NORMAL HISTOLOGY. 



canals and concentric lamellae are present in the thicker parts, as the 

 head and the base of the short process of the malleus. All surfaces 

 of contact, including the articular facets, are invested by hyaline 

 cartilage. The cavity of the ambo-malleal articulation is sub- 

 divided by a minute intra-articular plate of fibrous cartilage. An 

 investment of cartilage covers the malleus on all parts of the sur- 

 face of its attachment to the tympanic membrane, the perichondrium 

 becoming firmly united with the fibrous tissue of the lamina propria. 

 The entire base of the stapes also is covered with a plate of car- 

 tilage directly applied to the fenestra ovalis ; the space intervening 

 between the stapes and the margin of the oval window is occupied 

 by the ring of fibrous tissue constituting the annular ligament. 



The Eustachian tube consists of two parts, the supporting 

 framework, composed partly of bone and partly of cartilage, and 



the mucous membrane. Neither 

 the osseous nor the cartilaginous 

 tissue of the canal constitutes a com- 

 plete wall, since the tube is imperfect, 

 being completed by the fibrous and 

 other tissue which bridges the cleft left 

 by the insufficient hard parts. 



Within the canal formed by the os- 

 seous, cartilaginous, and fibrous tissues 

 the soft tube of mucous membrane 

 lies, its lower division supplemented 

 by a stratum of submucous tissue, 

 its upper part closely united with the 

 periosteum of the bony walls. 



The epithelium lining the Eu- 

 stachian tube is ciliated stratified 

 columnar in type, the cells clothing 

 the pharyngeal division of the tube 

 being tall columnar elements, while 

 those lining the upper bony part are 

 low cuboidal, although ciliated, and 

 resemble the epithelium of the tym- 

 panum. 



The tunica propria presents a 

 stratum of loose connective tissue, 

 rich in cells and defined from the sub- 

 mucous tissue by a denser layer; in 

 many places the reticular connec- 

 tive tissue is infiltrated with lymphoid cells and constitutes an 

 adenoid structure. The profusion and distribution of this lymphoid 



Section through cartilaginous portion of 

 human Eustachian tube : i, bent plate of 

 cartilage with its hook (i') ; 2, fibrous 

 tissue with fat (3) ; 4, tubo-pharyngeal 

 fascia ; 5, dilator tubae muscle ; 6, mucous 

 membrane of tube with prominent fold 

 (6') below; 7, mucous glands; 8, lumen 

 of tube expanding above into so-called 

 safety-tube (8') ; 9, connective tissue 

 uniting tube with base of skull ; 10, le- 

 vator palati muscle. (After Testut.) 



