586 THE TYMPANIC CAVITY. [SECT. 232. 



also with the cutis lining the latter. At its origin, this fibrous 

 plate is composed of a dense band of fibres, the majority of which 

 are circular, and form the so-called annulus cartilagineus ; the 

 outer surface of this membrane is formed by radiating fibres, 

 diverging from the handle of the malleus which is inserted here 5 

 the inner surface is made up of more circular elements. The two 

 layers may be separated from each other, and they are both com- 

 posed of bundles of connective tissue with plasmatic cells. On 

 the outer aspect of the membrana t} r mpani, a delicate covering of 

 epidermis is prolonged from the external auditory meatus, along 

 with a process from the corium {Arnold, v. Troltsch), but this 

 latter can scarcely be regarded as a complete covering (Gerlacli). 



The ossicula auditus chiefly consist of spongy osseous substance 

 with a delicate compact cortex, and their articulations and liga- 

 ments are exact representations in miniature — even down to a layer 

 of cartilage in a single lamina — of similar structures elsewhere. 

 Their muscles are transversely striped like those of the external 

 ear. — The Eustachian tube is mainly composed of a cartilaginous 

 basis, which in its structure approaches the true cartilages, but 

 generally has a pale fibrous matrix; in this cartilaginous part, 

 especially towards its mouth, the tube is provided with numerous 

 racemose mucous glands of exactly the same nature as those of 

 the pharynx, the mucous membrane of which is continued without 

 any perceptible boundary into that of the tube. — The external ear 

 is provided with vessels and nerves in the same manner as the 

 outer skin. In the middle ear, the mucous membrane of the walls 

 of the tympanic cavity and tuba Eustachii are especially rich in ves- 

 sels. The membrana tympani is also plentifully supplied; and here 

 the largest arteries and veins run along the handle of the malleus, 

 in the outer layer of cutis, and form arterial and venous vascular 

 rings at the circumference of the membrane, besides ramifying 

 abundantly in the mucous membrane. The nerves are chiefly 

 from the fifth pair, and from the glosso-pharyngeal ; taken as a 

 Avhole, they ramify scantily in the mucous membrane. Their 

 terminations are unknown; except that the tympanic nerve has 

 been found to contain numerous large ganglionic cells, isolated 

 or in groups. On the membrana tympani, the chief nervous trunk, 

 which lies in the outer layer of cutis (from the vagus (?), according 

 to Sappey) , descends from the periosteum at the upper border of 

 the meatus, gives off branches in the neighbourhood of the pro- 

 cessus brevis, and then proceeds in the direction of the handle of 

 the malleus and may be followed beneath it, dividing into fine 



