432 MUSCULAR MOTION. 



the peronei muscles, the line of motion will be from the insertion to 

 the point of reflection; precisely as a rope passing over a pulley raises 

 the weight in a line drawn from the weight to the pulley. 



The circular muscles, which have no precise origin or insertion, are 

 inservient to the contraction of the apertures around which they are 

 placed. 



In executing the complex movements of any part of the frame, a 

 combination of the action of the different muscles attached to the part, 

 generally occurs, rendering the process one of a complicated charac- 

 ter. This, if no other cause existed, would render it extremely difficult 

 to calculate the precise degree of force, which particular muscles, alone 

 or in combination, are capable of exerting. The mathematical physi- 

 ologists made multifarious attempts in this direction; but their con- 

 clusions were discrepant. When we bear in mind, that the force, capa- 

 ble of being exerted by any muscle, is dependent upon the proper 

 organization of the muscle, and likewise upon the degree of energy of 

 the brain, it will be apparent, that all attempts of the kind must be 

 futile. We can determine with nicety the effect of which the parts are 

 capable, supposing them inanimate structures. We can calculate the 

 disadvantages, caused by the insertion of the power near the fulcrum; 

 by the obliquity of the line of action of the power, &c. ; but we have 

 not the slightest data for estimating the effect produced by the nervous 

 influx, by that mysterious process, which generates a new force, and 

 infuses it into the muscles, in a manner so unlike that in which the 

 ordinary mechanical powers are exerted. The data necessary for such 

 a calculation would be the precise influx from the brain, the irrita- 

 bility of the muscle, the mechanical influences, dependent on the 

 straight or oblique direction of the fibres composing it, as regards the 

 tendon, the perpendicular or oblique direction in which the tendon is 

 attached to the bone, the particular variety of lever, the length of 

 the arm of the power and that of the resistance, the loss sustained 

 from friction, and the diminution of such loss caused by the cartilages 

 that tip the bones, and by the synovia, &c. data, which it is impossi- 

 ble to attain; and hence the solution of the problem is impracticable. : 



One great source of the combination of muscular motions is the 

 necessity for rendering one of the attachments fixed, in order that the 

 full force may be developed on the other. In but few of the muscles 

 is the part, whence the muscle originates, steady. To these few, the 

 muscles of the eye, which arise from the inner part of the orbit and 

 pass forward to be inserted into the organ, belong. To show how dis- 

 tant muscles may be concerned in this fixation of one end of a muscle, 

 when it is excited to the developement of plenary power, we may take 

 the case of the deltoid, which arises from the scapula and clavicle, and 

 is inserted into the os humeri : but the scapula and clavicle, themselves, 

 are not entirely fixed ; and, accordingly, if the deltoid were to contract 

 alone, it would draw down the scapula and clavicle, as well as elevate 

 the humerus. If, therefore, it be important to produce the latter effect 

 only, the scapula and clavicle must be fixed by appropriate muscles; 

 as by the rhomboidei, trapezius, &c. These muscles, however, arise 

 from, various vertebrae of the neck, which are themselves movable. It 



