Hyoid Apparatus

With recent interest in the hyoid apparatus, I would like to share what I have learned in my research and numerous dissections in relationship to the hyoid apparatus and bitting.

The hyoid apparatus suspends the tongue and the larynx in the floor of the throat. This includes a collection of five bones. The two long bones (stylohyoid) attaching on the upper end to the base of the temporal bone and on the bottom to the two short bones (ceratohyoid). Then at the bottom, the ceratohyoid connects to the basihyoid. The basihyoid is in the shape of a wishbone, the two ends attaching to the ceratohyoid and the single prong (lingual process) extends into the root of the tongue.

There are muscle connections that connect the hyoid apparatus to the occipital bone (occipital hyoid muscle) and to the tongue (styloglossal muscle) and to the shoulder (omohyoid muscle) and to the sternum (sternohyoid muscle).

There are also a couple main neurological connections. The hypoglossal nerve XII starts at the base of the brain, ending at the base and underside of the tongue, controlling one-third of the caudal portion of the tongue. Also the trigeminal nerve V, one branch of this nerve, the mandibular, controls two-thirds of the rostral portion of the tongue.

Due to the position of the hyoid bones, they are very protected on the sides by the jawbone, but may be more vulnerable straight up from the bottom, between the jaw bones.

The hyoid apparatus is important to how the bit sits on the tongue, because the basi hyoid is shaped like a spur with the rowel pointing forward. The branches on the other end should be level from side to side. If there is tension or clinical changes further up the chain of bones, the tongue will lay unbalanced on the floor of the mouth.

If the bit you have chosen is sending most of the messages to the tongue, and the tongue is unlevel, there may not be an even sensation. You may want to try a bit that is going to communicate to the bars and leave the tongue to move freely under the port. The only way to know is to use trial and error to find the best option.

Due to attachment of the hyoid apparatus to the temporal bones (base of the ear), this will influence the horse’s balance. The horse uses the ears and pelvis as a balance point so if there is uneven tension on the ears it will disrupt the horse’s balance.

For the past 15 years I have been including these findings in all my lectures and educational discussions I have with riders, communicating the importance of balance throughout the horse’s body. Any time you have an imbalance, there will be some type of compensation in the body. The unbalanced tension in any paired bone or muscle is not about the amount of pressure, as it can be a minuet amount of tension over an extended period that creates the compensation.

Understanding balance in all parts ofthe body, including muscles, bones, breathing, blood flow, gut flora, neurological systems, etc. is what allows the body to maintain itself at a healthier level.

All the explanations above are at a basic level, as there are so many connections that can only be learned through studying equine anatomy. There are good anatomy coloring books available that will allow you to learn proper anatomy. We recommend The Horse Anatomy Work Book by Maggie Raynor.

The more you understand anatomy the more you will realize how quickly all the parts of the body communicate with one another. You cannot affect one body part or system without affecting another system or part instantly.

In future educational sessions we will cover the involvement of the hyoid apparatus in more detail and its effects on bits and bitting.