with the nasal chambers ; 

 their precise use is unknown, but 

 they probably enlarge the nasal 

 openings during respiratory exertion. 

 The inferior commissure is large 

 and round, presenting, at a short 

 distance within, an opening, some- 

 times double, which is the inferior 

 orifice of the lachrymal conduit. In 

 the ass and mule this opening is 

 situated on the deep surface of the 

 external ala near to the superior 



Fio. 110. 



Cartilaginous framework of the nostril 

 — seen fronr^abOTe. a a. Right alar carti- 

 lage ; a' a'. Left alar cartilage ; b. Termi- 

 nal portion of the septum nasi. 



commissure. 



Each of the alar cartilages resembles an incomplete ring, the 

 incomplete portion being directed outwards. They are loosely 

 attached to the anterior extremity of the septum nasi and to 

 each other, and they serve to keep the nostrils open, permit 

 dilatation, and protect the nasal peak. They are divided into a 

 superior and inferior part. The former is large and flat, and 

 situated within the substance of the internal ala, being covered 

 by the dilatator haris 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 alaeque nasi are attached. The skin which covers the 



