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4.4.5 Muscles of mastication: temporalis and masseter

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(3.35)

Before adding the next muscle, the temporalis, to the picture we’ll put the coronoid process back in place, since that’s where the temporalis inserts.

Here’s temporalis, the largest of the muscles of mastication. It’s shaped like a fan. The temporalis arises from the wide area on the side of the skull that lies within the temporal line.

The fibers of temporalis converge from above, and from behind, on the coronoid process. They insert insert on the outer aspect, and the inner aspect of the coronoid process, and also here on the anterior part of the ramus of the mandible.

Now we’ll put the zygomatic arch back into the picture. The temporalis muscle lies inside the zygomatic arch. Near its insertion the temporalis is a thick muscle. It occupies the whole of the infratemporal fossa.

The temporalis muscle is covered over by this dense layer of deep temporal fascia. The fascia is attached to bone along the zygomatic arch, and all the way round the temporal line.

Lastly we’ll add the masseter muscle to the picture. Here’s the masseter. It’s a thick, powerful muscle. The masseter arises from the anterior two thirds of the lower border of the zygomatic arch on its outer aspect, and from the whole length of the arch on its inner aspect.

The fibers of the masseter muscle that arise on the outside run downwards and backwards, those on the inside run straight downwards. The masseter inserts into this wide area on the angle and ramus of the mandible. The masseter muscle on the outside, and the medial pterygoid muscle on the inside, converge on the angle of the mandible in very similar ways.

Now let’s take a look at the actions of the muscles that we’ve just seen. The action of closing the jaw is ...

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(3.35)

Before adding the next muscle, the temporalis, to the picture we’ll put the coronoid process back in place, since that’s where the temporalis inserts.

Here’s temporalis, the largest of the muscles of mastication. It’s shaped like a fan. The temporalis arises from the wide area on the side of the skull that lies within the temporal line.

The fibers of temporalis converge from above, and from behind, on the coronoid process. They insert insert on the outer aspect, and the inner aspect of the coronoid process, and also here on the anterior part of the ramus of the mandible.

Now we’ll put the zygomatic arch back into the picture. The temporalis muscle lies inside the zygomatic arch. Near its insertion the temporalis is a thick muscle. It occupies the whole of the infratemporal fossa.

The temporalis muscle is covered over by this dense layer of deep temporal fascia. The fascia is attached to bone along the zygomatic arch, and all the way round the temporal line.

Lastly we’ll add the masseter muscle to the picture. Here’s the masseter. It’s a thick, powerful muscle. The masseter arises from the anterior two thirds of the lower border of the zygomatic arch on its outer aspect, and from the whole length of the arch on its inner aspect.

The fibers of the masseter muscle that arise on the outside run downwards and backwards, those on the inside run straight downwards. The masseter inserts into this wide area on the angle and ramus of the mandible. The masseter muscle on the outside, and the medial pterygoid muscle on the inside, converge on the angle of the mandible in very similar ways.

Now let’s take a look at the actions of the muscles that we’ve just seen. The action of closing the jaw is performed by the upward pull of the temporalis, the masseter, and and the medial pterygoid muscles.

Opening of the jaw is brought about partly by the force of gravity, partly by the forward pull of the lateral pterygoid muscles, and partly by the backward and downward pull of muscles we’ll see in a minute, that act by way of the hyoid bone.

We've not yet seen the two accessory ligaments that restrain forward movement of the mandible. These are the stylomandibular ligament and the sphenomandibular ligament. The stylomandibular ligament goes from the styloid process, to the angle of the mandible. The sphenomandibular ligament goes from this small projection, the spine of the sphenoid, to the lingula.

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