Cranium

Cranium

  • Synonym: Skull

Definition

The cranium, also known as the bony skull, can be divided into two groups of bones. The bones surrounding the brain are called the neurocranium (which form the cranial cavity), while the bones of skull contributing to the facial skeleton are known as the viscerocranium. These skull bones are connected through special joints called sutures.

NEUROCRANIUM:

The neurocranium consists of the calvaria and the skull base. The calvaria (i.e. the skull cap) is the domed roof of the cranial cavity. The skull base makes up the floor of the cranial cavity, internally. The same skull base has notable features for the attachment of muscles and ligaments when viewed from below, externally.

The neurocranium is made up of several bones, some of which are paired and others are unpaired. Paired bones include parietal, temporal, and the middle ear ossicles such as the malleus, incus, and stapes. Unpaired bones include the frontal, occipital, sphenoid, and ethmoid bones.

VISCEROCRANIUM:

The viscerocranium consists of the skull bones contributing to the facial skeleton.

The viscerocranium is also composed of several bones, some paired and others unpaired. Paired bones include the maxilla, zygomatic, nasal, lacrimal, palatine, and inferior nasal concha bones. Unpaired bones include the vomer and mandible.

Multiple bony cavities in the head open into the facial skeleton. For example, there are two cone-shaped bony chambers called orbital cavities, with their bases facing forward onto the face and their apices directed posteromedially. They are located below the frontal aspect of the cranial cavity floor. The orbits contain the eyeballs and surrounding structures, including the extra-ocular muscles.

Additionally, there are nasal cavities situated between the two orbital cavities and resting above the oral cavity. The walls of the nasal cavities are bony and cartilaginous, opening anteriorly onto the face as the anterior nasal apertures or nostrils. They communicate posteriorly with the nasopharynx through the posterior nasal apertures or choanae. The nasal cavities extend laterally as four pairs of paranasal sinuses into the bones of the cranial cavity and the facial skeleton.

Finally, the oral cavity can be found just below the nasal cavities, separated by the hard and soft palate. Anteriorly, the oral cavity opens to the exterior as the mouth, while posteriorly it connects with the oropharynx through the oropharyngeal isthmus.

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Text written by Muhammad A. Javaid, MD, PhD © 2023 IMAIOS (reviewed 2024).

  • Drake, R.L., Vogl, A.W. and Mitchell, A.W.M. (2009). ‘Chapter 8: Head and Neck’ in Gray’s anatomy for Students. (2nd ed.) Philadelphia PA 19103-2899: Elsevier, pp. 812-827.

  • Anderson, B.W., Kortz, M.W. and Al Kharazi, K.A. (2022). Anatomy, Head and Neck, Skull. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499834/


Comparative anatomy in animals

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