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 hyoglossus 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 fill 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 smali 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 petroliyoids 
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 lingue ”’ 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. ‘lhe 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 of the 
problem of the respiration of the frog *, hitherto misunderstood, 
* In Arch. f. Anat. u. Physiol, Physiol. Abth, 1900, Suppl. Bd. p. 36. 
