Biology 128 – the skull and a study of joints (arthrology)

Bones of the Skull:

- Back side and bottom = Occipital bone,

- Sides = Parietal Bones

- In Front over Eyes – Frontal Bone

- Bones below parietals that include the ear openings – Temporal bones

- Cheekbones = Zygomatic bones

- Face bones = mostly the Maxillary bones

- Bridge of nose between orbits = Nasal bones

- Movable Jaw bone = Mandible

- In nasal aperture the middle bone = Vomer

- On sides of nasal aperture = Inferior nasal conchal bones

- Back of the orbits = Sphenoid bone

- One bone between the eyes – forms medial side of each orbit = Ethmoid bone

- Bones just behind spur of the maxilla bone and the Nasal bones with a groove in it are the Lacrimal bones

- Back part of the roof of the mouth are the Palatine bones

In the ear are a set of tiny bones that form a linkage between the eardrum and the auditory sensing organ of the inner ear. These bones (only seen embedded in plastic) are the malleus, incus, and stapes.

All of which brings us to the subject of joints that hold the skeleton together ...

Joints that should not move very much –

- Suture joints – Look at the jagged junctions between cranial bones (there are 4 subtypes of sutures, some of which are very strong and rigid.

- Syndesmoses – think of the sacroiliac joint that only moves in late pregnancy – or between the upper part of the two leg bones – the Tibia and Fibula

- Gomphoses – the little plug-in joints between teeth and jaws (a special form of syndesmoses)

Joints that move a little, and are supposed to:

- Synarthroses – joined by stiff cartilage – like ribs to sternum – they allow you to breathe

- Symphyses – joined by fibrous cartilage – like the intervertebral disks

Joints that should move fairly easily:

- Synovial Joints – usually have slippery cartilage and fluids in the joints. Most of the time, the bones would fall apart if it were not for the ligaments that hold the bones together, but (usually) are outside the joints. Synovial joints differ according to how many directions of movement are allowed at that joint. – the more movement, the weaker the joint (usually) and the more muscles are needed to stabilize the joint.

o One direction of movement

§ Hinge joints – like the elbow, or your fingers –flexion and extension is about all

§ Pivot joints – the top two cervical vertebrae let you turn your head – or, the radius and ulna when you rotate your hand from front to palm facing backward (pronation)

o Two directions of movement

§ Saddle joints – the base of the thumb

o Ellipsoidal joints – try the wrist or the ankle – flexion and extension, abduction and adduction and a movement called circumduction too (this is also true for the saddle joints)

o Many directions of movement

§ Planar joints – little flat surfaces that let bones slip over each other in just about any direction – the carpals slip a little against each other, and so to the facets between vertebrae

§ Ball-and-socket joints – humerus toshoulder or hip to femur. Can do just about any movement from flexion to extension, abduction and adduction, and, rotation around the long axis of the leg.