In this first section we'll look at the way the head is attached to the body, and how it moves. We'll start by looking at the bones that are involved, then we'll look at the joints and ligaments that connect them. After that we'll look at the muscles that maintain the position of the head and cause it to move.
The bones that are involved in support and movement of the head are the thoracic and cervical vertebrae, the upper ribs, the clavicles, and this part of the underside of the skull, that's called the occiput.
The skull consists of the cranium and the facial skeleton. The cranium is the bony container for the brain, and the foundation for the facial skeleton. The cranium is made up of a number of originally separate bones. These lines of fusion, known as sutures, show where the bones are joined.
The principal bones that form the cranium are the occipital bone behind and below, the parietal bone, and temporal bone on each side, the sphenoid bone, and the frontal bone.
The two bones of the cranium that we're concerned with at present are the occipital bone, and the lower part of the adjoining temporal bone.
To see the full extent of the occipital bone, we'll take the mandible out of the picture. The occipital bone extends all the way from here at the back, to here underneath. The most striking feature of the occipital bone is this large opening, the foramen magnum, through which the spinal cord and its accompanying structures pass.
The part of the occipital bone in front of the foramen magnum is called the basilar part, often referred to as the base of the occiput. The two temporal bones converge on it from each side. We'll look at them in a minute.
Let’s look at the occipital bone on the inside, in a skull that’s been divided in the mid-line. Here’s the foramen magnum, here’s the basilar part of the occipital bone. It slopes forwards and upwards, more steeply on the inside than on the underside, since it’s triangular in sagittal section.
Let’s look at some more details in a skull that hasn’t been colored.
On each side of the anterior half of the foramen magnum are the two occipital condyles. The occipital condyles are the joint surfaces which articulate with the atlas vertebra to form the atlanto-occipital joints. We'll look at these joints in a minute.
The outline of the front and the top of the cranium is well known
to us from our everyday observation of surface anatomy. It's perhaps surprising to see how far round the back of the cranium curves, and what an extensive overhang there is behind. The overhang is formed by the part of the occipital bone that's behind the foramen magnum, the squamous part.
The overhang is obscured by the neck muscles that are attached to this broad area on the occipital bone. The bone bears the marks of their attachment.
This lump in the middle is the external occipital protuberance. This faint ridge, leading out toward the mastoid process, is the superior nuchal line, below it is the inferior nuchal line. We’ll meet the structures that are attached here, later in this section.