EXTERNAL AUDITORY MEATUS 



1085 



longer than the posterior and superior. It consists of a lateral cartilaginous and 

 a medial osseous portion. The canal describes an S-shaped curve in both hori- 

 zontal and vertical directions. Near the auricular end it is convex anteriorly and 

 inferiorly, while at the tympanic end the curve is reversed, and is concave in the 

 same direction. The lumen is irregularly elliptical in outline, the longer axis 

 being vertical at the auricular, but nearly horizontal at its tympanic end. The 

 meatus is constricted at about its centre, and also near the tympanum. 



Fig. 829. — Vertical Section of the Middle and External Ear. 



Semi-circulax Glands in os- 



canals (ducts) secus meatus 



Tympanic membrane \ \ 



Cochlea 



Cavity of tympanum 



Cartilaginous tuba auditiva 



Cartilage 



_Jl — i_ Auricle 



Cartilaginous 

 meatus 



Osseous 

 meatus 

 Cartilage of 

 external 

 meatus 

 Parotid gland 



Styloid process 



Internal 

 carotid artery 



Osseous tuba auditiva 



Relations. — The anterior wall is in relation with the condyle of the mandible medially, and 

 with the parotid gland laterally; the inferior wall is closely bound to the parotid gland; and 

 the -posterior wall of the bony part is separated by only a thin plate of bone from the mastoid 

 cells. The superior wall is separated at its medial end by a thin plate of bone from the epi- 

 tympanic recess, and laterally a thicker layer of bone separates it from the cranial cavity. 



Structure of the meatus. — The walls of the meatus are formed laterally of 

 fibro-cartilage and medially of bone, lined internally by skin. The cartilage is 

 folded upon itself to form a groove, deficient in its dorsal part, where the edges 

 ofj^the cartilage are united by dense connective tissue. The cartilaginous groove 

 is thus converted into a canal. Medially, the cartilage forms about one-third of 

 the circumference; laterally, two-thirds. Two fissures {incisures of Santorini) 

 usually occur in its anterior wall (fig. 828). Laterally the cartilage is directly 

 continuous with the cartilage of the auricle and medially it is firmly connected 

 with the lateral lip of the osseous portion. The osseous portion, which forms 

 slightly more than half the canal, is formed by the tympanic portion of the 

 temporal bone; it is described in connection with that bone. 



The skin of the meatus forms a continuous covering for the canal and t3''mpanic 

 membrane. It is thick in the cartilaginous, but very thin in the bony, part of the 

 meatus, especially near the tympanic end, where it is tightly bound to the perios- 

 teum. In the cartilaginous meatus it contains numerous fine hairs and sebaceous 

 glands, but neither hairs nor sebaceous glands are found in the bony meatus. 

 Tubular ceruminous glands, which secrete the cerumen (ear wax), form a nearly 

 continuous layer throughout the cartilaginous, but occur on only a small part of 

 the posterior and superior wall of the bony, meatus. The openings of their ducts 

 appear as dark points to the naked eye (fig. 829). 



