The shot of the tongue is one of the characteristic features of all chameleons. This article explores the anatomy of the tongue and explains how the tongue shot works. We would like to point out that there are pictures of prepared hyoid legs and opened dead chameleons to be seen here.
The hyoid is the holding apparatus of the tongue, so to speak, and consists of bones and cartilage. Almost every vertebrate has a hyoid bone – including humans – but it is always differently shaped. In chameleon, the hyoid consists of the rather cartilaginous entoglossal process (3) and the two bony keratobranchial branches (1). All three meet on the so-called basihyoid, a very small spot at the entoglossal process. In front of the keratobranchial branches of the hyoid lie even smaller, soft cartilage, the keratohyal processes (2).
The entire lingual apparatus is suspended with muscles and connective tissue between the back of the head and the lower jaw of the chameleon.
Among other things, the hyoglossus muscle (4) is important for the function of the tongue. This muscle is attached to the keratobranchial processes of the hyoid (1) and leads to the lingual accelerator muscle (6). This lies around the long entoglossal process (1) of the hyoid. For a long time it was thought that the tongue shot was carried out with pure muscle power. Today we know that none of the tongue muscles can muster the necessary strength. So there must be another mechanism that enables the tongue to shoot. And there is! More than ten thin layers of collagen fibres (5) lie under the lingual accelerator muscle around the hyoid. They are responsible for almost all the force needed for the shot in the tongue. On the outside, this collagen fibre layer is connected to the lingual accelerator muscle, while at the back it is connected to the hyoglossal muscle.
The tip of the tongue is formed by the so-called tongue pad (7) and the tongue poach (8) located inside it. This table gives a rough overview of the muscles involved in the lingual apparatus of the chameleon.
The tongue shooting
Chameleon prey hunting can be divided into four phases. First the chameleon estimates the distance to the prey with its eyes, and already stores the tongue a bit in front of it.
When the tongue is presented in the mouth before the shot, the lingual accelerator muscle expands the collagen fibre layer and thus loads it with potential energy. This energy is released explosively when the shot is fired. This is the second stage of the prey catch. With an acceleration of up to 486 m/sec², the Musculus accelerator linguae, including tongue pad, shoots beyond the hyoid. In doing so, the pulled hyoglossus muscle is extended to up to 600% of its original length. Put simply, the whole thing works like a kind of catapult with an elastic band.
The extended tongue is with chameleons about one and a half body lengths long, very small species can have a tongue on even two and a half times body length. This is particularly impressive with large species such as the Parsons Chameleons: the tongue can shoot half a metre away.
At best, the tongue catches a food animal, this is the third phase. Here, chameleons make use of the so-called tongue pocket, which is formed by the genioglossus muscle and the two longitudinal linguae muscles when shot. The very viscous saliva helps to hold the prey firmly to the tongue by means of adhesion. The recoil of the “shot down” tongue, together with the hyoglossus muscle, helps to move the shot out accelerator linguae muscle and the tongue pad back into the oral cavity in the fourth phase. The tongue is relatively flaccid and the entoglossal extension of the hyoid in the mouth is clearly visible. As the tongue is retracted, the chameleon closes its eyes reflexively to prevent injury to the sensitive organs.
Depending on the species, the entire tongue shot lasts only a few tenths of a millisecond. Smaller chameleons have a larger lingual apparatus in relation to their body size and a higher acceleration when shooting the tongue than large chameleons. It is assumed that a higher shooting range can be achieved, which offers an advantage to a smaller animal in the search for food. You have to eat more than big chameleons in relation to your height.
Tongue testing behaviour
What every chameleon holder has certainly observed before is the so-called tongue test behaviour. The leisurely running chameleon shifts its tongue a bit forward, so that two small appendages become visible at the tip of the tongue. With these the animal then licks branches or leaves. This behaviour occurs more often when chameleons get to know a new environment.
The exact purpose of this behaviour is still unclear. There are assumptions that olfactory particles can be better presented to Jacobson’s organ, but the sense of smell is very limited in chameleons. However, it could be possible that sexual hormones (pheromones) can be detected with the tongue test – thus the behaviour could help in the search for partners. It would also be possible for chameleons to recognise markings made by other chameleons or predators such as snakes.
…and if the tongue doesn’t work?
In terraristics as in nature, tongue injuries sometimes occur. If there is no cure for the tongue tissue, the treating veterinarian will have to amputate a tongue in chameleons from time to time. Similarly, there is metabolic bone disease, which can lead to deformities of the hyoid and then prevent a normal shot in the tongue. In fact, chameleons manage well without their long tongues as long as they are fed by hand.