IG INTRODUCTION. 



by particles of phosphate of lime. In the MoUusca, the Crustacea, and 

 Insects, where they are external, and composed of a calcareous or horny 

 substance that exudes between the skin and epidermis, they are called 

 shells, crusts, and scales. 



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

 fibres of a gelatinous 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 motion, which are also restrained by cords or envelopes, attached to 

 the sides of the articulations, called ligaments. 



It is from the various arrangements of this bony and muscular appara- 

 tus, and the form and proportion of the members therefrom resulting, that 

 animals are capable of executing the innumerable movements that enter 

 into walking and leaping, flight and natation. 



The muscular fibres, appropriated to digestion and the circulation, are 

 independent of the will ; they receive nerves, however, but the chief of 

 them are subdi\'ided and arranged in a manner which seems to have for its 

 object their independence of the me. It is only in paroxysms of the pas- 

 sions and other powerful affections of the soul, which break down these 

 barriers, that the empire of the me is perceptible, and even then it is al- 

 most always to disorder these vegetative functions. It is, also, in a state 

 of sickness only that these functions are accompanied with sensations : di- 

 gestion is usually performed unconsciously. 



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

 constitute the food, is swallowed by the muscular movements of the hinder 

 parts of the mouth and throat, and deposited in the first portions of the ali- 

 mentary canal that are usually expanded into one or more stomachs ; there 

 it is penetrated with juices fitted to dissolve it. Passing thence through 

 the rest of the canal, it receives other juices destined to complete its pre- 

 paration. The parietes of the canal are pierced with pores which extiact 

 from this alimentary mass its nutritious portion ; the useless residuum is 

 rejected as excrement. 



The canal in which this first act of nutrition is performed, is a conti- 

 nuation of the skin, and is composed of similar layers ; even the fibres 

 that encircle it are analogous to those which adliere to the internal sur- 

 face of the skin, called the fleshy pannicle. Throughout the whole inte- 

 rior 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 absorption of the skin is even very analogous to 

 that of the intestines. It is only in the lowest ord^r of animals that the ex- 

 crements are rejected by the mouth, their intestines resembling a sac, 

 having but one opening. 



