FLORIDA STATE MUSEUM
THE EPAXIAL MUSCULATURE
OF SIREN, AMPHIUMA,
AND NECTURUS (AMPHIBIA)
The numbers of THE BULLETIN OF THE FLORIDA STATE MUSEUM,
BIOLOGICAL SCIENCES, will be phllished at irrciul.ir intervals. Volumes
will contain about 300 pages and will not necessarily be completed in any one
Oururn L. Atsiix. J-.. Editor
lThe publication of this number of THE BUL-
LETIN has been nmde possible by a grant
from the Graduate School, University of Florida.
All coninournications concerning purchase or exchange of the publication should
be addressed to the Curator of Biological Sciences, Florida State Museum, Seagle
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BULLETIN, Flint Ha.ll University of Florida, Gainesville. Florida.
Published 21 May 195P)
Prct hn thi, issuir 8 25
THE EPAXIAL MUSC(UL AT.U'E OF SIRE\V, .A11PHIUMA.
AND VECTIURS (ANIPHIBIA)
W\,1:rii At HI.'iL\BlG '
'1 sorsis Almost ll o i t i st (dis d.1 rl:it g -\itl thll t k I mu I ll..ilalht of
IOd lcs hlII beeIn i-sttlid to lthe h11\p1,l seriue. In this sitndi tlihe cp.imt.
I tli tn r(T l dores ,d In l mus ll iN- iss d l i l to tlli 'tl i mlli i int I sl i o l t lt ]a i )l
fisher ttlachmi 'nt E Lcll intL v in trii pn rvi-ded wvit h l ,rral r d stsitt fibei trattit'
doltish. d from a pr]i ii In eti\l. ran pli tniyoseiptal '.st(in. "I l its lliiun coniIp \M -
ti, air d 1 esrih ed i l fiarls tO i l ppi ~\itii t' a/t, ircCtioll. a nid ALLLchlin-lt ill tih
thu ih-nll.i studr 'id. All th 'e enp r IIa Ia \'
sIIII fiit l hii-n trIacts. I t ta si.d L tn tile dI tr INp l rlt Ii \'I( '' li" u 1 9 mIt11 plli n tl-i<
S 3r'N Ili(d Aimp lihi IIia llstr1Itm (ex rtal sil C 1ix>li11itin11 invt il\ Cd in llll ll cN thisi 11
Ill n biit o, f Il is t l, i Thr "l l i ahi ons ir a ppalnti[\ Idop''id 'ntl\ dr-
ri\ d 1 lh II' aJA. lItIt n- 11u t o if Illt\eI ol tI) atLlt.1siI l ntl- 11d o ainJtLu'mI Ol'blr.l o\ siCt ls
Iitor, d tcll 41 1 dthi)iped (tr i f teniipl rs of sh 11( s I c)( ii/difliini,
TI "(>II)o t ( TIO\
Stnalies of ntsclahttre Ii the (arodeles hat\e tbte restrictent larsell
to the, lbrachllial, hypa\ial and append'licOIIla]r areas. Th'i, main reason
for this is that tlih ir 'lpaial trunk l insmnll c laltiur lias Iurln(rall\ Ibu(' con't -
sidert-h to be a mass of fibeis \hicluh, it oriented. at all, \ierie so co[iit -
ple:x lani hiterlaci that ino serious attempt \\'s Cvl'Ti madluI to stin(l
the fiber tracts. Thulls the epaxial complex is lgenerally rctrc'rd to
ined illn tries of' filber attac'ln nts.,,
Dlrill a stod\ of Recent and fossil \ trt<-brai of a nulimber olf sal-
a iandetrs it became ob\io us that in the Sirenidae t-hese elemisents 'ie
Ilnite distinctive. Thi\li differ 11arkied l from i other lmodcle veriteh)rae
in a number of wtays, and particular inll tlhe shape of thIe neural arch
In lno other kilo \\ li \inl amphibian is the posteriol portion of the
arch shaped into a hlorizonitall\-orielihed V-shliiaped notch \\ ith its ape\
directed aniteriorly. The two raised ains of thie hal\c b)teent termed
'I h, aitlhor is ,i1 Associatc li ti' Flulidai Sttt M usm,, \sifi t l'i,
(If lihO tloic l S(_I-ItL s Al t d I 1 rltl ll nl i t cltcll iit paIhtltol)ltolllo ( f l l 1w it l l < iir itl
Inof I in, Cid oi ll [tinus, I [is m ost n pl rtaint (o< \ tril)]tioins C1d \tlitNN Ik 'tI fO ,ssil
11ist0i o\ s0 iIll titp 1 ilA Mns I Ci-Id I S. \1 til i 11 11 scripIt s Il nitti d N I 1 1 2 1 !,
251 BULLEITIN FLOIHI)A\ STT VII Nit Sl1i1 \,) l 4
the alliform piocesscs (GCoin and Auflenberg. 1935). These processes
are presumably formed by o)(ni y outgrowths of the dorsal surface by
the neural arch itself, rather than Ib an Ipturnlio of the posterior
edei of tie neural arch. As a result, the roof of the neural canal
is complete and forms a; "floor" between the thin vertical V-shaped
alhform processes. This condition is so singular that isolated fossil
cvrtebral elements of this group of salamanders are easily recog-
inzed. whlicli has recently permitted the extension of the known
fossil history of this group to the Lower Cretaceous (Goin and \uffen-
The peculiar structural features ol the vertebrae of this family of
salamanders led to the present study. The unusual \ crtebral )processes
of thle Sirenidae suggest that thle epatial muscle fiber tracts are prob-
ably mIore complex than tlose of most other living urodeles. The
complexity and yet distinctiveness of the fiber tracts suggest that
mulch might be gleaned trom a study of tle "dorsal muscle mass" of
other urodeles as well. For comparative purposes the epaxial muscle
complex of Amp hiuma and Ncclturus were also studied.
Most of the problems associated with a study i of this kind are
related to the necessity of studying only fiber direction and attach-
ments. There are no clear demarcations between muscle masses
in the nature of delimliting fascicular connective tissue. Muscles de-
limited by fascia are found only in the appendicular and branchial
areas. In1 Siren these ha\e been studied mainly by Wilder (1891)
and Maurcr (1892).
A particularly bothersome point xr(wheni dealii with only fiber
direction is that it is almost impossible to establish homologou s rela-
tionships. For this reason the \arious epaxial fibei tracts are not
named with respect to possible hoolnT ogouls structures in higher verte-
brates. The entire dorsal muscle mass is easily divided ilto a number
of units based on fiber attachments. Each unit is in turn provided
with several distinct fiber tracts, derived from a primitive and simple
inoseptal system. These specialized minor complexities in the fiber
tracts are described in regard to approximate size, direction, and at-
tachments, and are designated by a simple letter system. This avoids
the problem of hom ologues for the present, and still allows for a
"terilinolotgy" necessary for comparison with the epaxial system of
other nrodeles. The following data were obtained fromin the dissection
and partial maceration of three adult specimens of Siron laccrlina
anId one adult each of Necturus Inacuilatius and -ki phiuma inmcan.
J'J5J At I IENBERC. VPAXIAL Nit SCILATURE O(' SIJ.,\ 255
E1I'AXIAL TI1TT K MNISCI LAIU-IiH.
Three main subdivisions of tihe epa\ial muscle mass can be dis-
tiiguished in each of the genera examined Each di vision need not
be of equal importance, or of equal distinctness. These are. (1) inter-
im\ oseptal fibers, (2) in) oseptal-vertebral fibers and (3) inter\ crtebral
IV-5 MV-3 I 6
Fioitre 1.- EpaLi.il filth tlicts in Siren laC'tinai. IM) Inteini)os'ptal filbirs,
I\' I [nter irtclnrl fih is, NM I)e -ptal- v rt'brzl fibers. [S\' Sbubv'rtcbrialis
complex, (TR) TraiNversus.
SirN.- Figure 1. This is not only tie most superficial of tIh
main fiber trait (inisions in the rodeles, blt the most extensive oin,.
covering the largest part of the dorsal surface of the bodv. It evi-
dentlv represents the most primitive group of tih' three di\ visions.
Fibers from this di\ixsion extent out distally to all parts of tilt'he dorsal
area and attach to the imier surface of the skin, making it somewhat
difficult to renm e. The myotomal septa attach proximally along the
upper edge of the allitorm processes and distally to the skin In the
region above theth vertebrae they bill o\\ out to present a surface con-
cave posteriorly, convex anterior Iv. Lateral\ the myotoinal septa
indulate in a regular pattern. Muscle fibers run longitudinally and
ico ieet adjacent septae. As a group these fibers form thick muscle
segments that compose much of the subsurface imuselattre of the
entire posteranial epaxial area. The ivotomal fibers run candocraniad
B3-,LETIN FLO I ID\ S I'AT' FI \, SE M
and arc noit cul 'l distributed, but tend to occur in groups or tracts.
These tracts are only slightly separated from one another.
* -.:- '- '
IlI t Is iI l n A iipi/ l l
AmP ilrmlA.-FigurIe 2. As in Sirn the intennyoseptal filer co\S er
the entire external part of the epa\ial complex. Fiber tracts 111ii from
.sec)tium to septucii. with mini fiLlrs attaching distill to to le internal
siniace of the skin. The Inmotomal septa are considerably more con-
plex than in Sirln, Eachl septum attaches anteliorl to lth poisteo-
dorsal surface of a trainsvers process. Distally the selttmu attatches
to the lndersurface of the skin. BLicts(en tise( tAwo points of attach-
imeCt the septIum billows out )postTeiorII\. Medially it is attached to
the sharp ridge oil the dorso-lateral surface of each neural arch, a
structure quite characteristik of tlhew ertebrae of .injmptiai (Fir,.
2). ITo tlhi ridge is attached anotIher septulln, Xertical in position, and
close to he neural spine dorsally. Anteriorly il attacLIWs to the lat-
erali ex]N)andcd pIosterior raised portion oit thie nural ac-h Within
the pocket olrmoid het'een this septull and lthi lateral sNrface of the
t\ itbra a seIies of fiber bundles run from one septum to allther or1
froin tlle \erteblra to the septIm. Some of these will be discussed ii)
IL H 2. 11 Kpa\ i l I M pt.d i 11FAT L",H tIIIt ii ( fil 'lr
AWI)M'\ IJi l L ;iI Fi-1iiw I
It)~' l AUL'FI \i, 11-.iL I-F'A I \L Nil ('L I.-T I ()1 SI I ,\ 257
more Idetail hetlw, In uhldition to tihe iiiterseptal fibers it this .small
pocket, other fil]r biudle's rmi behtwill thel motre obiLiots main sep-
tnoI ltteiJullk \s inl Sirin, aill of tliest' fibcrs itn11 1 tcrl o-postcriol .
Tihe acllditional spt')tmni d s.crbll d abiln ( is tur)l\ diiricull to fi(],
pt Itic IlIrly% i wve( spe-imitens. Till striietur r is ml(m lreadil o \ se'i\ (ld
X lit'i dxr It al]toI)CT) be c S more oi\ ioitus all'r a sliort ptrll(d of imat-
('ati'ion. After it's disc'o (T iln Anphittilot it \iwas searcn t d lor sel\ eral
ti'lcs wxithiout success' il hbotlh Sio;' t. \rcl't ttiV licturt( 2 sh1io\\s
thli ctIo lex tsptttl iarlaii-(nicnt and filbl tract attu(chmn111'tts in .\;-
N-i.( ist .-01 the three
is silinples t Ni e(mr.s. Tith interseptal fibers are c\ttiisi e as ill
Amipltim uaiid Stfir Xs fex t'r fil)ers ruin distall\ to attac]i to thli
udherside of the ski n in nectiiur's- thie derni.s is more easily rien\ed
thian.i i the oIther two gent'ra examiliie. TIit( sept arei loosetl attached
to the undertside of the skin. MIedIalaxv the'x' are atlclied to thie pos-
tenor ed_(ge of tle nettural Uareh of one etel trra. tle( coniieetion tlien
extendingl posteriorj\ to ti'e succeediiiih \erteblra alonu Ohe dorsal sur-
tac'e of its tanisx erlse ptitees) s atnd theice distallx dorsal to the ri-l
where it joins thle main horizontal stptum. D)orso-lattallx the epa\ial
portion of th(e s('pttmt l)illo\s out poste)ricl l IS il tlie txxo other'
mIore( similar to Ith
true of thi septal
"']he septae and their colileticctli fibel" tracts ale
ose in Sit'cn than in .A-plhiu m T 'ns is particiihuli'
N I oseptal-Ver 'br'al Fibi s
IDoisail to thie \ itebrae. and entiral to the iiterseptal fiblons tracts
tie a mora e 1 ml ( irniplt\ roulip of filehr Iracts which are of muo comicern
f(r p lurlposets of the' president study heit ti erm t trti te in\ ose'ptal-\ erte-
bral fibers. It is tlh ctmthplxity below the inltersept'il fibers which
is of most interest as regards tine epa\ial muisclatur'e (it thie sirtlid
StIlt\.- l'iti~ie 1.) O()rtnl three tracis hia\ e 1)een retcoinized as
liav inl, attahliments with th i< Iotomoal septa at one en(id ;nd the
\eitulbrat' at tlhe other. These tracts are as follows:
MV-1.--The vertebral attachment for these fillers is at the postero-
lateral 'ed'e oi the trattnsverse process. Ifere e fibers coalesce wxith
somll niters' e irtlbral libers inltniitti firon onie transverse process of ione
\eltebra to tlhe t rans\ierse process (of anotlihr \ertebra. The fibers lil
postc'i orl\ froi tlie' tialis\rser plol.ss to attact'li ntea thle upper edice
BULLETIN FI.)Ii)D\ STA\TI 1 M SFt 1
of the septumn. near its confluence with the skin, and lateral to the tip
of the transverse process of the succeedingl vertebra.
MV -2.-These are septall to zygapophysial fibers. running from
the posterior edige of the postzygapoplivscs posteriorly to the myno-
septum of the sulccedin'g S rthera.
.' -3.-Fibers belonging to this group run from the superior sur-
lace ol the dorsal lamina of the transierse process posteriorl to near
thie distal cd(Icg o moept ofhe oset tle same vertebra.
A PIri'NMA.-(Figure 2.)
IV -1.-The fibers of this group, as in Siren. run from the trans-
\vers process of one vertebra to a myoseptiio. In Amphiliaoi the
hiber tract runs from each septum posteriorly to the antero-dorsal
surface of the transierse ( process of the succeeding vertebra and an-
other set iruiingi anteriorly to the post(ro-dorsal surface of the trais-
'crsc process of the preceding s \crtebra.
Vl\-2.-These are fibers which attach at one cend to the septum,
and at the other end to the ztgapophyses. As in the \V-I1 tract.
the \IV-2 tract in Ampliiona seems to be quite different thal those
found in Siren. The fibers are attached at one end to tch dorso-
anterior surface of the pire gapop lysial process, but run anteriorly
to the posterior surface of tlhe preceding septum.
Amphiromn has two additional fiber tracts that apparently do not
occur in Siren. These are.
lMV-3.-This is a series of fibers running from the anterior half
of the lateral surface( of tihe neural arch to the posterior surface of
the selptum of lf the preceding vertebra.
,\V-4.-Fibers iom this group make lup a long tract rIunningl from
the lateial surface of the neural spine and the adjacent part of the
neural arch to the anterior surface of thlie sptum of the succeeding
N le( Irns. The inyioseptal-vertebrhlal fibers in thle epa\ial area
of this Cgenus are \ery simple compared \with those in Sirt-c and Am-
MV-1.--Of all the tiacts of this division il N'cciuruiy this is the
most wecll developed. The fibers run Irom the postero-dorsal surface
of the transit rsc process of one c rtebra posteriorly to the anterior
surface of the succeeding septiu, and from the posterior surface of
this septumll to thlie alntcro-dorsal surface of the succeeding trans\erse
process Thus fillers run anteriorlh and po1steriorly to each septum
1959) At FIENBIERG EPA\LAL MUSCit L.ATUE OF SIRl.EN 259
fromiii tire p)recl(ring uricd steet'cmg tran isserse po a in 's Iss,11
MV-2.-This tract is also fairly\ well developed in Necturns. \s
in .\lnjpiurnr, the fibers ruln rom the lateral surface of the neural
arch and the neural spine, as well as from the dorsal surface of the
postzyzgapophysial process, anteriorly v t the preceding septnnm.
No fiber tracts corresponding to t lhe -\I 4 series could be discerned
ill tile dissection of Nrctursrrry. The lMV 3 group iln NcIturuts is simply
represcnttd by modified, lmore anteriorly placed and slightly dillfer
ently oriented fibers of the t-[ 2 series.
These fibers are apparently' the most important ol all of the groups
for comnparati\e purposes. Some ol the tracts seem closest to what
might be considered honrologs of epaxiatl muscles in the higher vertc-
brates. Certain functional analogs are rather oh \ious in some cases.
It is certainly that developmental hioinolo"gies cannot be more tllan
casually suggested at the present tmne. Several main tracts ha e been
retornizedl in all thrce genera studied.
SIIfLN. -(Figre 1.)
IV-1.-The fibers of this series bcgin near the mCedio-anterior drr-
sal surface of the projected anteriior upper edge olf the neural arch.
The fibers therlce continue anteriorlx, connecting ) to the posterior
surface of the entire length of each of the arms of the V-shapcd alli-
ormll processes (Figure 1). Apparently the incieasucd length of this
tract is ilnvol\edth in priridinr ireater nlecdlainicll efficiency, pretlsull-
ablv ir intmo ing tlie body up and to the side. hi action the tract miust
be similar to thie nmultifidus muscle of some of the reptiles with ai ps-
teriorly] e\tended neural arch, as is found iin the snakes. There is nI
reason to suppose that these units are hormnolorous, since e th mltifidus
attaches to the upper posterior surface of tlie neural arch, whereas the
track tinl Sirni' attaches at the anterior upper sirliface.
IV-2.-Thris is a rather large fiber tract connecting adjacent erlte-
brare )b inrg) ll r om tihe dorsal part of the entire lnerlli air-ci olne
vertebrae. including the anterior surface of tlie alliform process, au-
terior to the ftrloor of tihe allilforl piocess and thll posterior edlge
of tilt preccdinug s ertebra. In action it must hie \( ry sninilar to tie
intervertebralis of higher \ertebrates and is probably a true hiomolog
ol this muscle.
IV- .-(.eirtam fibers which I become. interlaced with those ol thli('
IV-2 series originated on the puiezI) 4apophlIsis of thei next posterior \Ir-
tclra. to inlsert \it th ibr 2 o th l s o I n the alli fonn process. 'lThese
libel s cinll tllh s lie ,sa l to s)panl oet i ilt brat' it t tilt iilberts arte so ill-
e'\ti ';ilia I ill li\\ I i \\ ith th e of tile i -2 series that tlheI canl
I trdlh Ie tiniied at dlist ict tract hi tlc'iem Ts X cs. Fui til 'rliior, not a ll
ot tf.'sc fibclrs oiti ic il o lIh allifotll ] o( t' lloni ( t tli il t'(
InI ii f l, t inl'. to t i I]llt])p "r sI il 'h ( (It ti aI d]a c' t \ I lrtti'l)t i iC- 1 a ,i .11
l ic ftioll tillhe lltlr fibel s of tihe IV-2 aiilln tlios of thei I\ -3 slrit-s plro(-i
atil lli\i' ian l tl i -\ t t S ll ilar l (ti (o t ha it of Ill issiiiui i '(loln L( lI(\ )of
S tli 1( l It it "< r p tilcs.
l\-1.--T!ic hl jilt.'i ti ct is a smaI I ll oi t, atttaclil in l t ti n' (11e (iNlI to
tlin ('lilanI i ils l 1ii(d o(f (thi t insic\ ('r.s ()i oc'i'ss. il tlich slot bctt\x cei
I IliC (!(a al anilti \ilital la in:iiuil of(t tli It ])riocess. a l( t tit' othel r clal Id
to th1 (:i111 Il h) tolot1 ol the postyti'aiposph lyis of the adiiacet it prc-
( df t I r 'l( chlI' a.
l\V--.- This is a fail l large )fi 'r tlI(i tllllll'o l ll cI a I l lill s-
\ tsr proI' )Lesses&, At 1e etnd ol to l fib)ers' are atta'led to thi ('ranial
edie of tlwe central lamtina of ilh iW] l posl iiol \crlel)ra. Flroi tliis
point t!l'e fibl'rs rlm ante'riorl\ to attacli alonlli tlit' dorsal stirface of
tfl dorsal lallina of the tlr ls\ r 1ro(ss Of th\e next \ t'rtCbl)ra. ()tlit'r
lihnis iIo from the an'trior edge of t (le' N itial larn ai ol the tralls-
\csf pi cs of a I) ( st ii ) NT'r'i ( Irt( ra al ld runI al ntU liorl \ to atlaclh alonw
till, entire postuli ir cd o l till tial st\rsc process of til' proce dilln
\ tilcl)ra as \\' l li' as t l adla:'('nt p)it of tilhc c( nt(liI of tli( salme ('le-
a'11 tNil4.- ( 1imrt 2,)
I -1.-- In i .i pii tixnia thiis series is \VerV InlII(ch modified Irom tilli
conith n o)Isci\ l r11 i 1'nl. '' fie il'r ill ar attached muc h l()more d(i)r-
sall\ and niediaill\. mo\erfit. the lateral surface of the anterior part of
thlie neuraIl l .sple as \well as the adjaci t dorlso-latral part of tlwe non-
I1a I a i ell. r 1o11m these are l ieas fiIbers rIl anteriorr\ to the post(erlill
position of thit post/\iapopll liysial process. Tille fibers ruln antcro-
laterallI,. Tl'le\ appear to ( e modified inter( t ertebralis filbei s, alnd
p)ll)al)l [iilmetion ill Illimu h te smell Imallllnner.
l'- -Tie helr tract Idesignatedl as
to tlhe smite series in bir '. The'l' fiber direction is aitkern-posteriorl,
TFlite\ atlaclh ,lonII tlic postlcrior lcdic of thlie nIictlral spine iand ilit e Ia( d-
a( Ient arlc!. and Lil ten( d poster iorl to ailonli the entire lateral sur-
lit 1A.Fj 1\ I 11"HIDS, S1 UE Vit SW m
iJ5 ALt IFI]\BER(C. FPAXIAL \MI'SCi L \ lt HE (II IlHE'V 2(i1
i.ice of the neural spine anl tlit entlir dtrsal surface oi the neural
The series designated as the IV- andi IV-4 tracts il Siren have
iot lbeen lotild il Aiplina. [Ho er. several otllher iroullps hale
I een distniguislIhd which seeiin to b)e lactkiih inl Sir'ri.
I" -.5- As in Sii 'n 'ithl fibi'rs of thi1s tract 1rn1 ilttwvi'el n llact'ntl
t;In1s\ crstc pl]) uc'sss.
IV-o -' l]is >. ri' s 11, inot loI[lll ill Sio/re In A.i pluint. it lto ii
a t<\ Iarl lc l, i roilp, ith fi)lis I illlln/ l\ from thl( larl e' I IitrioI
telior slacc (e t tif th \ertitia keel oin thl nl \t \ crtctIl;a anitetriorl .
IV'-7.- Tih fibers o this tils ct aiso Xsl n] to bn' liisiill ill S ni'l).
o(r alI i ii flilt'ied tha I thlil\ hl a\ i tolit l)t- n rc( )1 o Iii/cd as Nftc. 'l'The\
(do not Ilrlil a \crt\ illpoltai nt or llrSe S tr tnu of fibliSiz. Tl 1 trH
attaches at 'one cad( t io ith( anterior sif'acc' ofl thlc pr-u/ plt iistal
buttress of olle' vcitl a to tilt' postr'ior porlio n ol tile tliin\t sl
pnrc\s.s oI ti(- plrecldini \ lcicehlra
NL( itN mis.- T ie int I <'rt(brlidl sC'iCs in this g'Cnllls of salaI,1mander N
is l\e\ tliicl shil ll r thll that s lin in Str'n o( AmihiumII TI IV\-1
and ill -2 (seris
ol)scl\ahl>c. "I'hc entire ma1,ss ol fibers flia Iroin tlt posterior surlacc
iof thn incural spine and polst)/\!;a)opll 'sial battrltsses ipostclrio( l\ to
attach alow.i thl riitire dlorsal surihwac ol lit noiural achb. As discrata
units the IV-3 and IV-4 secrm to be coiplrtull missing in c'l-tuius.
Thei 1T\-3 series is i)prcsnt. runiming lom transit iest pmtocss to trans-
\erse process in a manner \'r\ similar to that fond inl Sircn aldl
Amphimnit. \n IV' f6i tract is pirsent, Imut is mnilih less obvious than
in A-mphillnl Thc 1\ -7 1tens swuls to bc' colpletelty lackil(+t inll
HI P'AXIAI THINK 'M\ in IT \I Ill,.
Maiill er [I l1 )'1 1911) and otltiIr.s hai\c dealt vxtcnhnsi l\-l with tit,
nImlll 's ol this s-rit S. Thuse publi.ati(ois \il not he' rY\i('\\cd here.
Howl(cr. certain Ivathrmes of the details i sol e of tMhse illmscl.s Lia\(
Toot bIcn previousl' descrilbcd. Malrcr. \,oble 11931) anid otliurs
hia\u cdiscn ssed the o K'.7Clral ('ohitionrm andt fllnct'ionl sia nitfianlc
oft fhl \ariabilit\ ot this series ill thle irod lcs, but the matter is
olniousl\ not as clear asl mclli ht be desi'rrd. \s \lmaur 11911) hlas
pointed out. (onsidelrabcl parallel dc\1lopment has occurrTed in tli
evolution of certain features of Oie hpa iarl uomiiple]x. Its Ie\ oliition
262 B( LI.LET IN FLORIDA S I ATE ML\ SE'M \ol. 4
seems dependent on bodh form. ph)logeny and function. The im-
portance of each of these has not been clearly delimited.
The fiber tracts composing the muscle mass immediately below
the vertebrae ale more complex ini terms of attachments than previous
workers have indicated. These tracts make up a large part of what
Matrer terns the "suni ertebralis complex, More specifically it is
part of what he described as the \I. suiertebrahs medialis.
This small proximal portion of the subvertebralis complex differs
considerahlv in the three gellera examined during the course of the
present studi. In some cases these differences seem quite basic.
In Sircn tl e deeper inter\crtebral filers of this complex can be
separated into two series. In one series the fibers run diagonally
from the lower surface of the tratnserse process hath anteriorly
and posteriorly to the lateral surfaces of the central of Ioth preced-
inig, and succeeding vertehra. another series of fibers run longitudi-
nally from the bod\ of one centrum 1o t he body of another preced-
ing or siuceeding centrum. An cxen more superficial group of fibers
extends from one septum to another. This is the group which is
seen when the animal is eviscerated preparatory to dissection of the
internal iypaxial muscles.
In Amphiumna these three groups of fiber tracts are present and
as well dehloped as the are in Sircn. In addition a fourth group
appears as a modified intercentral fiber tract. Eachi tract of this
group extends diagonalth from the hasipophysial process of olie \crte-
bra anteriorly to the antero-lateral surface of the centrumi of the pre-
ceding element. This group is quite sui)erficial and can be seen
alter the animal is c\iscerated and without dissection.
In s\ctlurns the system is generally somewhat more simple than
that in Siren and Amphiuma. Diagonally directed fiber tracts extend
alteriorly and posteriorly to the lateral surfaces of the centruim hom
both the trans\crsc processes and the inmospta A third series runs
longititulinally from myoseptuin to im(sep)tun.
Lateral to this mIllediately sul\ erteliral medilial co(lplex in Siren
is an almost transversely directed series of fibers n which is not stronudll-
segmelted, and wliich cmoers a larec part of the internal dortso-lateral
\ all. This has been termed the traunseisuis t\iauir. 1S92). Lateral
to the large trans\ersus in Siren is another selects in which the fibers
run mIore or less tranls\ersel. This is the M. obliquus internuls which
(covers most of thle area of the lateral wall. In Amphinlia the sub-
vertebralis complex is more obviously split into two distinct series:
i c: that which is immediately siubertebral in position, the medial
1-5c \L'FFlI'NBEHC,. EPAXIAL MU\S(. LA LUIE OF BIREN 26 i
portion ol the stub\ertthralis, and a \enr large more lateral portion,
the siubli rtebralis laeralis. The latter covers most of the area en-
compasse d I' the transversus in Siren. Ventro-lateral to the sub-
N ertehralis complexx i A a l ArIAiona is a completely Insemllented tralls-
Nersis, more lateral in position than in Sircen. In Amphliuona tie'
Ol)hIquis internus can o0nly e seen )by rellecting the trans 'rsus. Ncc-
tw'us is similar to Amphiioa in this particular regard. However, the
trancisecrs is located more laterally, and the lateral portion of the
sull\ ertelIrailis is ouch larger ili Nrc/lrusi. than in Amphtilna.
D)lsc (:l StoN
The fiber tracts of thle epaxial muscle mwass in lrodeles are de-
scribed in as mllcl detail as is possible at this time. It is assum.s ed
that ilCTrcasinfl ceoliplexity of fiber tracts is a condition advanced
i er that of less complex systems. All tlhre of the genera studied
show r si arrangement in the more superficial intcrmyoseptal
fiber tracts. In regards to the deeper tracts. Siren is quite dilferenl
from the t\\o other generca examined. It illustrates a fair complexity
in the fibler tracts, particuilali of the intervertebral series. Fiber
tiacts rnllllinl from tile preCZv apopllysial processes of one \crtebra
to thi post/ gapophysial processes ol an adjacent vertcbrla, and
tracts rlniilIIg from th ti traLnsersc process of on( \ ertebra to the
postzyLapophyIsial process of another \-ertebra are examples. Of the
three genera examined Nccturu.s is decidedly the most priiniti\e in
its cpaxial fiber tracts. The deeper intiere rtebral portions of the
complex are siimplyl an extension ot tile mIetalmeric m1iotomal system
onto thle vertebral elements. sitli but very slight iodification- Amplti-
mua illistrates a -cry specialized condition, but one quite different
fliml Ithat fomlnd s ll S This s well slho bv tl great complexity
of the septal arrangem'ent medially. In addition, there are certain
speciahliations IlI tle iutervertebral fiber tracts, such as the dc\clop-
mecat of a series of fibers colnnecting the plwzygapopli sial buttress
and thle tiRIns\ rs t process. I)res(UInabIl tile flln tionl is thli salle las
inl the specialized transverse process-postzy:apoplhsial tract in Siren.
The cpaxial muscle' ciolnmplex is one which is seemi'gnly most im-
portant ill raisillng certain portions of tilh bodl as a colcaxe ar. It
is probably much less important ill lateral blendinig, which lI unction
is pisuirablyd shared (in a more pr'imitie condition) in conjuinction
with the hypaxial complex. \, tihe x erteiral column becain ll ore
doisall\ located ill tle cross sectional area of tihe b(odI these imusclels
played a less important role ill lateral undulations The more snake-
20il i I.A'l f\ 1L()HJll)\ T\I l \k F ,hE \11 lT. 4
like illodele] such t as Ampl\iial)l(I SIIll]il 'tl are quite capable of Id-
hII tilt' Ikd\ \erthIall\ to a 'reat de tree. Presumably the specializa-
tiomN, which allom\ these lonms to bmnd in this plane imnolc specialila-
tions in the (paial Imscl (niatlre. TheNlic speciali/ations would ilmol\ c
a(t lasIt L paifial ahbandonmen. t ol ]nllosepltal attichinits 'The inter-
.lrtc!ral \IsteSms w(ld bec> me mire developed. TIhi is illusttllat
hl. tl t, eipa i l ni musulatli. I Ic of btl 0 irn 1 a di an\ Am tpl iam Forms \ il1i
a similar bod fr(ImI and inodc of )loti ItoioinI. lhowc\ (.i, ctai; in I c IM\i
(Iiffi'rIeIc s xhntJ c ii tIhe t\\ o iIIlicate that t llhe arrai'.n iin t is indc-
penId intlt\ (de'ri\led in tlhe two ier. Th sp
ro (l can LImore aiiil bhe d(lri\( d f )ro tih pl nnifive condition m \ r-in-
Il, thait c'Lan (Ilhos' of 1ir .,
( oiccrrnini the l lpat\i
snhdertntualis complex is basicallv similar i& all thrl',c tnc'ra. Accept
tl Ilthe strow, hasipoplisi;al attack nie'its ni \tmpi iuna. TIh s hhl 'rs
are appar:'ntly iniportailt in biendihi the hnd\ dio\ anld to tlhe side.
In Siren a scri'es of lihl s rin ina fiom thl s11111 .anterior procm ss on
the x central ainiin;it of thiI' hli'nIs\ crsc lproc',SS to the side o(f tlIc c IlItr mll
oft the pr-c '( di ilIr \ ertebra apparently function similar .
The lateral li paxia] miuscilatmre is quite dilfereit ni the flnet
tenera examined. It is sinplest in N rctrums. The mnscles in this
al'ea il \('<'l N rmus ar( noit 10iJli specialized or forinitnu an are oif a
short radius in thi- sneak -lik-e irmns, sutc n as \i/philtit ] and Sn'nl ,
the loss of se imenitation in some of the muscles of this unlph'x ap-
paicntly prom idc' g c'atcr ni'cliha ical L(ficicil-\ ill this t\ pt'). of im -\<'
n'int. s lihas beeiln pointed (out I Maurer 10921 .Amphliitnm is most
specialized in this regard since both the tiansl\cIsus and obhquus
('\tc ius sapcrficialis arc unnsc incnted, In Siren onl the tlrans\crls\ts
is tnnsc-' cntc.(, and thelin onl partially so. T'I'le 1)'ltctr dc\clopinelnt
of more latmal epaxial intervcrtchral muscles in Siwin may take over
this function. In addition, Sircn possess a rectus laleralis ta mIscic
pruts intably \iT\ im|)ortatt in lateral motion in other toinis, TI'his
muscle is lacking in Amphimna. recordingg to Manrer Sii'iin possesses
few\\er muscle it\ ers in thlie bodv than do certain primitive loimins.
"This reduction is thoul'lht b\ sc(\Cral \Norkeis ito 1)e or ot the main
themes inll thle e\olution of the hipaxial series. A imphili possesses s
moreI laeis, but is specialized in other \va\l s.
ThelIc present stud Oi c) epa\ial iiscilatuire and \lMauiCi's aind
others work on the hlipa\ial mluscullatliure how liht .1a mphillnitn and
Siwn liave parallel deeloplnenlt in muscle exolultioni probalb)l\ in-
fluienced bv similar modes of existence. The differences in these
1lc)' AL.MIFENBERG. EPAXIAL MlSCULATI1RE OF SIREN 265
structuiires between the two genera semi to be basic and support the
Widely held concept ot their distant relationship.
Li LniATUtF C(i 1 )
'aici,i E I'. B
1 .3 1. T iih .tiiitom l t [In th iliatui iiadt r. (Oxfold Clritlldonl PCrins, pp. I-N\17i.
(Cmiil. C [. l \\. A\ flnNilc rii
1)53. I l hi', il s ,unklll.ncibl ofl tilt .iinlll Sir itidAii. Bull Mus. Comp, iZo l..
d ii 1 1 I i. 7, pp. V)i7-51 1
IC)- Nc \Vi\ sallal jinlcdi-i ofl t hll ,WiilV S111' Ii(il, frn11 th ,t (C tac'iis oI Nuorth
\Im I ia. Filiiunli G (cohl ,c1l .ll nO 3 ) pp 1t 1- '
M\l, I, F.
1 .92. I)er Aiiftl iI il hiI I- llf\\lt.klllll 1 r \c- i ir tlc i iu cl o pllli cCiilatil I'i
(dtIi LurnllI(it Amphi ltnii i ni d uI n It /il Itim'h _'[ /1 thd n II1]101 1] I I \11n-
kiln d('1i S laclhi u Ltindr Teleostier. Mo lrph. Iliri ., 1]1 IS pp 7- -1 7!
1911. l)i) i' ve tiA liiriplif lskil.tL, iir \i \o r uii n /,InU lII r ,,ncpmIu i td
pjiiunt! \'N I lllrllt-h ln lit icn Ittliti del l M usk'lnii ,mildird l rI
IiuTL d. /titchii o] 17. pp. 1- 10
IfJl6 /IIi n i,-1 I l, i< \r ,t
ii thI. \ l 1. pp 1 >i-:'i .
\NhIi, C K.
1')i Il- it iol4,o \ IiI tih \hipla/ibi \N w c uuik. Mc(;iL -Ilill pp 1-577
S iI\ l r, )I II
I i( I uiiict1ibutcinl ti., the .itiiEcl o iii of ,S Ia / tictnaU. Zool ,ti til ., \hit. cl
\1lphi C I 1 pp. (i31 -f6i
U -* 70, I
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