INTEODUCTION. 



25 



ing extensor on the other aspect, these two muscles must be 

 opposed to and antagonize each other. This belief is founded 

 on what I regard as an erroneous assumption, viz., that muscles 

 have only the power of shortening, and that when one 

 muscle, say the flexor, shortens, it must drag out and forcibly 

 elongate the corresponding extensor, and the converse. This 

 would be a mere waste of power. Nature never works 

 against herself. There are good grounds for believing, as I 

 have stated elsewhere,^ that there is no such thing as antagon- 



FiG. 5. Shows the muscular cyole formed by the biceps (a) or flexor muscle, 

 and the triceps (b) or extensor muscle of the human arm. At i the centri- 

 petal or shortening action of the biceps is seen, and at j the centrifugal or 

 elongating action of the triceps (vide arrows). The present figure represents 

 the forearm as flexed upon the arm. As a consequence, the long axes of the 

 sarcous elements or ultimate particles of the biceps (i) are arranged in a 

 more or less horizontal direction; the long axes of the sarcous elements of 

 the triceps (j) being arranged in a nearly vertical direction. When the fore- 

 arm is extended, the long axes of the sarcous elements of the biceps and 

 triceps are reversed. The present figure shows how the bones of the ex- 

 tremities form levers, and how they are moved by muscular action If, 

 e.g., the biceps (a) shortens and the triceps (b) elongates, they cause tlie fore- 

 arm and haiid(h) to move towards the shoulder (d). If, on the other hand, the 

 triceps [b] shortens and the biceps (a) elongates, they cause the forearm and 

 hand (h) to move away from the shoulder. In these actions the biceps (a) and 

 triceps (6) are the power ; the elbow-joint {g) the fulcrum, and the forearm 

 and hand (h) the weight to be elevated or depressed. If the hand repre- 

 sented a travelling surface which operated on the earth, the water, or the 

 air, it is not difficult to understand how, when it was made to move by 

 the action of the muscles of the arm, it would in turn move the body to 

 which it belonged, d Coracoid process of the scapula, from which the internal 

 or short head of the biceps (a) arises, e Insertion of the biceps into the 

 radius. / Long head of the triceps (b). g Insertion of the triceps into the 

 olecranon process of the ulna. — Original. 



ism in muscular movements ; the several muscles known as 

 flexors and extensors; abductors and adductors; pronators 

 and supinators, being simply correlated. Muscles, when they 



1 " Lectures on the Physiology of the Circulation in Plants, in the Lower 

 Animals, and in Man."— Edinburgh Medical Journal for January and Feb- 

 ruary 1873. 



