FEB 1 1 1919

LIBRARY

BOOK I.

DISEASES

OF THE

NASAL PASSAGES AND PHARYNX.

CHAPTER I.

DEVELOPMENT, GENERAL DESCRIPTIVE ANATOMY, AND PHYSIOLOGY OF THE UPPER AIR-PASSAGES.

1. Development of the Upper Air-passages.--The upper air-passages from nostril to larynx are developed from three different starting-points during embryonic formation. The nasal or olfactory fosse begin in the form of two pits between and at the level of the embryonic eyes. They are separated from each other by the relatively very thick median frontal process, the lower curved end of which becomes transformed into the upper lip. Underneath this area the broad fissure constituting the primitive mouth reaches at first inward only as far as the closed anterior or ventral wall of the esophageal end of the intestinal tract. The intestinal tube itself extends in the form of a blind pouch up to the rear end of the base of the skull. The subsequent coalescence of mouth. and esophageal pouch forms the pharynx. Meanwhile the nasal fossæ continue to grow inward and to elongate downward. At this period they are but shallow longitudinal fissures, opening merely in front. The external nose covering the facial end of the nasal passages is a product of a much later stage of fetal development. The floor that separates the nasal fossæ from the mouth —the primeval palate—is the matrix of the intermaxillary

bone, and has nothing to do with the subsequent true palate.

In the next place the nasal pits perforate into the mouth. For a time the nasal passages, separated from each other by the thick septum, form one continuous space with mouth and pharynx. A relatively rapid growth of the nasal fissures takes place in the direction from the facial orifice to the pharynx, while the median wall between the nasal fissures is being prolonged by a downward growth of a partition from the base of the skull as well as by the elongation of the primitive septum. The final nasal septum is thus formed from an anterior, as well as from an upper rear starting-point. This double development is indicated during subsequent life by separate arterial and nervous supply of the front and posterior areas of the median nasal wall.

From the matrix of the superior maxillary and palatal bones transverse plates begin to grow, which, by joining finally in the median line, form the palate and thus separate the nasal passages from the mouth. An arrest of development of these plates constitutes the deformity known as cleft palate. The orifices which remain at the rear end of the nasal fissures after the completion of the palate form the posterior choanæ.

2. By the time the palatal plates have united with each other and with the buccal edge of the nasal septum each nasal passage has become surrounded with a cartilaginous capsule, of which the portion common to both sides is formed by the cartilaginous plate in the septum. On the external wall of each nasal passage a series of ridges, usually six in number, but with accessory extensions, now develop in the lining, which is transformed gradually into mucous membrane. The ridges, curved with the convexity downward, converge from the front and the roof of the nose toward the posterior choanæ. As these ridges change into projecting crests, cartilaginous lamellæ, more or less curved, develop in them and form the turbinal processes, or conchæ. In man but two of

these projecting lamellæ retain a pronounced prominence -the inferior and the middle turbinal. The othersviz., the two below the middle turbinal (the ethmoid bulla and the uncinate process), as well as all above the middle turbinal (the ethmoturbinals)—recede relatively in development, become more or less curved upon themselves, and coalesce to some extent. The space between the septum and the turbinal processes represents, finally, the olfactory fissure and the nasal passage proper, whereas the spaces included between the coalesced turbinal processes develop into the accessory cavities or nasal sinuses. The formation of the ethmoid cells is thus a relatively simple inclusion, while the frontal and maxillary sinuses grow by further extension into the corresponding bones. The sphenoid sinus, however, represents really the posterior (upper) portion of the nasal passage itself, shut off by accessory turbinal partitions. It is only after birth that these temporary walls around the sphenoid sinus atrophy and leave the cavity surrounded by its permanent bony capsule, formed by the body of the sphenoid bone.

3. The infantile nasal passage differs from the fully developed cavity not alone in its absolute, but also in its relative, dimensions. The olfactory area, or, more properly defined, the region bounded by the ethmoid bone, is developed during fetal life more fully than the lower or respiratory channel outlined by the maxillary and palatal bones. The subsequent growth in the vertical height of the nose hence depends mostly on the postnatal elongation of the superior maxilla. The nasal passage of the infant is relatively very narrow, although the extreme width of the fetal septum has become reduced at birth to the proportion maintained during adult life. The inferior turbinal is, however, so close to the floor and relatively so broad that the inferior nasal meatus is scarcely apparent until about the third year; hence inflammatory swelling during acute coryza is more serious in babes than in later life.

Growth also occurs in the sagittal direction. Until the sixth year the transverse plane of the posterior choanæ corresponds to the level of the infantile molar tooth (second bicuspid of the adult). In the course of the second dentition the palate, and with it the nasal walls, elongate so that finally the choanæ lie in a plane with the third molar teeth. The accessory sinuses are all relatively very small and imperfectly developed at birth. Their growth is slow until after the second dentition.

The pharynx at birth is about one-half the size of the adult cavity, except in its width, it being rather more than one-half as wide. The growth of the maxilla and the vertical plate of the palatal bones causes a gradual displacement of the pharyngeal orifices of the Eustachian tubes relative to the floor of the nose. These orifices, situated below the palate in the fetus, reach the level of the palate at birth and ascend, until the eighth year, to the height of the rear end of the inferior turbinal.

4. General Descriptive Anatomy.-The Nasal Cavity. The gateway to the nasal cavity is the pyriform aperture, bounded above by the nasal bones, on the sides and below by the edge of the superior maxillary bones. The intermaxillary portion of the latter forms a sharp-pointed median crest-the anterior nasal spine. The bridge of the nose is built up by the nasal process of the frontal bone, the frontal process of the superior maxilla, and the two nasal bones joined in the median line, while on the internal side of this junction the nasal septum is inserted. The relative extent of cartilaginous portion of the septum and bony portion (perpendicular plate of the ethmoid) participating in this articulation varies considerably in different subjects. The shape and strength of the bridge of the nose protect the septum. against traumatic fracture from a blow unless this be sufficiently intense to fracture the bridge itself. The shape and prominence of the nasal bones are pronounced racial characteristics. By its protruding nasal bridge the Caucasian skull can be distinguished from that of other races.