By Elizabeth A. Murray, Mount St. Joseph University
Standing facing forward, with your feet slightly apart, and your palms facing the front is pretty much the definition of a standard anatomical position. And, like other standards, the beauty of this is that it universally fixes the body in space, to provide a common frame of reference, regardless of the various positions we can get ourselves into. This position becomes a reference point that is universal.
The Standard Model for Anatomical Positions
The standard anatomical position allows us to apply directional terms that never change, whether we are standing up, lying down, or even standing on our heads. The importance of the palms facing forward was decided somewhere long ago in the study of anatomy. In this position, the two bones of the forearm—the radius and ulna—are parallel from the elbow to the wrist.
When we turn our palms to face backward, the radius crosses over the ulna like an ‘X’. You can feel this if you put your hand around your opposite forearm and rotate that palm—a movement which, by the way, happens at the elbow, not at the wrist.
From the standard position, anatomy uses specific terms to express body directionality. For example, superior means ‘up’, away from the pull of gravity, so in humans, that’s the head end. Inferior means ‘down’, toward the pull of gravity, or toward the ground. Anterior means ‘forward’, or in the direction that you move, while posterior means ‘backward’, or opposite the direction of your typical movement.
Equivalent Phrases
Did you notice that those four terms—superior, inferior, anterior, and posterior—all relate to the space around us in which we navigate? We also have equivalent directional terms that relate to parts of the body. Cranial—or cephalic in some references—means ‘the head end’, and caudal means ‘toward the tail end’.
So, considering that, which of the four terms—superior, inferior, anterior, or posterior—is equivalent to cranial? That’s superior. Which body term means the same thing as inferior? That’s caudal. And while you might say, “Well, I don’t have a tail,” you did as an embryo. What’s more, cranial and caudal are usually used to refer to the head and trunk of the body—of course, you’re not an elephant, but you probably know where your trunk is!
Other terms of directionality are used for the limbs. So, in a human, superior and cranial are interchangeable, and inferior and caudal mean the same thing. How about anterior and posterior? We also have body part terms that are equivalent to them. You’ve probably heard of dorsal, related to the dorsal fin on a shark; the dorsal side is the spine side in animals with a backbone.
So, with regard to anterior or posterior, the anatomical equivalent of dorsal is posterior. Since posterior means ‘opposite the direction of movement’, its body part equivalent is the dorsal side of the body. And anterior is the same as the ventral side of the human body—that’s in the direction we typically navigate.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Stomach Problems
By the way, the front of the body is not the stomach. The stomach is a food-holding digestive organ inside the body. The ventral side of the torso can also be called the belly side. Now, most people think belly is just a cutesy little word, but it’s a perfectly adequate anatomical term for the side of the body opposite the spine. So, in humans, ventral equals anterior—but ventral relates to the body itself, while anterior means ‘in the direction an animal moves’.
So, as an aside, if anterior means ‘in the direction of movement’, does anterior equal ventral in your dog or cat? No. Anterior equals cranial in a four-legged creature, since its head is the same direction in which it moves. Posterior, then, equals caudal—your dog or cat’s tail end.
So, what is the equivalent of ventral in a dog? If you said inferior, you’re right! Dorsal—as the spine side—would be superior in a four-legged animal. That helps to reinforce that superior, inferior, anterior, and posterior refer to the space around us, while cranial, caudal, dorsal, and ventral relate to parts of the body itself.
It’s All About Comparison
Other anatomical terms include medial and lateral. Medial means ‘closer to the midline of the body’, and lateral means ‘toward the side of the body’. So, when comparing the clavicle to the shoulder, which is lateral? If you said shoulder, you’re correct. In that comparison, the clavicle is also said to be medial to the shoulder—the terms switch depending on the question asked.
But what if you compare the clavicle to the sternum? Then the clavicle is lateral and the sternum is medial—the relationships change depending on which two structures are being compared. In fact, the sternum could be said to be median, which refers to being on the midline of the body.
But other than median structures, since there is only one midline, it’s all about comparison. You could never simply say, “The clavicle is medial,” because that would beg the question, “Medial to what”? These directional terms are used to compare structures to each other, and the relationships change depending on what’s being compared.
Common Questions about the Standard Anatomical Position
The decision to have the palms face forward in standard anatomical position was made long ago when it became obvious that the benefit of the palms facing forward is that it makes the radius, and ulna, the bones of the forearm run parallel to each other from the elbow to the wrist. But if the palms were to face backwards, the two bones would run over each other making an X shape.
The standard anatomical position is special in the sense that it provides a universal point of reference so it makes both naming structures and discussing them easier, no matter in what position the body is.
In humans, using the standard anatomical position, the two terms may reference the same thing but they relate to two different categories of anatomical terms. Ventral, is related to the body while anterior relates to the direction of movement.
