Contains the mastoid and styloid processes.Originates as a separate bone (the tympanic bone) which fuses with the temporal bone.Curved plate below the squamous portion.Contains the internal auditory meatus for cranial nerves VII and VIII.Shaped like a fish scale (for which it is named).The temporal bone consists of four main parts: squamous, petrous, tympanic and mastoid. The temporal bone is a complex anatomical structure that transmits many veins, arteries and nerves into and out of the skull. The foramen magnum is considered part of the skull base Temporal bone The clivus is technically part of the skull base. The part of the occipital bone that is horizontal and creates the posterior cranial fossa for the occipital lobe is part of the skull base. It forms the anterior cranial fossa for the frontal lobe.

The orbital plate of the frontal bone is technically part of the skull base, as it lies below the brain. We will first briefly revisit the bones of the calvarium that contribute to the skull base (frontal and occipital) and then discuss the temporal, sphenoid and ethmoid bones in some more detail. Anteriorly, the occipital bone joins to the sphenoid and temporal bones. The clivus is an incline in the occipital bone that the ventral pons and medulla rest on. Either side of the foramen magnum are the hypoglossal canals for cranial nerve XII. The foramen magnum, housing the brainstem, is also a part of the occipital bone. It contains an external occipital protuberance that can be felt on the back of your head. The occipital bone is joined superiorly to the parietal bones by the lambdoidal suture. The occipital bone forms a cup for the occipital lobe of the brain to sit in. This is why raising your eyebrows can create the appearance that the back of the head is moving. The galea joins the frontalis muscle belly anteriorly to the occipitalis muscle belly posteriorly. Overlying the parietal bones is a thick connective tissue layer known as the galea aponeurotica. They are each joined anteriorly to the frontal bone by the coronal suture.

The two parietal bones join in the sagittal line to form the sagittal suture. Supraorbital notch: nerves supplying the forehead to emerge through this apertureįigure 4.Glabella: the brow ridge that serves as an attachment point for the frontalis muscle and superior portion of the orbicularis oculi.Orbital plate of the frontal bone: forms the roof of the orbital cavity and separates the frontal lobe of the brain from the eye.There are three important parts of the frontal bone to know: The fusion of these frontal bones forms a metopic suture, which may be visible in some skull specimens. During childhood and adolescence, these two bones fuse into one. The frontal bones start as two paired bones. Bones of the skull (lateral) 2 Frontal bone These bones of the skull cap contain two thin layers of cortical bone separated by diploë, which is synonymous with the spongy bone seen in long bones.ĭiploë provides structural integrity and transmits forces along the length of the bones of the skull cap.įigure 3. Of particular importance is the strength of these bones relative to how thin they are. The parts of these bones that lie inferior to the brain are considered to be a part of the skull base (mentioned below). These bones protect the brain superiorly, but also provide an anchor for important muscles of facial expression and eye movement. The calvarium, also known as the roof or skull cap, consists of three bones: The fontanelles undergo complete ossification within 9 – 18 months from birth.Ĭlinical relevance: Fontanelle abnormalitiesĪn enlarged anterior fontanelle can be due to endocrine pathologies like congenital hypothyroidism.Ī bulging anterior or posterior fontanelle may suggest raised intracranial pressure, which may occur in hydrocephalus.Ī sunken anterior or posterior fontanelle may suggest dehydration. Posterior fontanelle: the soft region on the back of the infant’s head.Anterior fontanelle: the soft region on the front of the infant’s head.Base: the sphenoid, ethmoid, occipital and temporal bones tend to grow slightly laterīy week 37, the cartilaginous frame for the skull is almost entirely replaced by bone, and only two relatively small cartilaginous structures remain:.Calvarium (roof): the frontal, occipital and parietal bones tend to grow slightly earlier.This process occurs at different rates in two different regions of the skull: A cartilaginous mould begins to grow and is slowly replaced by bone in a process called intramembranous ossification. The skull begins to form prior to week 12 of embryogenesis. You might also be interested in our Anatomy Flashcard Collection which contains over 2000 anatomy flashcards in addition to advanced features such as spaced repetition.

The 8 bones in the human skull