THE TARSUS: THE ASTRAGALUS, THE CUBOID. 303 



Achillis, Plantaris, Abductor hallucis, Abductor minimi digiti, Flexor brevis digi- 

 torum, Flexor accessorius, and Extensor brevis digitorum. 



The Astragalus. 



The Astragalus (d0rpdyaJio<;, a die) is the largest of the tarsal bones, next to 

 the os calcis. It occupies the middle and upper part of the tarsus, supporting the 

 tibia above, articulating with the malleoli on either side, resting below upon the 

 os calcis, and joined in front to the navicular. This bone may easily be recognized 

 by its large rounded head, by the broad articular facet on its upper convex surface, 

 or 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, a broad smooth trochlear surface 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 ligaments. 

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

 The groove runs obliquely forward and outward, becoming gradually broader 

 and deeper in front : it corresponds with a similar groove upon the upper surface 

 of the os calcis, and forms, when articulated with that bone, a canal, fille'd up in 

 the recent state by the interosseous calcaneo-astragaloid ligament. Of the two 

 articular facets, the posterior is the larger, of an oblong form and deeply concave 

 from side to side ; the anterior, although nearly of equal length, is narrower, of an 

 elongated oval form, convex longitudinally, and often subdivided into two by an 

 elevated ridge ; of these, the posterior articulates with the lesser process of the os 

 calcis ; the anterior, with the upper surface of the inferior calcaneo-navicular liga- 

 ment. The internal surface presents at its upper part a pear-shaped articular facet 

 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, 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, convex and rounded, forms 

 the head of the astragalus ; it is smooth, of an oval form, and directed obliquely 

 inward and downward; it articulates with the navicular. On its under 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 calcaneo- 

 navicular ligament, being separated from it by the synovial membrane, which is 

 prolonged from the anterior calcaneo-astragaloid joint to the astragalo-navicular 

 joint. The head is surrounded by a constricted portion, the neck of the astragalus. 

 The posterior surface is narrow, and traversed by a groove, which runs obliquely 

 downward and inward, and transmits the tendon of the Flexor longus hallucis, 

 external to which is a prominent tubercle, to which the posterior fasciculus of the 

 external lateral ligament is attached. To the inner side of the groove is a second, 

 but less marked tubercle. 



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 navicular. 



The Cuboid. 



The Cuboid (xyySoc, a cube ; doo^. like) bone is placed on the outer side of 

 the foot, in front of the os calcis, and behind the fourth and fifth metatarsal bones. 

 It is of a pyramidal shape, its base being directed upward and inward, its apex 

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



