Terms used in anatomy

Many parts of the body are symmetrically arranged. For example the right and left limbs are similar; there are right and left eyes and ear, right and left lungs, and right and left kidneys. But there is also a good deal of asymmetry in the arrangement of the body. The spleen lies entirely on the left side; the larger part of the liver lies on the right side; the pancreas lies partly on each side.

    The human body is studied from the erect position with the arms by the sides and the palms of the hands facing forwards, the head erect the eyes looking straight in front. This is describes as the anatomical position.

    The various part of the body is then described in relation to certain imaginary lines or plane. The median plane runs through the center of the body. Any structure which lies nearer to the median plane of the body than another is said to be medial to that other. For example the hamstring muscles which lie on the inner side of the thigh are nearer the median plane than those which lie on the outer side and are therefore medial to the other group which as described as lateral. Similarly the inner side of the thigh is described as the medial aspect and the outer as the lateral aspect.

   The term internal and external are used to describe the relative distance of an organ or structure from the center of a cavity. The ribs for example have an internal surface which is near the chest cavity and an external surface which is on the outer side, farther away from the cavity. The internal carotid artery, is within the cranial cavity and the external is outside the cavity.

     The terms superficial and deep are used to denote relative distance from the surface of the body, and the term superior and inferior denote positions relatively high or low, particularly in relation to the trunk, such as the and inferior surfaces of the clavicle.

   The terms anterior and posterior are synonymous with ventral and dorsal. These terms are only applied to man in the erect attitude or ‘anatomical position’. For example the anterior and posterior tibial arteries lie in the front and behind in the leg.

    In describing the hand the terms palmar and dorsal are used instead of anterior and posterior, and in describing the foot the terms plantar and dorsal are similarly employed.

   The terms proximal or distal are employed to described nearness to, or distance from a given point, particularly in relation to the limbs. For example the proximal phalanges are nearer to the wrist and distal ones are the farthest away. When three structures in a line running from the median plane of the body outwards, they are described as being placed in medial, intermediate and lateral positions. An example of this is seen in the arrangement of three cuneiform bones of the foot. Similarly when three structure run from front to back (anterior to posterior) or from above downwards (superior to inferior), these are described as anterior, middle and posterior as happens in the arrangement of the three fossae of the skull and superior, middle and inferior, as occurs in the arrangement of the superior. Middle and inferior radio-ulnar joints.