APPLICATION OF MECHANICAL PRINCIPLES. 427 



be taken into account, the deltoid will have to contract with a force 

 equal to 1,284 pounds, to raise fifty-five pounds at the elbow. It is 

 farther contended by Borelli, Sturm, and Haller, that the force of the 

 muscle, as estimated in the preceding calculations, must be doubled, 

 seeing that it has to exert as much force in resisting the bone which 

 affords a fixed point at one extremity, as in elevating the weight at the 

 other. This estimate, if admitted, would elevate the force, to be exerted 

 by the deltoid in raising the fifty pounds, to 2,568 pounds. Lastly : 

 Much force is spent when a muscle passes over many joints; antagonist 

 muscles must, likewise, exert an influence of the kind, consuming a cer- 

 tain portion of the force developed in the contraction of the muscle. 



On the other hand, there are arrangements that augment the power 

 developed by muscles ; as the thick articular extremities of bones; the 

 patella and sesamoid bones in general ; all of which enlarge the angle, 

 at which the tendon is inserted into the bone or lever. The projecting 

 processes for muscular attachments, as the trochanters, protuberance 

 of the os calcis, spinous processes of the vertebrae, &c., augment the 

 arm of the lever, and are thus inservient to a like valuable purpose. 

 The smoothness of the articular surfaces of bones, tipped, as they are, 

 with cartilage, and the synovia, which lubricates the joints, by dimin- 

 ishing friction, as well as the bursae mucosae, which are interposed wher- 

 ever there is much pressure or friction, also aids the power. Trochleae or 

 pulleys act only in directing the force, without augmenting its amount ; 

 and the same may be said of the bony canals and tendinous sheaths, by 

 which the tendons of the muscles, especially those passing to the fingers 

 and toes, are kept in their proper course. Still, it must be admitted, 

 that, as regards the effort to be exerted by muscles, it must, in almost 

 all cases, be much greater than the resistance to be overcome. The 

 very fact of the lever of the third kind being that which prevails in our 

 movements shows this. The mere mechanician has conceived this to be 

 an unwise construction: and that there is a needless expense of force 

 for the attainment of a determinate end. In all cases we find, that the 

 expense of power has been but little regarded in the construction of the 

 frame ; nor is it necessary that it should have been. It must be recol- 

 lected, that the contraction of the muscle is under the nervous influ- 

 ence, and that, within certain limits, the force, to be employed, is regu- 

 lated by the influx sent by it into the muscle. The great object in the 

 formation of the body appears to have been to unite symmetry and 

 convenience with the attainment of great velocity and extent of motion, 

 so that whilst the power is moving through a small space, the weight 

 or resistance shall move rapidly through one more extensive. We have 

 seen that, in these respects, the lever of the third kind is most fitting. 

 With the others less power might be required ; but there would be less 

 extent of motion and velocity, whilst the symmetry and convenience of 

 the body would be destroyed. Suppose, for example, that in Fig. 179, 

 the biceps instead of being inserted at E, near the elbow had passed 

 on to the wrist, or, to simplify the matter, to the extremity of the 

 member; it would assuredly have acted with more force the lever 

 having been changed into one of the second kind, but the hand would 

 have lost that velocity and extent of motion, which are so important to 



