vations of living larvae as well as with the merit to the mucilaginous floor of the oro- i 



help of electrical excitation of individual pharyngeal cavity, may act both on the for- 



muscles (in large axolotls). To observe the ward portion of the floor of the oro-pharyn- 



movements of the hyobranchial apparatus living geal cavity, by means of the turn of the 



larvae were placed in a chamber with a mirror hyoid, and on the floor of the gill region; 



bottom. A binocular microscope was focused on thus it sharply strengthens the whole action 



the reflection of the base of the oropharyn- f depression. After the prey has entered 



geal cavity through which the contours of the the mouth the jaws close. During the action 



cartilage and muscle were visible through the f the hyobranchial apparatus the floor of 



skin. Through a large number of observations, the oro-pharyngeal cavity begins to rise and 



a clear picture of the movements of the hyo- pushes almost all of the water which entered 



branchial apparatus was compiled. In addition, the mou th during the capture of the prey 



observations were made on the movement of the through the opening gill slit. This lifting 



hyobranchial apparatus in the fry of pike and movement takes place more slowly than the 



in addition three series of sections from the movement of depression. The M- ' ntermand i bu - 



larvae of Neoceratodus and Protopterus were laris posterior and the Mm- interhyoidei 



studied as well as preparations of skulls of anterior and posterior play a primary role in 



neotenic stegocephal i d ( Dvinosaurus primus this move ment. During their contraction the 



Amalitzki No. 39, 40, 41 and Tunqussoqyr i nus floop of the oro . pnarvngea i cavit y swells and 



bsnjjj from the collect ion of the Paleonto- at the same time rises> The ^ j ntermand i bu - 



logical Museum of the Academy of Sciences of laris posterior has a point of attachment on 



the UboH. ^ e i ower j aW) the M. i nterhyo i deus anter i or 



on the posterior end of the cera tohyale and 

 through the above mentioned ligaments onto the 

 skull, and the M. ipterhyo j deus posterior 



UMAMtH 1 is connected on the end of ceratobranch i ale i 



which is connected with the skull only by means 



THE EVOLUTION OF THE HYOBRANCHIAL APPARATUS IN of the M . leva t or arcus branchialis I In 



THE LARVAE OF URODELA. the mo tTo n ^rTT?t7nTThe Mm. leva tores arcuun 



branch ialum also play a role and they extend 



All Urodelan larvae which are "waiting upward to the dorsal ends of the gin arches 



predators" generally feed on zooplankton. and tf)e ^ suba rcuales obi . JJ., J_M facili- 



The prey is captured at a distance w.th the tate a protra ction of the ceratobranch iale . 



aid of a stream of water which is induced by A significant role in the described movement 



depression of the base of the oro-pharyngeal is pl d b „ # oen iohyo idelJs . whicn in pull . 



cavity and opening of the mouth. Upon entry ing the copula defines the movement of the 



of the prey the gill arches are closed by hyoidal arch to its original position. The 



the gill flaps. The depression of the floor protraction of the copula during the action 



of the oro-pharyngeal cavity occurs by the of t he M. gen iohyo i deus is conditioned by 



action of the hyobranchial apparatus. The the fact th at it rests on the symphysis of the 



constriction of M. sternohvo ideus elicits a i„,,„ ;,,, ,,u ,u ;, f\~„A ,i tw .. ..„,»,,„* ,o 



— - ■*— : lower jaw, which is fixed at this moment as 



retraction of the copula. The hyoid, which x u i- x m 



^ J * a consequence of the contraction of M. 



is suspended from the skull on two liqa- • , .„. . .„•, „_■ „ ■ ■ _ 



r , ,, - , i ntermand i bular i s anter i or . 



ments, then turns due to the presence of the 



free movinq hyocopulatory articulation with TL x- x x j x i t l il 



., . • ' , .' . v - uia u The ingestion of food takes place at the 



its anterior or forward end downward. The _i x .. j ± ■ x iL n x il 



. ,, , ... end of the upward motion of the floor of the 



copula is lowered simultaneously without „u»_ ,i -... t u t u:- *:»,„ *u„ „;n 



—* r ., , , . , . J oro-pharynqeal cavity. At this time the gill 



changinq its horizontal position. The foi — , , . ,, ,■ x „ . 



, 3 3 .. . ., , K , ,, , , arches close under the action of M. transversus 

 ward portion of the base of the oro-pharynqeal . n • n , T , r ,, ~l 



., . ,, , , , ,, ventral is IV. The pressure of the water re- 



cavity is consequently depressed. At the same : : : 7, ■ i i u 



,.;.., , , ■ , , ma i n i nq in the oro-pharynqeal cavity has in- 



line the M. ceratohyo i deus exterior, a muscle j , ,.,,! x ,, ,, 



, . , , T, ■ , — Z : — I 1 creased due to the liftinq of the floor, and 



which at this moment has a point of support on ,, , . , , , ,. ' 



,, ... . . . . . . ,, rr , the contained food qoes to the reqion of lower 



the hyoidal arch and is fixed by the contrac- ,, , , . . 



,. r „ L .j ,, .,. r pressure, that is, to the esophagus whence it 

 tion of M. sternohyo i deus and by position of ,, . T , ,. .. , 



— ' ' r is swallowed. The M. subarcual ' s rect . \_ 



the hyoid liqaments, is contracted. The j. • u ■ i- j *u' 



, '. /? ' X ^'"^-'■•=' J ' ,llc serves as a sinergist in this motion, and this 



posterior, (,. e. , dorsal) end of the muscle , n fixi t he gill arches to the 



ceratobranch. ale i extends ventrally but its hyoidal creates a point of support for the M. 



action extends to all of the gill arches so transversus ventral is IV. 

 that the ventral and dorsal ends of cerato - 

 branch i ale are united by cartilaginous This mechanism for the capture of food 



ridges — l unturae proximales and comissurae is used by the larvae of all Urodela investi- 



termmales . During the action of the M. gate d. We were not able to observe the 



ceratohyoideus ex_terior the back portion of the movements of the hyobranchial apparatus which 



floor of the oro-pharyngeal cavity is depressed. are espec ially* connected with breathing. The 



similar action is seen in all of the forms in- external gills, organs for gas exchange in the 



V l i! 9 u 6XCept f °i- Proteus anquineus, in larvae of Urodela, move independently of the 



7 ich *• sternohyoideus , because of its greater hyobranchial apparatus; movements of the latter 

 development and more extensive area of attach- 



