Anatomy of the forearm and elbow joint

The forearm consists of two bones lying longitudinally and adjacent to each other. They are called "flints". The upper bone adjacent to the thumb is thinner and is called the upper “flint”. The lower one, which is adjacent to the little finger, is thicker, since it carries weights, and it is called the lower “flint”. The upper “flint” is useful because thanks to it, rotational movements of the forearm are carried out, and the lower “flint” is useful because thanks to it, flexion and extension of the forearm are carried out. The middle of both of these bones is thin because they are surrounded by thick muscles and do not need to be aggravatingly thick. And their ends are thickened due to the fact that many ligaments extend from them, because when the joints move, they often experience sharp shocks and blows and, moreover, are not covered by meat and muscles.

The upper “flint” is curved and seems to come from the inside and, bending, slightly deviates outward. The usefulness of this is its good adaptability to rotational movements. And the lower “flint” is straight, since this shape is more suitable for extension and bending.

As for the elbow joint, it is made up of the articulation of the upper “flint” and the lower “flint” with the shoulder.

At the end of the upper “flint” there is a hole in which the protrusion of the outer end of the humerus is located, connected to it by a ligament. The rotation of this protrusion in the fossa causes the movement of supination and pronation. As for the lower “flint”, it has two processes, between which there is a groove similar to the letter sin in Greek writing, namely this: U. The surface of the recess of this groove is convex so that it can fit into the groove at the end of the shoulder bones. The latter has a concave shape, but its outline resembles the convexity of a circle. Thanks to the entry of the groove between the two processes of the lower “flint” into this groove, the elbow joint is formed; when one groove moves back and down on the other groove, the arm extends; when the groove of the steep wall blocks the path of the first groove with a hole that locks the process, it delays it and prevents the arm from extending further, so that the arm from the shoulder to the elbow and forearm stops, forming a straight line. And when one of the grooves moves up and forward on the other, the arm bends so that the forearm touches the part of the arm from the shoulder to the elbow from the inside and the front. The lower ends of both “flints” come together, forming, as it were, something single, and a wide common depression is formed in them, most of which is located in the lower “flint”. The place where there should not be a recess remains convex and smooth, so that there is less risk of damage. An oblong process grows behind the depression of the lower flint. We'll talk about its usefulness shortly.