244 THE VISCERA. 



the horizontal plate formed by the vomer and ethmoid, and 

 opens caudad at the choanae into the nasopharynx. The 

 dorsal or superior meatus of the nose lies just ventrad of the 

 superior nasal concha, next to the median septum ; it leads to 

 the frontal sinus, the lamina cribrosa, and the caudal parts of 

 the ethmoid. The middle meatus of the nose has almost dis- 

 appeared in the cat ; it is simply the narrow space between the 

 superior and inferior meati. It is practically filled by the 

 ethmoid, into the cells of which it leads. The mucosa is con- 

 tinued from the nasal cavity into the sinuses of the frontals and 

 presphenoid. 



At the sides of the nasal septum, near the ventral edge, 

 and about one to one and a half centimeters caudad of the 

 nares, there is on each side a small curved cartilaginous tube, 

 about one centimeter or less in length. This, the vomeronasal 

 organ, or organ of Jacobson, lies against the septum, between 

 it and the mucosa. It begins at the incisive canal or anterior 

 palatine foramen, in the roof of the mouth, curves thence 

 caudodorsad close against the side of the nasal septum, and 

 ends blindly in the nasal cavity. 



The nares or cranial openings of the nasal cavity are sup- 

 ported by a number of cartilages which form the framework of 

 the snout or external nose. The cartilaginous continuation of 

 the lamina perpendicularis extends some distance craniad of 

 the tips of the nasal and premaxillary bones, forming the 

 septum of the external nose (Fig. 103, a). 

 From the dorsal edge of this projecting car- 

 tilaginous septum, two thin cartilaginous wings 

 (b] extend laterad, forming the dorsal wall of 

 FIG. 103. CROSS- the narial opening. Each then turns ventrad 



SECTION OF THE . 



CARTILAGES OF to form the lateral wall of the opening, but 



THE EXTERNAL d oes no t form the ventral floor; instead it 

 NOSE. 



a, cartilage of the curves mediad and finally dorsad, thus ex- 

 median septum; t>, tending from the floor of the opening as a 



"wings"; c, ridge . . ' 



formed by internal prominent ridge (c) within the nares. The 

 portion of wing. cartilaginous wing is thus rolled into a sort of 

 spiral, ending with a free edge within the narial opening. 

 From the ventral edge of the median cartilaginous septum there 



