THE MIDDLE EAR 611 



promontory, and which indicates the position of the first or broadest 

 turn of the spiral canal of the cochlea. Beneath this prominence is 

 a recess leading to a bony "window," the fenestra rotunda, which, 

 in life, is closed by a delicate membrane. Behind the promontory 

 and at a slightly higher level a deep recess, the pelvis ovalis, leads 

 inward to the fenestra ovalis, which is closed by the base of the 

 stapes; the body of this ossicle is entirely contained within the 

 pelvic recess, and near its mouth the stapes articulates with the 

 orbicular extremity of the long process of the incus.- The superior 

 portion of this deep recess is encroached upon by the projecting 

 wall of the aqueductus Fallopii which transmits the facial nerve, 

 and posteriorly, near the point where it merges with the general 

 tympanic cavity, a low, conical, bony projection known as the pyra- 

 mid transmits the stapedius muscle. The canal of the tensor tym- 

 pani muscle contained within a still more prominent, conical, bony 

 projection, the processus cochleariformis, is found near the antero- 

 internal angle of the tympanic cavity just above and parallel to the 

 Eustachian tube. The narrowest portion of the tympanum is, per- 

 haps, almost its very center, and is included between the promon- 

 tory on the inner and the tympanic membrane on the outer side. 

 Extending from this narrowed central portion upward, backward, 

 and inward, are expanded recesses which are partially occupied 

 by the three auditory ossicles ; the remaining portions of the tym- 

 panum are filled by air which gains access to the cavity through 

 the Eustachian tube. 



The tympanic mucosa consists of a thin but dense tunica pro- 

 pria which is firmly attached to the underlying periosteum and 

 softer parts by loose connective tissue, and is clothed with a layer 

 of flattened epithelium, which, in the vicinity of the origin of the 

 Eustachian tube, is of low columnar form and is provided with cilia, 

 but in most other portions of the tympanum is squamous in char- 

 acter and of the tessellated type, closely resembling endothelium. 

 The floor of the tympanum and the lower portions of its anterior, 

 internal, and posterior walls also possesses a partial clothing of low 

 ciliated cells (Kessel*). Occasional gland-like folds of the mucosa 

 occur near the orifice of the Eustachian tube, though the true 

 glandular character of these folds is very questionable. 



The mastoid cells are numerous small spaces situated within the 

 mastoid process of the temporal bone ; they are lined by a continua- 

 tion of the tympanic mucosa, which is everywhere clothed by flat- 

 * Strieker's Handbook, vol. iii. 



