THE TIBIA. 249 



and rounded proxinially, and flat distally. Proximally it is crossed by the 

 linea poplitea (popliteal line), which runs distally and medially, from the fibular 

 facet to the medial border on a level with the junction of the middle with 

 the proximal third of the body. To this line the deep transverse fascia is 

 attached, whilst distal to it, as well as from the medial border of the bone 

 distally, the soleus muscle takes origin. Into the bulk of the triangular area 

 proximal to it the popliteus muscle is inserted. Arising from the middle of the 

 popliteal line there is a vertical ridge, which passes distally and divides the 

 posterior aspect of the body into two surfaces a lateral for the tibial origin of 

 the tibialis posterior muscle, and a medial for the flexor digitorum longus muscle. 

 The distal third of this surface of the body is free from muscular attachments, 

 but is overlain by the tendons of the above muscles, together with that of the flexor 

 hallucis longus. A large nutrient canal, having a distal direction, opens on the 

 posterior surface of the body a little distal to the popliteal line and just lateral 

 to the vertical ridge which springs from it. 



The distal extremity of the tibia displays an expanded quadrangular form. 

 It is furnished with a saddle-shaped articular surface on its distal surface (facies 

 articularis inferior), which is concave from before backwards and slightly convex 

 from side to side. This rests upon the upper articular surface of the body 

 of the talus, and is bounded in front and behind by well-defined borders. The 

 anterior border is the rounder and thicker, and is oftentimes channelled by a 

 groove for the attachment of the anterior ligament of the joint ; further, it is occa- 

 sionally provided with a pressure facet caused by the locking of the bone against 

 the neck of the talus in extreme flexion. Laterally the edge of the articular area 

 corresponds to the base of the triangle formed by the splitting of the interosseous 

 ridge into two parts. Where these two lines join it, both in front and behind, the 

 bone is elevated into the form of tubercles, in the hollow between which (incisura 

 fibularis) the distal end of the fibula is lodged, being held in position by powerful 

 ligaments. The cartilage-covered surface occasionally extends for some little 

 distance proximal to the base of the triangle. Medially there is a process projecting 

 distally, and called the medial malleolus, the medial aspect of which is subcutaneous 

 and forms the projection of the medial ankle. Its lateral surface is furnished 

 with a piriform facet (facies articularis malleolaris), confluent with the cartilage- 

 covered area on the tarsal surface of the distal extremity ; this articulates with a 

 corresponding area on the medial surface of the body of the talus. Distally 

 the malleolus is pointed in front, but notched behind for the attachment of the 

 deltoid or tibial collateral ligament of the ankle. Eunning obliquely along the 

 posterior surface of the malleolus there is a broad groove (sulcus malleolaris) in which 

 the tendons of the tibialis posterior and flexor digitorum longus muscles are 

 lodged ; whilst a little to the fibular side of this, and running distally over 

 the posterior surface of the distal extremity of the bone, there is another groove, 

 often faintly marked, for the lodgment of the tendon of the flexor hallucis longus 

 muscle. 



The proportionate length of the tibia to the body height is as 1 is to 4 < 32-4 > 80. 



Arterial Foramina. Nutrient canals are seen piercing the proximal extremity of the bone 

 around its circumference and proximal to the tuberosity. The floors of the intercondyloid fossae 

 are also similarly pierced, and there is usually a canal of large size opening on the summit of 

 the intercondyloid eminence. Two or three foramina of fair size are seen running proximally 

 into the substance of the bone a little distal to and to the medial side of the tuberosity, while the 

 principal vessel for the body passes distally into the bone on its posterior surface, about the 

 level of the junction of the proximal and middle thirds. The medial surface of the medial 

 malleolus, as well as the anterior and posterior borders of the distal extremity, are likewise 

 pitted by the orifices of small vascular channels. 



Connexions. Proximally the tibia supports the condyles of the femur, and is connected in 

 front with the patella by means of the patellar ligament. Articulating laterally with the fibula 

 proximally and distally, it is united to that bone throughout nearly its entire length by the inter- 

 osseous membrane. The anterior crest and medial surface can be readily examined, as they are 

 subcutaneous, except proximally, where the medial surface is overlain by the thin tendinous 

 aponeuroses of the muscles passing over the medial side of the knee. The form of the distal part 

 of the knee in front is determined by the condyles on either side crossed centrally by the liga- 

 mentum patellae. Distally the medial malleolus forms the projection of the medial ankle, which 

 is wider, not so low, less pointed, and extends further forwards than the projection of the lateral 



