LOCOMOTION. [CHAP. YI. 



wards, and well suited by its rigidity to oppose bending ; but on its 

 upper surface the compact tissue is thin, and the reticular texture 

 consists of somewhat arched fibres freely interwoven, running parallel 

 to that surface, and disposed so as to present a surface to resist the 

 direct influence of pressure (fig. 18, p. 102). The direction of the 

 fibres of the reticular texture of the inferior part of the neck is 

 chiefly downwards to the trochanter minor, and it seems to establish 

 a communication between the osseous tissue of the head of the bone, 

 and the dense structure which forms the lower part of the neck. 



The lower extremity of the femur is almost entirely composed of 

 cancellated texture, and affords a broad surface for articulation with 

 the head of the tibia to form the knee-joint. As the tibia is placed 

 vertically under it, it not only transfers the weight from above to 

 that bone, but it is particularly exposed to suffer from concussions 

 conveyed upwards by the tibia. Its structure seems disposed so as 

 to facilitate the dispersion of such concussions, the sides of the 

 condyles projecting considerably beyond the surface of the shaft of 

 the bone, and there being but little continuity of tissue between it 

 and the lower end of the bone. 



Of the bones of the leg, the tibia, from its strength and size, is 

 evidently that which is destined to support the thigh ; the fibula 

 must be regarded as entirely accessory in its office, affording at- 

 tachment to the interosseous ligament, and forming a greater ex- 

 tent of surface for the origin of muscles. By its lower extremity it 

 supports the ankle-joint on the outside. 



The tibia rests upon the astragalus, and through that bone trans- 

 mits the weight to the foot. The length of this organ, its breadth, 

 and its arched form, adapt it as a basis of support for the body in 

 the erect posture, and as an instrument of locomotion. It obtains 

 elasticity, and a certain amount of mobility, from its being composed 

 of several small and light bones articulated together. These bones, 

 although almost entirely composed of reticular texture, possess con- 

 siderable power of resistance to direct pressure in those directions 

 in which the strain would chiefly bear in the movements of the 

 organ, and this is to be attributed to the direction of the fibres 

 their cancellous tissue. The principal elasticity of the foot is lon- 

 gitudinal, by reason of its arch being in that direction, resting upoi 

 the heel behind, and on the toes in front ; but it also yields som< 

 what in the transverse direction, or that of the arch formed by tl 

 cuneiform bones. The extension of the os calcis backwards m 

 only adds to the length of the longitudinal arch, but it also afford: 

 a considerable leverage to the muscles of the calf of the leg. 



