The skull is divided into two main parts:

• Neurocranium - or the cranial vault which covers the brain and lined by dura mater.
• Viscerocranium - bones that make up the facial part of the skull and the hyoid bone.

The viscerocranium consists of bones that form the face, lower jaw and hyoid.
They are derived from neural crest mesenchyme of the first three pharyngeal arches.
The maxillary process of the first pharyngeal arch gives rise to the maxilla, zygomatic and the squamous part of the temporal bone.
The mandibular process forms the malleus and incus and parts of the middle ear cavity.
The mandible forms via intramembranous ossification.
The second and third pharyngeal arches form the stapes and styloid process along with the hyoid bone.

The neurocranium surrounds and protects the brain.
The bones that form the neurocranium develop by both intramembranous and endochondral ossification and are derived from mesenchyme of both neural crest and somitic mesoderm origin.

The part of the neurocranium that develops by endochondral ossification, the base, is the chondrocranium.

The part formed by intramembranous ossification, the dome, is the dermatocranium. So called because of its relemblence to dermal plates seen in the heads of lower vertebrates.

The chondrocranium, which is the base of the skull, develops by endochondral ossification from mesenchyme of both neural crest and somitic mesoderm origin.

The arrow marks the cranial end of the notochord.
The bones of neural crest origin (blue) include:

• ethmoid bones
• greater and lesser wings of the sphenoid bone
• anterior part of the sella turcica

• posterior part of the sella turcica
• body of the sphenoid
• base of the occipital bone
• petrous part of the temporal bone.

The membranous neurocranium (dermatocranium) consists of the flat bones of the roof of the skull that form by intramembranous ossification.

The bones of neural crest origin (blue) include:

• frontal bone

• parietal bones
• upper part of the occipital bone

At birth the flat bones of the skull are separated by connective tissue, which will eventually form the sutures of the skull. The fontanelles, located where more than two bones meet, are generally wide. This allows the bones of the skull to overlap during birth. After birth, the bones move back to their original position. The fontanelles also allow the brain to continue to grow at the same rapid pace as it had prenatally during the first few years of life (through ~age 5). The emphasis on growth of the neurocranium is reflected in its disproportionate size in the neonate (~4/5ths of skull volume) relative to the smaller size of the face (~1/5th). At around 5 to 7 years old, the child has nearly all of the cranial volume and subsequent growth of the skull is due to increase in the size of the facial skeleton. In adults, the facial skeleton and the cranial vault are each about 50% of the skull volume.

Palpation of the anterior fontanelle can provide information about the normal progress of ossification of the skull and whether intracranial pressure is normal.
 
The posterior fontanelle generally closes around the second month after birth while the larger anterior fontanelle closes around the 18th month post partum.

Somites first appear in the cranial region around day 20.

In this day 22 embryo, pairs of somites lie along the neural tube.

Recall that the neural tube forms by fusion of neural folds, beginning in the middle of the embryo and proceeding simultaneously in cranial and caudal directions as indicated by the double red arrow.

The anterior and posterior neuropores usually close by day 25 and day 28 respectively. Failure to do so may result in cranial or vertebral defects.

In the image of a typical lumbar vertebra the original relationships between neural tube and notochord and the parts of the vertebra that are formed from the sclerotome are shown.
The vertebral arch is formed by two pedicles and laminae and one spinous process.

The notochord disappears within the bodies of the vertebrae, but persists in the intervertebral discs as the nucleus pulposus.

Caudal segment of the 4th occipital sclerotome (O4) (yellow) fuses with the cranial part of the first cervical sclerotome (C1) (yellow) to form the base of the occipital bone in the skull.
C1 spinal nerve emerges through the space between the (base of the skull) occipital bone and C1 (atlas) (top red circle).
All cervical spinal nerves emerge from the intervertebral foramen superior to their correspondingly numbered vertebra ending with the C7 nerve.

C8 spinal nerve passes between the C7 and T1 vertebrae.

Beginning with the T1 spinal nerve (bottom red circle), all spinal nerves emerge from the intervertebral foramen inferior to their correspondingly numbered vertebra.
 
This information is useful in evaluating patients who present with sensory or motor deficits that suggest involvement of a specific spinal nerve or nerves.