Ulna

Generality

The ulna is the even bone which, together with the radius (with respect to which it is in the medial position), makes up the skeleton of each forearm.

Located between the humerus (above) and the carpal bones (below), it contributes to the constitution of two joints essential for the movement of the entire upper limb: the elbow joint and the wrist joint.
To simplify the study, anatomical experts divide it into three portions: the proximal end (or proximal epiphysis), the body (or shaft) and the distal end (or distal epiphysis).
The proximal end is the bony portion closest to the humerus and with which it articulates.
The body is the central portion, including the proximal epiphysis and the distal epiphysis.
Finally, the distal end is the portion adjacent to the carpal bones, which represent the first part of the skeleton of the hand.

So is Ulna

The ulna is the even bone which, together with the radius, makes up the skeleton of each forearm.
The forearm is the anatomical region of the upper limb between the upper arm and the lower hand.
Belonging to the category of long bones, the ulna is the protagonist of two important joints of the human body: one with the arm bone (the humerus), called the elbow joint, and another with the carpal bones of the hand, called wrist joint.

POSITION WITH RESPECT TO THE RADIO

The ulna runs parallel to the radius, in a medial position if the hand is turned with the palm towards the viewer.
An explanation of the concept of medial (and its opposite meaning, i.e. lateral) is present in the box below.