36 ANATOMY OF THE RAT 



trian^lar 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 sur- 

 faces. 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 inter condyloid 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 (astra- 

 galus) 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 dor- 

 sally, 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 sesa- 

 moid bones in the tarsus. There are five long, cylindrical 

 metatarsal bones in the foot, those of the great toe, or 



