Anterior refers to what is in front for example your abdomen is anterior whereas your back is posterior relative to eachother. Another example is that your nose is anterior to your brain. Anterior and posterior are relative terms.
Anterior means to the front (posterior means to the back). Here are some sentences. A dog's nose is anterior to its tail. The bow of a ship is anterior to the stern. The injury is along the anterior wall of the heart.
anterior part of anterior limb = supplied by anterior cerebral artery posterior part of anterior limb + genu + posterior limb = supplied by middle cerebral artery retrolentiform + sublentiform parts = supplied by anterior choroidal artery
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).