1. Terms of Description

  1. Special features of the embryo
    1. THE ADULT: it is assumed that the body is erect, with the arms by the sides and the palm directed forward - the anatomic position. The terms anterior or ventral and posterior or dorsal describe the front or back of the body or limbs, as well as the relations of structures inside the body to one another. Superior and inferior indicate the relative levels of different structures.
    2. THE EMBRYO is curved (or flexed), therefore a reference position is not as easily defined as in the adult. In the embryo, the terms dorsal and ventral are nearly always used, and cranial (cephalic) and caudal commonly denote relationships to the head and tail ends, respectively
      1. The term rostral indicates the relationships of structures to the nose
      2. The terms proximal or distal are described as distances from the source of attachment of a structure; , in the upper limb, the elbow is proximal to the wrist and the wrist is distal to the elbow
  2. Planes of section: the classic planes of space seen in 3 dimensions in the embryo and fetus are the same as described in the adult, only the terminology is special, with the subject described as being in the upright position facing the observer. However, due to embryonic flexion, the reciprocal relationships of the frontal and transverse planes are modified; thus, a section which may be frontal at the level of the head can be transverse at the level of the trunk
    1. THE MEDIAN PLANE is a vertical plane passing through the center of the body. Median sections divide the body into right and left halves. Lateral and medial refer to structures that are, respectively, farther from or nearer to the median plane of the body
    2. THE SAGITTAL PLANE is any vertical plane perpendicular to the forehead and parallel with the long axis of the nose and the median plane that divides the subject into right and left parts. "Parasagittal" and "median sagittal" are redundant terms
    3. THE TRANSVERSE OR HORIZONTAL PLANE is any plane at right angles to both the median and frontal planes. It is parallel with an imaginary line joining the eyes and divides the subject into superior and inferior or top and bottom parts
    4. A FRONTAL OR CORONAL PLANE is any vertical plane that intersects the median plane at right angles. It is parallel with the forehead and divides the subject into front (anterior or ventral) and back (posterior or dorsal) parts
  3. Embryonic sections usually used
    1. A MEDIAN (MIDSAGITTAL) SECTION is cut through the median plane. Longitudinal sections parallel to the median plane, but not through it, are called sagittal sections
    2. A FRONTAL OR CORONAL SECTION is a vertical section through the frontal or coronal plane
    3. TRANSVERSE OR HORIZONTAL SECTIONS are sections through the transverse plane; they also are called cross-sections
    4. OBLIQUE SECTIONS are neither perpendicular nor horizontal but are inclined or slanted
terms of description: image #1