426 



HUMAN ANATOMY. 



Its identity is quite evident in cases in wliich, though fused, it projects as a hook. 

 It may be represented by the sesamoid bone in the tendon of the tibiahs posticus. 

 Near the outer end of the plantar surface there is almost always a slight projection 

 by the side of the cuboid which may be very much developed, extending to near 

 the notch in front of the sustentaculum of the calcaneum, in which case it is known as 

 the secondary cuboid. The external surface is narrow and rough, resting against 

 the cuboid, with which it articulates in about half the cases by a facet near the dor- 

 sum, which rarely extends far towards the sole.^ The posterior surface is con- 

 cave, in the main oval and completely articular. Usually the regularity of the 

 lower border is interrupted near the outer part by the external knob of the plantar 

 surface. If this be much developed the shape of the posterior surface is changed 

 from oval into quadrilateral, but it is always articular throughout. The anterior 

 surface is slightly convex and entirely articular, except when the process just men- 

 tioned is so large as to appear below it. The articular surface is divided into three 



Fig. 439. 



Fig. 440. 



Dorsal surface 



Dorsal surface 



Tuber- 

 osity 



For head of astragalus 

 Right scaphoid from behind, proximal aspect. 



External 

 cuneiform 



Middle 

 cuneiform 



Internal Tuberosity 

 cuneiform 



Right scaphoid from in front. 



facets, in the main triangular, corresponding to the outline of the bases of the three 

 cuneiform bones. The character of these facets is not constant : the inner is usually 

 convex and the outer concave. 



The scaphoid articulates with the astragalus, the three cuneiform bones, often 

 with the cuboid, and exceptionally it touches or joins the calcaneum. The secondary 

 cuboid, above al-luded to, has but once been seen isolated, although we have met with 

 one foot in which it seemed possible that it might have been distinct earlier. It is 

 fused with either the cuboid or the scaphoid, but apparently much more frequently 

 with the latter, in which it occupies the position above described, lying at the weak 

 part of the inferior calcaneo-scaphoid ligament. 



Development. — It is generally held that ossification begins in the fourth or 

 fifth year, but, according to Gegenbaur, it begins in the first. The tibiale externum 

 exists as a separate cartilage at the second month of foetal life. Usually this fuses 

 with the rest, but it may have a centre of its own. 



THE THREE CUNEIFORM BONES. 



These wedge-shaped bones, placed between the scaphoid and the three inner 

 metatarsals, and abutting externally on the cuboid, form an important part of the 

 transverse arch of the foot. The thin edge of the internal cuneiform, which is much 

 the largest, points up, that of the others down. The middle cuneiform is the smallest 

 and shortest, so that the second metatarsal bone lies in a mortise between the inner 

 and outer. 



THE INTERNAL CUNEIFORM. 

 The internal cuneiform,^ besides the proximal and distal surfaces, has aa internal, 

 an external, and an inferior. The posterior, or proximal surface, rounded below 

 and pointed above, is slightly concave and wholly articular. The anterior, or distal, 

 surface, also articular, is kidney-shaped, with the notch in the outer border. The 

 inner surface has a small ridge in its distal half, pointing upward, which is the 



'Pfitzner: Morph. Arbeiten, Bd. vi., 1896. 



^Os cuncifi)rme primi'm. 



