MIDDLE EAR. 



393 



found on the floor of the cavity. In its anterior part, small alveolar mu- 

 cous glands occur very sparingly. Capillaries form wide meshed networks 

 in the connective tissue, and lymphatic vessels are found in the periosteum. 

 The auditory tube includes an osseous part toward the tympanum, and 

 a cartilaginous part toward the pharynx. Its mucosa consists of fibrillar 

 connective tissue, together with a ciliated columnar epithelium which be- 

 comes stratified as it approaches the pharynx. The stroke of the cilia is 

 toward the pharyngeal orifice. In the osseous portion the mucosa is 

 without glands and very thin; it adheres closely to the surrounding bone. 

 Along its floor there are pockets containing air, the cellulae pneu- 

 maticae. In the cartilaginous part the mucosa is thicker; near the pharynx 

 it contains many mucous glands (Fig. 441). Lymphocytes are abundant 

 in the surrounding connective tissue, forming nodules near the end of the 

 tube and blending with the pharyngeal tonsil. The cartilage, which only 

 partly surrounds the auclitory tube, is hyaline near its junction with the 

 bone of the osseous portion; it may contain here and there coarse fibers 

 which are not elastic. Distally the matrix contains thick nets of elastic, 

 tissue, and the cartilage is consequently elastic. 



EXTERNAL EAR. 



Between the middle ear and the external ear is the tympanic membrane, 

 which consists, from without inward, of the following strata: the cutaneum, 

 radiatum, circulare and mucosum (Fig. 442). 

 The stratum cutaneum is a thin skin without 

 papillae in its corium, except along the handle 

 or manubrium of the malleus. There it is a 

 thicker layer containing the vessels and nerves 

 which descend along the manubrium and spread 

 from it radially. In addition to the venous 

 plexus which accompanies the artery in that 

 situation, there is a plexus of veins at the per- 

 iphery of the membrane. The latter receives 

 vessels both from the stratum cutaneum and 

 the less vascular stratum mucosum. The radiate 

 and circular strata consist of compact bundles of 

 fibrous and elastic tissue arranged so as to sug- 

 gest tendon. The fibers of the radial layer blend 



with the perichondrium of the hyaline cartilage covering the manubrium. 

 Peripherally the fiber layers form a fibre-cartilaginous ring which con- 

 nects with the surrounding bone. The stratum mucosum is a thin layer 

 of connective tissue covered with a simple non-ciliated flat epithelium 



FIG. 442. CROSS SECTION OF 

 THE MEMBRANA TYMPANI 

 BELOW THE MANUBRIUM. 

 X .450. (After Kolliker.) 



a, Stratum cutaneum (show- 

 ing the corneum and 

 germinativum) : b, strat- 

 um radiatum, its fibers 

 cut across; c, stratum cir- 

 culare; d, stratum mu- 

 cosum. 



