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.

are numerous.

The efferent veins of the nose are not large, but they 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

channels in the soft palate and pharyngeal walls into the cervical lymph-passages and glands. In animals a communication has been shown between the subarachnoid spaces and the nasal lymph-channels. In man this connection has not been demonstrated. Injection of the lymph-vessels allows the fluid to escape through the tubular perforations in the basement membrane into the epithelial layer, even up to the free surface.

9. The Nerve Supply of the Upper Respiratory Tract.— The specific nerve of smell is the olfactory nerve, which sends its branches through perforations in the lamina cribrosa in two rows, of which the inner row descends along the septum, whereas the outer spreads over the external wall as far as the attachment of the middle turbinal. The nerves of ordinary sensation of the nose are branches of the fifth nerve. The embryonic formation. of the septum-and, to a certain extent, of the nasal walls-from two distinct areas of development accounts. for the peculiar double supply of nerve-fibers. A branch of the first division of the fifth nerve-the ethmoidenters the nose through the ethmoid canal and supplies the anterior area of the septum and the external wall. The entire rear region, however, derives its fibers-the postnasal nerves-from the second division of the trigeminus. These fibers, coming from Meckel's ganglion, enter above and posteriorly from the sphenopalatine fossa. The pharynx receives its sensory fibers from the pharyngeal plexus, which is made up of branches from the vagus, spinal accessory, and glossopharyngeal nerves. This plexus supplies also motor nerves to the pharyngeal and palatal muscles, except the tensor palati muscle, which is innervated by the internal pterygoid branch of the trigeminus. The muscles of the external nose, which dilate the nostrils, are under the control of the facial

nerve.

10. Physiology of the Upper Respiratory Passages. -The nasal passage fulfils a double purpose. It contains the organ of smell, and it serves as the main channel for