518 



RESPIRATORY APPARATUS IN MAMMALIA. 



The Nasal Cavities. 



These cavities are two in number — a right and left — and offer for study : their 

 entrance, or nostrils — the fossce, properly called, which constitute these cavities ; 

 and the diverticuli named sinuses. 



Preparation. — Remove the lower jaw from three heads. On the first of these make two 

 transverse sections, one passing between the second and third molar tooth, the other behind 

 the dental arch. Saw through the second head longitudinally and vertically, a little to one 

 side of the median line. On the third make a horizontal section in such a manner as to obtain 

 an inferior portion analogous to that shown in Fig. 41. On this the organ of Jacobson may 

 be studied. 



Fig. 306. 



1. The Nosteils. 



The nostrils (or anterior or inferior nares) are two oblong, lateral openings, 

 situated at the extremity of the nose, circumscribed by lips or movable ivings 

 (alee) disposed in an obhque direction downwards and inwards, and slightly 

 curved on themselves, so as to present theu' concavity to the external side. 



The lips or alee of the nostril are enveloped, inwardly and outwardly, by a 

 thin, delicate skin, covered by fine, short hairs. The external is concave on its 

 free margin ; the internal is convex. The commissure which unites these two 

 wings superiorly, fonns a slight arch curved inwards. When the finger is 

 introduced into this commissure it does not enter the nasal cavity, but the false 

 nostril — a conical pouch formed by the skin, extending 

 to the angle comprised between the nasal spine and the 

 ascending process of the premaxillary bone. 



In the Ass, according to Goubaux, the false nostrU is 

 areolated at the posterior extremity, which ascends beyond 

 the summit of the re-entering angle formed by the nasal 

 and premaxillary prolongation. 



The inferior commissure is round and wide, and, to- 

 wards the bottom, presents an opening, sometimes double^ 

 which looks as if punched out ; this is the inferior orifice 

 of the lachrymal duct, which, in the Ass and Mule, is 

 carried to the inner face of the external wing, near the 

 superior commissure. 



Steucture. — The nostril is composed of a carti" 

 laginous frameivorlc, muscles to move it, and shin, vessels^ 

 and nerves. 



Cartilaginous frameworlc (Fig. 306). — This framework 

 is formed by a cartilage, bent like a comma, and which, in 

 its middle part, lies against that of the opposite side, the 

 two making a kind of figure X. Fixed in a movable 

 manner to the inferior extremity of the middle septum 

 of the nose, by means of short intei-posed fibres, this cartilage offers : a wide upper 

 part, situated in the substance of the inner wing of the nostril, and covered by 

 the dilatator naris transversalis of the nose (Fig. 306, 1) ; and an inferior portion, 

 which, after passing into the lower commissure, is prolonged, in a blunt point, to 

 the external wing, where it receives the insertion of several fasciculi belonging to 

 the orbicularis muscle of the lips, the dilatator naris lateralis, and the levator 

 labii superioris (Fig. 306, 2). Each wing, therefore, possesses its cartilaginous 



CARTILAGES OF THE 



NOSTRILS 



1, 1, Wide portion, forming 

 the base of the internal 

 wing of the nostril ; 2, 

 2, narrow extremity pro- 

 longed into the external 

 wing; 3, superior or an- 

 terior border of the nasal 

 septum. 



