2o6 HEAD AND NECK. 



Ears. — The organs of hearing, on each side of the 

 head, are divided into the external ear ; the middle ear 

 (tympanum) ; and the internal ear {labyrinth). " The 

 external and middle ears are conducting ; the internal 

 ear is conducting and receptive. In the external ear 

 the vibrations travel through air ; in the middle ear 

 through solid structures^membranes and bones ; and in 

 the internal ear through fluid" (Kirkes). The vibra- 



Fig. 299. — Coffin Shape 

 of Head. 



tions of sound are transmitted far more readily through 

 solid structures than through air, as we may easily prove 

 by applying our ear to the end of a long plank of wood, 

 and getting another person to scratch lightly with the 

 nail of a finger or other hard object on the other end, 

 in which case we shall hear the sound of the scratching 

 much more plainly than if it were transmitted through 

 the air. We have a similar case by applying our ear to a 

 road, in order to hear the foot-falls of horses which are 

 moving on that road, at a long distance from us. Moles 

 have no external ears, because they use their organs of 

 hearing chiefly for finding the position of neighbouring 

 earth-worms (their natural food), which they do by 



