Parts of the Skull

Braincase

Portion of the cranium encasing the brain. It is the largest relative to the other parts of the skull in primates.

Rostrum

Portion of the cranium extending anteriorly from the front edge of the orbits or the base of the zygomatic arch. Corresponds to the externally visible muzzle or snout, and includes the upper jaw and the bones surrounding the nasal cavity.

Nasal bones

Paired bones forming the anteriormost roof of the nasal cavities.

Premaxillae

A pair of bones forming the lower margin of the outer nasal openings and anteriormost portion of the roof of the palate. The upper incisors always reside on these bones

• in most mammals each premaxilla has an elongate process extending along one side of the nasal cavity and a second process meeting the other premaxilla at the midline of the palate

Maxillae

These two tooth bearing bones make up a large part of the sides of the rostrum and the palate posterior to, and adjooining, the premaxillae.

• The anterior base of each zygomatic arch usually consists of an extension of the maxilla, termed the zygomatic process of the maxilla.

Frontal bones

A pair of bones just posterior to the nasals and dorsal, extending to the maxillae

• Antlers and horns of terrestrial cetariodactls are growths to the frontal bones.

• In many mammals, each frontal bone has a lateral pointed projection, the posorbital process, which marks the posterior border of the orbit.

• In some mammals, (primates, perissodactyla, some cetariodactyla) the postorbital process is joined with the zygomatic arch to form a postorbital bar or plate.

  • In others like whales, each frontal extends laterally as a broad wing over the entire orbit, termed a supraorbital process.

Parietal bones

Located posterior to the frontals, these paired bones form the bulk of the roof of the braincase.

Interparietal bone

When distinct, this is a single, often triangular-shaped bone centrally located on the braincase at the posterior junction of the parietal bones. Often it is fused with the occipital bone in adults.

• Rodents generally have a prominent interparietal

Squamosal bones

Each of these two bones is located lateral and ventral to the corresponding parietal bone.

• Each squamosal bone bears a ventral articular surface, the mandibular fossa, which forms part of the hinge supporting the lower jaw.

• The posterior base of the zygomatic arch consists of the zygomatic process of the squamosal.

  • When the squamosal is fused with the tympanic bone the complex is termed the temporal bone; this fusion is found in most mammals with exceptions including marsupials and whales.

Jugal bones

Each of these bones forms the central portion of the zygomatic arch and is located between the zygomatic processes of the maxilla and squamosal.

• occasionally the jugal also is in contact with the lacrimal bone or the premaxilla.

• In marsupials, the jugal also makes up part of the mandibular fossa.

• When the zygomatic arch is absent or incomplete, the jugal often is absent.