Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/50

36 triangular proximal to this point. Thus the bone presents three surfaces: a concave anterolateral surface, a convex anteromedial surface, and a posterior surface with two pronounced longitudinal grooves. A ridge, the anterior crest, is located proximally on the anterior side of the bone at the angle formed by the lateral and medial surfaces. The bone articulates with the femur proximally. The articular surface is divided into two large concave condyles, separated from each other by a longitudinal groove, the intercondyloid fossa. Each of these is opposed to the convex surface of one of the femoral condyles. The tibia and fibula articulate distally with the talus (astragalus) bone of the heel. The tibial part of the articular surface contains two longitudinal grooves, separated by a ridge. The medial malleolus forms the medial boundary of the inner groove. The fibula bears the lateral malleolus upon its lateral surface. The slender fibula expands dorsally, where it is attached by a ligament to the external condyle of the tibia.

The patella is a sesamoid bone lying in front of the knee joint.

The tarsus, or ankle, contains eight bones arranged in two rows, one distal and one proximal, with one bone between the rows. The proximal row contains the talus and calcaneus. The talus articulates with the tibia and fibula. The calcaneus, or heel bone, is shovel-shaped and is the largest bone in the tarsus. The "handle," or heel process, is directed posteriorly, forming the support for the heel. When the toes are depressed the trochlea of the talus acts as a fulcrum, the heel process as a lever moved by the posterior leg muscles. The length of the heel process makes it a relatively efficient lever. There are also four sesamoid bones in the tarsus. There are five long, cylindrical metatarsal bones in the foot, those of the great toe, or