The Sense of Hearing. 



IT has been well remarked by the earliest authors, that 

 birds are not provided like other animals with an 

 external ear, because their passage through the air 

 would have been obstructed by long ears like those of the 

 hare or the ass. 



In owls there is a peculiar valve placed at the opening, 

 partly of a membranous, and partly of a muscular struc- 

 ture, which has by some authors been deemed analogous 

 to the human ear, and it is around this that the tuft of 

 feathers is arranged, so as to form a large funnel, which 

 is brought into view when the two folds or lips are 

 separated. The outer opening is very large, parted into 

 two chambers by a square bone, and forming a consider- 

 able upright slit in the form of an S, extending as high 

 as the head itself. 



The drum of the ear in birds bulges outwards in a 

 somewhat convex form, and consists of two membranes. 

 In order to support, distend, or relax the exterior mem- 

 brane there is a cartilaginous organ stretching from the 

 side of the passage almost to the middle of the membrane ; 

 while there is another cartilage divided into three 

 branches, the middle one of which, being the longest, is 

 joined to the top of the cartilaginous organ before- 

 mentioned, and assists in bearing up the exterior mem- 

 brane. The cartilage joins the top of the columella 

 (Ossiculnm auditus), which is a very fine, thin, light, 

 bony tube, the bottom of which expands into a plate 

 (Sperculum), corresponding to the base of the stirrup-bone 

 in the human ear, and, like it, fitting the oval hole, to 

 which it is braced all round by a very slender membrane. 



^107 



