The human head is a complex structure. The core structure, known as the skull, is composed of 22 bones. When including other bones functionally associated with the head, the total count increases to 29. The skull is divided into two primary sections: the cranium, which encases the brain, and the facial skeleton, which forms the framework for the face.
Defining the Skull: The 22 Core Bones
The anatomical skull consists of 22 bones tightly connected by immovable joints called sutures. The only exception is the mandible, or lower jawbone, which connects to the temporal bones with a movable joint for chewing and speaking.
The skull is functionally divided into the neurocranium (braincase) and the viscerocranium (facial skeleton). The neurocranium is formed by eight bones that protect the brain. The remaining 14 bones make up the facial skeleton, supporting the eyes, nose, and mouth.
The Eight Cranial Bones
The cranium is the protective vault for the brain, consisting of eight individual bones that create a rigid, enclosed space. The eight bones include one frontal bone, one occipital bone, one sphenoid bone, and one ethmoid bone.
The remaining four bones are paired, meaning there is one on the left and one on the right side of the head. These paired bones are the two parietal bones, which form the top and upper sides of the skull. They also include the two temporal bones, located on the sides and base, housing the structures of the inner ear.
The Fourteen Facial Bones
The 14 bones of the viscerocranium provide the physical structure for the face, supporting sensory organs and enabling functions like eating and speech. This group forms the orbits for the eyes, the nasal cavity, and the upper and lower jaws.
Only two of the 14 bones are unpaired: the mandible and the vomer. The mandible is the lower jawbone, the largest and strongest bone of the face, and the only fully movable bone in the skull. The vomer is a thin bone that forms the lower and posterior part of the nasal septum.
The remaining 12 bones are paired:
- Maxillae (2): Form the upper jaw and hold the upper teeth.
- Zygomatic bones (2): Known as the cheekbones, forming the prominence of the cheeks and part of the eye orbits.
- Nasal bones (2): Form the bridge of the nose.
- Lacrimal bones (2): Help form the tear ducts.
- Palatine bones (2): Form the posterior portion of the hard palate.
- Inferior nasal conchae (2): Scroll-shaped bones within the nasal cavity that help filter and warm inhaled air.
The Appendages: Ear Ossicles and Hyoid
The total count of bones increases from 22 to 29 when including the six auditory ossicles and the single hyoid bone. These seven bones are functionally associated with the head and neck region but are not typically included in the core skull count due to their distinct locations. The auditory ossicles are the smallest bones in the human body, found in the middle ear chamber of each temporal bone.
Auditory Ossicles
There are three ossicles on each side: the malleus (hammer), the incus (anvil), and the stapes (stirrup), totaling six. Their function is to form a chain that receives sound vibrations from the eardrum, amplifies them, and transmits them to the inner ear, allowing for hearing.
Hyoid Bone
The final bone is the hyoid, a solitary, horseshoe-shaped bone situated in the neck above the larynx. It is unique because it is the only bone in the body that does not articulate directly with any other bone. Instead, it serves as an anchor for the muscles of the tongue and throat involved in swallowing and speech.