Animal Mechanics Author:Charles Bell Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: III. THIGH The lower portion of the thigh has only a thin shell, but here its diameter is largest and filled with the cancellated structure, which especially ... more »in the lateral portions has a very definite arrangement ; the cancelli forming a series of pillars, which ascend very nearly vertically from the surfaces of the condyle to the walls of the bone above them, which are bent inwards as the bone diminishes its diameter towards the middle of the shaft. A corresponding arrangement exists in the two extremities of the tibia, where the surface which is the seat of pressure is sustained by columns of bony fibres extending to the walls above or below it, according as the upper or lower portion of the bone is examined. This structure has been distinctly figured and described by Bour- gery and Jacob.1 The cancelli are, as in the parts before described, prevented from lateral flexion by braces which are interposed at right angles to their direction. IV. ASTRAGALUS The tibia alone bearing vertically on the astragalus, this last bone will necessarily sustain in each foot one half the weight of the body, or the whole of it when it is supported on one foot. 1 Op. cit., Tome I. pp. 119 and 121, also PI. 43, Figs. 3,4, and 7.When the small size of the surface on which the tibia rests is borne in mind, it will be readily anticipated that in its internal structure it will give us another illustration of mechanical adaptation. The astragalus, though it receive so many shocks in the violent movements of the body and is called upon to resist so much vertical force, is nevertheless a light bone and presents areolae in its interior of large size. The astragalus rests below on the os calcis, by means of two articulating surfaces of different sizes, and in front on the scaphoid bone, so that wha...« less