One of the most difficult aspects of studying fossils has always been learning the vocabulary. So to make things easier, we'll take some time here to acquaint you with the terms we will use later on. We have made it a point to include these explanations later in the site, so don't worry about memorizing everything the first time around.

Let's use the modern mountain gorilla (Gorilla gorilla) as a representative ape skull, because it shows all of the basic anatomical features of the ape skull along with several robust, or strongly developed features, only seen in certain members of the human lineage.

We'll start with the frontal view. For starters, the skull is divided into two completely separate bony parts: the cranium, the upper part that houses the brain, and is what is generally meant by "skull," and the mandible, which is the lower jaw. The two orbits, or eye sockets, are easy to recognize. Above the orbits we see the supraorbital torus, or brow ridge that forms a prominent bony bridge above the eyes. The nasal opening or, nares, is below the orbits in the center of the skull. To either side of the opening, we see a small hollow area called the canine fossa (plural: fossae). The cheekbones lie to the sides of the nasal opening. The zygomatic arches extend to the sides of the face and connect the cheek bones to the braincase (actually easier to see in the lateral view below). At the top of the cranium (above and behind the supraorbital torus) we can see two lines converging to an angle at the top of the head. These are the temporal lines, where the temporalis muscles - used for chewing - attach to the skull.
In lateral view, we can more clearly see the distinction between cranium and mandible. The cranium has two parts, the face and the braincase. These two parts are much more distinct in the gorilla- and also in early human species- than they are in modern humans. The mandible is also divided into two portions, although this distinction is based on convenience rather than any clear border of bone. These two portions are the corpus, or the horizontal part that houses the teeth, and the ramus (plural: rami), which is the vertical portion to which most of the chewing muscles attach. We also note that the zygomatic arches (see above) form a large opening in the skull. Through this opening, the main chewing muscles (temporalis muscles)pass from the mandible, under the arches, and attach to the cranium. We see several new features in this view, too. The convergence of the temporal lines in frontal view leads to a bony ridge that runs along the length of the cranium. This is the sagittal crest (see Paranthropus aethiopicus for a good example of a sagittal crest). Near the back of the cranium, the sagittal crest meets another ridge of bone, this one running across the back of the skull. This ridge is the nuchal crest. It can be seen here angling up towards the right meeting the sagittal crest at the external occipital protuberance- the point at the far rear of the cranium. Often this rear portion of the skull is referred to as the occiput, or the occipital region. A flat portion of the skull is found below and behind the nuchal crest. This is called the nuchal plane.