THE PHALANGES. 317 



little way onto the dorsum, but bends strongly forward, ending in two lateral pro- 

 longations with a notch between them, on each of which a sesamoid bone plays. 

 The outer of these is the more prominent. The yiidrieyit foramen runs towards the 

 distal end. 



The second metacarpal has a base which is triangular when seen from the 

 end, and forked to straddle the point of the trapezoid. On the outer side is a small 

 square facet near the dorsum for the trapezium ; on the inner side there is a narrow 

 oblique surface for the os magnum, and in front of it one showing a tendency to 

 subdivide, articulating with the next bone. 



The third metacarpal has an oblong proximal surface, broadest on the dor- 

 sum, where a tubercle, the styloid process, projects towards the trapezoid. We have 

 found the third metacarpal touching this bone in forty per cent, of 100 specimens, 

 and sometimes this occurred when the styloid process was not particularly developed. 

 Externally there is a facet like the lower part of the inner one of the second, and 

 internally a double one to meet the next. 



The fourth metacarpal has a nearly square upper surface articulating with 

 the unciform, and therefore of uncertain nature, — sometimes convex, sometimes 

 concave. At the outer dorsal angle of this surface is a small distinct facet for a joint 

 with the OS magnum. On the outer side are two facets for the third, and on the 

 inner a long one, concave from dorsum to palm, for the fifth. 



The fifth metacarpal has a base generally broader than deep, concave from 

 side to side and convex from abo\'e downward. A single facet on the outer side 

 has a convexity to meet the concavity on the fourth. The inner side has, of course, 

 no facet, but a tubercle. The dorsal ridge on this bone is twisted, starting from the 

 inner side. 



Development. — Each bone has two centres, a primary one for the shaft, 

 appearing early in the third month of foetal life, and one for an end, appearing in the 

 third year. The secondary centre is for the distal end in the four inner metacarpals 

 and in the proximal of the first,— that is, at the end towards which the nutrient 

 artery does not run. They fuse at about eighteen. Rarely smaller epiphyses 

 appear at the other ends also, as in mammals generally. A centre for the styloid 

 process of the third is sometimes seen, and it may become distinct, as an extra carpal 

 bone, or it may fuse with one of the adjoining ones. 



THE PHALANGES. 



Features of Each Bone. — The phalanges ' of the first and second row differ 

 (except in size) only in the proximal ends. The dorsum of the shaft is rounded 

 from side to side ; xhe palmar surface is flat with raised edges for the sheaths which 

 bind down the tendons very closely. It is considerably overhung by the distal and 

 somewhat by the proximal end. The nutrient foramen, when present, runs distally. 



Th.e proximal end oi th.ef rst row is a concave articular surface, broadest trans- 

 versely. A groove runs round the end, except on the palmar surface, for the cap- 

 sule and for fibres from the extensor tendons of the fingers on the dorsum. Two 

 very slight inequalities in front mark the attachment of the glenoid ligament. There 

 is a rough tubercle on each side, just below the groove for the partial insertion of 

 the interosseous muscles. The distal end in both the first and second rows has an 

 articular surface which curves over two condylar prominences, separated by a median 

 furrow, onto the palmar aspect. This surface is seen on the dorsum only as a small 

 curved median facet which broadens as it passes over the end and continues to 

 expand to its termination. The lateral borders of the joint are well defined. A 

 depression with an overhanging tubercle is on each side of this end ; both depression 

 and tubercle give attachment to the lateral ligament. 



T\\e proximal ends of the second and third rows are essentially the same. They 

 differ from that of the first row because, while the latter fits onto the single rounded 

 end of a metacarpal, those of the two distal rows fit onto double condylar ends. 

 Thus the proximal articular surface presents a median elevation, separating two 

 hollows, continued into a projecting point on the surface front and back. In the 

 phalanges of the second row the dorsal point is the larger ; in the last row the points 



^ Phalanges dieitonim manus. 



