assist the capture and swallowing of food but not 

 breathing. The mechanism of action of this sys- 

 tem is based on rotation of the hyoidal arch in 

 the sagittal plane. We were able to show that 

 the mechanism for depressing the floor of the 

 oro-pharyngeal cavity derives from the buccal ' 

 pump and this is also true for the mechanism of 

 raising the floor of the oro-pharyngeal cavity. 

 Consequently, the mechanism for respiratory 

 motions in the ancestors of the terrestrial 

 vertebrate was transformed into a mechanism for 

 the capture of food by the larvae of Urodela. 

 This conditioned a high degree of homology of the 

 hyobranchial apparatus in fish and the larvae of 

 tailed Amphibia. Nonetheless, it was mainly the 

 loss of the breathing function that determined 

 the major sequential transformations of the hyo- 

 branchial apparatus, as shown both in a compari- 

 son of the larvae of Urodela with fishes as well 

 as in comparisons of the larvae of the investi- 

 gated species one with another. Already in 

 Rhipidistia the reduction of the dorsal regions 

 of the gill arches (pharyngeal and ep i branch ial) 

 is connected with the transition to pulmonary 

 respiration (Schmalhausen, 1°;64) and this re- 

 duction in the larvae of Urodela is supplemented 

 by a reduction of ventral elements. In all of 

 them the fifth arch has completely disappeared 

 (in the Proteidae, the IV arch as well) and 

 the hypo-element of the IV arch also disappears, 

 the hypo-elements of the I I I arch are reduced 

 (a rudiment of the hypobranch iale III is found 

 only in the larvae of Hynobiidae and Crypto- 

 branchidae) and even II (in Proteidae). This 

 process led to the disappearance of the postei — 

 ior gill slits. In the larvae of Urodela there 

 are three slits which are situated between I 

 and II, II and III, III and IV ceratobranch ial ia 

 (in the Proteidae two slits remain between I and 

 II, and II and III). Thus the most posterior 

 gill arch in the fish which is located between 

 the IVth and Vth arches (in the Proteidae the 

 preceeding one as well) and the most forward 

 slits between the hyoid and the first gill arch 

 are reduced. The position of this arch is 

 occupied by the ceratohyo i deus ex ter i or as a 

 homolog to the M. opercular i s in fishes. 



The reduction of the hyobranchial apparatus 

 occurs together with several changes associated 

 with the perfection of the mechanism for the 

 capture of food. First of these was a modifica- 

 tion of the movement most responsible for this. 

 process, namely the depression of the floor of 

 the oro-pharyngeal cavity. The union of the 

 urohyale and bas i branch iale from independent 

 elements of the hyobranchial skeleton in the 

 Rhipidistia to a single copula in the larvae of 

 Urodela facilitated a better transmission of the 

 action of Mm. sterno - and qeneohyo i de i to the 

 hyoidal arch. The transformation of the M. 

 opercular i s into the M. ceratohyo ideus exterior 

 and the associated appearance of comm i ssurae 

 term inal i s in the larvae of Urodela created a 

 possibility for depressing the posterior part of 

 the floor of the oro-pharyngeal tract. 



The mechanism for lifting the floor of 

 the oro-pharyngeal cavity remained virtually 

 unchanged; apparently the speed with which 

 water is expelled through the gill slits does 

 not have great biological significance, since 

 the capture of food is not determined by this. 

 The perfection of the mechanism for closing 

 the gill slits during the capture of food is 

 connected with the differentiation of M. 

 subarculari.s .r^ct. IV. In the larvae of 

 Hynobiidae, this muscle has one concavity which 

 extends from the fourth to the first gill arch 

 and it is thus a common constrictor of the 

 gill slits. In the larvae of Ambystomidae 

 and Salamandridae there are two supplemen- 

 tary portions of the M. subocularis rect . 

 IV which unite the IV arch directly with II 

 and III. Crests on the ventral ends of 

 ceratobr anchial ia serve to strengthen all 

 three parts. 



The reconstruction of the hyobranchial 

 apparatus driven by the need for perfection 

 of the prey captive mechanism is most clearly 

 seen (among the investigated forms) in the 

 Proteidae. Here a progressive development of 

 the M- sternohyoideus and M. ceratohyo i deus 

 exterior facilitates a stronger depression of 

 the floor of the oro-pharyngeal cavity than 

 is possible in the larvae of other Urodela. 

 The extension of the area of support of M. 

 sternohyoideus on the soft floor of the oro- 

 pharyngeal cavity was made possible by the high 

 degree of reduction of the gill arches. The 

 distinctiveness of the structure and mechanism 

 of action of the hyobranchial apparatus of 

 Proteidae is explained by the particular biology 

 of this blind cave form which is required to 

 feed on very mobile and quickly moving Crus- 

 tacea. There is time for a proteid to make 

 only one ingesting movement, at the moment the 

 tip of the snout touches the prey, and this 

 movement must be strong enough to promote a 

 high probability of capture. 



It is thus 

 the construct io 

 are i ns ign if ican 

 The larvae of hi 

 and Salamandrida 

 from the larvae 

 (Hynob i idae) by 

 ment of hyobranc 

 t ion of a more h 

 tus for closing 

 Proteidae was th 

 struction of the 

 the stab i 1 i ty i 

 tern corresponds 

 mechan ism f or tf, 



evident that differences in 



of the hyobranchial apparatus 

 t among the investigated forms. 

 gher families (Ambystomidae 

 e) are only distinguished 

 of the pr im i t i ve fam il i es 

 the disappearance of the rudi- 

 hiale Ml and by the acquisi- 

 ighly differentiated appara- 

 the gill si its. Only in the 

 ere a more significant recon- 

 hyobranchial apparatus. Thus 

 the construction of this sys- 

 to the stabil i ty of the 

 e capture of food. 



Comparative embryolog ical investigation 

 of the hyobranchial apparatus of Urodelan 

 larvae permitted us to estimate its evolutio n- 

 ary development, i.e., the establishment of 

 the basic qualities of organization which 

 define the above mentioned mechanism of action. 



