The Role of the Tongue and Hyoid in Equine Movement

Have you found during your work that dysfunction or asymmetry in the jaw is reflected in the shoulder and again in the pelvis? That when the sacroiliac is out, so is the jaw? Today, we pick apart one anatomical aspect of this connection and reflect on how the tongue and the hyoid bone affect the entire body.

Join me as we discuss the intricate anatomy of this bone, its direct muscular connections, the indirect connections, and how exactly a dysfunction or asymmetry of the hyoid can affect the movement of the poll, forelimbs and hindlimbs and, of course, all the puzzle pieces in between.

Let’s dive right into the anatomy of the tongue and the hyoid.

Anatomy of the Equine Hyoid:

The hyoid bone serves as the attachment for the tongue and pharynx, and is made up of paired stylohyoid, epihyoid, ceratohyoid and thyrohyoid bones, with a central basihyoid bone.  The central basihyoid bone supports the lingual process, to which the tongue is attached. The stylohyoid articulates with the temporal bone and allows cranial and caudal movement, somewhat like a pendulum. The base of the tongue is attached to the lingual process, the soft palate and pharynx.

Multiple muscles attach to the hyoid bone and can alter its position and shape.

The primary movement muscles are the omohyoideus, sternohyoideus and sternothyroideus.

• The sternothyroideus originates on the sternum and inserts on the thyroid cartilage.
• The sternohyoideus originates on the sternum and inserts on the basihyoid bone.
• The omohyoideus originates on the subscapular fascia near the shoulder joint and inserts on the basihyoid bone.

These three, however, are not the only muscles involved:

• The thyrohyoideus attaches to the lateral surface of the thyroid cartilage and inserts on the thyrohyoid bone, moving the hyoid bone caudally.
• The geniohyoideus moves the hyoid rostally.
• The genioglossus protracts the tongue.
• The styloglossus retracts the tongue.
• The occipitohyoid connects the hyoid bone to the occiput

Then there are:

• The mylohyoid
• The hyoglossus and
• The cricopharyngeal

So what are the connections?

Consider the sternohyoideus and sternothyroideus muscles; they directly connect the horse’s tongue and mouth to the chest of the horse. This fascial and muscular connection carries on through the pectoral muscles along the ventral aspect of the horse, along the abdominal muscles and into the pelvis.

The omohyoideus muscle connects to the fascia medial to the shoulder joint, linking into the ventral fascial chain that runs from the head, along the ventral aspect of the neck, medial to the shoulder and all the way to the toe on the hindlimb.

This gives a new depth of understanding to the term ‘riding from your leg to your hand’, and the connection between your leg aid and the activity of the hindlimb. In addition, the occipitohyoid muscle connects the hyoid to the poll, creating a direct chain from the shoulder through the hyoid to the poll, and from there through the nuchal ligament and the dorsal fascial line back to the hindquarter, creating a dynamic, connected chain.

The hyoid also plays an essential role in the horse’s ability to breath optimally, as movement of the hyoid has a direct impact on the suspended pharynx.

The tongue, hyoid and attaching muscles form a part of the deep ventral fascia line. This fascial line follows three pathways from the hindlimb to the head and encapsulate the thoracic and abdominal cavities and their organs, as well as the central nervous system, the deep ventral musculature of the spine and pelvis, and more. This fascial line creates a close connection between these deep structures of the body, including the pathway of the vagosympathetic trunk.

How is movement impacted?

We’ve established that the hyoid is connected not only directly to the tongue, forelimb and poll but also indirectly to the hindquarter. Therefore a restriction, pain or any dysfunction in the hyoid may have a direct impact on the mobility of the forelimb, leading to a possibly shortened or stilted gait. This can be transferred to the hindquarters as an inability to engage the hindlimbs.

So we see that the hyoid and the tongue affect the movement of the head, poll and jaw, and also of the forelimb. Indirectly it connects to the hindlimb as well, through muscular chains and the fascia. We can expect to see many areas affected by dysfunction in the hyoid bone, including the ability to perform lateral movement, the range of motion of the cervical spine, tension in the ventral muscles of the neck (and a tendency for the horse to go behind the bit to relieve that tension), a potentially hollow back and a shortened, stilted stride.

What can affect the hyoid bone?

Although the hyoid bone is in a protected area within the horse’s mouth, it is a delicate structure and can be injured, misaligned or even fractured. A bit and bridle that causes restriction of the tongue will restrict the movement of the hyoid and associated muscles, causing pain and tension in these muscle groups, affecting the whole myofascial chain and resulting in changes in movement. Practices where the tongue is handled can lead to a potential unbalancing of the hyoid or, in worst-case scenarios, a fracture of the hyoid bone. Luckily the balance of the hyoid can easily be appreciated from the bottom of the jaw, as well as from the symmetry of the supraorbital fossa. Dysfunction or asymmetry of the temporo-mandibular joint can impact the hyoid, and vice versa, and signs may be closely associated with each other.

Conclusion

And so we see that a small, seemingly insignificant bone suspended inside the jaw can have a massive effect on the whole body movement of our equine patients. Isn’t that so often the case? The smallest component of a picture may have a massive impact on the whole.

If I have missed any information here, or you would like to add something, please feel free to comment with your knowledge, thoughts and theories. I would love to get feedback from you.

Resources

If you would like to dive more deeply into the connections in the equine body from a theoretical and a treatment perspective, I highly recommend the following lectures in the Equine Members Portal:

1. Everything Fascia, a four part series by Tuulia Luomala
2. The Two T’s: The TM joint and the Tail by Marinette Teeling
3. Assessment and treatment of the SIJ by Lesley Goff
4. Fascinating Fascia by Marta Kulikowska