SOME COMMON MAMMALS. 133 



A pin should be inserted by the head end so as to show its 

 length. There is no doubt that the hearing organ is thus 

 specially protected from contact with the soil. Moles hear 

 very acutely ; as Shakespeare has it : 



"Pray you, tread softly, that the blind mole may not 

 Hear a foot fall ! " 



But it is extremely probable that the sensitiveness of the 

 mole is in great measure due to its feeling the vibrations of 

 footfalls through the solid earth. 



Perhaps the most noteworthy modification of the mole's 

 body to suit its subterranean life is that of its fore paws. 

 The whole fore limb looks extremely short, yet it is set so 

 closely to the head that when the limb is stretched forward 

 it reaches in front of the snout. It is turned outward more 

 than downward. These limbs do the excavating not the 

 sensitive snout, which probably simply pushes aside the 



SICKLE BONE RADIUS 



^^l^ 



- HUMERUS 



WRIST ULNA 



Fig. 42. Fore limb of Mole. 



broken earth. The upper region seems buried in the body, 

 it is very short, and the bone within it (humerus) is greatly 

 flattened and otherwise altered in form to allow of attach- 

 ment of the excessively developed muscles required for the 

 hard work of excavation (Fig. 42). 



The paw itself is broad and flat, the palm very tough and 

 leathery, and its inner margin is extended and strengthened 

 by the presence of an extra bone not found in the fore paws 

 of other animals, which on account of its shape is known as 

 the " sickle " bone. The claws of the five digits, which are 



