Anatomical terms of location

Anatomical terms of location are one of the categories of jargon that are a fact of life in paleontology. For our current purposes (generally dinosaurs), there are three major whole-body groups of terms and a few other smaller groups. They are most relevant to vertebrates and other animals that have bilateral symmetry. I am going to capitalize the terms so they stand out, but this is not how they are written (unless of course they start a sentence). (I reworked most of these definitions from the introduction of The Dinosauria [Weishampel, Dodson, and Osmolska, eds., 1992 edition.])

Several of the basic terms vary depending on the identity of the animal in question. This is because one set of terms originated with human anatomy, and another set originated with the anatomy of animals that do not walk with an erect spine. There is some mixing and repurposing of terminology. A straight-up application of human terms to other animals gives the following correspondences:
  • Anterior (on a human)=Ventral (on other animals)=toward the belly
  • Posterior=Dorsal=towards the back
  • Superior=Cranial=toward the head
  • Inferior=Caudal=toward the tail (or ground, in our case)
However, for animals other than humans, Anterior and Posterior are often used in place of Superior (Cranial) and Inferior (Posterior). This muddles with the original definitions, but has the advantage of not including the potentially confusing Cranial and Caudal. We'll let this helpful Sauropelta illustrate:

These terms are used relatively as well, i.e. x-feature is more dorsally positioned on a vertebra than y-feature. When we discuss a skull, Cranial is redundant (you're already there), and Rostral, referring to the tip (rostrum) of the head, is its replacement. For tails, Caudal has the same problem, and Cranial sounds kind of strange, but Anterior and Posterior still work. Proximal and Distal (see below) are also appropriate for some aspects.

Another set of directions is used when we consider the midline of an animal. Suppose we observe an animal along the center of the back, along the animal's length. Features close to the midline of the body are designated Medial (toward the midline), in opposition to features farther from the body's midline, which are designated Lateral (away from the midline). Again, we summon the helpful Sauropelta (doubly helpful by also illustrating Proximal and Distal).

The third main set of terms is used with the limbs and tail. The term Proximal refers to features or bones toward the mass of the body, while the term Distal refers to features away from the body. Thus, the hand of our friend is considered Distal compared to the upper arm, and in the hand itself the palm bones (metacarpals) are considered Proximal compared to the finger bones (unguals). This works the same way with features: a limb bone with an expansion on the end farthest from the body can be said to have a Distal expansion.

A number of other groups of terms exists as well. For example, the surface of a hand or foot in contact with the ground is known as Palmar or Plantar, respectively, and the opposite surface is known as Dorsal for both extremities. In teeth, the edge of the tooth facing Anteriorly or Rostrally (to the front of the jaw) is known as Mesial, while the opposite side, facing Posteriorly or Caudally (to the rear of the skull), is known as Distal. The surface of a tooth facing Medially (to the inside of the mouth) is known as Lingual, while the surface of a tooth facing Laterally (opposite the oral cavity) is known as Labial (in reference to lips) or Buccal (in reference to cheeks).

To summarize:

Group One:
Term: Human Equivalent: Meaning:
Ventral Anterior toward the belly
Dorsal Posterior toward the back
(often swapped with Anterior)
Superior toward the head ("up" on a human)
(often swapped with Posterior)
Inferior toward the tail or what passes for one
("down" on a human)

Group Two:
Term: Meaning:
Medial toward the midline of the body
Lateral away from the midline

Group Three:
Term: Meaning:
Proximal toward the mass of the body
Distal away from the mass of the body

Other Terms: Hands/Feet
Term: Meaning:
Palmar (hand) surface in contact with the ground
Plantar (foot)
Dorsal opposite surface

Other Terms: Teeth
Term: Meaning:
Mesial surface toward the front end of the jaw
Distal surface away from the front end of the jaw
Lingual surface toward the oral cavity
Labial (with lips) surface away from the oral cavity
Buccal (with cheeks)

1 comment:

  1. Wow! This was really helpful. Short and explanatory. Thank you so much for making me understand better