(From inter, between, and osa, bones). The cubical artery, in its course between the heads of the radius and ulna near the interosseous ligament, gives off these arteries, the internal and external.

The internal runs close to the ligament, till it reaches below the prunator teres, where it perforates the ligament, and passes to the convex side of the carpus, and back to the hand, where it communicates with the external interosseus, the radical and the cubical arteries. The external pierces the ligament about three fingers' breadth below the articulation, and sends off' a branch towards the external condile of the os humeri, under the ulnaris externus and anconaeus minimus, to which, and to the supinator brevis, it is distributed. The interosseous artery then runs downwards on the outside of the ligament, giving branches to the ulnaris, externus, extensor digitorum communis, the extensorcs pol-licis indicis, and minimi digiti. Having reached the lower extremity of the ulna, it unites with a branch of the internal interosseous artery, which at this place runs from within outwards, and is distributed with it on the convex side of the carpus and back of the hand, communicating with the radial artery and with abranch of the cubital. By these communications this artery forms an irregular arch, from whence branches are sent to the external interosseous muscles, and to the external lateral parts of the fingers.

Interossea ligamenta. The interosseous ligaments in the fore-arm arc fixed by one edge along the sharp angle of each ulna, and by the other along that of the radius. They principally consist of two very strong planes of fibres, which cross each other at oblique angles, and leave holes at different distances for the passages of blood vessels. The ligament ties the two bones closely together, and the two planes serve for the insertion of several muscles. In the supination of the hand it is very tight, but in the pronation it is folded a little lengthways.