142 



THE RMSPIBATOBY AFPABATUS IN MAMMALIA. 



Outer wall. — This is chiefly constituted by the supermaxillary bone, 

 is very rugged, and is divided into three meatuses, or passages, by the 

 turbinated bones — the irregular columns applied against the inner face of the 

 before-mentioned bone. 



The turbinated bones have already been described, and we will only now 

 refer to the principal features of their organisatiou. Each is formed of a 

 bony plate rolled upon itself (Fig. 223, 2, 3), and is divided, internally, into 

 two sections, the superior of wMch forms part of the sinus, and the in- 

 ferior belongs to the nasal fossse ; they are continued, inferiorly, by a fibro- 

 cartilaginous framework, which prolongs their nasal section to the external 

 orifice of the nose. The flexible appendix of the ethmoidal turbinated bone 

 is usually single, sometimes double, and disappears before reaching the alea 

 of the nose. That of the maxillary turbinated . bone is always bifurcated. 



Fig. 223. 



TRANSVERSE SECTION OF THE HEAD OF AN OLD HORSE, SHOWING THE AEEANQEMENT 

 OF THE NASAL CAVITIES AND MOnTH. 



1, Nasal fossa; 2, Superior turbiuated bone-, 3, Inferior ditto; 4, Median septum of 

 the nose ; 5, Central part of the buccal cavity (drawn more spacious than it 

 really is when the two jaws are brought together) ; 6, 6, Lateral portions of the 

 same ; 7, Section of the tongue. 



and its antero-superior branch is directly continued by the superior extremity 

 of the internal wing of the nostril. 



The meatuses are distinguished into superior, middle, and inferior, or into 

 anterior, middle, and posterior, as the head is inspected in a vertical or hori- 

 zontal^ position. The superior passes along the corresponding border of the 

 ethmoidal turbinated bone, and is confounded with the roof of the nasal 

 cavity ; it is prolonged, behind, to near the cribriform plate of the ethmoid 



