718 MAMMALIAN ANATOMY 



inside. It is scarcely any thicker from before backward than the 

 region of the shaft just above it. 



The internal surface is continuous above with the internal surface 

 of the shaft, and as this side of the bone is continued broadly down 

 beyond the rest of the lower extremity, to form the prominent pro- 

 jection on the inner side of the ankle-joint known as the internal rnal- 

 leolus, the internal surface is much longer than the other surfaces ; it 

 is also narrower than the other surfaces. Its anterior margin is dis- 

 tinct and nearly straight, but it curves a little backward at the lower 

 end ; it represents the lower part of the anterior border of the shaft. 

 The internal margin is faint, inasmuch as the internal border of the 

 shaft fades out before it reaches the end. The lower margin is nearly 

 straight, with rounded anterior and posterior angles ; just in front of 

 the posterior angle, however, is a deep notch which marks the end of 

 a longitudinal groove on the surface. 



The plane of the internal surface forms a decided angle with the 

 plane of the shaft, and faces upward as well as inward. From before 

 backward it is convex, from above downward it is at first slightly 

 concave, but near the inferior margin it becomes convex. At about 

 one-third the distance from the posterior margin it presents a well- 

 marked longitudinal groove, which begins faintly above near the shaft, 

 runs straight down nearly to the lower margin, and here curves for- 

 ward. Its lower part is overhung in front by a flat process whereof 

 the posterior arcuate border is connected with the posterior border of 

 the groove by a strong band of connective tissue to form a canal which 

 transmits the tendon of the tibialis posticus muscle. Behind this 

 groove, and separated from it by a raised line, more marked at the 

 lower part, is a second longitudinal groove, well defined only near 

 its lower end, and producing a decided notch in the lower margin of 

 the surface. This groove also differs from the other groove in being 

 almost straight. Its posterior margin is the posterior margin of the 

 surface. It also is converted by ligament into a canal for the tendon 

 of the flexor longus digitorum muscle. The internal surface is rough- 

 ened and gives attachment to a part of the internal lateral ligament 

 of the ankle-joint. 



The outline of the posterior surface is nearly that of a right- 

 angled triangle, the lower border being the hypothenuse, the base an 

 imaginary transverse line separating it from the posterior surface of 



