440 



TEE RESPIRATORY APPARATUS IN MAMMALIA. 



Preparation. Eemove 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 arcade. 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 figure 23. 



1. Tlie Nostrils. 



The nostrils are two oblong, lateral openings, situated at the extremity 

 of the nose, circumscribed by lips or movable wings (alee) disposed in an 

 oblique direction downwards and inwards, and slightly curved on them- 

 selves, so as to present their 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, forms a slight cross 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 elevated process of the pre- 

 maxillary bone. 



In the Ass, according to Goubaux, the false nostril 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, towards 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. 

 STRUCTURE. The nostril is composed of a cartilaginous framework, 

 muscles to move it, and integuments, vessels, and nerves. 



Cartilaginous framework (Fig. 222). 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 interposed fibres, this 

 cartilage offers : a wide upper part, situated in the 

 substance of the inner wing of the nostril, and covered 

 by the transverse muscle of the nose (Fig. 222, 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 pyramidal muscle of the nose, and 

 the supernaso-labialis (Fig. 222, 2). Each wing, 

 therefore, possesses a cartilaginous skeleton ; but that 

 of the external wing is very incomplete, in conse- 

 quence of its being only formed by the inferior ex- 

 tremity of the common cartilage. 



This cartilage, it will be understood, sustains the 

 of the nose, prevents their falling inwards, and 



Fig. 222. 



CARTILAGES OF THE NOSE. 



1, 1, Wide portion, form- 

 ing the base of the inter- 

 nal wing of the nostril , 

 2 r 2, Narrow extremity 



prolonged into the ex- alwayg keeps op - en the external orifices of the re- 

 ternal wing ; o, oupenor . * 

 or anterior border of the Spiratory apparatus. 



Muscles. The motor muscles of the alas are all 

 dilators in the domesticated animals. They are : the 



transversalis nasi (dilatator naris anterior Percivall), or transversalis of the 



septum. 



