EXTERNAL EAR— MIDDLE EAR 



873 



side to side. Owing to the obliquity of the membrana tympani, the floor is longer 

 than the roof, and the anterior longer than the posterior wall of the canal. 



Its cartilaginous portion, which is a little less than half an inch (11 mm.) in 

 length, is formed by the incomplete tube of cartilage already described, with 

 fibrous membrane to complete its upper and front part. 



The osseous portion of the tube, a little more than half an inch (14 mm. j in 

 length, is slight Iv curved, with its convexity looking upwards and backwards 

 (fig. 496). 



The lining membrane is a reflexion from the skin externally. It is thick and 

 strong in the cartilaginous, but becomes thinner in the osseous portion; especially 

 is this the case near the membrana tympani, over which it is reflected to form its 

 cuticular layer. In the cartilaginous portion the dermis is supplied with numerous 

 hairs, and sebaceous glands open into their follicles. Tubular ceruminous glands, 

 the orifices of which stud the whole of the cartilaginous portion, appear as dark 

 }»oints to the naked eye. 



Fig. 496.— Section of the Middle axd Exterxal Ear. 



SEMI- ^ GLANDS 

 CIRCULAR IN OSSEOUS 

 CANALS MEATUS 



Membrana 

 tympani 



COCHLEA 



CAVITY OF 

 TYMPANUM 



PINNA 



CARTILAGINOUS MEATUS 



OSSEOUS MEATUS 



CARTILAGE OF EXTERNAL 

 MEATUS 



'AROTIO GLAND 



STYLOID PROCESS 



Internal carotid 

 artery 



CARTILAGINOUS EUSTACHIAN 

 TUBE 



OSSEOUS EUSTACHIAN TUBE 



These glands extend a short distance into the upper and back part of the bony 

 meatus, in the form of a triangular patch, but elsewhere they appear to be absent. 



The arteries are derived from the posterior auricular, temporal, and internal 

 maxillary; and the nerves from the auriculo-temporal and the auricular branch 

 of the vasrus. 



THE MIDDLE EAR 



The Membrana Tympani is an irregularly rounded concave membrane stretched 

 oblicjuely across the bottom of the osseous meatus in sucli wise as to form an 

 obtuse angle with its upper wall (according to Von Troltsch, 140°) and an acute 

 one with its lower. 



The circumference of the membrane is lodged in the groove of the tympanic 



