THE EXTERNAL EAR 



1125 



the tympanic plate, which, in the fetus, exists as a separate ring (annulus tym- 

 panicus), incomplete at its upper part. (See Section on Osteology, p. 87.) 



The skin lining the meatus is very thin, adheres closely to the cartilaginous and 

 osseous portions of the tube, and covers the surface of the membrana tympani, 

 forming a very thin outer layer. After maceration the thin pouch of epidermis, 

 when withdrawn, preserves the form of the meatus. In the thick subcutaneous 

 tissue of the cartilaginous part of the meatus are numerous cemminous glands 

 (glandulae ceruminosae) which secrete the ear wax or cerumen. They resemble 

 in structure sweat glands, and their ducts open on the surface of the skin. 



FENESTRA OVALIS 

 CLOSED BY STAPES 



FIG. 834. Vertical section through the external auditory meatus and tympanum, passing in front of the 



fenestra ovalis. (Testut.) 



Relations of the Meatus. In front of the osseous part is the glenoid fossa, which receives the 

 condyle of the mandible (Fig. 825), which, however, is separated from the cartilaginous part by 

 the retromandibular part of the parotid aland. The movements of the mandible influence to some 

 extent the lumen of the cartilaginous portion. Behind the osseous part are the mastoid air cells 

 (cellulae mastoideae), separated from it by a thin layer of bone (Fig. 836). 



The arteries supplying the external meatus are branches from the posterior auricular, internal 

 maxillary, and superficial temporal. 



The veins of the external meatus accompany the corresponding arteries and pass to the 

 internal maxillary, temporal, and posterior auricular veins. The lymphatics accompany the 

 veins and enter the parotid and posterior auricular lymph nodes. The nerves are chiefly 

 derived from the auriculotemporal branch of the inferior maxillary nerve, the auricularis 

 magnus, and the auricular branch of the vagus. 



The point of junction of the osseous and cartilaginous portions of the tube is an obtuse angle, 

 which projects into the canal at its antero-jnferior wall. This produces a sort of constriction 

 in this situation, and renders it the narrowest portion of the canal an important point to be 

 borne in mind in connection with the presence of foreign bodies in the ear. The cartilaginous 

 is connected to the bony part by fibrous tissue, which renders the outer part of the tube very 

 movable, and therefore by drawing the pinna upward and backward the canal is rendered 

 almost straight. At the external orifice are a few short crisp hairs which serve to prevent the 

 entrance of small particles of dust, flies, or other insects. In the external auditory meatus the 

 secretion of the ceruminous glands serves to catch any small particles which may find their way 

 into the canal, and prevent their reaching the membrana tympani, where their presence might 

 excite irritation. In young children the meatus is short, the osseous part being very deficient, 

 and consisting merely of a bony ring (annulus tympanicus), which supports the membrana 

 tympani. In the fetus the osseous part is entirely absent. The shortness of the canal in children 



