ASTRAGALUS. 253 



outwards. It may be distinguished from the other tarsal bones by the exist- 

 ence of a deep groove on its under surface, for the tendon of the Peroneus 

 Longus muscle. It presents for examination six surfaces : three articular, and 

 three non-articular. 



The non-articular surfaces are the superior, inferior, and external. The 

 superior or dorsal surface, directed upwards and outwards, is rough, for the 

 attachment of numerous ligaments. The inferior or plantar surface presents in 

 front a deep groove, which runs obliquely from without, forwards and inwards; 

 it lodges the tendon of the Peroneus Longus, and is bounded behind by a 

 prominent ridge, terminating externally in an eminence, the tuberosity of the 

 cuboid, the surface of which presents a convex facet, for articulation with the 

 sesamoid bone of the tendon contained in the groove. The ridge and surface 

 of bone behind it are rough, for the attachment of the long .and short plantar 

 ligaments. A few fibres of the Flexor Brevis Pollicis may be traced to this 

 surface. The external surface, the smallest and narrowest of the three, presents 

 a deep notch formed by the commencement of the peroneal groove. 



The articular surfaces are the posterior, anterior, and internal. The posterior 

 surface is smooth, triangular, concavo-convex, for articulation with the anterior 

 surface of the os calcis. The anterior, of smaller size, but also irregularly 

 triangular, is divided by a vertical ridge into two facets: the inner facet, 

 quadrilateral in form, articulates with the fourth metatarsal bone; the outer 

 one, larger and more triangular, articulates with the fifth metatarsal. Tne 

 internal surface is broad, rough, irregularly quadrilateral, presenting at its mid- 

 dle and upper part a small oval facet, for articulation with the external cunei- 

 form bone ; and behind this (occasionally) a smaller facet, for articulation with 

 the scaphoid ; it is rough in the rest of its extent, for the attachment of strong 

 interosseous ligaments. 



To ascertain to which foot it belongs, hold the bone so that its under surface, 

 marked by the peroneal groove, looks downwards, and the large concavo- 

 convex articular surface backwards, towards the holder: the narrow, non- 

 articular surface, marked by the commencement of the peroneal groove, will 

 point to the side to which the bone belongs. 



Articulations. "With four bones : the os calcis, external cuneiform, and the 

 fourth and fifth metatarsal bones, occasionally with the scaphoid. 



Attachment of Muscles. Part of the Flexor Brevis Pollicis. 



THE ASTRAGALUS. 



The Astragalus (Fig. 180) 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 scaphoid. 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, con- 

 vex from before backwards, 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 forwards and outwards, 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, filled up in the recent state by the calcaneo-astragaloid inter- 

 osseous 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 longi- 



