08 THE MECHANICAL FUNCTIONS. 



particular intentions of its formation, sometimes 

 binds it tightly over these parts, and on other occa- 

 sions allows of a free and extensive motion. This 

 latter property is remarkably exemplified in the 

 Racoon, an animal whose skin hangs loosely on the 

 limbs, and encloses the body like a wide elastic 

 garment ; so that, however firmly a person may 

 attempt to grasp the animal by the neck, it can 

 easily turn its head completely round, and bite the 

 fingers that are holding it. In like manner, the 

 skin of the Frog is attached to the body only at a 

 few places, and may be readily stripped off. A 

 thin layer of muscular fibres is often found lying 

 immediately underneath the skin, and is provided 

 for the purpose of moving it over the subjacent 

 parts. In animals that roll themselves into a ball, 

 as the Hedge-hog, these muscles are of great size 

 and importance. We shall see that, in the Mol- 

 lusca, this muscular apparatus is inseparably 

 blended with the integument, and composes a pe- 

 culiar structure, termed the inantle. 



The outer portion of the corium is formed of a 

 great number of conical processes, or papillce, as 

 they are termed, projecting somewhat obliquely 

 from the surface, and disposed in regular series of 

 parallel rows, with intervening furrows. They 

 chiefly contain the terminations of the nervous 

 filaments distributed to the skin, and receive also a 

 small blood vessel. This outer layer of the corium, 

 which is termed the corpus paplllare, is, as we shall 

 afterwards find, the principal seat of the sense of 

 touch. 



The Corpus 3Tucosum, which immediately covers 

 the papillae, and is every where moulded on their 



