INTRODUCTION. ^^ 



are froquently much larger than the head, and of great variety 

 of shapes: their variations of form being of great importance m 

 classification. 



The internal border is generally much carved, and terminates 

 in an obtuse or acute projection, called the internal basal lobe (c) ; 

 the external border of the ear is of an irregular convex contour, 

 and ends anteriorly in a blunt and thickened fold of membrane— 

 the external basal lobe (ciy The tragus, or oreillon (e), is an 

 upright growth of membrane extending from the base of the 

 auricle up the centre of the external ear. The function of this 

 appendage is not known ; it probflbly acts as a valve to prevent 

 foreign substances entering the ear, or to prevent the volume of 

 sound received from such a large auricle in impinging too forcibly 

 upon the delicate tympanum. 



The nose is also frequently the seat of extensive dermal growths. 

 These appendages, situated about the nostrils, may be simple up- 

 right, triangular folds of skin, or they may be exceedingly compli- 

 cated in structure. No North American bat, with but one ex- 

 ception (31. californicus), has such a development. Though the 

 external ear is evidently intended to augment the sense of hear- 

 ing, there is some doubt whether the nose leaves hold the same 

 rcktion to the olfactory sense. These growths are composed of 

 reduplications of skin, and are not related to the lining mem- 

 brane of the nose. They are probably the agents for augmenting 

 the sense of touch alone, and in this way act conjointly with the 

 wing membranes. 



It is in this latter structure that the sense of touch chiefly re- 

 sides. The bones of the extremities being covered on either side 

 with an enduplication of skin, form a frame-work upon both sides 



' In the above cut tlie external basal lobe has been turned backwards 

 to disclose the base of tragus. 



