SECT. 232.] EXTERNAL EAR. 585 



destined for the reception and conduction of the undulations of 

 sound. 



§ 232. External and Middle Ear. — The auricle and the car- 

 tilaginous external auditory meatus are supported by the cartilage 

 of the car (cartilago auris), -}/' to 1'" in thickness, which is very 

 pliant when covered with its perichondrium, but is otherwise very 

 brittle. This cartilage, whose form is well known, approximates 

 in its structure to the yellow or reticulate cartilage, yet it is dis- 

 tinguished from it by a considerable preponderance of large 

 cartilage-cells, o - oi'" in size, in the striated matrix. It is covered 

 by the external skin, which scarcely contains any fat, except in the 

 lobules, and is closely adherent to the cartilage on the concave side 

 of the pinna, where it is characterised by its great abundance of 

 glands. The glands are, first, ordinary sebaceous glands, which 

 are most developed in the concha and scaphoid fossa, attaining 

 here a diameter of |'" to 1"; secondly, small sudoriparous glands, 

 jj", on the convex side of the pinna ; lastly, the ceruminous glands, 

 which have been previously described (§ 72), in the cartilaginous 

 external auditory passage itself. In the latter situation, the cutis 

 measures 4-'" to -i-"', without the epidermis, which is -y 1 ^-'" to -^ 6 '" 

 in thickness; besides the ceruminous glands, it possesses hairs 

 and sebaceous glands, lying in a dense subcutaneous tissue; in 

 the meatus osseus, on the other hand, the skin is very delicate, 

 studded up to the membrana tympani with numerous fine papillae 

 (Gerlach), and very firmly blended with the periosteum of the 

 meatus. 



The middle ear, together with the ossicula, tendons and nerves 

 contained in it, is lined in all its spaces by a delicate mucous 

 membrane, which is more fragile in the mastoid cells, upon the 

 ossicula (when it also forms the membrana obturatoria stapedis), 

 and upon the membrana tympani, than in the accessory cavities of 

 the nose ; it is thickest in the Eustachian tube. Its epithelium is, 

 at the places last mentioned, laminated and provided with cilia, 

 0'024'" thick ; this is transformed in the tympanic cavity into a 

 thin ciliated layer of pavement-cells, in one or two strata, which 

 extends to the accessory cavities ; this, however, is replaced at the 

 tympanic membrane by a simple non-ciliated pavement epithelium, 

 as we have lately found in an executed criminal. The membrane 

 of the tympanum consists of a middle fibrous plate, which com- 

 mences at the sulcus tympanicus in connection with the periosteum 

 lining the tympanum and the meatus osseus, and connected 



