480 



HISTOLOGY 



EXTERNAL EAR. 



Between the middle ear and the external ear is the tympanic mem- 

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

 cutaneum, radiatum, circular e and mucosum (Fig. 484). 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 situa- 

 tion, there is a plexus of veins at the periphery 

 of the membrane, receiving tributaries from both 

 the stratum cutaneum and the less vascular stra- 

 tum mucosum. The radiate and circular strata 

 consist of compact bundles of fibrous and elastic 

 tissue, arranged so as to suggest tendon. The 

 fibers of the radial layer blend with the perichon- 

 drium of the hyaline cartilage covering the manu- 

 brium. Peripherally the fiber layers form a fibro-cartilaginous ring which 

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

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



Epidermis. 



b c d 



FIG. 484. CROSS SECTION OF 

 THE MEMBRANA TYMPANI 

 BELOW THE MANUBRIUM. 

 X 4SO. (After Kolliker.) 

 a, Stratum cutaneum (show- 

 ing ^the corneum and 

 germinativum) ; b, stra- 

 tum radiatum, its fibers 

 cut across; c, stratum cir- 

 culare; d, stratum mu- 

 cosum. 



Hair sheath 

 Corium 



Excretory duct 



Young hair 



Coil of ceruminous gland. 



FIG. 485. FROM A VERTICAL SECTION THROUGH 

 THE SKIN OF THE EXTERNAL AUDITORY 

 MEATUS OF AN INFANT. X 50. The excre- 

 tory duct opens into the hair follicle. 



Membrana propria. 



Nuclei of smooth muscle fibers. 



Secretion. 



Gland cells. 



Secretion. 



, Cuticular border. 

 . Gland cells. 

 . Nuclei of smooth muscle 



fibers. 

 Membrana propria. 



FlG. 486. TUBLES OF THE CERUMINOUS GLANDS. 



A, Cross section, from an infant; B, longitu- 

 dinal section, from a boy 12 years old. 



continuous with the lining of the tympanic cavity. Peripherally, in 

 children, its cells may be taller and ciliated. As a whole the tympanic 

 membrane is divided into tense and flaccid portions. The latter is a rela- 

 tively small upper part in which the fibrous layers are deficient. 





