[Illustration: FIG. 103.--CROSS-SECTION OF THE CARTILAGES OF THE EXTERNAL NOSE. _a_, cartilage of the median septum; _b_, “wings”; _c_, ridge formed by internal portion of wing.] The =nares= or cranial openings of the nasal cavity are supported 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 cartilaginous septum, two thin cartilaginous wings (_b_) extend laterad, forming the dorsal wall of the narial opening. Each then turns ventrad to form the lateral wall of the opening, but does not form the ventral floor; instead it curves mediad and finally dorsad, thus extending from the floor of the opening as a prominent ridge (_c_) within the nares. The 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 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.