THE EXTERNAL EAR. 



363 



The auricle consists of integument and an enclosed plate of yellow elastic 

 cartilage, continuous with that of the meatus. It is also provided with several 

 ligaments and rudimentary muscles. The lobule, however, contains no car- 

 tilage, but only fibrous tissue and fat enclosed within the integumentary fold 

 The skin of the auricle is thin and closely adherent to the cartilage, espe- 

 cially on the outer surface. In certain parts it contains fine hairs and 

 sebaceous and sweat-glands. The hair-follicles are especially abundant over 

 the tragus, antitragus and the notch lying between them, the hairs guarding 



Internal auditory canal 

 ^-Auditory nerve 



Endolymphatic sac 



Cartilage 



FIG. 412. Diagram showing three subdivisions of ear; u, utricle; s, saccule ; blue is the bony, red the 

 membranous labyrinth of the internal ear. (Modified from Schwalbe.) 



the entrance into the external auditory canal, known as tragi, being excep- 

 tionally long. The sebaceous glands are especially well developed in the 

 cavity of the concha. 



The External Auditory Canal. The external auditory canal, or 

 meatus acusticus, leads from the cavity of the concha to the tympanic mem- 

 brane, which closes its inner extremity. It is composed of an outer carti- 

 lagino-membranous (cartilaginous) and an inner bony portion, both of which, 

 as well as the external surface of the tympanic membrane, are lined by skin. 

 The cartilagino-membranous part contributes something more than one third 

 of the entire length of the canal, and is a continuation of the cartilage of the 

 auricle. The cartilage of the canal, histologically of the elastic type, does 

 not form a complete tube, but is deficient at its upper back part, where it is 

 filled in by fibrous tissue. On approaching the bony portion, this deficiency 

 in the cartilage is more marked and the fibrous tissue correspondingly 

 increased. 



The skin lining the outer portion of the canal is closely attached to the 

 underlying cartilage and measures about 1.5 mm. in thickness. It is much 

 thinner within the bony canal, except along the roof, where it remains rela- 

 tively thick. Over the outer surface of the tympanic membrane, the skin is 

 reduced to a very delicate and smooth investment, covered by correspond- 

 ingly attenuated epidermis, and a very thin layer of subcutaneous tissue. 



