APPABATUS OF MOTION IN GENEBAL. 123 



257. Thus it would seem that, whilst volition proceeds 

 from the brain, the regulation of the movements proceeds from 

 the cerebellum ; whilst, in respect of those muscular actions 

 which are independent of the brain, the principle of action 

 seems to reside in the spinal marrow and ganglionary system. 



258. Duration and Force of the Muscular Con- 

 tractions. The contraction of the muscular fibres is a phe- 

 nomenon essentially intermittent; they relax and contract 

 alternately. Even the heart does this ; but the voluntary 

 muscles require a much longer interval of repose ; a lassitude 

 comes on at last, rendering all further action impossible. 



Muscular fatigue varies much in different individuals ; so 

 also does the strength of contraction displayed. In passion 

 and in a maniacal state it is prodigious. The development 

 of the muscular system is best seen in the athlete. 



Of the Apparatus of Motion in General. 



259. The function we have now to consider is chiefly 

 mechanical; it respects the various movements of animal 

 bodies. 



In the lowest animals the muscles are all connected with, 

 and dependencies of, the integument, which is soft and 

 flexible, and by acting on this, they move the body in whole 

 or in part ; but in animals of a more perfect structure, the 

 motor apparatus becomes more and more complex, and is 

 formed not only of muscles, but of a skeleton, itself com- 

 posed of solid parts calculated to augment the precision, the 

 extent, and the force of the movements, to protect the viscera 

 against external violence, and to determine the general form 

 of the body. 



260. This framework or skeleton, to which the muscles 

 are chiefly attached, is in man, and all animals called verte- 

 brate, situated internally, and is covered by the soft parts. 



In some fishes (as in the skate) the skeleton is formed of a 

 white, opaline, compact, homogeneous substance, at once very 

 resisting and elastic. It is called cartilage. In all animals, 

 when very young, the skeleton is at first cartilaginous ; but 

 this condition, which is permanent in certain fishes, is only 

 transitory in the greater number of animals, and the car- 

 tilaginous pieces soon become charged with calcareous salts, 

 by which they become firm, hard, comparatively brittle : in 

 this state they are called bones. 



