394 



HISTOLOGY. 



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. 



The external auditory meatus is lined with skin continuous with the 

 cutaneous layer of the tympanic membrane. In the deep or osseous portion 

 the skin is very thin, without hair or glands except along its upper wall. 

 There and in the outer or cartilaginous part ceruminous glands are abun- 

 dant. "They are branched tubulo-alveolar glands" (Huber) which in 

 many respects resemble large sweat glands. Their ducts are lined with 



Epidermis. 



Hair sheath. 

 Corium. - 



Excretory duct. 



Young hair. -i 



Coil of ceruminous gland. 



FIG. 443. 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. 



FIG. 444. TUBULES OF THE CERUMINOUS GLANDS. 

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

 dinal section, from a boy 12 years old. 



stratified epithelium. The coils consist of a single layer of secreting cells, 

 general cuboidal, surrounded by smooth muscle fibers and a well defined 

 basement membrane. They differ from sweat glands in that their coils 

 have a very large lumen especially in the adult, and their gland cells, 

 often with a distinct cuticular border, contain many pigment granules and 

 fat droplets. Their narrow ducts in adults end on the surface of the skin 

 close beside the hair sheaths; in children they empty into the sheaths (Fig. 

 443). The secretion consists of pigment, fat, and fatty cells, the latter de- 

 rived probably from the hair sheaths. 



The cartilage of the external auditory meatus and of the auricle is 

 elastic. 



