96 THE EAR. 



noticed below. Another well-marked fold has been already noticed in connection 

 with the tendon of the tensor tympani, and various other smaller folds are met 

 with. They often contain strands of fibrous tissue and sometimes osseous spicules. 

 All these folds are, however, very variable in their development. 



The mucous membrane which lines the cartilaginous part of the Eustachian tube 

 resembles much the membrane of the pharynx, with which it is immediately con- 

 tinuous ; it is thick and vascular, is covered by ciliated epithelium, and is provided 

 with many simple mucous glands which pour out a thick secretion : in the osseous 

 part of the tube, however, the membrane becomes gradually thinner. In the tym- 

 panum and the mastoid cells the mucous membrane is paler, thinner, and less 

 vascular, and secretes a small amount of less viscid, yellowish fluid. Accord- 

 ing to most observers no glands are normally met with in the tympanum, but 

 Krause has described and figured simple glands in parts, and Troltsch describes an 

 acinous gland on the external wall, anteriorly. Between the mucous membrane and 

 the periosteum is a network of fibrous bundles, which are here and there raised 

 above the general surface, causing corresponding projections of the mucous mem- 

 brane. In various places on the interlacing bundles, peculiar swellings occur of 

 various sizes, w^hich appear to be caused by the superaddition of concentrically 

 arranged fibres upon the smaller bundles, producing an appearance similar to that 

 of miniature Pacinian corpuscles (Politzer, Kessel). The epithelium in the 

 tympanic cavity is in part columnar and ciliated, with small cells between the 

 bases of the ciliated cells, but the promontory, the ossicula, and the membrana, are 

 covered with a simple layer of flattened non-ciliated cells (Kolliker) ; and a similar 

 non-ciliated epithelium is said to line the mastoid antrum and cells. 



Recesses or pouches of the tympanum. The ossicula, as well as the 

 ligaments which unite them with the w T all of the tympanum, and the chorda 

 tympani nerve, are all invested by folds of the lining mucous membrane, which in 

 many cases also pass across the spaces between the several ligaments and bony 

 projections. These uniting folds and the prominences which they cover and connect 

 thus mark off in certain places pouch-like portions of the general cavity. There is 

 a good deal of variation in the extent of development of these folds and pouches, 

 but some are fairly constant in their occurrence, and one pouch in particular, 

 between the heads of the malleus and incus and the external wall is nearly shut off 

 from the rest of the cavity by well marked folds, which pass down from the roof of 

 the tympanum in front of and behind the suspensory ligament of the malleus. 

 This pouch may be termed the superior external pouch. Immediately below it and 

 partly separated from it by the anterior and external ligaments of the malleus and a 

 fold of membrane which unites them, is another smaller pouch, described by 

 Prussak, which may be termed the infer o-external. It is bounded above by the 

 ligaments and folds just mentioned, externally by the membrana flaccida, below and 

 internally by the processus brevis mallei. In front it ends blindly, but behind it 

 opens into the general cavity of the tympanum. This pouch is of considerable 

 importance clinically and pathologically because fluid (e.g., pus) may accumulate in 

 it, especially since its opening into the rest of the posterior pouch is placed 

 somewhat above its floor. It is into this pouch that perforations of the membrana 

 flaccida occur. 



The fold which passes down from the roof of the cavity towards the mesial part 

 of the neck of the malleus, and which incloses in or near its free border the chorda 

 tympani nerve, also separates off tw r o pouches, one in front of and the other behind 

 the manubrium mallei, and both bounded externally by the membrana tympani. 

 These pouches are the anterior and posterior pouches of Troltsch. For a detailed 

 description of the various folds and pouches, the student is referred to certain of 

 the memoirs cited in the Bibliography. 



