THE PROTRACTILE APPARATUS O F THE ALOUTH O F THE: CATBSTORIID FISHES S I X FIGURER INTRODrCTION The famil>- (’atastomitlac (suckers) is among the bestknown and most easily recognized of the fresh-water fishes. They are cliara(~terizeC111)- the prcsence of a protractile mouth, fieshp, sucker-like lips, aiid toothless jaws, tlie mouth being protrusible to a greater extent tliaii iii other fishes. ‘I’hey are bottom feeders, liviiig chiefly upon vegetation, smaller Nollusea, Entomostraca, worms, larvae of aquatic iiisects, eggs of various kinds, aiid mud, wliicli they doubtless ingest f o r the organic matter it coiitaiiis. 111 tlie act of fcccling, the mouth is drawn tlownward aiitl foi-w\-artl from the uiiderside of tlie head like a spout. Food is taken into the mouth by sucticm, t o 11-hiclitlieiy protractile months a i d fleshy lips a r e peculiarly adapted. According t o Konleiigcr ( ’04), “tlic sliape, size and character of the mouth aiitl jaws, tlie extciit t o which they can protrude and retract largely depend upon cliffcrciices of liabit and f oocl. ’ ’ A review of tlic literature has rerealed iiotliiiig relative to the details of the modus opcraiidi of the protrusible mouth of tlic Catastomithe beyolid what is geiicrally recognized for fishes with protractile premaxillaries. At the suggestion of T’rof. Raymond C. Oshrii, tlie writer niidertook a study of the anatomy of the jaws and methods of feeding of tlie Catastomiclae in order t o determine the factors irivolved in the chai-acteristic protrusion of the mouth. 2.57 T H E 4N41’031IC1L ItICOlll), \ O L ,$$, NO 4 M A T EIZI41, A XI) i V ET 11 0 1 IS The piwblem was attacked with the idea iri miiicl of finding 0 1 -arrnitgcmetit of miisclcs or hoiics which liatl lwcome modified to hriiig about the characteristic moremcnts of the mouth. Three methods were employed-that of tlissectiori, tlie preparation of longitudinal aiid cross-sectioiis of tlic lil)s for microscopic cxamiiiatioii, a i d tliat of electrical stimiilatiori. In ortlei* to make comparisons with tlie skeletal t>lcments aiitl jam mixsculatiire of teleosts in general, tlie skiills of a iiuml)er of species in other families were dissected. r 1 1 I i c i i , iii view of maltiiig closer comparisons, the skulls of t l i ~ c a i y (C'ypi-iiiiis mrpio, Liiiiiaeus) aiid a millno\\( ('ampostoma anomalum, Rnfinesqixe) ~vei'e dissected, llotli of wliicli have sucking mouths, lint less modified. h i studying the mec*lt;inism of tlic protrusion of the mouth, tlie licatls of the following species of suckers were dissected : t l i c cwmmoii snclrer (('atostomiis commersoiiii, Lac6pktle) , the Iiogsuckci~ (C"atostomus nigricans, L e Suenu), tlie c o m m ~ i t i~vl-liorse( \loxostoma aureolum, T,e Snenr), the white-nosed silc~kcr ( Nosostoma aiiisuriim, Itafiiiesquc), the spottetl siicltei. (hliiiytiwna mclaiiops, Xafinesqne) and the clinhS I I C ~ ~ I( .bhimyzon siicetta obloiigiis, Rlitchill). The general : ~ i ~ i i i g e m ct ~ofi i tlic bites arid muscles was tlie same througltont except in miiior tlctails, a s will l w scc~iiin tlic follo~viiig t liscnssion. home special set AS .I TO bl Y O F 1'11 E J A 1VS rl'llc mterior margin of thc uppc.1- jaw is formecl 1))- the 1)1~cmnsillary( I ' M . , figs. 1 to 5), which terminates a h v e in a iiasal process o r premaxillary spine ( F ' w . ~ . ) . In most t eleosts this process pro.jects hackwai~lalmost a t riglit ;mgIc~s to tltci rest of tlic h i i e into a groove oii the etlimoicl ( E t h . ) , t hiis allowiiig a forwaid gliding motioit. However, iri the ('wtastomidae the premasillary spiiie, iiisteacl of gliding 011 the ~ t l i m o i d is , attached to the preetlimoid or rostra1 process ( I > ( , . , figs. 2 aii(1 3 ) 1 3 ~ 7 means of an elastic ligameiit (Li.q.1). Fnrtlicrmore, the spine is flesiblr, so tliat, wlieii the j a ~ wa r e PROTRACTILE APPARATUS O F T H E N O U T H 0 > I J E 259 rcti*actccl, it is beiit clownvvartl almost t o a vertical positioii the ligameiit is lax (fig. 2). l)uring protraction, howcl\-cr, it assumes ail almost liorizontal position (fig. 3). T l i ~ ligi1melit permits the fi-ec protrusion of the 1)remaxillar.y to tlie full extent of its length. 111 tlie various species of siickers wilt1 tlie montli is protrusiblc t o varying degrees, correspoiitliiig to tlic length of the spine as well as the ligament coiiiiecting it to the cmiiium. Tlie premaxillary is not attached to the i d a t i n e s , as is true of most Telcostei, and tliiis allo\vs for g - e a t e r freedom of movement of tlie upper jaw. The premaxillary is attached below by meaiis of a tencliitous ligament (Lig.2) to tlie ventral tip of the maxillary (LWux.). The maxillary is a flattened hone lying laterally and slightly posteriorly t o the premaxillarj-. The dorsal eiids of the maxillary meet and form a groove in whicli the premaxillary spine glides. A posterior coiidylc at this end of tlie maxillary is inserted into a cartilaginous rod ( P.Y., figs. 2 and 3) which connects the maxillary witli the romer ( TTo.). Tliis rod is well developed i i t tlie ('atastomidae a i d affords b'ig. 3 Lateral \ i e w of tlie jaws, with stliiie parts rcinorril as in figure 2 , sliowmg the position of thc ~~reiriaxillarp and rclatcd parts in protraction. Thtprciiiaxi1l:iry spine a m l ligament 1 assume a n almost horizontal position. a more or less movable joint. The maxillary is also attached to the palatiiies by meaiis of a ligament, and its ventral tip is coiiriected with the mandible in a similar manner. This coiiiiectioii is a t the angle of the mouth, and, as will be esplaiiied later, serves to pull the upper jaw d o m i v w d and forward when the mandible is depressed. The palatiiic (PaZ.) js a triangular (iiiequilateral) bone which flanks the vomer on either side. I n the perch, which may be considered a commoii representative of the Teleostei, a n anterior process of the palatine projects forward to articulate with a coiicavity in the maxillary. Hoa ever, as iiitlicatecl ahove, tlicre is 1 1 0 direct coiiiiectiori n i t h the maxill a r y esccyit hy meaiis of a ligament, thus allowing more fiwtlom of movemcwt of the upper jaw. ‘l’lie posterior hordci. of tlic palatilie artionlates x ith the mcscry)tcrv~:oid(Jfs.gtg., fig. 1) and its outer angle with the ptcrygoitl ( P f g . ) . TATiiig heliintl the former aiicl articulating with it, is the metaptcrygoid (J1t.ptk9.), and l ~ e l o wthe latter is tlic ciuatlrate ( Q d . ) , which in t i u ~ articulates i with the lowcr j?I\\- . The upper jaw liws 110 coiiiiectioii with the cwiiiium cJsce1)t :iiiteriorly where tlic palatilie abuts agaiiist tlie vomer. . i n at tnclimewt is partly effected posteriorly by meaiis of n s t i s ~~hiisorinm formed hy two boiics-the 11)-omaiidibular ( H i / / ) . ) ;tii(l symplcctic ( N y n , . ) . Tlie liyomanclibular articu1;itcs t l o 1 . sally with the pterotic ( P t r . ) a i i d spiieiiotic ( S p . ) a i i t l is joined vciiti*nlly hy ti c.artilnginous bar. with the symplectic., which i i i t n n i fits iiito a groove i n the qnaclratc aiid melri1)tcIrygoitl. ’l’lic lo\vei* jan. oi’ rnaiiclible cwiisists of two mmi, riglit >uid loft, joiiietl iii fiwiit 1 ) a~ movahle symphysis. ‘l’lie anterior Iwrtlcr of the maiic1il)lc is formed 1)y the toothless tlciitai*y ( I l i t . ) . 13eliiiitl this is tlie articulai’ ( A r t . ) , at tlic lo.\\-c.r aiiglc i ) f nliic*Ii is tlic small ;uigalai. (A/t<q.). ‘l’he ai-ticular has ;I decyly (wiicave sui*facc iit its Itostcrior extremity f o r articulatioil with tlie quaclrritc. Tlic latter thus serves as ;t I)e(liclc For the nttaclimeiit of tlie lowci*j a w and enables it to caomliiiir. its moremetits witli those of the upper jaw. ,4s O\veii (’66) ))oilits out, “the npper atid lon-el. jaws are st) eoi~icc.tec1in )sscwm Fishes tliut oiic c~~iiiiot be moved witiiont aff’wtiiig the other and both tire alike movahle. J’rotrusioti a i d r e t n c t i i ) i i affect them equally.” I lie sliapc of t h c mmitlihle is peculiar, especially as compared with siicli tcleosts as tlic perch. 111 the latter tlic rriaiitlil)lc esteiicls Iiorizoiitally forward from its pcdicle, \\,litlrens in tlie (’atastomidae it exteiids horizontally forward t o tlic a~ig~ilnr. where it turns almost at riglit aiigles tct pass r 7 PROTRACTILE APPARATUS O F T H E MOUTH 263 a id Y da$ f y , a Fig. 5 Lateral view of the heacl, showing the deep musculature of the jaws with the cut ends of addurtor rnnndibulae 1 and 2. Adm.3, adductor mandibulae 3 ; L.u.~.,levator arcus palatini ; Ph., protractor hyomandibular. ,dm.2. -Adm.l PROTRACTILE BI’L’AHATUS O F THE MOUTH 265 vertically upward, eiidiiig in the overliangiiig dentary. This type of maridible thus permits greater movemciit of the jaws aiid subsequently more proiiouiiccd protrusion, as will be explained later. Fig. 6 Ventral yirw of the head, showing the inusculaturc of t h e n~and1bleand liyoid region. G l i . , geniohyoideus; Itii., intcriiiantlihularis; Sh., stcrnohyoideus ; Sy., s>-mpliysisof the mandible. The muscles either directly or indirectly concerned in the protrusion of the mouth arc the geniohyoideus, sternohyoidcus, and protractor hyomandibularis (figs. 4 to 6). The geniohyoideus (GJi.) is a paired muscle lying on the ventral side of the licatl. It arises on the ceratoliyal, each 266 LINDEN P. EDWAHnS muscle exteiidiiig obliqnely forward to meet its fellow of the opposite side. These, in tnrn, continue for~7\rard,passing i i h w e the iiit.ermandibula.ris t:o their insertion on the t.ip of the mandible near the symphysis. The contractioii of this ~ by depressing the mandible. miiscle opens t . 1 mouth 111 it.s act.ioii a.s a depressor of the ma.ndible the genioliyoid~.'iisis assisi.eii hy tEic st,eriiohyoideus (A'?(.), which is tlie maiii rct.ract.or of t.he hyoid. This is a paired muscle 1ia.ving it H origin on t.he pec4ot-d girdle, from which it extends hackwai;d i l s the vent.ral abdominal muscles. The fibers of this m i d o exteutl forwa.rd longitudinally, to be iiiserted above t 1 1 ~ 1geniohyoi.dcus on t.lw basihyal. By t,he contraction of this miiscila thc liyoid is drawn downward and bac.k\vard. This motioii is, in turn, tra.nsferred to t,he ma.ndiblc thmugli t I i c acrt.iori (Jf the geiiiohyoideus, which accelerates and i I i c I'C*R s(:s it,. When t.he mandible is depressed the premasil1ai.y i s c h ~ ~ \ v i i i.Iowiwml and forwa.rd because of the tension on tlie ligainelit cwnnecting the upper a i d lower jaws a t the angle of the mouth. 'lY1e protrusion of the jaws is facilitakl by the following factors : First, t,Eie general looseness of the attachmelit of the premauiIla.ry to the ethmoid (ligament 1.) \diich, as previons1-y expla.iiietl, allows grca.t. freedom of mcircmen t. S.itrcondly,the peculiar charac?t.erof the mandible which permits i i more proiiounced prot.rusion. Thircll?-, thc action of the '1 )1*0tractor ~ i ~ ~ ) m a ~ ~ ~ l (iPlk ~ r .,i figs. i I a r4i and ~ 5) which aids in t1irrist.in.g forward 1)ot.h t.he upper a.nd lower jaws. This muscle arises 011 t.hc sphcnotic. and is iriserted on the outer .fac!c of tlic liyomandilniilar. M7h.en it. contracts it teiicls to t '1~ 'IT a tlic ]Iy omaritlihiilar 0-tit,u7ard ai id forwa r d , wlii ch , in trirn, thrusts for.c\.ard t.he izppcr mid lower jaws. 'I!liis occurs t)wwiiscL the Iiyomantlibnlar serves as thc suspeiisorium for 1:)ot.h the npper aiid lower ,ji1~7s,as has 1:)eeii prerionsly iq)laincil. Tlic muscle which retraots the jaws 1):- closing the mouth is tlie ndduct.or mantlibulae (-4dm., figs. 4 and 5). This musvlc lies on either sick of tlie head and is differentiated ii1t.o three fasciculi. In tlie perch, according t o Oweii ( ’66), it arises “from the tympanic petlicle ant3 anterior border of the preoperculum, and is inserted by the upper fasciculus into the maxillary; by a lower faseiculus into the mandible beliiiid tlic coronoitl process ; and by an aponeumsis into the mem1)aiie uniting the two jaws iiear the angle of the mouth.” I11 the Catastomidae the above description of the iiisertioii of this muscle does not hold true. Adductor 1 (Atlin.1) arises from the anterior border of the preopercular, aiicl, ext endiiip horizoiitallp forward, is inserted upon the outer face of the maxillary; adductor 2 ( A d i n . 2 ) ,lying anterior and ventral t o atlductor I, arises 011 the preopcrcnlar and mandible and, lmssing npward aiid forward, is inserted upon the masillary, its teiidoii overlapping diagonally that of adductor 1; adductor J), which is covered by tlie preceding fasciculi, arises from the quadrate and metapterygoid regions, its fibers exteiiclirig forward to be inserted by a crescent-shaped tendon iil)on the mandible near the angle of the mouth. The action of adductor 1 is to retract the upper jaw by drawing the maxillary posteriorly. This, in turn, retracts tllc prcmasillary, for, its previously clescrihed, the ventral tip of tlie premaxillary is attached to the ventral tip of tlie maxillaq- hy rneaiis of a ligament. Arlclixctor 3 assists in retracting the jaws hy pulling the angle of the mouth post eriorly, d i e r e a s adductor 2 closes the mouth. As previously stated, food is talicii into tlic moutli bj- suction. This is brought about h ) ~the alternate enlargement and coiistrictioii of the oral cavity. Thc oral ( ~ a ~ i tih > -enlarged by expanding its walls laterally arid hy (tpeniiig the month. The muscles involved in this a r e the protractor hpomandihularis, geiiiohyoidcus, sternoliyoideus, and the lei-ator arcus palatiiii. A s already explained, the protractor lipomandibularis pulls the Iiyomanclibiilar f orward ;iad ontivartl, tlius eiilarging the cavity. Likewisc, the geniohyoideus and sternohyoicleus have been described as the depressors of the mandible, tlius opening the moutli. Tlic l e ~ a t o arcus r pala tini ( L a p . , fig. 5) exteiicis outn.ard across the floor of the or1)it. 268 LIKDER F. EDWAlIDS A\iisiiig011 tlie pnrasplicrioid (Z’s.), the fibers pass laterally to he iiisertctl upon the outer face of tlic mesoptei*ygoid aiicl ~nctwpter~-goicl.The actioii of this muscle is to elevate tlie palatinc~rtyioii, thus assistiiig in tlie dilation of the oral cavit?. rt’litb01x1csarity is cwiistrictvd by tlic lateral cwiitrartioii of’ its \mils arid by thcl closing of tlie month. This is hronght a h i t 1)y the coiitractiou of the adductor hyomwndibularis, i I i t P ram a lit1 ibn 1a r i s , a lid t 11 e a tldu c t o 1‘ ma iicl i b nl a e . X s a 1re ad y ( lc sc 1.i he (1, 1lie a tlcluct o r ma 11tli ba la e closes t lie mo 11t 11. T1I c acltliictoi- lryom~iic~ihularis, wliich lies on the iiiterior of tlie sknll, takcs its origin from the parasplienoid ant1 primtic. It ostencli. Iatcrnlly f r o m its origiii to he inscited upon tlie iiiiiri. fwc*c~of the h!-omaiitlibul~~r. A s the name implies, its actioii i h t o atltluct the Ii;r-omaiitlibular, thus decreasing the sizcl of the ot’a1 cavity. T l i ~iiitcrmaiiclil)ularis (1117., fig. 6) is a i i 1111p a i w t l muscle lying 011 tlic ventral side of the licad. I t ])asst’s t ~.;iiisvcmelyfrom oiie i’ami~sof the mandihle to tlic othei., t(lii(1iiiq to draw t1ic.m togetlicr after they 11avci 1)c~cit cl i r a 1-ic’a t ed. 15 S 1’E It1R3 E N T A 1, I N V EST I(; A T 1 0 s 111 order to clemoiistrate that these muscles are iiir.ol\-cd i i i tlicn olwiiiiig aiicl closing of the jaws aiid the coiisequeiit prot rxctioii niitl rcitractioii of tlic pi*emaxillarj-, live fish i ~ t x i stimulated 1)y means of the current from iiii iiiductioii coil. 1 1 lhcb stimnlus w:is applied first to the siicltcr-like lips, hot11 IwforcL aiicl after severiiig the trigemiiial iierve. So appai’eiit ~ ) r o t r ~ i ~ sof i o rthe i month resulted. ‘I’his tciidecl t o tlemoiisti.;itc~ that iio muscle fibers were Imseiit in the l i p to aid iii tlie charactcristic protrnsioii of the mouth. Upon stimulatiiig tlicb geiiioliyoitlens and sterirohyoidcus, the prcmaxillai*>- was thrust d o \ ~ i i \ ~ \ - aaiid ~ * t lfor\vi11”d. 011 tlie other hand, \~liciltlic acltlnctor maiidihnlac was stimulated the jaws were retractetl. ~ PROTBACTILE APPARATUS O F T H E MOUTH 269 HISTOLOGICAL INVESTIGATION Sections were made of tlie lips of the various species of suckers, to determine if any muscle fibers could be detected ancl which would be likely to aid in their characteristic moremcnts. Botli longitudinal aiid cross-sectioiis were prepared, some of which were stained mith Delafield's hematosylin and counterstained with eosiii, mliile others were treated with Van Giesen's stain. The latter is ail excelleiit cliffereiitial stain, rcvealiiig the presence of muscle fibers, etc. Hou-cver, no muscle tissue could he detected by this method. COKCLTTSIONS It is evident, therefore, that protrusion of the mouth in the Catastomidae is broiiglit about by tlie same movements, vhich serve in other fishes to ope11 the jaws. The lnoiies arc. anatomically identical, hit. differ morphologically, nliile the miiscles differ but little except in attachment. The protrusion is, therefore, effected by the pulling do\vii\varcl atid forward of the prclmaxillai-y wlicn the maitdihle is clepressed. SUMMARY 1. The premaxillary spiiie of the Catastomidae is clistinctive in that it is attached to the preethmoicl by mcaiis of a lax ligament. 2. There is 110 ligament attaching the pi.emaxillary to the palatine, thus wllowing more f recdom of morement. 3. The maxillary is not articulated with thc palatine R S is true of most Teleostei. 4. A cartilaginous rod coniiects the maxillary with the vomer, t h i s affording a more or less movable joint. ,j.The mandible is peculiarly modified and permits greater protrnsion of the mouth. 6. The adcluctor mandibulae is peculiarly adapted to the type of jaws. 7. The protrusion of the premaxillary is brought about by the lowering and subsequent protraction of the mandible which increases the tension on the ligament connecting the lower and upper ja\t's a t the angle of the mouth. 270 LINDEN F. EDWARDS 8. Stimulating the muscles involved in the opening and closing of the jaws verified the above results. 9. Stained preparations of the lips failed to reveal the presence of muscle fibers in them. BIBLIOGRAPHY ADAXIS, L. A. 1919 A memoir on the phylogeny of the jaw muscles in recent and fossil vertebrates. Annals N. Y. Academy of Science, vol. 28. ALLIS, E. P. 1897 The cranial muscles and cranial and first spinal nerves in Amia calva. Jour. Morph., 1701. 12. BOULENGER, G. A. 1904 Fishes. Cambridge Natural History, vol. 12. BRIDGE,T. W. 1904 Fishes. Cambridge Natural History, vol. 12. FORBES, S. A., AND RICHARDSON, R. E. 1908 The fishes of Illinois. Natural History Survey of Illinois, vol. 3. GUNTHER1880 Introduction to the study of fishes. JORDAN, DAVIDSTARR 1904 Guide to the study of 'fishes. JORDAN, I). S., AND EVERMAN, B. W. 1916 American food and game fishes, vol. 8. OSBURN,R. C. 1901 Fishes of Ohio. OWEN,RICIIARD 1866 Anatomy of vertebrates, vol. 1. PARKER, T. J., AND BETTANY, G. T. 1877 The morphology of the skull. PARKER, T. J., AND HASWELL, W. A. 1910 Textbook of Zoology, vol. 2. SAGEMEIIL1891 Beitrage zur vergleichenden Anatomie der Fische. Morph. Jahr., Bd. 17. TEUTLEBEN, E. VON 1874 Ueber Kaumuskeln und Kaumechanismus bei den Wirbelthieren. Archiv. fur Natur. VETTER,B. 1874 Untersuchungen zur vergleichenden Anatomie der Kiemen und Kiefermusculature der Fische. Jena Zeits. fur Natur.