THE TARSUS: THE CALCANEUM. 199 



Fractures of the tibia alone are almost always the result of direct violence, except where the 

 uiallcolus is broken off' by twists of the foot. Fractures of the fibula alone may arise from 

 indirect or direct force, those of the lower end being usually the result of the former, and those 

 higher up being caused by a direct blow on the part. 



The tibia and fibula, like the femur, are frequently the seat of acute necrosis. Chronic 

 abscess is more frequently met with in the cancellous tissue of the head and lower end of the 

 tibia than in any other bone of the body. The abscess is of small size, very chronic, and prob- 

 ably the result of tuberculous osteitis in the highly vascular growing tissue at the end of the 

 shaft near the epiphyseal cartilage in the young subject. 



The tibia is the bone which is most frequently and most extensively distorted in rickets. It 

 gives way at the junction of the middle and lower third, its weakest part, and presents a curve 

 forward and outward. 



THE FOOT (Figs. 137, 138). 



The skeleton of the Foot consists of three divisions : the Tarsus, Metatarsus, 

 and Phalanges. 



The Tarsus. 



The bones of the Tarsus are seven in number : viz., the calcaneuin or os calcis, 

 astragalus, cuboid, navicular, internal, middle, and external cuneiform bones. 



The Calcaneum (Fig. 139). 



The Calcaneum, or Os Calcis (calx, the heel), is the largest and strongest of the 

 tarsal bones. It is irregularly cuboidal in form, having its long axis directed 

 forward and outward. It is situated at the lower and back part of the foot, 

 serving to transmit the weight of the body to the ground, and forming a strong 

 lever for the muscles of the calf. It presents for examination six surfaces : 

 superior, inferior, external, internal, anterior, and posterior. 



The superior surface is formed behind by the upper aspect of that part of the 

 os calcis which projects backward to form the heel. It varies in length in differ- 

 ent individuals; is convex from side to side, concave from before backward, and 

 corresponds above to a mass of adipose substance placed in front of the tendo 

 Achillis. In the middle of the superior surface are two (sometimes three) articular 

 facets, separated by a broad shallow groove, which, is directed obliquely forward 

 and outward, and is rough for the attachment of the interosseous ligament 

 connecting the astragalus and os calcis. Of the two articular surfaces, the external 

 is the larger, and situated on the body of the bone : it is of an oblong form, wider 

 behind than in front, and convex from before backward. The internal articular 

 surface is supported on a projecting process of bone, called the lesser process of 

 the calcaneum (sustentaeulum tali] ; it is also oblong, concave longitudinally, and 

 sometimes subdivided into two parts, which differ in size and shape. More 

 anteriorly is seen the upper surface of the greater process, marked by a rough 

 depression for the attachment of numerous ligaments, and a tubercle for the origin 

 of the Extensor brevis digitorum muscle. 



The inferior surface is narrow, rough, uneven, wider behind than in front 

 and convex from side to side ; it is bounded posteriorly by two tubercles separated 

 by a rough depression ; the external, small, prominent, and rounded, gives attach- 

 ment to part of the Abductor minimi digiti : the internal, broader and larger, for 

 the support of the heel, gives attachment, by its prominent inner margin, to the 

 Abductor hallucis, and in front to the Flexor brevis digitorum muscles and plantar 

 fascia; the depression between the tubercles gives attachment to the Abductor 

 minimi digiti. The rough surface in front of the tubercles gives attachment to the 

 long plantar ligament and to the outer head of the Flexor accessorius muscle ; 

 while to a prominent tubercle nearer the anterior part of this surface, as well as 

 to a transverse groove in front of it, is attached the short plantar ligament. 



The external surface is broad, flat, and almost subcutaneous ; it presents near 

 its centre a tubercle, for the attachment of the middle fasciculus of the external 

 lateral ligament. At its upper and anterior part this surface gives attachment to 



