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| With the Compliments of 7a g 


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: OLIVER S. STRONG, Naz, 
| Columbia College, 
DEPARTMENT OF BIOLOGY New York. 
: 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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FPOMPERENCERINT GO) DE acon dc eee Mr) Banach eee Sictlcns cue eumranmend den ncebadeoaiaccneab a. Neue re 103 

II. DETAILED DESCRIPTION OF THE NERVES AND THEIR COMPONENTS...... 106 
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Pee COMPARATIVE MORPHOLOGY OF COMPONENTS ........222...2-:cccnetensencetescssdorees 153 

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Bem AEsOn CHLATIEOUS OF CQLEKAE PIO: ofa. 2a..nacthicwanesssensi-d peed eee ode 158 

ED) eos C1518 Te PRA OEE Ee oe eo ‘bs boa fe UI 158 

(UA) LUIS SESS; be. ices ALS es Oe Se BE Cl aden 166 

2) UE GSITU ES cle Meee pf ae ce ee 2) ee 178 

al WISE RCCELCES, UIE MIE TATODS. | AE Neca act ands codon cok cnesnsiteannd conse sob dU SAREE EER Rae ge eat oe 180 

(CPST 901201 072 ES Sh ot Seon 8) ee ee 180 

REEMA EE Ny CLEC ACCS oe oc a eaccen en o-cen arto es TOG 

(ALOIS) CGS 5 ORS 208 5 ER cnn ta 188 

Pera tite Perk oe eel eS ws alt Blk ee oo oe na eee cn ch eR LL 197 

Ba COME TASTE “ZOELIE C PCL OSTONUES inn oo nw aan en nea sens senda REM Sc eoontos 193 

eee PNR, MONSIIE RATIONS ccc. ccackcveschcancentne ec necnoeno tae teneRene den orl soaontnnevnns 201 

ee CeeeaOrt Of CFANIGE AIHW SP2HAL LVEPVES. «5... acnnauteneeeee Ree esc ny Sasa 201 

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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150 STRONG. [Vor 


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 


[Von. X. 


*(wraTeIoey 
pe suvolunuiui0s -y) sieioey 02 youviq Bunvorunmuo0s (9) 
(‘y uorsued Ajoweu ‘xazduiod otuorsues 
X + XI jo wed jeutxoid ut uorsuey) 
"X + XI Jo 001 (gpz pur) pf jo yreg 
(Sen ‘A1ojIpneysog ‘TI 
SLe[NoTINe “yY) UlySs 0} ansdeos A10}1pne punose jesiop youeig -v 


‘(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. 


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2a 


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Amphiuma tridactylum nebst Bemerkungen tiber die Morphologie 
des R. ophthalmicus profundus trigemini. Zool. Jahrb., Abth. f. 
Anat. u. Ontog. d. Tiere, Bd. v, Heft 2. 1892. 

72. WRIGHT, R. RAMSAY. On the Nervous System and Sense Organs of 
Amiurus. Proc. Can. Jnst., Toronto, Vol. ii. 


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 


REE 


eae 


Ra eS 


Nageatne: 
MRS 


Regate 


iw 


ay 
a 


, Ss 


a 


ade < ( 
i i 
OR niet. 


¥ ce ta 
ae er (LS. 
ta 


nw 
; eis Mie 


tae 


| 


| 


i“ 


| 


cy 
pt OL669.S92 
nerves of Amphibia / By Oliv 


| 


INSTITUTI 


N 


&& I 


ill 
3 90 
The crania 


i 
_nhre 
| 


|