Anatomy of the tongue
The horse has a set of bones referred to as the hyoid. These small bones make-up a similar shape to the jaw bone.
Pronunciation of names:
lingual process (lin-gu-al pro-cess)
sternocephalic m. (ster-no-ce-pha-lic)
cutaneous colli m. (cu-ta-ne-ous co-lli)
There are several bony attachments to the hyoid but the one most concerning the tongue is a bony spine called the lingual process, which is embedded and attached at the root of the tongue. The hyoid also has attachments at the occipital bone of the horses poll and at the temporal bone on the sides of the head. There is a group of muscles that attach to the hyoid bones, some of these muscles are the omohyoid m., sternohyoid m., thyrohyoid m., and the stylohyiud m. Superficial muscles in this area of the neck are the sternocephalic m. and the cutaneous colli m. visible when the horse moves.
Sensitivity of the mouth
The mouth is a sensitive part of the horse, in addition to body language and, energy, it is our way of communicating subtle cues to him while riding and training. A horse with a tens mouth inevitably has tension throughout his body particularly in his poll and down his back to his tail. Horse’s experiencing mouth pain will often clamp the tail tight to the body, raise the head to avoid the pain, be hard in the mouth and/or bolt. Others may clamp the mouth shut, or pull the tongue over the bit for relief. Harsh bits such as the twisted wire, barmouth, waterford, cherry roller, and some bits with a medium to high port etc. will cause discomfort for the horse simply because of their design. The other factor is your personal sensitivity to your horse's mouth through your hands and your seat. If you are not aware of how you are affecting your horse, and at the same time using such bits, your horse is experiencing mouth pain and tension.
Now ask yourself how sensitive are you with your hands when your horse does not respond to your requests. Do you tend to pull back rather than give? Do you ride with tight fists? Are your fingers, elbows, and shoulders free or stiff? These are just a few questions one should ask and improve on to help the horse find more comfort and confidence with you.
To ensure your bit fits your horse’s mouth check the height of his palate and the shape of his tongue. Each horse is different but most find comfort and relaxation with a simple french link snaffle. This is because the french link takes the shape of the tongue and allows sufficient movement to prevent the metal from banging around the mouth.