Not sure of the context, but: Anterior = front posterior = rear
Anterior has four surfaces while posterior has five.
The anterior will look as if it is smiling. Also it is closer to the thick band on a worm.
posterior
The kidneys have their anterior and posterior surfaces. The foremost surface countenances towards the front stomach wall, while the back posterior surfaces confronting the posterior stomach wall. These surfaces are isolated by the edges of the kidney, which are the significant convexity horizontally, and minor concavity medially.
Anterior, posterior and lateral also.
The opposite of posterior is anterior. Anterior refers to the front of the body or a structure, while posterior refers to the back.
What animals? As anterior means front and posterior means back, then most-if not all animals have a front and back, or an anterior and posterior. They are usually characterized by a mouth(anterior) or rectum/anus (posterior).
Anterior
If you refer to lungs in humans, then the lungs are anterior to the spine
the opposite of anterior is Posterior.
Which structure lies posterior to the bladder and anterior to the rectum?