accessory sinuses. Close examination shows a somewhat uneven surface of the nasal mucous membrane, with minute ridges and furrows and miniature wart-like elevations. This unevenness of the surface is often grossly exaggerated in inflammatory hypertrophy. In the pharynx the mucous membrane is smoother but thicker; it is especially massive, however, where it is infiltrated with adenoid tissue so as to form the different tonsils. In the nose and accessory cavities the mucous membrane is inseparable from the periosteum. The transition from skin to mucous membrane begins at about the level of the projecting fold in the vestibule. Beyond this threshold, throughout the nose and pharynx, the membrane contains an abundance of branched tubular mucous glands; in the nasal sinuses, however, the glands are few in number. The surface epithelium consists of stratified cylindric cells, of which those on the free surface are ciliated. Interspersed are mucus-forming "beaker cells." In the pharynx, at about the level of the second vertebra, the epithelium changes into stratified pavement epithelium. The epithelial cells in the interior of the mucous glands are cuboid.

In the upper nasal region, which contains the nerves of smell, the structure of the lining membrane, and also of its epithelium, is peculiar. This area extends over the nasal surfaces above the middle turbinal and anterior to the sphenoid sinus, both on the septum and on the surface of the upper turbinal processes. Here the epithelial cells form large cylinders, not ciliated in the ordinary sense, but presenting a few coarse, hair-like "cilia," non-motile, but presumably the specific end-organs of the olfactory nerve.

Underneath the epithelium there is a well-defined structureless basement membrane, with a multitude of tubular perforations, which are probably the inlets (or outlets?) of the lymphatic system. The substance of the mucous membrane consists of a connective-tissue stromal with elastic fibers. Both connective-tissue and elastic

FIG. 7.-Histologic structure of the mucous membrane over the inferior turbinal: a, Ciliated cylindric epithelium; b, basement membrane; c, adenoid layer; f, follicle; p, elastic layer of periosteum; pc, cellular layer of periosteum; B, bone.

fibers are more or less continuous with the periosteum over the bony walls, with the perichondrium over the cartilaginous part of the septum, and with the pharyn

geal fascia. Where the surface is plane in the nose the mucous membrane is easily detached, but wherever there are bony crests or sharp angles it adheres firmly to the underlying structure, as it does also in the entire pharynx. Along the turbinals, most noticeably the middle. turbinal, the stroma dips into the smaller cellular spaces of the spongy bone and assumes a medullary structure with the presence of fat-cells. All larger bone-cells, however, are lined by very thin mucous membrane and epithelium.

Underneath the epithelium the stroma presents a uniform infiltration with lymphoid cells throughout its entire extent. These round cells are migratory, and are found penetrating into the epithelial layer. This is particularly the case in the region of the pharyngeal tonsil, where the epithelium is crowded with lymph-cells. The tonsils themselves (pharyngeal, faucial, and lingual) consist of lymphoid cells arranged in the form of follicles, with incomplete connective-tissue capsules in the substance of the mucous membrane.

8. The Vascular Supply of the Upper Respiratory Tract. -The whole lining of the respiratory tract is exceedingly vascular. The capillaries are arranged in three layers— a deep stratum close to the periosteum, a coil of capillaries around the glands, and an extensive network in the superficial adenoid stratum. Most peculiar, however, is the arrangement of the veins. Throughout the entire mucous membrane there is a dense network of veins with small meshes, the caliber of the vessels increasing in proportion to the distance of the vessels from the surface. The thickness of the mucous membrane depends largely on the development of the venous plexus. In several areas in the nose-viz., at the anterior end of the inferior turbinal, along the margin of the middle turbinal, at the rear ends of both inferior and middle turbinals, and to a less extent over the tuberculum of the septumthe venous plexus changes into true cavernous tissue. The vessels are relatively large, compared with the inter

FIG. 8.-Cross-section through the mucous membrane of inferior turbinal (posterior end) (Hartnack Obj. 4, Oc. 2). The glandular vessels in exaggerated magnification: a, a, Subepithelial layer with cortical vessels; b, the lacunar part of the cavernous body with arteries verging toward the subepithelial layer (Zuckerkandl).

spaces between them; but, on the other hand, they are individually short, on account of their fusion to form a network, and they present an enormous development of the muscular tunic not found in ordinary veins. When not artificially injected, these veins show an irregular puckered cross-section. The density of the venous network can be observed best in a corrosion specimen. These veins are fed only through the capillaries, and do not communicate directly with arteries. The thickness of the mucous membrane changes within wide limits, according to the degree of turgescence or collapse of the cavernous plexus.

The efferent veins of the nose are not large, but they are numerous. They emerge partly into the orbit through the ethmoid plate, into the cranial cavity, into the palate, and to some extent into the sides of the pharynx. Larger veins form a plexus around the pharynx external to the mucous membrane, and empty into the internal jugular vein.

The arteries of the nose and pharynx are likewise not large. The sphenopalatine artery, a branch of the internal maxillary, supplies the nose from the rear, emerging from the sphenopalatine fossa, and sends branches to both external wall and septum. A collateral supply is likewise obtained from the ethmoid and external nasal arteries.

The pharynx derives its blood supply mainly from the ascending pharyngeal artery, which ascends along, but outside of, the lateral pharyngeal wall, enters at the roof, and sends branches in all directions. There is, besides, free communication with all adjoining arteries. The internal carotid artery and internal jugular vein run parallel to the lateral pharyngeal wall, but are separated from the pharyngeal fascia by a layer of loose areolar tissue over a centimeter in width. Hence they are not endangered by ordinary pharyngeal operations.

The lymph-vessels form a close network in the substance of the mucous membrane, and empty through