90 THE MECHANICAL FUNCTIONS. 



termed the Epidermis, Cuticle, or scarf-skin; and between 

 these there is often found an intermediate layer denominated 

 the Rete Mucosum, or the Pigmentum. 



The corium is generally of considerable thickness, and is 

 composed of strong and tough fibres, closely compacted to- 

 gether, and pervaded by innumerable ramifications of blood- 

 vessels of every kind. It is endowed with great flexibility, 

 and is capable of being considerably extended; properties 

 which fit it for readily accommodating itself to all the move- 

 ments of the body and limbs, and to the variable bulk of the 

 parts it covers. Being also very elastic, it soon regains its 

 natural form and dimensions, when left to itself after being 

 stretched. The skin is connected with the subjacent muscles 

 and other parts by a large quantity of cellular texture, which, 

 according to the particular intentions of its formation, some- 

 times 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 ani- 

 mal in wdiich the skin hangs loosely on the limbs, and en- 

 closes 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 

 fino-ers 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 subja- 

 cent parts. In animals that roll themselves into a ball, as 

 the hedge-hog, these muscles are of great size and import- 

 ance. We shall see that in the mollusca, this muscular ap- 

 paratus is inseparably blended with the integument, and 

 composes a peculiar structure, termed the mantle. Imme- 

 mediately covering the corium is the Rete Mucosum, which 

 is a very thin layer of soft animal matter, composed of a net- 

 work of delicate fibres, and containing more or less of the 

 material from which the colour of the skin is derived. 



The Epidermis is a membrane of a very peculiar nature, 

 consisting of a thin expansion of albuminous matter appa- 



