THE FOOT. 285 



extremity. Posteriorly tliis surface terminates in a point 

 at about one and a half inches from the ala of os pedis, for 

 here the cartilage is inflected in a forward direction, form- 

 ing that portion of the cartilage which, running along the 

 inner surface of the wing of os pedis, gradually terminates 

 in blending with the white fibrous tissue joining the ex- 

 panded perforans tendon. Inwardly it is continued as a, 

 firm but fine layer of fibrous tissue, which serves to separate 

 the fibrous frog from the tendon. The inferior margin of 

 the cartilage in becoming attached to the bone helps to 

 form the foramen through which the lateral laminal artery 

 passes, and posteriorly, on its under surface, presents a 

 triangular continuation of the plantar surface of the bone 

 which affords attachment to the sensitive bars.^ The m- 

 ternal surface, as a whole, is concave, and looks in a direc- 

 tion inwards and slightly upwards. Its inferior part is 

 formed by the upper surface of the inflections of the carti- 

 lages, which here are closely united to the fibrous frog^ 

 many of the elastic fibres of which become attached to it. 

 This organ is separated from the main portion of _ thia 

 surface by a plexus of veins, which communicates with a 

 corresponding plexus on the external surface, not only by 

 branches proceeding ^through numerous foramina in the 

 cartilage, but also by junction of their resulting vessels 

 above the cartilage. The superior margin of the cartilage 

 is about its thinnest part ; the thickest is that just 

 behind os pedis. In contact with the plexus of vessels on 

 the external surface, centrally, hes the coronary secreting 

 substance, superiorly skin, interiorly the upper portions of 

 the lateral laminae, which are supplied by a special branch 

 detached from the lateral laminal artery running back- 



wards. 



OS NAVICTJLARE (SHUTTLE BONE) is a sesamoid 



bone situated behind and slightly resting upon os pedis. 

 It is elongated from side to side, and presents two sur- 

 faces, two margins, and two extremities. The superior 

 margin looks upwards and backwards ; it is straight, and 

 presents some articular foramina. To it is attached the 

 superior broad navicular ligament, which runs obliquely 

 upwards and backwards to blend with \he perforans tQi\d.on, 

 and with the superior band of the stellate ligament. At its 

 posterior edge a continuation of the posterior smooth sur- 

 face of the bone is visible. Thi^ posterior surface is covered 



