Terms of position and direction

All descriptions in human anatomy are expressed in relation to the anatomical position, a convention whereby the body is erect, with the head, eyes, and toes directed forward and the upper limbs by the side and held so that the palms of the hands face forward. There is no implication that the anatomical position is one of rest. It is often necessary, however, to describe the position of the viscera also in the recumbent posture, because this is a posture in which patients are frequently examined clinically.

The median plane is an imaginary vertical plane of section that passes longitudinally through the body and divides it into right and left halves. The median plane intersects the surface of the front and back of the body at what are called the anterior and posterior me dian lines. It is a common error, however, to refer to the" midline" when the median plane is meant.

Any vertical plane through the body that is parallel with the median plane is called a sagittal plane. The sagittal planes are named after the sagittal suture of the skull, to which they are parallel. The term "parasagittal" is redundant: anything parallel with a sagittal plane is still sagittal.

Any vertical plane that intersects the median plane at a right angle and separates the body into anterior and posterior parts is termed a coronal, or frontal, plane.

The term horizontal plane refers to a plane at a right angle to both the median and coronal planes: it separates the body into superior and inferior parts. This is often termed an axial plane, particularly in radiology.

The term transverse means at a right angle to the longitudinal axis of a structure. Thus, a transverse section through an artery is not necessarily horizontal. A transverse section through the hand is horizontal, whereas a transverse section through the foot is coronal (fig. 1-1).

The term medial means nearer to the median plane, and lateral means farther from it. Thus, in the anatomical position, the thumb is lateral to the little finger, whereas the big toe is medial to the little toe. Intermediate means lying between two structures, one of which is medial and the other lateral. In the upper limb radial means lateral and ulnar means medial: in the lower limb fibular or peroneal means lateral and tibial means medial. The border of a limb on which either the thumb or the big toe is situated is sometimes called preaxial, and the opposite border, postaxial. These two terms are based on the arrangement of the limbs in the embryo during the sixth postovulatory week, when the thumbs and the big toes are both on the rostral border of the limbs (see figs. 8-10 and 15-11).

Medial and lateral rotation (which should never be referred to as internal and external) means rotation (e.g., of the hip) around a vertical axis so that the anterior aspect of the part moves medially or laterally, respectively.

Anterior or ventral means nearer the front of the body.Posterior or dorsal means nearer the back. In the upper limb the term palmar (formerly volar) means anterior. In the foot, plantar means inferior, and the term dorsal is commonly used for superior in the foot.

Superior means nearer the top or upper end of the body. Inferior means nearer the lower end. Cranial or cephalic is sometimes used in stead of superior, and caudal instead of inferior. Rostral means nearer the "front end," that is, the region of the nose and mouth. this is superior in the most of the body althoug it represents the anterior aspect of the head.

The suffix "-ad" is sometimes added to a positional term to indicate the idea of motion. Thus, cephalad means proceeding toward the head. Such terms are useful occasionally in describing growth processes, but their application is best limited.

In the limbs, proximal and distal are used to indicate, respectively, nearer to and farther from the root or attached end of the limb. (Proximal and distal have a special meaning in the case of the teeth.)

Internal and external mean, respectively, nearer to and farther from the center of an organ or a cavity. Superficial and deep mean, respectively, nearer to and farther from the surface of the body.

The term middle is used for a structure lying between two others that are anterior and posterior, or superior and inferior, or internal and external.

In addition to the technical terms of position and direction, certain common expressions may be cautiously used in anatomical descriptions: front, back, in front of, behind, forward, backward, upper, lower, above, below, upward, downward, ascending, descending. These terms are free of ambiguity only if they are used in reference to the anatomical position. A number of other common terms, such as "under," however, are generally best avoided. In this work we will use technical terms of position and direction.

History of anatomy

Anatomy can be traced from the Greek period, B.C., and the Roman Empire, A.D., to Andreas Vesalius, who reformed the subject in his De humani corporis fabrica ("On the Workings of the Human Body") in 1543. Subsequent highlights include the discovery of the compound microscope (1590), the founding of microscopic anatomy by Malpighi (seventeenth century), the discovery of the circulation of the blood by Harvey (1628), the establishment of modern embryology by Wolff (eighteenth century), the gross classification of tissues by Bichat (1801), and many notable advances during the nineteenth and twentieth centuries.

The best general introduction to the history of anatomy is Singer, C., A Short History of Anatomy and Physiology from the Greeks to Harvey, Dover, New York, 1957. Two other interesting works are Saunders, J. B. de C. M., and O'Malley, C. D., The Illustrations from the Works of Andreas Vesalius of Brussels, World Publishing Co., Cleveland, 1950; and O'Malley, C. D., and Saunders, J. B. de C. M., Leonardo da Vinci on the Human Body, Schuman, New York, 1952.

Anatomical literature

In addition to journals (such as Acta Anatomica, American Journal of Anatomy, Anatomy and Embryology, the Journal of Anatomy and Clinical Anatomy), many detailed books are available. Some useful works are cited below.

Systemic anatomy

Quain's Elements of Anatomy, 11th ed., Longmans, Green, London, 1908-1929, several volumes. The most detailed account in English.

Regional anatomy

Gardner, E., Gray, D. J., and O'Rahilly, R., Anatomy: A Regional Study of Human Structure, 4th ed., W. B. Saunders Company, Philadelphia, 1975. Provides more detail than this book and includes extensive references to the literature.

Von Lanz, T., and Wachsmuth, W., Praktische Anatomie, Springer, Berlin, 1935-1979, several volumes.Contains superb illustrations.

Applied anatomy

Abrahams, P., and Webb, P., Clinical Anatomy of Practical Procedures, Pitman, Tunbridge Wells, 1975.

Lachman, E., and Faulkner, K. K., Case Studies in Anatomy, 3rd ed., Oxford University Press, New York, 1981.

Schneider, L. K., Anatomical Case Histories, Year Book, Chicago, 1976.