438 ANATOMY OF VERTEBRATES. 



draw forward the basihyal upon the ends of the ceratohyals, h, 

 which are steadied by the slender muscles ' ceratomandibularis/j^ 

 and ' ceratosternalis,' h : so that the inverted bony arch, from 

 being vertical, as at A, k, is made horizontal, as at u, h ; the basi- 

 liyal being brought forward about an inch, and with a force and 

 precision, due to the fixation of the ceratohyal tips, by their guy- 

 rope-like muscles, /"and h, which adds greatly to the propelling- 

 force. This force, added to, and acting consentaneously Avith, the 

 elongation of the annulose part of the tongue, b, a and B, jerks 

 out the swollen prehensile end of the tongue to the full extent 

 allowed by its elastic yielding tissue, which, on the cessation of 

 the muscular actions and their momentum, retracts the bulb ; and 

 the drawing back of the tongue is effected by the contraction of 

 the glossohyoidei, and of the elastic cellular tissue, readjusting 

 the sheath upon the glossohyal : also by the retraction of the hyoid, 

 through the sternohyoids muscles, fig. 297, A, C, g. These are 

 assisted by the omohyoidei, ib. a, i ; and the actions of e and g are 

 made more effective by the cooperation of f and It, in steadying 

 the points of the inverted arch upon which the swinging move- 

 ments to and fro of the basi- and glosso-hyals take place. The 

 mechanism and forces of the extension and contraction of the 

 Chameleon's tongue are essentially the same as those of the 

 tongue in Toads and Geckos, among which those species can 

 most elongate the organ, when the hyoid muscles jerk it out of 

 the mouth, which have the greatest proportion of ' linguales ' fibres 

 arranged so as to contract its breadth. 1 



The styliform glossohyal, besides supporting the retracted 

 tongue and increasing the force of the constricting ' linguales ' 

 fibres, enables aim to be taken at the object to be reached. The 

 Chameleon, having discerned its prey, brings its head into position, 

 opens the mouth to the extent required for the tongue's passage : 

 then, steadying the apparatus 'by a sort of tremulous rigid 

 movement,' shoots out the tongue, and retracts it with the fly, 

 the velocity of the action being such as to ' startle one afresh 

 every time it is witnessed." 2 



The tongue of the Crocodile, fig. 298, c, is slightly raised by 

 its fleshy portion above the level of the membranous floor of the 



1 The explanation above given agrees in essentials with that proposed by Hunter 

 (xx. vol. iii. p. 68), and Cuvier (xu. ed. 1, torn. iii. p. 273) ; other hypotheses are 

 cited in ccxxxix. torn. vi. p. 76, and ccxl. vol. iv. p. 1147. 



2 ccxl. p. 1150. The whole of Dr. Salter's excellent article is well worth careful 

 study. A previous dissection of a Gecko's tongue, after maceration, as the Chame- 

 leon's ought to be, in alcohol, facilitates the recognition of the circular arrangement 

 of non-striped ' linguales ' fibres, described by Hunter and Cuvier. 



