42 THE ENGINES OF THE HUMAN BODY 



combustion engines made on the same plan as that of a 

 motor cycle. We need not stop to explain that we have 

 substituted " push " engines for " pull " engines, and 

 that they act in a reverse direction. If we now wish to 

 unbend or extend the elbow we set the anterior engine at 

 work, and it extends the elbow, thus pushing the forearm 

 down. It will be observed that when the forearm is being 

 unbent the piston of the triceps engine must move upwards 



FORE. ARM 



Fig. 8. 



CONNECTING ROD 

 CRANK PIN 



Fig. 7. — Showing the anterior brachial muscle which flexes the forearm, and 

 the posterior brachial or triceps which extends it. 



Fig. 8. — Showing the brachial and triceps muscles replaced by internal- 

 combustion engines. 



to a corresponding degree. Likewise, if we bend the 

 elbow, by setting the triceps engine in motion, the 

 piston of the biceps must move upwards to a correspond- 

 ing degree. The one engine cannot move without a 

 reverse action taking place in its opponent or antagonist. 

 They have to work as reciprocal engines, and therefore 

 their strokes must be perfectly timed so that when the 

 piston of one is ascending that of the other must be 

 descending. It is clearly necessary that the two pistons 



