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(2.55)

Now that we’ve seen the mandible, let’s take a look at the joint that enables it to move: the temporomandibular joint. It’s a synovial joint, with articular cartilage on the bone surfaces, and a joint capsule that encloses synovial fluid. It’s a double joint: there are two separate synovial cavities, one above the other. These are separated by an articular disk that’s flexible and highly movable. This arrangement permits two kinds of movement, as we’ll see.

Here’s what the two joint surfaces look like in the living body: they’re shaped quite differently. The articular surface of the condyle is curved sharply from front to back. It’s almost pointed on the top. The articular surface of the temporal bone has a double curve: this concave part is the mandibular fossa; this convex part is formed by the downward bulge of the articular tubercle.

Here’s the temporomandibular joint with its joint capsule intact. Most of the capsule is thin and loose, to allow the various movements that we’ll see. On the lateral aspect the capsule is thickened by this lateral ligament.

The articular disk is inside the joint here. To see it, we’ll remove part of the capsule above and above and below it. Here’s the upper joint cavity, here’s the lower one. Here between them is the articular disk. It’s made of dense fibrous tissue. It’s attached to the joint capsule all the way round its edge. Here’s the articular disk by itself: it’s thin in front, and thick behind. It’s quite flexible.

The two kinds of movement that can occur at the temporo-mandibular joint are a hinging movement and a forward and backward gliding movement. The hinging movement takes place between the condyle and the disk, the backward and forward movement takes place mainly between the disk and the ...

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(2.55)

Now that we’ve seen the mandible, let’s take a look at the joint that enables it to move: the temporomandibular joint. It’s a synovial joint, with articular cartilage on the bone surfaces, and a joint capsule that encloses synovial fluid. It’s a double joint: there are two separate synovial cavities, one above the other. These are separated by an articular disk that’s flexible and highly movable. This arrangement permits two kinds of movement, as we’ll see.

Here’s what the two joint surfaces look like in the living body: they’re shaped quite differently. The articular surface of the condyle is curved sharply from front to back. It’s almost pointed on the top. The articular surface of the temporal bone has a double curve: this concave part is the mandibular fossa; this convex part is formed by the downward bulge of the articular tubercle.

Here’s the temporomandibular joint with its joint capsule intact. Most of the capsule is thin and loose, to allow the various movements that we’ll see. On the lateral aspect the capsule is thickened by this lateral ligament.

The articular disk is inside the joint here. To see it, we’ll remove part of the capsule above and above and below it. Here’s the upper joint cavity, here’s the lower one. Here between them is the articular disk. It’s made of dense fibrous tissue. It’s attached to the joint capsule all the way round its edge. Here’s the articular disk by itself: it’s thin in front, and thick behind. It’s quite flexible.

The two kinds of movement that can occur at the temporo-mandibular joint are a hinging movement and a forward and backward gliding movement. The hinging movement takes place between the condyle and the disk, the backward and forward movement takes place mainly between the disk and the temporal surface.

The normal opening and closing of the jaw is a combination of the two movements. If you put your finger here, you can feel the condyle moving forwards as the jaw opens.

Forward movement of the body of the mandible is held in check by two ligaments that lie outside the temporomandibular joint. We’ll add these to the picture after we’ve looked at the four principal muscles that move the jaw.

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