196 



THE SKELETON 



The anterior surface is somewhat quadrilateral in outline with rounded angles, and presents 

 a saddle-shaped articular surface for the cuboid. 



The posterior surface is oval in shape, rough, and convex. It is divided into three parts: — 

 an upper, smooth and separated by a bursa from the tendo Achillis; a middle part giving 

 attachment to the tendo Achillis and the plantaris, and a lower part in relation to the skin and 

 fat of the heel. The expanded posterior extremity of the bone is known as the tuber calcanei. 



Articulations. — ^The calcaneus articulates with two bones, the talus above and the cuboid 

 in front. 



Blood-supply. — The calcaneus is nourished by numerous branches from the posterior tibial 

 and the medial and lateral malleolar arteries. They enter the bone chieflj- on the inferior 

 and medial sm'faces. 



Fig. 233. — The Calcaneus at the Fifteenth Year, showing the Epiphysis. 



Appears at the tenth, and unites at the sixteenth year 



Ossification. — The primary nucleus appears in the sixth month of intra-uterine life. The 

 epiphysis, for its posterior extremity, begins to be ossified in the tenth year and is united to 

 tne body of the bone by the sixteenth year. It may extend over the whole of the posterior 

 surface, as shown in fig. 233, or over the lower two-thirds only, leaving a part above in relation 

 to the bursa beneath the tendo Achillis, which is formed from the primary nucleus. The 

 medial and lateral processes are formed by the epiphysis. 



The Navicular 



The navicular [os naviculare pedis] (figs. 234, 235) is oval in shape, flattened 

 from before backward, and situated between the talus behind and the three 

 cuneiform bones in front. It is characterised by a large oval, concave, articular 



Fig. 234. — The Left Navicular. (Anterior view.) 



For first cuneiform 



Medial border 



Tuberositj 



For second cuneiform 



Lateral border 



For third cuneiform 



facet on the posterior surface, which receives the head of the talus; a broad, rough, 

 rounded eminence on the medial surface, named the tuberosity of the navicular, 

 the lower part of which projects downward and gives insertion to the tendon of 



Fig. 235. — The Left Navicular, showing a Facet for the Cuboid. 



For first cuneiform, 



Tuberosity- 



For second cuneiform 



•For third cuneiform 

 For cuboid 



the tibialis posterior; and an oblong-shaped anterior surface, convex and divided 

 by two vertical ridges into three facets which articulate with the three cuneiform 

 bones. The superior (dorsal) surface is rough, convex, and slopes downward to 



