1.11: Directional Terms
Directional terms are essential for describing the relative locations of different body structures. For instance, an anatomist might describe one band of tissue as "inferior to" another, or a physician might describe a tumor as "superficial to" a deeper body structure. These terms often use comparative terms in pairs to trace out the relative locations of one body part to another or descriptions of body tissues like the deeper ones from superficially present with reference to the body's upright standard anatomical reference position.
Terms like anterior or ventral describe the front or direction toward the front of the body. The toes are anterior to the foot. In contrast, the posterior or dorsal describes the back or direction toward the back of the body. For example, the popliteus is posterior to the patella. The contrasting pair of terms, superior and inferior, refers to a position relative to the head and feet, respectively. Superior refers to a position above or higher than another part of the body. The orbits are superior to the Orbicularis oris. In contrast, inferior describes a position below or lower than another part of the body, near or toward the tail (in humans, the coccyx or lowest part of the spinal column). The pelvis is inferior to the abdomen.
Similarly, medial and lateral terms indicate the location towards or away from the body's midline. Lateral describes the side or direction toward the side of the body. The thumb (pollex) is lateral to the digits. Medial describes the middle or direction toward the middle of the body. The hallux is the medial toe.
The term "intermediate" is independently used often, which locates a structure present between two structures. For instance, a transverse colon is an intermediate between the ascending and descending colon. Also, the location of the collarbone is intermediate between the shoulder and the breastbone.
The other set of relative terms includes the proximal vs. distal, where the former describes the limb's position nearer to the body's trunk, and the latter points to the position farther from the body's trunk, such as the brachium is proximal to the antebrachium, and the crus is distal to the femur.
Likewise, the term superficial describes a position closer to the surface of the body. The skin is superficial to the bones. Deep describes a position farther from the surface of the body. The brain is deep in the skull.
In addition, a few rarely used terms, such as ipsilateral and contralateral, provide descriptions of the structure from another body structure located on the same or different sides of the body. For example, the position of the ascending colon and the gall bladder is ipsilateral; however, the ascending and descending colon is contralateral.
This text is partially adapted from Openstax, Anatomy and Physiology 2e, Section 1.6: Anatomical Terminology
