The Posterior Limb Skeleton. 



107 



THE TIBIA AND FIBULA. 



The tibia (Fig. 42) is the larger of the two bones of the leg, lying on 

 the medial side of the fibula, and fused with the latter for more than one- 

 half of its length. Its proximal extremity is triangular in section, the 

 main surfaces being respectively anterolateral, anteroniedial, and pos- 

 terior. The anterior border is formed by a stout ridge-like elevation, 

 the tuberosity of the tibia (tuberositas tibiae), which in the natural con- 

 dition serves for the insertion of the quadriceps femoris, the extensor 

 tendon being carried over the knee by the 

 patella and the patellar ligament. The arti- 

 cular portion is slightly differentiated into 

 medial and lateral condyles corresponding to 

 those of the distal end of the femur. On 

 the articular surface the concave areas for 

 the reception of the condyles of the femur 

 are separated from one another by a small 

 intervening, partly divided hillock, the inter- 

 condyloid eminence (eminentia intercondv- 

 loidea), and also posteriorly by a depression 

 of the articular border, the posterior inter- 

 condyloid fossa. A corresponding anterior 

 intercondyloid fossa lies in front of the inter- 

 condyloid eminence, but is poorly differ- 

 entiated. 



The fibula (Fig. 42) is the smaller, lateral 

 bone of the leg, and in the rabbit is so 

 extensively fused with the tibia that scarcely 

 more than a third of it is distinguishable. 

 The free portion forms a flattened bonv splint, 

 the medial margin of which is firmly united 

 with the tibia by the interosseous ligament of 

 the leg. Its pro.ximal extremity is connected 

 with the lateral condyle of the tibia by an 

 elongated epiphysis, the latter, like those of the 

 distal ends of the radius and ulna, being 

 distinguishable even in older animals. 



The combined distal extremities of the tibia 

 and fibula bear a roughly rectangular articular 

 surface for the tarsus. The tibial portion of 

 this surface presents two grooves, separated 

 by a ridge, for articulation with the trochlea 

 tali. On its medial side is a small projection, 

 the medial malleolus (malleolus medialis). 

 The fibular portion presents a trans- 

 verse groove for the convex articular surface of the calcaneus. Imme- 

 diately above it, on the lateral side of the bone, is a prominent projec- 

 tion, the lateral malleolus (malleolus lateralis). It forms the anterior 

 boundary of a groove which in the natural condition lodges the inser- 

 tion tendons of the peroneal muscles. 



mm 



Fig. 42. Anterior surface of the 

 left tibia (T) and fibula (F): 

 c.l. and cm., lateral and medial 

 condyles; f.a.s., proximal articular 

 surface for the femur; m.l. and 

 m.m., lateral and medial malleoli; 

 t.t., tuberosity of tibia. 



