CHAP, ii MECHANICS OF LOCOMOTOR APPARATUS 97 



I. Historical investigation into the action of the muscles on 

 the skeleton, and the mechanism of posture and locomotion, com- 

 menced with Borelli's classic De motu animalium, published in 

 1680. The writings of Barthez (1798) and of Gerdy (1832) con- 

 tain no real advance on the work of Borelli. Poisson (1833) 

 first attempted to calculate the work which a man performs in 

 walking. Real progress in this direction was made in the classical 

 publication of W. and E. Weber, Die Mechanik der menschlichen 

 Gehwerkzeuge, which appeared in 1836. The second half of the 

 nineteenth century brought many anatomical studies on the form 

 of the articular surfaces, and the significance of the ligaments, the 

 articular capsules, fascia, etc., more especially from Henke, Langer, 

 and H. Meyer. Among standard works Duchenne's Physiologic 

 des mouvements deserves mention, owing to the positive character 

 of the research and the accuracy of the descriptions, although it 

 does not compare in originality with the epoch-making researches 

 of Borelli and the Webers. After the application of the graphic 

 methods, more particularly by Marey and Carlet (1872), the study 

 of locomotion was carried to greater perfection. Still greater 

 advances were made after instantaneous photography had been 

 applied to the study of the successive phases of movement in man 

 and other animals, first by Muybridge, subsequently by Marey 

 (1882) and his successors with more perfect kinernatographic 

 methods. 



As a preliminary we require a general notion of the structure 

 of the bones, the passive organs, and the action of the muscles, 

 which are the active organs of movement. 



Taken as a whole, the bones may be regarded as rigid organs 

 in comparison with the forces which act on them during the 

 movements of the body. The ribs are an exception to this rule, 

 since (Vol. I. p. 407) they undergo a slight degree of flexion and 

 torsion round their long axis during thoracic inspiration. 



To the student of animal mechanics the histological structure 

 of the bones, which is more particularly of morphological interest, 

 appeals less than their architecture, which is such as to combine 

 the greatest amount of rigidity with the greatest possible lightness, 

 as first pointed out by H. Meyer in 1867. All the long bones 

 are hollow, which does not lessen their rigidity, since a hollow 

 cylinder presents the same resistance to pressure and traction as a 

 solid cylinder of the same 'diameter and identical material. The 

 marrow which fills the bony cavity contributes to the comparatively 

 light weight of bone, since it is rich in fat. The trabeculae which 

 constitute the spongy part of the extremities of the long bones are 

 so arranged as to support the surfaces destined to bear the greatest 

 pressure. 



The application of this mechanical principle is to be found in 

 all bones, but it is specially obvious in the femurs. 



VOL. Ill H 



