878 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



in contact with the side of the head, although they may by the influence 

 of various muscles be drawn into a more or less erect position. Such is 

 the case in the elephant and in the dog. In most mammals the auricle 



Fig. 399.— Diagram of the External Surface of the Left Tympanic 

 Membrane. {Hensen.) 



a, head of the malleus ; ft, incus : e. joint between malleus and incus ; between r and d is the flaccid 

 portion of the membrane ; ax, axis of rotation of ossicles. The deeply shaded central portion is called 

 the "umbo." 



is much more mobile than in man, and may be directed toward the source 

 of sound b}' the contraction of voluntary muscles and thus be enabled to 

 accomplish more successfully its functions. 



"~7f> 



Fig. 400.— Tympanic Membrane and Auditory Ossicles seen from the 

 Tympanic Cavity. (Lanrlois.) 



M. manubrium, or handle of the malleus; T, insertion of the tensor tympani : h head, 1 F Ions proc- 

 ess, of the malleus; a, incus with the short (K) and the long (1) processes; S, plate of the stapes; Ax, 

 Ax is the common axis of rotation of the auditory ossicles ; S, the pinion- wheel arrangement between the 

 malleus and incus. 



The external auditory meatus is a canal, partly cartilaginous and 

 partly bony, which varies in length according to the species. Thus, 

 while it is five or six centimeters long in ruminants, it is very short in 



