Applied anatomy and kinesiology; the mechanism of muscular movement . Fig. 33. -Abnormallposture of right scapula due to loss of the right trapezius.(Mollier.) We have noticed that the first part of the trapezius is admirablysituated for lifting the shoulders, and that when it is stimulated byelectric current it does so promptly. When we shrug the shoulders,therefore, it is natural to infer that it aids in the movement, butobservation of the kind we are considering now shows that it doesnothing of the kind, remaining in complete relaxation while themovement is being performed. To prove this we
Applied anatomy and kinesiology; the mechanism of muscular movement . Fig. 33. -Abnormallposture of right scapula due to loss of the right trapezius.(Mollier.) We have noticed that the first part of the trapezius is admirablysituated for lifting the shoulders, and that when it is stimulated byelectric current it does so promptly. When we shrug the shoulders,therefore, it is natural to infer that it aids in the movement, butobservation of the kind we are considering now shows that it doesnothing of the kind, remaining in complete relaxation while themovement is being performed. To prove this we need only to press the tips of two fingers down TRAPEZIUS 67 behind the outer third of the clavicle and then, while they arethere, to shrug the shoulders. The first part of the trapezius notonly fails to lift the fingers out from behind the clavicle but wecan remove the fingers, while the shoulders are lifted, and see thedeep pocket remaining there. To notice how actual contractionof the muscle affects it, raise the arm sideward above the level of. Fig. 34.—The trapezius in action. T, trapezius; D, deltoid. the shoulder and see how quickly the fingers are lifted out and thepocket obliterated. If the shrugging of the shoulders is donestrongly, against a resistance, the first part of the trapezius actsin some subjects, but not in all; the same is true in taking thedeepest possible breath. The reader should not infer from this illustration that a study ofwhat a muscle caii do is no indication of what it will do, for in the 68 MOVEMENTS OF THE SHOULDER GIRDLE great majority of cases all the muscles so situated as to be able tohelp in an exercise do so. There are, however, enough instanceslike this one to show that in the nervous control of the muscles inbodily exercise it is always necessary to supplement the study ofwhat a muscle might do by noticing what it actually does. Theseexceptions to the principle of economy, which is plainly violatedwhen a muscle that can help perform
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