Human Anatomy (with Fundamentals of Dynamic and Sports Morphology) - Ivanitsky M. F. 2008

Introduction to Anatomy
Axes and Planes of the Human Body, Structural Asymmetry

The parts of The Human Body are the torso, neck, HEAD, and two pairs of limbs: two upper limbs—the arms—and two lower limbs—the legs.

In anatomy, it is standard practice to study the body in a vertical, symmetrical position with the arms at the sides and the thumbs turned outward (supination position). Anatomical descriptions utilize planes and axes that pass through the body corresponding to the three planes and axes of a rectangular coordinate system. Of the three planes, one runs horizontally and is called the horizontal plane, while two perpendicular to it are vertical and are referred to as the frontal and sagittal planes, respectively. The horizontal plane runs parallel to the horizon; the frontal plane runs transversely, corresponding to the plane of the forehead, from which it derives its name (frans — forehead, frontalis — frontal); the sagittal plane passes through the body in an anteroposterior direction (sagitta — arrow). The sagittal plane passing strictly through the middle of the body and dividing it into right and left halves is called the median plane. The axes formed by the intersection of the horizontal and frontal planes are called transverse axes; those at the intersection of the horizontal and sagittal planes are called sagittal or anteroposterior axes; and those at the intersection of the frontal and sagittal planes are called vertical axes. Naturally, any number of frontal, horizontal, and sagittal planes can be passed through the body. The exception is the median plane, of which only one can exist.

The frontal plane passing through the longitudinal axis of the body divides it into anterior and posterior sections. The anterior section is also called ventral (venter—belly), and the posterior section is called dorsal (dorsum—back). The surface of any organ facing toward the anterior surface of the body is referred to as anterior or ventral, while the surface directed toward the back is called posterior or dorsal. The surface of an organ facing toward the median plane of the body is called internal or medial (medialis), and the opposite surface is called external or lateral (lateralis). The surface facing toward the head is called cranial (cranialis) or superior, while the opposite surface facing toward the pelvis is called caudal (caudalis) or inferior. Corresponding to the planes and axes of the body are the directional terms used to describe the Location of various Organs: upward or cranially, i.e., toward the head; downward or caudally, i.e., toward the pelvis; anteriorly or ventrally; posteriorly or dorsally; inwardly or medially; outwardly or laterally. The terms "cranial" and "caudal" are used exclusively when referring to the torso and neck. For the limbs, terms denoting a closer or more distant position relative to the torso are used: proximal and distal, respectively. The terms "proximally" and "distally" are used to define direction.

The two halves of the body created by the median plane are constructed on THE PRINCIPLE OF mirror Symmetry. However, they are not entirely identical in detail. This Asymmetry in body Structure is particularly evident in the structure and position of Internal Organs. Unpaired organs, such as The Stomach, Spleen, Heart, and others, are asymmetrical both in their structure and in their anatomical location. External body forms are likewise not perfectly symmetrical. For instance, in right-handed individuals, the right arm is typically more developed: it is not only stronger but also about a centimeter longer than the left. The reverse is true for left-handed individuals. A certain degree of leg asymmetry can also be observed. The spinal Column is likewise not entirely symmetrical and exhibits slight lateral curves. Almost all people exhibit some degree of facial asymmetry (for details, see p. 402).