The mechanism of the protrusion of the tongue of the anura [electronic resource] : preliminary note

From the A.nnai<s and Maoazink of Natural History,
Ser. 7, Vol. vii., June 1901.

77ie Mechanism of the Protrusion of the Tongue of the Anura.
— Preliminary Note. By Prof. Marcus Hartog3 M.A.,
D.Sc, F.L.S .*

For an explanation of the mechanism whereby the Anurous
Batrachia protrude and reverse their tongue one may seek in

* Translated by the Author and slightly modified. From the ' Oomptea
Rendu* de l'AcadSmie des Sciences,' March 4, 1901.

502 On the Protrusion of the Tongue of the Anura.

vain in general textbooks of zoology and in special mono-
graphs. Almost all authors have been content to repeat
after Fixsen that the genioglossus muscles are the " pro-
tractors " and the liyoglossus muscles the " retractors," though
the frog has served as the object for the initiation of the
student into the problems of anatomy and physiology for over
forty years. As my own annual course begins with the study
of the frog, this gap in our knowledge had long preoccupied
me. A very simple experiment has sufficed to till this gap
and to demonstrate how the frog throws forth its tongue and
turns it through an angle of 180°.

If we expose the tongue by removing the upper jaw and
front of the skull (cutting straight across behind the eyes
with a pair of stout scissors), remove the skin of the lower
jaw, and then inject air or -liquid through a small hole in the
mylohyoid (mandibular) muscle, the tongue rises up and
springs forward, especially if, at the same time, we draw
forward the hyoid bone. Again, if we inject with melted
cocoa-butter coloured with carmine or alkanet, and keep up the
pressure till the mass sets, we find that it fills an enormous
lymph-sac between the muscle and the body of the hyoid,
extending .through a median intermuscular fissure into the
tongue itself, sending branches between the fan-shaped rami-
fication of the intrinsic muscles at the edges of the tongue
and into its terminal dilatations.

The whole mechanism is now obvious. The petrohyoids
raise the hyoid bone and commence its protraction, an action
continued by the geniohyoids. The genioglossi and hyoglossi
may co-operate to some extent at first, shortening the tongue,
and so expanding its cavity ; but it is the mylohyoid which
by its contraction expels the lymph of the subhyoid space
into the tongue, and is the true " protrusor lingua? " muscle.
In retraction the intrinsic muscles pull the tip of the tongue
backwards, and the median portion of the genioglossi espe-
cially pull its base downwards and inwards. The sterno-
hyoids and omohyoids retract the body of the hyoid bone,
with its attachments to the tongue, and the closure of the
mouth by the levators of the mandible presses the tongue
against the roof of the mouth, and so expels the lymph from
its cavity. Clearly this sudden propulsion of the tongue of
the Anura is an erection, and is thus comparable with the
sluggish protrusion of the foot in Lamellibranchs, also too often
miscalled a " protraction."

Silvestro Baglioni, in his recent remarkable solution ot the
problem of the respiration of the frog *, hitherto misunderstood,
* In Arch. f. Anat. u. Physiol., Physiol. Abth. 1900,Suppl. Bd. p. 3(3.

On the Protrusion of the Tongue of the Anura. 503

has noted that during the contraction of the mylohyoid the
tongue " wird nach vorn und oben gezogen." For the further
development of this movement into the protrusion of the
tongue all that is required is the further simultaneous advance
of the hyoid bone and a more complete contraction of the
mylohyoid muscle.

I propose completing this study with a detailed account of
the dissection of the structures involved, for which I am
awaiting the supply of larger objects than the common grass-
frog, which is alone at my disposal at Cork.