ON THE STRUCTURE AND DEVELOPMENT OF THE VERTEBRAL COLUMN OF AMIA, HAY 1895

Thispeculiarity consists in the possession, throughoutthe greater portion of thetail region, of apparently twice asmany bral bodies as there are myomeres and neural and haemal arches.. T

FIELD COLUMBIAN MUSEUM

PUBLICATION 5.

Assistant Curator of Ichthyology

CHICAGO, U. S A

1. Description of the gross structureofthe vertebral column. 5

3. Discussion of the vertebralcolumnoffossil fishes 20

4. Discussionofthe vertebral column ofthe highervertebrata...24

5. The origin and development of the vertebraeof Amia ing itsearlierstages 25

extinctAmphibia

ON THE STRUCTURE AND DEVELOPMENT OF THE

VERTE-BRAL COLUMN OF AMIA. O P. HAY, PH D

COLUMN

For ourknowledge of the vertebral column of the fish Amia we

are indebted to a considerable numberof writers, whose works will

discussion proceeds

In again calling attention to the spinalcolumnof this fish, we mustfirstof allconsider a peculiarity whichhas struck all investiga-

tors, and whichdistinguishes this species from all other living

osse-ousfishes. Thispeculiarity consists in the possession, throughoutthe

greater portion of thetail region, of apparently twice asmany bral bodies as there are myomeres and neural and haemal arches

verte-Franque (26) appears to have been the first to remarkon this tural feature of this fish. He regarded those vertebral centra which

similar to those whichare found in certainsharks andrays. Hesays:

'

Sunt igitur corpora vertebrarum inter vertebras intercalata."

He refers tothefactthatamongtheRaysRhinobatus hasintercalatedvertebrae, while among the Squali Sphyrna malleus has intercalatedsuperiorarches Almost all other writerswho have dealt with thesubjecthave adopted the same interpretation, while it is the express

view On the other hand, Dr G Baur (9) and Dr Carl Zittel (60)

in each of the myomeres in question are "centra" and "tra," (pleurocentra* and hypocentra.), corresponding to those ele-

intercen-ments whichtogethermake up avertebralbodyin some of the cephali

Stego-I signify myacceptance of the opinion that the wholevertebral

columnof the ancestorsof Amia was composed, ineach myomere, of

*The term centrum haslongbeen in, use to distinguish the principal portion of thevertebra

independently ot any theory concerning its origin and composition. Toapplynowthis term to dis.

tinguishone of the elements thatmayenter into the construction of a vertebral body would

intro-duce confusion I prefer therefore to employ in this paper pleurocentrum and fiypocentrum to

des-ignate the elements of the body.

6 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL i.

other I find itimpossible to ignore the results of palaeontologicalresearcheswhen they are exhibited inso clear alight. Theseresults,

stegocephalous-vertebralcolumn and that of so many of the earlier osseous fishes,

been shown by embryology that the vertebral bodiesin thetwo casesarise inthe same way; and thishas certainly not yetbeendone

Ifwe shallregard apleurocentrum andahypocentrum in the tail

astogetherconstituting a vertebral body, the totalnumber of these

although thenumber mayvary somewhat Of this number

skeleton thirty-nine vertebrae in the trunk and forty-seven in the

tail. Inhis figure ofanother specimen he representsfifty segmentsinthetail, of which about fourteen are the so-calledintercalated pieces

The anterior fourto six caudal vertebrae are simple, andresemblein

allrespects those of the hinder dorsal region, exceptthat the lower

arches are closed belowto form the haemal canal Nearthe endofthetail, again,the intercalated pieces are not developed. Therefore,countingpleurocentrum and hypocentrum as one,we findabout sev-enty-five vertebra? inthewholecolumn, although the number maybe

Externally the vertebrae of Amia differ fromthose ofmostotherosseous fishesin the almost totallack ofexcavations, bonyridges and

subsidiaryprocesses Those ofthe trunk especiallymaybe regarded

end These disksbecome gradually shorter as we move from thehinderdorsal vertebrae towards the head In the tail the two ele-

ments, pleurocentrum and hypocentrum, taken separately, are siderably shorter thana hinder dorsal vertebra; but, if we consider

theircombinedlengths usuallyexceed somewhatthat ofa dorsal trum, while the length of an anterior caudal vertebra is onlyabout

cen-seventy-seven per centofthatofahinderdorsalvertebra Asfar

for-ward as the twenty-thirddorsal vertebra fromthe headthe length of

eachvertebral body remains nearly the same asthat of the most Infront of this grow that the most

hinder-OCT.1695. VERTEBRAL COLUMN OF AMIA HAY 7

anteriorisbut little more than half the length ofthe twenty-third.Schmidt's description, butnot his figure, would lead oneto suppose

thatthe first two vertebrae behind the head are shorter, when

In transverse section the dorsal vertebrae are somewhatbroaderthan high, the perpendicular axis of the first dorsal being about

eighty-fiveper cent of the transverse axis. As we move backward,

nearlycircular, the hindermost dorsal bodybeingnearlyperfectly so.

The caudalcentra, on the other hand, become more and more

com-pressed towards the tip of the tail. Thoroughly macerated

verte-brae, as well as sections through decalcified vertebrae in variousregions, show that the notochordhas notsuffered complete constric-

tion,but runscontinuouslythrough the vertebral column.

It is no unusual thing to find the pleurocentrum and

hypocen-trum of someof the myomeres of the middle portionof the tail solidated Stannius (58, p. 21) had observedthis unionof elements,

con-and that it occurred at different points in different individuals

Schmidt has called attention to the same phenomenon, and has

figured such a resulting vertebra In such cases there is the closestpossible resemblance between the vertebra so resultingand one ofthe anterior caudal vertebrae At the same time there canbe no

verte-braand any of thoseof the dorsal region.

Onthe other hand there may occur a union of the elements ofdifferentvertebrae A specimen in mypossession shows an evidentcaseof the consolidation of the hypocentrum with both the pleuro-

centrum in front of it and the one behind it.

Evenif weshould not beable to find in the middle tail region a

vertebra formed by such apparently abnormal union of

pleurocen-trum and hypocentrum,we might find it instructive to comparethese

caudal vertebra The general form of the two elements taken

to-getheristhe same asthat of the simple vertebral body In the case

on the hinder element, the intercentrum In the dorsal region thearches repose on the hinder half of the vertebral body. In

"both the middle and the anterior tail-regionsthe upper and the lower

arches are separated bysuture from the corresponding bodies If

we should form ourconclusions regarding the composition of the dor

sal and the anterior vertebrae from what a macroscopic view of

FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL i.

formedthrough a union of distinct parts, whether these be regarded

as pleurocentra and hypocentra or as principal and intercalated

ver-tebrae.

With reference to the relations ofthe upperarches to thebral bodies, authorshave notbeen whollyaccurate Franque figuresthree vertebral bodiesand twosuperior arches; the basesof the lat-

verte-ter reposing equally on the upper surfacesof two contiguous tebral bodies, so that the upper arches are intervertebral in posi-tion. Inhis figure of thecompleteskeleton, he represents the bases

way intervertebrally The bases of the succeeding simple vertebraeare represented as resting almost wholly on the bodies of theirrespective vertebrae, while the upper archesofthe remainderof the

quota-tion from Franque is produced:

'

Inter apophysin superiorem et corpus utrimque in parvaf

rep-eris, cui cartilaginisapophysisaffixa est,et eoquidem modout usque

cor-poribusaddicendasit."

Shufeldt (57) reproduces Franque's figures, and statesthat thebasesof theneural arches " articulatebetweeneach consecutive pair

of vertebrae, these latter havinga formto accommodate themselves

hinder border of the base of each arch is representedascoming intocontactwith the anteriorborderof the next base behind

fig-ures He affirms thathehas not been able to find, in hisspecimens,

tocome intocontact by their adjacent basal borders. In both histext andhis figureshe represents theupperarchesof the whole dor-

sal regionas sittingonthe hinderhalf of their respectivebodies, and

the head, a considerable interspace In so doing he has fallen into

as greatan error as that ofthe authorswhomhe attemptsto correct,but of an opposite kind

When we come to examine these parts accurately, wefind that

in the hinder portion of the tail, where pleurocentrum andtrum are both developed, the neural arches have their bases ex-

hypo-centra the anterior of the base

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 9

front, while the hinder border of its own hypocentrum is left

somewhatuncovered As we move forward we find the neuralbasesshifted graduallybackward, so that inthe case of the most anterior

extend-ing neither on the pleurocentrum in front nor on that behind Inthe hinder dorsal region we findthatthe neural bases are set still fur-

slightly the anterior border of the vertebra next behind This

backward displacement of the upper arches goes on until, in theanterior end of the vertebral column, the bases are placed be-

tween two vertebrae and rest equally on both That is, if we

regard eachdorsal vertebra as consisting of a pleurocentrum and a

hypocentrum united, we may observe that on passing from thetail

to the head the pairs ofneural baseschange from aposition of

rest-ingeach on its own hypocentrum and partly on itspleurocentrum tothat of resting partly on-its own hypocentrum and partly on the

As regards the distance of the bases of the successive arches

closely, if they do not come into actual contact Soon there

isa space developed between them, and this increases to near the

end of the tail. As regards therelations of the archesto the

had drawn his conclusions wholly from an examination of the riorend of the vertebral column, and Schmidt from the otherex-tremity

ante-At the hinder end of the head are two vertebrae which arestrongly united to the skull. Their presence is indicated by lines

movable neural arches The halves of each arch meet above the

is articulated acompressed inter-spinous bone (axonost). Sagemehl

has already recorded the occurrence of these vertebral bodies, thearchesand the axonosts The lateral halvesof the firstarch behind

To theirupper ends isarticulated by afreelymovable joint a

axo-nosts which support the rays of the dorsal fin. The succeeding

arches increase graduallyin length To the second is articulatedan

axonost similar but the one Intwo

io FIELD COLUMBIAN ZOOLOGY,

axo-nost, while the otherhalf lies free behindthe axonost The fourthaxonost islooselyattachedto the upper extremity of the fifth arch

I findonly fourof these axonosts, but Franquefiguresseven,onlyone

liebetweensuccessivearches, as do two of them in one of my

archesas being extended oiit into lateralhalves longer than those

Between the lateral halves of each of the neural arches and

overlying the neural canal is found apair of intercalated cartilages(Fig i, i c.). These are vertebral in position, as is usually thecase with the bonyfishes. In Lepisostcus Balfour found similar

car-tilages runs the superior longitudinal ligament In the adults thesecartilages become more or less ossified, and the bonylayer which

inve'sts each cartilage is continuous with that of the correspondinghalf of the neuralarch

Asregards the lower arches, we findthat those of the middle of

arches lack a little of reaching the anterior border of the

transverse processesarise from the veryhinderborderof the bral bodies (Fig. 2). As we advance towardsthe head thesetrans-verse processes aremoved a little forward, until at aboutthe middle

verte-of the dorsal region they occupyaposition near the middle of thelength of the vertebral body (Fig 3). Near the head again

the processesappearagain to be slightlynearer the hinder border ofthe body. With respect to the level of origin of the pro-cesses, itmay be observed that at the anterior end of the vertebral

column they springfrom the sides ofthe vertebrae halfwayup

Fur-therback the processes slowly descend, so that those of the last

dor-sal vertebra arise from its lower side. In length these processesincreasefrom the first to the middleof the trunk,and thengradually

grow shortertothe last dorsal vertebral body In the tail the lower

arches are joined to the centra by suture Below the haemal canalthe lateralhalvesunite to formaspine. The spines of the firstfour

to six caudal vertebrae are articulated to their respective arches

elevated origin of the transverse processes in the dorsal regionis no

has

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY n

Franque states that the first vertebra, omitting thetwo which

areconsolidated with the skull, has no transverse processes, while

before methe processes of the first vertebra are certainlynot spicuous, butthey can hardly be said tobeabsent They stand outeach as abonyringsurrounding ashallowpit, formed bya shrinking

con-of cartilage. In this specimen, too, these processes supporta pair

of ribs, each of which is as longasthe first five vertebrae taken

to-gether Shufeldt could find no ribs on the first vertebra In

pair on the second Schmidt figures the first pair of ribson thethirdvertebra Inlikemanner myspecimen hasribsonthe last dor-

sal vertebra, as also did the specimen figuredby Schmidt Neither

Franque nor Shufeldt found suchribs in the specimens investigated

pleuro-centra of the tail, in a line on each side with the bases of thearches, are found, in fresh specimens, slightly projectingmasses ofcartilage Schmidtdescribes theseand givesfigures ofthem viewed

externallyandinmicroscopicsection He regardsthem as

rudiment-aryarches, upper and lower, belonging to the intercalated vertebralbodies Stannius (58, p. 21) refers to these, and compares them to

and the arches resting on them But Franque had observed them

still earlier, as isshownin the paragraphalreadyquoted fromhim

Schmidthas describedanotherset of cartilages, which, heclaims,

ver-tebrae, and they fill up partially the space between the successivearches Schmidt regards these cartilages as homologous with thosejustdescribedasoccurring on the upper side of the "intercalated"bodiesofthe tail, and therefore asrudimentary upper arches I will

say here that I have examined thesemasses by means of transverse

and longitiidin^.1 sections, and find that they are not distinct

carti-lages, but the anterior portions of the masses which occurbetween

the several vertebral bodiesandtheirneural arches

Thereisanother systemof cartilages which is of much interest,

side of all thedorsal vertebrae, there beingtwo to each vertebra On

mostof the vertebrae these two cartilagesproject somewhat beyond

the surface of the bone in alinearform, and are placed oneon each

sideofthetractoccupiedbythedorsal aorta In the dried skeleton

i2 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL i.

and withthe axis of the vertebra In the more anterior vertebrae

theyare nearly circular. Here they lie nearer the front end of thevertebral body (Fig 4). In the succeeding vertebrae the anterior

ends of thecartilages comeclose to the anteriorends of their tive centra, but becomegradually moreextended backward Finally,

respec-in the hinder two-thirds of the trunk they are so lengthened asto

Thesecartilages are found even onthe vertebral bodies which are soclosely united with the head They appear to have been noticed

only by Dr M Sagemehl (54, 57) who observedthem on the brae atthe hinder endof theskull andfollowed them backwardalong

verte-the vertebral column He statesthat in young individualsthese tilages penetrate deeply into the substance of the centra, while inolder specimens only thin plates of cartilage can be recognizedrest-

car-ing superficially on the vertebrae He enters into noexplanation ofthese structures They will engage our attention later. We may,

described by Dr Joseph Leidy (44, p 185, pi. xxxii.) from the

of the vertebralbody apair of fossae, which occupyexactly the tion of the cartilages inAmia The same fossae have been observed

posi-andfigured by Prof E D Cope in species of Pappichthys, also

as two parallel fissures which further backward become oblong

fossae, and againnearthe caudal vertebrae are narrowed Prof Cope

further says that inthe caudal vertebrae these fossae are as well

devel-oped as are the neurapophysial pits, and are much like them He

evidentlyhad in mind here the articulatory surfaces of thehaemal

arches, whichare verydifferent things

The structure of the terminal portion of the vertebral column

hasbeenmore or less accurately describedby Franque (26), Kolliker

(43), Wilder (59), and Shufeldt (57). Of these accounts it seems to

methat that of Kolliker is the most complete and his figures the

mostaccurate Shufeldt presentsan original figure ofthisregion,but

he omits a representation of the cartilaginous elements, and, as it

appears to me, of some of the bones Dr Wilder had not seen

Kol-liker' s paperwhen he wrote his notes, and, through what appears to

401) he ascribed to Kollikerviews not heldby the latterauthor So

farasthey bear on the same points, Wilder's results coincide with

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 13

Kolliker's figuresand descriptionscover twelve vertebralbodies,the prolongationof the vertebral axis behind these, and the arches

andother parts connected with these tworegions. Of the centradescribedand figured,the anterior seven are called "complete," in-

asmuch asthey are provided withfully developedneural and haemal

arches The last five are "incomplete," that is, they have haemal

arches but not ossifiedneural arches Belonging to the seven

com-pletevertebras there are, however, onlysix neuralarches, since the

between the second and third centra, and belongs equally to both

As was first shown by Franque and later by Kolliker, the so-calledintercalated vertebral bodies are no longer developed inthis portion

of the vertebral column Shufeldt's figurerepresents the alternation

of pleurocentraand intercentra as endingin front of the tenth tebra fromthe tip of the ossified part of the vertebral axis. This

ver-failure of the "intercalated" centra to develop is only apart of thedegeneration which hasaffected thisregion andbeen associated with

the production of the heterocercal tail of Amia

In the case of three specimens examined by myself I find thatthe vertebracalled byKolliker the last complete one, beingthe last

one furnished withan osseous neural spine, showsadifferent stateof

affairs. Thereisno osseous neural arch, butthere are two

cartilag-inous plates present, which meet, or nearly meet, above thespinal cord. These are also segmented off from the cartilage

which represents the next segment behind Shufeldt represents

thisvertebra ashavinga neural spine, and hence we mayconclude

that the spineis sometimesdeveloped, sometimesnot

As Kolliker has shown, the haemalarch ofthevertebra just

men-tioned isdifferentfromthose which precede it. The latter allhave

and, as shown bysections, penetrating to the center of the vertebralbody The former arch, represented by a haemal spine, orhypural

bone, is co-ossified tothe lower side ofthe corresponding centrum

The five terminal vertebrae haveossified centra, and each hasits

place of these thereis acontinuousbandof cartilagewhich roofs over

the spinal canal, andis prolonged posteriorly to the end of the chord, some distance beyond the distal ends of the hypural bones

noto-The last five vertebrae are more orlessreduced in sizeas weproceed

whichoverroofs thelast five vertebrae represents, as

Kolli-14 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i.

ker indicates, theneural archesofthese vertebrae These archeshave

become expandedanterio-posteriorly andhave coalesced Belonging

bone Each isco-ossified with the underside of its propervertebra

vertebra The last three of the haemal arches are directed nearlyhorizontally backward These are followed by two other similarbones, which Kolliker says belong to the lastvertebra, the hinder-

most looking like a continuation of the vertebral column On thispoint I shall have something to saywhen I come to speak about the

microscopic structure of theseparts.

Lying between thebone last mentioned and the cartilagewhich

similarbone which does notreach the last centrum It functions as

.aray-bearer, and doubtlessis thelower archof a vertebra which has

ceased to attain development I findthisbonein two specimens.

Kolliker describes that portion of the cartilagewhich projectsbeyondthe lastvertebral bodyas consisting of atubewhich inclosesthe spinal cord, oritsrepresentative On theunderside ofthe carti-

laginous rod isa furrow, at first shallow, and in this lies the chord Posteriorly the furrowdeepens, and at length, nearthe ter-

of the cartilage. Everywhere there is, according to Kolliker, apartition of cartilage between the notochord and the spinal cord

the extension of cartilage behind the last vertebra as representing

not only theupper archesbut also the continuation of the vertebra]bodies It thus represents a cartilaginous vertebral column("eine

Thetail of Amiahas not attained the stage of completecercality, that is, it*snot hypocercal Therearestill a few fin-rays

hetero-lying above the vertebral axis. Of these epural fin-rays, Kollikerfigures five, all unsegmented Shufeldt figures apparently three,

three rays, only the most posterior being segmentedsparingly. Of

epural interspinous bones, Kolliker figures four, the mostposterior

cartilage Shufeldt figures sixinterspinousbones', the hindermostof

which isapparently the one which lies close tothe rod of cartilage

Thisseriesof bones, as shown by the author lastnamed, completely

fillsup the space between the lastdorsal rayandthe upper borderof

OCT.1895 VERTEBRAL COLUMN OF AMIA HAY 15

ex-planation of plateix.) thatthese bones, takenin connection with thefree spines (interspinous bones) foundover the vertebrae immediately

was continuous from the base of thecranium to thetail. In

Oligo-plciirus, of the Upper Jura, which has a farshorter dorsal fin, there

is aseriesof such bones occupyingthe wholespace between thehead and the dorsal fin (Zittel, 60; iii. 231.)

Ofthese epural interspinous bones I have found, intwo

rela-tion with the base of the next to thelastepural fin-ray, thesecondofthose found byme The fourth bone is closely bound tothe upper

surface of the prolonged cartilage Its proximal end reaches for*

ward so as to overlap somewhat the last butone ofthe ossifiedbral centra The distal end appears to be embraced by the lateralhalvesof the hindermostepural fin-ray.

verte-2. THE MINUTE STRUCTUREOF THE VERTEBRAL COLUMN

Kolliker has dealt with the microscopical structure of the nalportion of the tail. Schmidt has also described and illustratedwith a number of figures some points in the finer structure of thevertebral column

termi-In all the vertebras of this fish the bases of the arches, upper

-and lower, come into contact with the sheath of the notochord \In

my specimen, 12.5cm long, thesebases consist of clear cartilage, but

at the innerendsof the bases small portions of the cartilage aresorbed This process of absorption continues as the individualincreasesin size, until probably the greater part of the cartilage is

depos-ited, which look exactly like the bone deposited elsewhere in the

arches serves to define their boundaries See figures i, 5, 6, 7.

It is interesting to observethat inthe case of the simple

verte-brae, as those, of the dorsal region, the cartilage contained in the

cartilage enclosed within the centrum; while the cartilage of thearches in the middle of the tail is continuouswith that of the cen-trum

The cartilages which have alreadybeenreferred to asappearing

in pairs on the underside of each dorsal vertebra, may benow more

fully described They are shown in figures i, 5, 6. As seen in

FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL.

whose bases are seen on the surface of each of the vertebrae,while theirapices reach usually to thenotochordal sheath Thecar-tilageappearsto persist evenin adultlife It is ensheathedin a thinlayerof bone, and incross sections this is seen toextend outwardasfar as does the cartilage itself. Hence when the cartilage shrinks

Inmost of thetrunk region, the basesofthesecartilages do notcome

intocontactwith the intravertebral basesof the transverse processes(Fig i). In the posterior dorsal region, however, where the pro-jesseshave descended considerably, the cartilages inquestioncome

into contact with the intravertebral bases of the lower arches,

or inner, sides (Fig. 5). Toward the last dorsal vertebra thesecartilages, which, from theirrelation to theaorta, maybe calledtheaortal supports, become shorter In the last dorsalvertebra (Fig. 6)the cartilageisshort, andisattachedtothe intravertebral basis ofthe

vertebra In the vertebras of the tail the cartilages are missing

There is, however, in my younger specimen, what seemstobe tiges of themin the firstcaudal vertebra Nothing, however, can be

ves-morecertainthan that the lowerarches of the trunk are bent down

to form the arches of the tail, and that the aortal supports have

lastdorsal vertebra we find, atthe anterior end, theaortal supports

looking somewhat like the lower arch-bases Further back,

the aortal supports cling to theirinner surfaces (Fig 6). Figure

7 shows asectionthrough thefirst caudal The bases of the lower

arches are seenin same positionas inthe lastdorsal

The originandthehomologyoftheseaortalsupportswillbether considered when we come to examine youngerspecimens In

fur-many, if not most, of the osseous fishes, there isto be found on the

suspended In the anterior portion ofthe vertebral axis ofAcipenser

a plate of cartilage grows downward fromthe lower edgeofthebase

of each half of thehaemalarch, and gives support andprotection to

aportion of theaorta Furtherback, these cartilaginousplatesbend

enclosingitina canal It appearsto me that theaortalsupports of

pro-cesseswhich in Acipenser In Amiathe

m .0 nsmiosqa iBeiob lohaJnf:nsrfgooiriinoiloaS 1 giH

, siv tnorfooJon aril ol gniiEiJsnsqa^"1 auonigfifiliBO 5o eiir^q aaiiil adi gniwoila ,not

iswol erto lo saasd ariJ ,89iloi laqqu aril lo esafid arilnoqqoarioidw

.elioqqua Ijslios srflbns

jjDiworia namiosqa ifubfi lo Bidslisv Ifiaiob dl()8,,3ffi Jo waiv IsiinaV S -qua I^liojs gooniBlinO sdl ^d baiquooo SIBrioiriwancdaril ni zqsg aril

.aiioq UtibB io asidaliav Ifiaiob rlli-1 hni; di<:I in v/siv iBilnaV F, giH

.llubfi io Srtdsiiav iBaiobbni bnBlaf lo wsiv IsilnaV i- gi"*!

.nol .m D c.Sf ns^paqglo jsidaliav [saiob slBroillunaq lo noiloaS c i'i

.Jrr.1 erf 1

gjs nerniosqg smBalo jndaliav Ifiatob Jafil lo noiloaS 0 .gi'i

'Hi lo atbbirn aril

PLATE I.

Fig 1 Section throughananterior dorsal vertebra of a specimen 12.5 c ra

long,showingthe three pairs of cartilaginous rays penetrating to the notochord, viz.,

thecartilageswhichsupportthe bases of the upper arches, the bases of the lower

arches, andthe aortal supports.

Fig 2 Ventral view of the 3(5th dorsal vertebra of adult specimen, showing

especially the gaps in thebone whichare occupied by the cartilaginous aortal

sup-ports.

Fig 3 Ventral view of 13thand 14th dorsal vertebrae of adult.

Fig 4 Ventral view of 1stand 2nddorsal vertebrae of adult.

Fig 5 Section of penultimate dorsal vertebra ofspecimen12.5 c m. long.Fig 6 Section of last dorsal vertebra ofsame specimen as the last. Taken

O.P.H it: BMeisel lith.Bostm

AMIA

.nsmiosqa amis io id9Ji;> v lbjjf>

.gaol .fnm cl ,nmkgnuoy; loaoi^nVH^^BBI^BE

isqqu adJ io esasd sriJawodS

sdlnoJesi aavlasoiadi doid

.mm? ftiwl lo BidsJisv leaiob dJ8dgiioiriJnoiJosa saia

.8 .g

ri sdi bniriad-iaui

.G

PLATE II.

Fig 7 Section through the first caudal vertebra ofsamespecimen.

Fig 8 Sagittal section through the axialregionof ayoung Amia, 15 mm long.

Takenjustbehind the head. Showsthe bases of the upper arches placed between

the intercalatedcartilages,whichthemselves reston the elastica externa.

Fig' 9 Transverse section through 8th dorsal vertebra of Amia 27mm long.

0.?H iJe! B-MeisellitUwM.

AMIA

.III 3TAJC

I

lo list adJ lo9gdsdl JK noigai IBIXB aril riguoidl noiiosa iKrubuJi^ooJ 01 iHisqqu adl bnsd Jrfgn -)ri) no .vlfBiD^qHS f.-MoriZ ^nol mm 08 WtwKloaarniDaqa

isqqu stii )o noiJieoqisic; ;l*BS^9JfilE3i9Jniisv/of sdl briB

;biorioolon sril bn esdoiKi^qn 31

noasrfoiE iswol srf; Jo ?.s?.sd orfj nsswlddgniinsv/STJ;

aagEliJifi:)baJfilBDiaJni sdJ

.bnsri rfsl

sdJ lo noilioq bsievoonrj HE esriou, > ii nasvtftfad oals ;msdi

.biodooloa

.mrnf;S; trnwk ne lo^M^^Wl^MDrohsJeoqE dyooidJ noilosa-asoiD SI 1"?

lo aJnioq}zaih3aril lo noilEUlia srii ^HEiosqaaewodg

AND ACiPENSER.

PLATE III.

Fig 10 Longitudinal section through the axialregionat the base of the tail of

a specimenofAmia30 mm long. Shows especially, on the right hand, the upperandthe lower intercalated cartilages; on the left hand, theinterposition of the upper

intercalated cartilagesbetween the bases of the upperarches and the notochord; while the intercalated cartilages are wantingbetweenthe bases of the lower archeson

the left hand.

Fig 11 Side view of a portionof the dorsalregion of the vertebral columnof

Adpenser. Showsbases of upper and lower arches and the cartilages intercalated

betweenthem; also between the two series of arches an uncovered portion of the

notochord.

Fig 12 Cross-section through a posterior dorsal vertebra of an Amia 23mm.Shows

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 17

are apparentlysomewhat moreindependentof the haemalarches,butthereseemstobe no reason why this condition should notbethe re-

sultof specialization.

Amicroscopical examination of the caudal region of a specimen

value

similar to the vertebrae precedingit. Botharches,theupperandthelower, sit upon cartilaginous bases, and these latterpenetrate close

tothe notochord The next vertebra, like thecorresponding

neuralspine, while alsothe lateralhalves of the neural arch appearnottomeetoverthe spinal canal. Thecartilageson which the neu-

the moreanteriorvertebrae The haemal arch, onthe contrary, has

of the moreanterior vertebras are herewanting, and the lower side

spine isconsolidatedwith athin shellof bone which formsthe lower

side of the vertebral centrum The appearance presented suggests

periodin thedevelopmentof the individual, so that it hasnot stood

inthe wayof thegrowth of the notochord

just described, we findthateach possesses the upperarmsof thetilaginous crossand thatupon the endsof these arms, restthe edges

car-of the strip of cartilage which roofsoverthis partofthespinalcanal;

justasthe neural arches of the more anterior vertebrae rest on the

of theselast five vertebraeis almost wholly segmented off from that

the vertebra just preceding, presents a gradual transition between

the normalneural archesand those which have become concrescent;

so that it isquite certain thatthis anterior portionof the prolonged

cartilage ismade upalone of the neural arches It is also tobe served herethat the upper side of the notochordhas sufferedcon-

ob-striction atthe points touchedby the lower endsofthe intravertebral

i8 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL i.

re-spective vertebrae in the same wayas has been describedin thecase

of the vertebra immediatelypreceding No cartilage is present, but

crust of bone, possibly of cartilaginous origin, and to this is

cen-tra has, on the underside, undergone little constriction

Mylongitudinal sections do notconfirm Kolliker's view that the

next two hypurals are attached to the terminal centrum of the tail.

Whilethe baseofthe first of these hypuralsdoescomecloseup to thehinderborder of the last centrum, it is entirely distinct from thelat-

sup-ports itsown portion of the notochord The next hypural is in its

back, and isnot at all coossified with the last developed centrum

base closelyresembles that of the vertebrae in front; since there is,

next to the notochordal sheath, a layer of ossified cartilage. We

have therefore some reason to believe that the base of this hypuralhas become coossified with the lower portion (hypocentrum) of an

imperfectly developed vertebral centrum. The base of the last

rep-resents another rudimentary centrum It is notat all improbable that

at alater period oflifethese hypuralscoossify bytheirproximal ends

described by Kolliker

It is interesting to note that the notochord overthese two

hypu-rals just described, hassuffered slight constriction, as if in sympathy

with the effortto develop additional centra.

In my sagittal sections I find, in place of the staff-like bone

which is sometimesseenabove the lastdescribed hypural, and which

is itselfundoubtedly but another hypural, a row of three cartilages.

The two mostanterior of these nodules of cartilage are covered with

a layer of bone

Turning ourattentionnow to the bandor rod of cartilagewhich

the lateral halves of the twenty-first caudalray, wefind that ker, as already stated, regardsit as representing not only the upper

Kolli-arches, butalso the continuation ofthe vertebral centra According

to Kolliker's description and figures, the cartilage undertion forms, for some distance beyondthe lastvertebral body, a com-

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 19

the underside of this tubeis a furrow, at first shallow, but growing

Nearthe tipof the cartilage theedges of the furrowmeet and alesce below the notochord Kolliker's figures show a relativelythick wallof cartilage everywhere between the spinal cordand thenotochord In mysections there is, on the contrary, from the last ossified centrum to the tip of the notochord, no cartilage between

co-the latter and the spinal cord The narrow space between them is

occupied byloose connective tissue and blood-vessels The lower

bordersof the cartilage incline inward between the two structures,

butdonot meet The condition described by Kolliker is probably

.attained at amoreadvanced age. Fartherback, ata point some

dis-tance behind the distal ends of the hypurals, the cartilage

gradu-ally spreads downward over the sides of the notochord, and finally

downward extension ofcoalesced neural arches, and none of itfrom

this portion of the terminal cartilage seven shallow nicksalong its

lower border These suggest apartial separationinto distinct

seg-ments

-of the hinder tail region of the specimen 125111111. long, the chordal sheath is farfrom having a structurelessappearance Espec-

noto-ially alongthe portionwhere the incompletevertebrae are developed,

but also further backward, the sheath is traversed fromelastica to

with carmine Wherethe notochordisconstricted by the uppertion of the incompletevertebrae, these fibres appearto startfromthe

resem-ble thehairs ofa brush, butas theyapproach theinner surface ofthesheaththey become finer and lessnumerous

In this same region the inner cuticular sheath has undergone

vertebrae of the upturned portion of the tail have constricted thenotochord, especially on the upper side, we find that the outerhalf,

or somewhat less, of the cuticular sheath stains deeply One is

reminded of the modificationsuffered bythe sheathof thenotochord

of Lepisosteus, as described by Balfourand Parker (4, vol. i, 781;vol iv., pi. 41 (Fig. 69). InAmia, however, the pulley-like band somodified does not extend far forward and backward the

20 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL.

most constricted portion of the centrum InLepisosteusit

extends-in each direction to the end of the centrum In Amia the

fibres-described in the preceding paragraph appear to pass right through

the modified bandof the sheath

3. DISCUSSION OF THE VERTEBRAL COLUMN OF FOSSIL FISHES

Having nowconsidered the structure of the vertebral column ofthe living Amia, it is proper to determine whatlight we may obtain

may berelated to it. For a presentation of thefacts relating to the

Amioid fishesthe reader is referred to Dr Zittel's "Handbuch der

Palseontologie,

"

vol iii. Through Amia, Eurycornms, Callopterus,Caturus, and relatedgenera, we are apparentlyled back tomore and

moreprimitive arrangements. Froma studyofthese forms attempts

of the vertebraeof these fishes. Thatadopted byDr Zittelmay be

thusstated The hypocentrum (originally of twolateral halves) is

supports thelowerarch Ontheuppersideofthenotochordare

devel-oped two pleurocentral plates, which mayalso becomeconsolidatedinto onepiece. Suchan arrangement maybe found in Caturus In

fur-ther upward onthesides of the notochord, while the extremities of

ele-ments mayat lengthcomeinto contact, andthus coverin the whole

surface of thenotochord Suchaconditionmay be seen in some

por-tions ofthe vertebral column of Caturus and inthat of Callopterus.

hypocentrum meeting abovethe notochord, and thusforminga

com-plete ring In asimilar way, the pleurocentrum of each myomere

Onthe other hand, Ludwig Schmidtappears to regard the two

ringsin each myomere asthe primitive condition, and each of these

as a distinct vertebralcentrum, the one with, the other without,neuralarches As to the manner of development of the vertebralcentraofthe dorsalregion, Schmidtpresentstwocontradictor}7views

He at firststatesthat these vertebrae must be regardedas resulting

fromthe coalescence of two suchvertebras asare found in each mere of the tail (56, pp 755 and 760). And he presents as evi-

com-the anterior tail and the occasional fusion.

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 21

ofthe two centra in the middle tail region On another page of hispaper, when Schmidt comesto consider the fossil forms with rhachi-

tomous vertebrae, such as Eurycormus and Euthynotus, he explains

these structureson the hypothesis that,startingwith thetworings in

eachmyomere throughoutthe body, thehypocentrum hasgrown at

sizeandis confined to the upper side of the notochord Eurycormus

furnishes one stage ; Euthynotusa more advanced one At length

of the series, Schmidt finds the pleurocentrum represented by onlythesmall massesof cartilage, "the rudimentary upperarches,,"alleged

tolie in frontof thebases of the developedupperarches Of course,one or theother, or both, of these explanations mustbe wrong; and

neither of them explains the arrangement found in Caturus, as is

have resultedfromthe growth of the pleuro-and hypocentral plates,

seemscapable of explainingall the known facts.

Havingconsidered the mode of developmentof the vertebrae of

the Amioidei, it may be profitable to inquire whether or not any

so-calledGanoids first claim our attention

Our modern species of Lepisosteus show no indications in theiradult conditionofthe presence ofpleuro-and hypocentra But Aspi-

dorhynchus, a member of the Rhynchodontidae, haddorsal vertebrae

composed evidently of two portions. These formed rings, which

weredividedalongthesidesbysutures This being trueofthe dorsalregion, wecanhardlyfloubt that thecaudal vertebraealso originated

from oncedistinctpleuro-and hypocentra The tubular vertebrae ofBelonorhynchus, too, musthave hada similar origin

In the family Macrosemiidae, Cope ^Saurodontidae, Zittel) some generahave simple tubular vertebrae Others, as Eugnathus; have

thevertebrae composed each of two distinct pieces The species ofPholidophorus sometimes possess undividedvertebrae, butusually the

centra are made up of pleurocentra and hypocentra (Zittel, 60, p.

315) In the tailthese twopieces stand nearly opposite each other

and form a bony sheath on which rest the upper and the lower

arches It seems quite improbable that the closely related genera

fropterusand Histionotus should have developed vertebrae in an tirely different way

en-Little isknown concerning the state of the vertebral column of

the Sphaerodontidae and the Stylodontidae. At any rate, the

ossifica-tionswere feeble have had likevertebrae

22 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL.

meageraccounts of the vertebral structures of these fishesmake it

pleu-rocentraand hypocentra. And the same having beenshown to be

true, or highly probable, of every familyof the order Lepisostei,

we are, I think, justified in reaching the conclusion that whenever

ossification of the vertebral column has begun in membersof thisgroup, it hasbeen through the formation in each somite of alower

piece orpieces, on which rest the lateral halves of the haemal arch;while onthe upper side of thenotochord upper pieces of bone have

been depositedinthe region of the basesof the upperarch; that is,pleurocentra and hypocentra are normally constituents of the ver-tebralcentrum

Of the condition of the ancient Crossopterygia, as regards thevertebral column, we have littleknowledge Prof Cope (15, p. 19}states that in Ectosteorhachis (Megalichthys) the vertebrae are repre-sentedby annularossifications resembling those of Cricotus There

appears, however, to be only a single ring in each myomere.

From the foregoing survey of the condition of the vertebral

column in the different families of the so-called Ganoids, onemay

easilybecome convinced that originally the ossified vertebral centra

of allthe species that possessed suchwere composite in their ture; that is, each centrum included in its composition a pleurocen-

struc-trum and ahypocentrum Each of these twoelements wasdoubtless

itself, at an earlier period of its history, double If the centrum is

the coalescence at sometime in theanimal'slife ofthe two elements,

orpossibly sometimes from the suppressionof oneof them If we

bya solid vertebral body, and in another portion by twocomplete,

but distinct, rings; or in another fish the notochord in oneregion

protected by pleurocentra and hypocentra, while in another region

there are mererings, it appears quite improbable that these different

structures have no genetic connection. It is equally improbablethat

in species of the same family, orof closely related families, thetebralcenters originated sometimes as mere tubular incrustations ofthe notochord, sometimesasdouble rings, and sometimesas pleuro-

ver-and hypocentra. Some one of these structures must have been

calledpleuro-andhypocentra mustbe regarded asthe most primitive.

To what extentdo the conclusionswe havereached apply to the

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 23

By the consentofperhapsallmodernichthyologists, the ships of the Ganoidsand the Teleosts areveryclose. Dr Gill (31)regards thetwogroupsasdistinct subclasses, butadmitsthat in some

relation-of their members they approach closely. Liitken (46) excludes from

conception of the Ganoids as forminga distinctgroup Cope forms

of the bonyfishes, and someof the Ganoids, hissubclass Actinopteri

It ishardlyopentodoubtthattheTeleostshave descendedfrom more

intimately related to the Isospondyli, and have probably furnishedthe ancestors of the latter. Hence we might reasonablyexpect tofind in some of the recent or fossil Teleosts, in the stricter sense,traces of the composite natureof the vertebral centra And in fact

Prof Cope (22) expresses the opinion that the fossil generawhich

possess annularvertebrae, as Aspidorhynchus, should be assigned toIsospondyli According to theviewsof Liitken, mostof the genera

Teleosts The Hoplopleuridae, whose members range through theMesozoic, arenowusually assignedto theTeleost series. In someofthese the vertebral column is imperfectly or not atall ossified. Be-lonorhynchus has feebly ossified vertebrae The vertebral elements

points out the close resemblance of this fish to Be/onebelone, living

now in the Atlantic He states that if the vertebral column-of onorhynchus were ossified it would be difficult to distinguish the two

Bel-genera We are therefore justified in expecting that our living

Teleostswill in some way displayin their vertebral structure theexistence of the elements which we have found in so manyof theGanoids Nevertheless,we are not yetin a condition to demonstrate

the presence of such elements The vertebrae of ourfishes havenotyetbeen investigated sufficientlyfrom this point of view to enable

It is, of course, entirely possible that in the lapse of ages one orthe other of the elements of the vertebral centrum of the ancientfishes has entirely disappeared, while the other remains as its soleconstituent Andthis is whatProf Cope appears to believehas hap-pened He says(22, 1019):

inter-centra [hypointer-centra], asinthe Batrachia." This opinion maybe

cor-rect, butthe groundsonwhichitappears to have been based seem toafford insufficient "The and

24 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL.

Zittel render itperfectly clear that thefishesrarelydevelop complete

vertebral centra [pleurocentra], the order Halecomorphi being the

mimberof families are mentioned by Prof Zittelaspossessing centraand hypocentra.

pleu-4. DISCUSSION OF THE VERTEBRAL COLUMN OF THE HIGHER

VERTEBRATA

ele-mentswhichwehave found so well developed in the vertebrae of the

Amioid fishes. Hermann von Meyer wasthe first topoint out thatthe vertebrae of the fossil Archegosaurus, among the Amphibians,

were each made up of anumher ofdistinc tpieces Thisgenus, and

othersclosely related toit, show indeed aremarkable resemblance inthe structure of their vertebrae to the fishes related to Amia, espec

iailyto Caturus Others again, as Cricotus and Diplovertebron, have

the vertebrae of at least the tail constructed exactlylikethe vertebrae

as Mastodonsaurus, usually have solidly ossifiedvertebrae, but Von Meyer has shown that such vertebrae may, during the youth of theanimal,havetherhachitomousstructureof Archegosaurus Somespe-cies, again, as those classified as Lepospondyli, had simple tubular

vertebrae; but in closely relatedgenera, such vertebrae consisted each

of aright and left half, thetwo meetingbya suture alongthe dorsalandventral sides ofthe notochord Whether in such cases we have

twopleurocentra or two hypocentra, or the twoelements coalesced,

it mayyet beimpossibleto say Cope holds theview that the braeof modern Amphibians consist only of hypocentra This view

verte-will bediscussed further on

Onthe other hand it hasbeen shown by Cope, Albrecht, Dollo

and Baur, that the vertebral centra of the reptiles, birds and jnals are really pleurocentra, while the hypocentra appear onlyoccasionally in reptiles, especially as "

ani-subvertebral wedge-bones,"and in all Amniota asthe "

body" ofthe atlas.

The finding of the elements pleurocentraand hypocentra in thevertebral column of somany of the osseous fishes, the amphibians,

and the Amniota maywell lead usto suspectthatfutureinvestigationswill reveal astill moregeneralparticipation by them inthe structure

ofthe vertebral column Such investigations may furtherprove to

what extent these elements enter into the constitution of the

primi-from

OCT.1895. VERTEBRAL COLUMN OF AMIA HAY 25

5. THEORIGIN AND DEVELOPMENT OF THE VERTEBRAE OF AMIA DURING

ITS EARLY STAGES

Since my results obtained from the study of adult specimens

I havehad the good fortune to acquire a considerable amountof

lar-val and young material Some of this, consistingof larvae from 10

to i5mm. in length, wasreceivedfromDr.J E. Reighard, of the

Uni-versity of Michigan, through the kind offices of Dr Eycleshymer, ofthe University of Chicago Forthe possessionofthe young oflarger

Forbes, of the University of Illinois, and his assistant, Prof Frank

theIllinois river at Havana; andit was here that Prof.Smithsecuredthe materials sentme Asaresult of a studyof theyoung ofAmia,

lomm. in length An enlarged figure of a specimen of this length

walls of the vacuoles staindeeply with carmine, butnot, at least for

me, with hsematoxylin. Peripherally they pass into a layer

resem-bling in every way themselves, but thicker The thickness of thisexternal layer I make to be about .oo66mm. but it is thickerwhere

the vacuole walls enter it It apparently represents the epitheliallayer, which is seen at a later stage, butI find in itno traces of nu-

clei, or little else to suggest the presence of cells. Outside of it lies

a highly refractive, extremely thin layer, one of the sheathsof thenotoehord

Anteriorly the pointed end ofthe notochord isburiedin the'nective tissue closing in the pituitaryspace, but the greater portion

con-of the cranial division is enclosed in the well developed cartilage atthe base of the skull. Thiscartilage maybe followed backward, inlongitudinal sections, into the tworidges of the skeletogenoustissues

which giveorigin to the upper arches The specimensof the length

[hyaline cartilage In another, the cartilage at the base of the skullpasses insensibly intoprocartilage in the region of the neuralarches

In the intervals between the nerverootsmaybe seen the bases ofthe