(2.56)

The muscles that form the bulk of the tongue are intrinsic muscles, which run from one part of the tongue to another, and extrinsic muscles, which are attached to bone. There are three extrinsic muscles on each side. Of these the two largest, which we’ll see now, are hyoglossus, and genioglossus. The other one, stylo-glossus we’ll see later.

To get a view of the major extrinsic muscles we’ll divide the mandible along this line and remove the ramus, and the alveolar process. We’ll also remove all of the mucous membrane, from this line downwards.

Here are the hyoglossus, and genioglossus muscles, which together form the root of the tongue. To see the full extent of genioglossus, we’ll remove hyoglossus for a moment. All this is genioglossus. Genioglossus arises just above the genio-hyoid, from the upper part of the mental spine.

Its fibers fan out, the highest ones arching forward almost to the tip of the tongue, the lowest ones running straight backward to the most posterior part of the tongue. Genioglossus compacts the tongue, and pulls it forwards.

Now we’ll put hyoglossus back in the picture. Hyoglossus is a thin, flat sheet of muscle. Its fibers run upwards and forwards. Hyoglossus arises from the whole length of the greater horn of the hyoid bone (here’s the greater horn) and ends here, along the side of the tongue. Hyoglossus flattens the tongue, and pulls it backwards and downwards.

Here alongside hyoglossus is the third extrinsic tongue muscle, styloglossus, coming in from behind. We’ll see it later. Here’s the mylohyoid muscle, seen from behind.

The space between the mylohyoid and hyoglossus muscles is the pathway for the nerves to the tongue, and the submandibular duct, as we'll see in the next tape.

The intrinsic muscles of the tongue, which we won’t look at in detail, run both longitudinally and transversely, above and between the extrinsic muscles. They’re responsible for many of the fine movements that are involved in handling food, and in speech.

We’ve looked at a lot of muscles in this section: the muscles of mastication, the muscles of the hyoid bone, and the extrinsic tongue muscles. Later in this section, when we look at the salivary glands, and at the pharynx, we’ll have a chance to see how all the muscles fit together, that we’ve seen up to now.