The human body is a combination of organ systems, with a supporting framework of muscles and bones and an external covering of skin. The study of the body is divided into three sciences:

Anatomy-the study of body structures and the relation of one part to another.

Physiology-the study of the processes and functions of the body tissue and organs. Physiology is the study of how the body works and how the various parts function individually and in relation to each other.

Embryology-the study of the development of the body from a fertilized egg, or ovum.

TERMS OF POSITION AND DIRECTION

LEARNING OBJECTIVE: Identify anatomical terms of position and direction.

The planes of the body are imaginary lines dividing it into sections. These planes are used as reference points in locating anatomical structures. As shown in figure 1-1, the median, ormidsagittal, plane divides the body into right and left halves on its vertical axis. This plane passes through the sagittal suture of the cranium; therefore, any plane parallel to it is called a sagittal plane. Frontal planes are drawn perpendicular to the sagittal lines and divide the body into anterior (front) and posterior (rear) sections. Since this line passes through the coronal suture of the cranium, frontal planes are also called coronal planes. The horizontal, ortransverse, plane, which is drawn at right angles to both sagittal and frontal planes, divides the body into superior (upper) and inferior (lower) sections.

To aid in understanding the location of anatomical
structures, you should use a standard body position
called the anatomical position as a point of reference.
This anatomical position is assumed when the body

Figure 1-1.-Planes of the body.

stands erect with the arms hanging at the sides and the palms of the hands turned forward (fig. 1-2).

Other commonly used anatomical terms include the following:

Anterior or ventral-toward the front, or ventral (pertaining to the belly; abdomen), side of the body.

Posterior or dorsal-toward the back, or rear, side of the body.

Medial-near or toward the midline of the body.
Lateral-farther away from the midline of the body.

Internal-inside.
External-outside.
Proximal-nearer the point of origin or closer to the body.

Distal-away from the point of origin or away from the body.

Superior-higher than or above.
Cranial-toward the head.

Caudal-toward the lower end of the body.
Inferior-lower than or below.
Erect-normal standing position of the body.
Supine-lying position of the body, face up.
Prone-lying position of the body, face down.
Lateral recumbent-lying position of the body on either side.

Peripheral-the outward part or surface of a structure.