INTRODUCTION. 25 



The animal functions, or those proper to animals, that is to say, 

 sensibility and voluntary motion. 



The vital, vegetative functions, or those common to animals and 

 vegetables, i. e., nutrition and generation. 



Sensibility resides in the nervous system. 



The most general external sense is that of touch ; it is seated in 

 the skin, a membrane that envelopes the whole body, which is tra- 

 versed in every direction by nerves whose extreme filaments expand 

 on the surface into papillae, and are protected by the epidermis and 

 other insensible teguments, such as hairs, scales, &c. &c. Taste 

 and smell are merely delicate states of the sense of touch, for which 

 the skin of the mouth and nostrils is particularly organized : the first, 

 by means of papillae more convex and spongy ; the second, by its 

 extreme delicacy and the multiplication of its ever humid surface. 

 We have already spoken of the ear and the eye. In fine, sensations 

 more or less painful may originate in every part of the body through 

 accident or disease. 



Many animals have neither ears nor nostrils, several are without 

 eyes, and some are reduced to the single sense of touch, which is 

 never absent. 



The action received by the external organs is continued by the 

 nerves to the central masses of the nervous system, which, in the 

 higher animals, consists of the brain and spinal marrow. The more 

 elevated the nature of the animal, the more voluminous is the brain 

 and the more is the sensitive power concentrated there ; the lower 

 the animal, the more the medullary masses are dispersed, and in the 

 most imperfect genera, the entire nervous substance seems to melt 

 into the general matter of the body. 



That part of the body, which contains the brain and principal 

 organs of sense, is called the head. 



When the animal has received a sensation, and this has occasioned 

 volition, it is by the nerves, also, that this volition is transmitted to 

 the muscles. 



The muscles are bundles of fleshy fibres whose contractions pro- 

 duce all the movements of the animal body. The extension of the 

 limbs and every elongation, as well as every flexion and abbreviation 

 of parts, are the effects of muscular contraction. The muscles of 

 every animal are arranged, both as respects number and direction, 

 according to the movements it has to make ; and when these motions 

 require force, the muscles are inserted into hard parts, articulated 

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