100 Cuvierian System of Zoology, 



so disposed, as to perform the motions which it has to execute ; 

 and when these motions require great strength, the muscles 

 are inserted into hard jointed parts, which may be regarded 

 as levers. In vertebrated animals these parts are internal, and 

 are formed of gelatine, penetrated by particles of phosphate 

 of lime : they are called the bones. In the molluscous and 

 crustaceous animals, and in insects, these parts are external, 

 and are composed of lime or horny matter (cornee), which 

 transudes between the skin and the epidermis : they are called 

 shells, crusts, or scales. The fleshy fibres are inserted into 

 the hard parts by means of other fibres, of a gelatinous nature, 

 which appear to be a continuation of the muscles, and form 

 what are called tendons. 



The configuration of the surface of the joints of the bones, 

 shells, or crusts of animals limits their motions, which are still 

 farther restrained by ligaments attached to the sides of the 

 joints. According to the different arrangement of the bony 

 and muscular apparatus [appareil), and to the form and pro- 

 portion of the members which result from thence, the animals 

 are in a condition to perform the innumerable motions which 

 take place in walking, leaping, flying, and swimming. 



The muscular fibres concerned in digestion and circulation 

 are not subject to the power of volition ; nevertheless, they 

 are furnished with nerves, the principal of which undergo sub- 

 divisions and enlargements {renflemens), that appear to be 

 intended to withdraw these nerves from the power of volition. 

 It is only when under the influence of the passions, or power- 

 ful emotions of the mind, that the empire of volition extends 

 beyond these barriers, and it is always to disorder the vege- 

 tative functions. In a diseased state, likewise, these functions 

 are attended with sensation. Most commonly the digestion 

 goes on, without being perceived by the animal. 



The aliments, after being divided by the teeth and jaws, or 

 sucked in when the animal feeds on liquids, are swallowed by 

 the muscular motions of the lower part of the mouth and 

 the throat, and are deposited in the first part of the alimentary 

 canal, which is commonly swelled out into one or more 

 stomachs. There the food is penetrated by juices proper to 

 dissolve it. As the food advances along the other parts of the 

 alimentary canal, it receives other juices, to complete its pre- 

 paration. The internal surface of the canal has pores, which 

 extract from the alimentary mass the part which is suitable 

 for nutrition ; the useless residue is ejected as excrement. 



In the lowest class of animals the intestine is in the form of 

 a bag, without a vent, and the excrements are ejected by the 

 mouth. The number of animals is more considerable in which 



