230 



THE ESSENTIALS OF HISTOLOGY 



glands known as Bowman's glands (b). which open upon the surface 

 by fine ducts passing between the epithelium -cells. 



FIG. 267. SECTION OF OLFACTORY MUCOUS MEMBRANE. (Cadiat.) 

 , epithelium ; &, glands of Bowman ; c, nerve-bundles. 



STRUCTURE OF THE AUDITORY ORGAN. 



The external ear proper (pinna) is composed of elastic fibro-carti- 

 lage, invested by a thin, closely adherent skin. The skin is covered by 

 small hairs, and connected with these are the usual sebaceous follicles. 

 In some parts e.g. the lobule there is a considerable amount of 

 adipose tissue ; and voluntary muscular fibres are in places attached to 

 the cartilage and may be seen in sections of the ear. 



The external auditory meatus is a canal formed partly of cartilage 

 continuous with that of the pinna, partly of bone. It is lined by a 

 prolongation of the skin and is closed by the membrana tympani, over 

 which the skin is prolonged as a very thin layer. Near the orifice the 

 skin has hairs and sebaceous glands, and the meatus is also provided 

 throughout the cartilaginous part with small convoluted tubular glands 

 of a brownish-yellow colour, which yield a waxy secretion (ceruminous 

 glands}. They appear to represent modified sweat-glands. 



The tympanum is lined by a mucous membrane which is continuous 

 through the Eustachian tube with the mucous membrane of the 

 pharynx ; it is also prolonged into the mastoid cells. The epithelium 

 is columnar and ciliated in some parts, but in others e.g. roof, promon- 

 tory, ossicles, and membrana tympani it is a pavement-epithelium. 



The membrana tympani is a thin membrane formed of fibrous 

 bundles which radiate from the umbo. Within the radial fibres are a 

 few annular bundles. Covering the fibrous membrane externally is a thin 



