It is essential for students beginning their study of anatomy to become familiar with an internationally accepted vocabulary, allowing communication and understanding between all members of the medical and paramedical professions throughout the world. Perhaps the single, most important descriptive feature of this vocabulary is the adoption of an unequivocal position of the human body. This is known as the anatomical position. It is described as follows: the body is standing erect and facing forwards; the legs are together with the feet parallel so that the toes point forwards; the arms hang loosely by the sides with the palm of the hand facing forwards so that the thumb is lateral. All positional terminology is used with reference to this position, irrespective of the actual position of the body when performing an activity.
The following is a list of more commonly used terms which describe the position of anatomical structures:
- Anterior (ventral) To the front or in front, e.g. the patella lies anterior to the knee joint.
- Posterior (dorsal) To the rear or behind, e.g. gluteus maximus lies posterior to the hip joint. (Ventral and dorsal are used more commonly in quadrupeds.)
- Superior (cephalic) Above, e.g. the head is superior to the trunk.
- Inferior (caudal) Below, e.g. the knee is inferior to the hip.
- Cephalic (the head) Caudal (the tail) May be used in relation to the trunk.
- Lateral Away from the median plane or midline, e.g. the thumb lies lateral to the index finger.
- Medial Towards the median plane or midline, e.g. the index finger lies medial to the thumb.
- Distal Further away from the trunk or root of the limb, e.g. the foot is distal to the knee.
- Proximal Closer to the trunk or root of the limb, e.g. the elbow is proximal to the hand.
- Superficial Closer to the surface of the body or skin, e.g. the ulnar nerve passes superficial to the flexor retinaculum of the wrist.
- Deep Further away from the body surface or skin, e.g. the tendon of tibialis posterior passes deep to the flexor retinaculum at the ankle.
To facilitate the understanding of the relation of structures one to another and the movement of one segment with respect to another, imaginary reference planes pass through the body in such a way that they are mutually perpendicular to each other. Passing through the body from front to back and dividing it into two symmetrical right and left halves is the sagittal (median) plane. Any plane parallel to this is also known as a parasagittal (paramedian) plane.
Figure. Anatomical position showing the cardinal planes and directional terminology
A plane passing through the body from top to bottom and lying at right angles to the sagittal plane is the coronal (frontal) plane. This divides the body into anterior and posterior parts. All planes that divide the body in this way are known as coronal planes. Finally, a plane passing through the body at right angles to both the sagittal and coronal planes dividing it into upper and lower parts is known as a transverse (horizontal) plane. A whole family of parallel transverse planes exist; it is therefore usual when presenting a particular transverse section to specify the level at which it is taken. This may be done by specifying the vertebral level or the position within the limb, e.g. C6 or mid-shaft of humerus, respectively.
Within each plane a single axis can be identified, usually in association with a particular joint, about which movement takes place. An anteroposteriorly directed axis in the sagittal (or a paramedian) plane allows movement in a coronal plane. Similarly, a vertical axis in a coronal plane allows movement in a transverse plane. Lastly a transverse (right to left) axis in a coronal plane provides movement in a paramedian plane.
By arranging that these various axes intersect at the centre of joints, the movements possible at the joint can be broken down into simple components. It also becomes easier to understand how specific muscle groups produce particular movements, as well as to determine the resultant movement of combined muscle actions.
- Specific terms are used to describe the relationship of one body part/segment/region to another and are considered in relation to the anatomical position of the body.
- The anatomical position is: standing erect facing forwards, legs together toes pointing forwards, arms at the side and palms facing forwards.