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/ANATOMICAL NOMENCLATURE/PLANES, DIRECTIONS AND RELATIONSHIPS

ANATOMICAL NOMENCLATURE

Anatomy is the study of the structure of the body. It is conventionally divided into topographical or gross anatomy (which includes surface, or ‘living’, anatomy, neuroanatomy, endoscopic and imaging anatomy), microscopic anatomy or histology and embryology (the study of the embryo and fetus).

Anatomical language is one of the fundamental languages of medicine. The unambiguous description of thousands of structures is impossible without an extensive and often highly specialized vocabulary. Ideally, these terms, which are often derived from Latin or Greek, should be used to the exclusion of any other, throughout the world. In reality, many terms are vernacularized. The Terminologia Anatomica, drawn up by the Federative Committee on Anatomical Terminology (FCAT) in 1998, has served as our guide in preparing the 39th and 40th Editions of Gray’s Anatomy. Where we have anglicized some of the Latin terms, we have given the official form, at least once, in parentheses. We have also included eponyms, since these are often used, possibly more so by clinicians than anatomists. Indeed, certain eponyms are so firmly entrenched in the language of the clinician that to avoid them could lead to confusion: the eponymous term is often the only way to describe a particular structure, because there is no simple alternative anatomical term. (Short biographical details of the clinicians and anatomists whose names are used in this way are included in the electronic version of the book.)

PLANES, DIRECTIONS AND RELATIONSHIPS

To avoid ambiguity, all anatomical descriptions assume that the body is in the conventional ‘anatomical position’, i.e. standing erect and facing forwards, upper limbs by the side with the palms facing forwards, and lower limbs together with the toes facing forwards (Fig. 1). Descriptions are based on four imaginary planes, median, sagittal, coronal and horizontal, applied to a body in the anatomical position. The median plane passes longitudinally through the body and divides it into right and left halves. The sagittal plane is any vertical plane parallel with the median plane: although often used, ‘parasagittal’ is therefore redundant. The coronal (frontal) plane is orthogonal to the median plane and divides the body into anterior (front) and posterior (back). The horizontal (transverse) plane is orthogonal to both median and sagittal planes. Radiologists refer to transverse planes as (trans)axial: convention dictates that axial anatomy is viewed as though looking from the feet towards the head.

  

Fig. 1  The terminology widely used in descriptive anatomy. Abbreviations shown on arrows: AD, adduction; AB, abduction; FLEX, flexion (of the thigh at the hip joint); EXT, extension (of the leg at the knee joint).

Structures nearer the head are superior, cranial or (sometimes) cephalic, whereas structures closer to the feet are inferior; caudal is most often used in embryology to refer to the tail end of the embryo. Medial and lateral indicate closeness to the median plane, medial being closer than lateral: in the anatomical position, the little finger is medial to the thumb, the great toe is medial to the little toe. Specialized terms may also be used to indicate medial and lateral. Thus, in the upper limb, ulnar and radial are used to mean medial and lateral respectively, and in the lower limb, tibial and fibular (peroneal) are used to mean medial and lateral respectively. Terms may be based on embryological relationships: the border of the upper limb that includes the thumb, and the border of the lower limb that includes the great toe are the pre-axial borders, whilst the opposite borders are the post-axial borders. Various degrees of obliquity are acknowledged using compound terms, e.g. posterolateral.

When referring to structures in the trunk and upper limb we have used freely the synonyms anterior, ventral, flexor, palmar, volar, and posterior, dorsal and extensor. We recognize that these synonyms are not always satisfactory, e.g. the extensor aspect of the leg is anterior with respect to the knee and ankle joints, and superior in the foot and digits; the plantar (flexor) aspect of the foot is inferior. Dorsal (dorsum) and ventral are terms used particularly by embryologists and neuroanatomists: they therefore feature most often in Sections 2 and 3.

Distal and proximal are used particularly to describe structures in the limbs, taking the datum point as the attachment of the limb to the trunk (sometimes referred to as the root), such that a proximal structure is closer to the attachment of the limb than a distal structure. However, proximal and distal are also used in describing branching structures, e.g. bronchi, vessels and nerves.

External (outer) and internal (inner) refer to the distance from the centre of an organ or cavity, e.g. the layers of the body wall, or the cortex and medulla of the kidney. Superficial and deep are used to describe the relationships between adjacent structures. Ipsilateral refers to the same side (of the body, organ or structure), bilateral to both sides, and contralateral to the opposite side.

Teeth are described using specific terms which indicate their relationship to their neighbours and to their position within the dental arch: these terms are described in Chapter 30.

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