140 OUTLINES OF EQUINE ANATOMY. 



mity of the latter is continuous by means of a fold of 

 mucous membrane witb the inferior turbinated bone. 



Dilator naris anterior runs from the external sur- 

 face of one ala to that of the other, while the corneal 

 cartilages are connected together anteriorly by a direct 

 continuation of it, by some anatomists termed cor- 

 nealis transversus. Dilatores naris superior and inferior, 

 levator labii superioris alseque nasi, and retractor labii 

 superioris, also become attached to these cartilages. The 

 skin extends around the margin of the nostril, as formed 

 by these structures, and is continued for a short distance 

 in the nasal chamber, where it insensibly blends with the 

 mucous membrane. About the point of junction at the 

 outer side, inclined to the superior part of the nostril (infero 

 internal in the horse), is the anterior- opening of the ductus ad 

 nasum which looks as though " punched out of the mucous 

 membrane," On the outer side the common integument be- 

 comes very thin, hairless, and prolonged in the angle between 

 the superior process of the anterior maxilla and the free 

 margin of the nasal bones, to form a blind pouch, the false 

 nostril, which we have found filled with epithelial layers of 

 cells. To the posterior extremity of this a muscle which runs 

 from just above the anterior termination of the zygomatic 

 ridge is attached, also levator labii superioris alseque nasi. 

 Into this cavity the air passes directly from the anterior 

 naris ; it has to diverge slightly inwards to gain the nasal 

 chamber. The roof of the nasal chamber is formed by the 

 inferior concave surface of the nasal bone, posteriorly by 

 the nasal plate of the frontal bone. The outer wall pre- 

 sents the two ossa turbinata, by means of which the cavity 

 is divided into three meatus. 



The superior turbinated bone is attached to the inner 

 surface of the nasal bone, and consists of a. thin plate 

 curled from above downwards. Anteriorly it terminates 

 by a cartilaginous prolongation, which gradually blends 

 with the wall of the chamber ; posteriorly it is directly 

 continuous with the lateral mass of the ethmoid bone. 

 Its cavity is divided by a partition into two parts ; the ante- 

 rior helps to form the nasal chamber opening into the 

 middle meatus ; the posterior forms part of the superior 

 maxillary sinus. 



The inferior turbinated bone is attached to the inner 

 surface of the superior maxillary nasal plate. It is smaller 



