440 THE SENSORIAL FUNCTIONS. 



tympanum and columella are of greater length. 

 In the saurian reptiles the cavity of the tym- 

 panum is still more capacious, and the ear-drum 

 very distinctly marked ; and these animals pos- 

 sess great delicacy of hearing. The labyrinth 

 of the Crocodile is enclosed in bone, and con- 

 tains three calcareous bodies : it presents also 

 an appendage which has been regarded as the 

 earliest rudiment of a cochlea ; and there are 

 two folds of the skin, resembling eye-lids, at the 

 external orifice of the organ, which appear like 

 the first step towards the developement of an 

 external ear. 



The structure of the ear in the Crocodile is 

 but an approximation to that which we find pre- 

 vailing in Birds, where the organ is of large size 

 compared with that of the head. The rudi- 

 mental cochlea, as seen at k in Fig. 405, which 

 represents these organs in the Turkey, is of 

 large size, and slightly curved. In the cavity 

 of the tympanum (r) is seen the columella, which 

 extends to the fenestra ovalis ; and beyond it, the 

 semicircular canals (s), the bony cells (b) which 

 communicate with the tympanum, the os quad- 

 ratum (q), the zygomatic process (z), and the 

 lower jaw (j). The ear-drum is now no longer 

 met with at the surface, but lies concealed at the 

 bottom of a short meatus, the orifice of which is 

 surrounded with feathers, arranged so as to serve 

 as a kind of imperfect concha, or external ear» 



