THE FOOT 245 



be easily recognized by its large rounded head, by the broad articular facet on its 

 upper convex surface, and by the two articular facets separated by a deep groove 

 on its under concave surface. It presents six surfaces for examination. 



The superior surface presents, behind, & broad smooth trochlear surface (trochlea 

 tali) for articulation with the tibia. The trochlea is broader in front than behind, 

 convex from before backward, slightly concave from side to side; in front of it is 

 the upper surface of the neck of the astragalus, rough for the attachment of liga- 

 ments. 



The inferior surface presents two articular facets separated by a deep groove 

 (sulcus tali). The groove runs obliquely forward and outward, becoming gradu- 

 ally broader and deeper in front; it corresponds with a similar groove upon the 

 upper surface of the calcaneus, and forms, when articulated with that bone, a 

 canal (sinus tarsi), filled up in the recent state by the calcaneo-astragaloid liga- 

 ment. Of the two articular facets, the posterior articular facet (fades articularis 

 calcanea posterior] is the larger, of an oblong form and deeply concave from side 

 to side; it rests on the external articular surface of the os calcis; the anterior articular 

 facet is shorter and narrower, of an elongated oval form, convex longitudinally, 

 and often subdivided into two by an elevated ridge; of these, the posterior (fades 

 articularis calcanea media) articulates with the lesser process of the os calcis; 

 the anterior (fades articularis calcanea anterior), with the upper surface of the 

 inferior calcaneoscaphoid ligament. 



The internal surface presents at its upper part a pear-shaped articular facet (fades 

 malleolaris rnedialis) for the inner malleolus, continuous above with the trochlear 

 surface; below the articular surface is a rough depression, for the attachment 

 of the deep portion of the internal lateral ligament. 



The external surface presents a large triangular facet (fades malleolaris lateralis), 

 concave from above downward for articulation with the external malleolus; 

 it is continuous above with the trochlear surface; and in front of it is a rough 

 depression for the attachment of the anterior fasciculus of the external lateral 

 ligament of the ankle-joint. 



The anterior surface (fades articularis navicularis) forms the head of the astrag- 

 alus, is convex and rounded, smooth, of an oval form, and directed obliquely 

 inward and downward; it articulates with the scaphoid. On its under and inner 

 surface is a small facet, continuous in front with the articular surface of the head, 

 and behind with the smaller facet for the os calcis. This rests on the inferior 

 calcaneoscaphoid ligament, being separated from it by the synovial membrane. 

 The head is attached to the rest of the bone by a constricted portion, the neck 

 of the astragalus (collum tali). 



The posterior surface is traversed by a groove (sulcus m. flexoris halluds longi), 

 which runs obliquely downward and inward, and transmits the tendon of the 

 Flexor longus hallucis, external to which is the prominent external tubercle (pro- 

 cessus posterior tali), to which the posterior fasciculus of the external lateral 

 ligament is attached. This tubercle is sometimes separated from the rest of the 

 astragalus, and is then known as the os trigonum. 



To ascertain to which foot the bone belongs, hold it with the broad articular surface upward, 

 and the rounded head forward; the lateral triangular articular surface for the external malleolus 

 will then point to the side to which the bone belongs. 



Articulations. With four bones tibia, fibula, os calcis, and scaphoid. 



The Cuboid (os cuboideum) (Fig. 196). The cuboid is placed on the outer 

 side of the foot, in front of the os calcis, and behind the fourth and fifth meta 

 tarsal bones. It is of a pyramidal shape, its base being directed inward, its apex 

 outward. It may be distinguished from the other tarsal bones by the existence 



