768 SPECIAL HISTOLOGY. 



contains no organs of any kind, and is blended very intimately with the 

 periosteum of the canal. 



The middle ear, in all its cavities, together with the ossicles, tendons, 

 and nerves contained in it, is lined with a delicate mucous membrane, 

 which, in the mastoid cells and on the 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, 0-024 of a line thick, whilst in the 

 tympanic cavity it is changed into a thin, tessellated epithelium, com- 

 posed of one or two layers, extending as far as the accessory 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 tympanicus, in connection 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 inwards is 

 composed principally of slender radiating fasciculi converging towards 

 the centre, where the handle of the malleus is inserted into this mem- 

 brane, 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 is lined by a fine investment of the mucous mem- 

 brane of the tympanum, 



The ossicula auditus are composed principally of spongy osseous sub- 

 stance, with a thin compact cortex; and their articulations and liga- 

 ments resemble, in miniature, those of other similar organs in all re- 

 spects, even down to the cartilaginous 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 foun- 

 dation, 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 the largest arteries and veins run 

 along the manubrium of the malleus in the middle coat, constituting 

 arterial and venous circles around the periphery of the membrane, and 

 also ramifying abundantly in the mucous membrane. The nerves are 

 derived principally from the ninth and fifth pairs, and upon the whole 



