RESPIRATORY ORGANS. 245 



are likewise lateral extensions, which form part of the ventral 

 boundary of the nares ; these do not quite reach the ventral 

 parts of the dorsal wings, however, so that a small part of the 

 narial opening is not bounded by cartilage. A section of the 

 narial cartilages is shown in Fig. 103. The wings from the 

 dorsal edge of the septum do not extend quite to the cranial 

 tip of the nose, so that a notch is formed on the ventrolateral 

 side of the nares ; a section in this region would therefore differ 

 from that figured. 



The framework of the external nose thus formed is covered 

 externally by thick hairless skin, containing many glands. 

 From the ventral end of the internarial septum a groove passes 

 ventrad, partly dividing the upper lip. 



The inner surfaces of the cartilages are covered by the 

 mucosa, which forms a number of ridges. The narial opening 

 is almost completely divided by the prominent ridge which is 

 supported by the free edge {c) of the cartilaginous wing above 

 described. This free edge is covered by a thick layer of 

 mucosa, and the entire ridge so formed is continuous caudad 

 with the inferior nasal concha. On the medial side of the 

 partial partition formed by this ridge and near the ventral side 

 there begins a slight distance caudad of the outer opening 

 another ridge, supported by the ventrally incurved portion of 

 the cartilaginous ring. This soon becomes a thick swelling; 

 beneath it opens the lachrymal canal, and that part of the 

 passageway that lies ventromediad of it is the beginning of the 

 inferior meatus of the nose. About one or two centimeters 

 caudad of the external opening a third ridge projects from the 

 dorsolateral wall of the cavity toward the large ridge first 

 described ; dorsomediad of it is a narrow passage which is the 

 entrance to the superior meatus of the nose. 



The olfactory mucosa, or that part to which the olfactory 

 nerve is distributed, and which therefore acts as the sensory 

 surface, is confined to the dorsocaudal parts of the nasal 

 cavity, in the region occupied by the cells of the ethmoid. 

 The air penetrates to this region probably only by a definite 

 act of snuffing, the inferior meatus serving as the usual passage- 

 way of air to the lungs. 



