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: OLIVER S. STRONG, Naz,
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: Requesting exchanges in this and allied subjects.
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A Contribution to the Morphology of the

Vertebrate Nervous System

BY

OLIVER: S: STRONG

\
Columbia College, New Vork

SUBMITTED FOR THE DEGREE OF DocToR oF PHILOSOPHY

Reprinted from JOURNAL OF MORPHOLOGY, Vol. X., No. 1

BOSTON
GINN & COMPANY
1895

Tiss ASS ra} | , |
.

THE CRANIAL NERVES OF AMPHIBIA.

A CONTRIBUTION TO THE MORPHOLOGY OF THE VERTE-
BRATE NERVOUS SYSTEM.

OLIVER S. STRONG.

COLUMBIA COLLEGE.

ANALYSIS OF CONTENTS.

PAGE
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2. Relations of the Pre- and Post-Auditory Nerve ......22:-seeeeeeeerereeee 206

3. Bearings upon the Classification and Segmentation of the Nerves.... 208

eA EANP 2) oy OF SY DS Dyk pag BY DCH 8 BG (0. 0 F DA ee Ce en 211
INTRODUCTION.

Tuis research may be regarded as, in a manner, a continua-
tion of Professor Osborn’s work on the Amphibian brain. In
the introduction to his paper, “A Contribution to the Internal
Structure of the Amphibian Brain” (Journ. oF Morpu., Vol.

102 STRONG. [VoL. X.

II, No. 1, July, 1888), occur the following sentences : “Much
remains to be done in respect to the peripheral distribution
of the component parts of the several cranial nerves. Only
after this has been thoroughly worked out can we certainly
determine the homologies of the cranial nerves and their
segmental relations in the Amphibia. The present results go
far enough to show that the determination of definite nuclei
corresponding to definite peripheral sensory and motor areas is
well within the range of possibility. In fact, the provisional
character which I have given to some of the conclusions here
reached is chiefly due to the close connection between several
of the cranial nerves at, or close to, their exit, which makes
it necessary to follow each component bundle in continuous
sections peripherad to a point where their further distribu-
tion can be traced macroscopically. This, I believe, is possible
with several of the nerves, but has not as yet been successfully
accomplished.”

To supply some of these deficiencies was the immediate
aim of this investigation, and, I think, some of the obscure
points mentioned by Osborn in his paper are satisfactorily
cleared up. While very much remains to be done on the
forms here investigated, yet a firmer basis has been acquired
on which to make comparisons with the cranial nerves in other
forms and to draw conclusions as to their nature.

In the opinion of the writer much of the embryological work
upon the cranial nerves has been very defective and even mis-
leading, owing to the fact that their adult distribution and
function had not first been accurately worked out. I would
venture to predict that more light can and will be thrown
upon the nature of the cranial nerves in the immediate future
by means of anatomical and histological than by purely
embryological research.

This paper is by no means a monographical account of the
cranial nerves of Amphibia, but will be confined principally to
the V, VII, IX, and X nerves. Other nerves will be included
in the description as they come into connection with these.

The types upon which the bulk of the work has been done
and upon which the description is based are several common

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 103

species of Rana in the late larval stages of development. Other
Amphibia, especially the Amblystoma larvae, are brought in
incidentally as throwing light upon certain points.

This research was begun at Princeton in 1889 at the sug-
gestion and under the direction of Prof. Henry F. Osborn. A
summary of the results first obtained appeared in the Zoolo-
gischer Anzeiger, Nr. 348, 1890 (61). At the Lake Laboratory,
established by Mr. Allis at Milwaukee, I was enabled to make
some additions to these results, which appeared in the Anatom-
ascher Anzeiger, Nr. 15, 1892 (62). The final publication has
been delayed, owing partly to other duties and partly to further
observations made while Fellow in Biology at Columbia College,
and also during the past year.

I wish to express here my deep indebtedness to Professor
Osborn for many valuable suggestions and for his assistance in
many ways in this research. For the execution of the majority
of the drawings I am indebted to Dr. Arnold Graf, to whose
skill they bear witness.

I. TECHNIQUE.

A considerable part of the investigation was upon tadpoles
fixed in Perenyi’s fluid, stained zz ¢o¢o in carmine, imbedded in
paraffin and cut in serial sections. These were mounted in
order upon large glass slides, strips of thin mica being used as
covers. The carmine staining is not to be highly recommended,
as carmine solutions do not stain very differentially, and would
probably be even more unsuitable with forms where the tissues
are more compact than in the tadpole.

The osmium-bichromate mixture used for hardening in the
Golgi method gives in itself a very good stain for the medul-
lated fibres of the peripheral nerves, and sections prepared by
means of this method were thus doubly useful.

The Golgt Method.— For the terminations of the nerves and
for demonstrating certain tracts consisting of many non-
medullated fibres, the Golgi method proved invaluable. It may
be well to describe here in detail the precise procedure which
I have found useful and convenient.

104 STRONG. [Vor X.

Preliminary to hardening, the manner of cutting the tadpole
is a matter of some importance. The special region should be
opened up to some extent in order to insure a speedy and com-
plete penetration of the osmium-bichromate and the silver
nitrate solutions, as neither of them have much penetrating
power. On the other hand, by not cutting into too small
pieces the precipitate formed by the silver is not deposited so
extensively on all the surfaces, and many beautiful pictures can
thus be obtained not marred by its presence. In investigating
the head region I have found it best to cut the animal trans-
versely into three pieces, one cut being made a short distance
caudad of the auditory capsule and Vagus, and the other passing
just through the anterior surfaces of the eyeballs. It is, per-
haps, best to allow the animal to remain in the fixing fluid half an
hour or so first, to acquire a better consistency for this cutting.

With respect to the osmzum-bichromate mixture, a consider-
able latitude in the proportions may be taken and good impreg-
nations obtained; the same holds good as to the strength of
the szlver nitrate solution. For example, good preparations
were obtained from a tadpole impregnated as follows: Pot.
bich. sat. sol. 140 cc. + osmic 1% 10 cc., 21 days, silver nitrate
10%, 3 days. The following, however, are the two solutions
chiefly used, the first one (1) being after Berkley (10) and the
second (2) very much like that recommended by Ramon y Cajal:
(1) Pot: bich. 5% 84) ce: 4 esmic 2% 16 ce. and (2) Pot!) bich
3%4% 4 vols. + osmic 1% I vol. I cannot say that I have found
much choice between the two.

As seen above, impregnations may be obtained after harden-
ing for 21 days ina solution containing /ess osmic. On the
other hand good impregnations of the more superficial parts
were obtained in one case as follows: Pot. bich. 314% 4 vols.
+ osmic 1% 1 vol., 22 hours, during the first 11 hours in a
solution which had been previously used, silver nitrate 349%,
2% days. This shows that here again there may be a con-
siderable range within which good results are obtainable.
There is a certain hardening period, however, which is much
the most favorable; this is 2 to 5 days, and probably about 3
days will usually give the best results throughout the pieces.

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 105

Lithium Bichromate Modification for Adult Braims.— I have
made a number of attempts to dispense with osmic acid in
the fixing fluid, but without success for the tadpole. A modifi-
cation was discovered, however, which gives some very fine
impregnations in the adult mammalian cerebrum and cerebel-
lum, dispensing with osmic acid and yet requiring only a few
days for the process. It consists simply in the use of “thzum
bichromate instead of potassium bichromate. This salt is very
soluble in water and makes a solution somewhat darker than
the potassium bichromate, which it resembles. It hardens very
much more rapidly than the latter, so that small pieces of brain
placed in a 3% solution require only a day or two instead of
20 to 30 days to reach the condition favorable for impregna-
tion. This favorable condition, however, is passed through very
quickly. I have not had opportunity, as yet, to test this
method thoroughly, but have obtained splendid pictures of the
Purkinje and pyramid cells, and also in the fowl’s brain of the
granule cells, showing the 7-shaped division of their axis
cylinders in the molecular layer of the cerebellum.

Sodium Sulphate Modification for Increased Penetration. —
One of the defects of the Golgi method, especially of the
rapid method, seems to lie in the poor penetration of the silver
nitrate, resulting in irregular and defective impregnations. It
occurred to me that by combining the silver solution with some
salt that would be indifferent chemically in the reduction of
the silver, but would facilitate its penetration, the results might
be improved. Two salts were tried, namely, sodium sulphate
and zinc sulphate. Both seemed to tend to produce the
desired effect, for some of the best and most thorough impreg-
nations were obtained from specimens treated especially by the
former. The mixture of silver nitrate and the sodium sulphate
was made in varying proportions. In two of the most suc-
cessful impregnations the following were the solutions into
which the objects were brought from the osmium-bichromate
mixture: (1) Sodium sulphate 6% 1 vol. + silver nitrate 4%
I vol.; (2) sodium sulphate 8% 1 vol. + silver nitrate 1% 1 vol.
A precipitate is formed in mixing these, and it would be
advisable to so adjust the proportions as to prevent this.

106 STRONG. [VoL. X.

Equal volumes of 1% solution of each avoided this, and also
gave some good results. Zzuc sulphate seems to act similarly
to the sodium salt and can be mixed with the silver in larger
proportions without producing a precipitate.

It must not be understood that this latter modification gives
ideal results. In some cases it seems to be an improvement,
but further experience is necessary to ascertain its precise
value. In the tadpole it has yielded especially good prepara-
tions of the nerve terminations in the heart (Pl. IX, Fig. 14).
The specimens should be placed in pure silver nitrate a while
previous to placing them in alcohol, in order to wash out the
sulphate, otherwise the alcohol will precipitate the latter in
the tissues. The specimens are left in the dark while in the
osmium-bichromate and in the silver bath.

Preservation. — lf, for any reason, specimens cannot be cut
and mounted immediately after impregnation, they can be best
preserved in the silver bath. Specimens will often keep thus
for months, but there is considerable risk of deterioration.
This latter is probably due, as von Lenhossék suggests (37),
to a slow precipitation of the silver in solution, so that in time
the specimen is left simply in water which, in turn, bleaches
out the stain. Another cause of deterioration appears to be
a gradual darkening of the whole tissue. It is obvious from
this that if it is necessary to keep the specimens some time
before cutting, two precautions should be taken, (a) the speci-
men should be kept in a liberal supply of the silver solution
of full strength, and (0) it should be kept strictly in the dark
in order to prevent, as far as possible, a gradual secondary
reduction of the silver.

The double and triple impregnation, as recommended by
Cajal (13), was tried with good results. The exact details of
procedure in technique are placed in an appendix.

II. DETAILED DESCRIPTION OF THE NERVES AND THEIR
COMPONENTS.
The most direct treatment seemed to be, first, to examine

each nerve in detail, with a view to ascertaining its com-
ponents, each section concluding with a table summarizing the

No. I.] THE CRANIAL NERVES OF AMPHIBIA. IO7

results. The term ‘component’ is not necessarily synonymous
with ‘voot,’ for often two or more components different in fibre
structure, internal origin, distribution, and function are given
off as ove root, and vce versa, different roots may be composed
of similar components. ‘Root’ has reference to the number
of separate bundles by which a nerve issues from the central
nervous system — while by ‘component’ we refer to bundles
qualitatively different. In some cases, of course, the two are
identical.

A resumé of this part treats the nerves collectively as
regards their components,

Second, each of the main components thus determined
will be further considered as representing a system, and used
as the basis of homologizing the cranial nerves of the Amphibia
with those of other orders.

The chart (Pl. XII, A) was reconstructed from a series of
transverse sections through the tadpole by plotting out the
nerves, etc., upon a sheet of paper ruled in squares, the rela-
tion between the thickness of the sections and the magnification
having been first ascertained. For conciseness and precision
the numbers of the sections are used in the text to indicate
distances measured along the longitudinal axis. As the
sections were 10 thick, these numbers divided by 100 will
give the actual distances in millimeters and decimals of a milli-
meter. Each interval in the scale along the sides of the chart
equals 10 sections (= 100), and the numbering corresponds
to that used in the text. This correspondence, however, is not
always exact, owing to slight changes made in the chart in its
preparation.

1. The Trigeminus.

The Zrigeminus emerges from the side of the medulla
.10 mm. cephalad of the VII + VIII roots (866-848). Its exit
takes place principally just anterior to the entrance of the
posterior branch of the VIII into the auditory capsule. It
proceeds obliquely cephalad occupying, together with the other
nerves described below, a position in the cranium immediately
inside the ventral portion of the auditory capsule. The bulk

108 STRONG. [Von. X.

of its fibres are rather small, but with a number of medium-
sized fibres among them, and a still smaller number of large
fibres. The ascending tract of the V contains a few scattered
large fibres, and the ventral root of the V (V minor) is coarse
fibred.

After proceeding cephalad .7 mm. it becomes ganglionated,
.36 mm. further on its Gasserian ganglion begins to divide into
a dorsal and a ventral part, the ventral part at the same time
passing through the floor of the cranial cavity and conse-
quently lying in the roof of the mouth. Here this ventral por-
tion has lost its ganglion cells and becomes the Ramus ophthal-
micus trigemint. ‘This partial division of the anterior extremity
of the Gasserian ganglion is the only sign of separation
between the ganglia of the Rr. ophthalmicus and maxillo-
mandibularis trigemini respectively. The R. ophthalmicus con-
tinues cephalad and gradually dorsad, thus entering the orbital
cavity. .3 mm. cephalad of its separation from the rest of the
V, it comes into connection with the III nerve, which divides
on its inner side, one part of the III passing up around it, and
the other bending forwards beneath it.

During the remainder of its course the R. ophthalmicus gives
off several branches to the skin, which need not be described
more in detail here. When it breaks up in the anterior ex-
tremity of the head one branch is given off (170), which bends
down, pierces a layer of fibrous cartilage which separates the
skin from the oral subepithelial layers and divides. One divi-
sion, proceeding caudad, is continuous with a branch of the
R. palatinus VII. The significance of this connection will be
discussed in the description of the latter. The other division
of the R. ophthalmicus, possibly together with some fibres from
the R. palatinus VII, proceeds cephalad a short distance, and
breaks up into a rich plexus, terminating in the epithelium
of the roof of the anterior extremity of the oral cavity. This
plexus and its terminations are figured in Pl. VII, Fig. 3,
where the plane of the section enables one to obtain a view
of its mode of branching and termination.

The fibres of the R. ophthalmicus V are rather small, but of
variable size, and with, perhaps, a dozen and a half coarse

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 109

fibres scattered among them. As the different branches sepa-
rate from the main trunk they usually draw off several of these
larger fibres. The latter have apparently no special significance
as far as their peripheral distribution is concerned. They seem
to have the same cutaneous terminations as the smaller fibres.
Whether a more exhaustive study of them would reveal histo-
logical differences in their ultimate terminations, I do not
know. The presence of these large fibres in cutaneous branches
is readily accounted for by their presence also in the ascending
tract of the Trigeminus, in which they can be traced caudad to
the posterior columns of the cord.

The other and dorsal division of the V .46 mm. cephalad of
its separation from the R. ophthalmicus separates into the
Rr. maxillaris and mandibularis. The last ganglion cells dis-
appear .7 mm. cephalad of the first, thus making .7 mm. the
length of the Gasserian ganglion.

Slightly cephalad of the subdivision into the Rr. maxillaris
and mandibularis the motor branches of the Trigeminus to
Mm. pterygoideus and temporalis are given off. These branches
all arise together from the same point on the ventral side of
the Rk. mandibularis. Some distance cephalad of this, and in
about the same transverse plane as the posterior nares, the R.
mandibularis gives off branches innervating the M. masseter.
Still further along it bends mesad and gives off the musculo-
cutaneous branch to the M. submaxillaris (mylohyoideus ante-
rior) and the skin beneath it. As it finally breaks up it
innervates the Mm. submentalis and mandibulo-labialis of
Schulze (54).

The cutaneous branches which compose the bulk of the R.
mandibularis need not be described here. The general manner
of termination of cutaneous nerves will be touched upon
below. The character of the fibres of the R. mandibularis, as
well as of the fibres of the R. maxillaris, is similar to that of
the fibres of the R. ophthalmicus, and what has been said of
the latter applies to them also.

Besides its motor and cutaneous branches, the R. mandi-
bularis innervates a part of the epithelium of the mouth. At
200 a twig is detached which proceeds mesad to the mouth at

Pi© STRONG. [Vou. X.

150+, about in the same transverse plane as the termination of
the R. mandibularis VII, and innervates the epithelium lining
the under side of a lateral diverticulum of the oral cavity.

At the terminal portion of the R. mandibularis one branch
also proceeds dorsad and then along beneath the epithelium of
the labial cartilage (170+). It forms here a dense plexus in
the subepithelial connective tissue layer and apparently in close
apposition to the cartilage. The appearance of this plexus is
difficult to reproduce, but Pl. VII, Figs. 5, 6, and 7, will give
some idea of its character. The stain is not so black as that
of the other nerve fibres, and the fibres of the plexus certainly
appear to fuse with each other, forming a true network. This
appearance is not so apparent in sections in which the stain is
less complete — or in which the plexus is more diffuse, — and
may possibly be due to an excessive precipitation of the silver.
I am not inclined, however, in view of the appearances pre-
sented to accept this explanation. In this plexus are numerous
varicosities and many free endings terminating in small knobs
similar to the varicosities.

From this plexus arise at right angles innumerable twigs
which break up into arborisations in the epithelium surround-
ing the cartilage. The fibres of this plexus do not anastomose
but simply interlace. A good idea of their appearance is given
in Pl. VII, Fig. 5. he thicker fibres from which they arse
represent the perichondral plexus mentioned above and which
Figs. 6 and 7 represent in horizontal section.

It is noticeable that none of these fibres, or very few, pene-
trate more than about two-thirds of the thickness of the
epithelium. I think it is not unlikely that the explanation of
this lies in the character of the epithelium. The outer layers
of the latter consist of more flattened cells which are probably
partly cornified.

It is difficult to see exactly what the significance of the
plexus or network closely enveloping the cartilage is. It cor-
responds to the basal plexuses lying in, or under, other epider-
mal and epithelial structures and from which the terminal fibres
arise. Here, however, its unusually compact character, its
close apposition to the cartilage and the great number of

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. III

endings it contains would seem to indicate, in addition, some
special function.

With one exception the branches of the R. maxzllaris need
not be described further. This one is given off at about 310,
passes cephalad and mesad and here subdivides. One subdivi-
sion is continuous with a branch of the R. palatinus VII while
the other, together, apparently, with a portion of the R. pala-
tinus, proceeds cephalad along the side of the oral cavity sup-
plying its epithelium with fibres and finally breaking up at its
extreme anterior end (Pl. VII, Fig. 2).

Besides these branches of the Trigeminus there are a number
of others which have been but little noticed and yet, though
small, seem to be of some morphological importance. There
are usually three of these and all are given off in about the
same transverse plane, and about .3 mm. caudad of the division
of the V into its maxillary and mandibular branches. Two of
these arise from the inner side of the V, — from the inner side
of the anterior extremity of the Gasserian ganglion, — and one
can be traced caudad along its inner side almost to the point of
separation of the R. ophthalmicus. The third and largest
branch arises apparently from the outer side of the V but its
fibres can be seen passing mesad across the dorsal side of the
V, so that they ultimately originate from about the same point
as do the other two. These accessory branches seem to derive
their fibres, in part at least, from the few large ganglion cells
in the dorsal and mesal side of the trunk of the V, consti-
tuting the apex of the Gasserian ganglion.

These branches, like the other branches of the V, consist
principally of small fibres with a few large ones among them.
They fuse temporarily with certain branches of the VII, as will
be described below.

It will not be necessary to describe the branches of the V
further as no departures of importance from, or additions to,
the usual descriptions have been noted.

The cutaneous terminations of the fibres of the various
branches of the Trigeminus (Pl. VII, Figs. 1 and 4,) present no
especial differences among themselves. Their modes of branch-
ing and courses differ, however, in different tadpoles, and these

rl? STRONG. [ VOL. X.

differences evidently depend upon differences in the structure
of the skin, in the thickness of its different layers and the
form and arrangement of the epidermal cells. The branches
break up in the deepest layer of the cutis, bend at right angles
and form a heavy, coarse plexus of nerve fibres extending
parallel to the surface. From this plexus one or several fibres
pass vertically through the middle layer of the cutis and in the
superficial layer break up into terminal arborisations, the fibrils
of which pass into the epidermis, there to ramify still further.
The course and configuration of these ramifications is corre-
lated in a general way with the shape of the epidermal cells.
In passing through the middle layer of the cutis the vertical
fibres give off branches at right angles which course along
between the dense parallel strands of connective tissue which
constitute this layer. The endings in the different layers
appear to be always free and intercellular. The precipitate
formed on the surface often interferes with following them to
their final terminations.

Immediately beneath the middle layer of the cutis, and still
more abundantly in the superficial layer immediately beneath
the epidermis, a number of dark bodies are present (Fig. 4, +),
usually with a smooth oval outline, and are, apparently, a
species of pigment cell. While the nerve fibres now and then
lie close to these, there is no connection between the two.
I have not found any cells, such as those described by Eberth
and Bunge (16) in the foot of the frog. While negative evi-
dence, especially with Golgi preparations, is far from conclusive,
yet I think, judging even from their own figures, their results
are open to the criticisms made upon them by Van Gehuchten

(27).
2. The Factalis and Acusticus (Auditory).

The Faczalzs and Acustzcus present even greater difficulties in
the tadpole than in the Urodela. In the latter the exits of the
Acusticus, and what is here called the dorsal VII, are quite
distinct. The latter is considerably reduced in the tadpole and
tn proportion as it ts reduced the Acusticus is increased, the
exit of the VIII being extended so much dorsad that it and

No. I.] THE CRANIAL NERVES OF AMPHIBIA. ri2

the dorsal VII emerge from the medulla together and only
become separated later in their course. An interesting question
here arises. Does the Acusticus in its extension dorsad ap-
propriate a portion of the dorsal VII? This could best be
determined by a careful study of these nerves and their internal
origin through the stages of transformation into the frog. If
such a transference takes place it would lead to the remark-
able result that the Acusticus of the Urodela is not strictly
homologous with that of Anura. It should also then be
determined what structures in the ear receive this increased
nerve supply. Some further aspects of this question will be
dealt with later.

The exit of the VII+ VIII (899-876) occupies a large
portion of the side of the medulla. In the most caudad part
of this exit there may be seen fibres leaving the medulla
which, when traced internally, curve ventrad, and evidently
have an origin much inferior to that of the bulk of the VIII.
This root has been observed by Stieda (59) and others, and is
spoken of in Ecker and Wiedersheim’s Anatomy of the Frog.
(17) as derived from the motor trigeminal nucleus. Osborn
(45), however, has demonstrated that a similar ventral rootlet
in Cryptobranchus is derived directly from the posterior longi-
tudinal fasciculus. My sections, being of smaller brains, are
inadequate for the settlement of the derivation of this root in
the tadpole. I think it probable that some of the fibres origi-
nate from a portion of the trigeminal motor nucleus, and
possibly others may come from the posterior longitudinal
fasciculus. I have so indicated them in the chart.

These fibres, as they emerge from the medulla, form a
bundle close under the large root of the Acusticus. This
bundle was termed, in the abstract in the Zoologischer Anzeiger
(61), the “ ventral root of the ventral VII” or “ VIT ab.”

Slightly cephalad of this, and between it and the Acusticus,
another root can be distinguished, composed of fine fibres,
which are derived from a bundle representing the fasciculus
communis of Osborn (Pl. XI, Fig. 39). This was designated
“VII aa”’ in the Anzeiger abstract. It fuses with the first
root and these two ventral roots of the VII were, for con-

114 : STRONG. [Vou. X.

venience, together denominated the “‘ ventval V/J/,” a name, as
seen immediately below, not applicable to some other forms.
There is one remarkable peculiarity in connection with this
root in the larvae and adults of Anura as contrasted with
Urodela. In the -latter, as described by Osborn in Crypto-
branchus, its exit is just dorsal to the Acusticus, while in the
former, as described above, its exit is just ventral to the Acus-
ticus. This transference is probably connected with the change
in position of the Acusticus as noted above.

These two roots fuse with the ventral side of the root of the
VIII so closely that tracing them in the tadpole is a matter of
some difficulty.

The Acusticus shows the division into dorsal and ventral
roots described by K6oppen (35). In the caudal part of the
former the fibres are smaller than those of the latter, which
are of varying sizes but contain some very large fibres. The
fibres of the dorsal root proceed obliquely ectad and ventrad,
and immediately pass within the auditory capsule and enter the
posterior portion of the auditory ganglion, which is composed
of small ganglion cells. The dorsal part of the ganglion
further cephalad, however, becomes composed of large gan-
glion cells which supply the coarser fibres of the auditory
branches. The posterior branch of the VIII consists of both
coarse and smaller fibres, as does the anterior, but the latter
branch seems to contain a larger proportion of coarse fibres.
The larger part of the dorsal root of the VIII seems to supply
the posterior auditory branch and the larger part of the ventral
root the anterior branch. |

The most dorsal fibres, belonging apparently to the cephalic
portion of the VIII at its exit, separate from the VIII. They
form what was termed in the abstract the “dorsal VII’ or
“Vif hb. This reet'can be seen to; arise in’ partitrom abres
running longitudinally in the dorsal part of the medulla at this —
place. According to Osborn’s observations on Cryptobranchus
(45): they ultimately amse’ from, nuclei in this part ot the
medulla. It may be remarked here, however, that the con-
nection between ‘‘sensory’’ nuclei in the central nervous
system, such as those mentioned by Osborn, and the roots of

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. Il5

ganglionated nerves (as the root in question will be seen below
to be), must be considered now to be merely a physiological
and not an anatomical one. It is obvious, from more recent
investigations, that the only cells with which the fibres of
such roots are directly connected are those of the peripheral
ganglia belonging to these roots.

This being the case, it will be convenient to denominate
such internal nuclei, whose cells are not directly continuous
with the root fibres, ‘‘terminal nuclei,’ in distinction to those
nuclei whose cells are in direct continuity with root fibres
(ganglia of sensory roots and motor nuclei), which may be
called ‘nuclei of origin.” This distinction and terminology is
that adopted by Kolliker in his Gewebelehre (34) (“‘ Endkern”
and “ Ursprungskern”’).

In the tadpole it is difficult to determine whether some of the
acoustic fibres may not be similar to those of the dorsal VII.
From appearances in the tadpole, and from the fact that in the
frog the origin of a portion of the VIII is ascribed to similar
ganglion cells (Koppen), even from the mere fact of the per-
sistence of these cells after the disappearance of the dorsal
VII, this similarity might be inferred.

This root, the dorsal VII, already reduced in the tadpole,
disappears in adult Anura. The reasons for this disappearance
will become evident when its distribution is considered. It
may be well to point out here that this fact has caused some
confusion and apparent discrepancy in the accounts of the
Facialis by different observers, some of whom assert the origin
of the VII to be dorsal to the VIII, while others assert it to be
ventral. The latter refer to forms in which the dorsal VII has
disappeared; the former overlook the ventral portion of the
VII. Koppen (35), however, overlooking the ventral portion
in the frog, in which the dorsal root is lost, is obliged to look
for the VII in the Trigeminus. He is further misled by expect-
ing to find the Facialis a purely motor nerve.

At 852+ the ventral roots of the VII separate from the
VIII, the coarse-fibred root (VII 24) forming the outer and
lower portion of the bundle. The description of the dorsal
VII will be taken up first.

116 STRONG. [Vou. X.

The Dorsal VII («VII 6”).—When this separates from the
dorsal side of the VIII, a portion of the latter intervenes be-
tween it and the ventral VII (VII aa + VII ad). As the VIII
passes into the auditory capsule the V emerges from the
medulla, so that there is only a narrow space between the V
and the VIII. Into the upper part of this space the dorsal
VII is wedged; into the lower part the ventral VII (VII aa +
VII ad) (Pl. X, Fig. 25). The fibres of the ventral half of the
dorsal VII soon begin to bend ventrad, and at 842 separate
from the dorsal half. Caudad of this a few fibres pass ventro-
cephalad from this ventral half to unite with some fibres
detached from the ventral VII. The ventral half of the dorsal
VII, after its separation from the dorsal half, passes ventrad
between the V and VIII nerves, and comes to lie (832+)
immediately above the ventral VII, with which it unites. It
here lies immediately above the bundle of coarse fibres, VII a,
occupying the outer side of the ventral VII (Pl. X, Fig. 25).
The union of these two bundles now becomes so close that
they can only with some difficulty be distinguished; but the
course of their respective fibres can be stated with consider-
able certainty from three other grounds also, vzz., the distri-
bution of the dorsal half of the dorsal VII; the nature of the
fibres of certain branches in the distribution of the ventral
VII+ ¥% dorsal VII; and the relations of homologous bundles
in Amblystoma. Owing to the close relations of this portion
of the dorsal VII to the ventral VII its further course can,
however, be most conveniently described in connection with
the latter.

The dorsal half of the dorsal VII remains close to the V,
and as it proceeds cephalad comes gradually to lie immediately
above it. At 775 it becomes ganglionated, and at 751 divides
into two nearly equal parts.

The lower of these divisions (% VII 6,) passes ectad just
beneath the anterior extremity of the auditory capsule and
above the Gasserian ganglion. About here it gives off a twig
of a few fibres (1% VII 6,,, 732), which can be traced ectad to
lateral line sense organs lying in the skin some .15 mm. caudad
of the caudal surface of the eyeball.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 117

The main nerve, proceeding further ectad, soon gives off

another twig of several fibres (%4 VII 4,,, 727). This twig imme-
diately fuses with a fine-fibred twig, also very minute, which is
given off by the largest and outermost of the accessory tri-
geminal branches described above (p. 17) as issuing from the
anterior extremity of the Gasserian ganglion. These two
bundles of fibres thus brought together are distinguishable
from each other, owing to their difference in fibre calibre, and
soon separate, the trigeminal portion going caudad and dorsad,
and coming in contact temporarily with a division of the middle
of the accessory trigeminal twigs just above the outer edge of
the auditory capsule. The facial portion proceeds ectad and
has a distribution near and probably similar to the preceding
facial twig, though it could not be so clearly traced.
. The main nerve (% VII 8,) continuing ectad comes in contact
(726) with the outer of the accessory trigeminal branches.
This contact and temporary fusion is a peculiar one: the facial
passes through the trigeminal branch, each, however, seeming
to preserve its continuity. At this point of contact each gives
off a twig. That from the trigeminal portion is fine-fibred,
and fuses— temporarily, apparently —with the facial twig
(% VII @,,). The fibres of these very minute trigeminal twigs
are so fine that it is not possible to ascertain in ordinary prep-
arations whether some fibres may not remain with the facial
twigs. The main trigeminal branch now breaks up, and sup-
plies the skin of the region just ectad of the posterior surface
of the eyeball. The facial twig (1% VII 4,,) divides. One part
crosses and temporarily fuses with a trigeminal twig (700-687),
proceeding cephalad parallel with the principal facial branch.
Some of its fibres are traceable to a large lateral line sense-
organ in the epidermis, just below the cornea (625). The
remaining four fibres proceed further cephalad and innervate
a lateral line sense-organ cephalad of the latter and in a
similar position (588). The other part of this facial twig could
not be completely traced to lateral line sense-organs.

The main branch (%VII @,), after giving off these twigs,
bends forwards, proceeding cephalad under the eye. At intervals
it gives off small twigs of only a few fibres each. Many of these

118 STRONG. [VoL. X.

could not be traced into the lateral line sense-organs. When
this was the case, the cause must be sought in defects in the
preparations, especially where the twigs are so excessively min-
ute. It may be reasonably inferred that all of these twigs end
in these organs, whose line the main facial branch follows so
closely, especially as an organ is always found in the vicinity
of a twig though the complete connection be not present.
This branch can be followed, gradually diminishing owing to
the separation of twigs, nearly to the very anterior extremity
of the head.! |

Returning to the other subdivision of the dorsal VII
(%4 VII 6,, 751), this proceeds at first directly cephalad just
mesad of the lower part of the anterior extremity of the audi-
tory capsule, gradually leaving the Gasserian ganglion. As it
separates from the latter it receives a small, fine-fibred twig,
which can be traced around the Gasserian ganglion to the
sympathetic. Continuing cephalad and dorsad it is joined on
its ventral side (694) by the innermost of the three accessory
trigeminal branches. It here (687) gives off a twig from its
dorsal side which proceeds caudad and ectad (% VII 0,,) coming
in contact (717) with a division of the middle of the three
trigeminal branches, which proceeds to meet it. The sub-
divisions of the latter pursue courses in part parallel to twigs of
the facial, z.e., both proceed ectad and caudad, the facial supply-
ing one (or more) lateral sense-organs lying above the space
between the anterior extremity of the auditory capsule and the
posterior surface of the eyeball, and also above the latter.
Thus a part of the middle of these trigeminal branches is
connected with one subdivision of the dorsal VII, and another
part with the other subdivision (Pl. XII, A 2).

The innermost of these three trigeminal branches, after
coming in contact with the subdivision of the dorsal VII:
(14 VII 6,, 694), passes dorsad along the inner side of the
latter, fusing temporarily with it. From the ventral side of
the facial branch a portion of the latter separates. This branch

1 These sense organs in the tadpole, as is well known, are noticeable on the
exterior as rows of light dots. This appearance is owing to the absence of pig-

ment among their cells. They are not enclosed in canals, and each one is usually
slightly depressed.

MO: 1-] THE CRANIAL NERVES OF AMPHIBIA. I19

(3% VII 4,,) proceeds cephalad parallel to the main facial branch
and finally reunites with it (560), without having, apparently,
in the meanwhile, given off any fibres.

The main subdivision of the dorsal VII (% VII 6,) continues
cephalad along the dorsal surface of the head and inside the
eye to the extremity of the head. At intervals it gives off
twigs similar to those of the other subdivision; like them,
evidently supplying the line of lateral sense-organs in this
region.

The parallelisms in courses between the trigeminal and facial
twigs above described are very striking, and are often observed
even in very minute ramifications. The significance of these
parallelisms will be discussed below.

Somewhat more light is thrown upon the relations of these
trigeminal and facial branches by means of Golgi preparations.
The two facial branches, as they separate from the Gasserian
ganglion, seem to be composed exclusively of the coarse, heavily
medullated fibres so characteristic of them, nor do both, or even
one of them, always appear to receive directly a sympathetic
twig.

The trigeminal branches, however, contain, besides the
medullated fibres of varying sizes as already noted, a number of
fibres which do not appear to be medullated and are impreg-
nated. These appear to have rather the character of xervz
nervorum and some of them, at least, though apparently not all,
can be traced to the sympathetic. When fusions take place
with the facial branches, though the integrity of the two
branches is in the main preserved, yet a number of these fine
fibres pass from the trigeminal to the facial twig and join the
latter.

The ventral VII + ¥% the dorsal VII (Vilaa+Vilab+%
VII) consists, as above stated, of three components: one
(VII 2d), the most ventral in derivation, from a motor nucleus
(or the posterior longitudinal fasciculus or both), one (VII aa)
from the fasciculus communis and the third (% VII 4) from the
ventral half of the dorsal VII which later joins the two former.
Where the first two components are fused with the VIII the
ventral root (VII 2d) comes to occupy the outer position and

120 STRONG. [VOL. X.

forms a prominence on the ventral side of the Acusticus just
mesad of the foramen for the entrance of the posterior branch of
the latter into the auditory capsule. The ventral VII finally
separates from the Acusticus (852), occupying the position pre-
viously described (p. 116), and is joined by the ventral half of the
dorsal VII. This and what will be called hereafter the motor
root (VII 24) occupy the outer side of the nerve, the former
(% VII) lying above the latter (VII a4). The whole nerve
lies close to the ventral side of the Trigeminus in contact with
it but not completely fused with it, z.e., there is always visible
a line of demarcation between the two.

At 802+ the inner, fasciculus communis bundle (VII aa)
begins to slip ventrad past the other two so that the greater
part of it comes to lie below them instead of on their inner
side. It then soon becomes ganglionated (788). This ganglion
occupies the extreme ventral. part of the V+ VII, lying below
the other two facial components (% VII4 + VII ad). It
attains its greatest dimensions when the Gasserian ganglion
proper is just beginning to appear in the transverse sections,
z.e., one half of it lies caudad as well as ventrad of the Gasserian
ganglion proper. Its anterior part is fused with the ventral
side of the Gasserian ganglion, cephalad of 767, so that it is
somewhat difficult to distinguish between them at this point.
Finally the fibres of the fasciculus communis bundle are seen
emerging (760+) from the ventral part of the ganglion and
form the &. palatinus factalis. In about the same transverse
plane the other two components (% VII 4+ VII ad) begin to
pass ectad here from the Gasserian ganglion, a portion of them,
presumably that from the dorsal VII, which may now be called
the lateral line component, having first come into connection
with ganglion cells. They evidently separate, occupying the same
relative positions, z.2., the lateral line component uppermost. As
they separate from the ganglion these two components receive
on their ventral side a bundle from the ganglion of the fascic-
ulus communis component (VII aa, Pl. X, Fig. 26). The
branch of the Facialis thus constituted is the R. hyomandibu-
lavis. The R. palatinus VII is thus composed of the bulk of
the fasciculus communis component (with possibly the addition

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. ja |

of some trigeminal fibres and also of fibres from the sym-
pathetic), while the R. hyomandibularis comprises the ventral
half of the dorsal VII, the motor root and a part of the fascic-
ulus communis component (% VII 0+ VII aé-+ part of VII aa).
The possibility of its having also received some fibres, not
many, from the Trigeminus cannot be excluded, however, and
it also receives fibres from the sympathetic.

The course of the #. palatinus VII along the roof of the
pharynx is sufficiently indicated in the chart. There are some
features in its branching, however, which deserve special
attention.

At 400+ it gives off a branch which proceeds directly mesad
and innervates a curious fold which extends transversely across
the roof of the pharynx. This fold, which is described also by
F. E. Schulze (53), is directed cephalad and is partially con-
tinuous laterally with the surrounding pharyngeal epithelium so
as to forma shallow pocket opening anteriorly. This is the
way it appeared also in another tadpole examined macroscopi-
cally. In the two figures of this fold given (Pl. VIII, Figs. 8
and 10) one is taken from a section through its posterior part
so as to pass tangentially through its epithelium. The other is
from the next section cephalad. In other sections examined
this fold appears to be more free and to be directed posteriorly.
On and around the fold are a number of end buds (taste bulbs),
as are described below, which are innervated by the branch of
the R. palatinus just mentioned. This fold, as the figures seem
to demonstrate, is especially richly innervated. Nor is this due
merely to an inequality in the impregnation as is shown by the
presence of the branch from the main trunk, the largest branch
given off by the R. palatinus up to this point.

The location of this branch corresponds with that of the
vomerine teeth in the adult, possibly being slightly caudad of
the latter.

According to Wiedersheim, in the frog the epithelium in the
vicinity of these teeth is supplied with taste bulbs (quoted
in 17).

At the same place where the branch just described is given
off, another larger branch separates from the R. palatinus,

122 STRONG. [Vor. X.

proceeds cephalad and, turning ectad, becomes continuous with
a branch of the R. maxillaris V as already described (p. 111).
The remainder, much diminished, passes on cephalad and
becomes continuous with a branch of the R. ophthalmicus V
as already described (p. 108). :

From the nature of these curious anastomoses, it is difficult
to determine exactly where the Facialis ends and the Tri-
geminus begins. ‘Their significance lies, I believe, in the fact
that the R. palatinus VII, on the one hand, and the Rr. oph-
thalmicus and maxillaris V, on the other, innervate territories
morphologically distinct, and that in the region where these
fusions occur these two territories meet. In other words, they
occur just about on the boundary between the pharynx and the
stomodaeum. Of the part becoming continuous with the R.
ophthalmicus, it is not improbable that all which continues
cephalad beyond this commissure, though indicated as partly
composed of each element in the chart (g.v.), belongs to the
Trigeminus, and that the same is true of a considerable portion
of that which is caudad of this point of fusion. Along its
course this branch gives off a considerable number of fibres
which form a plexus around the openings of the posterior nares
into the pharynx. As a line drawn through the anterior part
of these openings would indicate the line of demarcation
between the stomodaeum and pharynx, it is not impossible that
these fibres represent the last fibres from the R. palatinus
proper, and that the remainder of the branch consists entirely
of fibres coming caudad from the R. ophthalmicus. A still
more minute study of this portion, however, would be neces-
sary to determine this point exactly, from observation, and the
possibility must also be admitted that the regions innervated
by fibres from the R. ophthalmicus V and the R. palatinus
VII, respectively, overlap to some extent. This, however,
would not impair the general validity of the view here put
forward as to the significance of these anastomoses.

What has been said above applies also to the anastomosis
between the R. palatinus VII and the R. maxillaris V. Here
again the exact delimitation of the R. palatinus cannot be
determined.

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 123

It may be remarked here that it would be extremely inter-
esting to study, from this point of view, the innervation of the
stomodaeum and pharynx of forms in which their relative
extents vary. Indeed, this will probably be necessary as sup-
plying one of the guides in reaching accurate knowledge of
the homologies of the nerves of this region in different forms,
and especially with the higher forms, where the relations are
so complicated.

The mode of branching of the R. palatinus VII in the adult
frog, and also its terminations in epithelium, glands, and blood
vessels, have already been described by Stirling and Macdonald
(60). These investigators made use of the gold method, and
it will be well to add some results obtained with the Golgi
method, especially as the endings in this region have not been
so fully described in the tadpole by Retzius (51), von Len-
hossék (38), and others, as in other forms.

The structures innervated are blood vessels, general epithe-
lium, glands, and end buds (taste bulbs). In the olfactory
region we have the mucous glands, which fall, in part at least,
in the trigeminal territory. My impregnations, however, have
not demonstrated much respecting the innervation of these
glands, merely showing some scattered fibres coursing around
their periphery.

Vaso-motor fibres, following the blood vessels and often
ending in their walls with little knob-like expansions, are
met with here and there. Whether these vaso-motor fibres
come merely from sympathetic fibres mixed with those of the
R. palatinus proper, or also from the latter, it is hardly possible
to determine. Stirling and Macdonald have described nerve
cells in this region with spiral fibres. I have also occasionally
met with nerve cells, though whether of this type or not I
could hardly determine.

Before treating further of the finer terminations of this nerve,
and in order to make clearer some points mentioned below
respecting the terminations of other nerves, it may be well to
indicate briefly the structures found in this region. These
have been described so clearly and admirably by F. E. Schulze
(53) that I cannot do better than give a brief résumé of a

124 STRONG. [VOL. X.

portion of his description. Schulze divides the roof of the
stomodaeo-pharyngeal cavity into five regions. These regions
are demarcated by certain folds and elevations or papillae.
The anterior region or field is that portion lying in front of the
transverse fold already mentioned; the middle field, free from
any high papillae, is bounded in front by the transverse fold,
laterally by a row of high papillae, and posteriorly by a fold.
On each side of it are the lateral fields characterized by the
presence of high papillae. The fold which forms the posterior
boundary of the middle and lateral fields has a scalloped out-
line and extends transversely across the cavity. Behind it is
the posterior field, in which the character of the epithelium
changes, being destitute of papillae and studded anteriorly
with “multicellular glands,” as they are designated by Schulze.
Posteriorly this epithelium merges into the oesophageal epithe-
lium. The papillae are elevations of the epithelium, the
interior being composed of connective tissue, and they bear
one or more ‘taste bulbs.” The latter are found as well
between the papillae, and also, according to my observations at
least, in the posterior field. The multicellular glands are com-
posed of a number of appressed elongated cells forming a cup-
shaped structure whose concavity forms a shallow depression
in the epithelial surface, and whose convexity projects slightly
into the subepithelial connective tissue.

The floor of the stomodaeo-pharyngeal cavity is divided,
according to Schulze, into five similar regions, the rudiment of
the tongue marking the boundary between the anterior and
middle fields. Here also is a similar transverse scalloped fold
marking off the posterior field. In the posterior field the gill
cavity opens and is partly covered by the folds formed by the
posterior field, z.e., the anterior and posterior velar folds
(‘“‘ Kiemendeckplatten’”’). On these folds the above mentioned
glands are so numerous that they form a continuous layer
without intervening indifferent epithelium, a condition which is
approached also on the posterior field of the roof in places. It
is on the edges and under side of the velar folds that these
glands are so numerous, and I may add, from my own observa-
tions, that those on the roof of the pharynx are so grouped as

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 125

to be most numerous always over the opening into the gill
cavity. In those parts of the roof not directly above this open-
ing they immediately dwindle away.

The nerve fibres, in my preparations, form beneath the
epithelium a dense plexus from which fibres pass upward into
the epithelium. In the thinner, indifferent epithelium, which
seems usually to be the least richly innervated, they run among
the cells irregularly, but do not as a rule seem to penetrate
more than about two-thirds through its thickness towards the
surface.

A number of nerve fibres approach the base of the ¢aste
bulbs and there break up, forming a dense structure (Pl. IX,
Figs. 15, 16, and 24), often, apparently, more of a granular than
fibrous character, and at times staining less black than the
nerve fibres. This structure evidently corresponds with that
described by von Lenhossék in fishes (38) and termed by him
the cupula. From this structure nerve fibres arise which
ramify around the bud, often rising nearly to its peripheral
surface. Whether they also penetrate between the cells of the
bud it is rather difficult to determine.

The nerve fibres passing immediately below the multicellular
glands send at right angles vertical fibres up into them or close
around them. The course of these fibres varies somewhat.
In some preparations they rise nearly parallel with each other
almost to the very surface of the epithelium where they end
in little knobs either among the cells of the bud or immediately
around them (Pl. IX, Fig. 17). In other cases the fibres rise
more irregularly, and when they have penetrated into the upper
third of the epithelium they turn and branch so as to form
a dense ring-like plexus apparently encircling or penetrating
the gland at this level. From this plexus a number of nearly
parallel fibres pass upwards converging towards the central axis
of the gland and end in enlargements in or very near the
Suriace of the epithelium (Fl. .1X, Figs..fa@-and) 1g). I am
inclined to believe that the latter fibres, at any rate, penetrate
into the gland near its free surface. Transitional forms are
abundant where the fibres from the subepithelial plexus pass
upward more as in the first mode of termination, but branch

120 STRONG. [Vot. X.

near the surface to a certain extent before terminating (Figs.
20 and 21). These terminations are often not simply rounded
knobs but have a more elongated club shape and are somewhat
irregular in outline (Figs. 18-21). As a number of fibres press
in from all sides towards the centre of the depression in the
epithelium formed by the gland, this locality is quite filled with
these bodies. The irregularity and size of these enlarged ter-
minations may be due to some irregularity in the staining, but
since they occur often in the cleanest impregnations and since
expansions of even greater size exist elsewhere, ¢.¢., in termina-
tions in muscles, they may be considered true pictures.

These appearances in the glands seem to me to be not easily
reconcilable with Dogiel’s (14) denial of free endings and
assertion of the prevalence of a closed network as the terminal
apparatus. It is, of course, possible that these enlargements
which lie immediately below the surface, almost in it, are not
the final terminations and that there are always, ¢.g., unstained
transverse fibres connecting them and forming closed meshes.
It is also true that the various methods of staining nerve fibres,
especially the Golgi method, are irregular and incomplete in
their action, yet it is not likely that the latter would always omit
certain fibres such as these hypothetical ones. The manner in
which these fibres terminate negatives still more strongly their
existence. That true anastomoses may occur is not to be
denied and sometimes the appearances favor their existence
(vide supra) but they can hardly be of universal occurrence.
Neither physiologically nor embryologically would there seem
to be any special reason for their existence in such peripheral
structures as epithelium, though they might easily occur now
and then owing to secondary fusions.

The 2. hyomandibularis factalts, as described above, leaves
the Gasserian ganglion at about the same transverse plane as
the R. palatinus (760+). As it leaves, it is composed, as has
been seen above, of three components, occupying the nerve in
the following order: The most dorsal is the dorsal VII com-
ponent (1% VII 2); next to this is the motor component (VII ad);

and most ventral is the fasciculus communis component (VII aa) |

(Pl. X, Fig. 26). The destination of the first and last compo-

es

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. b2y7

nents can be traced with certainty ; that of the second one is
not so easily made out, as will be seen below. This is partly
owing to the fact that the fibres of VII 4 are remarkable for
their uniform coarseness and heavy medullary sheath, and those
of ViIlaa for their fineness and very thin sheath. On the
other hand, those of VII aé, though tolerably coarse and well
sheathed, do not possess such well-marked characteristics.

As the R. hyomandibularis proceeds ectad, flattened out
under the quadrate, VII aa comes to occupy the inner side of
the nerve, .next to VII ad, while outermost is VII 4, which also
overlies VIIa@é. This is about their relation when joined by
the communicating branch from the IX+X (690), and is
shown in Fig. 27. This latter branch occupies, as is seen in
the figure, the outer third of the joint nerve. It is composed
of mixed fibres, similar to those of the Trigeminus.

As the R. hyomandibularis emerges from beneath the car-
tilage it acquires a round outline, as seen in transverse section,
but the relations of the components are much the same, except
that the portion from the IX + X takes up a somewhat more
dorsal position, pushing mesad ¥% VII. In Fig. 29 a
small twig is seen leaving the ventral side of the nerve and
deriving its fibres from VII ad (483). This twig passes ectad
close under the nerve, and after proceeding cephalad a short
distance enters a vertical muscle just outside the nerve, which
is identified as the M. orbitohyoideus described by F. E. Schulze
(54). A twisting and flattening of the nerve now takes place,
so that the positions seen in Fig. 30 are assumed. VIlIaa is
now uppermost, % VII and VII ad next, while the compo-
nent from the IX+X is ventral. Along in this part of the
nerve it is at times difficult, for the reasons mentioned above,
to trace VII ad. There is little doubt, however, but that its
course is as given here.

As indicated in Fig. 30, the nerve divides into two parts.
The ventral of these two divisions, the R. hyotdeus, is com-
posed largely of fibres from the IX +X, with the addition of
a bundle from VIIa@é. It proceeds ventrad (433) and caudad
through the M. orbitohyoideus, and then turns mesad. It then
divides (508), as indicated in the chart, one part supplying the

128 STRONG. [VoL. X.

M. mylohyoideus posterior (=submaxillaris post. = intermaxil-
laris post.=subhyoideus) and the other supplying the skin
below this muscle. There is, thus, quite a marked resem-
blance to the branch of the R. mandibularis V which innervates
the M. mylohyoideus anterior and the skin below it. The
R. hyoideus, however, is composed of fibres from ¢wo nerves,
the VII and the IX.

While it is difficult to distinguish the two sets of fibres in
the R. hyoideus VII, yet it is probable, from direct observation
alone, that the fibres from VII ad are those which innervate
the muscle.

It is obvious from the preceding that the cutaneous part of
the R. hyoideus does not belong to the lateral line system of
nerves to the head, and belonging to the VII. As this cutane-
ous component is derived from the IX + X, it will be further
treated below.

The remainder of the R. hyomandibularis proceeds cephalad,
and soon divides again (368). Of these two divisions the ven-
tral one comprises the remainder of the communicating branch
from the IX+ X and ¥% VII4, while the dorsal one comprises
the remainder of VII ad and all of VII aa (fasciculus communis).
The former is the R. mandibularis externus. It proceeds ven-
trad just inside the M.orbitohyoideus. The bulk of the coarse
fibres belonging to % VII0O have become aggregated on its
outer side. As the nerve emerges on the ventral side of the
muscle it becomes divided into two branches, an inner and
lower (mand. ex. a), composed of the finer fibres of the IX+ X
component, together with a few coarse fibres, and an outer
branch (mand. ex. 6) comprising the coarse fibres of % VII4,
together with a portion also of the finer fibres of the commu-
nicating branch from the IX + X.

The former of these two branches (mand. ex. a) sends off a
small twig, which is reénforced by fibres from the other branch,
and supplies the skin. The remainder, in every way resembling
the cutaneous portion of the R. hyoideus, proceeds caudad and
ventrad, and is distributed to the skin of the ventro-lateral
aspect of the body in this region. No connection was observed
between it and lateralsenseorgans. Itisa “general cutaneous”

Now rR. THE CRANIAL NERVES OF AMPHIBIA. I29

branch. This branch is probably the representative of the
R. auricularis VII in the frog (17).

The latter of these two branches, z.e., the outer (mand. ex. 0)
soon divides. The upper (dorsal) of these two subdivisions
(mand. ex. 4,) gives off twigs, containing the smaller fibres, to
the skin. The bulk of the remainder, consisting of coarse
fibres, proceeds caudad, supplying a line of lateral sense organs
along the side of the head ventrad to those under the eye. The
larger ventral subdivision (mand. ex 6,) proceeds caudad, par-
allel with the other, apparently supplying no lateral sense
organs until the dorsal subdivision has terminated. It also
appears to gradually lose its finer fibres. It divides at 585.
One part, proceeding caudad and dorsad, supplies lateral sense
organs with its coarse fibres. The other part proceeds caudad
and ventrad to about 800, where it bends mesad, proceeds
transversely across the ventral aspect of the body, and proba-
bly supplies a line of lateral sense organs present in this region.
There is, in addition to these branches of the R. mandibularis
externus, a small branch (mand. ex. c) which proceeds cephalad,
turning ventrad and caudad, as indicated in the chart.

The dorsal of the three principal divisions of the R. hyoman-
dibularis divides. The ventral of these two divisions contains
nearly all the remaining fibres of VII ad, and soon enters
(357-346) the two muscles lying just mesad of the nerve. A
few of the coarse fibres of VII ad remaining with the dorsal
(fasciculus communis) division separate and also enter these
muscles. Of these two muscles, one is identified as repre-
senting the Mm. suspensorio-angularis and quadrato-angularis
described by Schulze (54). It appears to be one muscle here,
though there are some evidences of a separation into two.
The other muscle is the cerato-hyo-angularis of Schulze.
The behavior of these two sharply contrasted bundles of fibres
(VII aa and VII aé) and the manner in which the coarse ones
are, as it were, picked out to innervate the muscles, is very
interesting and instructive. The remainder of the dorsal
division of the R. hyomandibularis consists now of a bundle of
fine, lightly-staining fibres, among which are a number of deeply-
stained but small fibres. By tracing it out we have seen that

130 STRONG. [VOL. X.

this bundle represents the fasciculus communis component.
When it separates from the R. hyomandibularis it is the
R. mandibularis internus facialts. ‘This nerve now proceeds
cephalad and bends mesad under the quadrate (310 +) to the
angle of the pharynx. It proceeds cephalad along the pharynx,
supplying some fibres to its mucous membrane. Its main dis-
tribution is not general, however, but is principally to one
locality. This is shown in Pl. VIII, Fig. 11. A great number
of the fibres are here seen to supply a large papilla or eleva-
tion of the epithelium about at the boundary between the
pharynx and mouth. A number of fibres proceed mesad to
innervate the floor of the pharyngo-oral cavity. This is in the
same transverse plane as the location of the future tongue, as
is shown by the N. hypoglossus and R. lingualis glossopharyn-
gaei. I have examined sections of the frog also, with reference
to this point, and find that the termination of this nerve, the
R. mandibularis internus facialis, is in the region of the
anterior part of the attachment of the tongue, and that a part
of it, at least, seems to send branches into the anterior part of
the tongue itself.

It may be well to point out here that these observations
confirm, in most respects, what would be considered a priovi
as the most probable destinations of these components. As
the dorsal division of the dorsal VII (VII 4) was found to
supply sense organs of the lateral line system, a similar destina-
tion would be the natural supposition respecting the distribution
of that ventral portion going over into the R. hyomandibularis.
Again, as one portion of the fasciculus communis component
(VII aa) was found to be distributed, as the R. palatinus VII,
to the roof of the pharynx, it is most consistent that the
portion entering the R. hyomandibularis should likewise supply
a portion of the pharynx. By elimination merely, this would
leave the third component, z.¢., the motor root (VII ad), and
also the R. communicans IX ad VII to supply the general
cutaneous (z.¢., cutaneous excluding the specialized lateral line
system) and motor branches. VII ad has the position and
characteristics of a motor root, and is the one which would be
considered most likely to enter the motor branches. In this

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 131

connection an observation of Volkmann (64) may be cited.
Volkmann found, by stimulation, that the communicating
branch from the IX + X did not contain motor fibres.

These observations are partially checked in another way by
a most beautiful extirpation experiment performed by nature.
In the frog the lateral line system of sense organs disappears
and, as I have verified myself in the common frog, in the toad,
and in one of the Hylidae, the dorsal VII (VII 4) disappears
also. Consequently the various rami (see table below) derived
from this root are wanting in these forms, but on the other
hand, such cutaneous branches as do not belong to this system
persist. Accordingly we find in the frog, for example, a
cutaneous branch from the R. hyoideus. Furthermore, this
affords a firm basis in determining the R. auricularis VII (17)
and in excluding, as possible homologues, those cutaneous
branches derived from the dorsal VII.

The question of certain homologies is discussed in another
portion of this paper. Some, however, are assumed in the
table given here, which presents in a convenient form an
analytical summary of the N. facialis.

I may add that an examination of serial sections through the
brain and proximal portions of the nerves of the frog, stained
by Weigert’s method, show very clearly the two components
of the VII, before joining the V, namely, on the outer side
the coarse-fibred motor part and mesad the fine-fibred fasciculus
communis component. Although somewhat out of place here,
it may be remarked that a bundle of fibres can be traced in
the V which preserve their integrity through the Gasserian
ganglion entering the R. mandibularis, and which, tracing them
proximad, appear to be derived from the motor root of the V.

In Amblystoma larvae the relations of these roots are some-
what different. They are shown in the figure occupying the
corner of the chart (Pl. XII, C). Here the principal differ-
ence lies in the fact that the VII is not pushed forward into
the V. There are also other differences: in the Amblystoma
larva the dorsal VII is considerably larger than in the tadpole,
while the Auditory is smaller relatively, not only to the dorsal
VII but to the medulla. Furthermore, it is separated from

132 STRONG. [Vor. X.

the dorsal VII by an interval; and in that interval, and dorsal
to the Auditory, emerges the fasciculus communis root.

“In Amblystoma (Pl. XII, C) the fasciculus communis com-
ponent of the VII, shortly after emerging from the medulla,
enters a ganglion lying partly under the anterior extremity of
the auditory ganglion and partly anterior to it. From the
anterior end of this ganglion emerges the R. palatinus, which
then dips downwards piercing the roof of the mouth and pro-
ceeding forwards along the latter. Laterally to this and also
from the ganglion near its extremity, a small branch is given
off which passes directly outwards and forms the most ventral
portion of the trunk of the VII. It soon separates, proceeding
outwards and downwards to the side of the oral cavity, where it
proceeds forwards along it and along the inner side of the lower
jaw. It is thus in every respect, except that it is not pushed
forwards into the V, identical with the R. mandibularis of
Anura, thereby confirming the view that the latter is derived
from the fasciculus communis.

“The ventral root, or rootlets, of the VII (VII ad) could, in
part at least, be traced out, and forms the portion of the trunk
of the VII, as it passes outwards, which lies immediately above
the fasciculus communis branch just described. Though fused
with the latter and with a part of the dorsal VII (VII 4) men-
tioned below, it can yet be traced continuously until it likewise
separates and is distributed to the Mm. digastricus and mylo-
hyoideus posterior, corresponding to the motor branches of the
R. hyomandibularis in Anura, and showing the derivation
inferred for them in the latter to be correct.

“The dorsal VII (VII 4) divides soon after its exit, part
passing directly cephalad along the dorsal side of the Gasserian
ganglion. It is here this part enters its ganglion, which is
fused with the Gasserian ganglion proper. ‘The ventral half of
the dorsal VII passes downwards as well as forwards, and then
bends outwards directly under the auditory capsule and just
anterior to the entrance of the anterior branch of the VII into
the capsule. It here fuses with the other components of the
VII mentioned, forming the dorsal part of the trunk. In this
part of its course and under the outer edge of the auditory

THE CRANIAL NERVES OF AMPHIBIA. 133

No. 1.]

ee ee ee ee

Veo JO\AQUITOEA UD UTS) | Se REI TMOMIE Ny
‘1ol193sod snoplofyorAur "J jo pesjuea uryG | * - + + - *snaproky yf Jo oe b aero Ree
; youriq Ssuryeotunuruos
‘ror1eysod sneptodyojAui "| * * + * + *sneprokyy jozred |- + + * 4001 10}0;q
‘sliejnsue-oAy-07e109 pue ‘Sue

-oyerpenb ‘srrejnsue-orosuedsns ‘snoprofyoyqio ‘wy | + + + + + * * poweujou'ry |* ° + * 4001 10;074 sliejnqipuewoty “y

‘xudreyd 1orieyue jo 100, | * * * * snusozur suenqrpuew yy | * stunuUIOD snqnoroseg

‘w[no1edo pue vjnqipueul ‘suvsi0 suas [erayey | ~ ° * *snuso}xXe ste[nqripuemy |* * * TTA [esiop %

‘NOLLAGIYLSIG “SHHONVUG ‘SLNANOUWOD

‘(2 °b) sisejnqipueMioAy, yy Jo qred |< = + == = (gn 77 ,) Joor 1010TN

‘(2 °d) stxepnqtpuewoXky “y Jo y1ed

snuneyed a (oP TTA ‘poyeuorsues) stunurmios sn{nosey

‘xuAreyd jo jzooy

‘(2°6) stretnqipuewoky “y joyred | - * - (payeuors
-ues) jyey yerjue, ‘z
‘sued10 9suas JO dUT] [eyqso-eAjU] | * * * * * * sayouerq q[eUIS (9 ILA) ILA Tesiod
Jayjyo pue snoijo ‘y ‘syeoonq yr] * * * = (pazeuors

‘suesI0 osuas Jo our] [eyqro-eidng | * ITA steysedns snowyeyzydo -y)| -ue8) jpey yesioq °1

‘NOILAGIUISIG ‘SHHONVUG ‘(SINANOdWOD) SLOOY

‘SITVIOV,Y AHL dO AUVWWAS IVOILAIVNY

134 STRONG. [VOL. X.

capsule it passes into its ganglion, composed of large ganglion
cells. It is a cutaneous nerve; and probably, as in the tadpole,
supplies the lateral sense-organs. These are here more irregu-
larly arranged.

‘‘Thus the dorsal VII has two ganglia, one on each of its
two main divisions, while the fasciculus communis component
has one at its point of forking. The motor portion (VII ad) is,
of course, non-ganglionated.’’— Quoted from (62).

The Abducens.— As this nerve enters into close relations
with the VII and V, that part of its course connected with
them will be described here. It makes its exit from the ven-
tral side of the medulla in the same transverse plane as the
exit of the second root of the IX +X. It proceeds ectad and
curves cephalad lying a short distance mesad of the sympa-
thetic nerve. At 912 it crosses the sympathetic, now lying
ectad of the latter. At 806 it comes in contact with the ventral
side of the VII. It is imbedded in the mesal side of the ganglion
of the fasciculus communis component of the VII. Emerging
from the anterior end of this it separates from the R. palatinus
VIl as the latter passes ventrad through the roof of the mouth,
lying immediately above the R. palatinus (747+) and below the
ganglion of the R. ophthalmicus trigemini. It now unites with
the ventral side of the R. ophthalmicus trigemini (734), slipping
around to the outer side of the latter. There seem to be
ganglion cells in connection with it (703), although these may
belong to the oculomotor nerve. The VI leaves the R. ophthal-
micus (697), and divides, the larger part proceeding cephalad
and ectad to the M. rectus externus, which it innervates.

It may be as well to restate here concisely the relation to the
Gasserian ganglion proper of the various nerves and ganglia
which are connected with it.

Running along the dorsal side of the Gasserian ganglion
proper is the dorsal half of the dorsal VII. Its ganglion is
fused with the dorsal side of the Gasserian ganglion. Next,
ventrally, are the ganglia of the Rr. maxillo-mandibularis and
ophthalmicus trigemini, which compose the great bulk of this
ganglionic mass, and constitute the Gasserian ganglion proper.
The ophthalmic portion — mostly indistinguishable from the

Nome 222 eChAWAE NERVES “OF “AMPITIBIA. 135

other — seems to occupy more the anterior portion of the
ventral side. Occupying the posterior portion of the ventral
side we have the ganglion of the fasciculus communis compo-
nent of the VII, from which come the R. palatinus VII and the
smaller branch which goes over into the R. hyomandibularis
VII. In the outer side of the whole ganglion, and between
the Gasserian ganglion proper and the ganglion of the fasci-
culus communis component, there are ganglion cells which
must be regarded as constituting the ganglion of the ventral
half of the dorsal VII, which subsequently forms part of the
R. hyomandibularis. Besides these ganglia, we have also non-
ganglionated bundles of fibres. There is the bundle of motor
fibres. of the portio minor of the Trigeminus, passing through
the Gasserian ganglion. There is also the motor bundle of the
VII which passes, with the ventral half of the dorsal VII,
through the outer side of the ganglion. The course of the
Abducens has been described. It is in the lower part of the
inner side of the whole ganglion. Finally, there are sympa-
thetic twigs which join the various branches emerging from
this ganglionic complex (see pp. 118, I19, and 151).

3. Lhe Glossopharyngeus and Vagus.

The determination of the composition of these nerves
presents considerable difficulty in the tadpole, principally
because of the manner in which they are, as it were, pushed
together and out of position by the auditory capsule. Fol-
lowing the different roots through the ganglia accurately can
hardly be accomplished, yet I believe the general nature of
these ganglia is as described below. Some of the peripheral
branches also have not been traced as completely as could be
desired.

Five roots can usually be distinguished composing the
IX-+ X. They are represented on the chart somewhat spread
out, in some particulars, for clearness. The first root, z.e., that
one most cephalad, emerges from the medulla at 911. It
leaves the medulla at a more dorsal level than the other roots
and, as seen in the chart, as it approaches the medulla it

1 36 STRONG. [Vo. X.

curves cephalad. The fibres of this root are exclusively coarse,
very uniform in size, and apparently have an internal origin
similar to those of the dorsal VII, which they resemble in every
way. At 926 it separates from the medulla and proceeds ecto-
caudo-ventrad a short distance when it is joined on its ventral
side by the second root of the IX + X.

The second root emerges from the medulla (936) at some in-
terval from the first and, as mentioned above, at a lower level
(Pl. XI, Fig. 37). The bulk of its fibres are derived from the
fasciculus communis. It is joined, however, on its ventral side
by a slender bundle of fibres which, as they penetrate further
into the medulla, curve ventrad and have an origin considerably
further inward and ventral to that of the rest of the root.
They, apparently, are connected with a group of cells, but no
actual continuity with processes of cells was observed. These
fibres are coarser than those from the fasciculus communis.
This is, undoubtedly, a motor rootlet and seems to be com-
parable in position and general characteristics with the motor
roots of the Trigeminus and Facialis. It is not represented in
Fig. 37, which is drawn from a Golgi preparation in which the
fibres of this ventral rootlet were not impregnated. As will be
observed in the figure, the fibres of this second root break
through the ascending Trigeminus tract in order to reach the
exterior.

The ¢hird root, preceded sometimes by a minute intermediate
rootlet, often emerges in close juxtaposition with the second
root. ‘This root has, at least, a threefold origin. As shown in
Fig. 36, the dorsal position of this root is derived from the
ascending tract of the Trigeminus. This derivation is, un-
doubtedly, contrary to the views generally held as to the origin
of the IX + X, but is, I believe, shown to be correct not only
by a study of the origin of the roots themselves but also by the
nature of certain of the branches of the IX + X as described
hereafter. As seen in Fig. 36, these fibres come from the
lower part of the ascending Trigeminus tract, while those
from the fasciculus communis descend on the inner side of
this tract in the medulla and, turning outward, emerge below,
forming another of the components of this root. This is in

No. 1.] TE (CRANIAL NERVES (Of AMPHIBIA. 13 /

contrast to the second root where these fibres passed through
the upper part of the ascending Trigeminus. In the Golgi
preparation, from which the figure is taken, a considerable
number of the fibres from the fasciculus communis are impreg-
nated and appear as straight, delicate fibres proceeding parallel
with each other and forming a compact bundle. Carmine
preparations show the same characteristic appearances for the
fibres from this source, and Weigert preparations of the frog’s
brain show that here these fibres, proceeding in a similar
manner, are fine and delicately sheathed. In the Golgi prepara-
tion only a small proportion of the fibres composing the bundle
from the ascending Trigeminus is impregnated, and these
exhibit a marked contrast to those from the fasciculus com-
munis. They are coarser, more varicose, and have a more
irregular, sinuous course. The bulk of this latter bundle issues
slightly cephalad of the bundle from the fasciculus communis.
In addition to these two components there is a more ventral
motor rootlet, similar to that emerging with the second root.
It is a possibility that some ascending Trigeminus fibres also
pass out with the second root, but this is not certain.

The fourth root is indicated in Fig. 35. It is separated bya
well-marked interval from the third root. Here, also, the fibres
from the fasciculus communis curve down, around, and below
the ascending Trigeminus in several compact bundles. No
fibres emerge from the ascending Trigeminus, and there is
present here, also, a ventral rootlet. As can be seen in the
figures, the bundles from the fasciculus communis entering
these roots diminish in bulk as we proceed caudad, z.e., those
entering the caudal roots are smaller. Emerging with the
ventral rootlet of the fourth root, and further caudad than the
other bundles, is sometimes to be seen still another very
minute bundle from the fasciculus communis.

The fifth root, emerging some distance caudad of the fourth
root, seems to derive its fibres from one source only. Its
fibres can be traced caudad in the medulla some distance
until lost among the longitudinal fibres of the lateral region of
the medulla. This is the bundle which Osborn has identified,
though erroneously as we shall see, with the fasciculus solitarius,

138 STRONG. [VoL. X.

and has traced it caudad into the lateral columns of the cord.
According to Osborn it contributes, in Cryptobranchus (45),
to at least two of the Vagus roots.

This root is very probably motor, but would appear to be
quite different in character from the ventral motor rootlets
mentioned above.

A further description of the fasciculus communis will be
found in another place in this paper.

All these roots now enter the vago-glossopharyngeal gan-
glionic complex. The general shape of this complex is indi-
cated in the chart. It curves around the posterior end of the
auditory capsule, as though pushed back by the extension of
the latter, a peculiarity probably due to the very anterior po-
sition of the gill clefts and other parts relatively to the auditory

capsule. The ganglion attached to its inner portion posteriorly.

is the sympathetic ganglion. It is drawn too large in the
chart.

It is not possible to trace the exact relations of the various
roots through this complex; yet, the composition of the latter
can, I think, be determined in a general way, and eae,
to throw considerable light upon its morphology.

In the first place, it appears that this complex falls into three
main divisions which are indicated by the shading in the chart.
The most proximal ganghonic division is connected with the
nerves before they pass around the hinder apex of the auditory
capsule. Immediately beyond this lies another ganglion, and
still further along, and quite upon the outside of the auditory
capsule, the third ganglion. It will be necessary to describe
the various branches of the IX + X before discussing the char-
acter of these three ganglia.

The first root, on account of its large fibres, can be readily
followed, and its destination may be finally treated here. Just
before entering the vago-glossopharyngeal ganglionic complex
it divides. The dorsal division (Z), remaining in the dorsal
part of the ganglion, curves around the auditory capsule and
separates. The ventral division (5) becomes separated from
the dorsal by an intervening bundle of fibres. It remains
longer in connection with other fibres of the IX + X, pro-

a i

No. I.] THE CRANIAL NERVES OF AMPHIBIA. I 39

ceeding cephalad for a distance after rounding the auditory
capsule, and then finally separates.

These two branches arising thus from the first root are the
lateral line nerves supplying the lateral line sense organs of the
body; (£) soon subdivides.

Besides these principal branches, a small bundle of fibres
separates from the ventral division of the first root while still
in the vago-glossopharyngeal complex. It proceeds cephalad
in the upper inner part of the IX + X trunk, separating as a
twig (5) at 897. It will be again treated in its proper place
below.

The ganglionated portion of this nerve appears to be in the
region of its forking, thus forming a part of the inner of the
three divisions of the vago-glossopharyngeal ganglionic complex,
though sometimes a few scattered ganglion cells are found
farther out along its course.

The remaining branches of the IX + X will now be described
in the order in which they separate from the ganglia, beginning
with those most caudal. The frst branch is the dorsal division
of the bundle from the first root (7), as described above.

The second branch (2) is the bundle interposed between the two
divisions of the first root. It consists of rather small or medium
fibres with a few large ones intermingled ; in other words, it
resembles those branches of the Trigeminus and the Hyo-
mandibularis, which we have seen to have a general cutaneous
distribution. It proceeds cephalad close to the auditory cap-
sule to 956, where it turns ecto-dorsad, and is distributed to
the skin dorsad and mesad of the caudal extremity of the
auditory capsule. It has no connection with lateral sense
organs. This branch is evidently the same as the one in the
frog, known as the R. cutaneus dorsalis. Thus the statement
made in Ecker’s Anatomy of the Frog (p. 174), that this branch
is the persistent portion of the R. lateralis vagi in the tadpole,
is erroneous. The supposition of Stannius and Fiirbringer,
there referred to, that it is the homologue of the R. auricularis,
is evidently correct —if by this it is meant that the Rr.
auricularis and cutaneus dorsalis in the frog are similar
branches. If it is meant that this branch is the homologue of

140 STRONG. Vier: x

the R. auricularis vagi of higher forms, this is also correct.
But this branch is not a part of the lateral line system.

Along this portion of the main trunk, the ganglion cells,
which are nearly or entirely absent from that part of the trunk
lying outside the apex of the auditory capsule (z.e., separated
by the tip of the capsule from the inner part in transverse
sections), increase in number, forming the second ganglion
mentioned. This ganglion, however, is confined to the outer
part of the trunk, and there is a large bundle of non-ganglion-
ated fibres running along just inside it and close to the auditory
capsule.

The ¢hzrd branch (3) separates from this outer ganglionated
part of the trunk (931-949) and proceeds ventrad, sloping
mesad and caudad (Pl. XI, Fig. 40). It contains ganglion cells
along its course, and finally, on a level with the oesophagus,
contains a considerable group of ganglion cells, meriting the
name ganglion. The fibres of this branch are principally fine
and many of them impregnate in Golgi preparations, as is
shown in the figure. Where the branch separates from the main
trunk, a small twig is given off from its dorsal side, as shown
in the figure, which apparently contains mixed fibres, some of
which innervate a blood vessel proceeding dorsad here (cuta-
neous artery ?) and some of which possibly innervate a muscle
just outside the auditory capsule.

Three principal branches proceed usually from the group of
ganglion cells. They proceed caudad, some giving off branches
to the oesophagus. Others were not traced completely, but
they are probably pulmonary or gastric branches. One branch
soon curves mesad and, proceeding cephalad, reaches the heart,
which it innervates. It is ganglionated on the auriculo-ventric-
ular septum (Bidder’s ganglion). From this ganglion the
nerve passes down along the ventricle, giving off innumerable
branches, which penetrate to every portion. The general
appearance of this plexus is indicated in Pl. IX, Fig. 14. As this
shows, there are also numerous fibres innervating the walls of
the auricles.

The third branch is the R#. vzsceralis.

In addition to these branches there are other minute twigs

———— a ee ee — —

No. 1.] TIPE CRANIAL WNERVES (OF AMPHIBIA. IA!

from the clump of ganglion cells mentioned above. One
branch, containing coarse and fine fibres, proceeds cephalad
and supplies, in part at least, one of the Mm. levatores arcuum
branchialium.

The fourth branch (4+ 5) from the main trunk emerges close
to the third, immediately cephalad of it. This really consists
of two branches, and immediately divides. The dorsal division
(5) is the ventral division of the first root, which has been
already described, and which separates here (929) to form one
of the Rr. laterales. The other division (4) consists of rather
large and small fibres intermingled. It immediately separates
from the R. lateralis, proceeds directly ventrad a short distance
and then bends cephalad. It divides at 938; the outer, smaller
division (4a), containing most of the coarse fibres, soon enters
the M. levator (?) lying just outside. The remainder (4 0) pro-
ceeds cephalad giving off a minute twig, which appears to enter
another M. levator (898). At 888 it divides again, the outer
subdivision (4 6,) apparently containing about all the remaining
coarse fibres. The inner subdivision (4 0,), the R. laryngeus,
turns mesad (882) and enters the laryngeal muscles (860 +).
The outer subdivision (4 6,) has a complicated and peculiar
course. It proceeds directly cephalad, coming to lie immedi-
ately above the heart. It now, still proceeding cephalad, slips
ventrad close beside the heart, and at 720 appears to give
off a fibre or two to a longitudinal muscle near it and near the
heart. It divides at 700, and the outer division at 550 + enters
a longitudinal muscle lying above it here. At 627 some fibres
which previously separated from the inner division go over to
the outer, which divides and innervates the muscle just men-
tioned. The remainder of the inner division finally unites with
the Hypoglossus, and cannot be followed further as a separate
bundle. None but motor branches were observed from the
Hypoglossus; and from this fact, as well as from the distribu-
tion of the outer division of this branch, that portion uniting
with the Hypoglossus may be inferred to have a motor distri-
bution. This muscle, or muscles, innervated, certainly corre-
spond, in part at least, to Schulze’s M. diaphragmato-branchialis
medialis.

142 STRONG. [VOL. X.

In Ecker’s Anatomy of the Frog, p. 183, it is said that “ Hoff-
mann describes a communicating branch of the Hypoglossus
to the ‘pneumogastric nerve,’ which the translator has not
been able to discover and which no other observer has men-
tioned.” It is quite probable that this is the corresponding
branch in the tadpole, thus partly verifying Hoffmann’s obser-
vation. In a tadpole examined in which the metamorphosis
had begun this branch did not unite with the Hypoglossus. It
appeared here to innervate possibly the M. interbranchialis also.
Whether it was concerned with the innervation of any of the
Mm. marginales could not be certainly determined. Branches
3, 4, 5,6, and 7 are given off practically together, and from
them some coarse fibres separate, forming the R. accessorius to
a capito-scapular muscle probably representing the M. cucul-
lanis \(=— Zia):

At the point of separation at 929 of the branch just
described, the trunk of the IX-+X consists of two portions.
The outer of these is mainly fine-fibred, but with some
coarse fibres also. It is still ganglionated, the ganglion cells
belonging apparently to the fine fibres. The inner portion is
described below. The outer ganglionated portion now bends
ventrad, separating from the inner, and divides (910) (6 and 7).
It here also loses its ganglion cells. The ventral. of the two
divisions (6) gives off two or three fine-fibred twigs, which
supply the epithelium of the outer angle of the pharynx in this
region and some distance cephalad. One of these twigs (6 6)
proceeds cephalad and at 759 gives off a twig which contains a
few ganglion cells and supplies the mucous membrane of the
pharynx ventral to it. At 757 the nerve contains a clump of
ganglion cells, and here divides. The inner part (6 0,) passes
mesad to the mucous membrane of the roof of the pharynx.
The outer part (6 4,) supplies the membrane of the roof of the
gill cavity, which opens into the pharynx here. The remainder
proceeds caudad to g19, around one of the Mm. levatores, and
bends cephalad under the latter, giving off a small twig (6c)
proceeding ectad, which could not be traced further. This twig
takes from the nerve the few coarse fibres it contained. There
is reason to believe (see p. 143) that this twig has finally a cutane-

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 143

ous distribution. The main nerve (6) now proceeds cephalad
under one of the gill bars, a blood-vessel lying below it. At
822 it sends a branch around outside the cartilage to its dorsal
side. At 788 the remainder assumes the same position. Its
distribution is partly to the gill-raker attached to the dorsal
side of the cartilage. Ganglion cells appear in it in places along
its course, especially as it nears the point where the gill mem-
brane is merged with the pharyngeal mucous membrane. Here
(690 +) the nerve lies in the floor of the pharynx, near the heart.
It breaks up here, part of it turning caudad, and all of it being
distributed, as far as could be observed, to the pharyngeal
epithelium. It is obviously a R. branchialis.

Returning to 910, the dorsal of the two divisions (7) receives
a short, reénforcing branch from the other, and proceeds
cephalad and ectad as far as 840 +, where it proceeds ventrad
along the dorsal and outer side of the blood-vessel and turns
caudad, still proceeding ventrad and thus rounding one of the
Mm. levatores, where it again turns cephalad. This nerve con-
tains two very large and prominent fibres. As it turns (870 +) it
gives off a twig (7 a) containing these two coarse fibres, together
with a number of smaller ones. It is evident that this twig
resembles the one (6c) given off from the preceding nerve,
which could not be traced. This twig is larger, however, and
can be traced to its distribution. It divides just subsequently
to its separation. One portion (74@,), containing one of the
coarse fibres, proceeds cephalad around the angle of the
branchial cavity, through a thin muscle in the body wall, and
thus becomes subcutaneous. It does not appear to give any
fibres to the muscle, and is distributed to the skin. This divi-
sion of the twig is thus probably of the ‘general cutaneous ’”’
type. The other division (7 @,) rounds the angle of the body
cavity at 777, and is in every way similar to7a@,. After giving
off this twig, the main nerve (7) passes under one of the gill
‘bars —the one next to the one under which the last-described
branch ran. At 807 a fibre or two comes off, which proceeds
ventrad, but could be traced only a few sections. At 767 a
small branch separates, which could be traced cephalad some
distance, running near a blood vessel. At 613 the nerve,

144 STRONG. [Vou x

having in the meanwhile, like the other, passed around to the
dorsal side of the cartilage and lying in the gill-raker attached,
bends mesad, nears the place of transition of the gill membrane
into pharyngeal epithelium, and rounds the extremity of a
small, pouch-like evagination, or pocket, of the pharyngeal
cavity, which projects anteriorly. The distribution of this
nerve seems to be in every respect similar to the preceding
one. It also contains ganglion cells. This branch is also
obviously a KR. bvanchialss.

At 923, at about the point of seperation of the last two
branches, the remainder of the trunk of the IX + X becomes
ganglionated. A wedge-shaped bundle in the outer central
portion of this part of the trunk consists exclusively, or nearly
so, of fine fibres, the other portions contain mixed fibres. The
ganglion cells are small and seem to be confined especially to
the fine-fibred portion.

At 897 a small twig (S) separates from the inner side of the
trunk. It is coarse-fibred, and proceeds ectad and cephalad
from under the edge of the auditory capsule and then turns
directly cephalad in the lowest, loose connective tissue, layer of
the skin. At 838 it divides. The two divisions proceed
cephalad and probably supply lateral sense organs, though only
traceable to their vicinity. Its fibres resemble those of the
other lateral line branches, and it is the portion which has been
described above (p. 139) as separating from the ventral division
of the lateral line bundle while in the vago-glossopharyngeal
complex. It is this small branch which has been described in
fishes by several observers as arising from the IX and innervat-
ing a canal organ, and which has been confused with the R.
cutaneus dorsalis (auricularis vagi) in the frog (vzde supra).
It may be called the R. supratemporalis.

At 854 the main trunk of the IX + X falls into two divisions.
The outer of these divisions (9) comprises the exclusively fine-
fibred bundle and a portion of the mixed fibres, viz., that portion
on the outer side of the fine fibres. The inner division (70)
comprises the remainder of the mixed fibres. The ganglion
cells still found in the outer division are in the fine fibred
portion.

No. I.] THE CRANIAL NERVES OF AMPHIBIA. I45

The outer division (9) soon subdivides ($52 +) into a lower or
ventral subdivision (9 2) composed of a portion of the fine fibres,
and an upper, or dorsal, and larger subdivision (9 0) composed
of the remainder of the fine fibres and the mixed fibres. The
lower subdivision (9a) proceeds along the roof of the pharynx
a considerable distance, giving fibres to it and to some portions
of the filtering apparatus. It finally turns meso-ventrad, runs
inward along the floor of the pharynx and supplies the
epithelium of the roof of the gill cavity. This branch is ob-
viously similar to those described previously (6 4, etc.) as
innervating other portions of the pharynx. It is one of the
Rr. pharynget.

The upper subdivision (90) (852) proceeds cephalad and
ectad, supplying fibres to the M. levator arcus branchialis in
its vicinity, and comes to lie outside the outer angle of the
pharynx. At 654 it turns ventrad, passing through a thin
muscle lying in the body wall, and divides (9 6, and 9 @,).

Before this division occurs, the fibres in the upper subdivision
(9 6) were so arranged that the mixed fibres occupied the outer
and the fine fibres the inner side of the nerve. When the
division takes place, however, the anterior, larger branch (9 0,)
receives the fine fibres and also a bundle of coarse fibres (with
sheaths deeply stained), and the posterior branch (9 0,) receives
mixed fibres.

The anterior, larger branch (90,) proceeds cephalad and
ventrad along near the inner side of the body wall, z.e., around
outside the gill cavity. It then bends cephalad, and again
mesad, around under the gill cavity. During this part of its
course the coarse fibres are very plainly seen occupying its
ventral side. The fine fibres constitute the bulk of the nerve.
Finally, as the nerve proceeds mesad the majority of the coarse
fibres separate out (530+). As they separate out (9 0,,) there
is a small group of ganglion cells apparently on the coarse-
fibred bundle. Some of the fibres of this branch innervate a
muscle which appears to correspond with Schulze’s M.
ceratohyobranchialis. Other fibres seem to merely scatter in
the loose connective tissue and could not be traced. This
apparent peculiarity was observed in more than one specimen.

146 STRONG. [Vou. X.

A few coarse fibres remaining in the main nerve soon
separate and appear to innervate a minute muscle lying near
the one previously described, and which might be identified as
Schulze’s M. basihyobranchialis. The main nerve (96,) then
proceeds cephalad in the floor of the pharynx, giving off twigs
to its epithelium. It finally terminates at the rudiment of the
tongue, taking at this point a sharp little turn mesad. This is,
of course, the R. léngualis glossopharynget.

Returning to 654, the posterior division (9 0,), consisting of
mixed fibres, proceeds caudad and ventrad along the inner side
of the body wall until at 740 + it curves, first ventrad and then
dorsad and ectad (ru-shaped), around the angle of a fold of the
body cavity wall and thus becomes subcutaneous. The bulk of
it proceeds cephalad and lies, at 698 +, near a lateral line branch.
It breaks up to supply the skin of this region and ventral to
this. It is at once apparent that this posterior branch is
similar to the two twigs (6c and 7a) given off by the two
previously described Vagus branches, one of which could be
traced to a cutaneous distribution.

Returning to 854, the other inner division of mixed fibres
(70) is the R. communicans ad factalem to the R. hyomandibu-
laris. Its final distribution is described in connection with the
latter, and it has there been found to be a general cutaneous
nerve.

Now that the branches have been described, their relations
to the ganglia may be made more intelligible. As described
above, the most distal ganglion (C), from which issues the R.
lingualis, belongs to the fine fibred portion of the nerve at this
point. The larger mixed fibres which pass off into the R.
communicans ad facialem and the cutaneous branches do not
appear to be ganglionated here. The majority of them form a
bundle on the inner side of the nerve next to the auditory
capsule. As we pass further proximad along the nerve trunk,
the fine fibres cease to be ganglionated and form the wedge-
shaped bundle mentioned, occupying the outer central part of
the trunk.

The proximal portion of this ganglion is slightly overlapped |
externally by the second ganglion (6). From the distal apex

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 147

of this ganglion emerges the Rr. branchiales, to whose fine
fibres this part of the ganglion belongs. This is apparently to
some extent distinct from the proximal part (B,) of the second
ganglion, being partially separated from the latter by the lateral
nerve issuing here. From this proximal part of the second gan-
glion (£,) the R. visceralis emerges. Along the inner side of
this ganglion also proceed the non-ganglionated fibres mentioned
above, together with additional fibres from the cutaneous and
motor branches which have in the interval been given off.
The fine-fibred R. visceralis must be in part, and perhaps is
mostly motor, yet it seems to be ganglionated. Whether it is
entirely ganglionated, however, could not be determined.

The innermost or proximal ganglion (A) belongs chiefly to
the cutaneous branches whose fibres, we have seen, pass by
mesad of the two distal ganglia, and also to the N. lateralis. The
former are in all probability derived from the ascending Trige-
minus. It is very probable, however, that some of the fine fibres,
especially, perhaps, those of the R. visceralis, are also gan-
glionated here.

These ganglia may be designated A, B, and C, as already
indicated, A being the most proximal one. #& may be sub-
divided into B1 and £2.

In the older tadpole above referred to (p. 142), the trunk of
the IX + X, after giving off 7 and just as it gives off 2, divides.
From the upper and outer division are given off 3, 4, 5, 0, and
7, from the lower and inner division are given off g and zo. As
in the other tadpoles, this latter division is ganglionated further
distally (ganglion C). The Rr. branchiales are reduced and the
R. visceralis has apparently increased.

It will be necessary now to describe some points in the finer
terminations of certain of these branches. The velar folds
mentioned above, a small portion of the filter apparatus, indif-
ferent epithelium, and also some taste bulbs, both on the roof
of the pharynx and on its floor in the region of the gill open-
ings, are innervated by the pharyngeal branches described
above. The innervation of the taste bulbs is as described
above under the R. palatinus VII. That of the glands, which
are so plentiful here, requires further notice on account of its

148 STRONG. [Vou. X.

remarkable richness. It is not unlikely that the appearances
may be exaggerated by inequalities of impregnation, but in
Golgi preparations all of this epithelium presents pictures
remarkably rich in nerve fibres. We have seen above (p. 124)
that the glands in this region are so numerous as to be prac-
tically continuous and not separated by indifferent epithelium.
In such places the superficial nerve plexus belonging to these
glands and described above (pp. 125, 126), naturally is also con-
tinuous, and there is consequently a dense plexus extending
throughout the superficial part of this epithelium. Its general
appearance is indicated in Pl. 1X, Fig. 23, and is still more dense
in preparations from a larger and probably older specimen.

The greater part of the filtering apparatus, and also the gills,
are innervated by the Rr. branchiales. There is a great differ-
ence in my preparations between the innervation of these two
structures. While in the former are demonstrated a great
number of fibres, very few are shown in the gills proper.
These latter fibres are very delicate and cannot usually be
followed very far into the gills. They proceed along with the
blood vessels and seem to be vaso-motor. It is not improbable
that the fibres in gills do not impregnate readily, and that the
supply is greater than the preparations would indicate.

Into the filtering apparatus bundles of fibres pass upward
from the Rr. branchiales. These pass along in the loose con-
nective tissue in the interior of these structures, send fibres
into the smaller subdivisions, or side-pockets, and fill these
with a snarl or tangle of fibres (Pl. VIII, Fig. 9). Endings
are frequently seen on these fibres in the shape of small gran-
ules, or sometimes, apparently, several granules. Sometimes
the two granular terminations of two fibres seem to meet each
other (%, Fig. 9). Very often these terminations are in the
very outer surface of the filament of the filtering apparatus.
The fibres do not usually, at any rate, anastomose.

These gill filters, together with the glandular epithelium
described above, evidently form an important apparatus, physi-
ologically. There would seem to be a physiological similarity
between these glands and those on the endostyle of Amphi-
OXUS.

THE CRANIAL NERVES OF AMPHIBIA. I49

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The preceding table of the roots and branches of the IX+ X
is given for clearness. It is imperfect in some particulars and
a number of points are assumed. The motor fibres especially
require further investigation, nor can the different roots be
followed through separately, if, indeed, they do remain sepa-
rate, which is not probable. Yet it will give, I believe, some
insight into the composition of this complex.

4. Lhe Sympathetec.

The general relations of the sympathetic to the vago-glosso-
pharyngeal and Gasserian ganglia may be quite briefly ex-
pressed. From the ganglion cervicale sympathicum (see chart)
one or more branches pass to the vago-glossopharyngeal gan-
glia. One twig especially can be traced curving around the
inner and then the dorsal side of the caudal apex of the inner
ganglion. The greater part of this twig unites with the R.
auricularis. Other minute twigs may be seen ramifying around
the ganglia and appear to pass off, in part, to the various
branches. I have not observed any especial supply to the R.
visceralis and the latter must be regarded as composed very
largely of fibres from the Vagus. The same probably applies
to its subdivision, the R. cardiacus.

From the various parts of the IX + X, especially the fine-
fibred portions of the trunk and branches, are often seen vaso-
motor fibres given off to blood vessels. Along these nerves
also, especially the R. visceralis and Rr. pharyngei, particularly
among their twigs, are found ganglion cells. These cells usu-
ally have a bipolar appearance, but when examined closely
one or both of their processes show here and there a splitting
indicating a multiple character (Pl. XI, Figs. 41, 42, and 43).
The process or processes from one end may supply a blood
vessel, as is beautifully shown in Pl. VIII, Fig. 13. At other
times it apparently innervates epithelium, though this is not so
certain. Whether all these vaso-motor fibres are derived from
the sympathetic, cannot be determined, but I regard it highly
probable that they are not, and that a proportion of them are
from the Vago-glossopharyngeus. This is what would be

No. I.] THE CRANIAL NERVES OF AMPHIBIA. I51

expected from the innervation of the heart. The ganglia in
the latter might be regarded as collections of the ganglion cells
just described.

The remainder of the sympathetic passes within the cranium
through the vago-glossopharyngeal exit and forwards to the
Gasserian ganglion. Its destination here has already been
partly described. It supplies the various branches from this
ganglion, as already mentioned by De Watteville (66). The
lateral line branches appear to be, at times, unsupplied. This
deficiency is possibly provided for by the smaller trigeminal
branches, as described already (p. 119), from which, apparently,
sympathetic fibres pass over into the lateral line branches.

Vaso-motor fibres can be seen at times coming from the
trigeminal branches, and they are derived from the fine,
probably non-medullated fibres, which are impregnated by
Golgi’s method, and which are seen in all the trigeminal
branches. I have not observed any ganglion cells in connec-
tion with these fibres. Whether they are partly or wholly
from the sympathetic, I have not determined.

5. Recapitulation of Nerve Components.

From the above description it is evident that we have in
each nerve the following components, distinguishable by the
nature of their fibres, their peripheral distribution and their
internal origin:

Trigeminus. — (a) What may be termed general cutaneous
fibres, z.¢., those supplying the skin exclusive of the specialized
lateral line sense organs. The majority of these fibres are small
but there are also among them a number of fibres of medium
size as well as some coarse fibres. The bulk of this component
is derived from the ascending trigeminal tract which is a
continuation of the dorsal columns of the spinal cord. The
ganglion (or ganglia) of this component is the ganglion of the
maxillo-mandibularis and ophthamicus trigemini, namely, the
Gasserian ganglion proper.

(0) Motor Fibres. — These are mainly coarse, innervate the
jaw muscles supplied by the Trigeminus, and are derived from
the trigeminal motor nucleus (and descending tract ?).

152 STRONG. [Vou se

Factalis. — (a) What may be termed speczal cutaneous fibres,
z.e., those innervating the specialized lateral line sense organs.
These fibres are uniformly coarse and enter the dorsal part of
the medulla. There are two ganglia belonging to this com-
ponent. One, the ganglion of the Rr. opthalmicus superficialis
and buccalis (and oticus) facialis, has its permanent position
above the Gasserian ganglion proper and in contact with it.
The other, the ganglion of the R. mandibularis externus VII,
is, in the tadpole, imbedded in the outer side of the Gasserian
ganglion, or rather between the latter and the ganglion of the
next mentioned component. In Amblystoma, however, this
ganglion has no relation to the Gasserian ganglion and lies
beneath the outer side of the auditory capsule ectad of
the ganglion of the next component and of the auditory
ganglion.

(6) What may be termed the fasciculus communis com-
ponent. This innervates the anterior portion of the pharynx.
This component is composed principally of very fine fibres with
a number of slightly larger fibres interspersed ; it is derived
from Osborn’s fasciculus communis. Further remarks upon
this tract and its distribution will be made elsewhere. This
component possesses one ganglion which is fused in the tadpole
with the ventral side of the caudal portion of the Gasserian gan-
glion proper. In Amblystoma, however, this ganglion has no
connection with the Gasserian and lies beneath the cephalic
end of the auditory ganglion.

(c) Motor fibres in part similar to Trigeminus (0) and in
part derived directly from the posterior longitudinal fasciculus
(Osborn).

Glossopharyngeus and Vagus. — (a) General cutaneous fibres
similar to Trigeminus (a) and derived from the ascending
Trigeminus. The ganglion of this component is a portion of
the mass of ganglion cells on the trunk of the IX+ X nearest
the medulla (ganglion A).

(0) Spectal cutaneous fibres similar to Facialis (2) in every
respect and passing into the Rr. laterales. The ganglion of
this component lies in the dorsal part of the ganglionic mass
just mentioned (z.¢., of ganglion A).

No. I.] THE CRANIAL NERVES OF AMPAHIBIA. 153

(c) Fasciculus communis fibres similar to Facialis (0), its
distribution being to the alimentary canal and its outgrowths
caudad of the area of distribution of Facialis (6). There seem
to be at least three ganglia belonging to this component, one
of these being a portion of the ganglionic mass mentioned (A)
and the other two the two ganglia lying farther out on the
trunk of the IX+X (ganglia B and C).

(2) Motor fibres probably similar to Trigeminus (6).

Besides the above there are other portions of the IX+xX
whose nature and position is not clear. One of these is the
“fasciculus solitarius’’ mentioned by Osborn, but erroneously
so called (vzde znfra, p. 186), and which is also present in the
tadpole. It is almost certainly motor.

Rearranging the above, we have at least four components:

I. General cutaneous, including V (a) and IX+ X (a).
II. Spectal cutaneous, or lateral line, including VII (a) and
IX X (0).

Ill. Fasciculus communis, including VII (6) and IX+ X (c).

IV. Motor, to branchial muscles (including jaw), including
V (0), VII (c), and IX+ X (@).

It is not to be supposed that this forms an exhaustive
analysis of these nerves. Reasons may easily be adduced
from this research, as well as from other sources, to show that
this analysis is not complete. It is carried as far as can be
conveniently done with the means employed, and will form a
basis for additional results in the future.

III. COMPARATIVE MORPHOLOGY OF THE COMPONENTS.

1. General Cutaneous.

General Cutaneous Component. — V (a) and IX+ X (a). The
part of the V belonging to this component is very constant
apparently in the vertebrate series. We find that the Trige-
minus has an ascending tract from the spinal cord in Petro-
myzon (Ahlborn), in Acipenser (Goronowitsch), in Selachians
(Rohon), and in Teleosts (Mayser, Wright). Furthermore, this
tract seems subject to less variation in size than other tracts
and the character of its fibres is about the same. As seen

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‘(soyetyoueiq touejnd -1y7) seyoueiq
yeryouviq oy} woz suljeredes sayouviq snosueynd jeraaas (¢)

‘(snutuesiy, Ssuipusose)
snosuejyng [e1euer)

STRONG.

‘(slizjnqipueur “y) Mel 1amo] pue pray jo apts -p

*(sue][Ixeur *yy) Tewqsovsuy +2 (‘essex uolsues)
‘iodoid (A1osuas) snutwesizy,

*(snorwmyeyiydo -y) deep ynq ‘feyquoeidns -¢ ‘A1oyIpnesig ‘|

‘JIqio opIsul soyouvlq [[eUIs [eIeAeS -v

‘aTAVL

154

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 155

hereafter, some portions of the medulla oblongata undergo
remarkable variations in size and development in the different
types and in this respect the tract under consideration seems
to stand in contrast. This is natural when it is considered
that it forms the supply to the skin exclusive of the specialized
cutaneous sense organs which are peculiar to certain types
only, or, at least, in certain types obtain a much greater
relative development.

Respecting the nature of this component there can be no
question, I think, that it is similar (homodynamous) to the
dorsal spinal roots, if internal origin, character of fibres and
their distribution are criteria of any weight. Its fibres are
a direct continuation of those in the posterior columns of the
cord, which they resemble, and are distributed to the skin
exclusive of any differentiations in the latter which belong
especially to the branchial region. This is also Gaskell’s view
(23 and 24).

It follows from this that the sensory Trigeminus is largely
equivalent to the dorsal spinal roots, minus, possibly, their
splanchnic fibres. Besides the Trigeminus, however, the same
component is represented in the vago-glossopharyngeal group,
and that to a greater extent than is commonly supposed. The
homology of what is here denominated the R. auricularis vagi
has already been touched upon. The branches, or branch,
which Stannius and others have homologized with the R.
auricularis vagi in higher forms, appear to be the supratemporal
branches to lateral-line organs. There is every reason to sup-
pose, however, that the lateral-line system of nerves completely
disappears in the higher forms, especially as the root which
supplies them disappears. One of these supratemporal branches
in the tadpole is described above. Consequently the homologue
of the R. auricularis vagi in higher forms must be the branch
in the tadpole which I have described above as the R. auricu-
laris, which has no connection with the lateral-line system
and belongs to the general cutaneous system. The question
arises, then, as to what is the homologue in /ower forms of the
R. auricularis vagi of the tadpole. JI may here simply say that
I believe that future investigation will bring out more clearly a

156 STRONG. [Vor. X.

system of general cutaneous branches in this region coexistent
with the lateral-line nerves. I have noticed in certain descrip-
tions that dorsal branches are described which the investigator
has been unable to trace to lateral sense-organs. Furthermore,
Shore (56), in his work on the vagus nerve in Selachians, has
described a dorsal cutaneous branch of medium fibres.

Ewart (18) also mentions a dorsal branch from the Glosso-
pharyngeus, immediately beyond its ganglion, which passes
upwards through the cranium to reach the skin over the audi-
tory region, and ‘‘which apparently does not assist in supplying
either mucous canals or sensory tubes.”’ We have, in addition
to this, one or two branches which separate from the lateral
nerve before its exit from the cranium to supply the aural and
part of the occipital mucous-canals, and which are homologous
with the minute twig from the lateral-line root in the tadpole
(S). Ewart and Mitchell further state (19): ‘The lateralis
nerve behind the first branchial cleft consists entirely of special
sensory, somatic fibres; in front it seems to be accompanied by
a few ordinary, sensory fibres, which reach the skin.”

It is possible that the R. meningeus and R. tympanicus in
human anatomy are also represented by some of these general
cutaneous branches in the tadpole, the R. tympanicus possibly
being represented by the R. communicans ad facialem.

A further inference may be made respecting the ganglia. It
has been seen above that the ganglionated portion of these gen-
eral cutaneous nerves lies in the most proximal ganglion (gan-
glion A). It would follow from this and from what has gone
before that this ganglion, or ganglia, would represent, in part
at least, the two proximal, or jugular, ganglia! of the IX+X.
This conclusion seems to be similar to Shore’s from his study
of Selachians (55 and 56).

By a comparison of the tadpole with the higher vertebrates
it would seem that there is a considerably larger supply of
these general cutaneous fibres, relatively, in the former than in
the latter. This is readily accounted for, I believe, by consider-

1 There appears to be some confusion in the nomenclature of these ganglia in
the text-books of human anatomy. It is not necessary to enter into this here,

however, and there need be no confusion if it is understood that the two proximal
ganglia on the IX + X are meant.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 157

ing the region thus innervated in the tadpole. It is in general
the opercular region; and when, with the loss of gills, ezc., it
either disappears or is largely reduced, the nerve supply is
correspondingly diminished. Thus in the higher forms we
have here not only a disappearance of the lateral-line nerves,
but a reduction of the general cutaneous nerves of this region.

The homologies of the R. communicans ad facialem present
considerable difficulty. In Petromyzon we have a branch,
described by Ahlborn and others, which runs around outside
the auditory capsule and connects the VII with the IX + X.
This branch, however, belongs, according to the observations of
Ahlborn, Dohrn (15), and others, to the lateral-line system, and,
consequently, cannot be the homologue of the R. communicans
ad facialem in the tadpole and frog. This is still further
brought out by the fact that while in the tadpole and frog this
branch is given off by the IX+X, and passes forwards to
reénforce the VII, in Petromyzon the reverse is what occurs,
the communicating branch here being given off by the VII and
passing backwards around the auditory capsule to reénforce the
IX + X, forming a considerable part of the N. lateralis.
Kupffer considers this nerve to be a remnant of the “ epi-
branchial’’ commissure found in Ammocoetes. This view can
be best discussed under the consideration of the III component.
(See, also, p. 200.)

Goronowitsch (28) describes a communicating branch between
the Facialis and the Glossopharyngeus. The nature of this
branch can be also best considered later. From his description
it would not contain cutaneous fibres.

In Urodela there are described two communicating branches
between the IX + X and the VII. One of these, a fine branch,
is considered to be the cephalic part of the sympathetic; while
the other, stouter branch, does not seem to be always present
(Fischer, Hoffmann). Respecting the latter, Fischer (20)
remarks that it might pass into either the cutaneous or mus-
cular twigs of the facial branch with which it unites ; and,
further, according to Volkmann’s researches (64), it contains no
motor fibres. This agrees with the results above obtained, and
this branch is probably the homologue of the R. communicans

158 SHRONG 7 [Vou x.

ad facialem of the tadpole. Its manner of union with the VII
is also similar to that in the tadpole. A further study of this
nerve in these forms is desirable, especially as it is stated that
this branch does not exist in Menobranchus; and yet the R.
jugularis has some fine cutaneous twigs. Naturally, Fischer
does not distinguish between the cutaneous nerves belonging
to this component and those belonging to that next described.
From what has been shown, however, there is reason to believe
that the cutaneous fibres accompanying the motor branch to
the M. mylohyoideus posterior belong to the former, z.e., to the
general cutaneous component.

2. Special Cutaneous or Lateral Line System.

a. Comparison with other Amphibia.— The second component
has been designated, in contradistinction to the preceding,
the “special cutaneous’’ component. It includes VII (a2) and
IX + X (4). Inasmuch as it is distributed to the lateral sense
organs of head and trunk it may also be called the ‘lateral
component.’

This component is in many respects a remarkable one. Its
internal origin or, rather, termination is in certain tracts (and
nuclei, Osborn) immediately dorsad to those constituting the
origin of the Auditory. These tracts do not seem to be in any
way directly continuous with spinal cord tracts as is the case
with the ascending Trigeminus. The origin of this component
composes, apparently, then, a structure peculiar to the medulla
oblongata. The fibres are large and present considerable uni-
formity in size. This component has evidently a constant and
definite distribution, vzz., to the lines of sense organs ranged
along the head and trunk of the tadpole. The arrangement of
these branches and their ganglia has already been described;
one point may be here added, namely, that the ganglion cells
are not very numerous and do not usually seem to produce any
strongly marked ganglionic swelling. There are not, however,
very many fibres in these nerves in the tadpole, a fact which
accounts for the peculiarity above mentioned. Besides this, its
ganglion cells are possibly bipolar (comp. Stannius, 57).

THE CRANIAL NERVES OF AMPHIBIA. 159

No. I.]

*xo[duro9 'X + XI Jo }001 [es1op
"So[V1O}L] “IY pue sim} peroduis} [jews ouoysues KX + XJ Jo yszed yeurxoid pure (o1eydes) ro119,ue ysoy]
pue [esiop ul uol[sueds saArtou [ei0je'] ‘A1oyIpNeysog “[I]
(‘uolsued
: SS d
peoy ueliossey) JO yred yerqUdA YjTM Pea [-tonpny -17]
jO apis pue mel romoy uO (j1eY9 pue yun} siy} uo uoT[sueDy) ‘sey
99S) SayoUvIG [BI9AVS OUI SOprATp -nqipuewofy snouniy, Surwi0f snyy

yoryM — snuiojx9 siiejnqipueur “yy | pue ‘TTA JO $}OOI SLUNUIWIOD sn[NoTOSeF
pue iojow Suturof uoistaip [erjua, ‘z
(ILA 3001 [es10q)
‘Aloyipnesig ‘T

“(ILA stfesonq -y) Teyqioeszuy (2)

“CITA siferoysed
-ns snorumypeyyydo *yy) Tewqroeidns (¢)

‘(uor[sued
uellassey) OAOqe UOT[suUes) SnUTUIESII],

eaoqe Sulpssdoid UOISIAIp [esiog ‘I
"(1039 ‘snoI}O *yY)
JIqiO apIsur S#IM} [Tews Te19Aeg (z)

‘ATAV

wia}sks aul] [e10ye'yT

160 STRONG. [VoL. X.

The homologies of this system are in the main clear. The
preauditory portion is represented in Urodela by Osborn’s
«74 and /,” which divides after its exit, and a part of which he
saw proceed forward to the Gasserian ganglion (45, p. 67, Note).
This latter part (7 ), passing to the Gasserian ganglion in Cryp-
tobranchus, corresponds to the division in the tadpole, which
passes forwards dorsad of the Trigeminus and, after passing
through its ganglion above the Gasserian ganglion, divides into
the infraorbital R. buccalis VII and the supraorbital R. ophthal-
micus superficialis VII, together with smaller branches as
already described. These supra- and infraorbital branches have
been observed in the tadpole by Fischer (20) and Gotte (29),
who calls the branch from the VII the radix accessoria. Both
investigators correctly surmised their connection with the
lateral line system. The ventral division to the R. hyomandi-
bularis, however, seems to have hitherto escaped notice in
the tadpole. Fischer describes only four and sometimes only
three branches from the Gasserian ganglion in Urodela, and
these branches include the usual Rr. ophthalmicus, maxillaris
and mandibularis of the Trigeminus proper. The fourth
branch, in Siredon, extends directly forwards from the dorsal
surface of the Gasserian ganglion, dorsad and mesad of the eye
to the nasal region. Itiscutaneous. ‘This branch is obviously
the R. ophthalmicus superficialis and, indeed, Fischer himself
conjectures that it is the homologue of the anterior part of the
lateral system found in fishes. For the R. buccalis VII and
minor twigs of the lateral system we must look among smaller
branches from the Gasserian ganglion not noticed especially in
Fischer’s description, perhaps because bound up with the
Trigeminus branches,—a tendency noticeable, as has been
seen, in the tadpole. To properly separate these will require
microscopic examination. The cause of this difference between
the tadpole and urodele forms is probably found in the differ-
ent arrangement of the sense organs supplied. In the tadpole
they are arranged linearly, in Urodela they appear to be
scattered quite irregularly over the head, though exhibiting a
tendency to concentration along certain lines. It is possible
that the Urodela first pass through the linear arrangement in
the course of their development.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 161

That ventral half of the lateral line component of the Facialis
which apparently unites with the VIII, actually, we have seen,
unites with the motor and fasciculus communis portions of the
VII, thereby forming the trunk of the Hyomandibularis. It is
distributed, we have seen, in the tadpole to lateral line organs
lying along the side of the head, and also to a line proceeding
around under the ventral side. Here, again, we have in Urodela,
as is evident from Osborn’s account, a similar division of the
lateral component (“VII Z2’’), but it is not certain, in all cases,
exactly into what branches it finally passes, for the arrange-
ment of the organs is, apparently, different, a fact not surpris-
ing when the anatomical differences obtaining between the
tadpole and Urodela are considered.

In general, according to Fischer, the arrangement of the
Facialis in Urodela is as follows: A reénforcing branch is
sent forwards to the Trigeminus, as above discussed. The re-
mainder sends off the R. palatinus and, further along, the R.
alveolaris. The discussion of these branches properly comes
in another place. Besides these, there are two principal
branches, the R. jugularis and the R. mentalis. Either before
the separation into these latter two branches or from the R.
jugularis, twigs are given off to the M. digastricus. The R.
jugularis receives a communicating branch from the IX and
supplies the M. mylohyoideus posterior and the subjacent skin.
The R. mentalis divides into a branch along the side of the
lower jaw, and another branch more mesal. A comparison
with the figures of Amblystoma and of the tadpole will, I think,
make the homologies perfectly clear. In the tadpole the com-
municating branch from the IX is received before the VII
divides (as is also the case in some of the Urodela) into the
R. hyoideus to the M. mylohyoideus and adjacent skin, which =
the R. jugularis and the R. mandibularis externus, which =the
R. mentalis. Consequently the R. mentalis is the branch
belonging to the lateral line system. This homology must be
taken with the provision that other fibres, such as general
cutaneous fibres from the communicating branch from the IX,
may also compose a part of the R. mentalis. A partial mingling
of this kind we have found exists in the tadpole. Only a

162 STRONG. [ VOL. X.

microscopical examination of serial sections, probably, can
determine such a point.

It is evident from the above that Osborn was mistaken in
his conjecture that the lower of the two most dorsal Facialis
bundles, z.¢., “VIIZ,” is motor. Judging from Amblystoma
also, there seems to be no functional difference between the
distributions of the two divisions of the dorsal VII. Biirckhardt
(12), probably following Osborn, seems to have fallen into the
same error of supposing this ventral division to be motor.

The postauditory part of the lateral line component, going
into the IX + X and emerging as the Rr. laterales is represented
by Osborn’s most anterior (cephalic) root of the IX (IX 1).
Its similar origin to VII w and Zis brought out in his paper.
Urodela resemble the tadpole in having several Rr. laterales
(Fischer, Ecker). In fishes subdivisions take place further
caudad.

A paper by von Plessen and Rabinovicz (48) on the cranial
nerves in larvae of Salamandra maculata demands some notice,
especially as it seems to require correction in several points
which are liable to lead to confusion. The authors distinguish
two ganglia belonging to the Trigeminus, a “ principal gan-
glion”’ and, above it, an “accessory ganglion,’ connected with
the Facialis root by their “ Radix dorsalis.’ From the principal
ganglion are derived two main branches, (I) the R. mandibularis
and (II) the R. nasalis. (I) divides into (2) R. communicans
cum supramaxillaris, (4) R. supramaxillaris inf., (c) motor twig
to the M. pterygo-temporalis, (¢) motor twig to the masseter,
(ec) cutaneous twig to jaw angle, and (f) R. mentalis. (II)
divides into (a) twig to rectus superior (?), (4) nasal branch,
(c) R. palatinus, (d@) cutaneous branch to snout. From the
accessory ganglion arise (1) R. communicans c. n. faciali (from
the Radix dorsalis) (II) R. frontalis, cutaneous and supraorbital,
(III) R. supramax. sup., infraorbital and cutaneous, and giving
off a communicating branch to the R. palatinus facialis.

Continuing, they describe the Facialis as arising with the
Acusticus. While traversing the auditory capsule it gives off
(I) the R. palatinus. After separating from the Acusticus it
divides into (II) the R. buccalis and (III) R. hyoideo-mandi-

No.1.] THE CRANIAL NERVES OF AMPHIBIA. 163

bularis. (II) after giving off the (2) R. alveolaris, termination
not stated, divides into (4) a branch accompanying the R.
hyoideo-mandibularis, cutaneous, and a (c) cutaneous branch
along the outer side of the lower jaw. (III) receives the com-
municating branch from the IX and supplies the M. depressor
maxillae inferioris, M. intermaxillaris posterior and skin of
the lower jaw.

The following criticisms may be offered upon these results:
Their “accessory ganglion’ evidently corresponds to the lateral
ganglion above the Gasserian ganglion, from which proceed
the R. ophthalmicus superficialis VII and R. buccalis VII. So
R. frontalis — R. ophthalmicus superficialis, and R. supra-
maxillaris sup. = R. buccalis, excluding any trigeminal elements
that may be fused with them. The communicating branch
between the latter and the R. palatinus VII, should be between
the R. maxillaris V and the R. palatinus. As the R. max. V
seems to be reduced or absent (= their R. supramax. inf. ?)
and their R. supramax. sup. contains trigeminal elements (from »
their principal ganglion), this discrepancy may be more ap-
parent than real. In Wiedersheim’s Grunzdriss this connection
is in one place, by some error, spoken of as between the R.
palatinus and R. ophthalmicus profundus.

It is obvious that the branch named R. buccalis by von
Plessen and Rabinovicz is misnamed. The branch so named by
them corresponds to the R. mandibularis externus (= Fischer’s
R. mentalis, which they have overlooked in his description, or
confused with the V proper), and is derived from the ventral
division of the lateral root (— their R. communicans c. n. faciali).

The connection between this system of nerves, z.¢., R. oph-
thalmicus superficialis VII (R. frontalis), R. buccalis (R. supra-
maxillaris), and R. mandibularis externus (R. buccalis), and
the lateral line system, seems to have been entirely overlooked
by the above authors, probably for the reason, above mentioned,
that these organs do not form definite lines in many Urodela,
but are more scattered. Their homology of the R. hyoideo-
mandibularis with Fischer’s R. jugularis is correct.

These authors have also overlooked the motor and fasciculus
communis roots of the VII, owing to their close adhesion to

164 STRONG. [VoL. X.

the VIII, and also the ganglion on the fasciculus communis
root, which should be at the point where the R. palatinus is
given off. The “ganglion buccalis’’ (= ganglion on ventral
half of dorsal VII) of the authors, as shall be seen below, has
nothing to do with the ganglion geniculi nor their R. buccalis
(R. mandibularis externus) with the chorda tympani.

Another correction of their paper is to be made in connec-
tion with the IX + X. According to their text and figures,
the anterior (farthest cephalad) and undoubtedly lateral line
root emerges from the ganglion, not as the N. lateralis, but as
the N. glossopharyngeus. I have traced this coarse-fibred
anterior root in Amblystoma larvae through the vago-glosso-
pharyngeal ganglionic complex until it emerges posteriorly as
the N. lateralis just dorsal to and parallel with the R. visceralis
(R. intestinalis), as figured also by von Plessen and Rabino-
vicz. This error probably arose from these authors supposing
that the most anterior root of the IX+X series must be the
Glossopharyngeus.

Arnold (5) has described an interesting condition in Pzpa
Americana, where the VIII, VII, and V are fused at their
origin, and the VII and V remain in continuity as far as the
Gasserian ganglion. As his work was done upon young speci-
mens, it is possible the lateral line nerves are among those
described, and, in fact, the R. ophthalmicus superficialis VII is
apparently there identified. What other nerves are to be identt-
fied as belonging to this system it is hardly possible to point
out, especially as their fusion with the trigeminal branches is
here probably carried to an extreme.

I have myself observed in members of the Hylidae, that the
separation between the roots of these nerves is quite slight.

Another difference observable between the condition of this
component in the tadpole and in Urodela, as seen in Amblys-
toma and Cryptobranchus, is that it is relatively considerably
larger in the latter type. Its final disappearance in the Anura
seems to be foreshadowed in the tadpole. (An excellent in-
stance of developing embryonic abbreviation.)

A peculiar circumstance connected with this diminution in
the tadpole is the fact, already referred to, that the space

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 165

relinquished by the dorsal VII is taken up by the VIII. The
dorsal VII completely disappears in adult Anura, and the inter-
esting question arises: Does the dorsal VII really atrophy, or
does it merely pass over into the VIII? This part of the VII
is much more distinct from the VIII in Urodela than in the
tadpole. In the former it has a distinctly separate exit; in the
latter it and the VIII emerge from the medulla together, the
dorsal VII soon separating, apparently as a branch from the
VIII. It is certain that when the dorsal VII has disappeared
its place is completely occupied by the VIII. The question,
however, as to whether there is an extinction or a transference
of the dorsal VII can only be answered by following the
central terminations of the two nerves on through to the final
disappearance of the dorsal VII.

This disappearance of the lateral line component of the VII
probably invalidates homologies which have been advanced
between its branches in lower forms and its supposed repre-
sentatives in higher. One of these homologies (R. auricularis)
has already been noticed, and another will be discussed
below.

In connection with the question here raised arises the inter-
esting problem of the relation of the auditory organ to the
lateral line system. The idea that the auditory organ is
connected genetically with this system, advanced by Mayser
and later by Beard and developed so ably by Ayers, seems
likely to find general acceptance. It is not intended to enter
into this question in this paper, but it may be remarked that a
general survey of the facts of the innervation of these two
organs certainly points strongly to a close connection between
them.

Incidentally, another point may here be mentioned about
which there seems to have been some confusion and which
here receives its solution. Osborn says (45, p. 66): “It is
seen that, whatever may prove to be the peripheral distribution
of the fibres of the fasciculus communis and posterior longi-
tudinal fasciculus, whether to the 7th or 8th, two facts remain:
first that the 8th arises ventral to the 7th, although a purely
sensory nerve.” In a footnote he states that Dr. E. C. Spitzka

166 STRONG. [Vow. X.

“questions the determination of the upper bundles, 7 #—J, in
Fig. 15, as parts of the Facial, on the ground that the ventral
position of the Auditory reverses the usual order.” It is
evident that Spitzka meant by the VII the motor portion which
actually is ventral to the VIII and present in nearly all verte-
brates, possibly in all. Whether the “VII z and 2” which
disappears in the higher forms shall be also denominated the
VII is largely a question of terminology.

It will now be advisable to compare the condition of these
nerves in the tadpole with that in the lower vertebrates. It is
not intended, however, to make here a complete analysis of
these nerves in fishes especially as I have not made any
extended personal investigation upon them.

b. Comparison with the Fishes. —In considering the homo-
logue of this component among lower forms, Goronowitsch’s
results on Aczfenser (28) form a convenient starting-point and
may be analyzed as follows: Respecting the origin of the N.
lineae lateralis, he states that it emerges from the medulla
somewhat more dorsally than the Acusticus and between the
exits of the Acusticus and Glossopharyngeus. It derives its
fibres, which are coarse, from the ‘“dorso-lateral’’ tract. The
fibres form both ascending and descending systems, the latter
being notably the larger, of somewhat coarser fibres and trace-
able to the cerebellum. The Acusticus likewise emerges from
the dorso-lateral tract, dorsal to the dorsal root of the VII,
“VII” here being used, as we shall see, in a narrower sense.
Its principal contingents are from an ascending system in the
dorso-lateral tract and a descending system traceable to the
lateral part of the cerebellum. The Acusticus also receives
fibres from the “durchkreuzten Fasern der hinteren Langs-
biindel,’”’ a part of which are interrupted by the cells of the
anterior horn. Some fibres are also received from a group of
large cells ventrad of the dorsal root of the VII, which latter
root originates from the lobus vagi. Besides these two nerves
from the dorso-lateral tract we have the coarse-fibred ventral
root of “Trigeminus II”’ arising from this tract. This root
likewise consists of contingents from ascending and descending
systems, the former not traceable, the latter, not distinguishable

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 167

from the other fibres of the dorso-lateral tract, to the cere-
bellum. A small contingent is derived from the same group
of cells that supply a portion of the Acusticus. The exit of
this root is somewhat anterior and dorsal to the Facialis and,
it may be added from a study of his figures, dorsal also to the
Acusticus.

Besides the ventral root of Trigeminus II he describes its
dorsal root which has its source in the lobus trigemini. This
latter structure reaches distally as far as the exit of the N.
lineae lateralis and is separated from the dorso-lateral by the
cerebellar “‘ridge.’”’ It consists of a central ganglionic mass
which furnishes the principal contingent of fibres to the outer
layer consisting of fibres. Relations of fibres to other cell
groups which are described need not be dwelt upon here.

Still further cephalad are given off, according to Gorono-
witsch, the two roots of ‘‘Trigeminus I.’’ The dorsal fine-fibred
root derived from an ascending system, which he has not traced,
and a descending system partly to the lateral portion of the
cerebellum and partly to the mid-brain. It is to be observed
from the figures given that the immediate source of its fibres
is ventral to the dorso-lateral tract. It is this root which
we have already identified as the homologue mainly of the
Trigeminus major of higher forms. Its ventral coarse-fibred
root is derived chiefly from the posterior longitudinal fascicu-
lus, partly also from some cells lying near the curve made
by this bundle as it emerges (‘‘Zwischenzellen”’). It will be
spoken of later.

Goronowitsch, in order to overthrow Balfour’s hypothesis as
to primitive nerves of a mixed type and to show that Bell’s law
obtains also for the head, points out that the six roots of the
facio-trigeminal complex may be arranged in three pairs, each
having a fine-fibred dorsal and a coarse-fibred ventral root,
namely :—

FACIALIS dorsal root from lobus vagi.

ventral root from posterior longitudinal fasciculus.
TRIGEMINUS II dorsal root from lobus trigemini.

ventral root from dorso-lateral tract.

TRIGEMINUS I dorsal root from ascending and descending systems.
ventral root from posterior longitudinal fasciculus.

168 STRONG. [VoL. X.

After stating that stimulation had shown some of these roots
to be motor and the difficulty of distinguishing them in embryo-
logical stages, Goronowitsch lays down the following criteria of
a complete spinal nerve :—

(1) The dorsal and ventral roots have different internal
origins.

(2) It arises with two roots, a fine-fibred dorsal and a coarse-
fibred ventral.

(3) It possesses a ganglion:

It is further remarked by him that the distinction as to thick-
ness of fibre is not very essential.

I may offer the following criticism. These three criteria
appear to me hardly sufficient, —the dorsal root should be a
ganglionated sensory (afferent) root and the ventral root a
non-ganglionated motor (efferent) root. Now in respect to
the Facialis and Trigeminus I, the ventral roots spring, con-
sistently, from a bundle (or from ventral cells) which, there is
every reason to believe, is efferent. This is not the case, how-
ever, with the ventral root of Trigeminus II derived from the
dorso-lateral tract. The two other nerves arising from this
tract, the Acusticus and Lateralis are semsory and the ventral
root in question even derives a few of its fibres from the cell
group likewise giving origin to a portion of the Acusticus.

My criticism is not especially directed against Goronowitsch’s
views on the relation between cranial and spinal nerves, but
simply to show, from his own observations, that there is no
sufficient reason for supposing that the ventral root of Tri-
geminus II is motor ; and thereby to remove, in advance, a
possible objection to the homology which I advocate, namely,
that Goronowitsch’s “ventral root of Trigeminus II” in Aci-
penser is the same as the one described in the tadpole as the
dorsal VII, and that it and the N. lineae lateralis together
compose the lateral line system. The character of the fibres
and their similar internal origin both point to this homology
and, as will be seen below, so probably does their distribution.
Moreover, Stannius did not find these roots to be motor.

The above being true, the question naturally arises: what is
the homologue in Amphibia of the lobus trigemini? At first

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 169

sight it would be naturally suggested that the root coming
from the lobus trigemini, the dorsal root of Trigeminus I], is
represented in Urodela by the upper of Osborn’s two Facial
roots, z.¢., “ VII z.”’ This, however, I believe is not the case.
mis) has, been mentioned, both Vil. “2” and “2°” together
probably correspond to the dorsal VII in the tadpole, as is also
shown by Amblystoma. Furthermore, the root from the lobus
trigemini is fine-fibred, and though Osborn mentions that the
fibres of VII wz are smaller than those of VII Z, yet the differ-
ence is slight and both are coarse-fibred. From my own
observations, and from such investigations as those of Gas-
kell and others, I am inclined to believe that the size of the
fibres is more constant, and consequently of more importance in
determining homologies than would at first sight be supposed.
Before looking further for the homologue of the lobus tri-
gemini in Amphibia, a glance will be taken at the condition in
the Zeleosts. In the teleostean medulla oblongata, as is well
known, there are three greatly hypertrophied portions known
usually as the lobus vagi, the lobus trigemini, and the tuber-
culum acusticum. Mayser (41) speaks of the common origin
of the Acusticus and R. vagi lateralis, and is so much impressed
by it that he terms the latter a posterior acoustic root and,
further, considers the sense organs supplied by the latter as an
accessory auditory organ. He also quotes Leydig, to show the
similarity between the semicircular canals and their ampullae
and the mucous tubes of the lateral line. Speaking of the
same organs on the head he says: ‘Auch diese Schleimrohren
haben nach Stannius nur breite Nervenfasern und zwar aus der
II Wurzel des Trigeminus. Die II Quintuswurzel des Stannius
entspringt aus dem Tuberculum acusticum und ist bei den
Cyprinoiden, wie jener Autor, p. 28, sagt, ‘fast ganz verdeckt
von der ITI Wurzel,’ d. h. unserer dorsalen geknieten”’ (= root
from lobus trigemini). From this the homology of the tuber-
culum acusticum with the centre in the medulla of the dorsal
VII and N. lateralis of the tadpole, and with the “ dorso-lateral
Strang”’ of Goronowitsch in Acipenser is quite evident.
According to Goronowitsch, Trigeminus II gives off the
following branches: R. ophthalmicus superficialis, R. buccalis,

170 STRONG. [ VOL. X.

a small reénforcing branch to the R. oticus, and a stout branch
reénforcing the R. hyoideus of the truncus hyoideomandibularis.
This agrees with the course of the branches of the dorsal VII
in the tadpole, including the stout branch to the R. hyoideus,
which obviously represents the ventral half of the dorsal VII
which passes ventrad and unites with the Facialis proper in
the tadpole. The fact remains, however, that his Trigeminus
II includes the dorsal fine-fibred root from the lobus trigemini,
obviously the same root as that known as the dorsal genicu-
lated root from the lobus trigemini in Teleosts.

Wright, in his researches on Amzurus (72), has traced to
a considerable extent, the fibres from these various roots.
According to him, the bulk of the fibres of the Rr. buccalis,
oticus, and ophthalmicus superficialis come from the broad-
fibred tuberculum acusticum root or roots, and the motor VII
is also reénforced by the latter fibres, and by others “of
narrower diameter from the ganglionic complex.” The bulk
of the R. lateralis trigemini and ophthalmicus (profundus) are
derived from the fine-fibred dorsal geniculate root. Besides
these branches two strands are formed: an “ infero-medial ”
derived principally, but not exclusively, from the dorsal genic-
ulate root, and a “ supero-lateral ’ derived principally from the
“broad motor’”’ (?) “fibres of the ascending and transverse root.”
From the former strand, and consequently principally from the
dorsal geniculate root, come the Rr. palatinus and cutaneus
palatinus to the mucous membrane of the roof of the mouth
and gill cover ; from the latter strand, and consequently from
the ascending and transverse root, a branch proceeds to the
musc. abductor mandibulae. These two strands are then re-
_ arranged so that both the R. maxillaris and R. mandibularis
receive a portion of each strand. The latter divides into an
externus and internus, the internus proceeding along the inner
aspect of the jaw and ending in the mandibular barblets, teeth,
and mucous membrane, as well as the intermandibular muscle.
Wright is probably mistaken in speaking of the ascending and
transverse root as motor. The former, ascending part, must
be sensory, while the transverse is motor. That the former is
not all motor may even be inferred from his own description,

Now| THE CRANIAL NERVES OF AMPHIBIA. D770

inasmuch as while the R. maxillaris receives a portion of this
root, yet no motor branches are mentioned in its distribution.
This ascending part is the sensory Trigeminus proper.

Wright’s account agrees with that of Goronowitsch in some
respects, but differs in others. Trigeminus II, or a root from
the tuberculum acusticum plus one from the lobus trigemini,
gives rise to the Rr. ophthalmicus superficialis, buccalis, and
oticus, and reénforces the VII. On the other hand, according
to Wright, the ophthalmicus profundus is derived from the
lobus trigemini; according to Goronowitsch, from the non-
homologous Trigeminus I. There appears to be no R. lateralis
trigemini in Acipenser. Another important difference is that
Wright assigns two Rr. palatini to the Trigeminus, derived
from the lobus trigemini, while Goronowitsch denies the exist-
ence of any such branches from the Trigeminus, and asserts that
they belong exclusively to the Facialis. This latter point will
be discussed later. There should be three Rr. ophthalmici,
one the profundus and the other two Rr. ophthalmici super-
ficiales, of which one belongs to the Trigeminus proper
(= Trigeminus I), and the other is derived from the Facialis
(ventral root of Trigeminus II — dorsal VII plus, in some cases
at least, fibres from a root emerging from the lobus trigemini).
Both Goronowitsch and Wright appear, however, to describe
only two. This, together with the fact above mentioned, that
the ophthalmicus profundus of one does not seem to be strictly
homologous with that of the other, is difficult to account for.

It is in Stannius’ splendid memoir, Das peripherische
Nervensystem der Fische (57), that we find the most accurate
account, it seems to me, of the peripheral nervous system of
fishes. Stannius not merely dissected but also checked his
results by stimulating the roots, and, likewise, investigated the
character of the fibres composing the roots and branches.

For the N. trigeminus cum nervo faciali in forms where the
roots are most separated (Pleuronectes), Stannius describes
the following roots:

Ist root, stout ; mixed fibres, vzz., mostly medium, with a
number of very large fibres and a smaller number of fine fibres.
Contains a motor element to the jaw muscles.

172 STRONG. [Vou. X.

2d and 3d roots, more dorsal (“nach hintere oder obere’’)
and originating from the Lobus medullae oblongatae, s. Lobus
posterior (which also gives rise to R. lateralis nervi vagi).
Fibres exclusively large, some being as large as motor fibres,
e.g., those of the oculomotor, and others, in smaller number, still
larger. After their exit these roots exhibit no perceptible gan-
glionic swelling, but closer investigation shows their fibres to
be continuous with bipolar ganglion cells. These roots are
non-motor. One goes over into the Trigeminus, the other into
the Facialis.

4th root, “entspringt abwadrts von den vorigen etwas mehr
aufwarts oder hinterwarts als die erste Wurzel, aus der Seite
der Medulla oblongata.”’ Fibres fine and ganglionated, but not
so apparently connected with ganglion cells, which are seldom
bipolar. Non-motor. A part goes over to the Trigeminus, a
part to the Facialis, and a part composes the bulk of the R.
palatinus.

5th root, smallest, furthest caudad, issuing immediately in
front of the first acoustic root. Fibres exclusively large.
Motor. Goes over entirely into the Facialis.

In Raja, according to Stannius, we have only three roots,
which closer examination resolves into four, inasmuch as roots
3 and 4 of bony fishes are in close apposition.

I. Emerges in two strands, is composed of fibres of various
size and also of mixed functions, the motor fibres being in the
ventral part. This root corresponds to root 1 of bony fishes.

2. Emerging close to VIII, principally from corpus resti-
forme. Part goes over into V and part into VII. Fibres are
partly broad and partly half as broad. Some of the fibres are
motor, which belong to the VII exclusively.

3. A large “hintere oder obere’’ root, arising above the
preceding, of broad fibres and non-motor. A part mingles
with 2 and part goes over into the V.

Stannius summarizes as follows:

Root I.— Motor and sensory. Fibres mixed. Belongs to the
Trigeminus proper. Sometimes divided.

Root II.— Non-motor, “hintere,’ sometimes single, some-
times divided. From corpus restiforme. Only broad fibres

No.1.]- Z7THE CRANIAL NERVES OF AMPHIBIA. 703)

connected with bipolar ganglion cells. Principally distributed
to mucous canals.

Root III. — Non-motor, “hintere.’’ Only fine fibres. Large
ganglionic masses. Distributed especially to mucous mem-
branes, skin, and touch organs, especially on the barbels.

Root IV.— Exclusively motor, arising close in front of the
Acusticus and going over into the VII (coarse-fibred).

The numbers vary owing to subdivisions and fusions.

According to Stannius the Facialis proper (Hyoideo-mandi-
bularis) divides into a posterior, or more caudal branch, the R.
hyoideus, and a more anterior one, the R. mandibularis, pro-
ceeding along the lower jaw, which either gives off a branch to
the mucous membrane of the mouth or subdivides into a R.
mandibularis externus to the skin and mucous canals, anda R.
mandibularis internus to the mucous membrane of the mouth.

In the first account (Pleuronectes), root 1, evidently, is the
Trigeminus proper, 2 and 3 are the lateral line roots, and § the
motor root. Root 4, probably, is the one described by Stannius
elsewhere and by other authors as arising from the lobus
trigemini. The question of its homologue in Amphibia will
be discussed below. There is, however, some obscurity in
Stannius’ account of this root. It would appear from his
description to lie sometimes ventral and sometimes (¢.g., com-
pare his account of Cyprinoids) dorsal to 2 and 3.

Gegenbaur (26) describes, in Hexanchus, the Trigeminus as
arising from two trunks, an anterior and a posterior one
(“vordere”’ Va and “hintere’”’ V4). The former is composed
of two roots with difficulty distinguishable. The posterior
trunk is also composed of two roots, one, the most dorsal (V a)
arising from a large swelling overhanging the fourth ventricle,
and the other more ventral (V 6) emerging from the medulla
close above the Facialis, and somewhat cephalad and dorsad
to the Acusticus. VJ proceeds above Va and the two enter
the Gasserian ganglion, there being an intermingling of fibres.
The R. ophthalmicus is derived principally, but not exclusively,
from V a.

Jackson and Clarke (32) describe the Trigeminus as arising
in Lchtnorhinus from two main trunks. (1) Va, furthest

174 STRONG. [Vor. X.

cephalad, more ventral, and issuing from the medulla by two
roots, and (2) V @ further caudad and dorsad, and issuing from
the lobus trigemini by two rootlets, one dorsal to the other.
VB proceeds above Va and is closely united also to the
Facialis root V y VII, part of whose fibres issue just above the
VIII.

Gegenbaur’s anterior root, Va, is the Trigeminus proper,
including both the sensory element from the ascending tract
and the motor root. His most dorsal root of V J, z.e., Va, is
the one derived from the lobus trigemini. V 8 is, probably, the
lateral line root from the tuberculum acusticum. His Facialis
is the motor root plus, possibly, a root from the lobus vagi
(vide infra, p. 193).

In Jackson and Clarke’s account, Va= Gegenbaur’s Va and
V B=Gegenbaur’s Va. Vy VII is probably compound.
That portion of its fibres issuing above the VIII may be
derived from the tuberculum acusticum, —in fact must be
unless Jackson and Clarke are mistaken in deriving doth
rootlets of V 8 from the lobus trigemini — and may be also, in
part, derived from the lobus vagi (compare Goronowitsch and
see below, p. 193). This root must also, of course, contain
motor fibres.

Marshall and Spencer (43) describe, in Scyldzum, a R. oph-
thalmicus superficialis from the VII having a course closely
parallel and superficial to the corresponding trigeminal branch,
a buccal branch whose proximal portion forms a connecting
branch with the V, and whose distal portion proceeds parallel
and superficial to the maxillary branch of the V, and a posterior
or hyoidean branch. With respect to the first two, the princi-
pal difference between it here and in Amphibia seems to be
that the forking into the two branches, Rr. ophthalmicus
superficialis and buccalis, takes place more distally in the
latter, so that the common trunk of the two forms the connect-
ing branch and contains the ganglion. Respecting the hyoidean
branch, they do not seem to be aware that the cutaneous R.
mandibularis externus is, in part, a nerve to mucous canals
similar to the two preceding branches. They also fall into the

error, the existence of which seems to have been first pointed

No: F.] THE CRANIAL NERVES OF AMPHIBIA. 175

out by Allis in Amia, and later by the writer in the tadpole,
of supposing that the Trigeminus takes part in the innerva-
tion of the lateral sense organs of the head, an error repeated
in most of the text-books.

In treating of the roots, Marshall and Spencer come to the
following conclusions: The fifth nerve in the adult arises by
two roots: (a), an anterior non-ganglionic arising by two root-
lets (Vy) = “Ist root of Stannius, the anterior root (Va) of
Gegenbaur, the anterior inferior root (Va) of Jackson and
Clarke, and the anterior root (1) of Balfour.”

«(6) A posterior, larger ganglionic root, the ventral or sec-
ondary root (V 8)” =—‘<‘anterior part of the second root of
Stannius, the ventral division (8) of the posterior root (4) of the
the fifth of Gegenbaur; apparently the inferior rootlet of the
second root (V 8), and possibly part of the third root (V y and
VII) as well, of Jackson and Clarke ; the second root (2) of the
fifth of Balfour.”

“The seventh nerve in the adult arises by two roots: (2) A
dorsal root arising far up the side of the medulla, at the
junction of the thickened sides and thin roof of the fourth
ventricle” (“ primary” root of VII, VIIa). ‘This root is the
third or dorsal root of Stannius; the dorsal rootlet (a) of the
posterior trunk () of the fifth of Gegenbaur; the superior
rootlet of the second root (V #) of Jackson and Clarke, and
the dorsal and posterior root (3) of the fifth of Balfour.”

(6) A ventral root arising from the side of the medulla at a
rather lower level than the posterior root of the fifth”’ (“‘ second-
ary” root of VII, VII 8). In the adult it comes to lie in close
contact with the secondary root of the fifth. ‘“ This root is the
posterior part of the second root of Stannius, the root of the
seventh of Gegenbaur ; part, or possibly the whole of the third
root (V y and VII) of Jackson and Clarke ; and the single root
of the seventh of Balfour.”

These investigators first showed that the R. buccalis belongs
to the VII. Their homologies do not appear to me, however,
to be entirely correct. Their second posterior ganglionated
root (4) of the V is plainly the sensory root of the Trigeminus
proper. As such, it corresponds, together with the motor root-

176 STRONG. [VoL. X.

lets ‘sometimes apparently distinct and sometimes fused with
the sensory portion, to Stannius’s first root, to Gegenbaur’s
V a, and to Jackson and Clarke’s Va. Their first dorsal root
(z) of the VII is the one derived from the lobus trigemini in
all probability, and is correctly homologized. Their second ven-
tral root (4) of the VII must be regarded as compound, consist-
ing of a lateral line portion, a motor, and possibly a root from
the lobus vagi. Compare tadpole (see below) and Gorono-
witsch’s account of Acipenser.

Ewart (18) has described these roots in Laemargus as fol-
lows : the ophthalmicus profundus arises by a separate root in
front of the main Trigeminus. The latter arises by a large
root on a line with the ventral roots of the Facialis complex.
Its branches are the ophthalmicus superficialis, maxillaris, and
mandibularis. The Facialis includes four separate nerves:
(1) Ophthalmicus superficialis, arising from the so-called tri-
geminal nucleus by a root dorsad and caudad of all the others.
It communicates with the buccalis as it passes through the
cranial walls at a higher level than the Trigeminus and oph-
thalmicus profundus. (2) Buccalis arises behind and at a slightly
higher level than the trigeminal. It is infraorbital. (3) Pala-
tinus and hyomandibularis arise by a large root between the
Trigeminus and Auditory, and partly under cover of the bucca-
lis. It receives fibres from (1), and then passes outwards with
the Auditory, giving off the R. palatinus, and finally dividing
into branches to muscles and to canals and ampullae not sup-
plied by (1), nor (2), nor the R. lateralis.

Here (2) and part of (3) are lateral-line roots. (3) must be
regarded as in reality compound, comprising motor and, prob-
ably, lobus vagi roots, as well as lateral-line fibres.

Burckhardt (11) has designated the most dorsal root of the
Acustico-facialis ‘‘ VII,” and attributed to it a motor character.
There can be little doubt that this is in reality the preauditory
lateral-line root, and the error noted above (p. 162) has been
here repeated. (See, also, page 185.)

The following table shows the probable homologies of the
preauditory lateral-line roots in the descriptions of these inves-
tigators:

THE CRANIAL NERVES OF AMPHIBIA. B77

No. I.]

‘QUIIOJIISOA snd105

‘gUIIOFIJSAI Snd105

‘ysod ‘qoy] ‘s ovjJeSuO]qoO oeI[npow snqoT
‘uINdTJsNoV wWN{NI1eqQN J,

‘uINdTsHoV WIN,NIIEqnN J,

"yOVI} ,, [e19}L]-OSIO] ,,

“NOILVNINGA LT TVYLNAD

‘SLOOW ANIT

(a P ILA») « ILA Testop 5,

‘TIA

[eq pue ‘puewodyy jo x1ed pur sieoong
9 IIA jo wed

‘Ayqeqoid ‘TTA 4 A jo j1ed

‘DA

* O01 pz

* () oor pz
Se eae eos Sool poapuene

(‘dns ‘ydo pue snotjo ‘stpeoonq *1y7)

"JOO [eIWUDA ,“T]T SNUIWIOSIIT ,,

«7 PUS TIA ss

*SLOOY

* Buoys

yprVy ying

eM

iaoueds pur |[eysieyl
ayIV[D puv uosyor{
inequesex)

* sntuue}s
sniuuvy}s

sniuurys

STM

Joskey

YISJIMOUOLOL)

u1oqsO

“ALIVOHLAY

TIVUALVT AYOLIGNVANG AO ATAV EE

eInUYy JO svAILT
sn1i9jdoj01g
snsIvUlsv’]

st + umrpfog
* snulysouryoy
snyouexopy

* (adj poztperoues))
eley

* sayouoINeg

‘ * sninmy
sprouridk>

‘ iasuedpy

snyoueiqoydkig

‘AdAL

178 STRONG. [VoL. X.

Regarding the N. lateralis, we find that it has in Selachii a
similar character from Shore’s account also of the Vagus in the
shark. According to him, the lateral-line portion of the Vagus
is coarse-fibred and distinct in origin from the rest of the
nerve. It also possesses its own ganglion of rather scattered
ganglion cells. Its internal organ is not traced. A peculiar
feature, however, is that the lateral-line part of the Vagus arises
from a number of fasciculi forming the most posterior (2.e.,
caudal) of the roots of the Vagus, and somewhat more ventral
than the others. This account differs from the exit of this
root in Amphibia, Ganoids, and Teleosts, judging from the
writer's observations and the papers of Goronowitsch, Mayser,
Wright, and Ewart, as shown above. In all of these the
R. lateralis has its exit cephalad and dorsad of the rest of the
vago-glossopharyngeal roots.

I may add that in some dissections made at the Marine
Biological Laboratory at Woods Holl during the summers of
1892 and 1894, upon Galeus canis and Galeocerdo maculatus, I
found also that the R. lateralis invariably arose by a single
root cephalad and dorsad of the other roots of the IX+X. I
cannot reconcile Shore’s account in this respect with those of
other investigators or with my own observations.

The lateral-line nerve, I found, may be reénforced by fibres
from one or both of the next two Vagus roots. What the
character of these fibres is can only be surmised, and will be
discussed below. Ewart and Mitchell (19) have made a similar
observation, and judging from what has been quoted (p. 156),
some of these at least would be general cutaneous fibres.

(c) Résumé of the Roots tn Fishes.— In generat, <he arrange-
ment of these roots and principal branches seems to be as follows :

1. The Trigeminus proper, with fibres of varying sizes,
which sometimes arises by two roots, in which case the one
cephalad is the R. ophthalmicus profundus. Besides this latter
it divides into the R. ophthalmicus superficialis, the R. maxil-
laris, and the R. mandibularis. It is this Trigeminus proper,
the central continuation of which is an ascending tract from the
cord, which has also a ventral motor root added, and is constant
in the main throughout the vertebrate series.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 179

2. One or usually two broad-fibred roots arising from the
tuberculum acusticum (~lobus posterior medullae oblongatae,
Stannius = corpus restiforme — dorso-lateral tract, Gorono-
witsch). One of these passes forwards over the Trigeminus
proper and Gasserian ganglion and there divides into the supra-
orbital R. ophthalmicus superficialis and the infraorbital R.
buccalis. The other root, nearest the Acusticus, unites with a
motor root, and passes into the hyoideo-mandibularis — the
Facialis proper.

3. A root, most dorsal of any, from the lobus trigemini
(=lobus impar). This root divides in such a way as to send
fibres to both divisions of No. 2. While that part of No. 2
joining the Trigeminus does not seem to necessarily form an
intimate union with the latter, No. 3 seems to completely
mingle with No. 2. Besides mingling with the latter, however,
No. 3 in some cases forms a R. palatinus and a R. lateralis,
besides other smaller branches. Often the R. ophthalmicus super-
ficialis VII appears to be especially connected with this root.

4. A broad-fibred motor root close to the Acusticus and
passing exclusively into the hyoideo-mandibularis.

5. In some cases, at least, a fine-fibred root from the lobus
vagi (Goronowitsch).

The N. lateralis vagi always arises by a broad-fibred root
from the tuberculum acusticum, dorsad and cephalad of the
Geer roots of the IX ++ X.

I may add here that this arrangement of the roots is con-
firmed by my own dissections of Selachians.

It is No. 2 which innervates the lateral canals in all cases, a
fact which Stannius seems to have clearly recognized, though
he does not always seem to have distinguished clearly between
its branches and those of the Trigeminus proper. Marshall
and Spencer, and Van Wijhe, I believe, were the first to make
this clear. The fact that the Trigeminus proper does not par-
ticipate in the innervation of the lateral-line system has also been
brought out by Allis (Amia), by Ewart (Laemargus and Raja),
and by the writer (tadpole).

It is very evident from the above that the lateral-line system
of nerves are alike in their main arrangement in all the forms

line oes

180 STRONG. [Vou. X.

in which they have been studied and carefully distinguished.
The agreement between the larval forms of Anura and the
fishes is quite remarkable. The same general plan holds for
both. It is owing principally to the labors of Allis and Ewart
that this general plan has been made clear in fishes. As in the
latter forms many variations are found, such, doubtless, will be
found the case also in amphibian larvae and in Urodela, both in
the arrangement of the organs and the courses and smaller
ramifications of their nerve supply; but the roots and principal
divisions and their arrangement will probably be found to hold
good for all.

One very important difference, apparently, between the con-
ditions in fishes and Amphibia, has emerged however; and
this relates to root No. 3. The question of the fate of this
root can be most conveniently considered with the next com-
ponent, though in many respects it falls most properly under
the component just discussed.

3. fasciculus Communts.

a. Amphibia. — The third component is, as has been de-
scribed, derived from the fasciculus communis.

TABLE.

( R. palatinus — roof of pharynx.
< R. mandibularis — portion of

[ floor of pharynx.

Preauditory —
one root (gang.)

Fasciculus communis

(+ adjoining nu- R. lingualis 1X — part of floor
cleus ?). of pharynx.
Rr. pharyngei — pharynx and

part of filtering apparatus.

r. branchiales — gills, part

of filtering apparatus and

pharynx.

R. visceralis — heart, lungs,
oesophagus, etc.

| Postauditory —
L several roots (gang.) we

This remarkable tract appears in transverse sections of that
part of the medulla of the tadpole just cephalad of the opening
of the fourth ventricle, as an oval island, as it were, imbedded

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 181

in the ganglion cells of the central gray. It is here almost in
the extreme dorsal part and quite close to the ventricle. It
can be traced caudad into the spinal cord a short distance only,
in the adult frog. It lies then in the posterior columns close
to the median line. Judging from Weigert preparations it con-
tains in this portion only a very few medullated fibres. Accord-
ing to Golgi preparations in the tadpole there are few fibres
in it in this region (PI. XI, Fig. 31). The remainder is made up
apparently, of a ‘ground substance.”’ The change in position
and character of this structure as we advance cephalad is well
shown in the Golgi preparations from which Figs. 31-39
inclusive were drawn. The tract gradually comes to le further
ventrad and laterad and also increases in size. The number of
fibres in it, all fine and with a thin sheath or none, also
increases very greatly as shown both by the Golgi and Weigert
preparations. The maximum is reached at the level of the
exit of the second root of the IX-+ X, which, as we have
seen, derives a considerable portion of its fibres from the
fasciculus. Cephalad of this, it continues as a small bundle,
rather difficult to follow in the tadpole, until it passes out
in one of the facial roots as described above (p. 113, see also
Fig. 39). Whether a portion of it continues on still further
cephalad could not be ascertained in the tadpole. According
to Osborn (45), it does continue forward in Cryptobranchus.
As seen in the figures (31-39) its course is nearly parallel with
the ascending Trigeminus tract. Both undergo, on entering
the medulla, a downward deflection. Consequently, if the
ascending Trigeminus (and this tract?) represent morpho-
logically, in the medulla, the posterior columns of the cord,
the tracts and nuclei connected with the lateral line system
are superadded structures, inasmuch as they lie dorsal to these.
(Compare Ahlborn on Petromyzon.)

As the fasciculus communis retreats from the immediate
vicinity of the ventricle or, rather, central, canal and from the
mass of cells surrounding the latter in the tadpole, a number
of the cells are detached with it and form a group on its inner
ventral side. This group of small cells, as shown in ordinary
carmine preparations, accompanies the fasciculus throughout

182 STRONG. [VoL. X.

its course and, moreover, seems to vary in size part passu with
the variations in size of the fasciculus. It nearly or quite
disappears cephalad of the second root of the IX+X.

The fibres of the fasciculus communis do not appear to be
connected directly with nerve cells in the medulla, though,
as indicated in Fig. 12, the surrounding cells frequently send
their protoplasmic processes into it. As the nerves originating
from it are ganglionated, such ganglia are to be considered as
its nuclei of origin (‘‘ Ursprungskern,” Kolliker 34), while the
group of cells above described are to be considered possibly
as its terminal nucleus (‘‘Endkern,”’ Kolliker 34). It is pos-
sible that some fibres of these roots proceed directly to the
nucleus without passing into the fasciculus. From Osborn’s
description this would seem to be the case in Cryptobranchus,
for besides the nuclei corresponding probably to the lateral
line nuclei and the motor nuclei we have another nucleus
(whose character is considered doubtful by Osborn).

The diminishing size of the fasciculus from the level of the
exits of its roots on caudad in the medulla is due to the
gradual loss of its fibres as they terminate freely along their
route. The peculiar compound character of the fasciculus as
described by Osborn is explicable when we consider that the
fibres grow into the medulla by means of the various roots
and there unite to form the fasciculus.

It is evident that this tract is composed exclusively or almost
exclusively of uvzsceral (splanchnic) fibres innervating the ali-
mentary canal and its appendages. Whether, however, it is
composed of efferent or afferent fibres or both, is not so clear.
It would seem quite certain, however, that many, or most,
of the fibres terminating in epithelium are to be regarded
as afferent. This is true also of many of the fibres innervating
the filtering apparatus. The character of the fibres so richly
innervating the curious glands found in the vicinity of the
opening of the gill clefts into the pharynx is not soclear. If
we assume the existence of secretory fibres, it would seem
certain that some of them must be of this character. We have
also seen that some of the vaso-motor fibres, including those to
the heart, appear to belong to this component. The fact that

No. 1.] THE CRANIAL NERVES OF AMPATBIA. 183

these fibres have peripheral ganglia as their nuclei of origin
does not necessarily disprove this, as they may in this respect
resemble the sympathetic. Altogether it seems most reason-
able to regard this tract together with its nucleus as composed
of both afferent and efferent fibres.

This tract has been noticed by several writers, apparently,
and I can hardly agree with Osborn when he speaks of it as
a bundle not hitherto described if he means this to apply to
Amphibia in general. Stieda, in his account of Axvolodl (59)
says: ‘Die starkste oder die vorderste Vaguswurzel, welche
etwa dem N. glossopharyngeus der Sauger zu vergleichen ware,
verhalt sich etwas anders als die hinteren Wurzeln. Bereits
ziemlich weit hinten markirt sich im oberen Abschnitt der
‘grauen Substanz und zwar in der Kernzone eine lichte Stelle ;
hier sammeln sich allmalig feine Nervenfasern zu einem
betrachtlichen Langsbundel, welches durch Vermittelung
vieler kleiner dicht auf einander folgender Wurzelbiindel-
chen das Mark verlasst. Das ist die Hauptwurzel des Vagus.”
And again in his description of the central nervous system of
the frog: ‘Bereits in der Gegend der Uebergangstelle des
Riickenmarks in die Medulla oblongata macht sich auf Quer-
schnitten dicht zu beiden Seiten des erweiterten Central-
eimals; ein rundlicher Fleck bemerkbar (Fig. 9) u) 10 2),
welcher durch einige Kerne und kleine Nervenzellen einge-
fasst, sich von der iibrigen grauen Substanz abgrenzt. Bei
Untersuchung einer ganzen Reihe hinter einander liegender
Querschnitte erscheinen in dieser runden Gewebsinsel anfangs
sparlich, spater reichlich querdurchschnittene Nervenfasern in
kleinen Biindelchen. Dabei riicken die kleinen Biindelchen
immer noch in der Gewebsinsel eingeschlossen allmalig der
lateralen Peripherie naher, bis sie endlich derselben ganz nahe
gekommen sind. Unterdess ist die scharfe Begrenzung der
Biindel durch die sie begleitende Grundsubstanz verloren
gegangen und statt des querdurchschnittenen Langsbiindels
ist auf dem nachsten Querschnitte ein starkes schrag abwarts
geneigtes, abtretendes Wurzelbiindel des Vagus sichtbar, dem
sich ein oder zwei der friiher beschriebenen Querbiindel
anschliessen (Fig. 11 7).’’ Stieda was unable to trace these

184 STRONG. [Vor xt

fibres to any cells. Koppen (35) seems to refer to this tract
when he says: “Schon kurz vor der Eroffnung des Central-
canals, bald nachdem die letzte dorsale Wurzel das Riicken-
mark verlassen hat, tritt dorsal in der grauen Substanz ein
Langsbiindel feiner Fasern zu Tage, eingelagert in einer
dichten grauen Masse, die sich kreisformig von der ibrigen
abgrenzt (Substantia gelatinosa Rolando), s. Taf. I, Fig. 3 S.
g. R. Diese Substanz ist nur die Fortsetzung der gelatinosen
Masse, welche wir im Rickenmark, innen vor den dorsalen
Wurzeln, fanden. In ihr zeigen sich nun einige Langsfasern,
ein aufstergendes Wurzelbiindel des Vagus und des Trigeminus.
Es riickt allmalig aus der grauen Substanz immer mehr dem
Rande zu und liegt schliesslich median von dem Seitenstrang
und den Dorsalstrangen.’’ Koppen seems to have recognized
the fact that this tract is continued cephalad of the IX+X but
refers it to the Trigeminus instead of the Facialis. As he
seems to have overlooked also the motor bundle of the VII
which makes its exit with the VIII or, rather, refers it to
the VIII, he is compelled to seek for the VII in the V and
derives both the VII and the motor portion of the V from the
motor nucleus of the V. Osborn remarks: “At this point he
(Koppen) fails to distinguish between the Facial and Auditory
elements, for his dorsal Auditory root, p. 9, is probably the
main portion of the Facial. This error, if error it be, arises
from the fact that he expects to find the facial a purely motor

nerve, p. 10.1) Meppen must be acquitted) om this point,
however, for the “main portion of the Facial” referred to
(Osborn’s “7 # and 7” =“dorsal VII” to lateral sense organs)

has disappeared in the frog. Koppen’s real error is in not
distinguishing between the V and VII and into this error he
may have been led as Osborn suggests.

Osborn gives a correct account of the exit of this bundle,
but was unable to determine whether it ultimately went to
the VIII or the VII. As shown above, the latter is the case.
There exists a remarkable difference, however, between the
exit of the fasciculus communis in Urodela, on the one hand,
and in Anura and tadpoles on the other. In the former the
exit of this fasciculus to the VII takes place just dorsal to the

No. I.] THE GRANIAL NERVES OF AMPHIBIA. 185

VIII, while in the latter it is just venwtval to the VIII. This
change is perhaps correlated with the change in position of the
Auditory, which has already been touched upon.

It may be most conveniently noted here that Burckhardt (11)
describes in Pvotopterus a dorsal root belonging to the VII,
partly motor, a root beneath it from the fasciculus communis,
which he attributes to the VIII (‘«V///,’’) in his nomenclature,
a second and largest root to the VIII (“V///2”) below this,
then finally and most ventral a root derived partly from the
posterior longitudinal fasciculus and partly from a motor
nucleus. This latter he also attributes to the VIII (“V//7 3, 4’).
Burckhardt probably follows Osborn in this assignment of
these roots, which are so very similar to those in Crypto-
branchus. In this, as we have seen already, he is mistaken.
The dorsal root is the lateral line root, and is entirely sensory.
The fasciculus communis root and the most ventral root should
be -assioned to the VII and not to the VIII. The VIII is
represented entirely by the largest root (““V/// 2”) between
the two last mentioned.

The most interesting fact to be noticed here is that in the
position of its fasciculus communis root, Protopterus agrees
with the Urodela and differs from the tadpole, from Anura,
from Acipenser, and not improbably, if the views taken on
Pp. 193 be proved correct, from Selachii in this respect.

(0) Higher Vertebrates.— Before looking further at the
lower vertebrates it may be well to take a glance at the higher
forms. In the human medulla, as is well known, the prin-
Gipal sources of the I[X-+X are three, (1) from a motor
nucleus, the nucleus ambiguus, (2) from a so-called sensory
nucleus, and (3) from the fasciculus solitarius. We have also
the motor nuclei of the XI, principally similar or identical with
those of the IX + X.

Kolliker, in the latest edition of his Gewebelehre, gives a
very clear and complete account of the fasciculus solitarius.
It is apparent some distance caudad of the calamus scriptorius
lying latero-dorsad of the sensory terminal nucleus of the
IX + X, and consequently quite near the median line in the
dorsal part of the cord. It gradually increases in size as it

186 STRONG. (Vion. xe

proceeds cephalad, and also gradually becomes further removed
from the median line. It finally passes out into the IX + X
by some 8 or 10 rootlets, which break through the ascending
trigeminal tract to make their exit. It is here this fasciculus
attains its greatest dimensions. A small portion of it, how-
ever, continues cephalad, and emerges as the portio intermedia
Wrisbergii of the VII. It is accompanied as far as the exits
of the 1X + X on its inner side by the “ sensory”’ nucleus of
the Ix +X. The finer structure of this bundle is as follows:
it consists of the finest fibres with gray matter intermingled ;
the fibres both divide and give off collaterals which encircle
the nearest ganglion cells.

It is evident, from the above brief résumé of Kolliker’s
account, that the fasczculus communis corresponds with the
fasciculus solitarius in every detail, and that the nucleus on the
inner side of the former corresponds with the so-called sensory
nucleus of the IX + X.

Furthermore, inasmuch as the fasciculus solitarius is con-
tinued cephalad into the portio intermedia, it is evident that the
portio intermedia is represented in the tadpole by the fasciculus
communis root of the VII, the ganglion geniculs by the ganglion
of this root, fused in the tadpole with the ganglion Gasseri, but
separate in Amblystoma, and the chorda tympanz by that portion
of the fasciculus communis which, on emerging from its gan-
glion, unites with the hyomandibularis VII, separates as the
R. mandibularis internus, and innervates portions of the floor
of the pharynx, especially that part, in the tadpole, near the
site of the future tongue. The R. mandibularis internus thus
corresponds, point by point, with the chorda tympani, having
the same character of fibres, the same internal origin, and the
same course and final termination.

That the R. palatinus would correspond, in part at least, to
the R. superficialis major, would seem probable. One objec-
tion to this view, z.e., that the latter is a motor nerve to the
muscles of the palate, has been removed by Turner (63), who
has shown that probably the muscles of the soft palate derive
their motor supply from the pharyngeal plexus through the
pharyngeal branch of the Vagus. Another serious objection,

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 187

however, arises from von Lenhossék’s discovery (39), that the
fibres of the superficialis major are not connected with the
geniculate ganglion. As we shall see later, the innervation of
the mouth (in the broader sense) is a complicated problem.

The homology of the R. mandibularis internus with the
chorda tympani was first briefly discussed by me in the articles
in the Zoologischer and Anatomischer Anzeigers. Since then
Gaupp (25), reasoning from topographical relations, has come
to a similar conclusion.

In Urodela the R. mandibularis internus, or chorda tympani,
is represented by the R. alveolaris VII, which usually, for part
of its course, proceeds in a canal in the lower jaw. Fischer
was not able, apparently, to determine its distribution clearly.
He mentions, however, twigs to the skin. This is probably
either incorrect, or such twigs leave the proximal part of this
branch and are composed of cutaneous fibres not properly
belonging to the R. alveolaris. Von Plessen and Rabinovicz
do not mention its final distribution.

Although anticipating somewhat, it may be here noted that
Ewart describes a bundle of fibres continuous with the root of
the R. palatinus and running forwards to end in the “fold of
mucous membrane lying between the hyoidean and mandi-
bular cartilages.”’ This he regards as the homologue of the
chorda tympani. Pollard (49) also regards the R. mandibularis
internus as the chorda, and correctly homologizes it with the
R. alveolaris in Urodela. The other view of Froriep (22),
that the chorda is represented by a sensory branch to the
lower jaw similar to the R. ophthalmicus superficialis and
buccalis, z.¢., a lateral line branch is certainly not correct. In
addition to the criticism made by Wiedersheim (67, p. 286),
the chorda in every way corresponds to the R. mandibularis
internus, as stated above, and not to the R. mandibularis
externus, which innervates lateral line organs.

It is possible, however, if, as Kupffer (36) suggests, Froriep
really treats of epibranchial and not lateral ganglia, that he
had the correct nerve, but was mistaken in assigning it to the
lateral line system.

In the IX +X the two outer ganglia on these nerves

188 STRONG. [VoL. X.

(B and C), which belong more especially, apparently, to the
fasciculus communis component, would correspond to the two
outer ganglia on the IX and X in the higher vertebrates,
namely, those usually designated the ganglion petrosum IX
and ganglion trunci vagi. They would be partially, at least,
homodynamous with the ganglion geniculi.

(c) Comparison with the Fishes.—It is evident that so
important a tract as the fasciculus communis must be rep-
resented among the forms below Amphibia, and it is tolerably
certain that the homologue is the /obus vagz of fishes.

In Goronowitsch’s article on the brain and cranial nerves of
Actpenser (28) is the following: ‘‘In der Gegend des Calamus
scriptorius ist, wie gesagt, die graue Substanz des Hinterhornes
breiter entfaltet. Sie hat dieselbe Struktur wie im Riicken-
mark. Medial vom Hinterhorne erscheint allmahlich eine neue
Lage von grauer Substanz. Sie besteht aus feinkornigem
Grundgewebe, in welchem viele kleine Nervenzellen eingebettet
liegen (Fig. 45 Lv.). Zwischen diesen Zellen verlaufen die
feinsten Fasern in verschiedenen Richtungen. In proximalen
Abschnitten wachst die Querschnittsoberflache dieser Sub-
stanz. Sie verbreitet sich in dorsaler Richtung und verdranet
lateral den Hinterhornkopf. In proximalen Ebenen bildet
diese graue Substanzlage einen Vorsprung im ventriculus IV.
Es ist das der Lobus vagi.’’ Goronowitsch mentions, as do
other writers, the series of swellings visible in the wall of the
ventricle, and caused by the lobus vagi, and says they corre-
spond to the bundles making their exit from it. They form the
dorsal source of the Vagus and Glossopharyngeus roots, exclu-
sive of the N. lateralis, and are fine-fibred. Goronowitsch also
finds that a bundle is given off from the lobus vagi to the
Facialis.

In all accounts there is a remarkable agreement, — the situa-
tion in which it appears, in the vicinity of the opening of the
fourth ventricle, its peculiar appearance and composition
there which leads to its description as ‘eine lichte Stelle,”
“ein rundlicher Fleck,” “eine runde Gewebsinsel,” “ein Langs-
biindel feiner Fasern eingelagert in einer dichten grauen
Masse,” ‘“‘eine neue Lage von grauer Substanz,” consisting of

No.1.] THE CRANIAL NERVES OF AMPHIBIA. 189

”

“feinkérnigem Grundgewebe,” the appearance in it of fine
fibres which form the chief supply of the IX + X,—all these
peculiarities demonstrate the homology here suggested.

This tract is described by other investigators of the medulla
of fishes, and there seems to be essential agreement between
all their accounts, with variations respecting the number of
enlargements presented by it. Rohon (52) gives a more de-
tailed account of it in Selachi, and considers it as representing
the summation of a number of nerve nuclei. The nerves
originating from these he considers homologous to dorsal
spinal roots, —a view which is discussed elsewhere.

Among the Teleosts, Mayser (41) gives a detailed account
of the structure of the lobus vagi, which is here enormously
developed. Mayser distinguishes five parts in the lobus vagi:
(1) The outermost layer, comprising the bulk of the fine-fibred
roots, of which there are two layers —a thicker outer of medul-
lated fibres, and a thinner inner layer of non-medullated fibres.
(2) The gelatinous substance, consisting of a dense ground-
substance with numerous nerve cells interspersed. There are
also solitary bundles of fine fibres here which join the first
layer. (3) The secondary vagus-tract, consisting of fibres from
(2) and from the “spongy substance,” which is to be considered
the central gray. This tract is joined by the secondary tract
from the lobus trigemini, and proceeds cephalad to the higher
centres. (4) The origin of the thick-fibred motor vagus-roots.
(5) Ependyma.

Mayser, it may as well be added here, describes the lobus
trigemini as having much the same structure as the lobus vagi,
and on this ground and from the fusing of their secondary
tracts he regards them as practically identical. He finally says
that we have thus in Cyprinoids three great cranial nerve roots
arising from a common nucleus, 2.e., the continuous substantia
gelatinosa of the medulla and spinal cord, these three roots
being the ascending and dorsal geniculate (lobus trigemini)
Trigeminus, and the sensory Vagus. The ascending and the
dorsal geniculate Trigeminus roots together represent the
ascending Trigeminus of the higher vertebrates.

Mayser apparently includes more in the lobus vagi than, for

190 STRONG. [VOL. X.

example, Goronowitsch, namely, the nuclei of the motor roots.
This, of course, does not affect the actual similarities existing.
When we compare this description with the condition in the
Amphibia we find them, I think, similar. Excluding the motor
nuclei, we have in both cases the bundles of fine fibres, the
ground substance, and nerve cells, arranged in practically the
same manner. The fasciculus communis itself represents
the outer layer described by Mayser, the peculiar ground-sub-
stance the second layer, and the nerve cells found by Mayser
are represented in the tadpole by the group of ganglion cells
accompanying the fasciculus; in Cryptobranchus partly, at
least, by Osborn’s “nucleus of small sensory cells by which
the fasciculus communis is apparently reénforced”’ (45); and
in the higher forms by the “‘sensory nucleus” of the IX + X,
and probably by other cells in the vicinity of the fasciculus
solitarius.

One great difference is apparent between this tract, or tracts,
in fishes, on the one hand, and in Amphibia — especially Anura,
— together with the higher vertebrates, on the other, namely,
that in the fishes it is much more developed. This is easily
intelligible when it is considered that it is essentially the
central organ of the branchial nerve supply. Its great develop-
ment in fishes is correlated with the development of the gills,
and where these are in process of reduction or lost it is
correspondingly reduced.

The fine-fibred branches of the postauditory portion of this
component (see Table, p. 180) correspond, of course, with the
similar branches constituting the fine-fibred, visceral portion of
the IX + X in fishes, as distinguished by Stannius, Shore, and
others. This excludes the larger-fibred branchio-motor portion.
The regular arrangement of the roots, ganglia, and branches, as
seen in many fishes, is, in the tadpole, mostly obscured, owing
to causes noted above (p. 135). This arrangement is partly pre-
served, however, in the series of roots from the fasciculus com-
munis. The ganglion of the IX (ganglion C) is still separate,
but the ganglia of the Rr. branchiales are fused with each other
and also, partly, with that of the R. visceralis. Owing not only
to the forward position of the gills relative to the auditory cap-

Nov t.] THE GRANIAL NERVES OF AMP HIBIA. I9I

sule, but also to the forward position of the heart and part of
the viscera, the courses of these branches are likewise altered.

It will now be well to discuss the character of the lobus
trigemini. It has already been seen that the root from this
structure, where best developed, supplies fibres to the various
branches of the Facialis, and also independently gives origin
to a R. palatinus, R. lateralis, and other recurrent branches.
Stannius has already stated (v. supra) his belief that this root
was concerned largely in the innervation of the terminal buds
which are found so abundantly over the surface of the head,
gular plate, dorsal part of the body in some cases at least, and
in the mouth and gill cavities. Wright has made similar obser-
vations as to the innervation of these organs by nerves from
this root, especially around and on the barbels where the buds
are so concentrated. Whether this root is devoted to the
terminal buds as exclusively as those from the tuberculum
acusticum are devoted to the canal organs, will require further
investigation; that it is largely concerned with the innervation
of the buds seems quite certain.

Stannius is not always clear in his description of this root.
In some forms — Spinax and Selachians generally — his fine-
fibred root emerges quite ventrally, on a level with the motor
root of the VII. We have seen, however, that other investi-
gators in Selachians have always described the root from the
lobus trigemini as the most dorsal, and that this is its position
in Teleosts. From this ventral fine-fibred root of Stannius is
derived the R. palatinus. When we consider this, and also that
Mayser and Wright do not describe any root of the Facialis
derived from the lobus vagi; that Mayser considers the lobus
vagi and lobus trigemini to be similar; that the fasciculus
communis root of the VII in Amphibia sometimes emerges dor-
sal and sometimes ventral to the VIII (though always ventral to
the lateral-line root); and that there is apparently in Amphibia
no lobus trigemini root, it would seem not improbable that we
were really dealing here with the same root, which simply
shifted its position. On the other hand, as we have just seen,
while Stannius describes this fine-fibred root as rather ventral in
Selachians, others find in Selachians a dorsal root arising typic-

192 STRONG. [ Von.Xe

ally from the lobus trigemini. Finally, we have in Acipenser
(Goronowitsch, 28), as seen above, doth roots present, 2.2. a
fine-fibred most dorsal root from the lobus trigemini, and
another fine-fibred root emerging ventrally with the motor root
of the VII.

The accounts of the R. palatinus also seem to vary. Accord-
ing to Stannius, it is sometimes given off by the V, sometimes
by the VII, and sometimes is independent. It is sometimes
reénforced by a branch from the IX (Stannius, Goronowitsch),
and by Pollard (49), in Polypterus, is described as composed of
united branches from the V, VII, and IX nerves. Goronowitsch
denies the existence of any R. palatinus trigemini, and asserts
that the R. palatinus belongs to the Facialis. In Amphibia
the latter is true. It will not be possible to reconcile these
apparent discrepancies until special investigations have been
made upon more of the different types. It would seem quite
certain that in some cases, at least, a part of the R. palatinus
is derived from the lobus trigemini (Stannius, Wright), and
that the significance of this lies in the existence in the mouth
of numerous end buds to be innervated. It does not seem
possible, however, to relegate the supply of all these buds to
this source, inasmuch as we have some of them supplied by the
R. lingualis IX and even, possibly, by some of the Rr.
pharyngei and branchiales X in Amphibia. In this connection,
the view of Mayser that the lobus trigemini and lobus vagi are
similar structures comes again into consideration. While these
two structures obviously, from the final distribution of their
nerves, must be considered as largely different, yet the latter
may be conceived as containing a number of fibres to end buds
in the pharynx, while the lobus trigemini has been specialized
off to supply the great bulk of these structures in the mouth
and over the head and body.

Respecting these preauditory roots, on a careful examination
of the most ventral root of the VII in Selachians I found this
root presented the appearance of a double root. Ewart seems
to have observed a similar appearance. As far as could be
judged from dissections merely, the R. palatinus consists of
fibres from both this double root and from the lobus trigemini

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 193

root. One part of this double root must, of course, be motor
and pass into the R. hyomandibularis, the other part will, I
believe, be found to arise from the lobus vagi as in Acipenser.
I am inclined to believe that this will be found to be the con-
dition in all fishes, namely, the coéxistence of doth a root from
the lobus vagi and one from the lobus trigemini, and, further-
more, always a R. palatinus from the former at least, the
variable element in the palatine nerves being the part played
by the lobus trigemini root in their formation.

Again, we have the discrepancy, which has been mentioned,
with regard to the R. ophthalmicus profundus, which, according
to some investigators, belongs to the Trigeminus proper and
according to others (e.g., Wright) is derived from the lobus
trigemini. It is possible that here again there is not a com-
plete separation or specialization of the fibres to end buds in
some forms (see below, however, on this point).

This branch, the ophthalmicus profundus, has been discussed
by H. H. Wilder (71), who comes to the conclusion that the
ophthalmic branch of the Trigeminus in Amphibia represents
the united ophthalmicus profundus and ophthalmicus super-
ficialis trigemini. It seems to me that this is probably correct,
but the fusion has already taken place, in Salamandra maculata,
to which Wilder refers, inasmuch as the R. frontalis of Plessen
and Rabinovicz is, as we have seen, the R. ophthalmicus super-
ficialis facialis and not the R. ophthalmicus superficialis
trigemini. The latter, then, does not appear to be present as
an independent branch, and has already united with the
ophthalmicus profundus. The ganglion of the latter has
already fused, forming a part of the Gasserian ganglion, for the
“ Nebenganglion”’ is a facial ganglion.

Our view as tothe fate of the ophthalmicus profundus,
however, will partly depend upon whether we find it to belong
to the Trigeminus proper or to the lobus trigemini root. If
the latter, it very possibly would have either undergone a
reduction or aborted, owing to loss of end buds in the nasal
region.

The results of the majority of investigators, however,
certainly favor the view that the R. ophthalmicus profundus

Tl seth ST een eo Ba

194 STRONG. [Vou. X.

belongs to the general cutaneous system (Ahlborn, Gorono-
witsch, Ewart).

I may add, in support of Wilder’s view, the relation of the
R. ophthalmicus trigemini, in the tadpole, to the III and IV
nerves. It lies in the fork formed by the division of the III
into its inferior and superior branches, and likewise comes into
relation with the IV. In Galeus canis the R. ophthalmicus
profundus bears precisely the same relation to the III while the
R. ophthalmicus superfictalts V bears the same relation with
the IV that the single R. ophthalmicus trigemini bears to these
two nerves in the tadpole.

As far as I can ascertain, the root from the lobus trigemini
is probably coarse-fibred in Selachians. As the roots from the
tuberculum acusticum are devoted to the canals, it would seem
likely that those fibres in the lateral line nerves of the head
derived from the lobus trigemini are devoted to the innervation
of the ampullae. If this were true, as further research is nec-
essary to show, the ampullae would represent the end buds of
other fishes. The absence of a R. lateralis from the lobus tri-
gemini in Selachians and the concomitant absence of such
organs on the trunk is significant in this connection.

The innervation of the pit organs should be studied in this
connection. If innervated by fibres from the lobus trigemini,
it would appear that they have been secondarily specialized
from the end buds and added to the lateral line system.

If it is true, furthermore, that the fine-fibred root from the
lobus trigemini in Teleosts and Ganoids is represented by a
coarse-fibred root in Selachians, we have a most interesting
case bearing upon the significance of fibre-calibre. Here the
principal change, apparently, in the structure innervated is a
sinking below the surface and a probable increase in size.

As has been seen, there seems to be no lobus trigemini in
Amphibia. This is not difficult to understand now when it is
considered that the end buds are confined to the mouth in
Amphibia, and, consequently, much reduced in number. The
Trigeminus, however, as described by Osborn, derives its fibres
internally from the following sources: (1) The ascending
tract from the cervical region, reinforced by (2) fibres from the

MONT: | THE CRANIAL NERVES OF AMPHIBIA. I95

deep motor nucleus, representing two tracts. (3) Fibres from
the sensory nucleus. (4) The descending tract from the mes-
encephale mucleus.. (5) Lhe dinect, encephalic tract... .
«The sensory nucleus is very large and extends forwards
beyond the level of the cerebellum.”’ It is possible this sensory
nucleus is representative, partly, of the lobus trigemin1.

In any case, the disappearance of this system of nerves as a
separate system in Amphibia in correlation with the dis-
appearance of these cutaneous organs is a most interesting
phenomenon. In the Amphibia, then, we have a reduction
already accomplished in the disappearance of the end bud
nerves, and in the Anura another reduction in process of
accomplishment in the loss of the lateral line nerves, in several
forms at least, as the fully developed anurous condition is
attained.

These questions all have an intimate bearing upon the origin
of taste and upon the vexed question of the innervation of the
taste buds in the higher vertebrates. It is easily seen that the
problem is one of extreme complexity. It is not unreasonable
to expect, however, that thorough comparative researches upon
the exact composition of the cranial nerves will clear up these
obscure points.

Stated briefly, we seem to have the following alternatives:
(2) The taste buds (end buds) are innervated in the lower
forms by the root from the lobus trigemini only. As the latter
diminishes, owing to the loss of the end buds on the exterior,
these fibres fuse with the Trigeminus proper. This view does
not seem to harmonize well with the facts in Amphibia, as stated
above, namely, the innervation of end buds by the R. mandi-
bularis internus VII, R. lingualis IX, e¢c. The R. palatinus,
and even the R. mandibularis internus VII, might indeed
receive the fibres in question through the anastomoses with
the V. This would tend to show that the V is the nerve of
taste in the higher forms.

(4) The innervation of these structures can be regarded as
shifted from one set of nerves to another, z.e., from those
issuing from the lobus trigemini as this diminishes or is lost,
to those issuing from the lobus vagi (fasciculus communis).

196 STRONG. [VoL. X.

This involves questions hardly settled, as to change of function
of nerves, the innervation of the buds being taken up second-
arily in this case by sensory visceral nerves.

(c) We may regard, with Mayser, the lobus vagi and tri-
_ gemini as equivalent structures, in which case there is no diffi-
culty presented by the innervation of the buds by various
nerves from these two structures. This ignores, however,
the greatly different innervation territory, which the lobus
vagi has, in other respects, as compared with the lobus
trigemini. i

A modification of the latter view seems most probable. The
lobus vagi and lobus trigemini cannot be regarded as entirely
equivalent structures, but the latter may be considered as
devoted to the innervation of the end buds, and the former
may be considered to contain similar fibres, in addition, how-
ever, to others of a different nature. We have already seen
(p. 189) that Mayser distinguishes two sets of fibres, medullated
and non-medullated, in the lobus vagi and have also found in
the tadpole, in such branches as the R. palatinus VII and R.
mandibularis internus VII, two sets of fibres, one somewhat
coarser and with a sheath staining much more darkly than the
other. This may partly account for the diminishing of the
lobus vagi, where the branchial cavities — which are supplied
with these buds in fishes — disappear.

One fact is very apparent, both from the investigation of the
Amphibia and the comparison with the results of other workers
upon the fishes, namely, that there is no direct genetic connec-
tion between the lateral line system and its nerves and the
sense of taste and its nerve supply. The suggestion of Beard
upon this subject has already been criticised in my preliminary
communication in the Anatomzscher Anzeiger (62). Both may
have been derived from a more generalized and older form of
sense organ, the end bud, present generally on the body and in
the mouth. The lateral-line system, whatever its origin, is a
specialized system, and its nerves are in every way sharply
contrasted with those connected with taste. The auditory
organ is the only one whose connection with the lateral-line
system is at all probable.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 197

It is also evident that the lateral-line system has no especially
segmental character, and that it cannot properly be used in the
manner in which it has been attempted to use it, as a general
guide in determining the segmentation of the head.

4. Motor Component.

The fourth, motor component, shall not be treated here at
length. In all the forms above the Cyclostomes we have
splanchnic motor roots to the V, VII, IX, and X.

Ahlborn describes no such roots, apparently, except for the
V, where it is very large. As Julin (33) and Dohrn (15) assert
that the VII has motor elements, it is possible a motor root
will yet be found for it. Ransom and Thompson (50) describe
large motor fibres, which unite with the Vagus in Petromyzon,
but not in Myxine. These fibres, however, are from anterior
roots. There are, besides, exceedingly fine fibres to the heart
and blood vessels.

It would appear, both judging from this and from the con-
ditions in the tadpole, that a distinction exists between vaso-
motor and branchio-motor nerves, though both are considered
visceral.

The following are these motor roots in the authorities
mentioned above:

FORMS. AUTHORITIES. NAMES OF ROOTS.
Sryprourauchus:. ».|-Osborn ... .'): =| VII-VIII 3 and 4.”
Acipenser. . . .|Goronowitsch . . .| ventral root of Facialis.
PUES oe) | MWWTISHE S02) 4) |) ss, | transverse root of VEL
Gyprmoids (=. |.) Mayser) 2)... . | ventral geniculate root/ef VII.
nicuronectes:-/ |). Stannius; 4.) ./ |). .'. *. | root. 5.
ceed ab rt) oul) CANTS Ne bay Si st Partiof rook 2.

Generalized type |.| Stannius’|..). . .. , - | root 4.

idemanehus, . |=). |(Gesenbaura 2)... . | Facialis.

Echinorhinus . .| Jackson and Clarke .|“VyVII.”

Scyllium . . . .| Marshall and Spencer | part of “VII 4”?

Laemargus . . .| Ewart . . . . . .|part of hyomandibular and palatine
root of VII.

Provopterus .°. |. | Burckhardt... \2 0... | “ VIIT 3, 4.”

198 STRONG. [VoL. X.

It must be remembered, however, as shown above, that there
is reason for believing these roots, except those in Crypto-
branchus and Protopterus, are in reality compound, and include
a component from the fasciculus communis (lobus vag).

The motor root and the fasciculus communis root forms, as
we have seen, the constant part of the Facialis, including the
portio intermedia, which persists in the higher vertebrates. It
is, of course, this motor root which becomes so much more
important in the highest forms owing to the development of
the facial musculature.

5. Comparison with the Cyclostomes.

It will be well to take a glance at the conditions among
Cyclostomes, which, probably, present very primitive condi-
tions, and which should throw much light upon the origin of
the various differentiations existing among the cranial nerves
of the higher fishes. There have been many contradictory
statements made, however, concerning the Cyclostome periph-
eral nervous system, and I think it will be evident that our
knowledge of it is still far from accurate.

Langerhans (40) describes two kinds of cutaneous sensory
organs. One is situated in papillae, which are especially
numerous around the mouth and on the dorsal “fin,” but are
also found scattered over the body and in the mouth and
pharynx. The other is situated at the bottom of pits, and
these pits are arranged irregularly in lines, there being a line
above and a line below the gills, other lines proceeding along
the side of the body, above the middle; and still other lines
around the mouth and over the head, around the eye. These
sunken organs he homologizes with the lateral-line system.

According to Ahlborn (1 and 2), the Trigeminus springs
from the medulla by three roots, one above the other. The
most dorsal is the ophthalmicus, and arises from the ascending
trigeminal tract. It has a separate ganglion. The next is the
remainder of the sensory Trigeminus, and has the same origin.
The most ventral motor root arises from the motor trigeminal
nucleus and a descending tract. The ascending Trigeminus is

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 199

a direct continuation of the dorsal funiculus of the cord. It
consists principally of fine, with a few medium-sized, fibres.

The Vagus roots fall into two divisions. The four roots
emerging farthest caudad terminate internally in the “ upper
lateral ganglion,” which is a continuation of the dorsal column
of cells in the cord. The four roots emerging most cephalad
have the same internal termination as the Acusticus.

The terminal nuclei of the Acustico-facialis, and the four
roots just mentioned, lying as they do above the ascending
Trigeminus and upper lateral ganglion, which represent con-
tinuations of the cord, are thus, according to Ahlborn, some-
thing superadded in the medulla oblongata, and are equivalent
to the higher brain centres. They are not represented by any
portion of the cord, or, at the most, by a very small band mesad
of the dorsal funiculus, of which band one can only say that it
exists. The nucleus of the Facialis lies well above and sepa-
rated from that of the Acusticus. The cells in it are small and
the fibres of the Facialis issuing from it are fine and of a very
uniform size. The Acusticus emerges in two roots, one above
the other.

Of the IX + X roots, the four composing the first (cephalic)
set unite to form R. branchialis I, which sends a twig to the
Hypoglossus. The first two of the second set are joined by a
recurrent branch from the Facialis to form the fine-fibred
N. lateralis. The last two roots form the Pneumogastricus,
which is connected with the N. lateralis through the ganglion
of the same.

The first fact that impresses one in this arrangement is that
the first set of roots from the Acusticus region do not form
the N. lateralis, but the R. branchialis I. Furthermore, the
N. lateralis is formed partly by a recurrent branch from the
Facialis passing around outside the auditory capsule — a thing
which does not occur in the N. lateralis in the higher forms.
Again, on comparing the course of the N. lateralis with the
arrangement of the pits, it is evident that only a small pro-
portion of them would be innervated by this nerve, which has
a position near the mid-dorsal line. When these facts are con-
sidered — especially the non-derivation of this nerve from the

200 STRONG. [Vou. X.

Acusticus center, thus differing from the origin so universal for
the N. lateralis in all other forms—jit must be regarded as
very probable that this nerve does not represent the N. late-
ralis vagi of higher forms. Stannius has also called attention
to some of these difficulties and reached a similar conclusion
(57, p.96). What it does represent is probably the R. lateralis
trigemini, so-called, of Teleosts—a nerve which is formed
principally, as we have seen, by a recurrent branch of the Fa-
cialis, derived from the lobus trigemini, and which is reénforced
by a branch from the Vagus. It would then much more prob-
ably innervate the papillae which are so numerous on the dorsal
fin, and which probably correspond to the structures innervated
by the so-called R. lateralis trigemini. The R. branchialis I
would, apparently, represent the R. lateralis. I am forced to
believe that the exact anatomy of these nerves is not yet accu-
rately known, nor have their connections with the cutaneous
sense-organs been sufficiently worked out. With respect to the
remainder of the Facialis, it has been asserted by Julin (33)
and Dohrn (15) to contain motor elements. If this be true, it
probably does not arise merely by the one root, as described.
If the character of the so-called N. lateralis be as above sup-
posed, the most dorsal nucleus of the Acustico-facialis center,
from which the Facialis emerges, would correspond to the lobus
trigemini. Its structure, as described by Ahlborn, would seem
to support this view. If this be the case, it is evident that the
distinction between the lobus trigemini, on the one hand, and
the ascending Trigeminus and lobus vagi, on the other, is
already here sharply drawn, and is quite a primitive feature.
This would be in opposition to Mayser’s views quoted above
(p. 189). The course of the Facialis in the head is not decisive
on this point, inasmuch as we have seen that in higher forms
the lobus trigemini and lateral-line components go together.
In comparison with Kupffer’s observations (36), it would
seem probable that, in general, Kupffer’s medial elements
derived from the neural crest and cagmmon to both spinal and
cranial nerves, would be represented by such ganglionated
nerves as emerge from the ascending Trigeminus. It must
be remembered, however, that, according to Mayser, not only

No. 1.] THE CRANIAL NERVES OF AMPLHIBIA. 201

the ascending Trigeminus, but the lobus vagi and lobus tri-
gemini taken together, represent continuations of the spinal
cord; that in the tadpole the lobus vagi (fasciculus communis) -
can be traced, enormously diminished, into the cord a short
distance at least ; and that, according to Ahlborn (1), and also
according to Ransom and Thompson (50), the Vagus, as well
as the Trigeminus, in Cyclostomes, come from centers rep-
resenting continuations of parts, though different parts, of the
cord. Mayser (41) and Ahlborn are in accord, however, in
considering the Acusticus-lateralis center as something distinct
and superadded. Even in Cyclostomes, however, the Vagus
center is a considerably enlarged and developed center in the
medulla.

Returning to Kupffer, it would next seem probable that his
lateral element, which is derived from the dorsal fusion with
the epiblast, is represented by the lateral-line element, plus,
perhaps, that to the end buds; and that, finally, his epibranchial
ganglia are represented by the ganglia of nerves terminating
centrally in the lobus vagi (=fasciculus communis + terminal
nucleus = fasciculus solitarius + sensory nucleus IX + X).
Whether the ganglia of the nerves supplying the end buds can
be considered as belonging to or representing this series rather
than the preceding is a question whose answer depends upon
the answer to the correlated question, already considered, as to
the relation between the lobus trigemini and lobus vagi.

IV. GENERAL CONSIDERATIONS.

1. Relation of Cranial and Spinal Nerves.

Hatschek (30) has made some interesting and suggestive
comparisons between the nerves of Amphioxus and Ammo-
coetes, which at the same time throw more light upon the
origin of such nerves as the lateralis and visceralis, and of the
differences obtaining between the cranial and spinal nerves.
In brief, this view is as follows: In Amphioxus the dorsal root
divides into a dorsal and ventral branch. The dorsal branch
subdivides into a N. cutaneus dorsalis and a N. lateralis dor-
salis.’ —The ventral branch divides into a N. cutaneus ventralis,

202 STRONG. [vou x

a N. lateralis ventralis, and a N. visceralis. Only the latter
contains motor as well as sensory fibres (motor to the splanch-
nic muscles). This primitive relation is retained by the cranial
nerves, and the loss of this relation and of certain branches
by the spinal nerves is owing to the usurpation of the
long trunk-branches of the cranial nerves. The course of the
spinal dorsal nerves inside the body muscles he regards as due
to the shortening of the dorsal nerve. Kupffer, however,
regards the spinal dorsal nerve as a new acquisition. This
peculiarity presented by the spinal nerves is very important,
and its satisfactory explanation must be a crucial point in any
theory of the cranial and spinal nerves.

Two general criticisms that may be made upon Hatschek’s
views, I think, are that they do not take sufficiently into
account qualitative differences in the nerves under discussion,
his conclusions being based more upon simply topographical
relations, and, secondly, that they consider the nerves too much
apart from correlated structures, from those innervated by them
especially, and, consequently, offer no explanation why the
usurpation in question took place.

We have seen that in the cranial nerves of the higher fishes
there are three kinds of cutaneous nerves distinguishable by
peculiarities of their fibres, of their distribution, and of their
internal origin, z.e., (1) mixed fibres of a general cutaneous
character continuous with the posterior columns of the cord,
(2) coarse fibres innervating the lateral line organs and ter-
minating centrally in the differentiated tuberculum acusticum,
and (3) fine fibres innervating the terminal buds (coarse in
Selachians and innervating the ampullae?) and terminating
centrally (principally) in the lobus trigemini. The latter, z.¢.,
(3), 1s possibly not completely differentiated. Among the
Cyclostomes, it seems probable, this specialization has not been
carried so far, but this is not yet sufficiently known.

It is obvious that it is only similar and specialized structures
that are most likely to attain a more unified innervation, and,
accordingly, it seems most probable that such a process of
usurpation as that mentioned above would take place in con-
nection with the cutaneous sense organs. These latter would

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 203

concomitantly become more restricted to certain regions and
would, not improbably, undergo further specializations. Ac-
cording to this view, the cutaneous sense organs would have
had at first a more general innervation, and only later would
their nerve supply proceed from only one or two nerves.

Another change which seems to have taken place, similar in
character to the above but affecting a different structure, is the
assumption by several nerves of the supply to the gills (and
other visceral structures ?) and concomitantly the creation in
the medulla of a special center for this nerve supply (lobus vagi).

Hatschek points out the superficial position of the ganglia in
Amphioxus as compared with the spinal ganglia in vertebrates.
If the above homologies (p. 200), with Kupffer’s results, be
correct, it is precisely the branchio-visceral ganglia of the
VII-IX—X (epibranchial ganglia), and the special cutaneous
ganglia (lateral line ganglia and ganglia of nerves to end buds
also, perhaps) which arise from special epiblastic thickenings as
opposed to those ganglia derived from the neural crest, and it
is precisely these ganglia which belong to the cranial nerves
with long trunk branches, in other words, those which have
taken the place of certain portions of the spinal nerves. The
ganglia, then, of the cranial nerves, arising in connection with
epiblastic thickenings, are the ganglia which the spinal nerves
do not possess, having probably lost them. This would explain
this difference in the mode of origin of cranial and spinal
ganelia.

The fusions described, in connection with the Trigeminus,
by Beard and Kupffer possibly belong to the lateral line gan-
glion which lies over the Gasserian ganglion proper, possibly,
also, to nerves to end buds.

Of course the presence of the lateral motor roots in cranial
nerves constitutes a difference of another character from the
above. ‘This and the correlated problem of the sympathetic do
not fall within the scope of the present discussion.

There are several anatomical peculiarities which afford further
support to Hatschek’s comparison, as amended above. These
are the remarkable parallelisms existing between these three
systems of cutaneous nerves. I have called attention to the

204 STRONG. [Vor. X.

existence of this peculiarity in the relations between certain
minor branches of the Trigeminus and the lateral line nerves
to the head. The parallelism is carried further than this, how-
ever. The R. ophthalmicus superficialis VII parallels the R.
ophthalmicus V, the R. buccalis VII parallels the R. maxillaris
V, the R. communicans IX ad VII parallels the R. mandt-
bularis externus VII, and the postauditory R. supratemporalis
parallels the R. auricularis vagi. In fishes this: is still more
striking where the two pairs first mentioned are in close
apposition and can only be separated with difficulty. We
have, besides, in fishes the element from the lobus trigemini,
whose fibres are not merely in close apposition but, probably,
mingle with the lateral-line fibres, forming thereby a still closer
union. On the trunk we have the two long branches: the R.
lateralis trigemini (facialis) and the N. lateralis.

These parallelisms might be partly explained by the sub-
jection of the nerves in their growth to similar influences by
the other parts, but this could hardly explain such close
parallelisms. Nor are such parallelisms easily reconcilable
with the theory that the lateral-line system of nerves represents
a system phylogenetically different from the others. The ex-
planation most naturally suggested is that these three systems
were originally one. Of the three, the general cutaneous
system to which the Trigeminus proper belongs would represent
most nearly the primitive nerves from which the others were
differentiated. Itis, naturally, only the differentiated cutaneous
nerves that we find extending over the trunk from the cranial
nerves ; or, to put it in another way, the spinal general cutane-
ous nerves bear the relation to the cranial special cutaneous
branches to the trunk that the general cutaneous branches from
the ascending Trigeminus bear to such branches in the head.
We might even advance a step further and say that the
more intimate fusion of the end bud and lateral line nerves
indicates the evolution of the latter from the former, a view
probable on other grounds and advocated in Wiedersheim’s
Grundriss (67).

Hatschek (30) has called attention to the morphological im-
portance of the dorsal rami as landmarks of former conditions.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 205

The other longer and principal branches have been more
influenced and extended by the development and topographical
changes in various parts, such as the jaws, sense organs, ec.
Hatschek, however, as we have seen, does not recognize the
fact that there are, even of these dorsal rami, qualitatively
three kinds. In determining segmentation, by means of them,
it is necessary to decide first, whether each can represent a
separate segment, or all must be taken together to represent
one segment. The former view would rest upon the supposition
that some of the components for any one segmental ramus
have been lost. The latter view would, perhaps, seem more
probable, and agree better with the views here advanced as to
the cause of these differentiations of cutaneous nerves.

It is questionable whether these components belong espe-
cially to different levels of the head and body, as Hatschek’s
comparison with Amphioxus would seem to indicate. Each
one of his four sensory branches might consist, actually or
potentially, of the three components. From the actual rela-
tions in fishes, however, the general cutaneous component is
naturally confined to no particular locality in its innervation
territory. Its roots are ventral to the other two. Of the
other two, in origin, the lateral line component is ventral to the
remaining one, and is lateral in its general distribution on
the body. On the head there is no difference, topograph-
ically, in this particular respect, between the three cutaneous
components. :

If Hatschek’s view, similar in some respects to Balfour’s, is
correct, and the cranial nerves most closely approach the primi-
tive conditions, the spinal nerves having lost elements, then
we would naturally find these tracts, peculiar to the medulla,
showing the remnants, at least, of continuations in the cord.
Whether this were true or not, however, the validity of this
view would hardly be affected.

It is useless to speculate further upon this subject. What
it is wished, however, to emphasize here, is the importance of
taking into full consideration, as a factor, the cutaneous sense
organs, in the attempt to obtain a philosophical understanding
of the changes undergone by the peripheral and central

206 STRONG. [Vor. X.

nervous systems. The development and specialization of these
structures have probably played an important part in the
changes leading to the organization of the vertebrate periph-
eral and central nervous systems. Furthermore, when we come
to compare the nervous systems of fishes and Urodela with the
higher vertebrates, without the general clue that these struc-
tures have disappeared, and the nerves supplying them likewise
either disappeared or metamorphosed, only false conclusions
are inevitable.

Nor is the question one merely affecting the peripheral
nervous system, inasmuch as it affects likewise the central
terminations of this nerve supply and indirectly other portions
of the central nervous system in physiological connection
therewith. A number of changes in the higher centers will
probably be found to be connected with these transformations.

As an instance of the effect of these changes upon the
central nervous system, aside from the medulla, it is possible,
I think, that the reduction of the cerebellum in Amphibia
may be correlated, to some extent, with the reduction in these
cutaneous organs. Its size in the higher forms would be,
perhaps, secondarily reacquired.

As these changes in cutaneous organs are largely affected
by habitat, it is obvious that animals widely separated may, by
changing their habitat, undergo changes in their nervous
system quite similar in character. Here, again, we meet the
phenomenon of parallel changes in different forms, due to
similar conditions of environment, and, in such cases, of physi-
ological rather than morphological value.

2. Relations of the Pre- and Postauditory Nerves.

A peculiarity to which attention may be called here is the
position of the Auditory among the nerves.

It is evident, from the description of the nerves of the
tadpole, that the pre- and postauditory nerves are not totally
different by any means; yet, in general, there are marked
differences in the relative development of the different com-
ponents corresponding to the differences in the character of

No. 1.] THE CRANIAL NERVES OF AMPAHIBIA. 207

the innervation regions. In the preauditory nerves we have a
large general cutaneous element for the supply of the exten-
sive surface of that portion of the head, while the preauditory
supply for visceral surfaces is naturally comparatively small.
We have a large viscero-motor supply, however, for the en-
larged branchial (jaw) musculature. In the postauditory region
the general cutaneous supply is small, owing to a reduction of
the surface supplied, due to the breaking through of the gills,
and also possibly to encroachments by trunk nerves. On the
other hand, the visceral surfaces supplied are extensive and
these nerves correspondingly developed.

The manner in which the auditory organ is interposed, as it
were, is evidenced by the many anastomoses around it. In the
tadpole, while one half of the lateral-line nerves is related to
the V, the other half comes into relation with a general cuta-
meous nerve from the IX-+ X= (R. com. IX + X ad VID,
which unites with it in a manner similar to that in which the
first half of the lateral nerves unite with the V, and between
their respective branches similar parallelisms seem to exist.

While the trunk nerve to the lateral line issues with the
IX + X, the parallel trunk nerve to the end buds of the trunk
(R. lateralis trigemini) has a preauditory exit. Furthermore,
among the fishes, the palatine nerve would appear to be formed
by a union of post- and preauditory nerves (Goronowitsch,
Pollard). The development of the auditory organ has probably
caused a separation of nerves formerly more closely connected.
This is evidenced also by the manner in which the lateral-line
nerves converge mesad of the auditory capsule just before
entering the medulla. Ayers (6) has brought forward reasons
for supposing that the acustico-lateralis system was originally
double. We might even go a step further and suggest the
possibility that it was once single.

In any case, the general relations of the pre- and postauditory
nerves point, I think, to the conclusion that the auditory organ
is a neomorph interposed among the nerves and altering their
primitive courses.

208 STRONG. [Vom xe

3. Bearings upon the Classification and Segmentation
of the Nerves.

The foregoing comparative study of the cranial nerves shows
that the present numerical classification ts unphilosophical.

One principal cause lies in the fact that the classification,
with its serial numbering of the nerves, is based upon the con-
ditions existing among the higher vertebrates. Now, as we
have seen, the cranial nerves of the higher vertebrates have
undergone considerable reduction of primary components.

Much time has been spent in ascertaining whether those
preauditory roots, issuing from the tuberculum acusticum and
lobus trigemini, belong to the V or VII nerves. For con-
venience and to emphasize their distinction from the V they
have been considered in this paper as belonging to the VII, in
accordance with recent researches. If, however, we take the
cranial nerves of the higher vertebrata as a basis, which is
practically done in the existing nomenclature, these components
or roots in question do not belong to either the Trigeminus or
Facialis ; they are actually different nerves from either of the
above, existing in the lower but not in the higher vertebrates.
The principal reason they have been assigned by recent investi-
gators to the VII is because their branches have been shown
to originate from these roots lying caudad of the Trigeminus
proper, and, consequently, by implication, belonging to the
segment of the VII. This, however, is not logical, inasmuch
as segmental character is not the basis of existing nomenclature,
nor, indeed, would it be possible with our present knowledge to
propose a nomenclature for the cranial nerves on this basis.
Furthermore, it has not actually been determined to what seg-
ment or segments these special cutaneous roots belong.

It will therefore ultimately be necessary to remodel our cranial
nerve terminology, but, in my opinion, their exact composition
has not yet been sufficiently determined in order to do this
successfully.

It may be well to indicate here the weak point in Gaskell’s ©
analysis of the nerves (23 and 24), namely, that it does not
take account of all the qualitative differences among them.

Noe. 1] THE CRANIAL NERVES OF AMPHIBIA. 209

For example, the lateral-line system is obviously different,
whatever may have been its origin, from such cutaneous nerves
as the Trigeminus, yet in Gaskell’s nomenclature they are
both simply classed together as ganglionated afferent somatic
nerves. In fact, Gaskell’s system also ignores the differences
between these nerves and those of the special sense organs, for
these latter would also fall under the above category. The chief
defects in Gaskell’s work appear to arise from the fact that it
has been confined to the highest vertebrate types, that it is not
comparative. Nevertheless, it is upon lines of work approach-
ing those of Gaskell that, in my opinion, the most fruitful
results will be obtained.

It is also evident that an exact determination of the compo-
nent parts of the nerves is a necessary preliminary step to deal-
ing with questions of segmentation. This fact has already been
recognized to a certain extent, as is evidenced by the numerous
attempts to find the corresponding ventral roots for dorsal
roots, and wzce versa. In these attempts, however, many other
differences in the character of the nerves have been ignored.
His, Van Wijhe, Gaskell, and others have demonstrated the
presence of two sets of motor nerves, and it is evident that
further differences, especially in the sensory nerves, must also
be taken into account. For example, in the tadpole, the Tri-
geminus proper, the “dorsal VII” and the “fasciculus com-
munis” root of the VII, are mainly sensory yet all different ;
either all three must be included in a complete “segmental
nerve ’’ or, if one is omitted, it must be shown why. That some
particular component may disappear in certain cases is evident,
and the cause is then to be sought in some peripheral change.

In the study of segmentation from the standpoint of the
neuromeres, as developed by Béraneck, Orr, McClure, Waters,
Platt, and others, these qualitative differences should likewise
be taken into account. When the results of these two lines of
work shall have been brought into correlation with each other,
a better insight will be afforded, on the one hand, into the
significance and value of the neuromeres, and, on the other
hand, into the transpositions and other changes undergone by
the various components.

210 STRONG. [VOL. X.

Finally, without a recognition of these nerve components,
embryological research, it appears to me, becomes partly
meaningless. The fact that certain ganglia are connected, in
course of development, with epiblastic thickenings while others,
apparently, are not, is correlated with some difference, structural
and physiological, which either exists now or has existed. How
can we determine what value to attach to such differences of
origin until we know with what differences in the adult
structure they are correlated and, as a consequence, what was
the original cause of their appearance? A knowledge of the
structure itself may be fairly considered a necessary preliminary
to ascertaining its embryological origin.

DEPARTMENT OF BIOLOGY,
COLUMBIA COLLEGE, July, 1894.

No. I.] THE CRANIAL NERVES OF AMPHIBIA. 211

APPENDIX ON TECHNIQUE.

Although nearly every one who takes up any especial line of work
evolves, to a certain extent, his own technique, and although the Golgi
method is described in a number of articles and books, yet it may be well
to give the details of manipulation, as found convenient in my experience,
to benefit those who are not familiar with the subject and literature.

1. Hardening of Small Pieces in Osmtum-bichromate.— The size of
the pieces will naturally depend upon the character of the tissue, but, as a
rule, one dimension should not exceed 3 to4mm. Perhaps the best mixture
for general use is potassium bichromate, 31%4%, 4 vols. + osmic acid, 1%,
1 vol. The time of hardening must be largely a matter of experience,
depending upon such factors as the character of the tissue, its stage of
development, whether embryonic or adult, temperature, and the character
of the impregnation aimed at. In general, this time will lie between 2 and
5 days, embryonic tissue requiring less than adult. For the cortex of an
8-months’ human embryo, however, I have found from 3 to 5 days —and
especially the latter period —gives the best results when using Berkley’s
mixture. 30 to 50 cc. are required for a medium-sized tadpole. It is best
to put the specimen in a smaller quantity first, —a solution that has been
used once will answer, — and then change after an hour or so, putting the
specimen in the full quantity. The fluid should be changed at any time if
it becomes cloudy or ceases to smell quite strongly of the osmic acid.

2. The Silver Bath.—1% may be taken as a standard solution. The
pieces of tissue should be washed in several changes of the silver solution
(that which has been used once being available), until, after 10 to 15
minutes, the fluid ceases to cloud up with the silver chromate, which is
formed when the bichromate and silver solution meet each other. The
pieces should be left in a liberal supply of the silver solution — at least
double the quantity of osmium bichromate which has been used. Impreg-
nation takes place in 24 to 12 hours, or even less, but it is well to allow the
tissue to remain in the silver several days in the dark. Keeping the tissue
in the dark in 1. and 2. is not really essential to obtain the reaction, but is
preferable, especially if it remains in the silver bath some time (see below).

3. Cutting and Mounting.—(a) The pieces are transferred imme-
diately, and left % to1 hour in 95% alcohol, this being changed several
times in the meanwhile; (4) next % to 1 hour in absolute alcohol; (c) 10
to 15 minutes in alcohol and ether, equal volumes; (2) ¥% to1 hour in
thin celloidin; (¢) a few minutes in thick celloidin; (/) mounted on a
microtome block, and the celloidin hardened in chloroform. This process
applies especially to the tadpole, which, when put in the alcohol, is cut
transversely into several more pieces to facilitate the washing and, especially,
the penetration of the celloidin. For solid tissues, especially the central
nervous system, it is better simply to gum them to the block after the wash-
ing in alcohol, using celloidin and hardening it by only a short immersion in

22 STRONG. [VoL. X.

chloroform or 80% alcohol. A partial infiltration with celloidin and harden-
ing the latter is apt to crack the tissue inside. With the tadpole and similar
tissues it is necessary to fill up the interstices with celloidin in order to
obtain complete and coherent sections. When this is done, chloroform is,
in my opinion, the best fluid to harden the celloidin. It does this quite
rapidly, and does not, for some time at least, seem to affect the impregna-
tion. Specimens may be often left in it over night, apparently without
injury.

The sections, 50 to 70 mw thick, usually, are removed from the knife
with a camel’s-hair brush or piece of tissue paper, and arranged on the
slide. 95% alcohol is used in the cutting. The alcohol is then blotted off
by gently pressing a piece of filter paper on the slide, and a few drops of
absolute alcohol are put on. This is then carefully drained off, — not
blotted as before, — and all superfluous alcohol allowed to evaporate, though
the sections should not be allowed to dry. The celloidin, softened by the
absolute alcohol, will then adhere to the slide during the remaining treat-
ment. The sections are then cleared by means of ol. origanum cveficz, and
the latter is washed off with xylol. They are then mounted in dammar
balsam, without a cover slip. The dammar is used in the condition in which
it is obtained —a thick fluid. After it is spread over the sections it must
be watched for a while, as it tends to run off the sections and accumulate
around the edges of the mount, probably owing to diffusion currents. The
aim should be, in covering with balsam, to get an even layer of balsam, as
thin as is consistent with covering the sections. If too thick it does not
dry rapidly, even in the oven, and where yellowing takes place subsequently
it is most liable to occur where the balsam is thickest. When mounted, the
slides are put in an oven, at about 50° C., for a day or two, care being taken
that they shall be level. Heat does not seem to affect the preparations, and
the sooner the balsam is dried the better. If the balsam should dry off the
sections in spots leaving them exposed, the dry places should be first
moistened with xylol and then balsam added as required, and the slide
dried again in the oven. In my experience, origanum and xylol are much
preferable to creosote and turpentine, which are recommended by Golgi.
This is especially true with the central nervous system, where turpentine
tends to crack the sections. The origanum does not allow the balsam to
dry so readily as does xylol and will also, after a while, affect the impreg-
nation, hence the washing with xylol.

The best way to mount loose sections is to transfer them from the xylol
into a dish of quite thick balsam instead of immediately to the slide. In
this way the above-mentioned diffusion currents upon the slide are avoided.

Note. — Since the above writing, I have found that the period of hardening
may be reduced to a day or so and yet good impregnations of adult brains be
obtained also by adding formalin (e.g., 4%) to a potassium bichromate solution.
How this will compare with the lithium bichromate method, I can hardly, as
yet, say.

No. 1.] THE CRANIAL NERVES OF AMPHIBIA. 213

Il.

nz

14.

BG:

16.

LITERATURE QUOTED.

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V7.
18.

19.

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ac

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218

Anast.
aud. cap.
aur.

Bid. gang.
bl. ves.
cap.

cart.

ch. tymp.
con. tis.
Cup.

cut.

Cute

Cutae

Cul
dors. VII.
epid.
epith.

epith. plex.

fasc. com.

fib. Mauth.

gang.

gang. Gass.
gl. n. plex.

wnf. gl. n. plex.

entermed.n. plex.

mot.
MUSC.
O€S.

perich. plex.

prem. ¢.

post. long. fase.

prot. proc.

STRONG.

anastomosis.
auditory capsule.
auricle.

Bidder’s ganglion.
blood vessel.
capillaries.
cartilage.

chorda tympani.
connective tissue.
cupula.

cutis.

outer layer of cutis.

middle layer of cutis.

inner layer of cutis.

dorsal VII.

epidermis.

epithelium.

epithelial nerve
plexus.

fasciculus communis.

fibre of Mauthner.

ganglion.

ganglion Gasseri.

glandular nerve
plexus.

inferior glandular
nerve plexus.

intermediate nerve
plexus.

motor.

muscle.

oesophagus.

perichondral nerve
plexus.

pigment cell.

posterior longitudi-
nal fasciculus.

protoplasmic process.

R.
Rr.

r.com.LX ad VI.

r. lat.

r. mand. tnt. VII.

vr. pal. VII.

vr. vise. X.
silu. prec.

subepith. n. plex.

sup. gl. n. plex.

symp.

term. n. plex.

vent.
PA

2ro0ttlX + X.

3 root LX + X.

4 roo LX + X.

V ase.

ABBREVIATIONS USED IN THE PLATES.

ramus.

rami.

ramus communicans
glossopharyngei ad
facialem.

ramus lateralis.

ramus mandibularis
internus facialis.

ramus palatinus faci-
alis.

ramus visceralis vagi.

silver precipitate.

subepithelial nerve
plexus.

superficial glandular
nerve plexus.

sympathetic.

terminal nerve plexus.

ventricle.

in Pl. XII, key, is
placed on points of
fusion between ac-
cessory branches of
the Trigeminus
and lateral-line
nerves.

Second root of Glos-
sopharyngeus and
Vagus.

Third root of Glos-
sopharyngeus and
Vagus.

Fourth root of Glos-
sopharyngeus and
Vagus.

Ascending tract of the

Trigeminus.

220 STRONG.

EXPLANATION OF PLATE VII.

Fic. 1. Vertical section through the epidermis of a tadpole, showing termina-
tions of the Trigeminus. X 155.

Fic. 2. Somewhat oblique vertical section through the oral epithelium,
showing the terminal plexus of the R. maxillaris V (+ palatinus VII?). X 192.

Fic. 3. Section similar to Fig. 2, showing the terminal plexus of the R. oph-
thalmicus V (+ palatinus VII). X 192.

Fic. 4. Section similar to Fig. 1. X 192.

Fic. 5. Section through the lower labial cartilage, showing the perichondral
plexus and the intraepithelial plexus arising therefrom of the R. mandibularis V.
X72.

Fic. 6. Horizontal section through the above-mentioned perichondral nerve
plexus.

Fic. 7. Similar section through the above, showing also the entire end of the
labial cartilage. X 315.

Fourn. Mort PLVII

LAW I7

Fourn. Morph. Vol. X

selv. prec.

con. Urs,

cut.1
CU ean
Cul, ~---------»

x
>

term. n. plex.

epith.

Bonnar pith, cell

cart, --
PUM C= =

term. n. plex.

vee
ia
ee nes

740372 STRONG.

EXPLANATION OF PLATE VIII.

Fic. 8. Vertical transverse section through a part of the roof of the pharynx,
passing through the transverse fold of the epithelium and showing the termina-
tions of a branch of the R. palatinus VII in the epithelium and taste bulbs (end
buds). X58.

Fic. 9. Terminations of one of the Rr. branchiales X in the terminal pockets
of the filtering apparatus. X 424.

Fic. to. The next section caudad of the one drawn in Fig. 8. X58.

Fic. 11. Transverse section through the pharynx, showing the terminal rami-
fications of the R. mandibularis internus VII (chorda tympani) in a large papilla
in the lateral angle of the pharynx. X4qI.

Fic. 12. Transverse section through the fasciculus communis. X 315.

Fic. 13. Section showing innervation of a small blood vessel by fibres from
one of the ganglion cells found along the course of the visceral nerves. XIII.

vr. pal. F

“

-

fast

- == a

oa

Fourn. Morph. VITT

Fourn. Morph. Vol. X

FLVITT

CN -

taste bulb

os
— St

(AA) SRE
[SARS CNA
YE Weg SSW gal
LERNER RR SON
Wop Ue SRE NMAC.
YOY SONNY Sao eee Cpe
Y) iy ie Fe CENA Ny See ecera oP
Ue ULL LP AORRRESEO
VRE Se Vinee
Hf ZEEE ere

ix
Ac
NN
4,

prot. proc.

—-

\"

.

r. mand. int. VII
(ch. tymp.)

224 STRONG.

EXPLANATION OF PLATE IX.

Fic. 14. Longitudinal (frontal) section through the heart, showing the rami-
fications of the Rr. cardiaci X.

Fic. 15. Vertical section through the pharyngeal epithelium, showing the
innervation of a taste bulb (end bud). X315.

Fic. 16. Similar to Fig. 15.

Fic. 17. Vertical section through the epithelium of the roof of the pharynx,
showing the innervation of the multicellular glands of F. E. Schulze. 155.

Fic. 18. Section similar to Fig. 17, showing the superficial glandular nerve
plexus. X 265.

Fic. 19. Similar to Fig. 18. X3I5.

Fics. 20 and 21. Similar to the preceding and showing more precisely the
individual nerve endings. X 424.

Fic. 22. Horizontal section through superficial glandular nerve plexus. X 192.

Fic. 23. Vertical section through the epithelium of the roof of the pharynx,
showing the continuous superficial glandular nerve plexus where the glands are
continuous. X72.

Fic. 24. Horizontal section through pharyngeal epithelium passing through
the cupula of a taste bulb. 315.

Fourn. Morph. Vol.X PLIX

29

KYAS GG (a
AAOER eh

SERS

iy

end knobs 19

sage ’
Nias aaa
“a

ESS
SIS

Ven a
PURVIS as
YN
Ae
D)

in

\ f
: e: <S /
sup.gl. n. plex.

226 STRONG.

EXPLANATION OF PLATE X.

Fics. 25-30. Sections through the Hyomandibularis VII at different points
along its course, proceeding cephalad (distad), according to the numbering, and
showing the components of the nerve. The outlines accompanying each section
are to show more clearly the position of the components and to facilitate their
designation. Fig. 26 is an oblique section; the others are transverse. X 137.

a

29

<(

mot. VIL (VIT ab)
r. com, 1X ad VII

(VIL b)-—
ad)

4
/
‘

dors. VIL
snot. VIT (VII

Fourn. Morph. Vol. X

1
1

fase. com. ( VIL aa)

=
SS
8
N
ea
N
~~
NY
Ny
N
ws
Ss
NS

xy. com. LIX ad VII

fast. com. (VIT aa)

pe

%
es

@

i.

dors. VII (VII 6)

2.

ol eam

4

Fz

ZZ
fase. com. (VII aa)

g
‘2

oe

<2

7

Ze

Lp

ste
ay,

mot. VII (VIT ab)

SP,

dors. VII (VIL 6)

ZL

2,

cf

>
(e)

nee

D
At)

eau a
aay

nel Ne!

Peers! |

RRL S)
if

Khe

228 STRONG.

EXPLANATION OF PLATE XI.

FIGs. 31-39. Transverse sections through the medulla proceeding cephalad.
They show the position of the fasciculus communis, ascending V and, incidentally,
the posterior longitudinal fasciculus and fibres of Mauthner.

Fic. 40. Transverse section through that portion of the vago-glossopharyngeal
complex lying just outside the auditory capsule.

Fics. 41-43. Some of the nerve cells found along the course of the ramifica-
tions of the visceral nerves beneath the epithelium of the pharynx. The dotted
line in Fig. 41 indicates the inner boundary of the epithelium.

Fics. 1, 2, 4, and 17 are from preparations by the ordinary rapid Golgi method,
somewhat modified, in some cases, in the proportions in the fluids used. Figs.
5, 6, 7, 18, 19, and 24 are from a series prepared by the triple impregnation modi-
fication of Cajal. Figs. 3, 8, 10-16, 31-39, and 4o are from a series prepared by
means of the sulphate modification. Figs. 9, 20-23, and 41-43 are from other
series prepared by the same modification. Figs. 25-30 are from preparations in
which the nerves are stained with osmic acid.

Journ Morph, VX ) FL X7

Journ Morph. VAX

- fast. com. Re
d Se --fasc. com.

we pra _Jasc. com.
V ase.
tb. Mauth.
“Post. bong. fase. \ Sib. Mauth

Py Post. long. fase.

Fasc. com.

< 2 root LX -|-

NS
ae
‘S

ie es 3 root Pee. X (1X)

4 root IX+X

ZE~.post. long. Fasc.

SOSC. comz-f... 4
VITI-\ ”
V asc

Jhb. Mauth ---> =
post. long. Jase

SYMP --% A
Dost. long. fase.”

230 | STRONG.

EXPLANATION OF PLATE XII.

A. A reconstruction of the V, VII, IX, and X nerves of the tadpole, showing
the different components of these nerves in different colors. One half the head
is shown in a horizontal plane and dorsal aspect (see also text, p. 107). X 35.

8. A reconstruction showing the roots of the V, VII, and VIII nerves, the
first two as far as the Gasserian ganglion. Lateral aspect.

C. A reconstruction showing the roots of the V and VII nerves in the Am-
blystoma larva. Dorsal aspect.

The eye, ear, and brain are indicated in faint neutral tint, with dotted outlines,
portions of the brain being omitted, however, where it overlaps certain of the
nerves.

——— OO

Journ. Mo

BP

a Ca
¥

= (010)
O0€

Ventral side

Dorsat side

— ool

ool

: 3 : g e 3 3 iS
Journ. Morph. Vol. X. © ° 8 ° S 8 s 8 PLXL
a ee ae ee Sisco ae ete ic) 2 a a eer ne atne el enetmnet ll <ten py mora tor pol Ata n area pcwcuce wo nena Wh qodow now on a
rm) ————
° —
°o _— ‘s
ee a porle.alveotarys

— B Ft palatinas VT
= : Ventral side ame 72 yomand VIL

genaal cutancous (asc. V /

lateral line /spectal cutaneous).

FASCICULILS COMMUNES.

=
a
[ie

WLOCOr.

ooo!

006

00s

OOL

009

oos

> Lt. tuecalts VIL

Dorsal side
dorsal Vil R.opthal sip Vil
(Vib)

Prema
iy

anast H.opnv
oR. palVir

eeeteemten tial a) [ie ed Ve ee a oe Ws a VL CeCe TPM HP Gp as gh yy Me Ah th roa
BMoisel, lith Bostan.

ooe
o0z
oo)

sae

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iw

ay
a

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a

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ta

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