

THE CALCANEUS. 

 The Calcaneus, 



259 



The calcaneus is the largest of the tarsal bones. It supports the talus on its 

 dorsal surface and articulates with the cuboid anteriorly. On the plantar aspect and 

 behind, its posterior extremity, or tuberosity (tuber calcanei), forms the heel, on 

 which so large a proportion of the body weight rests. The long axis of the bone 

 inclines forwards and a little laterally and upwards. 



The dorsal surface of the calcaneus is divisible into two parts a posterior non- 

 articular part and an anterior articular portion. The length of the former varies 

 according to the projection of the heel ; rounded from side to side, it is slightly con- 

 cave from before backwards. In front of this there is a convex articular area of 

 variable shape (facies articularis posterior), sometimes nearly circular, at other times 

 oval and occasionally almost triangular. This is directed upwards and forwards, 

 and articulates with the posterior calcanean facet on the plantar surface of the 

 talus. Anterior to this facet the bone is deeply excavated, forming a fossa from 



FOB CUBOID 



FOE CUBOID 



Surface for 

 attachment 



Ian tar 

 calcaneo- 

 cuboid 

 ligament 



/ofp: 



S o.alci 



SUSTENTA- 



CULUM 



TALI 



GROOVE FOR 



FLEXOR 



HALLUCIS 



LONOUS 



Surface for 

 attachment 

 of long 

 plantar liga- 

 ment 



MEDIAL 

 PROCESS 



FIG. 259. THE RIGHT CALCANEUS. 



TUBEROSITY 

 B 

 A. Seen from above ; B. Seen from below. 



which a groove (sulcus calcanei) leads backwards and medially around the antero- 

 medial border of the articular surface. When the calcaneus is placed in contact 

 with the talus, this groove coincides with the sulcus on the plantar surface of 

 the talus, and so forms a canal or tunnel (sinus tarsi) in which the strong 

 interosseous ligament which unites the two bones is lodged. To the front and 

 medial side of this groove there is an elongated articular facet directed obliquely 

 from behind forwards and laterally, and concave in the direction of its long axis. 

 This is frequently divided into two smaller oval areas by an intermediate non- 

 articular surface. Of these facets the posterior (facies articularis media) articulates 

 with the middle calcanean facet on the plantar surface of the talus, whilst the 

 anterior (facies articularis anterior) supports the plantar surface of the head of the 

 talus (facies articularis calcanei anterior). The lateral side of the anterior extremity 

 of the dorsal surface of the bone is rough, and to this is attached the origin of 

 the short extensor muscle of the toes. 



The plantar surface of the bone is slightly concave from before backwards, and 

 convex from side to side. The plantar aspect of the tuberosity is provided with two 

 tubercles, a medial (processus medialis tuberis calcanei) and a lateral (processus laterahs 

 tuberis calcanei), of which the former is the larger. From the medial process the short 

 flexor of the toes and the abductor hallucis muscle arise, whilst from both tubercles 



