THE FOOT. 283 



about three eiglitlis of an inch, from the posterior angles 

 of the articulatory surfaces. The point where the ridges 

 bend backwards form posteriorly smooth grooves, through 

 which the plantar arteries run downwards in their course 

 between the inferior broad ligament of the navicular bone 

 and the perforaus tendon to the foramen on the infero- 

 posterior surface of os pedis. 



The postero-inferior surface of the bone is mainly occu- 

 pied by the plantar surface, semilunar in form, bounded 

 by two margins, which meet posteriorly at acute angles. 

 Thus this surface is broadest centrally, and gradually 

 decreases in size posteriorly. It presents a slant from the 

 greater or outer to the lesser or inner curved margin, and 

 is perforated by foramina, which are most numerous at 

 the angles and at the outer circumferent margin ; and at 

 the line of junction of this with the antero-lateral surface 

 is a series of openings larger than the rest. Extending 

 backwards from the posterior margin is a roughened space, 

 bounded posteriorly by the articulatory surface for os 

 naviculare, which on either side extends slightly on to this 

 face of the bone. This roughened space is divided on 

 either side into two parts by a groove extending from 

 behind forwards, to terminate in a foramen. Through 

 this the terminal portion of the plantar artery runs, and 

 thus gains a canal extending through the substance of the 

 hone from one foramen to the other, in which it anasto- 

 moses with its fellow, completing the circulus anteriosus 

 of the foot. The walls of the grooves, as well as those 

 of the canal, are perforated by foramina, through which 

 branches pass outwards. The space between these grooves 

 and the navicular articulatory surface is roughened for 

 attachment of the inferior broad navicular ligament ; it 

 is perforated by articular foramina. That space between 

 the grooves and the posterior margin of the plantar sur- 

 face is about three eighths of an inch broad in the centre, 

 and is rough for attachment of the extensor pedis tendon. 

 The antero-lateral surface is largest centrally, and gra- 

 dually diminishes in size posteriorly. At its superior part 

 it presents a smoother portion of bone than the rest, of a 

 pyramidal shape, having its apex superiorly placed. This 

 is the coronal process ; around its superior part, at about 

 a quarter of an inch from its superior margin, runs a line 

 marking out the inferior attachment of extensor pedis, 



