THE TARSUS: THE CALCANEUM. 301 



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 bv a broad shallow groove, which is directed obliquely forward 

 and outward, ana 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 (svMentaculum taK) ; 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 ; the 

 depression between the tubercles gives attachment to the Abductor minimi digiti 

 and plantar fascia. 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 : and 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 liga- 

 ment. 



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 

 the external calcaneo-astragaloid ligament ; and in front of the tubercle it presents 

 a narrow surface marked by two oblique grooves, separated by an elevated ridge 

 which varies much in size in different bones ; it is named the peroneal ridge, and 

 gives attachment to a fibrous process from the external annular ligament. The 

 xuf'/rior ciro'jct- transmits the tendon of the Peroneus brevis ; the inferior, the 

 tendon of the Peroneus longus. 



The internal surface presents a deep concavity, directed obliquely downward 

 and forward, for the transmission of the plantar vessels and nerves into the sole 

 of the foot ; it affords attachment to part of the Flexor accessorius muscle. This 

 surface presents an eminence of bone, the lesser process or sustentaculum tali, 

 which projects horizontally inward from its upper and fore part, and to which a 

 slip of the tendon of the Tibialis posticus is attached. This process is concave 

 above, and supports the anterior articular surface of the astragalus ; below, it is 

 grooved for the tendon of the Flexor longus hallucis. Its free margin is rough, 

 for the attachment of part of the internal lateral ligament of the ankle-joint. 



The anterior surface, of a somewhat triangular form, articulates with the 

 cuboid. It is concave from above downward and outward, and convex in the 

 opposite direction. Its inner border gives attachment to the inferior calcaneo- 

 navicular ligament. 



The posterior surface is rough, prominent, convex, and wider below than above. 

 Its lower part is rough, for the attachment of the tendo Achillis and of the Plan- 

 taris muscle : its upper part is smooth, and is covered by a bursa which separates 

 the tendon from the bone. 



Articulations. With two bones : the astragalus and cuboid. 



