The straight shaft throughout its length is triangular in section. One side of the bone is gently convex; this may be named for convenience the outside. The two parts which make up the other side are inclined, and have the angle in which they meet rounded; one part looks upward and inward, the other downward and inward. Towards the proximal end the bone widens and thickens, and the moiety of the inner side which is away from the heel becomes cleft, and has the sides of the depression rounded to form a large pneumatic foramen. The articular surface looks upward and a little outward on the side of the pneumatic foramen. It consists of two semicircular concave grooves, separated by an intervening low convexity. The outer of these grooves extends from the margin of the extreme proximal point of the heel to the widest point of the bone; the other groove more deeply concave, is a third shorter, extending from inside the pneumatic foramen to the heel. Here both grooves converge, terminating in a point, exterior to which a little distally is a hemispherical mammilate eminence. On the distal side of the eminence there is a depression so as to make the angle behind the heel almost hemispherically rounded. This articulation fits on to the distal articulation of the wing-metacarpal.
When the proximal epiphysis forming the heel comes away, it leaves a large sub-circular pit with a depressed narrow border.
On nearing the distal end, the angle of the inner side of the shaft becomes more depressed; and the articulation becomes an elongated oval, slightly convex transversely and convex in length so as to extend distally in a curve in such way that the articulation looks downward and outward from an aspect of the bone exactly opposite to the aspect from which the proximal articulation looks upward and inward. Hence the two articular surfaces are sub-parallel; but the distal one at its distal termination is bent inward, so as to make the adjacent lateral outline of the bone concave on the inside at its termination. The articulation does not cover the most proximal part of the distal surface.
Case. Comp. Tablet. Specimen. =J= _b_ 7 1-14
On this tablet are mounted 14 specimens. Nos. 1 to 9 are examples of the proximal end of the second phalange. If there were more than two phalanges, of which there is no osteological evidence, it is possible that proximal ends of succeeding phalanges may be included with these. They all however resemble each, other so closely as to lend no support to such a supposition. Nos. ?10 to ?14 have been mounted with the proximal ends because they appear to be portions of the middle of the shaft of the second phalange; they indicate a rapid distal attenuation, favouring the idea of there being but two phalanges.