2^O THE EVOLUTION OF MAN. 



Mammals. Most of these have even lost it entirely ; this 

 is so, for example, in the Sea-cows and Whales, and most 

 Seals. On the other hand, in the great majority of Pouched 

 Animals (Marsupialia) and Placental Animals (Placentcdia), 

 the ear-shell is well developed, receives and concentrates the 

 waves of sound, and is provided with a highly-developed 

 muscular apparatus, by means of which it can be turned 

 freely to all sides, and at the same time can be changed in 

 form. Every one must have noticed how strongly and freely 

 our domestic Mammals, Horses, Cows, Dogs, Rabbits, etc., 

 can " prick " their ears, erect them and turn them in different 

 directions. Most Apes yet retain the power of doing this, 

 and our ancient Ape progenitors could also do it. The more 



FIG. 250. Kudimentary ear-muscles on the human skull: a, upward 

 muscle (TO. attollens) ; b, forward muscle (m. attrahens) ; c, backward muscle 

 (m. retrahens) ; d, larger muscle of the helix (m. helicis major); e, smaller 

 muscle of the helix (m. helicis minor'); f, muscle of the tragus (m. tragicus) ; 

 g, muscle of the antitragus (m. antitragicus) . (After H. Meyer.) 



recent Ape ancestors, common to Men and to the Anthropoid 

 Apes (Gorilla, Chimpanzee, etc.), discontinued the habit of 

 moving their ears, and hence the motor muscles gradually 



