Note: These instructions are derived from the writings of John Chester, MD, made available here
When using power tools, please observe safety precautions--particularly protecting your eyes!
This is one of the easiest joints to adapt, so it also makes a great place to start. The first time you drill into the skeleton can induce a bit of anxiety, so just know going into it that you will make mistakes (I know I have). But rarely is a mistake unfixable...drill another hole. The skeleton doesn't mind. So take your time and be safe!
Adapting the skeleton
Start by gathering:
- A sharpie
- A cigarette lighter
- Two 8" segments of 3/32" bungie cord
- A dremel with a 1/8" drill bit installed
- A skull and mandible from a disarticulated skeleton
You may need to prep the skull and mandible by unscrewing any springs holding them together, and then use some pliers to rip out the rubber plug that lines each of the fossa. Now for the fun part:
Step 1: Drill holes in the jaw
Eyeball the center of the condyle and use your dremel to tunnel through the center as shown in this picture..
Step 2: Mark holes for the skull
Turn the skull upside down (easier when you remove the top part). Set the jaw in place and visualize a route that passes through the holes you drilled in Step 1 and into either side of the fossa. Mark those pass-through points with the sharpie.
Step 3: Drill holes for the skull
Drill through the sharpie marks to create a path for the bungee cord.
Step 5: Bind it together
Secure the mandible to the skull with the two pieces of bungee cord. Play with various levels of tension to get the amount of play that you like. Tie a good square knot, dab some superglue on it, trim the excess bungee and singe the ends of the cord with the cigarette lighter to keep them from getting frayed. Congrats, you are done!
Comparison with the Real Deal
There are a few basic movements that we should be able to duplicate:
- Protrusion/Retrusion - the condyle slides forward and down causing the chin to protrude
- Elevation/Depression - while protruded, the jaw pivots at the condyles and the mouth opens
- Lateral movements - one condyle remains retruded while the other protrudes. It results in a lateral movement as seen in chewing
Check the video below for a demonstration of these actions.
For comparison you can observe the typical skeletal model which fixes the jaw in place with a rigid piece of plastic. Just a couple pieces of flexible string lead to something much more valuable as a tool for understanding movement.
Next, move on to assembling the pelvis and hips.
Anatomical Sketch: Henry Vandyke Carter [Public domain], via Wikimedia Commons