HEARING. 47 



the tuft of feathers already mentioned 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 considerable upright slit in 

 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 mem- 

 branes. In order to support, distend, or relax the 

 exterior membrane, 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 membrane. The cartilage 

 joins the top of the columella (pssiculum audit us), 

 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 



Drum of the Ear in Birds. (Enlarged from Derham's figure.) 



* Elumenbacb, Comp. Anat. 263. t Blainville, p. 532. 



F 



