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metacarpal bone of the thumb its direction is downwards. This is in accordance with the law which regulates the union of the epiphyses.

How to distinguish the metacarpal bones.

The metacarpal bone of the thumb is distinguished by the characteristic saddle-shaped surface at the base, which articulates with the trapezium. Besides which, its shaft is shorter, broader, and stronger than the others, in accordance with the many and powerful muscles which act upon it. There are no less than nine muscles to work the thumb. Observe that the great mobility of the thumb depends upon this saddle-shaped joint at its base; and that its power of antagonizing the fingers is owing to its base being set off on a plane anterior to them.

Hold the bone with the base towards you, and the dorsal surface uppermost. The facet on one side of the base (indicating the insertion of the extensor ossis metacarpi pollicis) will look away from the side to which the bone belongs.

The metacarpal bone of the fore-finger is distinguished by its zig-zag surface at the base, so as to be immoveably wedged with three of the carpal bones; also by having only one lateral facet.

Hold the bone with the base towards you and the dorsal surface upwards: the lateral facet will be on the side to which the bone belongs.

The metacarpal bone of the middle finger may be known by its having a smooth surface at the base for the os magnum, and an angular projection at the corner of it for the insertion of the "extensor carpi radialis brevior." It has also lateral facets on each side.

With the base towards you, and the dorsal surface uppermost, the corner of the base which has no projection will be on the side to which the base belongs.

The metacarpal bone of the ring-finger articulates with the unciform and part of the os magnum. It may be distinguished by its smaller size; by the absence of the angular projection at the base, which is flat, and by its having lateral facets on each side. With the base towards you and the dorsal surface uppermost, the base has a slight inclination towards the side it belongs to.

The metacarpal bone of the little finger may be recognised by its concavo-convex surface at the base to articulate with the unciform bone, and by its having only one lateral facet.

With the base towards you and the dorsal surface uppermost, the side of the base which has no facet will look to the side to which the bone belongs.

Ossification of

The structure of each metacarpal bone is premetacarpal bones, cisely like that of the great long bones; and a longitudinal section through one of them would display the medullary cavity, and the great thickness of the compact wall of the shaft. Hence a broken metacarpal bone is comparatively rare. Like all the long bones, each metacarpal bone has a centre of ossification for the shaft and one for each of the articular ends. In the first metacarpal, the artery of the marrow runs towards the lower end, therefore the lower epiphysis unites sooner than the upper to the shaft. This is just the reverse of what takes place in all the other metacarpals, in which the artery of the marrow runs towards the upper end.

THE BONES OF THE FINGERS.

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Each finger consists of three bones, successively decreasing in size, and termed, respectively, the first, second, and last or ungual phalanx." The thumb has only two phalanges, and these correspond to the first and last of those of the fingers. A general description will suffice for all.

The structure of each phalanx is precisely like that of the great long bones, and a longitudinal section through one of them would display the great thickness of the compact wall of the shaft. A broken phalanx is comparatively rare.

Considering the phalanges as "long" bones, we speak of their shafts and their articular ends. The shafts are convex on the dorsal surface, and flat on the palmar, for the convenient play of the flexor tendons: and here we have to observe, that on each side of this flat surface there is a slight ridge for the attachment of the fibrous sheath (theca), which keeps the tendons in their place.

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