Human Skull Anatomy: Bones, Sutures, and Fontanelles

Cranial Bones and Features

• Frontal Bone:

  • Forms the forehead, the superior part of the orbits, and the anterior cranial fossa.

  • It articulates posteriorly with the two parietal bones at the coronal suture.

• Parietal Bones:

  • Two bones that form the superior and lateral aspects of the cranium.

  • They meet at the sagittal suture medially, articulate with the frontal bone anteriorly at the coronal suture, and with the occipital bone posteriorly at the lambdoid suture.

• Occipital Bone:

  • Forms the posterior and inferior part of the cranium.

  • It contains the foramen magnum, a large opening through which the brainstem connects to the spinal cord.

  • Articulates with the parietal bones superiorly and the temporal bones laterally.

Facial Bones

• Maxilla (Maxillary Bones):

  • Paired bones that form the upper jaw.

  • Considered keystone bones of the face as they articulate with all facial bones except the mandible.

  • Form part of the hard palate, the floor of the orbits, and the lateral walls of the nasal cavity.

  • House the upper teeth.

• Mandible:

  • The single, largest, and strongest bone of the face, forming the lower jaw.

  • It is the only movable bone of the skull, articulating with the temporal bones at the temporomandibular joints (TMJ).

  • Houses the lower teeth.

Sutures of the Cranium

• Coronal Suture:

  • A dense, fibrous joint connecting the frontal bone to the two parietal bones.

  • In adults, sutures are immobile and provide structural integrity to the skull.

  • In infants, these areas allow for slight movement that facilitates passage through the birth canal and accommodate rapid brain growth.

Fontanelles (Soft Spots) of the Infant Skull

Fontanelles are fibrous membranes connecting the cranial bones of fetal and infant skulls. Their primary functions include:

1. Accommodation for Brain Growth: They allow the skull to expand rapidly as the brain develops post-natally.

2. Passage through Birth Canal: They permit the skull to compress and change shape (molding) during childbirth.

• Sphenoidal Fontanelle:

  • Located on the lateral aspect of the skull, near the sphenoid bone, between the frontal, parietal, temporal, and sphenoid bones.

  • Typically closes around $2-3$ months after birth.

  • One of the paired anterolateral fontanelles.

• Posterior Fontanelle:

  • Located at the junction of the two parietal bones and the occipital bone (at the lambda).

  • Relatively small compared to the anterior fontanelle.

  • Key detail from transcript: Ossifies (closes) at approximately $6$ months after birth.

  • Also known as the occipital fontanelle, it is one of the paired posterolateral fontanelles, although often referred to singularly near the occipital bone.