712 MAMMALIAN ANATOMY 



The anterior surface (Fig. 545) which connects the two tuberosities 

 is the downward prolongation of the superior surface. That portion 

 which is seen when the bone is viewed directly from the front is nearly 

 square ; it is bounded above by the general proximal or superior sur- 

 face, on the sides by the narrow parts of the internal and external 

 surfaces, and below by the upper transverse margin of the tubercle. 

 It is roughened, and faces upward and forward. 



The posterior surface (Fig. 546) is merely the roughened posterior 

 border of the superior surface. It overhangs the posterior surface of 

 the shaft, and is deeply depressed in the middle by the popliteal notch, 

 in which the tibial end of the posterior crucial ligament is fastened. 



The Shaft is nearly straight, with a curve so faintly sinuous that 

 the upper end is directed slightly outward and the lower end slightly 

 inward. It is also somewhat twisted on its long axis ; the front part, 

 therefore, faces also slightly outward above and below. The shaft has 

 three borders, the anterior, the external, and the internal, which limit 

 three surfaces, the external, the internal, and the posterior. These are 

 all clearly marked above, but they are apt to be indefinite below, where 

 the bone becomes more nearly round. 



The anterior border (Fig. 545) is distinct down to the middle, 

 beyond which it may become obscure. It is subcutaneous, and is called 

 the crest of the tibia, or the shin. At its upper end is a flattened 

 rectangular space which is about twice as wide as long and faces 

 upward and forward. It receives the insertion of the ligamentum 

 patellae, and is called the tubercle of the tibia. The beginning of 

 the crest is as wide as the tubercle itself, but it rapidly narrows to a 

 sharp border. Its upper part lies on the outer side of the long axis 

 of the bone, but at the junction of the upper and middle thirds it 

 comes directly to the front, and at the lower third is seen midway 

 between the real anterior line and the internal border. The anterior 

 border affords attachment for almost its entire length to the aponeurotic 

 termination of the biceps femoris. In its upper fourth it limits the 

 anterior margin of the area of origin of the tibialis anticus muscle. 



The external border (Fig. 544) is always well defined, inasmuch 

 as it is the line of attachment of the strong interosseous membrane 

 which unites the tibia with the fibula, and gives additional area of 

 origin to the anterior and posterior muscles of the leg. It begins at 

 the posterior angle of the outer tuberosity, just behind the articular 



