42 SPINY ANIMALS. 



muscle on their heads that the spines are raised from a 

 recumbent to a vertical position when the creature rolls 

 itself up into a ball an action of which all porcupines are 

 quite incapable. Not only does the hedgehog differ from 

 the porcupine in this respect, but it is likewise peculiar in 

 using its spines as a means of protection when throwing 

 itself down a vertical bank or precipice, and by this means 

 is able to accomplish a vertical descent of over a dozen 

 feet without the slightest harm. As regards the develop- 

 ment of its spiny armour, the hedgehog is perhaps the 

 most highly specialized of all the spiny mammals, in spite 

 of the inferior length of its spines as compared with those 

 of the porcupine. Hedgehogs are now represented by 

 about a score of species ranging over Europe, Africa, and 

 a considerable portion of Asia ; while the existing genus 

 dates from the middle portion of the Miocene division of 

 the Tertiary period. That the spines characterizing the 

 existing forms have been independently developed within 

 the limits of the group is pretty conclusively indicated by 

 the close affinity of the hedgehogs to the long-tailed and 

 spineless Malayan insectivores known as gymnuras ; fossil 

 types apparently indicating an almost complete transition 

 from the gymnuras to the hedgehogs. In case anyone 

 should suggest that the latter, and not the former, might 

 be the ancestral stock, it may be mentioned that while the 

 gymnuras have a generalized type of dentition and long 

 tails, the hedgehogs have the teeth much reduced in 

 number and specialized in character, and short tails. 



In Madagascar the place of the hedgehogs is taken by 

 an entirely different group of insectivores known as the 

 tenrecs, all of which have a certain number of spines 

 mingled with the fur, at least in the young condition, 

 and some of which are so hedgehog-like in general 

 appearance that by the non-zoological observer they 

 would certainly be regarded as members of the Erinaceidse. 

 The tenrecs differ, however, from the hedgehogs pre- 

 cisely in the same manner as the golden moles differ 

 from the true moles. That is to say, whereas in 

 the latter the crowns of the upper molar teeth are 

 quadrangular, with their cusps arranged in a somewhat 



