NERVE-MUSCULAR APPARATUS. 85 



centres to the muscles they contract, and produce 

 movements. Here, then, in the higher animals, 

 the nerve-mechanism and the muscles produce the 

 movements, and the joint action of these two por- 

 tions of the body is necessary to the production 

 of movements ; this has been proven by numerous 

 experiments in many subjects. 



The kind of movements that we have to do with 

 in the study of expression in man are nerve- 

 muscular signs, and it is essential to obtain clear 

 ideas on this point, in order that the principles and 

 modes of expression in man may be understood. 

 The simplest nerve-muscular apparatus consists of 

 a muscle, a nerve-centre or collection of nerve-cells, 

 and a nerve-fibre conveying currents from the nerve- 

 centre to the muscle; the whole must, of course, 

 be duly supplied with blood and nourished. Force 

 is generated in the nerve-centre by its nutrition, 

 and is conveyed to the muscle by the nerve-fibre. 

 When the centre sends force to the muscle it con- 

 tracts ; the muscle serves as an index showing the 

 times of discharge of force by the centre. It is not 

 necessary here to give any detailed account of the 

 structure and arrangement of the nerve-centres; 

 suffice it to say they are situated in the brain and 

 spinal cord. 



It is, then, convenient for our purposes in the 

 study of the principles and modes of expression to 

 speak of " nerve-muscular action " or signs. In 

 the study of the brain and spinal cord we know 

 when a current of nerve-force is sent out from a 

 nerve-centre by the effect of that current on mus- 



