26 INTRODUCTION. 



the vertebratecl animals, where they are internal, and formed of a gelatinous mass, 

 penetrated with molecules of phosphate of lime. In mollusks, crustaceans, and insects, 

 where they are external, and composed of a calcareous or corneous substance that 

 exudes between the skin and epidermis, they are termed shells, crusts, and scales. 



The fleshy fibres are attached to the hard parts by means of other fibres of a gela- 

 tinous nature, which seem to be a continuation of the former, constituting what are 

 called tendons. 



The configuration of the articulating surfaces of the hard parts limits their move- 

 ments, which are further restrained by cords or envelopes attached to the sides of the 

 articulations, and which are termed ligaments. 



It is from the various dispositions of this bony and muscular apparatus, and from 

 the form and proportions of the members which result therefrom, that animals are 

 capable of executing those innumerable movements which enter into walking, leaping, 

 flight, and swimming. 



The muscular fibres appropriated to digestion and circulation are independent of the 

 will ; they receive nerves, however, but, as we have said, the chief of them exhibit 

 subdivisions and enlargements which appear to have for their object the estrangement 

 of the empire of the me. It is only in paroxysms of the passions and other powerful 

 mental emotions, which break down these barriers, that the empire of the me becomes 

 perceptible ; and even then its effect is almost always to disorder these vegetative 

 functions. It is also in a state of sickness only that these functions are accompanied 

 by sensations. Digestion is ordinarily performed unconsciously. 



The aliment, divided by the jaws and teeth, or sucked up when liquids con- 

 stitute the food, is swallowed by the muscular movements of the back part of the 

 mouth and throat, and deposited in the first portion of the alimentary canal, usually 

 expanded into one or more stomachs ; it there is penetrated with juices proper to dis- 

 solve it. Conducted thence along the rest of the canal, it receives other juices destined 

 to complete its preparation. The parietes of the canal have pores which extract from 

 this alimentary mass its nutritious portion, and the useless residue is rejected as 

 excrement. 



The canal in which this first act of nutrition is performed, is a continuation of the 

 skin, and is composed of similar layers ; even the fibres which encircle it are analogous 

 to those which adhere to the internal surface of the skin, called the fleshy pannicle. 

 Throughout the whole interior of this canal there is a transudation, which has some 

 connexion with the cutaneous perspiration, and which becomes more abundant when 

 the latter is suppressed ; the skin even exercises an absorption very analogous to that 

 of the intestines. 



It is only in the lowest animals that the excrements are rejected by the mouth, and 

 in wdiich the intestine has the form of a sac without issue. 



Among those even in which the intestinal canal has two orifices, there are many in 

 which the nutritive juices, absorbed by the coats of the intestine, are immediately 

 diffused over the whole spongy substance of the body : this appears to be the case 

 with the whole class of insects. 



But, ascending from the arachnides and worms, the nutritive fluids circulate in a 

 system of confined vessels, the ultimate ramifications of which alone dispense its molecules 

 to the parts that are nourished by it ; those particular vessels which convey it are named 



