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 begiris 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. 
