x THE ENGINES OF THE HUMAN BODY 



FIG. 



14. The bones forming the arch of the foot, seen from the inner 

 side 





10. The skull as a lever of the first order . .... 50 



ir. (A) The opening in the base of the skull, by which the brain 

 stem passes to the spinal canal ; (B) The parts of the socket 

 on the ring of the atlas 53 



12. (A). The original parts of the first or atlas vertebra ; (B) Show- 



ing the "body" of the first vertebra fixed to the second, thus 

 forming the pivot on which the head turns . . . -55 



13. Showing a chisel used as a lever of the second order . 58 



50 



15. Showing the crank-pin of an engine at : (A) First dead centre ; 



(B) First maximum leverage ; (C) Second dead centre ; 

 (D) Second maximum leverage 61 



16. The arch of the foot from the inner side, showing some of the 



muscles which maintain it 63 



17A. A chisel used as a lever of the third order. (W) Weight ; 



(P) Power ; (F) Fulcrum 65 



1 7B. The forearm and hand as a lever of the third order ... 66 



18. Showing the action of the brachialis anticus in the arm of an 



anthropoid ape 67 



19. In this figure the following sections of the thigh-bone at various 



stages of growth are shown : — Section of the thigh-bone at 

 birth to show its structure. Its lower end enlarged to show 

 the centre of ossification and trail of blood-vessels. Section 

 at the fifth year. Section at the fifteenth year. Section at 

 the twenty-fifth year 71 



20. An X-ray picture to show the design or construction of the 



upper end of the thigh-bone 76 



21. The construction of the upper end of the thigh-bone, as de- 



picted by Professor F. Dixon, compared with a drawing of 

 Fairbairn's crane (W. Finerty) yy 



22. (A) The upper end of a thigh-bone at the fifth year, above 



which is indicated the position which the head and neck will 

 occupy when the fifteenth year is reached ; (B) The form 

 which the upper end of the femur would assume if there was 

 no remodelling 78 



23. A vertical section of the ankle-joint, exposing the lower end of 



the tibia and astragalus 83 



