THE BONES OF THE LOWER EXTREMITY 101 



downward and outward slightly. To its outer side is 

 the fibula. 



The tibia presents an upper and lower extremity, 

 and shaft. 



THE UPPER EXTREMITY OR HEAD. This is large 

 and expanded on either side into the internal and 

 external tuberosities. The superior surface of each 

 tuberosity presents a concave articular surface, which 

 receives the condyles of the femur above. The inner 

 facet is oval, the outer circular. Posteriorly the 

 external tuberosity presents a facet for articulation 

 with the head of the fibula. The anterior surfaces of 

 the tuberosities of the tibia are continuous with one 

 another, thus forming a surface which is triangular 

 in shape and at the lower part is the tubercle, which 

 receives the ligamentum patellae. 



THE SHAFT. The shaft of the tibia is long and tri- 

 angular, broad above, gradually decreasing in size 

 to its most slender part the commencement of the 

 lower fourth; it then enlarges again at its lower ex- 

 tremity. It presents internal, external, and posterior 

 surfaces; internal, external, and anterior borders, the 

 anterior border forms the shin, so-called. 



THE LOWER EXTREMITY. This, much smaller than 

 the upper, presents five surfaces anterior, posterior, 

 internal, external, and inferior. The anterior surface 

 is smooth and rounded above, and crossed by the ex- 

 tensor tendons of the toes and tibialis anticus muscle. 

 The external surface is a rough, triangular depression for 

 the attachment of the interosseous membrane above, at 

 its lower part is a smooth hollow surface covered by car- 

 tilage, for articulation with the lower end of the fibula. 

 The inferior surface is quadrilateral and articulates with 

 the upper aspect of the astragalus, one of the tarsal 

 bones; this surface is continuous with the articular 

 surface of the internal malleolus. The internal surface 

 is practically the internal malleolus, a pyramidal process 

 of bone, flattened from without inward. The inner 



