524 THE SOLIDS. 



this the handle of the malleus is inserted : the blood vessels 

 which supply the tympanum pass along the handle of the 

 above-named bone, and follow the same radiated course as the 

 fibres themselves ; the inner and third lamina is composed of 

 cells of ciliated epithelium, similar to those lining the tym- 

 panic cavity. 



The tympanic cavity is lined by a fibrous membrane, divisi- 

 ble into two layers ; the fibres entering into the composition 

 of one of these follow a longitudinal course, while those of 

 the other layer are circularly disposed ; these fibres are, for 

 the most part, nucleated, and would appear to be of the 

 elastic kind : in the longitudinal layer, the fibres are dis- 

 posed in bundles, and are possibly contractile : on the surface 

 of this membrane and lining immediately the tympanic 

 cavity, is a layer of ciliated epithelium, continuous on the 

 one hand with that of the tympanic membrane ; and on the 

 other, with that clothing the interior surface of the Eusta- 

 chian tube. 



Posteriorly, the tympanic cavity exhibits the openings of 

 the mastoid cells ; anteriorly, the orifice of the Eustachian 

 tube may be noticed, while the internal wall of the tym- 

 panum presents two orifices which communicate with the 

 internal ear : these are the fenestra ovalis, leading into the 

 vestibule ; and the fenestra rotunda, opening into the cochlea. 



The whole length of the tympanic cavity is traversed by a 

 chain of three bones, united to each other by muscles of the 

 striped kind ; one extremity of this chain is attached, as 

 already noticed, to the tympanum, while the other, formed by 

 the base of the stapes, is in connection with the fenestra 

 ovalis. 



In the tympanic cavity of the ear of the sheep, cells, con- 

 taining pigment, may very generally be observed ; amongst 

 these, I have noticed the occurrence of numerous delicate 

 transparent cells, similar to those of the white substance of 

 the brain and spinal marrow* 



