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THE COLUMELLA AURIS IN AMPHIBIA.

Srconp ConrrRiIBurion. —o

B. F. KINGSBURY AND H. D. REED.
besos

TABLE OF CONTENTS.

PAGE
(SS UTORS TLRS" SAN ae de Mae oe 549

II. Descriptive.
JUV INSTA OTE a C00K61 2220 1s ig a rc 2 ae ee 554
CUES Bs 70 thy SIR DT T0010 ye mee ee ge a PO 563
“TTY S ey SAVE TST COST aie a 556
IMEI GRIEEN IOS) 03 Fete a oe ee ee ee 569
MIEMILEHVILUS muVALICLESCENS” Chiesa rns wae occa eS ccaoee wee 574
Same tae ATTVO OME eo... cus kins sisi « oelak Blake Moe elie oo 576
LD SSID TEAM AM HITS MT EDISTORT, . lala Ope A ole ee it tater yet | ieee me 584
WO SATU 21 SV ee a a a 586
Pea SEAN COIOSUSH Che tc fie Sor eR one roe oa oo ek. 589
ery provranctus allegheniemsis ©... . 40.00. .cec eee eee cous 591
PEON IrAChUS, JADOWICUS? | os ...c5.. 002% con ee) dled oa cioietee aks 595
See RST TSE ek ee ae _ 596
SUED) VGA (RE ek Os Meat a i eae a 598

Ill. General.

MUeSSUSPEUSOLIal COMNEELION: <0... j0e2. ak nc eess ca ee been ne 600
sees COlmela ale <Operculum: <.!. 40) . oo. hc sk. ods oho ne 603
SHAD CrAN OM eayviith VANIIT Er Ae cleo... 05 Sane o's eels Choad kes os eo de 608
Pa CUED OULEC ER GAMES ele ate. ot Sate AA awh Ot. Wis 5 sock % oaks aura oe Bink ae Gill
The Hyomandibular-symplectic Homology ................... 612
“TUDE TVG CURE Bow Ae eae BA pee O47 a 618
ER OEMH LON ara g Fiera wen Fe eve, eiaiaie rcveias ce Sane’ «vv eleva 6.0 Sem eee 621
MINGLE LUE C Mivors in cyt cr 98) Os ERS cin, dives + cs es Gevewianc Maa eicte, . 624
SBME VT DIAOMNGR 5 nce cy 7 peaeen ns Peale crcis Kerasctice bak hehe eee 627

VII. Explanation of Plates.
VIII. Plates I-X.

In 1908 the authors published a partial report! upon the morpho-
logical relations of the so-called Sound-transmitting Apparatus in
representative Urodeles with a view to establishing the type or types

‘Anatomical Record, Vol. II, No. 3, June, 1908, pp. 81-91.

THD JOURNAL OF MORPHOLOGY.—VOL. XX, No. 4.

550 B. F. Kingsbury and H. D. Reed.

and their modifications. In this study the following possible gen-
eral aspects were kept in mind: (1) The primary (primitive) and
secondary character of the connections and relations of the struc-
tures occupying the fenestra vestibuli more generally designated as.
constituting the Columella auris, (2) comparison with the forms
below (fishes) the amphibian group (the hyomandibular homology),
(3) homology with the reptilian Columella and mammalian Ossicula
auditus, (4) the comparison and homology in Urodela and Anura,
(5) the relationships of the different urodele families, (6) the fune-
tion and functional importance of these structures in the tailed
amphibia, (7) the variation in the arrangement of the parts of the
apparatus and its significance.

It is not necessary to repeat here the reasons that led us to believe
an extensive re-examination of the comparative morphology of the
structures fitting into the fenestra vestibulc in urodeles to be neces-
sary, as they were briefly set forth in the first paper and previously
by others (Gaupp, 798; Driiner, 703). In the examination of the
different forms, there have been kept in mind the following morpho-

logical relationships :

1. Relation (connection by fusion, articulation or ligament) of the Colu-
mella (stilus columelle) to

(a) the os. squamosum (paraquadratum, Gaupp),

(b) os. quadratum or palatoquadratum,

(c) hyoid (ceratohyale) ;

2. Relation to the carotid artery (Arteria carotis interna) and jugular vein
(Vena petroso-lateralis) ;

3. Relation to the otic capsule (lips of the fenestra vestibuli) ;

4. Relation to facial nerve (ramus hyomandibularis VIL) ;

5. The ligaments coming into relation with the parts involyed,—

(a) Ligamentum squamoso-columelare,

(bd) Ligamentum hyo-suspensoriale,

(c) Ligamentum hyo-mandibulare,

(d) Ligamentum hyo-columellare;

6. Musculus opercularis.

Since early in the investigation it became apparent that there
were two morphologically distinct elements appearing in the different
forms, comparable, at least, if not homologous (vide subseq.) as we
believe with the plectrum (columella) and opereulum in the frog. it

The Columella Auris in Amphibia. 551

became necessary to keep in mind the development of each element
in its relation to the ear capsule. In the present paper a detailed
presentation of the developmental changes, even as far as they have
been worked out, is not included.

In addition to the forms briefly described in the first publication
made by us, there have been examined by means of serial sections
through the head, 14 species representing 1 family and 12 genera.
The total number comprises 8 families, 21 genera, and 23 species,
in the case of all save 9 of which the structure and morphology in
both larvee and adults were investigated. Bearing in mind that the
total number of the familes and genera of tailed amphibia is 8 and
45 respectively, it may be seen that a comprehensive and at the
same time detailed view has been gained of the relations of the
urodele “sound-transmitting”’ apparatus.

Without entering upon a full discussion of the bearing of our
investigation, which is reserved for the last portion of this paper,
the more important results may be stated briefly at this point.

1. In the tailed Amphibia, there may be developed two separate
fenestral elements fitting into the fenestra vestibult. These have
been termed by us Columella and Operculum respectively.

2. The Coluwmella typically possesses a Stilus which is connected
primarily with the ventral (or ventro-caudal) edge of the squam-
osum. The Stilus columell@ may secondarily become joined to the
palatoquadrate.

3. In development its proton appears outside the otic capsule as a
group of cells continuous with the cells between the otic process of
the palatoquadrate, squamosum and ear capsule.

4, The facial nerve in the forms examined is entirely below (and
in front of) the columella save in Necturus, Proteus and Typh-
lomolge, in which the Ramus jugularis VII passes above the
squamoso-columellar connection.

5. The Operculum is developed out of the otic capsule. Its posi-
tion relative to the columella is caudal and medial. It possesses
no skeletal connections but gives-attachment to the MZ. opercularis.

6. In one group of forms, the columella only is present. In the
Ambystomidz the columella is present during the larval period but

552 B. F. Kingsbury and H. D. Reed.

becomes fused with the ear capsule at transformation when an oper-
culum is formed. A further reduction and fusion of the columella
is encountered in Salamandra, Triton and Diemictylus (Salaman-
dride and Pleurodelide, Cope). In the Plethodontide and Des-
mognathide the fenestral plate of the columella embodies a repre-
sentative of the operculum which is not separately developed.

7. The hyomandibular homology of the Columella is strengthened.

How widely the results of a detailed examination of a large
number of forms depart from the interpretations at present accepted
based upon the available information as to the morphology in a more
limited number of salamanders, may be seen from a comparison of
the above with. the statements in two of the standard works: The
Comparative Anatomy of Vertebrates, by Dr. Robert Wiedersheim,
and the section upon the development of the skull, by Dr. Ernst
Gaupp, in Hertwig’s Handbuch der Entwickelungsgeschichte der
Wirbeltiere.

The former (’06) describes” the fenestra vestibuli as filled by a
cartilaginous plate, the so-called Stapedial plate or Operculum which
is joined to the Palatoquadrate and Paraquadrate (squamosum) by
ligaments, cartilage or bone. This bridge between the stapedial plate
and the quadrate (or paraquadrate) is called Columella and together
with the Operculum, in a phylogenetic sense, corresponds with the
proximal segment of the hyoid arch (hyomandibulare or possibly
symplecticum). Ontogenetically such a relation does not occur, both
operculum and columella arising by differentiation in the territory
of the otic capsule.

Professor Gaupp (’05) in Hertwig’s Handbuch (pp. 696, 697,
605) designates the entire “stapedial” element as Columella aurts,

2«Sie [Fenestra ovalis] wird von einem-durch Bandmassen oder auch durch
Knorpel oder Knochen an das Quadratum und Paraquadratum befestigten
Knorpeldeckel, der sog, Stapesplatte (St) oder dem Operculum, verschlossen
und soll uns bei der Anatomie des Gehér-Organs wieder beschiftigen. Jene
zwischen Stapesplatte und Quadratum resp. Paraquadratum sich erstreckende
Briicke heisst Colwmella und entspricht zusamt dem Operculum in phylo-
genetischer Beziehung dem oberen Abschnitt des Hyoidbogens. Ontogenetisch
ist yon diesen Beziehungen nichts mehr nachzuweisen, sondern es handelt
sich sowohl fiir die Columella als fiir das Operculum hinsichtlich ihrer
Entstehung um Differenzierungsprocesse im Bereich der Labyrinthkapsel.”

The Columella Auris in Amphibia. 553

consisting of an Operculwm which may or may not bear a process,
the Stilus columelle. The process when present is usually connected
by means of a ligament (Ligamentum suspensorio-columellare) with
the Paraquadratum, Palatoquadratum or with both. The facial
nerve in most forms passes below the suspensorio-columellar connec-
tion. It is stated, however, that there are two such connections, one
above and one below the facial nerve. The operculum with a stilus
is regarded as the more primitive condition and as such is probably
to be homologized with the Hyomandibulare. In the Anura the
Columella auris consists of two elements, Operculum and Plectrum,
the latter (Pars mterna plectri) probably to be interpreted as a
stilus which has become secondarily dissociated from the operculum.

Nomenclature. The question of nomenclature’is a perplexing one.
Gaupp has termed the entire fenestral structure, Columella auris,
consisting in Anura of two elements, Operculum and Plectrum, in
Urodela of Operculum and (typically) its process, Stilus Colum-
elle. The direct application of the terms used by Gaupp, though
desirable, becomes difficult in the hght of the existence of a stilus-
bearing fenestral plate and a non-stilus-bearing fenestral plate in the
same form and at the same time. While there are objections to both
the terms Columella and Operculwm, it seemed better to avoid the
introduction of new terms and to employ the term Operculum for the
stilus-free structure and to restrict the name Columella to the stulus-
bearing element. This use of terms seems to necessitate less depar-
ture from the earlier use of the names. The operculum of Anura is
directly comparable with that which is termed by us operculum in
the Urodela. ‘This in Siredon was termed Operculum cartilageneum
by Windischmann in 1831 and subsequently has often been designated
Operculum in other salamanders. Columella was, of course, applied
to the anuran structure now named Plectrum by Gaupp, and to the
stilus in Urodeles, or to the entire element (Hasse, ’73) called
columella by us.

As an indifferent name for bony or cartilaginous plate fitting into
the fenestra vestibuli we employ the term fenestral plate. A back-
ward extension of the Cavum perilymphaticum beneath the operc-
ulum we designate Recessus perilymphaticus. For the bulging por-

554 B. F. Kingsbury and H. D. Reed.

tion of the ear capsule associated with the outpocketing of the peri-
lymphatic space we employ the name Prominentia perilymphatica.
Without going into a discussion of homologies, we designate as Os
squamosum the Os paraquadratum of Gaupp, but in the use of other
names we adhere,to the terms used by him. The term proton is used
as the equivalent of the German word Anlage. .

We depart from the usages of the preliminary paper? in substi-
tuting Vena petroso-lateralis for Vena jugularis interna of which it
is a direct continuation, employing the name used by Driiner, like-
wise using his term, Musculus cephalo-dorso-mandibularis for Mus-
cularis depressor mandibuli. Palatoquadratum is substituted for
Quadratum.

Acknowledgments. We have received material for study and help-
ful criticism from many sources and wish especially to express our
indebtedness to Professors Wilder and Gage and Dr. W. A. Hilton of
Cornell University, Professor Robert Wiedersheim of the University
of Freiburg and Mr. B. G. Smith of Syracuse University. Aside
from personal obligations we wish to express our appreciation of the
works of Wiedersheim and Gaupp in this field of research.

AMBYSTOMIDAE.

Ambystoma! punctatum. Two reasons determined the choice of
this form as one of the species in which to work out quite thoroughly
the development of the ear region: (a) the ease with which a large
number of stages, larval, transforming and adult, could be procured ;
(b) its systematic rank as a typical urodele- In all, some forty
series were examined and four models prepared. In this way was
obtained a complete history of the transformations through which

°Arrata. At this point we desire to correct errors that were allowed to
creep into manuscript and proof in the earlier paper:

(1) p. 83, line 2, Hemidactylum should read Hemidactylium.

(2) p. 83, line 11, 4-6 mm. should read 12-14 mm.

(3) p. 83, line 17, 1888 should read 1879.

(4) p. 86, line 2, caudal should read dorso-caudal.

(5) p. 87, line 4, Hemidactylum should read Hemidactylium.

(6) p. 87, Fig. 4, D.e. should read D.p.—Ductus perilymphaticus.

*The same as Ambystoma according to older usage.

The Columella Auris in Amphibia. 555

the structures under consideration pass. The results of the study
in this species were given in concise form in our first or preliminary
paper. ‘The evidence ,upon which the conclusions were based was
not submitted at that time, however, and may be given now, together
with such further details as are important in this connection.

The first definite trace of the columella is to be found in embryos
of 11-13 mm. in length, a short time before hatching. At this
period while the cupola of the otic capsule is chondrified, the basal
plate is still in the pre-cartilage (chondroblastema) stage so that
the ventral boundary of the primary fenestra is not yet sharply
defined, and the ditticulty of delimiting its ventro-medial side is
further increased by the fact that the cells of the future floor as well
as those occupying the site of the future membrane are equally rich
in yolk granules, in which respect they differ from the cells of the
surrounding mesenchyma. The squamosum is just appearing as a
minute scale of bone above and behind the otic process of the
palatoquadrate.

Below and beneath the squamosum, filling in the space between
otic capsule, squamosum and otic process of the palatoquadrate, and
extending down upon the outer side of the vena petroso-lateralis to
the yolk-bearing cells occupying the site of the future membrane, is
a dense tissue, with numerous cells and homogeneous matrix, which
embodies the proton of the columella, stilus and squamoso-columellar
ligament. The derivation of these cells was not definitely deter-
mined. Younger embryos lend some support to the view that they
migrate down around the vein. The different appearance of the cells
of the otic capsule adjoining the lower end of this cell-group argues
against their origin from this portion of the otic capsule (membrane
or floor).

In a 13-14 mm. specimen the demarcation of the columellar tissue
is sharper and the portion against the fenestral membrane denser.
The condition at this stage is reproduced in a photograph, Fig. 39,
Pl. IV, col. At about this time, chondrification begins and in
the larva 14-15 mm. in length there is a small cone of cartilage,
whose base is against the membrane and whose apex projects out into
the dense tissue still connecting with the cell-group between squa-

556 B. F. Kingsbury and H. D. Reed.

mosum, otic capsule and otic process of the palatoquadrate. The
stilus appears to chondrify out into this tissue, the unchondrified
portion of which becomes the Lig. squamoso-columellare,

The development as given above agrees completely with the con-
cise description of Killian (’90) for the development in Siredon.
He terms the columella Operculum and had no knowledge of the
interesting changes occurring at transformation.

During the period of larval growth the portion of the columella
fitting into the membrane increases greatly in size, becoming an
elongated plate of cartilage which for purposes of convenient refer-
ence may be designated F'enestral Plate. If at first it is outside the
fenestral tissue, it becomes in the process of growth a part of that
structure. Whether the enlargement of the plate takes place through
marginal growth with the incorporation of fenestral tissue, or through
interstitial growth with a simple displacement of the bordering mem-
brane, has not yet been determined. In late lirval life the columella
apparently becomes joined to the dorso-cephalic margin of the
fenestra by delicate cartilage and subsequently more closely con-
nected with the ventro-cephalic edge. Ossification appears late.
Two plates of bone are formed, one upon the inner surface of the
columella, the other upon its outer surface also extends out upon the
stilus. This method of ossification of the columella is quite charae-
teristic for other urodeles as well. Fig. 33 (PI. III) illustrates
the development attained by a 35 mm. larva.

The condition shortly before ‘transformation is shown in Fig.
22 (Plate I), from the model of the ear region in an individual
about 45 mm. long. The fenestra vestibuli (/. v.) whose complete
outline cannot of course be seen from the figure, is an elongated oval
whose dorsal border is formed by the crest of cartilage where the
lamina horizontalis of the lateral semicircular canal passes into the
lateral wall. For purposes of reference we shall refer to this as
the Crista semicircularis (Cr. s.). At the cephalic end of the
fenestra the “lips” join to form an elongated prominence with which
the processus basalis palatoquadrati articulates. Its interior is oceu-
pied by a cephalic extension of the cavum perilymphaticum. The
caudal end of the fenestra attains nearly the end of the caudal

The Columella Auris in Amphibia. 557

cupola of the otic capsule. It may be noted that the fenestra vesti-
buli is in the lateral wall of the ear capsule, becoming more ventral
in its cephalic portion.

The fenestral plate occupies the larger portion of the window,
being most widely separated from the margin of the fenestra at its
caudal end. In the model the relations of the arteria carotis interna
and vena petroso-lateralis are shown crossing and partially covering
the fenestral plate. In Fig. 23 (Plate I), however, in a somewhat
later stage, the complete outline of the fenestral plate can be seen.
At the cephalic end, on both ventral and dorsal margins, new ecar-
tilage, not shown in the model, is just beginning to join the columella
to the margin of the fenestra vestibuli. The stilus and ligament con-
nect the fenestral plate with the ventral edge of the squamosum. The
palatoquadrate cartilage does not become connected with the liga-
ment. <A blunt process of the quadrate underlying the squamosum
is not brought into relation with the ligament at this stage.

At transformation the fenestral plate becomes joined to the lips
of the opening on all sides save the caudal and the caudal portion of
the ventral side. There is, however, a portion of the primary fenestra
behind the stilus where even in the fully grown salamander the wall
of the otic capsule is very thin,—membranous or filled in with a thin
lamina of cartilage (See Fig. 24, Pl. I, “F”). In Fig. 23 the
outlines of the old fenestral plate still shows. The delicate new
eartilage just forming was not modeled. In Fig. 24, the fusion
of the plate with the edge of the fenestra is nearly complete. The
outline of the old columella and the newly formed cartilage can be
distinguished.

In the process of transformation, due to the shifting of the sus-
pensorium, the attachment of the stilus becomes largely transferred
from the squamosum to the palatoquadrate cartilage (Pl. I, Fig. 24).

The operculum present in the transformed salamander (PI. I,
Fig. 24, Op.; Pl. II, Fig. 25) occupies the caudal portion of the
new fenestra (definitiva) whose dorso-cephalic margin includes the
cephalic end of the operculum; the caudal end projects freely and
to it is attached the M, opereularis whose tendon fits into and fills
a depression upon its external surface (Pl. IV, Fig. 35).

558 B. F. Kingsbury and H. D. Reed.

The operculum is formed out of the wall of the ear capsule upon
the medial side of the caudal portion of the fenestra. Fig. 23
shows the operculum in process of formation. Along the line mark-
ing the medial border of the new fenestra the cartilage breaks down
and is absorbed, cutting out in this way a large plate from the ventral
wall near the caudal end of the ear capsule. In this histolysis, while
the end result is a backward and medial extension of the fenestral
opening, it is not accomplished by an actual extension back of the
fenestra, but the cartilage is absorbed all along the line of separation,
several irregular clefts appearing first which afterwards become con-
fluent with each other and with the fenestra. At its caudal end the
separation of the operculum comes later and at this point a new
formation of cartilage occurs extending the operculum in that direc-

St.,C.

Fic. 1. Schema illustrating the fusion of the columella with the ear
capsule.

tion outside the ear capsule. New cartilage is, however, formed at
the edge of the fenestra as well and in the operculum itself which
attains massive dimensions in the fully grown Ambystoma (PI. IV,
Fig. 35).

The inclusion of the cephalic end of the operculum by the lips
of the fenestra (Pl. I, Fig. 24) is accomplished by a deposit of
new cartilage which cements in solidly the fenestral plate and
extends the fenestral lip backward outside the operculum. The
dorso-cephalic portion of the margin is thus formed by the ventral
and caudal edges of the larval columella extended by new cartilage
formation, while the ventro-cephalic margin is new cartilage formed
upon the ventral lip of the primary fenestra which extends to meet
that deposited on the fenestral plate. The diagram, Fig. 1, will

The Columella Auris in Amphibia. 559

illustrate the transformation and the filling in of the primary
fenestra and the incorporation of the fenestral plate. The columella,
stilus columelle, and operculum are indicated by Col., St. C., and
Op. respectively ; the new cartilage is line-shaded, while the region
of earliest fusion is cross-hatched. The outline of the included por-
tion of the operculum is marked by a broken line.

In the larva approaching transformation (Fig. 22, Pl. I), the
operculum is not well outlined, although a shght groove causes a
prominence of the wall which later becomes the operculum. As shown
in Fig. 31 (Pl. IIT), in the sections of the ear-capsule of mature
larvee, the region from which the operculum will form, may be
recognized. Compare Figs. 31 and 32, in the latter of which the
histolysis of the thin cartilage on the medial side of the future oper-
culum is severing its continuity with the remainder of the floor of
the otic capsule. The operculum thus arises from a portion of the
floor of the ear capsule while the secondary fenestra with the plate
of the columella is in the lateral wall. (Cf. Figs. 32 and 33.)

The interior of the ear capsule, opposite the region to become the
operculum, is occupied by the cavum perilymphaticum (Figs. 31
and 32, Pl. IIT). In the transformed animal this portion of the
ear capsule becomes somewhat prominent and may be termed the
Perilymphatic Prominence (Prominentia perilymphatica) (Figs. 30
and 35). The outward and backward extension of the perilym-
phatic space on the inner side of the operculum, as stated above, is
termed Recessus perilymphaticus.

The muscle attaching to the operculum to which Gaupp (’93)
gave the name of M. opercularis® extends caudad and at its caudal
end is attached to the outer side of the Suprascapula. Yn the larval
Ambystoma it is not present. Early in the transformation myo-
blasts upon the outer edge of the ventral spinal musculature (M.

5This muscle in the frog was regarded as a portion of the “Occipito-sub-
scapularis” by Dugés (’35), the Levator anguli scapule of Ecker. Cope
(88 a and b) has termed it M. stapedius, Iwanzoff, M. protrahens scapule.
Gaupp subsequently (96) designated it the “Pars opercularis of the M. Leva-
tor scapule superior.” In Urodela it seems to deserve recognition as a
distinct muscle, and its development apparently differs somewhat in the two
groups.

560 B. F. Kingsbury and H. D. Reed.

intertransversarius capitis inferior of the frog, Gaupp, 796) develop
into a fascicle of small fibers which becomes separated off from the
above mentioned muscle and gains the attachments to the developing
operculum and the suprascapula. Its opercular attachment is shown
in the models pictured in Figs. 23 and 24 (Pl. I) and also-in Fig.
37 (Pl. IV) in which both attachments are shown.

In accord with the statement of Hasse (’73), the facial nerve
is entirely below (in front of) the columellar-squamosal connection,
the deseriptions of other authors who have given its relations being
therefore incorrect. In Fig. 22, the three branches of the hyoman-
dibular division, ramus mandibularis internus, ramus mandibularis
externus, and ramus jugularis, are shown. Joining the R. jugularis
is the R. communicans IX (not shown) which pursues a course
dorsad to the carotid artery to join the R. jugularis where it passes
under the hgament.

In Ambystoma, therefore, there are two fenestral structures which
succeed one another at transformation. The first which appears in
the larva, is the columella, whose stilus connects with the squamosum
and whose fenestral plate becomes associated with the otic capsule
at its cephalic end. At transformation the columella becomes fused
with the ear capsule and a second fenestral plate, the Operculum,
is cut out. This second structure is caudal and medial to the first,
possesses no process (stilus), is not connected with the squamosum
or palatoquadrate, hut is joined by means of the M. opercularis to
the pectoral girdle. :

The examination by earlier workers of the otie region in Ambys-
toma or Siredon,—which is to be regarded as a permanent larva of

an Ambystoma,—has not lacked suggestion of the interesting condi-
tion found in this form. In Siredon, in which the condition has
usually been examined, Hasse (’78), Friedenreich and Gegenbaur
(749), as well as Wiedersheim (’77), Parker (’77), and Retzius
(781), described a well ossified “operculum” of conical form, the
base of the cone fitting into the fenestra, the apex of the cone pro-
longed into a bony process attached to the palatoquadrate cartilage
by ligament (Gaupp, 799, p. 1040). The plate that fits into the
window possesses, according to Retzius, a cartilaginous border and

The Columella Auris in Amphibia. 561

the tip of the stilus is likewise of cartilage. This description of the
condition in Siredon corresponds fairly well with the relations of the
columella in Ambystoma before transformation. The names ap-
plied to the structure varied: Opereulum ( Wiedersheim) ; Columella
(Hasse) ; Stapes (Parker). Windischmann (731), whose paper we
have not been able to examine, described in Siredon a stilus whose
(fenestral) plate he termed Patina, while behind the Patina there
was an Operculum cartilagineum joined with it only by connective
tissue. This description of Windischmann’s was discredited by later
workers. It is probable, however, in view of the possibility that
many, perhaps most, of the so-called Siredons were larval Ambys-
tomas and not super-larve (Axolotl) that Windischmann correctly
described the condition in a transforming individual. More recently
Iwanzoff (794) describes the condition in Siredon as follows, appar-
ently erring m ascribing the connection of the columella with the
squamosum to the operculum:

“Bei Siredon befestigt sich der Musculus protrahens scapulee mit
seinem proximalen Ende am rundlichen Knorpel auf der hinteren
Wand des Schadels. Parker und Wiedersheim halten diesen Knorpel
einfach fiir einen Teil des Knorpelschidels, um so mehr, da er
schwach von dem letzteren abgegrenzt ist. Aus dem nachgewiesenen
Grunde nehme ich ihn fiir den Stapes, um so mehr, als er demselben
auch nach seiner Lage entspricht. Desshalb ist der Teil, welchen
die genannten Autoren als Stapes annehmen, namlich die teils
knécherne, teils knorpelige und bindegewebige Bildung, die vom
Stapes zum Quadratknorpel und Squamosum, und dieselbe Lage,
wie das Band mit den Columellarknéchelchen bei Pelobates hat, fiir
die Columella zu halten. Auf diese Weise erscheint die gewohnliche
Behauptung, dass bei den Urodelen die Columella gar nicht existirt,
fiir Siredon und einige andere Formen, irrthiimlich.”

-Iwanzoff seems, therefore, to have scen two structures, though their
detailed relations were confused. The early description of Windisch-
mann portrays most closely the condition in Ambystoma, though all
the descriptions were doubtless approximately correct if the age
(larval or adult) is considered. No one seems to have recognized
the fact that the condition changes with age.

562 B. F. Kingsbury and H. D. Reed.

Turning now to the development of the ‘“sound-transmitting”
apparatus in Ambystoma, we find that only imperfect glimpses of
the true development were obtained, and it is not always easy to
determine to which structure they refer. Wiedersheim, Parker,
Stohr, Killian, Witebsky, Winslow, have examined one or more stages
in the larval Ambystoma or Siredon (Axolotl). Wiedersheim and
Winslow evidently described the development of the columella;
Witebsky saw the independent chondrification of the columella but
missed the connection of the stilus with the squamosum (or palato-
quadrate) and drew from his observations some quite irrelevant con-
clusions as to the homology of the columella for which he had no
sufficient basis in fact, as has been pointed out by Gaupp (98) from
whose paper our information is gained, Witebsky’s dissertation being
inaccessible to us here. Stoéhr made his examination of the develop-
ment in the Axolotl only incidental to a more detailed study of the
development in Triton, so that he simply ‘‘confirmed” the results of
Parker’s more extended investigation, stating that the “operculum”
grows out of the cartilaginous border of the fenestra vestibuli. He
gives no figures, so that it is difficult to interpret his results. It was
apparently the Colwmella (our use) that he had under observation.
Parker alone examined an extended series of larval Ambystoma
(Axolotl, Siredon) including an adult Ambystoma. For the first
seven stages neither his words nor his figures give indubitable proof
that he saw the development of the columella or recognized the stilus
or its connection. His description (p. 564) of the adult (Ambystoma
opacum) indicates that in his stapes he described the operculum.®
Tn two points there was probably mistaken identification ; ligament
and ossification were doubtless absent. The descriptions of two large
Axolotls (8144 and 814 inches long) undoubtedly applied to the
Columella,’ the recognition of the suspensorial connection above the
facial nerve being noteworthy.

“The bulging bony floor of the vestibule forms a widely crescentic bulla,
and in the notch the fenestra ovalis contains a small lenticular stapes, the
center only of which is ossified. The spiracular ligament fastens the stapes
to the back of the top of the suspensorium.”

"Page 559, “the stapes (Figs. 2, 4 and 5, st.) is unusually solid and pro-
jecting, its outstanding process looking a little forward. From that process

The Columella Auris in Amphibia. 563

Winslow (798), on the other hand, has described and figured models
of three stages of the chondrocranium of Ambystoma. He describes
the columella (Stapes) chondrifying as an independent center in a
12 mm. individual. The condition in a 37 mm. larva he describes
as follows: “The fenestra ovalis is now nearly filled by the stapes
(s), which has a slight prominence directed outwards and upwards
from the antero-dorsal angle of the cartilage towards the otie process
of the quadrate. These cartilages, however, do not become united
at any time during the development of Ambystoma as they do in
some other forms.” In a young adult, 69 mm. in length, he de-
scribes the stapes as in the posterior portion of the fenestra closely
apphed against the remnant of the cartilaginous wall of the capsule,
this time describing the operculum as stapes. His figure bears out
the brief description and shows the stilus of the fused columella
extending from the ear capsule to the palatoquadrate.

It is hardly necessary to comment on the difficulties of interpre-
tation in such a form as Ambystoma if the changes at transformation
are ignored. ‘Transformation occurs relatively quickly and at this
time the salamanders are less easily procured.

Chondrotus tenebrosus. ‘Three examples of this species were
examined; larval, transforming, and adult. It was not surprising
to find that the relations in this salamander closely resembled those
in Ambystoma because of the close relationships of the two genera.

The larva was well advanced (58 mm. long) and the morphological
relations diagrammatic in their clearness. The otic capsule as also
the remainder of the chondrocranium is unusually heavy, and the
columella shares this characteristic. As shown in Fig. 34 (PI.
IIT) there is a well developed stilus which articulates closely with
the lower edge of the squamosum. In no other form examined by
us has a single section shown the distal connection as well as the
central origin of the stilus from the fenestral plate, as a result of
a ligament arises which spreads into a fan-like fascia, which is inserted
along the under and outer edges of the suspensorium from the lobe of the
otic process to the lobe of the quadrate . . . it lies some height above
the portio dura. .. .” Page 562. “Thus we have here what may be

called a spiracular fascia, the counterpart of the spiracular cartilage and
bone of the Menopome and others.”

564 B. F. Kingsbury and H. D. Reed.

its more transverse course, since in Ambystoma as well as the other
forms examined it has a course outward, upward and also forward
(See, however, Siren, p. 598). The fenestral plate is at no point
connected with the otic capsule, at the edge of the fenestra or else-
where. A few sections farther forward the distal end of the stilus
is joined by connective tissue with the caudal edge of the palato-
quadrate, this junction not being as close, however, as that with the
squamosum. The relations of artery, vein and facial nerve are as
in Ambystoma (Pl. IIT, Fig. 34). |

The second specimen was well along in transformation (150 mm.
long, gills mere stumps). At this stage the columella is connected
by membrane with the lips of the fenestra everywhere save on its
cephalo-ventral border where cartilaginous fusion has begun. Its
stilus is massive and abuts against the palatoquadrate with which
it is joined by connective tissue (Pl. IV, Fig. 36, St. C.). The Os.
pterygordeum also comes into close relation with it, but the econnec-
tion with the squamosum existing in the larva is now much less
direct (Fig. 36). The characteristic inner and outer ossifications
are present, with accompanying changes in the cartilage.

The floor of the ear capsule medial to the caudal portion of the
fenestra is nearly completely cut out as the operculum (PI. IV, Fig.
38, Op). In its present development, it may be compared with the
stage in Ambystoma shown in Fig. 32 (PI. III). An opereular
muscle attaches to the operculum. The recessus perilymphaticus
is characteristically present.

The adult individual was 240 mm. long and was examined by
dissection. The condition found was much like that in the adult
Ambystoma. The columella, with its inner and outer bony surfaces,
the latter bearing a well ossified stilus, is completely fused with the
otic capsule forming the anterior boundary of the nearly cireular
fenestra into which was fitted a cartilaginous opereulum, roughly
hemispherical in form, its flattened surface bearing a tendon, doubt-
less that of the M. opereularis, which was not, however, dissected
out. Fusion with the otie capsule was apparently by cartilage only,
so that, by the use of some force, the stilus and plate could be and
were completely broken away. The distal end of the stilus was con-

The Columella Auris in Amphibia. 565

nected by syndesmosis with the under surface of the squamosal near
its caudal edge, and doubtless also with the palatoquadrate cartilage
as well, though this relation was not determined.

Examination of the condition in the adult of this salamander by
means of dissection was made partly because other adult members
of this family had been examined in this way. Of three Asiatic
genera, Hynobius (Ellipsoglossa neevius) Salamandrella (kaiser-
lingi), and Ranidens (Randon sibericus) the “opereulum’ (colu-
mella) is described by Wiedersheim, ’77, (503, 519) as a remark-
ably large cone of bone whose columella [stilus columelle] is closely
joined to the lower end of the quadrate. As a result of this intimate
connection Wiedersheim ‘called attention to the inevitable shaking

of the perilymph that must attend every violent closing of the jaw,
as in the seizing of prey,—an arrangement whose physiological
significance it is difficult to comprehend. Granting, however, that
as in Ambystoma and Chondrotus, the columellar plate is fused with
the ear capsule, the dificulty found in the close junction of stilus
and palatoquadrate disappears, a fused element not being subject
to violent agitation from movement. of the jaw, but on the contrary
offering a firmer support for the upper end of the quadrate.

The suggestion is, therefore, made that the columella will be
found fused in the other Ambystomidz, including these Asiatic
forms, and it is not without some direct evidence. Fig. 65 in Wie-
dersheim’s monograph (’77) shows the stilus in Ellipsoglossa (Hyno-
bius) arising, not from the opercular plate, but from the anterior
lp of the fenestra, as in Salamandra. This is also just as he
figures it in Ambystoma Weismanni (tigrinum) (779, Fig. 8),—quite
different, as might be expected, from the relations in the Axolotl
C79, Fig. 12). The operculum had been removed. His (’77) Fig.
67 (Ranidens), however, suggests a condition such as is found in
Cryptobranchus.

Okajima (’08) has recently given a short description of the col-
umella in another member of the family,—Onychodactylus japonicus.
An ossified plate, “hollow” in the center with cartilaginous border,
he states (p. 353, 354) fits into a lateral fenestra vestibuli. A carti-

laginous stilus is connected with the cartilaginous portion of the

566 B. F. Kingsbury and H. D. Reed.

quadrate. This is evidently the columella; an operculum was not
recognized. A text figure of a section through the ear capsule
recalls strongly the similar section in just transformed Chondrotus

(Pl. IV, Fig. 38), already described.

SALAMANDRA.

Salamandra maculosa has proved to be a form of rather unusual
interest with regard to its sound-transmitting apparatus both in
respect to the elements present and their relations when considered
in the light of conditions in other forms.

The skeletal elements of the head of Salamandra are quite fully
ossified. The os quadratum is composed of a thin outer shell of
bone very closely associated with the under surface of the superim-
posed squamosum. Underneath the os quadratum is the palato-
quadrate which is continued into the basal, otic and trabecular (as-
cending) processes. As has been pointed out by Wiedersheim (777),
the inclination of the supensorium to the long axis of the skull is
almost transverse, a condition not met with in many salamanders. The
inclination of these elements, whatever its cause, undoubtedly influ-
ences the nature of the suspensorio-columellar connection in all
forms.

Both columella and operculum are present in the adult. The
columella is a plate of partly calcified cartilage fused with the lips
of the fenestra vestibuli except in the caudal third of its cireum-
ference where it forms the cephalic margin of the definitive fenestra.
Fig. 40 (Pl. V) is a photograph of a section through the cephalic
portion of the columella and shows how completely it is fused with
the ear capsule in this region. Jn the same figure is shown the short
and thick stilus which projects from the dorso-lateral aspect of the
columella. It is composed of hyalin cartilage distally continuous
with the cartilage of the palatoquadrate; proximally it passes over
into the plate of the columella whose cartilage, calcified where it
joins the ear capsule, may also be seen in this figure. To the squa-
mosum it is joined by connective tissue representing a short ligament.
Describing the “stapes” in Salamandra, Parker (’82a) observes :—
(pp. 174-5) “There is a well ossified lip, like the mouth of a pitcher,

The Columella Auris in Amphibia. 567

to the fenestra ovalis: it looks outwards and backwards; the thick,
oval closely fitting stapes (operculum) remains cartilaginous and is
only attached to the supensorium by hgaments.’” In a footnote he
adds: “Mr. A. Doran has shown me a stapes, said to belong to this
species, which is ossified and has a stalk. I find nothing of the kind
in the specimen dissected by me; and I think it probable that that
specimen (in the Hunterian museum) belonged to another kind.”
It is quite likely that Mr. Doran was correct and that the stilus had
by some accident been torn from Parker’s specimen. The relation
of the stilus to the artery, vein and facial nerve is typical.

The operculum occupies the typical position below and behind
the columella filling the definitive fenestra vestibuli. It is a
relatively large hemispherical mass of cartilage free all round, at-
tached to the lips of the fenestra by membrane only. The cephalic
fourth is overlapped by the caudal margin of the columella precisely
as in Ambystoma. This is made clearer by an examination of
Fig. 41 (Pl. V), a photograph showing the operculum internal to
an overhanging lip of cartilage, the columella, which conceals the
entire cephalic and a portion of the dorsal margin of the operculum.
In tracing it forward, it gradually diminishes and finally disappears
in the middle region of the perilymphatic prominence. ‘The photo-
graph reproduced in Fig. 42 (Pl. V) is of a section in this region,
and shows a small lip of cartilage, a backward continuation of the
columella, projecting from the ear capsule upon the dorsal margin
of the fenestra. Fig. 65 (Pl. X) is a schematic representation of
the position and relations of the columella and operculum as viewed
from the side. .

The perilymphatic prominence is pronounced. ‘To the caudal
surface of the operculum is attached the strong M, opercularis which
extends caudad to the suprascapula.

Wiedersheim (’77, p. 504), in commenting upon the columella
in Salamandra, says: “It is cartilaginous throughout life and rests
suspended by the connective tissue in the foramen ovale which is
bordered by two thick, crest-like lips. These lips now pass forward
and outward in a thin cartilaginous process and this joins the
quadrate cartilage,—a remarkable variation of the relations described

568 B. F. Kingsbury and H. D. Reed.

above.” We are able to confirm these early observations and in the
light of the changes which take place in Ambystoma at transforma:
tion, offer an interpretation of the presence of the fourth process
connecting the palatoquadrate with the ear capsule. Undoubtedly
as in Ambystoma the columella becomes fused with the margin of
the fenestra and maintains its connection with the suspensorium
through the stilus which is without doubt the cartilaginous process
from the fenestral lip to the quadrate cartilage seen by Wiedersheim.

We feel no hesitation in offering this interpretation of the structures
in this form even though developmental stages have not been studied
by us. The sound-transmitting apparatus in Salamandra is in all
essential respects identical with that of Ambystoma in which a very
large number of developmentad stages have been studied carefully,
permitting an interpretation of the adult condition which without
them would be difficult. Fuchs (07) has figured and described the
chondrification of the otic capsule in Salamandra, giving in some
detail the formation of the fenestra vestibuli and operculum. Em-
ploying the nomenclature of Gaupp, he describes the operculum as
formed chiefly by a cutting out of the already chondrified ear capsule
and partly by the chondrification of the chondroblastema filling in
the fenestra. The latter he recognizes existent from the beginning
as an unchondrified portion of the otic capsule. The development
of the Operculwm of Salamandra he undoubtedly gives correctly
and in the figures of models of three stages shows it forming upon
the medial and caudal sides of the fenestra in the manner stated
above just as the operculum is formed in Ambystoma and in Triton
presently to be described. He neither discusses nor shows in his
figures, however, the process described by Wiedersheim, the detailed
development of which in this form would be of particular interest.
No hint is given of its origin or relations except in Fig. 3 on page
11 where a shght projection from the dorsal boundary of the fenestra
appears to be what we are inclined to interpret as the caudal tip of
the columella. A comparison might also be made between his Figs.
3, I, and our Figs. 1 and 23 (Pl. I) of Ambystoma and Fig. 27 (PI.
Il) of Triton.

Fuchs gives no intimation of the ages or sizes of the larve or

The Columella Auris in Amphibia. 569

embryos studied. His theoretical conclusions drawn from the devel-
opment of the operculum in Salamandra will be referred to in the
second part of the paper.

Triron anp Dremicryuus.

In Cope’s family of the Pleurodelide, the condition of reduction
and incorporation,—if we may so state it,—is carried farther than
in the form just described,—Salamandra. The connection with
the squamosum and palatoquadratum is absent, and the fenestral
plate forms the portion of the ear capsule bounding the cephalic
part of the fenestra vestibuli above and in front. In the adult,

the identity is entirely lost and it would be impossible to recognize
the true morphological relations were it not for the condition in the
larva. In fact, at the time of our first contribution, the existence
of the columella in Diemictylus was not recognized even though
larvee had been examined. At that time we expressed confidence
in its presence at some stage in the development of the larva, but
thought that it was absorbed or became incorporated,—possibly with
the operculum. It was, indeed, subsequently found to be present
and incorporated not with the operculum, but with the edge of the
fenestra. It was in the light of the conditions in Salamandra that
the relations in Diemictylus became clear. The existence of the
columella was first determined in a 19 mm. larva, the subsequent
examination of Triton larve bringing confirmation. In this last
form the significance of the morphological relations is more apparent
so that it may best be considered first.

Triton cristatus. Through the kindness of Professor Robert
Wiedersheim, we were enabled to examine a series of specimens ot
this form, serial sections being prepared of larvee 18, 20, 25, 34, 36,
and 37 mm. in length. In the smallest individual at our disposal
(18 mm.) both opereulum and columella are present, of cartilage,
the latter fused more or less completely with the crista semicircularis,
hence it has been impossible to determine how early this structure
appears; whether at any time its proton is as obviously outside the
membrana fenestre as it is in Ambystoma, or whether it undergoes
chondrification separate and distinct from the edge of the primary

570 B. F. Kingsbury and H. D. Reed.

fenestra, later becoming fused with it. There is some evidence in
our series that leads us to believe that it will be found to chondrify
as a separate piece of cartilage:—(a) its cartilage differs in its
staining from that compesns the crista semicircularis, presenting
the appearance of “younger” cartilage; (b) it lies outside what might
be considered the ideal plane of the fenestra and apparently outside
the fenestral membrane; (¢) in some of the larve a small cleft is left
between the crista semicircularis and the columella. This cleft is
especially well marked in the 36 mm. larva (Fig. 48, Pl. VIL), but
present on one side only, being therefore variable in its extent and
doubtless simply an indication of imperfect fusion. The columella
as in Ambystoma fills in the anterior portion of the primitive fenestra
in its dorsal part; if the fusion with the ventral lp occurs early
it is conceivable that the dorsal fusion may be delayed.

As to the mode of formation of the operculum, the evidence is
indubitable; it is forming in the “floor” of the ear capsule as a
chondrification in the “‘opercular tissue” (membrana fenestra) in
its caudal and medial portions. In the 18 and 20 mm. specimens,
the operculum is already outlined, but broadly continuous on its
medial and caudal sides with the cartilage of the floor, and were it
modelled, would doubtless present the appearance shown in the model
of a 20 mm. Triton teeniatus published by Gaupp (705, p, 695, Fig.
350). In the older larvee, save for the larger size of the operculum
and its more complete separation from the floor of the otie capsule,
conditions have not been essentially changed. A model was made
of this region in a 34 mm. larva which is reproduced in Fig. 27
(Plate IT). Here the operculum is shown forming in the caudal
portion of the fenestra still rather broadly connected with the floor
of the otic capsule caudally and medially. The rudimentary fenes-
tral plate is shown fused with the anterior portion of the erista
semicircularis. The closure of the anterior portion of the primary
fenestra is also being accomplished by a growth of cartilage upon its
ventral side. This figure showing the primitive fenestra and its
contained cartilages may be directly compared with the stage in
Ambystoma shown in Fig. 24, Pl. I, and its diagrammatic elucida-
tion in Text Fig. 1.

The Columella Auris in Amphibia. 571

Three photographs (Pl. VII, Figs. 48, 49 and 50) of sections
from the 36 mm. larval Triton are submitted in illustration of what
has been said above. Tig, 48 is through the ear capsule cephalad
of the (secondary) fenestra at a point where the columella is fused
with the ventral lip of the (primary) fenestra (cf. Fig. 27, Pl. IL).
Tt shows the cleft between the dorsal margin and the crista semi-
circularis whose existence has been mentioned above. It might also
be compared with Figs. 28-and 29, Plate XV, of Gaupp’s (793)
monograph upon the Chondrocranium of the Frog. Fig. 49 is five
sections (75 microns) farther caudad through the columella and
just ahead of the tip of the operculum, while Fig. 50 is still farther
back (210 microns) behind the caudal end of the columella and
through the operculum. The position of the artery and vein may
be noted, in comparison with Figs. 8, 9 and 10 of Stohr (79). It
may be remarked that in the oldest of the larval Tritons examined
(37 mm.) the M. opercularis has not yet appeared nor has the oper-
culum become completely separated off from the cartilaginous ear
capsule.

By comparing these figures (Pl. VII, Figs. 48-50) and the two
similar ones of a Diemictylus larva (Text Figs. 4-5) with the sections
through the ear capsule of the larval and transforming Ambystoma
(Pl. ILI, Figs. 31-32-33) the basis of the homologies for Triton
becomes evident. In a comparison of Triton and Ambystoma the
early appearance of the operculum in Triton is noteworthy. Its
proton is already partially outlined at 18 mm. in length, and doubt-
less recognizable at a still earlier stage, while in Ambystoma its
appearance comes only with the beginning of transformation, and
in the larva it is a part of the otic capsule. The columella element,
on the contrary, while already evident in the youngest Triton larva,
becomes more prominent in the later larval stages; in Ambystoma it
appears very early. The growth of the columellar plate in Triton
during the larval period with an increasing distinctness of demarea-
tion from the crista semicircularis suggests, it must be admitted,
the interpretation of a differentiation out of “fenestral tissue” as
the fenestra increases in extent. As has been said, the available
material does not permit us to determine the early transformations

572 B. F. Kingsbury and H. D. Reed.

that take place in the ear capsule in Triton. The presence of a
rudimentary columella seems clearly established. The problem of its
phylogeny may be better discussed from a comparative view-point.

No trace of a stilus or connection with the squamosum or pala-
toquadrate was to be found unless, possibly, a scanty group of cells
extending from the columella around the outer side of the vena
petroso-lateralis was its representative.

In the adult Triton the conditions are much altered. The otic
capsule is strongly ossified; the operculum being an oval plate of
cartilage filling in the relatively small fenestra vestibuli and pro-
jecting back a short distance. On its outer side it gives attachment
to a well developed M. opercularis; on its inner side is the cavum
perilymphaticum and its backward extension outside the otic capsule
is the recessus perilymphaticus. To the otic capsule behind and to
the edge of the fenestra the operculum is attached by membrane only.
The fenestral margin is osseous behind; dorsal and ventral cartila-
ginous lips join to form the cephalic border of the fenestra, the ceph-
alic end of the operculum being slightly included. The columella is
completely merged with the otic capsule, though doubtless the dorsal
and cephalic cartilaginous margin of the fenestra, in part at least,
represents it. Figs. 43 (Pl. V) and 44 (Pl. VI) show the relations,
shape and cartilaginous consistency of the operculum. The latter
figure may be compared with Fig. 42 (Pl. V) of Salamandra in
illustration of the more massive character of the operculum in that
form. Recurring again to the columella, in these two forms, Triton
presents a condition of much greater reduction and incorporation in
the absence (in the adult) of a recognizable fenestral plate and stilus
columelle (cf. Figs. 41 and 43, Pl. V).

The development of the otic capsule in Triton has been followed
in more or less detail by Reichert ’38, Semmer ’72, Parker ’82b,
Wiedersheim ’77, and Stohr ’79. From the reduced condition of
the columella in this salamander, it was to be expected that its
presence, not to mention significance, should be entirely overlooked
and that the development of the operculum should be given correctly
in all essential points. Hence we find Reichert, Semmer, Wieder-
sheim, Parker, and finally, Stohr describing the operculum as formed

The Columella Auris in Amphibia. 573

out of the otic capsule in this Urodele. Stohr’s classical investiga-
tion was undertaken primarily to describe whether or not after all
the columella (of reptiles) was not of double origin,—one portion
derived from the ear capsule (opercular plate) and a second portion
from the hyoid arch, and as a preparatory study it seemed best to
him to re-examine conditions in the amphibia (p. 480). Parker,
in the meantime, published his first paper, dealing largely with the
development of the skull of the Axolotl (to which reference has
already been made, p. 562, but including a brief description of
the skull of the larval and adult Salamandrina (Seironota) perspi-
eillata. His second paper, dealing with Triton, appeared subse-
quently to Stohr’s. Wiedersheim (’77) had described (apparently
in Triton alpestris) the development of the operculum as cut out
of the otic capsule by a circular thinning of the cartilage, which
by extension completely separates the operculum from the remainder
of the otic capsule as a nearly circular disc.* With this mode of
development as with Reichert’s view that the operculum appeared as
a chondrification in the fenestral membrane, Stohr disagreed. While
he examined, apparently, larve of different ages, he described,
modelled and figured the condition in a 24 mm. specimen. He
says: “Vom vorderen Rande des knorpeligen Fensterrahmens ent-
springt ein kurzer nach hinten gerichteter Fortsatz (O), der auf der
hautigen Fenestra ovalis aufliegt. Zu beiden Seiten des Fortsatzes
liegen grosse Blutgefisse (die Rinnen sind auf der Figur sichtbar),
die bei der Vergrésserung desselben in so fern eine Rolle spielen
mogen, als sie durch Druck die knorpeligen Rinnen, welchen sie
anliegen, immer mehr vertiefen und schliesslich den Boden der Rinnen
zum volligen Schwund bringen. Die Vergrésserung des Fortsatzes
erfolgt aber gewiss auch durch eignes Wachstum. Bei Triton cristatus

-8(77, p. 501). “Kurz nach Verschmelzung der Parachordal-Elemente mit
den Gehoérblasen sieht man am iiusseren Rand ihrer Unterfliiche eine ring-
férmige Zone auftreten, welche bei genauerem Studium sich als eine circuliire
Verdiinnung der Knorpelwand herausstellt. Letztere schreitet immer weiter
fort wnd schliesslich hat sich eine rundlich-ovale Knorpelscheibe aus der
Labyrinthwand (Fig. 6, Fov, Op) herausgeschniirt, ein deutlicher Beweis,
dass das Operculum der Urodelen ontogenetisch nicht vom Kiemen-Apparat,
sondern von der Gehorkapsel selbst herzuleiten ist.”

574 B. F. Kingsbury and H. D. Reed.

sowohl, wie bei Triton teeniatus bleibt der Fortsatz nicht lange mit
dem knorpeligen Fensterrahmen in knorpeliger Verbindung; ehe er
noch eine Grosse erreicht, schniirt er sich von seinem Mutterboden
ab und stellt nun ein freies, auf der Fenestra ovalis aufliegendes
Knorpelplittchen dar; das Operculum. * * * Das Operculum ist
demnach ein Theil der knorpeligen Ohrkapsel, hervorgewachsen vom
vordern Umfang des ovalen Fensters. Mit dem Hyowdbogen steht es
genetisch in keiner Beziehung.” Interestingly enough, the deserip-
tion and figures indicate that the structure he identified as the Oper-
culum was not the Operculum but the Columella. Its shape, con-
nection with the anterior border of the fenestra, and its position be-
tween artery and vein, leave small doubt of this. The development
of the operculum he seems to have entirely missed, and the mode
of development advanced by Wiedérsheim appears to be more nearly
correct, though doubtless chondrification of opercular tissue in the
fenestra vestibuli also contributes to its growth. It seems certain
that in the growth of the larva both the fenestra and the operculum
increase in size, and observation of this enlargement and extension
of the rather cleft-like fenestra (vide Gaupp 705, Fig. 350) doubt-
less caused Parker to believe that the oval window arose by “dehis-
cence,” and explains also the mode of origin of the operculum
advanced by Semmer and by Wiedersheim. On the other hand,
Stohr’s contention that the fenestra exists from the beginning as an
unchondrified portion of the ear capsule, is without doubt true for
Triton as we find it to be for Diemictylus, but describes the origin
of the primary rather than the secondary fenestra. Stohr, in a year-
old Triton, figures the true operculum.

Parker’s brief statements (’82b, pp. 198, 199, 203, 206, 209)
upon the operculum (Stapes) and fenestra vestibuli (ovalis) in
larval and adult Triton (Triton punctatus) are too indefinite to
permit of any conclusions being based on them as to what the con-
ditions were. In the adult he comments upon the cartilaginous
nature of the operculum (Stapes) and the lack of a stilus (columella),

Diemictylus viridescens. aittle need be said of the conditions in
this form since in all essentials it resembles Triton closely. In the
transformed salamander (red form) as also in the fully adult (Figs.

The Columella Auris in Amphibia. 515

2-3), the operculum is plate-like, of cartilage, having the same
relations to the fenestral margin as in Triton. It is somewhat more
massive; the fenestral margin is cartilaginous only in front and
above where the cartilage extends back to the caudal end of the
fenestra. Below, cartilage extends back only as far as the anterior
tip of the operculum. A well developed M. opercularis is present.

During the larval stage the morphological relations are essentially
those of Triton larve, the vestigial plate being somewhat more
closely joined to the crista semicircularis (Fig. 4, Cr. s.), but its

Iie lave, 8).

Fic. 2. Diemictylus viridescens, land form. (C.1., canalis lateralis; C.p.,
cavum perilymphaticum; D.p., ductus perilymphaticus; H., ceratohyale;
Op., operculum ; Sq., oS Squamosum.

Fic. 3. Diemictylus viridescens, land form. 0.1, canalis lateralis; C.p.,
cavum perilymphaticum; D.p., ductus perilymphaticus; H., ceratohyale ;
Op., operculum; ?.p., recessus perilymphaticus ; Sq., oS squamosum.

ventral edge more evidently outside the membrana fenestra. At
15 mm. in length, neither columella nor operculum have appeared.
In a 17 mm. specimen, the columella is developing upon the fenes-
tral membrane in continuity with the fenestral margin above and in
front. The operculum is forming on the medial edge of the fenestra
in continuity with the cartilage of the capsule. Aside from growth
and a more marked differentiation of the operculum, there has been
but slight change in a larva 19 mm, long. At 37 mm. the operculum
and also the columellar plate are well developed. The relations

57

_
~~

B. F. Kingsbury and H. D. Reed.

of the two structures may be seen from the accompanying figures,
4-5, .

These figures may be compared with the similar figures of the
36 mm. Triton larva (Pl. VII, Figs. 49 and 50). Fig. 4 may also
be compared with Fig. 41, Plate V, of Salamandra and Be 32,
Plate III, of transforming Aeabestoma:

ecanits descriptions of the “sound-transmitting apporatel in
Diemictylus are lacking. Parker (’82a) describes the condition
in both larva and adult (pp. 179, 181), but each statement is brief
and without significance; more significant is his comment when

Fic. 4. Diemictylus viridescens, larva 37 mm. long. C., arteria carotis
interna; C.1., canalis lateralis; Col., columella; C.p., cavum perilymphaticum ;
Cr.s., crista semicircularis; Op., operculum ; V.p-l., vena petroso-lateralis.

Fie. 5. Diemictylus viridescens, larva 37 mm. long. OC., arteria carotis
interna; Col., columella; C.p., cavum perilymphaticum; Op., operculfam ;
V.p-l., vena petroso-lateralis.

characterizing the skull of Spelerpes (See foot-note on p. 578). Cope
(788) is not sufficiently detailed and Wiedersheim (’77) does not
particularly emphasize the relations in this portion of the skull of
Diemictylus.

PLETHODONTIDAE.

Representatives of all the genera of this family have been exam-
ined as follows: Batracoseps, Hemidactylium, Manculus, and Auto-
dax, the adult stage only ; Gyrinophilus, Plethodon, and Stereochilus,
both larva and adult; Spelerpes, adult and a series of twelve devel-
opmental stages of larvee from 15 to 55 mm. in length.

The Columella Auris in Amphibia. 517

In the fenestra vestibuli of the adult there is a single plate, irregu-
larly oval in outline and free from the ear capsule except on its
ventro-cephalic margin where a fusion is found (Pl. X, Fig. 67).
From the cephalic and dorsal portion of this plate there projects
upwards and forwards a slender stilus (Fig. 67) which in the adult
articulates with both quadrate and squamosum. It is slender in all
forms except Batracoseps where it is absent or vestigial. In the
caudal portion, the fenestral plate extends behind the caudal margin
of the fenestra and swells outward, forming a prominence in this
region. The cavity of this prominence is an outward and backward
extension of the cavum perilymphaticum. In a relatively deep de-
pression on the caudo-lateral aspect of this prominence the M. oper-
cularis is attached. ‘The fenestral plate in the Plethodontide is,
as are all the related parts, finer and much less massive than in the
families already considered. The stilus is relatively a long and
slender rod between the vena petroso-lateralis above and the arteria
carotis interna and facial nerve below. ‘The lips of the fenestra
vestibuli remain cartilaginous and are connected with the fenestral
plate by membrane only, save in the cephalo-ventral portion mentioned
above.

The inner and outer bony plates so characteristic of the columella
in other forms are here co-ossified, the cartilage persisting only at the
circumference. In the central portion of the plate the cartilage
which is subsequently replaced by bone, varies markedly in thick-
ness even in the same genus,—for example, in Spelerpes bislineatus
it is small in amount and early replaced by bone, while in Sperlerpes
ruber quite the reverse is true. A similar comparison could be made
between genera. The ossification of the fenestral structures in this
family corresponds to the ossification of the skull as a whole, both
in time and extent,

Accompanying this marked ossification of the plate there is com-
plete ossification of the base of the stilus; distally it 1s composed
of a shell of bone enclosing a cartilaginous core. In regard to the
relation of the peripheral end of the stilus, it should be stated that
the articulation with the squamosum, quadrate and palatoquadrate
mentioned above applies only to the adult. In the larvee of the forms

578 B. F. Kingsbury and H. D. Reed.

studied (Gyrinophilus, Plethodon, Stereochilus, Spelerpes) the con-
nection was with the squamosum only. In the adult there is a very
wide variation, from a close articulation with the squamosum only (as
in Manculus) to an intimate connection of the stilus with a cartila-
ginous process of the palatoquadrate, as in Stereochilus, Autodax
and Plethodon. The other genera show an intermediate condition ;
in Hemidactylium and Spelerpes the connection with the squamosum
is the closest, while in Gyrinophilus there is an equally close articula-
tion with the subsquamosal process of the quadrate ; in no one of them
was the cartilaginous process of the palatoquadrate as well developed
as in Stereochilus, Autodax, and especially Plethodon.

The variation in the connections of the distal end of the stilus
is undoubtedly associated with the inclination of the suspensorium
to the long axis of the skull. During the period of growth, due to
the relative displacement of parts, the distal end of the suspensorium
is “drawn” forward, bringing its long axis more nearly parallel with
that of the skull.

The definitive fenestra vestibuli of the Plethodontide is large and
lateral in position, more nearly representing the primary fenestra
of other urodeles,

a condition recognized by Parker.® 'The columella
is correspondingly large, nicely filling the opening, and projecting
slightly back of it, as presently to be described. ‘The plan of ossifi-
eation in the columella is so characteristic that we have come to
consider it as the Plethodontid type.

The M. opercularis, though absent in the larva, is a well devel-
oped structure in the adult. It attaches to the caudal portion of
the fenestral plate, which there possesses a decided excavation oceu-
pied by the tendon of the muscle, giving the “scooped out” appearance
noted by Parker,

*Parker, ’82, p. 199. ‘The under face of this ear capsule (in Spelerpes) is
very different from that of most high “‘Urodelous” skulls.

“In those massive typical Caducibranch skulls just described, e. g. Notoph-
thalmus (Pl. XVII) and Cynops (Pl. XVIII), the vestibule is in the form of
a smooth bulla, with the stapes set on behind; and that plate is either quite
soft or very slightly ossified; it is also relatively small.

“In Spelerpes (Pl. XXI, Figs. 2, 3, and Pl. XVIII, Fig. 10) the vestibule
is but little protuberant; its fenestra is lateral, and corresponding with the
stapes, very large.”

The Columella Auris in Amphibia. 579

Despite the depression for the M. opercularis the ear capsule has
in this region a bulging appearance due to the growth of the fenes-
tral plate backwards beyond the margin of the fenestra vestibuli.
Fig. 47 (Pl. V1) shows not only that the prominence has extended
beyond the margin of the fenestra, but also that within the promi-
nence there is a recessus which is continuous with the cavum peri-
lymphaticum.

Earlier in this paper it has been shown that in Ambystoma and
others there is a perilymphatic prominence in the region of the

Fies. Gand 7. Plethodon cinereus, embryo. C©., arteria carotis interna;
C.l., canalis lateralis; Col., columella; H., ceratohyale; L.h-e., ligamentum
hyo-columellare; J/., musculus cephalo-dorso-mandibularis. Sp., os squa-
mosum; V.p-l., vena petroso-lateralis.

fenestra vestibuli formed by the outward and backward growth of
the operculum and that to the lateral aspect of this structure the M.
opercularis is attached. Within the perilymphatic prominence is
the recessus perilymphaticus, a caudal continuation of the peri-
lymphatic cavity. In these respects there is a striking similarity
between the caudal portion of the fenestral plate in the Plethodon-
tide and the operculum of other forms. Further than the similari-
ties mentioned in the preceding paragraph there is, in the adult, no
evidence as to the constitution of the fenestral plate in the Pletho-
dontide. In the light of development, however, the condition is

580 B. F. Kingsbury and H. D. Reed.

somewhat better understood. Eleven larvee of Spelerpes bislineatus
ranging in length from 15 to 55 mm. were studied by means of
serial sections. Just when the columella makes its appearance we
can not say, but in larve 15 and 17 mm. long there is present a deli-
cate cord of cells outside the ear capsule extending from the under
side of the squamosum towards the fenestral membrane to which
it is not closely related at this stage. In a larval Plethodon cinereus
(Figs. 6 and 7) of a similar stage of development this cord is
composed of a greater number of cells and is consequently more com-

Fic. 8. Spelerpes bislineatus, larva 23 mm. long. C., arteria carotis
interna; ©.l., canalis lateralis; Col., columella; C.p., cavum perilymphaticum ;
V.p-l., vena petroso-lateratis.

pact and larger. Here also, as in Spelerpes, this group of cells is
not closely connected with the fenestral membrane. It extends for-
ward to the under side of the squamosum and apparently is joined
to the ceratohyal by a less marked cord of cells. Figs. 8 and 9
from two sections 25 microns apart may serve to illustrate the extra-
otic position of the columella. Comparison with the figures of like
stages of Ambystoma and Cryptobranchus is suggested.

In Sperlerpes larvee 23 mm. long the lower end of this cord of cells
has become intimately associated with the fenestral membrane at
the cephalo-ventral margin of the fenestra. At this point the fenes-

The Columella Auris in Amphibia. 581

tral plate remains permanently fused with the ear capsule. Chon-
drification has occurred, forming a stilus and a small fenestral plate
(Figs. 8 and 10).

From the place of its attachment the fenestral plate gradually
extends backwards, growth being the result of the deposition of carti-
lage in the free margins of the plate, particularly the caudal. Thus
successive rings are added until the plate fills the opening in the ear
capsule. In the caudal portion of the fenestra vestibuli the mem-

Fig. 9. Spelerpes ruber, larva 71 mm. long. F.p., fenestral plate; L.p.,
recessus perilymphaticus.

brane forms an outpocketing or prominence (Fig. 12) long before
it is invaded by cartilage, but before transformation the extension
of the prominence behind the lips of the fenestra is slight if present
at all. The prominence forms the outer walls of a recessus which
has the same relations as that of the adult. Until transformation
there is no indication of the M. opercularis, it apparently having no
function until adult life is assumed. The conditions in the adult
Plethodontide are well illustrated by the photographs of Gyrino-
philus in Figs. 45, 46, 47 (Pl. VI).

582 B. F. Kingsbury and H. D. Reed.

It appears that the definitive plate of the adult is the result of a
direct and continuous growth of cartilage in the membrane which
covers the foramen vestibuli. At no time during development are
there found separate centers of chondrification in either stilus or
fenestral plate.

There appears to be a wide divergence between the sound-trans-
mitting apparatus in the Plethodontide and that in Ambystoma.
This seems particularly true of the development, and as a consequence
is also true of the homology of parts. A brief review of the devel-
opment of the fenestral elements in the forms thus far considered
may, therefore, render the situation easier to grasp. In Ambystoma
the ear capsule chondrifies early and the columella fills the fenestra
vestibuli. At transformation (there being no room for growth) the
operculum is cut out from the cartilage of the ear capsule itself;
an adaptation, it might seem, to mechanical needs. In Triton and
Diemictylus the columella relatively early fuses completely with the

I'ia. 10. Spelerpes bislineatus, larva 43 mm. long. C., arteria carotis
interna; C.l., canalis lateralis; C.p., cavum perilymphaticum; F.p., fenestral
plate; Z., lagena; M., musculus cephalo-dorso-mandibularis.

ear capsule, leaving the foramen free. Here it is found that, while
there is a slight cutting out of the operculum from the ear capsule,
it results largely from a growth of the cartilage cephalad into the fen-
estral membrane. ‘The situation in the Plethodontide differs from
either of these. The columella, when first coming into intimate rela-
tion with the ear-capsule, is small as compared with the size of the for-

The Columella Auris in Amphibia. 583

amen which increases in size with the growth of the skull. The early
ossification of the ear capsule renders impossible the formation of
an operculum by either the cutting out process or by forward growth
into the fenestral membrane. A comparison of Figs. 11 and 12 will
help to make clear that the membrane filling the caudal portion of
the fenestra corresponds in its position and relation to other parts
to that portion of the fenestra in Ambystoma which is occupied by
the operculum. This, together with the formation of a prominence
by the fenestral membrane in this region, which when chondrified
affords attachment for the M. opercularis, suggests that it is oper-
cular tissue. Taking this view it is perhaps not inappropriate to
consider that the caudal portion of the fenestral plate in the Pletho-
dontide: represents the operculum of other forms.

Fic. 11. Ambystoma punctatum, transforming larva. OC./., canalis later-
alis; C.p., cavum perilymphaticum; D.p., ductus perilymphaticus. M.. musculus
cephalo-dorso-mandibularis; Op., operculum.

Fic. 12. Spelerpes bislineatus, larva, 55 mm. long. Lettering as in Fig. 11.

This is from the viewpoint of groups in which the operculum is
formed as a separate structure. Looking at it from the reverse
point of view the Plethodontide might be considered as representing
the less specialized condition. It is conceivable that in those forms
in which an operculum is developed the columellar blastema became
fused with the edge of the primitive fenestra both in front and be-
hind, so that when it came to chondrification there were almost of
necessity, developed two plates: (1) the fenestral plate of the col-
umella joined to the otic capsule in front, and (2) the operculum
joined to the ear capsule on the caudal and medial side. The oper-
culum would thus be a dissociated part of the fenestral plate. In

584 B. F. Kingsbury and H. D. Reed.

the Plethodontide, due possibly to an early fusion of the columellar
blastema in front only, such a division of the plate does not occur.
It seems quite possible that a comparative study of the primitive
fenestra in urodeles might afford some evidence of this view. What
bearing this interpretation might have upon the periotic origin of
the operculum is evident.

DESMOGNATHIDAE.

Desmognathus fusca. In this species, the only member of ‘the
)

small family examined, the ‘“‘sound-transmitting”’ apparatus mark-

Fic. 13. Desmognathus fusca, larva 26 mm. long. C., arteria carotis in-
terna; H., ceratohyale; L.h-c., ligamentum hyo-columellare; Z.s-c., ligamentum
squamoso-columellare; Sp., os squamosum; S¢#.0., stilus columelle; V.p-l.,
vena petroso-lateralis; V/J., neryus facialis.

edly resembles in its general structure and relations that of the Ple-
thodontide just described. In fact, they are of the same type. A
bony plate with cartilaginous border fits into the fenestra and pro-
jects caudad upon the outer wall of the recessus perilymphaticus.
The caudal portion is concave externally, and in the depression there
is inserted the M. opercularis. The cephalo-ventral border is con-
tinuous with the cartilaginous border of the fenestra. The stilus is
osseous with a cartilaginous core, the distal portion being of carti-
lage alone. ‘Two figures of an adult, one (Fig. 15) through the cau-
dal portion showing the concave fenestral plate and the recessus;
the second (Fig. 14) through the insertion of the stilus, may be

The Columella Auris in Amphibia. 585

directly compared with the sections through the same regions in
the plethodontid, Gyrinophilus (P]. VI, Figs. 46 and 47). Similar
comparison may be made with Spelerpes (Figs. 6 and 7).

The relations of the stilus to the squamosum, quadrate, facial
nerve, artery and vein, have been described in some detail by Kings-
bury (03, pp. 321-825) for larva and adult, two sizes of each, and
as our investigations have not added significant details, it will be
sufficient to state in confirmation of the description there given that
while in the larva the stilus is most closely joined to the ventral
edge of the squamosum (Fig. 13); in the adult it becomes shifted
so as to articulate closely with the os quadratum, less closely with the
cartilaginous process of the palatoquadrate. The relation to artery,
vein and nerve is that typical of the majority of urodeles,

Fic. 14. Desmognathus fusca, adult. Col., columella; C.p., cavum peri-
lymphaticum ; Sq., oS squamosum; S?.C., stilus columelle.

An examination of young larve and embryos which would deter-
mine the origin or origins of the stilus and fenestral plate, has not
been undertaken. The mode of insertion of the stilus upon the
fenestral plate, as shown in Fig. 14 (compare also Pl. VI, Fig. 46,
Gyrinophilus), might suggest that the stilus alone developed outside
the otic capsule, as the description of Parker would indicate. Since
the columella in Desmognathus doubtless develops in essentially the
same manner as in the Plethodontide (Spelerpes, Plethodon) refer-
ence may be made to the description of its development in that
family, as given on p. 580.

586 B. F. Kingsbury and H. D. Reed.

Desmognathus possesses a short but well developed ligamentum
hyo-columellare, in this respect also agreeing with many of the Ple-
thodentide. In Fig. 15 it is indicated in the larva.

TyPHLOMOLGE.

A single adult 95 mm. long was studied by means of serial sec-
tions and a model of the entire skull in the otic region. The fenestra
vestibuli is filled by a single plate as in the Plethodontidz, connected
by a long and slender stilus with the suspensorium. On the ceplialo-
ventral margin the fenestral plate is fused with the ear capsule.

Fie. 15. Desmognathus fusca, adult. O.p., cavum perilymphaticum; M.op.,
musculus opercularis; Op., operculum; I.p., Recessus perilymphaticus.

The stilus is relatively longer than in any of the other forms exam-
ined. This is probably due to the extreme flattening of the skull,
which has brought the long axis of the suspensorium more nearly
parallel with that of the skull, thus throwing the attachment of
the stilus to the suspensorium farther cephalad. It seems likely that
this flat condition of the head is the result of an adaptation to sub-

The Columella Auris in Amphibia. 587

terranean life where a wedge-shaped form is more convenient for
making progress in narrow quarters.

Miss Ellen Tucker Emerson, 2d (’05), states in substance that
the operculum is not connected with the suspensorium, and her figures
show a short stilus, labelled columella, projecting freely from a
basal portion in the fenestra vestibuli called operculum. Serial sec-
tions and the model of the specimen studied by us show that the
columella is morphologically connected with the suspensorium but
interrupted. On the right side of our specimen the stilus begins to
grow smaller in diameter a litle beyond the middle of its extent and
finally disappears for a distance of 210 microns. Then it appears
again, gradually assuming its normal diameter, and continues unin-
terruptedly to the suspensorium. Here it is joined to the squamosum,
the os quadratum and the palato-quadrate (Pl. Il, Fig. 28).
Between the free ends of the segments is a well defined ligament
within which a few cartilage cells are found at intervals.

On the left side there are three segments (Pl. X, Fig. 68) pro-
duced by two interruptions. One of these corresponds in position
and extent with the single interruption on the right side. The second
occurs just before the stilus joins the suspensorium and is about the
same in extent as the first. On this side the distal or third segment
extends for a distance along the ventral edge of the squamosal, join-
ing the edge of the os quadratum as well, but without relation to
the palato-quadrate. It should be noted in this connection that Kings-
bury (03) described the stilus in adult Spelerpes as connected with
a rod of cartilage lying along the ventral edge of the squamosum,
a condition similar to what is found on the left side of our specimen
of Typhlomolge.

It may be questioned whether the interrupted condition of the
stilus in Typhlomolge results from tension and a consequent separa-
tion of what otherwise would remain, as developed, a continuous
bar of cartilage, or is reminiscent of the condition found in the frog
where there are separate centers of chondrification. It should be
recalled, however, that in the urodeles where development has been
studied, chondrification of the stilus and columella is continuous.
Furthermore it is to be noted that in the Plethodontide there is a

588 B. F. Kingsbury and H. D. Reed.

loose connection of the stilus with the suspensorium, probably due
to the tilting of the latter in its relation to the long axis of the skull.
In Typhlomolge this tilting of the suspensorium is extreme and it
is, therefore, a fair question as to whether or not the segmentation
in the stilus is the result of tension during development. ‘The attach-
ment of the stilus to both suspensorium and columella are at the same
horizontal level, there being a slight outward and downward curva-
ture as shown in Plate III], Fig. 28.

The relation of the stilus to the blood vessels and nerves in this
region is that found in Necturus, namely, the vena petroso-lateralis
and the ramus jugularis of the facial nerve are above, while the main
trunk of the facial nerve and the internal carotid artery are below.
This condition is illustrated by Fig. 28 (Pl. II) and Text-
figure 16.

St. C-@

Fic. 16. Typhlomolge, adult. @Q., os quadratum; R.j.V/7., Ramus jugularis
VII.; St. C., stilus columella; Sq., oS squamosum.

The fenestra vestibuli is irregularly elliptic in outline as is the
fenestral plate. The dorsal and ventral portions are not filled by the
plate, there being a relatively wide space both above and below filled
only by membrane. In the caudal portion there is a slight outward
swelling forming a prominence which projects slightly beyond the
caudal lip of the fenestra and which contains a small but well defined
recessus within. The M. opercularis is absent.

The lips, both of the fenestra vestibuli and the fenestral plate,

The Columella Auris in Amphibia. 589

remain cartilaginous throughout the greater part of their extent, the
bony portion of the plate being much thinner than the margin as
in the Plethodontide. At its base the stilus is composed entirely of
bone (Fig. 17) which gradually becomes a sheath surrounding a core
of cartilage. In the distal half (Fig. 16) the stilus is composed of
cartilage alone.

Between the distal end of the ceratohyal and the otie region of the
skull is a wide sheet of fascia, the caudal portion of which is attached
to the stilus and in this region becomes ‘a relatively strong ligament
between the columella and hyoid (Pl. X, Fig. 68). |

Developmental stages have not been studied, but it appears that
in Typhlomolge the type of sound-transmitting apparatus is essen-
tially that of the Plethodontide. : Z .

Vig. 17. Typhlomolge, adult. (C.1., canalis lateralis; Col., columella; St.¢.,
stilus columelle; Sq., os squamosum.

Nercrurvs.

Although the relations and development of the otic region of the
skull in Necturus have been already quite well worked out by several
persons, because of its historic interest in this connection and the
general acceptance of its low systematic rank, it has been included
for brief consideration. In illustration of the conditions in this
form four photographs are introduced, Figs. 57, 58, 59 (Pl. VIIT),
and 60 (Pl. TX).

Miss Platt (97), p. 430, described the early development in the
ear capsule in Necturus. In a 19 mm. larva the “opereulum’’ is

590 B. F. Kingsbury and H. D. Reed.

pre-cartilage, forming neither from the otic capsule nor the fenestral
membrane, but independently lying primarily anterior to the fenestra.
She suggested at this time the possible homology of the urodele
operculum with the pars interna plectri which is supported in this
paper; but evidently without much faith in its correctness, for in a
footnote in which she states her objection to the term “operculum”
she adds that this cartilage (operculum, 7. e., columella) is not the
equivalent of the “columella” (plectrum) of the Anura and is of
questionable homology with the “stapes” of higher vertebrates. -
Kingsbury (’03) examined the early development in Necturus.
He confirmed Miss Platt’s results and in addition described the
‘primary connection with the squamosum and the cells underlying it:
“At this stage, the operculum is just beginning to chondrify as a
distinct center, and from it a chord of cells is continued forward,
ventral to the vena jugularis and the ramus jugularis, to the cells
surrounding the developing squamosum, becoming continuous with
them a short distance (50 microns) back of the processus oticus
quadrati. The cells are of course continuous with those of the
squamosum and also with the cells between that bone and the
quadratum, so that the squamosum, the quadratum, and the lga-
ment-anlage, may be said to be joined together by a common mass of
cells. In the just hatched larva, likewise, the ligament-anlage
clearly goes to the underside of the squamosum and inserts itself
between that bone and the processus oticus quadrati, so that it
might be interpreted as going to both structures. As soon as the
connective tissue fibers develop, however, the relation is seen to be
with the squamosum and not with the quadratum. In later stages
a strong ligamentum squamoso-columellare develops, which connects
the stilus columellee to the columellar process of the squamosum.”
Wilder (’03) in a monograph upon the Skeletal System of Nec-
turus takes, however, a different view. He regards the operculum
(columella, our term) as a “detached portion of the otie capsule”
basing his view upon the condition in a 44 mm. larva which was
essentially the same as in a 26 mm, individual examined by him.
In the light of the work by Stohr on Triton and Siredon he regards
the statements of Miss Platt as unfounded, admitting, however,

The Columella Auris in Amphibia. 591

that the proton described by her might represent “‘a true columella
or hyomandibular cartilage which may become fused with the true
operculum,” although he could find no trace of such a double origin.
In comment on the above it may be said that to determine the first
development it is necessary to go back of the condition in a 26 mm.
larva as was done by Miss Platt. There is certainly no indication
of a double origin, although the increase in size in the columella of
Necturus, as in Ambystoma (p. 556), admits of two possibilities of
interpretation. ‘The development of the opereulum as described by
Stohr in Triton and Siredon has been discussed on p. 573.

The ramus jugularis VII passes over the ligament (Pl. VITI,
Fig. 58), as in Proteus and Typhlomolge described above.

The relations of the columella, squamosum and facial nerve in
Necturus are well known through the work of Cope, Driiner, Kings-
bury and Wilder, though the significance of the relations has not
been adequately considered.

Huxley’s classic paper on the skull of Necturus was in respect
to his description of the relation of the columella, facial nerve, and
suspensorium incorrect and misleading, occasioning a wrong idea
of the urodele type, persistent even up to the present time. We find
no trace of his ligamentum suspensorio-stapiale, over which the
facial nerve passes. Operculum (our use) and M. opercularis are
lacking.

Proteus agrees in all essentials with Necturus (Wiedersheim,
Driiner, Kingsbury).

CRYPTOBRANCHIDAE.

Oryptobranchus allegheniensis. Through the generosity of Mr.
b. G. Smith, of Syracuse University, who kindly sent us a series of
embryo, larval and adult specimens, we were enabled to examine the
relations in this interesting form with quite satisfactory results.

As the publications of Wiedersheim (’77), Parker (’82b) and
Cope (’88) have shown, the Columella in the adult possesses a well
developed stilus which articulates with the under (inner) surface
of the squamosum. This relation is strikingly shown in the series
of sections through the head of an adult 140 mm. long (PI. VII,

592 B. F. Kingsbury and H. D. Reed.

Figs. 5455; Pl. VIII, Fig. 56) which was at our disposal. The
squamosum, furthermore, is the only skeletal element to which the
columella is attached, save the os pterygoideum which works its way
well up on the inner surface (Pl. VII, Fig. 54) of the palatoquad-
rate and whose upper edge is somewhat loosely connected with the
end of the stilus columelle. As though determined by the excessive
flattening of the head in this form, the mandibular end of the
palatoquadrate is well back and lateral, while the cranial attachment
by means of the usual three processes is unusually far forward
(cephalad). The whole suspensorium is therefore rotated from an
“ideal” transverse position, and it would seem as though this dis-
placement might well explain in a mechanical way (a) why the
stilus columellz joins the under surface of the squamosum instead
of its caudal edge as in so many of the forms; (b) how it is possible
for the os pterygoideum to come into such close relation to the
columella; (c) the absence (in the young adult at least) of a con-
nection of the stilus with the palatoquadrate or os quadratum.”

A second interesting feature found in this skull is the presence of
what might be interpreted as a Ligamentum hyo-columellare (PI.
VII, Fig. 55, L. h. e.) which is essentially a thickening of the
fascia covering the inner (under) surface of the M. cephalo-dorso-
mandibularis. It extends from the ceratohyal to the outer surface
of the stilus, extending with it to its attachment to the squamosum.
As this ligamentous thickening of the fascia is relatively more marked
in the larva, it will be mentioned again in connection with that
stage.

The columella appears to ossify in the typical way; at the stage
of our specimen it consists of a cartilaginous body (PI. VIT, Fig.
55; Pl. VIII, Fig. 56) with an inner and outer plate of perichondral
bone, the latter extending out upon the stilus for a distance. The
distal portion possesses no bony sheath and it was doubtless this that
led Parker to distinguish here two elements, a Stapes (bony and

“Krom this bone as a center the ossification of the quadrate cartilage appar-
ently proceeds. Kingsbury referred to it as “bone X,’” Gaupp has suggested
tentatively the homology with the os quadrato-maxillare of Anura. Its final
interpretation requires additional comparative investigation.

The Columella Auris in Amphibia. 593

fitting into the fenestra) and articulated with a Pharyngohyal,"
consisting of cartilage. This is, of course, incorrect, due to the
inadequacy of the method of gross dissection, upon which he based
his conclusions.

From the caudal edge of the palatoquadrate a rather delicate
process of cartilage extends back to the ceratohyal to which it is
applied, curving slightly over its upper surface. The name of
Epihyal which Parker gave to this process of the quadrate is like-
wise certainly incorrect. Cope (’88) has termed this the “Hyo-
suspensorial cartilage ;”
hyoideus palatoquadrati, since an articulation with the quadrate
as described by him is not found. In other respects the description
of Cope is essentially correct. Wiedersheim, likewise, describes the

it might more correctly be called Processus

squamosal connection of the stilus and the position of the facial nerve
correctly, though he apparently overlooked the condition here in the
general portion of his paper.

Larval Cryptobranchus. Serial sections were made through the
head of four Cryptobranchus larve whose lengths were, respectively,
28 mm., 34 mm., 45 mm., and one just hatched. Since in these series
the morphological relations are in all essentials the same, it will be
sufficient for the purposes of this paper to describe briefly the rela-
tions in the one which is of intermediate size (34 mm.), and sup-
plement this with comments on some interesting features in the
youngest,—the newly hatched larva.

The columella in this larva (34 mm.) consists of a roughly oval
plate of cartilage resting upon the membrane closing the fenestra
vestibuli. From the cartilaginous border of the fenestra the colum-
ella is separated by the membrane everywhere except at the cephalic
edge where it articulates with the cartilaginous ear capsule at the
erista semicircularis. In larve 28 mm. and 45 mm. long, the
fenestral plate does not come into articular relation with the carti-

“Parker in his earlier paper (’76, pp. 559 and 587) referred to this cartilage
as homologous with the elasmobranchian “Spiracular cartilage’ and the
annulus tympanicus of the Frog, the facial nerve passing below it. In the
second paper, however, in which he terms it a pharyngohyal, the facial nerve
is described as passing over it.

594 B. F. Kingsbury and H. D. Reed.

lage of the car capsule, so that doubtless this is a variable feature.
In the adult there appears to be a very slender cartilaginous connec
tion. The portion of the fenestra vestibuli not occupied by the
columella is thus a crescent of somewhat horse-shoe shape.

The stilus of the columella arises gradually from the cephalic half
of the fenestral plate, passing at first more laterally and then in a
curve cephalad and slightly dorsad to become closely attached to the
lower edge of the squamosum. In its course it passes between the
vein and artery, as is typical, the vein being above (Pl. VII, Fig.
51). The facial nerve is entirely ventral to it, though the jugular
branch and ramus communicans IX come very close, the latter lying
at first upon the dorsal side of the columella; it slips over the outer
side, however, and joins the R. jugularis in gliding under the stilus
just as the latter joins the squamosum.

The sheet of fascia covering the inner surface of the M. cephalo-
dorso-mandibularis possesses two thickenings of morphological
importance. The more dorsal of these (Ligamentum hyo-columel-
lare) arises over the outer side of the ceratohyal, curves around its
upper surface and passes forward to join the stilus columelle at its
bend and, as a sheath upon its outer side, accompanies the latter to
its articulation with the squamosum. Fig. 51 (Pl. VII) illus-
trates the location of this ligament in its course from hyoid to
columella and shows the muscle “bellying against” the ligament as
a full sail against a rope. A portion of this seems to have been
Parker’s stapedio-suspensorial ligament. The more ventral and
band-like ligamentous thickening passes from the ceratohyal to the
caudal edge of the quadrate. It curves around this element and a
portion of it joins the tendon of the M. cephalo-dorso-mandibularis
at its insertion on the os angulare. This ligament must embody the
ligamentum hyo-suspensoriale and as well the ligamentum hyo-
mandibulare. In connection with the former, in the adult is devel-
oped the cartilaginous. process of the palatoquadrate already
described. Whether this process develops from an independent
center or not, and at what stage it appears, cannot be determined
from the material at hand.

In the larva, the suspensorium has not the “rotated” position that

The Columella Auris in Amphibia. 595

it has in the adult, and the columella has no connection with the
palatoquadrate, os pterygoideum or os quadratum. Furthermore,
it is to be noted that it articulates with the lower edge of the squa-
mosum and not with its under surface.

The newly hatched Cryptobranchus is of interest in this connec-
tion for two reasons: (a) the columella is represented by a con-
densation of cells from which a cord of cells passes cephalad (PI.
VII, Figs. 52-53) and dorsad to the group of cells in whose midst
the squamosum is just appearing as a homogeneous scale of bone ;
(b) the columella at this stage is pre-cartilage and is distinctly form-
ing outside the ear capsule. The chondrocranium is cartilaginous,
the fenestra clearly demarcated, and the precartilaginous columella
external to the membrana fenestre (Fig. 52). The development at
this stage closely parallels that of Necturus, as already described
(p. 590). It seems to us safe, therefore, to add Cryptobranchus to
Necturus and Ambystoma as a form showing the extra-otic appear-
ance of the columella, and its early connection with the squamosum.
It is likewise noteworthy that the columella in all the larvee exam-
ined shows no cartilaginous connection with the otic capsule; and
in the adult the fusion is very slender,—if indeed it exists. The
source of the cells that form the columella could not be determined
from the material at hand, although two embryos were examined.
Neither operculum nor opercular muscle are developed.

It is interesting to note in concluding that Cryptobranchus is the
only form in which there has been general agreement as to the con-
nection of stilus with squamosum; not so, however, the relation to
the facial nerve. Both Wiedersheim (’77) and Parker (’82b)
described the relation correctly and subsequently altered their state-
ments.
Megalobatrachus. From the description of Parker (’82b),
Wiedersheim (’77), Osawa (’99), as from the dissection of a single
specimen in connection with this study, suffice it to state that it
shows essentially the same relations as Cryptobranchus. Osawa
(as quoted) describes the stilus as joining the palatoquadrate.
Parker states that the hyo-suspensorial cartilage (his epihyal) articu-
lates with the palatoquadrate ; in Cryptobranchus there is continuity.

596 B. F. Kingsbury and H. D. Reed.

AMPHIUMA.

In Amphiuma a single plate fills the fenestra vestibuli and is free
except on its cephalic end where it is fused with the ear capsule
which is cartilaginous. The very large stilus is articulated at its
distal end with the squasmosum and continuous with a process of the
palatoquadrate. Its relation to the facial nerve and blood vessels
is typical. On both inner and outer surfaces of the fenestral plate
there is a layer of bone (Fig. 18) which is continued for a short

Fic. 18. Amphiuma means, adult. 0.1, canalis lateralis; Col., columella ;
Sq., oS squamosum ; St.¢., stilus columellze; VJ/., nervus facialis.

distance upon the base of the stilus. A distinct but not strong liga-
mentum hyo-columellare is present. Its diagrammatic representa-
tion is given in Pl. X, Fig. 71.

The fenestral plate becomes narrower in its caudal third and
finally tapers to a point. In that portion of the ear capsule forming
the caudal margin of the fenestra there is a pronounced prominence
within which there is a continuation of the perilymphatie cavity of
the ear (Fig. 20).

While complete developmental stages have not been studied, sec-
tions through the head of a larva soon after hatching, a transform-
ing individual and an adult furnish some data regarding develop-
ment. In the youngest larva the fenestral plate is relatively small

The Columella Auris in Amphibia. 597

and free from the ear capsule all round. Although closely associated
with, it appears to be wholly outside of, the fenestral membrane.
At transformation the columella is fused in front with the ear
capsule and just fills the opening. Below and behind the columella
a portion of the floor of the ear capsule becomes greatly thickened,
especially in its lateral half, which is almost completely separated
from the capsule (Fig. 19). In this stage there are a few muscle

yi pl,

O
O

¢ Go

Fic. 19. Amphiuma means, transforming larva. ©., arteria carotis in-
terna; O.p., cavum perilymphaticum ; Sq., os squamosum; V.p-l., vena petroso-
lateralis; J/.i.c.i., a portion of the musculus intertransversarius capitis in-
ferior.

fibers partly differentiated off from the M. intertransversarius capitis
inferior which have a slight attachment to this portion of the ear
capsule.

This portion of the floor of the ear capsule which was thickened
and partly separated off in the transforming individual is in the
adult very much thickened, forming the pronounced prominence which
encloses an extension of the perilymphatic cavity as shown in Fig.
20. The M. intertransversarius capitis inferior comes into close
relation with the prominence of the adult, but there is no differentia-
tion of a distinct opercular muscle.

598 B. F. Kingsbury and H. D. Reed.

By comparing Fig. 11 and Fig. 31 (Pl. III) of Ambystoma
and Fig. 50 (Pl. VII) of Triton it is evident that this portion
of the otic floor corresponds in position to the operculum. It would
seem as though at transformation a beginning of operculum forma-
tion was made which does not go through to completion.

Fic. 20. Amphiuma means, adult. C.p., cavum perilymphaticum; Para-_
sphen., OS parasphenoideum; Prom. p., prominentia perilymphatica. Sq., os
squamosum.

SIREN.

The only material examined was an adult specimen 133 mm.
long. The fenestra vestibuli is here, as in some other forms, filled
by a single plate which is cartilaginous in our specimen although
Cope (’88) states that it is bony in this species. It is elliptic in
outline, facing outwards and downwards with a short stilus ‘stand-
ing almost vertical to the plate and slight inclination being in a back-
ward and downward direction. The connection of the columella
with the suspensorium, if it ever existed, has disappeared. The
relation of the stilus to the blood vessels and nerves in this region
is typical,

The Columella Auris in Amphibia. 599

The fenestral plate is fused throughout its entire cephalic margin
with the ear capsule. This fusion is much greater in extent, rela-
tively, than in either Typhlomolge or the Plethodontide.

The ceratohyal is much produced caudally, its faleate distal por-
tion extending beyond the otic region. A short distance before the
caudal extremity is reached there arises from the dorsal edge a broad.
and strong ligament extending forwards for insertion upon the
fenestral plate (Pl. X, Fig. 72). The stilus projects directly into
this just cephalad of which there arises another, the hyo-suspensorial
ligament, which passes cephalad for insertion upon the palatoquad-
rate. These ligaments are considered by Cope as one, namely, a
hyo-suspensorial ligament extending from the quadrate across the
ear capsule to the exoccipital. Parker treats them as two separate
and distinct ligaments. That portion extending to the quadrate he
ealls the hyo-suspensorial while to the columellar portion he applies
the name suspensorio-stapedial. Functionally they are probably to
be considered as distinct, but in serial sections they appear to be
thickenings of the same sheet of fascia.

The short and free stilus projecting into the ligamentum hyo-
columellare is more comprehensible in the light of the segmented
condition of this structure in Typhlomolge. Thus in Siren all sus-
pensorial communication of the fenestral plate with the exterior,
such as is found in other forms, is cut off. But it will be noted that
the ligamentum hyo-columellare in this form is strongly developed
which together with its firm attachment to the fenestral plate may
compensate for the absence of the usual skeletal connections. The
relation of the stilus to the facial nerve and blood vessels is that
found in the majority of forms.

_ Three figures (Pl. IX) illustrate the relations of the columella,
stilus and hyo-columellar ligament. In Fig. 61 the short stilus
is shown projecting out into the dense ligament, the diminutive plate
joined to the margin of the fenestra by connective tissue. Fig.
62 is through the caudal end of the columella of the opposite side.
In Fig. 63 the section is through the perilymphatic prominence,
a caudo-lateral extension of the ear capsule. Slightly farther for-
wards the cartilage is hollowed out by a small recessus. The fenestra

600 B. F. Kingsbury and H. D. Reed.

and the caudal lip of the columella appear in the lateral wall of the
prominence. In all essentials, save as noted, the sound-transmitting
apparatus of the adult is like that of Amphiuma.

GENERAL.

In perusing the preceding portion of this paper, it will have
become obvious that considerable confusion in the interpretation
of the sound-transmitting apparatus in Amphibia,—particularly the
Urodela,—has been caused by discrepant statements and conflicting
descriptions of the conditions existing in the different forms. The
differences that apparently existed concern principally (a) the rela-
tion to the suspensorium, (b) the relation of the facial nerve to the
stilus columelle, (¢) the mode of development of the fenestral struc-
tures.

The Suspensorial Connection. Gaupp in his paper on the sound-
transmitting apparatus of Vertebrates ((98) was led to the conclu-
sion that there existed two types of connection between the suspen-
sorium and the skeletal element filling the fenestra vestibuli,—one
above and one below the facial nerve, and the same view has been
taken by Driiner (’03). Gaupp later (05) says: ‘Die oft citierte
Angabe von Wiedersheim, dass der Nerv bei allen Urodelen ohne
Ausnahme iiber diese Briicke hinweglaufe, ist irrig; vielmehr scheint
der Verlauf der Nerven ventral von der fraglichen Briicke das
haufigere zu sein. Letzteres findet sich bei Amphiuma (Hay 1890,
auf Grund eines von Prof. Norris hergestellten Modelles kann ich
diese Angabe bestitigen), Siredon (Hasse 1873, Parker 1877) und
zahlreichen anderen Urodelen (Proteus, Desmognathus fusca,
Spelerpes bilineatus, nach soeben verOffenthchten Untersuchungen
von Kingsbury); der Verlauf des R. jugularis facialis uber die
erwahnte Verbindung findet sich bei Necturus (Huxley) und Proteus
(Driiner, Kingsbury). Es sind somit 2 verschiedene suspensorio-
columellare Briicken aus einander zu halten, eine tiber und eine unter
dem Facialis (Gaupp 1899).”

For this divergence of statement, Huxley seems to have been
primarily responsible, inasmuch as in Necturus he described a
“Ligamentum suspensorio-stapediale” and stated that “the hyo-

The Columella Auris in Amphibia. 601

mandibular branch of the seventh nerve (VIL) passes above this liga-
ment to its distribution, just as it passes above the Colwmella auris
in the frog.”

The real connection of the stilus with the special process of
the squamosum'” (Processus columellaris) he seems to have missed
entirely. The reference to Huxley of a recognition of such a
connection by Gaupp in the passage quoted above is incorrect. It
should be remembered, however, that Huxley’s observations were
based upon minute dissections, in which a strand of fascia could
easily be made to assume the appearance of a ligamentous structure,
and the obvious passage of the hyomandibular division of the seventh
nerve over the columella in the frog and the relation in mammals
would incline one a priori to a similar interpretation in urodeles.
Wiedersheim appears to have accepted his statement of relations,
and without paying special attention to the point, gave as the uni-
versal condition in urodeles that the facial nerve passed above the
suspensorial connection. Huxley’s description doubtless imfluenced
his friend, W. K. Parker,'? who in several forms described the
facial nerve as below the columella, yet sometimes located it above,
or was vague in his descriptions.

One result of this study is to show that a “‘suspensorial connection”
does indeed exist, in all save four of the salamanders examined
(Diemictylus, Triton, Siren, Batracoseps) the nervus facialis being
below and in front (see, however, p. 610). The connection is not
primarily with the palatoquadrate, as has been heretofore believed,
but with the bone, partly overlying the palatoquadrate and partly
over the lateral semicircular canal of the ear, which we have regarded
as squamosum. This primary connection of the columella through

“The correct relation was described subsequently by Cope (’88, ’89), Wilder

(03), Driiner (11), and Kingsbury (03); the relation to the facial nerve,
by the last two.
. 8Parker, ’77 (p. 559), in a footnote says: “Professor Huxley pointed out
this anomaly to me, showing me that this ligament cannot correspond to the
“suspensorio-stapedial” ligament of Menobranchus (op. cit., p. 192).”’ The
reference is to the squamoso-columellar ligament in Ambystoma, which is, of
course, above the facial nerve. See footnote on page 562 for Parker’s descrip-
tion.

602 B. F. Kingsbury and H. D. Reed.

its stilus with the squamosum is now reported’ for Necturus
maculatus, Proteus, Typhlomolge, Typhlotriton, Spelerpes _bis-
lineatus and ruber, Gyrinophilus prophyriticus, Hemidactylium
scutatum, Plethodon cinereus, Stereochilus marginatus, Autodax
lugubris, Manculus quadridigitatus, Desmognathus fusca, Ambys-
toma punctatum, Chondrotus tenebrosus, Cryptobranchus allegheni-
ensis, Megalobatrachus maximus.

In certain of the forms, however, at transformation,—before or
after it,—the connection of the stilus tends to shift to the palato-
quadrate, presumably in the change of the position and direction
of the suspensorium to which Wiedersheim called attention (77).
In this displacement of parts as we interpret it, the squamosum, as
in Ambystoma, comes to lie more on the dorsal surface of the palato-
quadrate. In certain forms a special process of the palatoquadrate
develops (e. g., Plethodon, Amphiuma) which may reach a rela-
tively great length (Amphiuma). Hence we see how the more
obvious connection has become accepted as the typical one, and the
primary connection with the squamosum”’ is overlooked, even though
occurring throughout life as the direct articulation in many of the
forms. If the anatomical relation of parts is such that the palato-
quadrate does not come into the proximity of the distal end of the
stilus in the shifting, a connection with it is not established,—as in
the case of Cryptobranchus (young adult) where the connection of
the stilus moves from the caudal edge to the under side of the
squamosum. Whether the stilus columelle maintains the primary
relation with the squamosum or becomes more closely joined to the
palatoquadrate, any physiological value it may possess as a “sus-
pensorial connection”? remains unaffected, so closely is the lower

“Cope, ’89, describes the correct condition in Necturus and Proteus (p. 22) ;
of the remaining urodeles he says: “The stapes [columella] has no connec-
tion with the suspensorium in the adult except in the Cryptobranchide and
Amphiumidae. It is connected with the suspensory cartilage, which is con-
tinuous with the quadrate cartilage in the latter families, and in the young
of other Urodela” (p. 29).

“The development of the stilus columella has not been studied in Sala-
mandra, nor in Amphiuma has the earliest development been yet worked out
(see Kingsbury, ’03, p. 325). The squamosal connection will doubtless be
found in all salamanders possessing a well developed stilus.

The Columella Auris in Amphibia. 603

end of the squamosum joined to the quadrate. From a morphological
viewpoint, however, it is not a matter of indifferent significance.
The connection of the columella with the squamosum and its forma-
tive cells is a primary one, while the direct articulation or junction
with the palatoquadrate is only secondarily established. The sig-
nificance of the relation becomes more impressive when the develop-
ment of the columella is considered. In the forms in which the
early development has been traced,—Necturus, Ambystoma, Crypto-
branchus, Spelerpes, Plethodon,—before cartilage has appeared in the
columella, when the squamosum is but a delicate scale of bone, a cord
of cells proceeds from the proton of the columella to the cells under-
lying the forming bone. The developmental relations will be considered
again in connection with the question of hyomandibular homology.
Columella and Operculum. A second complication exists in
Amphibia due to the existence of two structures that are found fitting
into the fenestra vestibuli, and the failure to recognize this fact has
added another source of confusion in the elucidation of the relations
in this group. It is the first of these two elements, distinguished by
us as Columella, which possesses a suspensorial connection. The sec-
ond, termed by us the Operculum, possesses no such relation. In its
typical form as it exists in the adult Ambystoma, Diemictylus or
Salamandra, the operculum is a spheroid filling in the definitive
fenestra with whose lips it is connected by membrane only or pos-
sesses a slight cartilaginous connection at its caudal end. It may
be massive (spheroidal) as in Salamandra, or more plate-like as in
Triton. The cephalic end is included by the lip of the fenestra;
the caudal end projects freely, covers the recessus perilymphaticus
externally and affords attachment to the M. opercularis. In the
families of the Plethodontidze and Desmognathide the condition is
characteristic and unique; the oval window has fitted into it a plate
whose cephalic portion possesses a well developed stilus and whose
eaudal portion offers attachment to the M. opercularis and covers
externally a recessus perilymphaticus; it seems therefore to repre-
sent both columella and operculum.
The statement of Gaupp (’05) in reviewing the Amphibian sound-
transmitting apparatus (p. 605), that only by a stretch of the

604 B. F. Kingsbury and H. D. Reed.

imagination could an extra-otic origin be ascribed to the element
filling the fenestra vestibuli in this group, was made in the light of
the condition existing in Triton and the fragmentary developmental
evidence already at hand, and without knowledge of the existence of
two structures in urodeles. It applies, therefore, with full force to
the development of the operculum. The columella, however, develops
in quite a different manner, and here the evidence of an extra-otic
origin is much stronger. Killian (’90) first described this structure
as developing outside the ear capsule in Ambystoma, and Miss Platt
(97) in Necturus advanced the same view. Kingsbury subsequently
examined the condition in larval and embryo Necturi and came to the
same conclusion. In this paper we have shown evidence of an
entirely similar mode of origin of the columella, outside the fenestral
membrane, in Cryptobranchus, Spelerpes, and Plethedon, and con-
firmed Killian’s observations on Ambystoma. Supplementary evidence
of an extra-otic origin for the columella is to be found in the fact that
from the first, before chondrification has begun, the columella is
connected by a dense grouping of cells with the squamosal cells
around the outer side of the vena petroso-lateralis.

With the growth of the fenestral plate of the columella it becomes
associated or fused with the cephalic edge of the fenestra. This is
not, however, a primary connection but a secondary one. Hence the
statement that has been made (Winslow, Stohr) that the columella
grows out of the cephalic edge of the window is not correct. In the
descriptive portion of this paper, the difficulty in determining just
what occurs in the chondrification of the plate of the columella has
been pointed out. Even though the columella grew through the
incorporation of otic tissue, its origin from without the otic capsule
would not be invalidated, which is supported by its relation before
chondrification and its early and intimate connection with the sub-
squamosal cells.

The tendency of the columella to become fused with the cephalic
cartilaginous margin of the fenestra is in some forms carried to an
extreme, and results in a more or less complete incorporation of the
structure into the ear capsule by extensive fusion with it. In the
Ambystomidz its boundary is still distinguishable by the charac-

The Columella Auris in Amphibia. 605

teristic inner and outer bony plates, and by the stilus. Salamandra
lacks the ossification, the incorporation appears more intimate but
the stilus is persistent. In Triton and Diemictylus stilus and ossi-
fication are both lacking and incorporation into the edge of the
fenestra is complete.

Attending the fusion of the columella, there is the formation of
the operculum to inherit its position and function as a fenestral
structure. Concerning its origin and development there is not, as in
the case of the columella, opportunity for uncertainty. In Ambys-
toma, in which it appears late,—at the end of transformation,—it is
eut out of the floor of the otic capsule medial to the fenestra. In
Diemictylus and Triton, in which it appears early, “cutting out”
must play a more secondary part, and marginal growth by chondri-
fication of opercular tissue seems more important. It occupies in
either event the same position and seems to be a detached portion of
the otic capsule, although extensive cartilage formation in it may
give it a thickness several times that of the otic capsule. It under-
goes no ossification, remaining cartilaginous throughout life.’ Its

characteristic features, negative and positive, are the lack of connec-
tion with the skeleton outside the ear capsule, and the attachment of
the M. opereularis.

The fusion of the columella causing a more or less extensive
filling in of the cephalic portion of the fenestra vestibuli necessitates
the recognition of primary, secondary and definitive fenestra, of
somewhat different boundary and location, as in the Anura (Gaupp,
93). The question of in how far the cephalo-caudal succession of
fenestral elements or the (essentially) cephalo-caudal extension of
the fenestra itself is an expression of the play of factors of relative
growth of parts,—otic capsule, suspensorium, ete.,—is simply raised.
It is hardly necessary to state that the primary character of the
fenestra as an unchondrified portion of the otic capsule, as affirmed

It is interesting to find Parker (’82a) commenting on this condition; on
page 199 he says: ‘One more point of interest is to be noted here: the lowest
Perennibranchs have their stapes thoroughly ossified (7. e., the columella) ;
the highest Caducibranchs, like the Batrachia, have it (i. e., the operculum)
soft; here in Spelerpes it ossifies early, and becomes a very perfect and
elegant shutter to that small oval window.”

606 B. F. Kingsbury and H. D. Reed.

by Stohr and more recently by Fuchs (’07) as contrasted with an
appearance secondarily, by dehiscence or absorption, is abundantly
established. It must be understood, however, that this applies only
to the primary fenestra, while in the formation of the secondary and
definitive fenestree, in some forms, at least, the extension is accom-
plished essentially as a “dehiscence.” The developmental trans-
formations undergone by the primary fenestra require a more
detailed study in a number of salamanders before a full interpreta-
tion can be made.

In the Plethodontidze and Desmognathide, where the single fenes-
tral plate possesses some of the characters of operculum and colu-
mella combined, the development has been followed in Spelerpes
bislineatus. ‘There is no evidence of a fusion of two structures, the
cartilaginous and bony plate which bears the stilus by growth gains
the territory which in Ambystoma is occupied by the operculum and
may therefore be regarded as representing that structure without
embodying it."

On plate X are set forth in schematic form the morphological rela-
tions of the two structures under consideration as they occur in
typical forms. Examining the conditions in the Urodela, we find
that they may, with the figures of this plate as illustrations, be
divided into seven groups, the characters being compared in tabular
form on page 607.

Under these seven groups the forms studied distribute themselves
as follows: Group I; Necturus, Proteus (Typhlomolge). Group
IL; Larval Ambystoma and urodele larvee in general, Cryptobranchus, -
Megalobatrachus, Amphiuma. Group III; Adult Ambystoma, Adult
Chondrotus, probably other members of the Ambystomide. Group
IV; Salamandra, and possibly some of the Ambystomide. Group
V; Diemictylus, Triton, undoubtedly Salamandrina and other Pleur-
odelide. Group VI; Siren. Group VII; the Plethodontide (as
examined) ,—Typhlotriton, Spelerpes, Gyrinophilus, Hemidactylium,

“The differences between the Ambystomidz and the Plethodontide in respect
to the presence and absence of an operculum, are paralleled in the Anura by
the similar differences in the Frog (as an example of the type) and Pipa.

Gaupp’s very interesting discussion of the interpretation in the last case
(98, p. 1065) presents the problem for the first case as well.

The Columella Auris in Amphibia. 607

Plethodon, Stereochilus, Autodax, Manculus (Batracoseps). The
Desmognathide (Desmognathus fusca. )

Two forms are exceptional; Batracoseps, which otherwise falls
under group VII, possesses a vestigial stilus and therefore lacks the
connection with the suspensorium, usually well developed in the
Plethodontide. The interesting form T'yphlomolge is plethodontid
in the character of the fenestral plate, but possesses a fragmented
stilus. ‘The interesting course of the R. jug. VII over the stilus,
and the absence of the M. opercularis, however, places it in Group I.

TABLE TO SHOW THE SEVEN TYPES oF ‘ CoLUMELLA AURIS ”’ IN URODELES.

Group Columella Operculum | M. opere.
| v |
| ; car | 4
|Fusion with : | Relation
th eg fenestral | Stilus pone ore. of R. jug.
fe margin : VII to St.
I.| 6s | present “none or present | squamosum above absent absent
69 | slight | | |
a | |
| | —
ll. | 70 | present | none or present | squamosum below absent absent
all slight or Sq. and
| Pal-.Quad.
ary | hy |
Ill. | 64] present | extensive present | squamosum below present | present
| | and palato-
quadrate
IV.|65 | present, | complete present | palato- | below present | present
cartilage quadrate | |
V.| 66 present complete absent absent | present present
ne | | =
Vio 72 present moderate present? | ceratohyal absent | absent
VII. | 67 | prseent slight present |squamosum, below | not separ- | present
| quadrate, or | arately de-
palato-quad- veloped
| | | rate or all

Briefly classified from the point of view of the existence of two
fenestral structures, Columella and Operculum, these forms may be
divided into the following groups: A, groups I and II; the columella
present, free, connected with the suspensorium, no operculum or
opercular muscle. B, groups III and IV; the columella present,
fused with the otic capsule, connected with the suspensorium, oper-
culum and opercular muscle present. CC, group V; columella ves-
tigial, fused with the ear capsule, no connection with the suspensor-

608 B. F. Kingsbury and H. D. Reed.

ium. Opereulum and opercular muscle present. D, group VII;
columella present, joied to otic capsule, connected with the sus-
pensorium; the opercular muscle present, the operculum not devel-
oped as such. Up through the groups I to V, evidence of indubitable
value is presented of the incorporation and loss of an element (colu-
mella) with an attendant loss of its primary connection, a substi-
tute making its appearance (the operculum). The m. opercularis,
absent in groups I, II and VI, present in the others, appears to
deserve the name given it by Gaupp (’93), since in the Urodela it
possesses characteristic attachments and is not a portion of another
muscle (Levator anguli scapule). When an operculum is developed,
an opercular muscle is present, while its insertion in group VII is
suggestive, as is also equally, its absence in groups I and Il. From
the examination of larvee, it should be stated, however, that it appears
to be absent in all urodeles in the larval state. It will be referred
to subsequently in connection with the problem of the function of
the urodelan “sound-transmitting” apparatus.

Comparison with Anura. In the first contribution a comparison
was made of the conditions found in Ambystoma to the “columella
auris” of the frog, and further investigation has strengthened us in
the acceptance of the homologies then advanced,—the columella with
the plectrum (pars interna plectri), the operculum being homolo-
gized in the two groups. The resemblances and differences between
the two forms may perhaps best be presented in tabular form, in
parallel columns the resemblance being presented first, enumeration of
differences following. ‘The relations in the frog are taken from
Gaupp (’93, 705).

The first of the differences (No. 7) is of no marked significance,
since in other Anura (e. g., Dactylethra, Parker, Gaupp 798) the
plectrum may overlap the operculum. The next two contrasts par-
take more of the nature of resemblances than of differences, hence
items 10 and 11 are the only points of difference needing comment
here, a detailed discussion not being intended, since they are doubt-
less the ones that will be regarded as the most weighty.

As to the tenth item, it is only necessary to recall the numerous
instances of precocious and postponed development of homologous

10.

iE

The Columella Auris in Amphibia.

F'roc.

Two independent elements
(a) Pars interna plectri
(b) Operculum,

The plectrum develops in the
cephalic, the operculum in the
caudal portion of the second-
ary fenestra.

The operculum chondrifies in the
opercular tissue and becomes
joined to the cartilaginous
margin of the fenestra on its
dorso-caudal side; becomes
completely separated.

The plectrum chondrifies as an
independent center out into the
dense tissue connecting it to
the palatoquadrate.

The plectrum becomes connected
with the ventral (cephalo-ven-
tral) edge of the fenestra.

The M. opercularis inserts upon
the Operculum.

The cephalic end of the oper-
culum overlaps the fenestral
plate (pseudoperculum) of the
plectrum.

The cephalic portion of the sec-
ondary fenestra closes, exclud-
ing the pseudoperculum.

A cephalic extension of the
cayum perilymphaticum is be-
neath the pseudoperculum
(Ductus fenestre).

The operculum develops first; the
plectrum at transformation.

The hyomandibular nerve passes
above the plectrum.

609

AMBYSTOMA.

Two independent elements
(a) Columella
(0b) Operculum.

The columella develops in the cephalic,
the operculum in the caudal por-
tion of the secondary fenestra.

The operculum is cut out of the ear
capsule, remaining connected long-
est at its caudal end; becomes com-
pletely separated.

The columella chondrifies as an inde-
pendent center in dense tissue con-
necting it with the squamosum (and
palatoquadrate).

The columella becomes fused with the
cephalic (cephalo-ventral) edge of
the fenestra.

The M. opercularis inserts upon the
Operculum.

The cephalic end of the operculum
underlies the columella.

The cephalic portion of the secondary
fenestra closes, including (incorpo-
rating) the columella (fenestral
plate),

A caudal extension of the cavum
perilymphaticum is beneath the
operculum (Recessus perilymphati-
cus).

The columella develops first; the

operculum at transformation.

The hyomandibular nerve (VIIth) is
below the stilus columelle.

610° B. F. Kingsbury and H. D. Reed.

structures in different forms (Heterochronia) to appreciate that the
relative reversal of sequence in frog and salamander is not intrinsic
ally important. Among the Urodela themselves we have an instance
of partial reversal, the operculum appearing early in Triton (about
18 mm.) and late in Ambystoma (at transformation).

The opposite relation of the nervus facialis to the plectrum and
stilus columelle, is perhaps a more serious difference, since it is just
this criterion of relative position of sound-transmitting apparatus
and nerve that has been considered of decisive moment in the deter-
mination of homology. As has been stated above, Huxley introduced
confusion into the interpretation in Amphibia by faulty recognition
of indifferent connective tissue as the equivalent of the frog’s plec-
trum, hence the course of the facial nerve came to be interpreted as
over the suspensorial-columellar ligament or stilus, whereas in all
forms examined just the opposite relation holds,—the facial nerve is
below (cephalad or ventrad of) the columella, with three exceptions,—
Necturus, Proteus, and Typhlomolge,—and in these cases the
jugular branch alone passes above while the rami mandibulares,
internus and externus, are below and in front of the columella.

If the different relation of the facial nerve to the columella in
Urodela and Anura is prohibitive of the plectrum-columella homol-
ogy, there is necessary the recognition of three morphologically dis-
tinet squamoso-columellar connections in tailed amphibia, (1) in the
Proteida, (2) in Typhlomolge, (3) the remaining urodeles. This,
it is felt, is contrary to the ontogenetic evidence. There is involved
in this point the broader question of the value of the relation of
nerve to skeletal structure as a criterion of homology. The real
value of such a test of homology has already been questioned by one
of us (Kingsbury, ’03, p. 333) and a few instances given of varia-
tion in the relation of nerve, ligament and muscle,—instances which
could, of course, be easily multipled many fold; for example, in
the relation of the hyomandibular bone or cartilage to the hyoman-
dibular nerve, in fishes, ete. It was not deemed desirable to introduce
here further consideration of such evidence, as it would involve work
along broader comparative lines than was desirable at this time. Ad-
herence is given to the view entertained in the first contribution,—

The Columella Auris in Amphibia. 611

that the columella and its suspensorial connection is homologous
throughout the urodele group, and no valid reason is known why
the homology should not be extended to include the Anura as well.
Inasmuch as a study of the relations and development in that group
has not been made, the homology of columella and plectrum is not
presented with the emphasis of personal investigation.

Iigaments. The only muscle that is in the region of the head
involved in this study is the Musculus cephalo-dorso-mandibularis
(M. depressor mandibuli). It has its origin largely, and in some
of the forms entirely, from the squamosum, and inserts by means
of a longer or shorter tendon upon the retro-articular process of the
os articulare. Beneath the muscle, between it and the ear capsule,
palatoquadrate, hyoid and mandible, is the space filled in with con-
nective tissue containing the nerves and blood-vessels. The tissue
next the muscle is denser and comes into intimate relation with the
squamosum, palatoquadrate, stilus columelle, ceratohyal, and man-
dible. (For illustration, see Figs. 43, 51, 55, 61.)

This submuscular fascia appears to be the foundation, out of which,
by thickening of different portions three ligamentous structures may
be formed:
(b) Ligamentum hyo-mandibulare, (c) Ligamentum hyo-columellare.

(a) Ligamentum hyo-suspensoriale (palato-quadrate),

These may all be present in the same species, weakly or strongly de-
veloped. Of these the last two have long been recognized (Hux-
ley ’74) and are in general well described; the hyo-columellar liga-
ment, however, has not been as adequately considered and is of more
interest here because of its connection with the columella. It is
best developed in Siren (Fig. 61, 62, 63, Pl. IX), but its presence
has been mentioned in the first part of this paper in Amphiuma,
Cryptobranchus, Gyrinophilus, Spelerpes, Desmognathus; and seems
to be more or less well developed in the Plethodontide generally. It
will be referred to subsequently in connection with the discussion
of the function of the urodelan apparatus. It was not recognized
in Ambystoma, Triton, Diemictylus or Salamandra.

A ligamentum palatoquadrato-columellare corresponding to Hux-
ley’s suspensorio-stapedial ligament described by him in Necturus
it noticeably absent in that form as well as in other urodeles.

612 B. F. Kingsbury and H. D. Reed.

Beneath the facial nerve, between columella or operculum and pala-
toquadrate, is only loose connective tissue, denser in some forms
it is true,—especially Siren which possesses well developed hyo-
columellar and hyo-suspensorial hgaments giving a less direct sus-
pensorio-columellar bridge of dense connective tissue. It does not
seem in any form to possess relations of functional or morphological
importance as a “‘suspensorial” connection of the ‘“sound-transmit-
ting” apparatus.

While the presence or absence and relative development of these
lhgaments appears to be an expression of the mechanical needs, re-
quirements of support in the nature of a physiological adaptation
and therefore secondary phylogenetic importance, their existence
may possibly have a deeper significance; the ligamentum hyo-col-
umellare, for example, indicating a primary relationship of colum-
ella to the hyoid arch.

The junction of the ceratohyal with the palatoquadrate is quite
constant. It is in relation to the hyo-quadrate ligament that the
processus hyoideus palatoquadrati is developed in so many forms
(see Wiedersheim 777, p. 533).

The diagram reproduced as Fig. 21 illustrates the relations of
these three ligaments.

The Hyomandibular-Symplectic Homology. It may be safely
stated that from the phylogenetic side the hyomandibular homology
of the Amphibian sound-transmitting apparatus is at present gener-
ally accepted, as may be seen from the statements in the works of
Wiedersheim and Gaupp which were cited (p. 552) as expressing the
more recent interpretation. In the earlier form of the theory, how-
ever, only a portion was given a hyoid or hyomandibular homology ;
Reichert, Huxley, Parker, and others regarding the operculum as
purely of otic origin. |

This hyomandibular homology has been reiterated despite a dearth
of evidence from the ontogenetic side. In the Anura, it is true,
the embryological evidence has been furnished especially by the
monograph of Gaupp, and it has seemed to support the partial
homology of the older workers,—if supporting it at all. No direct
connection has been found with the ceratohyal in development. In

The Columella Auris in Amphibia. 613

the Urodela the condition is less satisfactory. Parker, Wiedersheim
and Stohr had emphatically declared the origin of the operculum
from the ear capsule and the absence of any association in develop-
ment with the hyoid arch.

More recently in a paper before the Anatomische Gesellschaft
Fuchs (’07) rejected completely the hyomandibular homology"®
of the amphibian structures, basing his conclusions upon the otic
origin of the operculum in Salamandra (See p. 568). The presence
of a stilus was regarded by him as secondary, the operculum without
stilus representing the primitive condition. In the discussion, the
homology with the hyomandibulare was upheld by several. Gaupp
at that time (’07, pp. 31 and 32) stated his conception of the primi-
tive “Columella auris” as consisting of an operculum and a stilus,
the latter articulated with the palatoquadrate. Since the hyoman-
dibulare in fishes is, in many forms, between the palatoquadrate and
the otic capsule, the connection of the stilus with the palatoquadrate
strongly suggests the homology. He admitted the lack of ontogenetic
evidence, but pointed out the difficulty attending the delimitation
of what might be hyal blastema from the periotic blastema. Since
the upper end of the hyoid arch closely adjoined the otic capsule,
blastema of the hyoid arch, it is easily conceivable, might be early
incorporated with the periotic, and the operculum might develop
apparently as part of the ear capsule and nevertheless be of hyoid
origin. In his rejoinder Fuchs (pp. 33, 34) affirmed his belief that
the operculum without stilus was the more primitive; that the fenes-
ra arose as a result of the action of a “biological factor” within
\the ear itself upon the assumption of terrestrial life; that the “rub-
bing” of the hyomandibulare could in no wise have caused the
appearance of the fenestra vestibuli, since in the numerous fish forms

*Muchs (07, p. 24): “Ich erachte das Operculum bezw. Operculum ++
Stilus der Urodelen fiir homolog dem Otostapes der Reptilien und beide fiir
homolog dem Stapes der Siiugetiere. Alle drei halte ich ontogenetisch fiir
Abkémmlinge der Gehérkapsel. Auch in phylogenetischer Hinsicht leite ich
auf dieselbe zuriick und bin ferner der Ansicht, dass sie nicht mit der Hyo-
mandibula der Fische zu vergleichen sind.” ‘“Ftir das Operculum, eventuell
Operculum + Stilus, der Urodelen wird dem ja wohl niemand mehr wider-
sprechen. |.) t),.”

614 B. F. Kingsbury and H. D. Reed.

in which it does come in contact with the periotic cartilage, no trace
of a thinning or fenestration results. Commenting on the position
of the hyomandibulare between palatoquadrate and the otic capsule, -
he expressed the conviction that we must look for the ancestors ©

of terrestrial vertebrates in the low elasmobranchs (Notidanide and
- Pro-Selachia) in which the hyomandibulare has no part in the sus-
pension of the jaw, but affords the hyoid arch an independent articu-
lation with the skull.

Since our results bear directly on the problem and from some points
of view, at least, seem to strengthen the homology of the amphibian
columella auris with the hyomandibulare, illuminating some of the
obscure points of development and relation, it seems desirable to
consider it briefly from the following view-points: (a) the extra-
otic origin of the columella, (b) the relation to the palatoquadrate,
(c) the connection with the squamosum, (d) the relation to the facial
nerve, (e) the relation of the columella auris to the ceratohyal.

As Fiirbringer pointed out in the discussion of the paper of
Fuchs, Salamandra is highly specialized and not a form upon which
to base conclusions of general applicability. This has been mark-
edly illustrated in this very problem. For the present, the operculum
(our use) may be regarded as a part of the otic capsule both in this
and the other forms that possess this structure. Fuchs, however,
dealt with but half the problem, as has been shown (p. 568). By
other workers, in other forms evidence has been given of an extra-
otic origin of a part, at least, of the fenestral structures:—In Nec-
turus by Miss Platt and by Kingsbury (not published) ; in Ambys-
toma by Killian and by ourselves in this paper; in Cryptobranchus,
Spelerpes and Plethodon, in this paper. In these salamanders, and
doubtless in all forms possessing a well developed columella (our
use), the first appearance of the sound-transmitting apparatus is as
a group of cells outside the otic capsule. Of this the evidence seems
quite strong; it is only necessary to refer once more to the figures
illustrating the condition (Pl. IV, Fig. 39; Pl. VII, Figs. 52 and
53; Text Figs. 6 and 7). In the growth of this blastema in close
association with the otic capsule, the chondrification as stilus and
fenestral plate, there is introduced the difficulty mentioned by Gaupp,

The Columella Auris in Amphibia. 615

namely, that of distinguishing cells of extra-otic origin from the
periotic blastema. It has, in fact, been so far impossible in Am-
bystoma and Spelerpes to determine whether or not the fenestral
plate of the columella embodied a periotic element. It may be said,
however, that in its chondrification and growth the stilus is an integral
part of the columella as a whole and not an element from outside
secondarily fused with the plate,—representing, therefore, a structure
which could by itself be homologized with the hyomandibulare, as
was done by Parker.

The articulation of the stilus columelle with the palatoquadrate,
which had been mentioned, as quoted above, by Gaupp (cf. Wieder-
sheim ’06, Gaupp ’05) as the significant relation for the hyomandib-
ular homology, has been shown to be a connection secondarily estab-
lished during growth and development apparently due to a shifting
of the connection from the. squamosum to the palatoquadrate, in
many forms a longer or shorter process of that cartilage developing
with which it is articulated or fused. If this connection is in the
nature of a secondary adaptation,—and this interpretation is the
more probable,—its phylogenetic significance becomes doubtful.
There is, however, an association of the two structures of a primary
ontogenetic character and suggestive of profound significance. It
is to be recalled that in those forms in which the early development
of the columella has been traced, the cell mass constituting the proton
of the columella is directly connected with the cells between squa-
mosum, the otic process of the palatoquadrate and the otic capsule
external to the lateral semicircular canal. If a connection with the
palatoquadrate is to be considered of value in determining the hyo-
mandibular homology, it would seem to us, therefore, to be expected
that in the displacement of the hyomandibulare from the suspen-
sorium, it would be that portion of the upper end of the palatoqua-
drate which comes to articulate with the otic capsule with which the
homolog of the hyomandibulare would be joined rather than a point
farther down. If, on the other hand, as maintained by Fuchs, the
ancestry of the Amphibia is to be sought far back among the primi-
tive elasmobranchs, it is in this region,—over the lateral semicircular
canal caudad of the otic articulation of the palatoquadrate,—that the
connection of its vestigium might be sought.

616 B. F. Kingsbury and H. D. Reed.

One of the characteristics of the urodele stilus is its early con-
nection with the ventral edge of the squamosum, and from the first
it has appealed to us as of profound morphological significance.
Its final interpretation, however, is not yet possible, and must await
the establishment of many facts of relation and development in the
domain of comparative morphology. Although from the develop-
ment of this bone over the lateral semicircular canal in urodeles
(Kingsbury 03; Thyng ’06) it is regarded by us as a squamosum,
other considerations led Gaupp to bestow upon it the indifferent
name of Paraquadratum. Granting that it is a squamosum, its de-
velopment requires further study, and its value in urodeles,—as
Dermo-, Auto- or Amphisquamosum has to be considered. As an
Autosquamosum deriving its cells (primarily?) from the periotic
blastema, it may be pointed out that it has precisely the position and
relation to the proton of the columella that would be required of it
if the hyomandibular homology of the latter is accepted, since in
fishes it seems to afford a portion of the articular surface for that
bone. Nor do two considerations that immediately occur appear
necessarily antagonistic to this view; the first, that in the event of
the acceptance of the elasmobranch origin of the Amphibia, no squa-
mosum (as such) existed in the ancestral forms; the second, that
the larval connection of the columella with the squamosum is but a
step in the shifting of the suspensorium (palatoquadrate) during
growth, which in its second phase again transfers the connection to
the palatoquadratum or the os quadratum.

The absence of any connection between the columella and the cera-
tohyal has possibly been most commonly regarded as the greatest
defect in the ontogenetic evidence for the hyomandibular homology.
Recognition of the existence of a columellar proton outside the otic eap-
sule, its relations to palatoquadrate, otic capsule, and facial nerve,
in comparison with the requirement of a first segment of the hyoid
arch, renders less important evidence of a connection of ceratohyal
and columella. Yet the evidence of an embryological relation of
the two structures seems stronger than is usually recognized. Miss
Platt (97), when describing the extra-otic origin of the columella
(her operculum) considered that its lack of connection with the

The Columella Auris in Amphibia. ~ oli

ceratohyal did not “demonstrate that the cartilage in question may
not be a rudimentary element of the hyoid arch, since each element
of the cartilaginous arches arises from an independent center of chon-
drification and secondary fusions of cartilaginous elements do not
necessarily show original association.”

The cord of cells which extends to the under surface of the squa-
mosum and which must be regarded as a part of the columella blas-
tema, is joined by an extension from the perichondral cells of the
ceratohyal, so that, at an early stage (19 mm.) the two structures
are in fact connected (Kingsbury ’03, p. 318, and Fig. 2a). In
Ambystoma there is a line of cells from the ceratohyal to the colum-
ella in the 13-14 mm. specimen. In Plethodon (Text Fig. 6) the
juxtaposition is still closer and a cellular continuity exists. In
Cryptobranchus the ceratohyal is not joined to the columella by cells
in the just hatched larva; just what the condition is at an earlier
stage we cannot say from lack of material at a suitable stage.

This early connection by cells does not seem a chance association,
but rather to indicate that columella and ceratohyal chondrify out
of acommon blastema. The Ligamentum hyo-columellare previously
described as existing in several forms seems to be a secondary devel-
opment, though it may express a primitive relationship. The dia-
gram introduced to illustrate the ligaments (Fig. 21) may also serve
to indicate the skeletal connections and relations of the columella
as a probable hyomandibulare.

The position of the columella above and behind the nervus facialis
satisfies the requirements of the hyomandibular homology. It is
but necessary to recall its position in elasmobranchs and Polypterus
(Ruge 796, Pollard ’92) to recognize this fact. No detailed study
has been made of the relation of this nerve in fishes, however; nor
has the significance of the rather constant position of the columella
between the vena petroso-lateralis and the arteria carotis interna been
investigated.

The connections and development of the columella do, we believe,
strengthen its homology with the Hyomandibulare of fishes, in sup-
port of which so much has been written.

618 B. F. Kingsbury and H. D. Reed.

Funcrion or THE “Sounp-TRANSMITTING’ APPARATUS.

In order to determine the precise function of the so-called sound-
transmitting apparatus in Urodeles a series of experiments upon
both larvee and adults is necessary. The skeletal connections of the
fenestral elements in the larva, the changes taking place upon the
assumption of the terrestrial life and the correlation of structure
and habit in certain adults furnishes, however, some basis for judging
the function of these structures.

P. ot.

P. ase.

Vie. 21. Schema to illustrate the relation of the ligaments found in this’

region. Ool., columella; H., ceratohyale; L.h-c., ligamentum hyo-columellare ;
L.h-m., ligamentum hyo-mandibulare; Z.h-s., ligamentum hyo-suspensoriale ;
L.s-c., ligamentum squamoso-columellare; M.C., Meckel’s cartilage; P.asc.,
processus ascendens palatoquadrati; P. bas., processus basalis palatoquadrati ;
P.ot., processus oticus palatoquadrati; Pq., palatoquadratum; S?.C., stilus
columellze; Sq., oS squamosum. ;

It is perhaps not assuming too much to believe that the sound- ,

transmitting apparatus serves as an organ of equilibration and the
detection of vibrations of low frequency when such come to the ani-

mal through a dense medium such as earth or water. ‘The nature .

and structure of the apparatus in urodeles seem to preclude the belief
that vibrations of any frequency whatsoever can be detected from
a medium as rare as the air. There is, however, nothing in the
nature of the apparatus to interfere with the view that vibrations

The Columella Auris in Amphibia. 619

of high frequency are not detected if transmitted to the animal
through a dense medium. Experimentation along this line may
prove very interesting and valuable,

During the larval period, and in aquatic or partly aquatic forms
during adult life, the connection of the fenestral plate is with the
suspensorium. Thus it would appear that jars or vibrations are
transmitted from the objects, upon which they are resting, to the
floor of the mouth, after which the course is through the suspen-
sorium to the columella and thence to the inner ear, as has been

Wig. 21a. Schema to illustrate the possible method of communication be-
tween the inner ear and the exterior for larve and thoroughly aquatic adult
forms. Col., Columella; F'.v., fenestra vestibuli; H.a., hyoid arch; L.s-c., liga-
mentum squamoso-columellare; M.l., skeleton of the lower jaw; Pq., paloto-
quadratum ; Sp., os squamosum; S?.C., stilus columell.

suggested by Gaupp (705, 07). The possibility of such a functional
mechanism is illustrated in Fig. 21a.

At transformation when terrestrial life is assumed, in certain
forms, a different type of communication with the exterior is formed.
The columella becomes fused with the ear capsule while a free plate,
the operculum, is formed behind and below as in Ambystoma or
the caudal portion of the fenestral plate remains free as in the
Plethodontide and some others. This plate is placed in communi-
cation with the exterior by the M. opercularis, connecting it with
the shoulder girdle. Thus jars and vibrations may be transmitted
through the arm to the M. opercularis, thence to the operculum and
finally to the inner ear, as shown in Fig. 21 0.

620 B. F. Kingsbury and H. D. Reed.

These connections appear to be an adaptation to the habits and
environment of the animal. During larval life and in such forms
as Necturus and Cryptobranchus the body is either supported by
water, or rests full length upon the bottom or some submerged object,
the arms and legs playing a small part, if any, in its support. The
primitive connections of the columella here persist and function as
the transmission line between the exterior and the inner ear. Some
evidence for this view is found in certain Anurans. In Pelobates
there is no tympanic cavity, and the eustachian tube is much reduced.
The fenestral plate in this form is connected by strong ligament

StC..-Cok

9

Op.

Fig. 21b. Same as Fig. 21a, for terrestrial forms. Col., columella; H.a.,
hyoid arch; Z.s-c., ligamentum squamoso-columellare; M.op., musculus oper-
cularis; M.l., skeleton of lower jaw; Op., operculum; Pq., palatoquadratum ;
Sq., 0S Squamosum; S.s., suprascapula; St.C., stilus columellae.

with the squamosum. Similar conditions obtain in Bombinator,
excepting that the fenestral plate is connected with the hyoid. In
either case the inner ear is placed in communication with the exterior
through the floor of the mouth. It is interesting to note in this
connection that Pelobates is a thoroughly burrowing form while
Bombinator is just as thoroughly an aquatic one.

In the urodele Siren, where the usual skeletal connections of
the fenestral plate are wanting, they seem to be compensated for by
the attachment of the stilus columelle to the hyoid by means of the
strong hyo-columellar ligament.

When terrestrial life is assumed the body is more or less supported

The Columella Auris in Amphibia. 621

by the limbs, thereby raising the floor of the mouth above the ground.
Thus communication of the internal ear with the exterior through
the suspensorium and floor of the mouth is lost. By the detachment
of a portion of the M. intertransversarius capitis inferior which
becomes the M. opecularis, the operculum is connected with the
shoulder girdle and communication of the inner ear with the
exterior is again established,—through the arm and shoulder girdle.

SUMMARY.

While to a certain extent (hyomandibular homology) comparison
has been made with fishes, comparisons between the amphibian audi-
tory apparatus and those of reptiles and mammals have not been
attempted. The terms “stapes” and “stapedial” have been purposely
avoided since it has seemed to us by no means conclusively shown
that the amphibian columella is simply the homolog of the first seg-
ment of the mammalian chain of bones. Although we have fully
appreciated that this investigation is but a part of the larger problem
as was indicated at the beginning of the paper, the main aim has
been the determination of facts for a large number of tailed am-
phibians, realizing that weaknesses in broad generalizations are
in most instances due to drawing conclusions from insufficient data ;
for illustration of which it is unnecessary to go outside the limited
field of investigation covered by this paper. The amphibian group
presents within itself many problems of both local importance and
general bearing that require further investigation, and it was this
narrower field that particularly engaged our attention. Some of the
general aspects of the problem we hope to deal with subsequently.

The main results were given in the first portion of the paper;
they are restated below in somewhat extended form.

1. Several (4 to 7) different types of “columella auris’
in urodeles.

2. There are two morphologically distinct fenestral structures
found in the group: Columella and Operculum.

3. The Columella possesses a stilus, tends to fuse with the cephalic
portion of the fenestral margin, and in ontogeny seems to come from
outside the otic capsule.

> are found

622 B. F. Kingsbury and H. D. Reed.

4. The Operculum develops out of the otic capsule of which it
appears to be primarily a part. It possesses no stilus but gives
attachment to a muscle (M. opercularis). Its morphological position
relative to the Columella is caudal and medial.

5. A Columella only is present in Necturus, Proteus, Crypto-
branchus, Amphiuma, Siren.

6. In Ambystoma and Chondrotus (Ambystomidz) a Columella
is present in the larva but it becomes fused with the otic capsule at
transformation, and an Operculum is then developed.

7. A vestigial and fused Columella is found in Salamandra, Triton
and Diemictylus (Salamandridz, Pleurodelidz, Cope).

8. An Operculum is found (in the adult) in the Ambystomide,
Salamandride, Pleurodelide.

9. The Plethodontide and Desmognathide possess a single fenes-
tral structure bearing a stilus but also giving attachment of the
opercular muscle.

10. Typhlomolge possesses a fenestral plate of plethodontid char-
acter. It has a fragmented stilus and lacks the M. opercularis.

11. The Musculus opercularis is absent in (a) Necturus, Proteus,
Cryptobranchus, Amphiuma, Siren, Typhlomolge; (b) in larve gen-
erally. It is present in the adult Ambystomide, Salamandride,
Pleurodelidz, Plethodontide, and Desmognathide.

12. The Stilus columelle is distally joined to the Squamosum,
Palatoquadratum, Quadratum, singly or in combination. In Nec-
turus, Proteus, Cryptobranchus, Typhlomolge and larve generally
(Ambystomide, Plethodontide, Desmognathidze) it is directly con-
nected with the squamosum.

13. During growth or at transformation the connection tends to
shift, usually to the Palatoquadratum.

14. The stilus is fragmented in Typhlomolge, vestigial in
Batracoseps and Siren, absent in Triton and Diemictylus. In Sala-
mandra its distal end is fused with the Palatoquadratum.

15. In development the proton of the Columella appears to be
outside the otic capsule in those forms in which its development has
been traced (Necturus, Ambystoma, Spelerpes, Plethodon, Crypto-
branchus).

The Columella Auris in Amphibia. 623

16. The proton of the Columella is connected by a distinct strand
of cells with a group of cells between Squamosum, Processus oticus
palatoquadrati and the Prominentia semicircularis lateralis of the
otic capsule.

17. The facial nerve is entirely below the Columella (stilus colum-
elle) in all forms except Necturus, Proteus, Typhlomolge; in these,
one ramus (R. jugularis) passes above the stilus.

18. The relation of the stilus to the blood vessels of the otic region
appears quite characteristic; i. e., below the vein and above the
artery.

19. A Ligamentum hyo-columellare is present in Siren, Amphi-
uma, Cryptobranchus, Desmognathus and many Plethodontide.

20. The hyomandibular homology is favorably discussed.

21. The homology of the Columella of Urodela and the Pars
interna plectri of Anura is accepted.

22. The Operculum is regarded as a secondary development in
those forms which possess it.

23. From the standpoint of functional adaptation, there seem to
be in the Urodela three types of communication of the internal ear
with the exterior: (a) through the floor of the mouth, mandible, sus-
pensorium and columella; (b) through the floor of the mouth, the
hyoid arch and columella; (c) through the manus, pectoral girdle,
M. opercularis and operculum.

24. Type (a) is the more usual and is found in typically aquatic
forms. Type (b) is best represented in Siren. Type (c) oceurs in
Salamandra, Triton and Diemictylus. A combination of (a), (b),
and (c) is found in the Plethodontidx and Desmognathide.

25. There appears a close correlation of the type present and the
habits of the form (aquatic, semi-aquatic, terrestrial, burrowing,
ete.).

CORNELL UNIVERSITY,
Ithaca, N. Y., June 22, 1909.

624. B. F. Kingsbury and H. D. Reed.

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The Columella Auris in Amphibia.

ABBREVIATIONS.

A. GENERAL SKELETON.
Col., columella.
H., ceratohyale.
H.a., Hyoid arch.
M.C., Meckel’s cartilage.
M.1., Skeleton of lower jaw.
Op., Operculum.
Parasphen., os parasphenoideum.
P.ase., Processus ascendens palatoquadrati.
P.bas., processus basalis palatoquadrati.
P.ot., processus oticus palatoquadrati.
P.h-p., processus hyoideus palatoquadrati.
P-q., palatoquadratum.
Pt., os pterygoideum.
Q., oS quadratum.
S.s., Suprascapula.
St.c., stilus columellae.
Sq., 0S Squamosum.

B. Har CAPsute.

C.l., Canalis semicircularis lateralis.
C.p., cavum perilymphaticum.

Cr.s., crista semicircularis.

D.p., ductus perilymphaticus.

“’’., secondary fenestra vestibuli.
F.p., fenestral plate.

F.y., fenestra vestibuli.

L., lagena.

Prom. 1., prominentia semicircularis lateralis.
Prom.p., prominentia perilymphatica.
R.p., recessus perilymphaticus.

C. LIGAMENTS.
L.h-¢e., ligamentum hyo-columellare.
L.h-m., ligamentum hyo-mandibulare.
L.h-s., ligamentum hyo-suspensoriale.
L.s-c., ligamentum squamoso-columellare.

D. NERVES.
VII, nervus facialis (VII).
R.h.VII, ramus hyomandibularis VII.
R.c., ramus communicans (IX-VITI).
R.j.VUI, ramus jugularis VII.
R.m.e.VII, ramus mandibularis externus VII.
R.m.i.VII, ramus mandibularis internus VII.

627

628 B. F. Kingsbury and H. D. Reed.

I. MUSCLES.
M., musculus cephalo-dorso-mandibularis.
M.op., musculus opercularis.
M.i.c.i., musculus intertransversarius capitis inferior.

F. Buioop VESSELS.
C., arteria carotis interna.
V.p.-l., vena petroso-lateralis.

PLateE I,

Models of the ear region of the skull of Ambystoma punctatum, drawn
from the side and slightly from the caudal and ventral aspects.

Fig. 22. Ambystoma punctatum, mature larva about 45 mm. in length,
beginning transformation, gills about one-half absorbed.

Fig. 23. Ambystoma punctatum, about-42 mm. in length, transformation
period, gills mere stumps. In comparison with Fig. 22, there is shown the
partially formed operculum with the opercular muscle.

Fig. 24. Ambystoma punctatum, young adult, about 52 mm. in length.
The columella is now nearly completely fused. Remnants of the secondary
fenestra are marked “F.” Operculum and opercular muscle.

“THE COLUMELLA AURIS IN AMPHIBIA.
: B. F. KINGSBURY AND H. D. RHED,

PLATE I.

R.j.VII
R.m.e. VII

I
IL Rwi VII

H
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THH JOURNAL or MorpHoLocy.—Von. MX, No. 4.

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AH LI
Drawings of models of the ear region of the skull.

Fig. 25. Ambystoma punctatum, adult. A portion of the ear region of

the skull showing the completely fused columella and the fully formed oper-
culum with its attached muscle.

Fig. 26. Salamandra maculosa, adult. The region and aspect as in Fig.
25 with which it may be directly compared. The boundary between muscle
and operculum is indicated by the broken line.

Fic. 27. Triton cristatus, larva 34 mm. long. The ventro-lateral aspect
of the cartilaginous ear capsule. The cephalic part of the fenestra is occu-
pied by the small and partially fused columella above, a growth of cartilage
below. ‘The operculum is still broadly joined to the ear capsule.

Fig. 28. Typhlomolge rathbuni, adult. Lateral aspect of the ear region.

Attention is particularly called to the segmented (fragmented) stilus colu-
mellze and its relation to the facial nerve (ramus jugularis).

THE COLUMELLA AURIS.IN AMPHIBIA.

B. F. KINGSBURY AND H. D. REED.

Sa H
L.s-e. Op. M.op.
Hire 25:

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a ene oe al

Col. Op. M.op.
Fig. 26.

Ss

Si: Vp.

Live, Ws},

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Col. CG.
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THe JOURNAL oF MorPHOLOGY.—VOuL, XX, No. 4.

PLATE II.

EXPLANATION OF PLATES III-IX.

A series of microphotographs to illustrate particularly the morphological
relations of columella and operculum, from sections through the ear region.

PrArns ii

Fig. 29. Ambystoma punctatum, adult. Section through the stilus colu-
mellae, showing the columellar ligament and its relation to vein and facial
nerve.

Fic. 30. The same. Section farther caudad. The fused columella is ex-
ternal to the cephalic end of the operculum.

Fig. 31. Ambystoma punctatum, larva, early transformation. There is
shown columella and the floor of the ear capsule to become operculum. Com-
pare with Fig. 32.

Fig. 32. Ambystoma punctatum, transformation period. The operculum
is, at this level, separated from the floor of the ear capsule.

Fig. 33. Ambystoma punctatum, larva, 35 mm. in length. It shows the ~
columella, stilus, squamoso-columellar ligament. Note the relation of the
vein and artery in this and the two preceding figures.

Fig. 34. Chondrotus tenebrosus, larva. Note the massive stilus articu-
lating with the squamosum and its relation to artery, vein and nerve.

Fic. 29.—Adult Ambystoma.

Sq.

V p-l : a Zz
> () : P L OX “

Fic, 31.—Larval Ambystoma. Fie. 32.—Larval Ambystoma.

R. j. VII

Fig. 33.—Larval Ambystoma. Fig. 34.—Larval Chondrotus,

THE COLUMELLA AURIS IN AMPHIBIA,

PLATE III.
B. F. KINGSBURY AND H. D. REED.

Be Patino
lig. 29.—Adult Ambystoma.

Fig. 33.—Larval Ambystoma. Ite. 384.—Larval Chondrotus,

)(Hn JOURNAL OF MorPHOLOGY.—VowL, XX, No. 4.

PLATE IV.

Vig. 35. Ambystoma punctatum, adult. Section farther caudad than Fig.
30. Operculum, opercular muscle and recessus perilymphaticus are shown.

Fig. 36. Chondrotus tenebrosus, transformation period. Section through
stilus columelle and the cephalic end of the developing operculum.

Fig. 37. Ambystoma punctatum, transforming. Horizontal section show-
ing columella, stilus, squamoso-columellar ligament, the developing operculum
and the M. opercularis attached in front to the opercular plate and behind
to the suprascapula.

Fig. 88. Chondrotus tenebrosus, transformation period. Section farther
caudad than Fig. 36. It shows the columella. The operculum is partially cut
out from the floor of the ear capsule.

Fig. 39. Ambystoma punctatum, embryo 13-14 mm. in length. The colu-
mella consists of a mass of cells against the membrane of the fenestra and
connected by a strand of dense tissue with the cells upon the prominence of
the lateral semicircular canal. Above the columellar proton is the vena
petroso-lateralis; below, the carotid artery.

Fic. 36.—Transforming Chondrotus.

a

y

Col.

M. aC

Fic. 38.—Transforming Chondrotus,

Fie. 37. Fie. 39.
Transforming Ambystoma. Embryo Ambystoma.

THE COLUMELLA AURIS IN AMPHIBIA, PLATE IV.

B. F. KINGSBURY AND H. D. REED.

Fic, 35.—Adult Ambystoma. Itc. 56.—Transforming Chondrotus.

IGE Si. Ftc. 388.—Transforming Chondrotus. Fie. 39.
Transforming Ambystoma. Embryo Ambystoma.

THE JOURNAL OF MORPHOLOGY.—VoL. XX, No. 4.

Ve Tae ay

eye

4
Ey

PLATE V.

Fig. 40. Salamandra maculosa, adult. Section through the stilus colu-
mellz which is continuous with the palatoquadrate.

Fig. 41. The same. Section farther caudad, through the cephalic end of
the operculum.

Fig. 42. The same. Section farther caudad through the operculum and
the recessus. The M. opercularis would be shown in a section farther caudad.

Fig. 43. Triton cristatus, adult. Section through the cephalic portion of
the operculum.

a

is.
Sd Pt

Fic. 40.—Adult Salamandra. Fic, 41.—Adult Salamandra.

Fic. 42.—Adult Salamandra. Fic. 48.—Adult Triton.

————— ee

THE COLUMELLA AURIS IN AMPHIBIA. PLATE V
B. F. KINGSBURY AND H. D. REED.

Fic. 40.—Adult Salamandra. Ite, 41.—Adult Salamandra.

"tt ro

Fic. 42.—Adult Salamandra. lic. 43.—Adult Triton.

THD JOURNAL OF MORPHOLOGY.—VOL, XX, No. 4.

PLATE VI.

Fig. 44. The same. Section farther caudad, showing the operculum, M.
opercularis and recessus perilymphaticus.

Fig. 45. Gyrinophilus porphyriticus, adult. Section through the cephalic
end of the fenestra vestibuli and the distal end of the stilus columellze show-
ing its articulation. Note the relation of blood vessels and facial nerve.

Fig. 46. The same. Section through the base of the stilus, a few sections
farther caudad.

Fig. 47. The same. Several sections farther caudad, through the caudal
portion of the fenestral plate, opercular muscle and recessus.

ie

Fie, 45.—Adult Gyrinophilus.

Fie. 44.—Adult Triton.

Iie. 46.—Adult Gyrinophilus. Fic. 47.—Adult Gyrinophilus.

‘THE COLUMELLA AURIS IN AMPHIBIA. PLATE VI.

B. F. KINGSBURY AND H. D. REED.

Adult Gyrinophilus.

Fic. 44.—Adult Triton. Fie. 45.

Fic. 46.—Adult Gyrinophilus. Fig. 47.—Adult Gyrinophilus.

THE JOURNAL OF MORPHOLOGY.—VOL, XX, No. 4.

«

PLATE VII.

Fig. 48. Triton cristatus, larva 36 mm. long. The section is through the
cephalic end of the columella where it is continuous with the ear capsule on
its medial side.

Fig. 49. The same, farther caudad, through the columella and just in front
of the cephalic end of the operculum.

Fig. 50. The same. A section still farther caudad, through the operculum
and back of the caudal end of the columella. Note the relations of the blood
vessels in this and the two preceding figures.

Fig. 51. Cryptobranchus allegheniensis, larva 34 mm. long. The liga-
mentum hyo-columellare is just joining the stilus at its bend.

Fic. 52. Crytobranchus allegheniensis. Just hatched larva. The proton of
the columella is seen between the artery and vein. :

Fic. 538. The same. A section farther cephalad to show the proton of the
squamosal connection of the columella.

Fig. 54. Cryptobranchus allegheniensis, adult. A section through the dis-
tal end of the stilus to show its articulation.

Fig. 55. The same. A section farther caudad showing the columella and
its large stilus illustrating the relation to artery, vein and nerve.

Col. C.

Fic. 48.—Larval Triton. Fic. 49.—Larval Triton.

Hie. Si:

I'ic, 54.—Adult Cryptobranchus.

Fig. 50.—Larval Triton.

Fic. 53.%
Just hatched Cryptobranchus.

Fic. 55.—Adult Cryptobranchus.

be Ceti

THE COLUMELLA AURIS IN AMPHIBIA.

B. F. KINGSBURY AND H. D. REED.

Fig. 51: Iie. 52.—Just hatched Cryptobranchus.
Larval Cryptobranchus.

% lA
Cryptobranchus.

Fic, 54.—Adult

THE JOURNAL OF MORPHOLOGY.—VOL, XX, No, 4.

)OnKes

PLATE VII.

50.—Larval Triton

Hie. 5a:

Puate VIII.
eae same. <A few sections farther caudad through the caudal
the fenestral plate. —

(. Necturus maculosus, larva. The ligamentum squamoso-columel-
st attaching to the ventral edge of the squamosum.

The same, a few sections farther caudad. The ramus jugularis
own passing over the ligament.

The same, still farther caudad through the base of the stilus

—.

L

Fig. 57.—Larval Necturus.

Fic. 56.—Adult Cryptobranchus.

R. j. VIL 54
L. s-¢. ee @
V. p-l

V. p-l.

I i Col.

Vig. 58.—Larval Necturus. Fic. 59.—Larval Necturus.

THE COLUMELLA AURIS IN AMPHIBIA,

B. F. KINGSBURY AND H. D. REED.

PLATE VIII.

Fig, 58.—Larval Necturus.

THD JOURNAL OF MORPHOLOGY.—VOL. XX, No. 4.

Wig. 57.—Larval Necturus.

Fic. 59.—Larval Necturus.

IPA) IOS
Tig. GO. The same, still farther caudad, showing the caudal portion of
the fenestral plate of the columella with its inner and outer bony plates.
Fic. 61. Siren lacertina, adult. Section showing the columella, ceratohyale

the hyo-columellar ligament, into which projects the short stilus, and the
cartilaginous portion of the ear capsule that forms the perilymphatic prom-

~ inence.

Fig. 62. The same, a few sections farther caudad. The caudal end of the
stilus is in the ligament. The perilymphatic prominence; position of artery
and vein.

Tig. 63. The same, farther caudad behind the fenestra and showing the
caudal portion of the perilymphatic prominence.

Fic. 60.—Larval Necturus.

Fic. 62.—Adult Siren.

Fic. 61.—Adult Siren.

Fic. 63.—Adult Siren.

—

THE COLUMELLA AURIS IN AMPHIBIA. PLATE IX.

B. F. KINGSBURY AND H. D. REED.

Fic. 60.—Larval Necturus. Fic. 61.—Adult Siren,

Fic. 62.—Adult Siren. Fic. 63.—Adult Siren.

THD JOURNAL OF MORPHOLOGY.—VOL, XX, No. 4.

BEDE
(Figures 64-72)

A series of schemas showing the number and relative position of the ele-
ments present in the fenestra vestibuli in the various groups of the tailed
Amphibia, together with the relation of these elements to the ear capsule,
suspensorium, hyoid arch, M. opercularis, and facial nerve. It should be
stated that they are to show relations only; the representation of the pro-
cesses of the palatoquadrate, for example, being purely diagrammatic. Ip
Wig. 67 the relation of the hyoid arch (H.) is intended to represent the con-
dition in certain forms only.

THE COLUMELLA AURIS IN AMPHIBIA, Puare X,

B. F. KINGSBURY AND H. D. REED.

Fic. 64.—Ambystoma. Ita. 65.—Salamandra Via. 66.—Triton and Diemictylus.

Fic. 67.—Plethodontidze and Fig. 68.—Typhlomolge. TIic. 69.—Necturus.
Desmognathidsx.

Fie. 70.—Cryptobranchus. Fie. 71.—Amphiuma., Fig, 72.—Siren.

| THE JOURNAL OF MorPHOLOGY.—VoL, XX, No. 4.

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