438 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



Helix. 



At the bottom of the auditory canal is the tympanic 

 membrane. It is an elliptical disc placed at an ob- 

 lique angle to the ear canal, with its antero-inferior 

 border most distant from the outer orifice. This 

 membrane is composed of three layers, an external 

 cutaneous, a middle fibrous, and an inner mucous. 

 The external layer is continuous with the integu- 

 mentary lining of the meatus and consists of a thin 

 layer of cutis covered by epidermis. The middle 

 layer, or membrana propria, consists of two sets of 



fibers, external or 

 radial fibers next to 

 the integument, and 

 internal or circular 

 fibers next to the in- 

 ner mucous lining. 

 The circular fibers 

 are numerous near 

 the circumference 

 but scattered and 

 few in number near 

 the center. In the 

 upper and anterior margin of the membrane is a 

 small triangular area that is thin and lax and is 

 called the pars flaccida. The main portion of the 

 membrane is, on the other hand, tightly stretched 

 and termed the pars tensa. Both radial and circular 

 fibers are absent from the pars flaccida. 



2. The Middle Ear. The middle ear, or tympanic 

 cavity, is a small air chamber in the tympanic bone, 

 intervening between the inner end of the external 

 auditory meatus and the outer wall of the internal 



Fossa of 



helix. 

 Anthelix. 



Concha. 



Antitragus. 



Fig. 301. External ear (Randall). 



