CHAP. VII.] ASSOCIATION OF MOVEMENTS. 195 



one effect. Even the consent of the fibres of a single muscle in 

 contraction is an instance of this fact. Among innumerable other 

 proofs of harmonious design in the construction of the animal body, 

 this might be singled out as a most convincing one, that not only 

 are the hard levers, and their joints and motive engines, so built up 

 as to be entirely proportioned and adapted to one another in shape, 

 strength, and position, and a system of nervous communications 

 established, by which the motor power can be at one excited, pro- 

 longed, or controuled in any particular muscle ; but that the mere 

 will, an emotion, an excitement of sense, or even one unconsciously 

 received, is able, by the correspondence existing between the dif- 

 ferent parts of the nervous system, to produce associated actions in 

 precisely those parts mechanically adapted to move in concert, and 

 this with exquisite exactitude as well as variety. 



Such is the nature of the nervous communications between cer- 

 tain muscles, that in numerous instances, one cannot be stimulated to 

 contraction without others contracting of necessity at the same time. 

 This depends very generally on the mechanical dispositions of mus- 

 cles, obliging certain of them to fix a point from which others may 

 act. Thus the scapula is continually being fixed by the muscles 

 connecting it with the trunk, in order that the arm may be wielded 

 upon it. Thus, also, the brow cannot be elevated by the frontalis 

 without the occipitalis fixing the intermediate tendon. But, in 

 other instances, this necessary consent is dependent on the symme- 

 trical arrangement of similar parts on the two sides of the body. 

 Some persons cannot close one eye keeping the other open; or 

 dilate one nostril without the other ; we cannot look up with one 

 eye, and down with the other ; nor compress the abdominal cavity by 

 the muscles of one side without those of the other. There is, 

 indeed, a general tendency to symmetrical movement, which it is 

 the part of education and habit to overcome within certain limits. 

 The movements of the hands those wonderfully versatile instru- 

 ments of man's intellect are, in his state of infancy, generally 

 symmetrical. The unsymmetrical actions of walking are a slow 

 acquisition. Most motions that are symmetrical are also harmo- 

 nious ; but there is one example in which symmetry gives way 

 to harmony of movement, viz., in the lateral motions of the eyes, 

 where symmetry would produce a squint, and derange the consent 

 of the images on the two retinae. Here, therefore, by the distribu- 

 tion of the nerves, non-symmetrical muscles are made to produce a 

 harmonious movement. 



The various attitudes of man may here be briefly explained. 



o 2 



