686 THE EAE 



deep recess, the pelvis ovalis, leads inward to the fenestra vestibuli (or 

 fenestra ovalis), which is closed by the base of the stapes; the body of 

 this ossicle is contained entirely 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 en- 

 croached 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 pyramid transmits the stapedius muscle. The canal of the 

 tensor tympani 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 

 auditory tube. The narrowest portion of the tympanum is, perhaps, 

 almost its very center, and is included between the promontory 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 tympanum are filled by air which 

 gains access to the cavity through the auditory tube. 



THE TYMPANIC MUCOSA 



The tympanic mucosa consists of a thin but dense tunica propria 

 which is firmly attached to the underlying periosteum and softer parts 

 by loose connective tissue, and is clothed with a layer of flattened ento- 

 dermal epithelium, which, in the vicinity of the origin of the auditory 

 tube, is of low columnar form and is provided with cilia, but in most 

 other portions of the tympanum is squamous in character and of the 

 tessellated type, closely resembling endothelium. The floor of the tym- 

 panum and the lower portions of its anterior, internal, and posterior 

 walls also possess a partial clothing of low ciliated cells (Kessel). Occa- 

 sional gland-like folds of the mucosa occur near the orifice of the audi- 

 tory tube, though the true glandular character of these folds is very 

 questionable. 



THE MASTOID CELLS 



The mastoid cells (cellules mastoidece sen pneumaticce) are numer- 

 ous small spaces situated within the mastoid process of the temporal 

 bone; they are lined by a continuation of the tympanic mucosa, which 

 is everywhere clothed by flattened epithelium. The corium is closely 

 attached to the periosteum of the bony wall, the periosteum also serving 



