This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The posterior surface differs from the anterior in the bones being more conspicuous - they are subcutaneous. Of the two the ulna is the more evident. At the elbow the olecranon and the capitellum to its outer side are well marked and some distance inwardly is the medial (internal) condyle. By palpation the ulna can be traced down the forearm almost subcutaneous, running from the olecranon process, in a gentle curve toward the median line, down to its styloid process at the back of the wrist. It is covered only by the skin and superficial and deep fascias. About 3 cm. (1 1/4 in.) to the outer side of the olecranon can be felt the lateral (external) condyle and capitellum. If the elbow is extended a dimple is seen just below the capitellum; it marks the position of the head of the radius, and by pressure the groove separating the head from the capitellum can be felt.
By placing the thumb of one hand in the dimple on the head of the radius, and rotating the hand of the patient with the other, one can feel the bone rotate and thus be assured that the radius is intact. Whenever fracture of the radius is suspected this is the procedure resorted to in order to determine whether or not it is broken.
The radius can be followed only for an inch or so below the dimple, when it disappears beneath the muscles to again become subcutaneous on the outer side of the forearm, about its middle, from thence it can be followed more or less distinctly down to the styloid process on the outer side of the wrist.
The ulna being subcutaneous, fracture can be determined by palpating it from the olecranon down the back of the forearm to the styloid process.
The line of the ulna is usually marked by the presence of a groove. To the ulnar side of the groove lie the flexor carpi ulnaris and the other flexors; to the radial side lie the extensor carpi ulnaris and the other extensors (Fig. 328).
From the dimple marking the head of the radius a groove in the muscles can be felt which runs to the middle of the outer surface of the radius. Anterior or to the palmar side of this groove lie the brachioradialis and extensor carpi radialis longior with the supinator (brevis) beneath. The muscles posterior or between the groove and the ulna are the extensor carpi radialis brevior, extensor communis digitorum, and extensor carpi ulnaris. Passing over the lower third of the outer side of the radius are the tendons of the extensor ossis metacarpi pollicis and extensor brevis pollicis muscles. As they are here subcutaneous, this is the point at which creaking can be felt when they are affected with tenosynovitis.