502 On tlie 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 piiysiology 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 

 cocca-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 lingute " muscle. 

 In retraction the intiinsic 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 

 ao-ainst 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 

 sluo-gish protrusion of the foot in Lamellibianchs, 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. 



