Posterior

The term "posterior" is based on the Latin "post," meaning after. In its broadest definition, the term means further back, or nearer to the end.

Anatomical Use

All vertebrates, including humans, have a body plan that consists of symmetrical right and left halves, when divided down the center. The term posterior – and it's opposite, anterior – refer to the end points of a vertebrate, both front and rear. In an animal with clear head and tail endpoints, such as a fish, for example, the anterior and posterior ends are easy to differentiate. However, these terms are also used for many other invertebrate organisms as well, even when distinct end points are not as easy to identify.

Anterior (often used synonymously with the term "rostral") and posterior (or "caudal") are just two of the directional terms used in the anatomical discussion of location. There are other common terms used as well, such as dorsal (back), ventral (belly), lateral (left and right sides), and medial (middle between the lateral sides).

In Humans

When the term posterior is used medically, or to describe humans, it refers to the back of the subject. It can also be used as a relative term. For example, the eyes are posterior to the nose, but anterior to the ears. More specifically, when used to describe spinal anatomy, the same usage holds true – it describes that which is nearer to the back or rear end. So, for example, a posterior lumbar interbody fusion is a spine surgery in which the procedure is performed from the back. This term can also be used to differentiate between the different sides of a spinal component, such as a vertebra.