Anatomical Position

Anatomical position is a stance in which a person stands erect with the feet flat on the floor, arms at the sides, and the palms, face, and eyes facing forward (fig. A.1). This position provides a precise and standard frame of reference for anatomical description and dissection. Without such a frame of reference, to say that a structure such as the sternum, thymus, or aorta is "above the heart" would be vague, since it would depend on whether the subject was standing, lying face down, or lying face up. From the

Anatomical Position

Figure A.1 Anatomical Position. The feet are flat on the floor and close together, the arms are held downward and supine, and the face is directed forward.

perspective of anatomical position, however, we can describe the thymus as superior to the heart, the sternum as anterior or ventral to the heart, and the aorta as posterior or dorsal to it. These descriptions remain valid regardless of the subject's position.

Unless stated otherwise, assume that all anatomical descriptions refer to anatomical position. Bear in mind that if a subject is facing you in anatomical position, the subject's left will be on your right and vice versa. In most anatomical illustrations, for example, the left atrium of the heart appears toward the right side of the page, and while the appendix is located in the right lower quadrant of the abdomen, it appears on the left side of most illustrations.

The forearm is said to be supine when the palms face up or forward and prone when they face down or rearward (fig. A.2). The difference is particularly important to descriptions of anatomy of this region. In the supine position, the two forearm bones (radius and ulna) are parallel and the radius is lateral to the ulna. In the prone position, the radius and ulna cross; the radius is lateral to the ulna at the elbow but medial to it at the wrist. Descriptions of nerves, muscles, blood vessels, and other structures of the forearm assume that the forearm is supine. (Supine also means lying face up and prone also means lying face down.)

Ulna Radius Anatomical Position

Figure A.2 Positions of the Forearm. When the forearm is supine, the palm faces forward; when prone, it faces rearward. Note the differences in the relationship of the radius to the ulna.

Figure A.1 Anatomical Position. The feet are flat on the floor and close together, the arms are held downward and supine, and the face is directed forward.

Figure A.2 Positions of the Forearm. When the forearm is supine, the palm faces forward; when prone, it faces rearward. Note the differences in the relationship of the radius to the ulna.

Saladin: Anatomy & I Atlas A General I Text I © The McGraw-Hill

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