204 THE SKELETON. 



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 liga- 

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

 astragalus, and is then known as the os trigonum. 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 (Fig. 141). 



The Cuboid (xu^oc, a cube ; eWo^, 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 



For eft. For fourth 



cuneiform. metatarsal. 



Occasional facet 

 for navicular. 



Groove for 



Peronetis longus. For os calcis. 

 Fur fifth metatarsal. 

 FIG. 141. The left cuboid. A. Antero-internal view. B. Pusteroexternal view. 



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 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 upward and outward, is rough, for the attach- 

 ment of numerous ligaments. The inferior or plantar surface presents in front a 

 deep groove, which runs obliquely from without, forward and inward ; it lodges 

 the tendon of the Peroneus longus, and is bounded behind by a prominent ridge, 

 to which is attached the long calcaneo-cuboid ligament. The ridge terminates 

 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 surface of bone behind the groove is rough, for the 

 attachment of the short plantar ligament, a few fibres of the Flexor brevis hallucis, 

 and a fasciculus from the tendon of the Tibialis posticus. 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, and concavo-convex, for articulation with the 

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

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

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

 larger and more triangular, articulates with the fifth metatarsal. The internal 

 surface is broad, rough, irregularly quadrilateral, presenting at its middle and 

 upper part a smooth oval facet, for articulation with the external cuneiform bone ; 

 and behind this (occasionally) a smaller facet, for articulation with the navic- 

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

 ligaments. 



