1052 



ORGANS OP' SPECIAL SENSE 



In the cartilaginous meatus it is supplied with numerous fine hairs and sebaceous 

 glands, neither of which are found in the bony meatus, and tubular ceruminous 

 glands, which secrete the cerumen (ear wax) , form a nearly continuous layer through- 

 out the cartilaginous, but occur on only a small part of the dorsal and superior wall 



Fio. 747. SECTION OF THE MIDDLE AND EXTERNAL EAR. 



SEMI- GLANDS 



CIRCULAR IN OSSEOUS 

 CANALS MEATUS 



Tympanic membrane 

 COCHLEA 



CAVITY OF TYMPANUM 



PINNA 



CARTILAGINOUS MEATUS 



OSSEOUS MEATUS 



CARTILAGE OF EXTERNAL 

 MEATUS 



PAROTID GLAND 



STYLOID PROCESS 



Internal carotid 

 artery 



CARTILAGINOUS TUBA AUDITIVA 



OSSEOUS TUBA AUDtTIVA 



ot the bony, meatus. The openings of their ducts appear as dark points to the naked 

 eye (fig. 747). 



The arteries are branches from the posterior auricular, superficial temporal, and deep auric- 

 ular (pp. 520 and 529). The veins and lymphatics connect with those of the auricle and empty 

 similarly. The nerves are branches from the auriculo-temporal and the auricular ramus of the 

 vagus. 



THE MIDDLE EAK 



The middle ear is completely separated from the external ear by the tympanic 

 membrane, which is stretched obliquely across the medial end of the external acoustic 

 meatus. 



The tympanic membrane is elliptical, its long axis measuring 9 to 10 mm., its 

 short axis, 8 to 9 mm. It slopes medially from the superior and dorsal to the inferior 

 and ventral wall of the meatus, forming, as a rule, with the superior wall, an angle 

 of 140 degrees (von Troltsch). It varies, however, greatly in form, size, and 

 obliquity. The semitransparent membrane, which sometimes has a reddish 

 tinge, is drawn medially and made funnel-shape by the mamibrium of the 

 malleus, but_the walls of the funnel bulge towards the meatus (fig. 750). The most 

 depressed point, the umbo, is slightly inferior and dorsal to the centre of the membrane, 

 and corresponds to the tip of the manubrium (fig. 748), and from it a whitish streak, 

 the malleolar stria, caused by the rnanubrium shining through, passes superiorly 

 towards the circumference. At the superior end of the stria a slight projection, 

 the malleolar prominence, is formed by the lateral process of the malleus, and from 

 it two folds, the anterior and posterior plicae, stretch to the extremities of the tym- 

 panic sulcus (fig. 748). The small triangular area of the membrane bounded by the 



