132 ORGANS OF OFFENCE AND DEFENCE. 



mammalia, by means of the muscular expansion, 

 termed panniculus carnosus. No trace of such a 

 muscular expansion exists in fishes. This fact is 

 worthy of attention, as in generalising on the sub- 

 ject of the hypodermal muscular system, in the 

 animal kingdom, an opposite view is often sug- 

 gested. For example, the hypodermal or sub- 

 cutaneous muscular system, as contrasted >vith the 

 skeleton muscles, is often represented as commencing 

 almost in a rudimentaiy state in man, under the 

 form of the slender sub-cutaneous muscular ex- 

 pansion on the fore part and sides of his neck, 

 termed plaiysma mt/oides, as growing in importance 

 in the mammalia under the term of panniculus 

 cat^nosus^ it enables the animal to make the whole 

 skin quiver, so as to shake off insects, and reaches 

 a greater importance in many of them, for example, 

 in the hedge-hog, and a great proportion of the 

 Edentates. In the first, it forms a species of cap, 

 resting on the back of the animal in its ordinary 

 state, yet so constructed, that it is capable of enve- 

 loping the extremities and whole body, when, on 

 being attacked, it assumes the well-known form of 

 a ball. Finally, that this hypodermal muscular 

 expansion attains its exti'eme developement, as we 

 descend in the scale of animals, until at last in the 

 avertebral tribes, the mollusca, the Crustacea, and 

 insects, it constitutes the whole of the muscular 

 system ; all the active organs of locomotion in these 

 being inserted into the integuments. This state- 

 ment, then, is true only when it receives an im- 



