PHYSIOLOGY 



321 



straight from a bar. Many of the muscles run nearly parallel with the parts on which they act, 

 but the tendons before their attachment are usually either carried over a bony prominence or 

 some fascia or Ugament acts as a pulley so that the tendon is inserted at an oblique angle. 

 At other times a process for the attachment of the tendon projects from the bone and causes 

 the force of the contracting muscle to be more advantageously exerted on the bone. It may, 

 of course, readily be seen that the greater the distance of the attachment of a muscle from the 

 joint over which it acts, the greater will be the power exerted by the muscle. 



In considering the movements of the body, it is convenient to recognise two 

 groups, simple and complex. To the former, which alone can be considered in 

 a text-book of anatomy, belong such movements as flexion, extension, adduc- 

 tion, rotation, etc., while to the latter belong those associated movements which 

 give rise to changes in the positions of the body as a whole or of extensive 

 regions of the body. 



In flexion the extremities of the trunk or limbs or special portions of these 

 regions are bent near to one another; in extension the reverse movement is 

 brought about. The parts are straightened or even bent beyond the straight 

 position (over-extension). ■ ■" 



Fig. 339. — Three Diagrams (after Testut) to Illustrate Different Types of Levers ix 

 THEIR Relations to the Mechanical Action of the Muscles. 



P F 



II 



m 



In abduction transverse movements are made, a part being bent away from 

 the median line of the body or limb; in adduction the reverse movement is 

 brought about. 



In rotation a part is turned on its longitudinal axis. The rotation of the 

 femur at the hip-joint is called medial rotation when the toes are turned medial- 

 ward, lateral rotation when the toes are turned lateralward. Rotation at the 

 shoulder-joint is called medial when the thumb is turned forward and medial- 

 ward toward the body, lateral when the reverse movement takes place. These 

 movements are also carried out at the elbow-joint, but here medial rotation is 

 called pronation, lateral rotation, supination. Fick prefers these terms also for 

 the rotation at other joints as at the shoulder, hip and knee. 



At the shoulder-joint the swinging of the arm toward the back is called exten- 

 sion; toward the front, flexion; and from the side, abduction. Moving the arm 

 toward the mid-dorsal or mid-ventral line is called adduction. 



Taking the body as a whole the musculature may be divided into two main 

 divisions, an expander division and acontradoi' division. In general the extensors, 

 abductors and lateral rotators expand, the flexors, adductors and medial rota- 

 tors contract. 



In the most expanded condition the head and spine are extended or even shghtly hyper- 

 extended (flexed dorsally), and the hmbs project laterally from the body with the backs of the 

 hands and feet facing dorsalward, the palms and soles ventralward, and the digits spread out. 

 In the fully formed human body it is not possible to put the lower extremity in the completely 

 expanded position, although it is in this position early in embryonic development. As develop- 

 ment proceeds the lower extremity is adducted and rotated medialward and the girdle is so fixed 

 that full abduction becomes no longer possible. In many of the lower vertebrates full abduction 

 is possible throughout life in the lower extremities just as it is throughout life in the upper 

 extremities in man. Full extension of the spinal column in man is also hindered in the thoraciC\ 

 region bj' the thorax, and in the sacro-coccygeal region by the osseous union of the vertebrae 

 with one another as well as by the attachment of the hip girdles. The lumbar region in man iB/ 

 in a condition of permanent hyper-extension. ^-^ 



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