THE EAR. 403 



II.— OF THE ORGAN OF HEARING. 



§ 232. 



The auditory organ consists of the proper sentient parts 

 with the expansion of the acoustic nerve, which are contained 

 in the osseous substance of the labyrinth; and of special 

 accessory apparatus, the external and middle ear, intended 

 chiefly for the reception and conduction of the undulations of 

 sound. 



§ 233. 



External and middle ear. — The auricle [pinna) and the car- 

 tilaginous external auditory canal, are supported by the carti- 

 lage of the ear (cartilago auris), J — V" thick, and while retain- 

 ing the thick perichondrium very flexible, but otherwise ex- 

 tremely brittle, and the form of which is well known. This 

 cartilage, in its more intimate structure, approaches the yellow 

 or reticular cartilages, though it is distinguished by a consi- 

 derable preponderance of cartilage-cells, O'Ol/" in diameter, in 

 the striated matrix. It is covered by the external integument, 

 which, except in the lobule, contains no fat and on the concave 

 side of the auricle is closely adherent to the cartilage, where it 

 is characterised by a great abundance of glands. These are, in 

 the first place, common sebaceous follicles, which are most 

 developed in the concha and fossa scaphoidea, where they attain 

 the diameter of \ — 1'" ; secondly, minute sudoriparous glands 

 of $" on the convex side of the pinna ; and, lastly, the ceru- 

 minous glands, already described (§ 71, 72), in the cartilaginous, 

 external auditory canal itself. In the latter, the cutis measures 

 I — I"' in thickness, without the epidermis, which is ^ — JL'" 

 thick ; and presents, besides the glandulce ceruminosa, hairs and 

 sebaceous follicles in a dense subcutaneous tissue, whilst in the 

 osseous part of the passage it is very thin, contains no organs 

 of any kind, and is blended very intimately with the periosteum 

 of the canal. 



The middle ear, in all its cavities, together with the ossicles, 

 tendons and nerves contained in it, is lined with a delicate 

 mucous membrane, which, in the mastoid cells and on the 



