CENTRE OF GRA VITY OF THE BOD Y. 257 



and elbow-joints; the hamstring muscles inserted into the bones of 

 the lower leg arise from the pelvis and pass over both the hip- and 

 knee-joints. There are certain advantages gained from this construc- 

 tion of the body, one of these being that, as the amount of shortening of 

 a muscle is in proportion to its length, a greater amount of shortening is 

 obtained from the long muscles under consideration. As Tick 1 has 

 pointed out, we are able by this arrangement to move two joints by 

 means of one muscle, and thus there is an economy in the amount 

 of muscular substance required. Thus, in order to perform the same 

 amount of work in extending the hip- and bending the knee-joint by 

 muscles passing over one joint alone, it would be necessary to have two 

 sets of muscles, each set equal to the combined masses of the 

 hamstring muscles. Not only, then, is the amount of movement of 

 a limb considerably increased, but the amount of work which can be 

 performed, say by bending the knee, is very greatly increased by this 

 arrangement. 



THE CENTRE OF GRAVITY OF THE BODY. 



Johannes Alphonsus Borellus 2 and the brothers Wilhelm and 

 Eduard Weber, 3 taking for granted that the centre of gravity lies in the 

 middle line of the body, determined its distance from the sole of the 

 foot, but failed to determine its position in the antero-posterior plane. 

 They placed a man flat on his back upon a board, and balanced the 

 board see-saw wise upon a wedge. The centre is situated roughly 

 between the pubes and buttocks, and is farther from the sole of the 

 foot than from the crown of the head. If the whole height of a man 

 be taken as 100, the distance of the centre of gravity from the ground 

 will, in the erect position, be 57 per cent, of the total height. This 

 result was verified by Harless 4 and Meyer, 5 whose measurements vary 

 within the limits of 3 per cent. This is, however, to be expected, for 

 no two individuals possess the same build a man with muscular 

 arms and shoulders will have his centre of gravity relatively high, 

 another man with strong legs and sloping shoulders will have his 

 centre of gravity relatively low. 



Meyer further determined the position of the centre of gravity in 

 the antero-posterior plane by the following method. A man standing 

 at " attention " bent forwards so that the weight of the body fell upon 

 the front of the feet ; a line plumb to this point passed through his 

 centre of gravity. He then extended his limbs at the ankle-joint until 

 he nearly fell backwards over his heels ; the line plumb to his heels 

 passed through the centre of gravity, which lay in the point of inter- 

 section of these two lines. Meyer found the centre to lie in the body 

 or canal of the second sacral vertebra. 



Kecently Braune and Fischer 6 have ascertained the position of the 

 centre of gravity. They proceeded as follows: A "subject" placed 

 flat on the back upon a board was frozen in this position. The frozen 



1 "Handbuch der Physiol.," Bd. i. Th. 2, S. 284. 

 "De Motu Animalium," Lugduni Batavorum, 1679. 

 " Mechanik der menschlichen Gehwerkzeuge," Gottingen, 1836. 



4 "Die statischen Momente der menschlichen Gliedmaasen," Koniyl. Bayr. Akad. d. 

 Wissensch. , 1860. 



5 " Statik und Mechanik des menschlichen Knochengeriistes," Leipzig, 1873. 

 c Abhandl. d. math.-phys. Cl. d. k. sacks. Gesellsch. d. Wissensch., Bd. xv. 



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