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little more than that of the tectum. Ossification has re-
moved nearly all of the cartilage of the capsule behind the
posterior end of the fenestra ovalis where the stapes is
now closely applied against the remnant of the cartilagi-
nous wall of the capsule.

The quadrate (q) has undergone important changes,
due in part to ossification and to the lateral expansion of
the skull. Its body is thicker antero-posteriorly and
stands out farther from the capsule. The descending
process is cylindrical in shape, presenting greater definite-
ness of outline than previously. Irregular perforations
of the cartilage occur along the line where the quadrate
joins the capsule. Most striking of all is the change
in the position of the pterygoid process (pt) which, in-
stead of being nearly parallel with the long axis of the
skull as in the previous stage, now slants from its base
outwards at an angle of about thirty degrees from that
axis.

The cartilaginous nasal capsules have reached their
highest stage of development and present many new and
important features. The nasal septum (Fig. 12, 7is) is nar-
rowed down to about half its former width. In front it
divides into two doubly curved plates which extend for-
wards and outwards to the cup-like anterior ends of the
capsules. From the ventro-median surface of each of
these plates a short knob-like process extends forwards and
terminates the capsule anteriorly.

A flattened band of cartilage which I have called the
ventral process (vp), in contradistinction to the dorsal



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA . 99

process (d) to be described later, passes backwards from
the ventral margin of the cup-like anterior end of the
capsule. At its posterior end this process fuses laterally
with the lamina cribrosa (Z) while medially it terminates
in a process projecting freely backward (Fig. 13, vp).

The cylindrical dorsal process (d) extends diagonally
across the anterior end of the olfactory organ from the
dorso-median margin of the cup to the anterior end of the
lamina cribrosa. A short connecting rod joins the dorsal
process and lamina cribrosa with the ventral process in
front of the nasal duct (nl). As in the preceding
stage, the lamina cribrosa forms a roof over the posterior
end of the olfactory organ. It now reaches downwards
to meet the outer end of the antorbital process thus en-
closing the orbito-nasal foramen {on), and outwards and
forwards to meet the ventral and dorsal processes as de-
scribed ai)ove. It is perforated near the lateral margin by
several small foramina through which pass a branch of the
ophthalmicus profundus (rj)) and some small blood ves-
sels (b). A branch of the nasalis internus (ni) passes
out of the capsule through the foramen in its median wall.

Desmognathus fusca (Fig. 14).

The chondrocranium of Desmognathus fusca, of which
I have modelled two stages, presents so great a similarity
to the earlier stages in Amblystoma that only a few words
need be devoted to it. Figure 14 represents the model of
the skull of an embryo about twenty mm. long.

The parachordals (p) are represented by three narrow
bands of cartilage ; one extending between the posterior
ends of the otic capsules and having the notochord partly
imbedded in it, and two other bands which connect the
apex of the notochord with the posterior ends of the tra-
beculae.



100 BULLETIN OF THE ESSEX INSTITUTE.

The entire absence of a stapes in the history of the
chondrocranium is the only noteworthy point of difference
between the formation of the ear capsules in Desmogna-
thus and in Amblystoma. The trabeculse and quadrates
present conditions essentially the same as those of a cor-
responding stage in Amblystoma, but owing, in part at
least, to the early appearance of the bony skull in Des-
mognathus no complex nasal capsule is formed. The
simple condition shoAvn in Fig. 14 is the highest state of
development reached by the anterior ends of the trabecu-
Ise. A small antorbital process develops in the usual place
upon the side of the trabecula. No pterygoid process of
the quadrate appears in either of the stages modelled.
As the older stage presents a state of development ap-
proximately equivalent to that found in the fifth stage of
Amblystoma the appearance of this process as figured by
Wiedersheim ('77) must be a comparatively very late
occurrence.

Plethodon glutinosum (Fig. 15).

From a specimen of Plethodon glutinosum twenty mm.
in length and showing the chondrocranium in an advanced
stage of development, I have modelled the nasal capsules.
In regard to the rest of the skull mention of a few points
will suflice.

In the main it corresponds closely with the skull of
Amblystoma as described in our fifth stage (Figs. 12 and
13). This similarity is especially noticeable in the posi-
tion of the pterygoid process. There is a stapes, the
antero-dorsal point of which, unlike that of Amblystoma,
is connected to the quadrate by a very slender stapedial
process. The otic and palato-basal processes present the
usual conditions.

Aside from the rod connecting the dorsal and ventral



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 101

processes in front of the narial duct all the parts described
for the nasal capsule of Amblystoma are found in approx-
imately the same positions in Plethodon with unimportant
modifications as to relative sizes. This similarity is even
more apparent in older specimens of Plethodon than in
the one from which this model was made. The two small
foramina in the lamina cribrosa mark the points at which
a branch of the ophthalmicus profundus (rj)) enters and
leaves the capsule.

Nectukus maculatus.

Cope ('89) has placed JVectiirus maculatus with its
American relative JSTecturus punctata and the European
Proteus in a group together under the name Proteida with
the remark that they occupy a position intermediate be-
tween the Stegocephali and the Urodela, and differ from
the latter mainly in the possession of an intercalary bone.
Descriptions of three stages in the development of the
chondrocranium of JVecturus maculatus are here given.

First stage. — The first stage represents the skull of
an embryo twenty-one mm. in length, and corresponds
approximately to the condition found in Amblystoma at
a time a little earlier than that represented in the third
stage of the latter (Figs. 4-7). The occipital arch con-
sists of two processes extending upward from the sides
of the notochord and ending freely above. At their bases
they are connected with the posterior ends of the para-
chordals.

The parachordals run forward from the bases of the
occipital processes, slightly removed from the sides of the
notochord. Between the posterior ends of the otic cap-
sules they bend inwards and touch the sides of the noto-
chord to which they are attached for a short distance, then
curve sharply outward, and, fusing laterally with the cap-



102 BULLETIN OF THE ESSEX INSTITUTE.

sular floors, continue forward into the trabecule. The
notochord projects forward some distance in front of the
most anterior point at which the parachordals touch its
sides. The otic capsules are widely separated and incom-
pletely formed. Their floors are partially attached to the
parachordals and the only traces of the median wall are
found around the inner mar<>:ins of its walls. A laro;e
fenestra ovalis, with no stapes, and a large foramen for
the exit of branches of the seventh nerve constitute the
only well defined apertures which are found in later stages.

The trabecule extend forwards from the anterior ends
of the parachordals as long slender rods running parallel
for the posterior three-fourths of their length and then
bending inward at an angle of about thirty degrees
towards the median line, which they do not reach. There
are, as yet, no foramina for the second and third nerves
and only a slight trace of a trabecular crest to which the
ascending process of the quadrate is attached.

The quadrate is wedge-shaped as seen either from the
side or in front, the point being directed ventrally. A
short otic process extends upward and backward from the
dorso-lateral angle of the wedge and fuses with the otic
capsule, while a longer ascending process extends up-
ward and forward from the dorso-median angle and fuses
with the dorsal end of the slightly developed trabecular
crest.

Second stage. — Our second model is that of an em-
bryo twenty-four mm. in length. The occi})ital processes
are fused distally with the walls of the otic capsules and
continue along the dorso-median angles of the capsules
as the beginnings of the synotic tectum. The jugular
foramen is at this staize a dorso-ventrally elongated slit.

In place of the distinctly outlined parachordals of the
previous stage we now have a continuous basilar plate



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 103

lying beneath that portion of the cranial cavity included
between the posterior halves of the otic capsules. As
before, the notochord projects freely forward in the me-
dian line. Laterally and in front the basilar plate merges
into the capsular floors and the trabeculfe.

The otic capsules present essentially the same condi-
tions found in stage three of Ambly stoma (Figs. 4-7)
except that the otic process of the quadrate is fused with
the antero-ventral surface of the capsule. A trabecular
crest just large enough to enclose the optic and oculo-
motor foramina and to form a point of attachment for the
ascending process is now developed. The appearance of
simple aiitorbital processes upon the sides of the trabecu-
lae is the only further change which needs mention here.

Third stage. — Larva forty-five mm. long (Fig. 16).
A continued fusion of the margin of the occipital process
with the wall of the otic capsule, resulting in a reduction
of the size of the jugular foramen is the most noticeable
change in this region. The synotic tectum is now fully
developed and presents the usual form. The basilar plate
remains the same as in the previous stage.

The otic capsules have reached their highest state of de-
velopment. The median wall is perforated by four foram-
ina which correspond almost exactly to those described
for the otic capsule of the fourth stage of Amblystoma
(Fig. 11). In iiict the onl}^ differences of any importance
between the otic regions of this skull and that described
as the fourth stage for Amblystoma are in the absence of
the parachordals at the anterior end of the notochord, and
the more median position of the foramen for the palatine
nerve iiml). A small crest is now developed along the
posterior half of the trabecula. A slender connecting rod
unites the posterior end of the crest with the opposite wall
of the otic capsule. Antorbital processes project outward
and forward from the sides of the trabecular.



104 BULLETIN OF THE ESSEX INSTITUTE.

By a fusion of the anterior ends of the trabecule in the
median lines a small ethmoid plate is formed, upon the
anterior end of which is a slight prominence, the only in-
dication we have of a nasal septum. Upon each side a
short forward-projecting process terminates the ethmoid
plate anteriorly.

Entirely separated from the rest of the cartilaginous
parts of the head there is now a delicate nasal capsule
(Fig. 16, nc). It consists of a curved rod, which runs
along the dorso-median surface of the olfactory organ, fol-
lowing more or less closely the direction of the anterior
end of the trabecula and the ethmoid plate, and a number
of shorter processes projecting laterally from this main
rod over the top of the olfactory organ. As Piukus
('94) has pointed out, there is some resemblance between
this nasal capsule and that of Protopterus, but it seems to
me hardly necessary, for reasons which will appear more
fully later, to attach any importance to this similarity other
than that of a coincidence.

One would seem justified in expecting that, if Necturus
occupy a position intermediate between the Stegocephali
and the Urodela, the chondrocranium of Necturus would
show more or greater differences from the typical Urodele
chondrocranium than are found in higher Urodeles, the
Urodela of Cope. But I am unable to discover that this
is the case. It would be difficult, rather, to point out a
form in which the chondrocranium is more typically Uro-
delan.

Amphiuma means.

The first of the two models of the chondrocranium of
Amphiuma means here described is the one which formed
the basis of the description of the chondrocranium in Dr.
Kingsley's preliminary paper upon "The Head of an
Embryo Amphiuma" ('92). The chondrocranium of



THE CHONDROCRANIUM IN THE ICHTHYOP8IDA. 105

another specimen from the same lot of embryos was also
described and figured by Professor O. P. Hay in his paper
of '90.

First STAGE. — (Figs. 17-18) . — The occipital processes
have fused with the otic capsules and their distal ends project
inward over the sides of the cranial cavity as the first steps
in the formation of the synotic tectum. The parachordals
(Fig. 18, jp) extend forward from the bases of the oc-
cipital processes, and, after curving inward to the sides
of the notochord and fusing beneath it, they each divide
into a median and a lateral band. The lateral bands of
the two sides curve outward and, fusing with the capsular
floors, pass forward to the posterior ends of the trabeculae.
The median bands separate in front of the apex of the
notochord, bend laterally and join the lateral bands again
at their junction with the trabeculae. Between these two
parts of each parachordal a fontanelle is enclosed.

The otic capsules present nearly the same condition as
that found in the fourth stage of the skull of Amblystoma.
But here, as was also noted in Necturus, the foramen for
the palatine branch of the seventh nerve {pal) is on the
median side of the median capsular wall.

The trabeculae extend from their union with the para-
chordals forward to the nasal region , where they fuse in a
small ethmoid plate which is terminated anteriorly by two
broad triangular cornua. Along the middle and posterior
end of each trabecula is a well-developed crest covering
in the optic and oculomotor foramina as usual. It is con-
nected postero-dorsally with the anterior end of the otic
capsule, and it is also connected with the median angle of
the quadrate by means of the ascending process («/>). The
point at which the ascending process joins the trabecula is
relatively farther anterior in Amphiuma than in Amblys-
toma, thus producing more elongate foramina for the exit

ESSEX INST. BULLETIN, VOL. XXVm 7*



106 BULLETIN or THE ESSEX INSTITUTE.

of the nerves coming from the Gasserian ganglion (Fig.
18, v). Antero-dorsally the crest gives rise to a rod of
irregular shape, which projects forward, outward and
downward. This is the lamina cribrosa (e). Below and
a little behind this the antorbital process is just beginning
to appear upon the side of the trabecula.

The quadrate is rhomboidal in outline when viewed from
the side. It is connected with the trabecular crest by the
ascending process, as mentioned above, but as yet it has
not fused with the otic capsule. From its posterior angle
a slender stapedial process (Fig. 17, sp) extends back-
ward into the anterior end of the fenestra ovalis where it
joins the small stapes. No pterygoid process is yet
developed. Meckel's cartilage articulates with the antero-
ventral surface of the quadrate.

Second STAGE. — (Fig. 19). — In the second stage of
the chondrocranium of Amphiuma, ossification is far ad-
vanced. The most important additions to the cartilages
are seen in the completed nasal capsule and the pterygoid
process (pt) of the quadrate which is now developed.

The distal ends of the occipital processes have devel-
oped into a narrow synotic tectum, while the notochord
and median portions of the parachordals have disappeared
except in the occipital region, where they form a ventral
band (p) connecting the two capsules. No changes
worthy of notice have taken place in the otic capsules
aside from the results of ossification.

The trabeculse are divided into anterior and posterior
portions by ossification in the orbital region. The pos-
terior portion remains essentially the same as in the first
stage, but the anterior portion is changed by the forma-
tion of the nasal capsule. The base of the antorbital
process (Fig. 19, anp) marks the posterior end of that
portion of the trabecula remaining unossified in front of



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 107

the optic foramen. A narrow column of the trabecular
crest projects upwards from just in front of the base of the
antorbital process, and upon the anterior end of the eth-
moid plate a thin nasal septum is developed. Two carti-
lages upon each side arise from the dorsal end of the
septum. From its posterior end a cylindrical rod, the tectal
cartilage ((e) extends backward and outward to the dorsal
point of the remnant of the trabecular crest. From the
posterior end of the septum a band of cartilage extends
forward and expands into a broad sheet, the nasal tectum,
roofing over the whole anterior portion of the olfactory
organ. Where the nasal duct passes out to the exterior
(nl) at the anterior end of the tectum, a complete ring of
cartilage encircles it. Laterally the nasal roof is con-
nected by a band curved ventrally with the cornu (c) of
the trabecula. And from the postero-lateral margin of
the tectum a flattened rod (?) passes backward to the tec-
tal cartilage, fusing with it at a point just above the an-
terior end of the antorbital process.

While it is impossible to homologize all the parts of the
nasal capsule of Amphiuma with those in Amblystoma
there are some points in which the similarity between them
is very close. The septa, ethmoid plates, and tectal car-
tilages are essentially alike in both. The lamina cribrosa
and dorsal process of Amblystoma are represented in Am-
phiuma by the rod connecting the tectal cartilage with the
nasal tectum. The open anterior end of the capsule of Am-
phiuma is quite different from the cup-like end of Ambly-
stoma to which it must be compared. This difference in
the capsules is, of course, correlated with the relative
change of position of the nostrils, which are at the ante-
rior end of the capsules in Amphiuma and in the middle
of the sides of the capsules in Amblystoma. In Amphi-



108 BULLETIN OF THE ESSEX INSTITUTE.

uma the antorbital process does not become fused with the
lamina cribrosa.

The quadrate is now supplied with a pterygoid process
{pt) which runs forward from the ventral surface of the
ascending process in close proximity with the ventral mar-
gin of the trabecula. Towards its anterior end it curves
laterally and broadens out into an oval plate. Its anterior
end lies a short distance postero-laterally from the base of
the antorbital process. Otic and palato-basal processes
unite the quadrate with the otic capsule. The stapes has
expanded into a broad plate nearly filling the fenestra
ovalis. It is still connected with the quadrate by a strong
stapedial process {sp).

Characteristics of the Urodele Chondrocranium.

From the preceding descriptions of the chondrocrania
of various Urodeles, we may briefly enumerate the more
important characteristics of the cartilaginous skull as found
in this group.

Two occipital processes, the early history and relation-
ships of which have been more fully treated by Ph.
Stohr ('79), arise independently at the sides of the noto-
chord in front of the first permanent vertebra. The sim-
ilarity between these processes and those of which the
vertebrae are formed clearly indicates the vertebral nature
and origin of the occipital arch. From the sides of the
notochord the occipital processes pass upward, fuse with the
walls of the otic capsules and bend over medially to form
the synotic tectum (Fig. 18, ocp). Two large jugular
foramina are enclosed between the bases of the occipital
processes and the posterior ends of the otic capsules.
Parachordals, varying in size and extent from the narrow
bands of Desmognathus (Fig. 14, p) to the complete



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 109

basilar plate of Amblystoma (Figs. 9 and 10 p), form
a more or less complete floor beneath the otic portion of
the brain cavity. The otic capsules are approximately
oval in shape and in all cases have a median wall distinctly
separating the cavity of the capsule from that of the brain.
There are generally four foramina in this wall through
which pass the seventh and eighth nerves and the endo-
lymphatic and perilymphatic ducts. In the ventro-lateral
wall of the capsule there is a large fenestra ovalis which
may or may not be occupied by a stapes. When present
the stapes appears first at the anterior end of the fenestra
and only later, if at all, does it reach back to the posterior
wall of this aperture. The stapes may be connected with
the quadrate by a stapedial process.

Trabeculse, either slender rods with barely enough crest
to cover in the optic and oculomotor foramina as in Des-
mognathus, or solid beams as in Amblystoma, connect the
parachordals and otic capsules with the nasal capsules.
At its posterior end there are two places at which each
trabecula joins the cartilages of the otic region. Of these
points of fusion, the ventral, joining the hixae of the tra-
becula with the parachordal, is formed early, while the
dorsal, joining the trabecular crest with the otic capsule, is
a later occurrence. Anteriorly the trabeculte usually bend
inward, and, fusing in the median line into an ethmoid
plate, take part in the formation of somewhat complex
nasal capsules. But here, again, Desmognathus, with
nothing more complex than cornua trabecula3 (Fig. 14, c),
proves an exception to the general rule.

An antorbital process projects outward and forward
from the side of the ventral margin of the trabecula be-
hind the olfactory organ. In some forms it later fuses
with the other parts of the nasal capsule. The variety
of forms .shown by the nasal capsules of the different



110 BULLETIN OF THE ESSEX INSTITUTE.

species described renders it difficult to make any accurate
statements in regard to these organs which shall apply to
the group as a whole. More extended study may show
the prevalence of a limited number of these types as is
suggested by the similarity between Amblystoma and
Plethodon.

Quadrates, arising independently near the anterior end
of the otic capsules, later become attached to the rest of
the skull by three or four processes. The ascending
process unites it with the trabecular crest ; the palato-
basal with the parachordal ; the otic with the otic capsule ;
and the stapedial process, when present, unites it with the
stapes. The palato-basal and otic processes become so
intimately related that the blood vessel running between
them is the only line of demarcation. A pterygoid process
running forward from the body of the quadrate may or
may not be present. When present it ends freely in front,
not coming in contact with the anterior end of the trabec-
ula and nasal capsule as occurs regularly in the Anura.
Ranodon forms the only known exception among the Uro-
deles to this last statement.

PlPA AMERICANA (FlgS. 20-21).

In the single stage of the chondrocranium of Pipa
which I have modelled, ossification has proceeded so far
that many of the cartilages appear only as remnants of
what they were earlier. A brief outline of this skull,
however, may serve as a basis from which, with the aid of
other studies upon the Anura, especially Gaupp's exhaus-
tive work upon Rana fusca, we may contrast the chondro-
cranium of this group with that of the Urodela.

The occipital processes have fused with the otic cap-
sules and their distal ends have developed into the synotic



THE CHONDROCKANIUM IN THE ICHTHYOPSIDA. Ill

tectum. The parachordals are reduced to a narrow trans-
verse band immediately in front of the base of the occip-
ital arch, and short lateral bands fused with the floors of
the otic capsules. The greater part of the wall of the otic
capsule is ossified, but enough of the lateral wall remains
to show the most important relationships. In this lateral
wall of the capsule, further dorsally than in the Urodele
skull described, is the fenestra ovalis and in it a small
stapes (Fig. 20, s) which is connected b}' a rod running
forward and downward with the lateral border of the
tympanic annulus (ta).

The trabeculoe are small, cylindrical rods extending
forward from the ventro-median angles of the anterior


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