26o 



THE EVOLUTION OF MAN. 



The ear of Vertebrates develops in many important 

 points similarly to the eye and nose, but yet in other 

 respects veiy differently >^^ The organ of hearing of the 

 developed human being resembles that of other Mammals 

 in all essential particulars, and is especially similar to that of 

 Apes. As in the la.tter, it consists of two principal parts, an 

 apparatus for the conveyance of sound (external and middle 

 ear) and an apparatus for producing the sensation of sound 

 (internal ear). The outer ear opens in the ear-shell [concha 



Fig. 244. — Auditory organ of man (left ear, seen from the front; natural 

 size) : a, ear-shell : I, external ear-canal ; c, drum, or tympanic membrane ; 

 d, cavity of drum ; e, ear-trumpet ; /, g, h, the three ear bonelets (/, hammer ; 

 g, anvil ; h, stirrup) ; i, ear-pouch (utriculus) ; k, the three semi-circular 

 canals ; I, ear-sac (sacculiis) ; m. snail (cochlea) ; n, auditory nerve. 



auris), situated at the side of the head (Fig. 224, a). From 

 this the outer ear-canal, which is usually about an inch long, 

 leads to the inside of the head (b). The inner end of this 



