INTRODUCTION. 25 



SUMMARy IDEA OF THE FUNCTIONS AND ORGANS OF THE BODIES OF ANIMALS, AND OF 

 THEIR VARIOUS DEGREES OF COMPLICATION. 



After what we have stated respecting the organic elements of the hody, its 

 chemical principles, and the forces which act within it, it remains only to give a sum- 

 mary idea in detail of the functions of which life is composed, and of their respective 

 organs. 



The functions of the animal body are divided into two classes : — 



The tlnimal 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 ; that is 

 to say, nutrition and generation. 



Sensibility resides in the nervous system. 



The most general external sense is that of touch ; its seat is in the skin, a mem- 

 brane enveloping the whole body, and traversed all over by nerves, of which the 

 extreme filaments expand on the surface into papilla;, and are protected by the epider- 

 mis, and by other insensible teguments, such as hairs, scales, &c. Taste and smell 

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

 nostrils is particularly organized ; the former by means of papillje more convex and 

 spongjr ; the latter, by its extreme delicacy and the multiplication of its ever humid 

 surface. We have already spoken of the eye and ear in general. The organ of gene- 

 ration is endowed with a si.xth sense, which is seated in its internal skin; that of the 

 stomach and intestines declares the state of those viscera by peculiar sensations. In 

 fine, sensations more or less painful may originate in all parts of the body through 

 accidents or diseases. 



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 through the nerves to the 

 central masses of the nervous system, which, in the higher animals, consists of the 

 brain and spinal chord. The more elevated the nature of the animal, the more volumi- 

 nous is the brain, and the more the sensitive power is concentrated there ; in propor- 

 tion as the animal is placed lower in the scale, the medullary masses are dispersed, and 

 in the lowest genera of all, the nervous substance appears to merge altogether, and 

 blend in the general matter of the body. 



That part of the body which contains the brain and the principal organs of sense, is 

 called the head. 



"When the animal has received a sensation, and which has induced in it an act of 

 vohtion, it is by [particular] nerves also that this volition is transmitted to the muscles. 



The muscles are bundles of fleshy fibres, the contractions of which produce all the 

 movements of the animal body. The extensions of the limbs, and all the lengthenings 

 of parts, are the eifect of muscular contractions, equally with flexions and abbreviations. 

 The muscles of each animal are disposed in number and direction according to the 

 movements which it has to execute ; and when these movements require to be effected 

 with some vigour, the muscles are inserted into hard parts, articulated one over 

 another, and may be considered as so many levers. These parts are called bones in 



