1488 



HUMAN ANATOMY. 



Cartilage 

 of auricle 



Tympanic 

 cavity 



Internal auditory 

 canal 



Tympanic 

 membrane 



inward, possibly slightly backward ; and finally, in its internal portion, forward, 

 downward and inward. Its supero-posterior wall measures about 25 mm. (i in.) in 



length, and the anterior 

 Fig. 1247. wall about 35 mm. (ifi 



in.), the greater length 

 of the anterior wall be- 

 ing due to the obliquity 

 of the drum-head and 

 the outward protrusion 

 of the tragus. The 

 canal is almost as long 

 in the infant as in the 

 adult. 



Structure. — The 

 external auditory canal 

 is composed of an outer 

 cartilagino-membranous 

 (cartilaginous) and of an 

 inner bony portion, both 

 of which, as well as the 

 external surface of the 

 tympanic membrane, are 

 lined by skin. The car- 

 tilagino- 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. 



Two or more slit-like apertures, the fissures of Santorini (incisurae cartilag- 

 inis meatus acustici externi) are usually found traversing the cartilagino-membranous 



Fig. 1248. 



Cartilagi 

 of canal 



Lateral sinus 



W 



Frontal section passing through right ear, showing external, middle, 

 and internal divisions; section is seen from in front. 



Condyle of jaw 



Cartilaginous canal 



Tympanic membrane 



External auditory canal 



Mastoid cells 



Ronv canal 



Eustachian tube 



Internal carotid artery 



ympanic cavity 



Lateral sinus 



Horizontal section passing through right ear, viewed from below. 



canal nearly at right angles (Fig. 1245); as they are filled with fibrous tissue, 

 they permit the anastomosis between the vessels of the anterior and posterior surfaces 



