404 SPECIAL HISTOLOGY. 



ossicula auditus, where it also forms the memb. obturatoria 

 stapedis, and on the membrana tympani, is still more delicate 

 than in the accessory sinuses of the nose, being thickest in 

 the Eustachian tube. In the latter situation, its epithelium 

 is of the squamose, ciliated kind, , 024 /// thick, whilst in the 

 tympanic cavity it is changed into a thin, tesselated epithelium, 

 composed of one or two layers, extending as far as the acces- 

 sory cavities. The membrana tympani, which, according to 

 Todd and Bowman, is furnished with a ciliated epithelium, 

 consists of a middle fibrous plate, which, at the sulcus tym- 

 panicus, in connexion with the periosteum of the cavity of the 

 tympanum and of the osseous meatus and with the cutis lining 

 the latter, commences in a dense tract of chiefly annular 

 fibres — the so-termed annulus cartilagineus, — and further in- 

 wards is composed principally of slender radiating fasciculi 

 converging towards the centre, where the handle of the malleus 

 is inserted into this membrane, and in part reticulated, with 

 undeveloped fine elastic fibres (" connective tissue corpuscles," 

 Virchow). Externally, this membrane is covered by a delicate 

 continuation of the epidermis of the external meatus, and 

 internally it is lined by a fine investment of the mucous mem- 

 brane of the tympanum. 



The ossicula auditus are composed principally of spongy 

 osseous substance, with a thin compact cortex; and their 

 articulations and ligaments resemble, in miniature, those of 

 other similar organs in all respects, even down to the carti- 

 laginous layer, consisting of scarcely more than a single 

 stratum. Their muscles, like those of the external ear, are 

 transversely striped. The Eustachian tube has in part, as a 

 foundation, a cartilage which in structure approaches the true 

 cartilages; usually, however, presenting a pale, fibrous matrix; 

 and containing, in the cartilaginous portion, especially towards 

 the aperture, numerous racemose mucous glands, of precisely 

 the same conformation as those of the pharynx, in the mucous 

 membrane of which organ that of the Eustachian tube is 

 imperceptibly lost. The external ear is supplied with vessels 

 and nerves, in the same manner as the external integuments. 

 In the middle ear, the mucous membrane, especially of the 

 walls of the tympanum, is highly vascular, as is also the 

 Eustachian tube and the membrana tympani, in which latter 



