Plate 11: The Hip, Knee and Ankle Joints
|March 15, 2012||Filled under All text of Paley Natural Theology, Chapter 8||
Fig. 1. The capsular ligament is here opened in order to show the ligament of the hip, named the round ligament. It allows considerable latitude of motion, at the same time that it is the great safeguard against dislocation.
Fig. 2 and 4. The crucial or internal ligaments of the knee-joint arise from each side of the depression between the condyles of the thigh-bone; the anterior is fixed into the centre, the posterior into the back of the articulation of the tibia. This structure properly limits the motions of the joint, and gives the firmness requisite for violent exertions. Viewing the form of the bones, we should consider it one of the weakest and most superficial, but the strength of its ligaments and the tendons passing over it, render it the most secure, and the least liable to dislocation of any joint in the whole body.
Fig. 3. One of the interarticular cartilages of the knee, from their shape called semilunar; it is also represented in situ, Fig. 2. The outer edge of each cartilage is thick, the inner concave edge thin; the sockets for the condyles of the thigh-bone are thus rendered deeper, and the cartilages are so fixed as to allow a little play on the tibia, by which the joint moves with great freedom.
A moving cartilage is not common, but is peculiar to those joints whose motions are very frequent, or which move under a great weight. It is a contrivance found at the jaw-bone, the inner head of the collar-bone and the articulation of the wrist, as well as at the knee. The obvious use is to lessen friction and facilitate motion.
Fig. 4. a, the fibula; b, the tibia, the lower extremities of which, c, d, form the outer and inner ankle, and receive, e, the great articulating bone of the foot, called the astragalus between them. When the foot sustains the weight of the body the joint is firm, but when raised it easily rolls on the ends of these bones, so that the toe is directed to the place on which we intend to step.