Below the nasal bones the external nose has a cartilaginous framework (Fig. 1). The septal or quadrangular cartilage gives off two approximately triangular wings, the triangular cartilages, which, forming the middle part of the side of the nose, adjoin the lower edge of the nasal bones, but overlap them on their internal side. Below this level the cartilaginous septum does not reach to the tip of the nose, the gap in the partition wall being completed by the movable membranous septum. The lower part of the nasal side contains the two cartilages of the nasal wing, each a thin plate reaching from the triangular cartilage to the tip and curved anteriorly so as to insert its "doubled" median border into the membranous septum. In the nasal wing this cartilage is fragmented vertically, thereby

FIG. 1.-Front view of

the external nose after removing the skin, showing the nasal bones, quadrangular and triangular cartilages (Zuckerkandl).

FIG. 2.-View of the nasal vestibule from below, showing the prominence of the fold (Zuckerkandl).

giving the nose flexibility. The triangular cartilage overlaps the lower cartilage likewise on the internal side,

and its prominent border appears as a projecting, horizontal fold, the plica vestibuli, which may be considered as the threshold of the nasal cavity, the space outside being the vestibule (Fig. 2).

The external skin lines the vestibule and changes gradually into mucous membrane at about the level of the protruding fold. As far as there is true skin the vestibule is protected against insects by coarse hairs— the vibrissæ. The external muscles surrounding the sides of the nose dilate the nostrils, while their relaxation results in collapse of the sides of the nose, variable with its degree of flexibility. The muscles are innervated by the facial nerve.

5. The nasal cavities are surrounded entirely by bony walls, but are separated from each other by the septum, which in its front portion remains cartilaginous. The floor of the nose is made up of the palatal process of the superior maxillary and the horizontal plates of the palate bones. It is a level, shallow gutter. The floor is the shortest of all the nasal walls, as the rear edge of the middle wall slopes backward and upward, besides being slightly concave toward the rear. As the free border of the septum determines the plane of the nasal opening into the pharynx, all nasal walls exceed the floor in length.

The middle wall or septum presents normally a nearly plane surface. The anatomic peculiarities of this wall will be considered in Chapter XVI.

The roof, completed in front by the awning of the nasal bones, consists of the cribriform plate of the ethmoid bone anteriorly, and of the body of the sphenoid bone in its posterior half. The ethmoid plate is the weakest part. The anterior surface of the sphenoid body slopes down and backward, while the inferior surface of this bone has, likewise, a slight slant toward the rear and down. The nasal space is hence considerably lower in the rear than in front (Fig. 3).

The external wall, the most complicated of all, is formed by three bones. The greater area below the floor of the orbit consists of the nasal surface of the superior maxilla, separating the nasal cavity from the maxillary sinus. From this there extends upward the narrow frontal process of the maxillary bone, which articulates posteriorly with the lamina papyracea of the

FIG. 3.-View of the external wall of the right nasal passage, with probes in the sphenoid sinus and in the nasal duct (Mihalkovics).

ethmoid bone, forming the partition wall between the orbit and the upper part of nose. At its rear edge the lamina papyracea joins the anterior surface of the sphenoid body, which, by its presence, reduces the height of the nasal passage. Below the sphenoid bone and posterior to the superior maxilla the external wall consists of the vertical plate of the palate bone.

The space inclosed by the nasal walls is approximately rectangular, but is encroached upon in such a manner by accessory bony structures, arising from the external wall, that each nasal cavity proper is reduced to a nearly triangular cross-section with a roof only 2 or 3 mm. wide, while near the floor each side is from 12 to 18 mm. wide. The bony ledges, which thus reduce the width of the

FIG. 4.-Frontal section through the nasal passages at the level of the orifice of the maxillary sinus. Anterior half seen from the rear: p, p, Uncinate process and, external to it, the hiatus semilunaris; c, anterior half of maxillary orifice; d, infundibulum; 7, 7, lamina papyracea (Zuckerkandl).

nasal passage, are the turbinate processes or turbinals (or concha). During embryonic formation there are six main turbinal ledges or projecting lamellæ, with a variable number of minor shelves between them. They follow a curve with its convexity downward and forward, and converge toward the posterior choana. By coalescence and partial arrest of development the number of turbinal ledges becomes reduced, so that at birth there

are but four or five. The inferior turbinal is a separate bone-a thin lamina in the form of a curved, overhanging ledge, a short distance above the floor, which begins within 1 cm. behind the pyriform aperture and ends in the plane of the posterior choanæ, where its end is slightly rolled upon itself. It articulates with superior maxilla, palate bone, and lamina papyracea of the eth

FIG. 5.-Frontal section through the rear part of the nasal passages: A, Roof; B, floor; f, external wall of nasal passages; C, C, alveolar process, high and spongy; a, a, a, the three nasal meati; b, b, middle turbinal; c, olfactory fissure; d, respiratory fissure (Zuckerkandl).

moid. The space underneath it is the lower meatus; the channel above it, the middle nasal meatus. The other turbinal processes are part of the ethmoid papyraceous plate. Of these, the middle turbinal is the most independent. It conforms, on the whole, with the shape and inclination of the inferior concha, begins about 1 cm. posterior to the front end of the latter, ending like the