The atlas is the first of the seven cervical vertebrae, and is called such because it bears the direct weight of the skull, just as the mythical Greek hero Atlas bore the world on his shoulders.  The atlas vertebra meets with the occipital condyles which flank the foramen magnum in the basilar part of the occipital bone of the skull.  This junction forms the atlanto-occipital joint, and is responsible for the primary articulation between the spine and the skull.  It is the only vertebra in the spine which has no vertebral body.  The atlas vertebra, in turn rests upon the axis vertebra, which is the second of the cervical vertebra in the spine, with the articulation between these two vertebra occurring at lateral articular surfaces and an unique juncture between a concave facet (on the atlas) and an upward-protruding structure on the axis called a dens.

The axis is the second of the seven cervical vertebrae, and is called such because it allows axial (rotational) movement of the skull.  The axis lies directly beneath the atlas vertebra, their junction occurring at lateral articular surfaces and an unique juncture between a concave facet (on the atlas) and an upward-protruding dens (on the axis).  This articulation is regulated by the alar ligament, which attaches to both atlas and axis.

Skull
The skull is one of the principle groups of bones in the human anatomy.  The skull consists of twenty-six bones: eight bones form the cranium, which houses the brain and ear ossicles, plus fourteen facial bones, which form the front of the face, jaw, nose, orbits, and the roof of the mouth, three more bones make up the inner ear ossicles, and one more, the hyoid bone, is in the neck and is attached to the temporal bone by ligaments.  The bones of the skull include the frontal bone (which makes up the forehead and roof of the orbits), the occipital bone (which forms the back and base of the skull), two parietal bones (which form the roof and upper sides of the skull), and two temporal bones (which form the lower sides of the skull and house the inner ear ossicles).  The lower rearmost part of each temporal bone is called the mastoid process, but because it is separated from the temporal bone, proper, by a suture, it is often considered a separate bone.  The sphenoid bone forms the central base of the skull and spans the skull from side to side, the greater wings forming side plates of the skull.

The occipital bone forms the back of the skull and the cranial base.  It is joined to the two parietal bones and to the mastoid processes of the temporal bones on the side by the lambdoid suture.  At the base of the occipital bone, at the basilar parts, the occipital bone is attached to the sphenoid bone.  The occipital bone features a significant bump, or external occipital protuberance, in the center of the back of the skull, while the Nuchal line (a low, bony ridge) defines the cusp at which the occipital bone curves under to the base.  The large opening, or foramen magnum, in the occipital bone can be seen in the inferior view of the skull, and allows the nerves of the upper spinal cord to pass through the skull between the brain and the rest of the spinal cord.

The sections of the ethmoid bone are positioned between the orbits, forming the walls and roof of the nasal cavity, while the three middle ear ossicles (stapes, malleus, and incus) are located within the temporal bones on each side of the skull.  The U-shaped hyoid bone is found in the neck, and is attached by ligaments to the temporal bones.  In the face, the two maxillary bones form much of the orbits, nose, upper jaw and roof of the mouth, while the malar (zygomatic) bones form the cheeks.  The lachrymal bones are located on the inner sides of the orbits and are attached to the ethmoid and maxillary bones.  Within the nasal cavity, the vomer is located in the low center and forms the thin flat bone of the nasal septum, while two inferior urbinates form the lower sides of the cavity and two palate bones form the floor of the nasal cavity as well as the roof of the mouth.  The mandible is the only movable part of the skull, forming the lower jaw and mounting the teeth.

The bones of the skull, with the exception of the mandible, are held together by very thin sutures, or seams, in which the periosteum of the individual bones interweave with each other, and are cemented by a fibrous, connective tissue.  In the newborn, these sutures are not yet developed, with the bones being attached by cartilage which ossifies over time as the bones of the skull fuse together.  The most evident external sutures of the cranium include the coronal suture, joining the frontal and parietal bones, the sagittal suture, joining the parietal bones to each other, the lambdoid suture, joining the occipital and parietal bones, the squamous suture, joining the temporal and sphenoid bones to the parietal bone on each side of the skull.  The pterion is the short segment of the suture joining the squamous and parietal bones.

The bones of the skull also feature a number of sinuses (cavities) and foramina (the plural of foramen, meaning hole or opening).  Four pairs of sinuses flank the nasal cavity (and are therefore called paranasal sinuses).  Two are found in the maxillary bone, and are called maxillary sinuses.  The sphenoid bone forms two paranasal sinuses called the sphenoids, and the ethmoid bone forms the two paranasal sinuses called ethmoids.  Additionally, the frontal sinuses are located in the frontal bone just behind the roof of each orbit.  The foramen magnum is a large, round opening in the base of the skull which admits the spinal cord, while at the base of each temporal bone is the external auditory meatus, which serve as the auditory canals.  Just above each orbit in the frontal bone is a small notch or hole, called a supraorbital foramen, and just below each orbit, in the maxillary bone, is an infraorbital foramen.  Two more openings, one on each side of the skull, can be found in the frontal processes of the malar (zygomatic) bones, and are called, therefore, zygomatofacial foramina.  On each side of the mandible, just below the lower canines, are the mental foramina.  These facial foramina serve to admit blood vessels and nerves through and into the bones.

The bones of the skull feature a number of foramina (the plural of foramen, meaning hole or opening).  The foramen magnum is the largest of these.  It is a round opening in the occipital bone at the base of the skull which allows the nerves of the upper spinal cord to pass through the skull.  The next largest openings are the external auditory meati, which are tunnels through the temporal bones for the auditory canals.  Other foramina include the supraorbital notches above each orbit in the frontal bone (supraorbital foramina), and the infraorbital foramina just below each orbit in the maxilla.  Two more openings, one on each side of the skull, can be found in the frontal processes of the malar (zygomatic) bones, and are called, therefore, zygomaticofacial foramina.  On each side of the mandible, just below the lower canines, are the mental foramina.  These facial foramina allow blood vessels and nerves to pass into and through the bone.

The teeth are mounted in the maxillary bone and the mandible, and are brought together for chewing by the hinge-like motion of the mandible (the lower jawbone). An average adult will have thirty-two teeth, evenly arrayed on the maxilla and mandible.

Marked differences may be noted in the newborn skull as compared to that of an adult.  The newborn skull comprises much more of the percentage of the body than in the adult human.  Additionally, the newborn's skull has no teeth erupted (grown out of the maxilla or mandible), as has the typical adult.  Because of this, the dental arcade, with the jawbone and palate, form a smaller percentage of the overall skull size than in the adult skull.  Furthermore, the newborn skull's bones are not rigidly sutured together, but are connected instead by flexible, cartilaginous membranes, called fontanelles.  These fontanelles allow the bones of the newborn's skull to deform somewhat during birth, facilitating passage through the birth canal.  The bones become sutured typically within the first year after birth.

In the newborn skull, the frontal bone and parietal bones are not yet solidly sutured.  Between these bones is located a cartilaginous membrane, called the anterior fontanelle.  In the newborn, this cartilage is still quite flexible, and the pulse may be seen on the surface of the head at this site.  The anterior fontanelle does not close completely, forming the intersection between the coronal and sagittal sutures, until the second year of life.

The parietal bones form the two sides and much of the top of the newborn skull.  The parietal bones of the neworn each feature a bulbous tuberosity.  This tuberosity gives the newborn skull a distinct bulge in the superior (top-down) view.  As the newborn grows, the skull wil begin to lose this tuberosity and the parietal bones will become more even on the sides of the skull.

The coronal suture passes laterally over the top of the skull and joins the frontal bone with the two parietal bones.  Its name derives from the Latin word "corona," which means "crown."

IAP: anterior
IAP: posterior
IAP: lateral
 

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