INSECTIVOROUS MAMMALIA. 527 



back from the abdomen, to which it could give 

 no effectual protection. Hence the animal, 

 when above ground, walks very awkwardly, and 

 is unable to advance but by an irregular and 

 vacillating pace.* 



We have seen that there is a tribe of fishes 

 armed externally with sharp spines, which they 

 are capable of erecting when in danger of attack. 

 A similar kind of defensive armour is furnished 

 to the Porcupine and the HedgeJiog, which be- 

 long to the family of insectivorous quadrupeds. 

 For the purpose of erecting these bristles, when 

 the animal is irritated or alarmed, there is pro- 

 vided a peculiar set of muscular bands, which 

 forms part of the usual subcutaneous layer, 

 termed the panniculus caniosus. In the hedge- 

 hog these muscles are very complicated, and 

 give the animal the power of rolling itself into 

 a ball. A minute description of these muscles 

 has been given by Cuvier, who found that the 

 whole body is enveloped in a large muscular 

 bag, or mantle, lying immediately under the in- 

 teguments ; and capable, by the contraction of 

 different portions of its fibres, of carrying the 



* The only quadrupeds which resemble the mole in the perfect 

 adaptation of their structure to the purposes of burrowing, are 

 the Wombat and the Koala, which are among the many extra- 

 ordinary animals inhabiting the continent of Australia. Their 

 hind legs are constructed in a manner very much resembling the 

 human fore-arm. (See Home, Lectures, &c. i. 134.) 



