THE NASAL CAVITIES. 441 



nose., a single muscle placed on the widened portion of the cartilaginous 

 pieces ; the supermaxillo-nasalis magnus (dilatator naris lateralis Percivall), 

 or pyramidal muscle of the nose, whose insertion occupies the whole extent 

 of the external wing; the supermaxillo-nasalis parvus (nasalis brevis labii 

 superioris Percivall), fixed, by its two portions, to the skin of the false 

 nostril; the middle anterior (depressor alse nasi Percivall) which is con- 

 founded, superiorly, with the external fasciculus of the preceding muscle, 

 it being attached to the inferior branch of the cartilaginous appendix of the 

 maxillary turbinated bone ; and, lastly, the supernaso-labialis (levator labii 

 superioris alwque nasi Percivall), whose anterior branch is inserted, in 

 part, into the external wing. All these muscles having been described in 

 the Myology (page 220), need not be further alluded to here. 



Integuments of the nose. The skin covering the alsB of the nose, ex- 

 ternally, is doubled over their free margin to line their internal face, being 

 prolonged over the entire extent of the false nostril, and is continued, in 

 the nasal fossas, properly called, by the pituitary membrane. This skin is 

 fine, thin, charged with colouring pigment, often marked by leprous spots, 

 and adheres closely to the muscles included between its duplicatures, through 

 the medium of a very dense and resisting fibro-cellular tissue. 



Vessels and nerves. The nostrils are supplied with blood by the superior 

 coronary, the external nasal, and the palato-labial arteries ; it is returned by the 

 glosso-facial veins, and partly by the venous network of the nasal mucous 

 membrane. The lymphatics, large and abundant, receive those of the 

 pituitary membrane, and join the submaxillary glands by passing over the 

 cheeks. The nerves are very numerous, the sensory being derived from 

 the maxillary branch of the fifth pair, and the motors from the facial 

 nerve. 



FUNCTIONS. The nostrils permit the entrance to the nasal cavities, 

 of the air which is to pass to the lungs. Their dilatability allows the 

 admission of a greater or less volume, according to the demands of 

 respiration. It is to be remarked that, in Solipeds, the nostrils constitute 

 the only channel by which the serial column can be introduced to the 

 trachea, in consequence of the great development of the soft palate, which is 

 opposed to the entrance of air by the mouth ; these orifices are also, for the 

 same reason, relatively larger than in the other domesticated animals, in 

 which the passage of air, by the buccal cavity, is easily accomplished. 



2. The Nasal FOSSM. (Figs 223,224.) 



Channeled in the substance of the head, above and in front of the palate, 

 and separated from one another, in the median plane, by a cartilaginous 

 septum which does not exist in the skeleton, the nasal fossaB extend from the 

 nostrils to the cribriform plate of the ethmoid bone, in a direction parallel 

 to the larger axis of the head. Their length is, therefore, exactly measured 

 by that of the face. See Fig. 223 for the whole of these cavities. 



The nasal fossaB are formed by two lateral walls, a roof or arch, a floor, and 

 Jwo extremities. 



Walls. The two walls are very close to each other, and the more so as 

 they are examined towards the ethmoid bone and the roof of the cavity. The 

 space separating them varies, in proportion as it is measured at the level of 

 the turbinated bones or at the meatuses. 



Inner wall. This is formed by the nasal septum, and is perfectly 

 smooth. 



