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roof, the 'canalis ethmoidalis' (ec) and the 'canalis pre-
orbitalis ' {pre). Dorsally these two are connected by a
deep groove.

The anterior end of the palato-pterygo-quadrate car-
tilage {ppt) is applied to the ventro-lateral surface of the
nasal capsule. From here it passes backward as a broad-
ening band to a point beneath the outer wall of the otic
capsule and the hyomandibular cartilage. In passing from
in front backward it twists from an approximately hori-
zontal to a nearly vertical plane.

The Trout {8ahno fontinalis) , (Figs. 28-29).

For a representative of the Teleostean skull I have
modelled the chondrocranium of a trout embryo twenty-
two mm. in length. The occipital arch is fused with the



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 125

otic capsules leaving no suggestion of their former sepa-
ration, except in the jugular foramina (Fig. 29 j). The
notochord extends forward beyond the middle of the otic
region. Its sides are embraced by the two halves of the
basilar plate. At its apex it projects freely forward for
a short distance. Except for a small fontanelle (/} , the bas-
ilar plate is continuous with the walls of the otic capsules
which are united above by a broad, arched synotic tec-
tum. The positions of the semicircular canals are clearly
indicated in the external surface of the otic capsules. No
median wall separates the cavity of the ear from that of
the brain. In front and a little below the jugular fora-
men there is another smaller foramen through which the
ninth nerve {ix) passes out of the cranium. Farther for-
ward there are three more apertures in the ventral wall of
the capsule. The posterior of these is the fontanelle men-
tioned above. The middle one of the three is small and
is traversed by the hyomandibular branch of the facial
nerve {hy) . The anterior foramen is for the exit of a
branch of the jugular vein (jv).

The basilar plate is continued forward into a trabecula
upon either side. These extend separately to a point in
front of the hypophysis and then unite along the median
line in a narrow tral)ecular band. This baud has the shape
of an inverted trough and reaches to the anterior end of
the skull, expanding in the nasal region into the ethmoid
plate which forms the floor of the nasal capsules. The
palatine branch of the seventh nerve (Fig. 28,paZ) passes
downward through a foramen in the posterior end of the
trabecula. Two slender supraorbital bands {sh) arise
from the anterior ends of the otic capsules and curve
forward and inward, until about half way from the otic to
the nasal region, where they enter the margins of the
arched tegmen cranii which covers the anterior end of the



126 BULLETIN OF THE ESSEX INSTITUTE.

cranial cavity. This cranial roof is fused anteriorly with
the dorsal end of the nasal septum (Fig. 28, ns.) In its
anterior end there are three apertures, a median fontanelle
and two small lateral foramina, through each of which
passes a branch of the ophthalmicus superficialis (rs). A
band of cartilage connecting the tegmen cranii and the
dorsal end of the septum with the lateral border of the
ethmoid plate separates the nasal region from the cranial
cavity. There is no cartilaginous roof or lateral wall to
the nasal capsule. The septum is thick and slightly ex-
panded dorsally and in front where it ends bluntly.

The anterior end of the pterygo-quadrate cartilage is
applied to the ventro-lateral margin of the ethmoid plate.
From here it extends backward as a slender rod to be-
neath the anterior end of the otic capsule where it broad-
ens into an irregular plate with an articular process
ventrally for the attachment of Meckel's cartilage. Its
posterior end is connected with the otic capsule by means
of the plate-like hyomandibular cartilage (h). The dor-
sal margin of this cartilage, the hyomandibular, lies
closely pressed against the external surface of the otic
capsule just beneath the horizontal canal. It is broad
and thin above and narrower and thicker below. From
its ventral end a long rod-like process runs forward be-
neath the posterior end of the pterygo-quadrate, reaching
almost to the point of articulation with Meckel's cartilage.
The hyomandibular branch of the seventh nerve passes
through a foramen just above the middle of this cartilage

The Chondrocranium in the Fishes.

The chondrocrania of the two types of this group
which have been described have many features in com-
mon, and it seems probable that a comparison of corres-



THE CHONDKOCRANIUM IN THE ICHTHYOPSIDA. 127

ponding stages in the development of the two forms would
show a still more marked similarity. The otic capsules
are connected dorsally by a solid synotic tectum and ven-
trally by an unbroken basilar plate formed by the fusion
of the parachordals aroiind the anterior end of the uoto-
chord. The median wall of the otic capsule is either ab-
sent or but slightly developed. Neither fenestra ovalis
nor stapes occurs.

The trabecule unite ventrally into a median band in
front of the hypophysis and continue forward to the end
of the skull. At its anterior end the trabecular band
broadens out into the ethmoid plate which forms the floor
of the nasal capsules. Supraorbital bands extend for-
ward from the anterior ends of the otic capsules to the
lateral margins of the tegmen cranii which roofs over the
anterior portion of the brain cavity.

The palato-pterygo-quadrate cartilage extends from the
lateral margin of the ethmoid plate backward to beneath
the anterior end of the otic capsule. Its posterior end is
supported to a greater or less degree by the ventral end
of the hyomandibular cartilage which has its dorsal end
closely applied against the outer wall of the otic capsule.
Meckel's cartilage articulates with the ventral surface of
the quadrate portion of the palato-pterygo-quadrate car-
tilage.

In discussing the relations of Polypterus to the Batra-
chia, Pollard said, "On comparing the primordial cranium
of a young Polypterus with that of Urodeles, the general
resemblance is seen to be so ofreat that an anatomist see-
ing it alone for the first time would certainly place it
among the latter." Considering the features which dis-
tinguish the chondrocranium of Polypterus in common
with the rest of the Fishes from that of the Batrachia, as
outlined in the preceding pages, so great a similarity can



128 BULLETIN OF THE ESSEX INSTITUTE.

hardly be admitted to exist. The great similarity pointed
out above between the skulls of Polypterus and the trout
and the many points in which they differ from the typical
skull of the Batrachia cause me to feel considerable hesi-
tancy about accepting the theory of the Crossopterygian
ancestry of the Batrachia. But, while the presence in
Polypterus of a large hyomandibular cartilage, a quadrate
well removed from the otic capsule and a strong supraor-
bital band, as well as the absence of any fenestra ovalis
or stapes, will remain important obstacles to this view
until transitional stages are found, perhaps these difficul-
ties are less than those attending the Dipnoan theory.
Attention may also be called to the fact that in Polypterus
there is a limited median capsular wall, which is not found
in either the trout or Protopterus but which regularly
occurs in the Batrachia.

Protopterus annectens (Figs. 30-32).

A model of the chondrocranium of Protopterus gives
us a basis from which to compare the Dipnoi on the one
hand with the Batrachia, to which they have been consid-
ered to be closely related, and on the other to the
Teleosts and Ganoids.

Viewed as a whole the massive character of many of
the cartilages of this skull is a most striking feature.
Ossification in the occipital region somewhat obscures the
relations between the skull and the first vertebra. The
occipital processes are fused with the otic capsules leaving
large jugular foramina in the usual position. The remnant
of the notochord is imbedded in a solid parachordal plate
extending from the posterior end of the skull forward to
the middle of the otic region. On each side of the me-
dian line at the anterior end of the parachordal plate is an



THE CHONUKOCRANIUM IN THE ICHTHYOPSIIM. 129

elongate fontanelle (Fig. 32,/). The walls of the otic cap-
sules are continuous ventrally with the parachordal plate
and dorsally with a strong synotic tectum. From the ex-
ternal margin of the otic capsule a broad ledge of cartilage
projects horizontally outward, widening as it passes from
behind forward where it terminates abruptly. There is
no median capsular wall.

Band-like trabeculse extend forward along the sides of
the brain from the dorsal anterior end of the otic capsules
to the optic region where they bend around ventrally to
form a large ethmoid plate. From the dorsal margin of the
anterior end of each trabecula a peculiarly bent antorbital
process (^anp) arises. It projects forward and outward,
coming into close proximity to, but not fusing with the
posterior end of the nasal capsule, and then it bends back-
ward, running along the margin of the upper lip. The
ethmoid plate narrows down in passing from behind for-
ward, and terminates in two processes which bend sharply
upward and fuse with the posterior end of the nasal
septum. Between these two terminal processes there is
an oval fontanelle.

The nasal capsule is a very peculiar one. The septum
is a thin dorsal plate behind, l)ut in front it becomes a
solid cylindrical mass of cartilage projecting ventrally
between the olfactory organs. The transition from one
condition to the oti)er is very abrupt. In front the septum
ends in two short laterally directed processes. Six bands
of cartilage extend outward and downward from the me-
dian septum to a curved marginal band (?«r). Between
these bands five apertures of various shapes and sizes are
enclosed. The anterior of the six transverse bands pro-
jects somewhat beyond its point of fusion with the mar-
ginal band. As is seen in the ventral view (Fiii;. 32) a
curved process extends inward and upward from the inner

ESSEX INST. BULLETIN, VOL. XXVIII 9



130 BULLETIN OF THE ESSEX INSTITUTE.

border of the marginal band. Its dorsal end is free. Just in
front of the bend of the antorbital process is an isolated
strip of cartilage occupying a diagonal position, one end
being dorso-medial and the other ventro-lateral. A small
cylindrical rod (tc) extends backward in the median line
from the posterior end of the nasal septum and ends freely
above the brain, a remnant of the ancestrally complete
tegmen cranii.

The quadrate has its base firmly fused with the otic
capsule and trabecula. It is a solid mass projecting down-
ward and forward, and presents upon its anterior end a
large articular surface for the enormous posterior end of
Meckel's cartilage (Fig. 30). Except for a short distance
in front of its point of articulation, Meckel's cartilage is of
only ordinary size. There are upon each side of the lower
jaw three labial cartilages (Ic). As shown in the figure
the posterior of these is separated from the jaw and
divided into two parts, but this occurred upon the right side
only. By mistake the anterior end of the lower jaw was
drawn nearly straight instead of curved sharply upward
as it should have been.

The ninth nerve {ix) passes out through a small fora-
men a short distance in front of the jugular foramen.
Five foramina grouped about the anterior end of the otic
capsule open upon the dorso-lateral surface of the skull.
I have designated the nerves passing through these fo-
ramina in accordance with the work of Pinkus ('94). The
third nerve passes through a small foramen (Fig. 30, oc)
near the dorsal margin of the trabecula. Just below the
foramen for the third is a larofer one for the ramus
ophthalmicus profundus of the fifth (77;), and still lower
is another for the ramus maxillaris of the fifth {rm). A
short distance behind this foramen are the openings of the
other two lying close together, one above the other. The



THE CHONDKOCRANIUM IN THE ICHTHYOPSIDA. 131

more dorsal of the two is tniversed by two nerves, the
ramus lateralis facialis of the seventh (rl) and the ramus
ophthalmicus superticialis of the fifth (rs). The more
ventral foramen is for a blood vessel (b) .

Three foramina open upon the ventral surface of the
skull in this same region (Fig. 32). Of these the anterior
and smallest is for the ramus palatinus superior (I'ps).
Tiie other two openings are close together. The more
median is for the main trunk of the seventh (v^'^) and the
ramus palatinus inferior (lyi). The more lateral open-
ing is the ventral end of the foramen for the blood vessel
mentioned above.

The Chondrocranium in the Dipnoi.

A comparison of the chondrocranium of Protopterus
with those of the Batrachia and Fishes at once reveals its
unique character. While resembling the typical chondro-
cranium of each of these groups in some respects, taken
as a whole it is very diflerent from either. The large otic
capsule, with thick walls and separate foramen for the
ninth nerve, and without a median wall or fenestra ovalis,
greatly reseml)les the capsule of Fishes. But the sus-
pensorial apparatus is entirely diflerent from that of most
Fishes and very similar to that of the Batrachia, that is
to say, it is autostylic. According to Huxley ('76) this
condition is also found in the Chimasroids and Marsipo-
branchii, but in none of the other Fishes. This is un-
doubtedly the strongest point of resemblance between the
chondrocrania of the Dipnoi and Batrachia. And here
the theory of the Dipnoan ancestry of the Batrachia is
decidedly at an advantage over the Crossopterygian
theory. But this similarity of the otic relations of the
quadrate in these two forms is counterbalanced by difler-



132 BULLETIN or THE ESSEX INSTITUTE.

ences in other respects. The absence of a palato-ptery-
goid cartilage is an especially noteworthy feature in this
connection which indicates the highly specialized nature
of this skull and renders it impossible to consider it a
very near approach to the ancestral Batrachian skull.

The trabeculse are unlike both those of the Fishes and
those of the Batrachia. When their posterior ends are
compared with the chondrocranium of the former group
they seem rather to represent the supraorbital bands,
arising as they do from the antero-dorsal surface of the
otic capsules. But in passing forward, instead of curv-
ing up over the eye as supraorbital bands should do, they
curve downward and fuse at their anterior ends into an
ethmoid plate very much as occurs in the Batrachia. The
antorbital process arises from the dorsal margin of the
trabecula, a condition found in none of the other forms
studied ; and the ethmoid plate, instead of continuing
forward to form a floor beneath the nasal capsules, as is
the general method in both Fishes and Batrachia, curves
sharply upward at its anterior end and fuses with the dor-
sally situated posterior end of the nasal septum. The
possession of a remnant of the tegmen cranii is another
fish-like character.

As was mentioned in the discussion of the chondro-
cranium of Necturus, there is some resemblance between
the nasal capsules of that form and those of Protopterus.
But, in view of the differences between the nasal capsules
of the various forms of Urodeles themselves and consid-
ering the many important points of difference in other
parts of the skull, it seems to me an entirely unwarrant-
able conclusion to assume any phyletic relationship be-
tween these two forms upon this account.

Giinther has described the skull of Ceratodus as
consisting " of a completely closed inner cartilaginous



THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 133

capsule and an outer incomplete osseous case, to which,
again, some other cartilaginous elements are appended."
From this description and from the fact that a cartilage
considered to be a remnant of the hyomandihular has
been found in Ceratodus it seems prol^able that the chon-
drocranium of this form resembles that of the Fishes more
than does that of Protopterus. But the evidence from the
chondrocranium of Protopterus, in so far as it may be con-
sidered to have value in determining the position of the
Dipnoi as a whole, appears to me to be entirely in agree-
ment with the conclusion of W. N. Parker that, " it is
certainly inadvisable to retain the Dipnoi among the
Fishes, as is still done by some zoologists, and it would
be still more undesirable to place them with the Amphi-
bia." It is to be remembered, however, that Protopterus
is one of the more specialized forms of the group.



Postscript.



Since the foregoing article passed into the hands of the
printer a paper by Miss Platt^ has appeared which deals
with the development of the cartilaginous skull of Nectu-
rus, giving special attention to the origin of the procar-
tilage cells. In the main our results in regard to the fully
chondritied parts entirely agree. Miss Piatt finds, how-
ever, that in Necturus the number of cartilages arising
independently is considerably larger than that desonl)ed
above for Amblystoma. Of these the synotic tectum
('tectum interoccipitale'), the trabecular crest, and the
ethmoid ('internasal ') plate are of particular interest

■ Piatt, J. B. The development of the cartilaginous skull and of the brauchlal
and hypoglossal musculature In Necturus. Morph. Jahrbuch. xxv, p. :fJT. 1897.



134 BULLETIN OF THE ESSEX INSTITUTE.

from the fact that I have not found them to appear as in-
dependent cartilages in any of the forms studied. This
may, in some cases, be due to the fact that the inde-
pendent condition is limited to the pro-cartilage stages or
to the incompleteness of my series of embryos. But I
feel confident that the parts mentioned do not appear as
independent cartilages in Amblystoma. The existence of
such a condition as that shown in Fig. 18, where there is
no sign of cartilage near the median line, and the appear-
ance of a complete tectum in an embryo but little older
form the basis of my conclusions in regard to the synotic
tectum. My evidence as to the formation of the trabecu-
lar crests and the ethmoid plate is of the same nature and
shows them to be outgrowths from the primitive trabeculse.



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