Occasional papers of the California Academy of Sciences

^T

OCCASIONAL PAPERS

OF THE

CALIFORNIA ACADEMY OF SCIENCES

No. 128, 78 pages, 31 figures, 1 table

June 22, 1978

Cranial Nerves of a Pereoid Fish, Polycentrus schomburgkii
(Family Nandidae), a Contribution to the Morphology and Classification

of the Order Perciformes
By

Warren C. Freihofer

Department of Ichthyology, California Academy of Sciences,
Golden Gate Park, San Francisco. California 94118

tfJ&E/lfy

SAN FRANCISCO

PUBLISHED BY THE ACADEMY

o

COMMITTEE ON PUBLICATIONS

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Table of Contents

Abstract v

Introduction 1

Methods 2

Literature on Nerves of Perciform Fishes 3

Family Nandidae 3

Names of Cranial Nerves 4

Nerve Components 4

Descriptions of Nerves 5

Radix Profundus 5

Fifth and Seventh Cranial Nerve Roots, Trunks, and Rami 6

Roots and ganglia of nervus trigeminus 8

Communis root and geniculate ganglion 8

Dorsal lateralis root of facial nerve 8

Gasserian ganglion of nervus trigeminus 9

Roots and ganglion of nervus facialis 9

Ramus communicans of nervus trigeminus 10

Truncus Supraorbitalis 10

Ramus ophthalmicus superficialis trigeminus and r. ophth. supf. facialis .... 10

Truncus Infraorbitalis 13

Ramus buccalis facialis 13

Ramus ma.xillaris trigeminus 15

Ramus mandibulars trigeminus 16

Ramus operculars trigeminus 16

Innervation of cheek muscle 17

Ramulus mandibulars cutaneus trigeminus 17

Ramulus mandibulars externus trigeminus 19

Ramulus mandibulars interims trigeminus 20

Ramus Oticus 20

Ramus Palatinus 21

Truncus Hyomandibularis 22

Ramus operculars profundus facialis 23

Ramus operculars superficialis facialis 23

Ramus hyoideus 24

Ramus mandibulars facialis 25

Ramus buccalis accessorius facialis 26

Ramus mandibulars externus facialis and ramus

mandibularis internus facialis 26

Ramus Lateralis Accessorius 29

The orbit o-pectoral branch (RLA-OP) 29

The parieto-dorsal branch (RLA-PD) 30

Innervation of the Gill Arches 30

Nervus Glossopharyngeus 31

Nervus Vagus 31

Intracranial dorsal vagal ramus 32

Rami cutanei dorsales vagi 33

Ramus operculars vagi 33

Ramus supratemporalis vagi 34

First vagal branchial trunk 34

Second vagal branchial trunk 35

Third vagal branchial trunk 36

Fourth vagal branchial trunk 37

Summary of Gill-Arch Muscle Innervation 37

Lateral Line Nerves of the Trunk 37

Nervus Linae Lateralis 38

Discussion 39

Free Cephalic Lateralis Organs 39

Comparison with Perca fluviatilus 39

Comparison with Menidia 40

Comparison with cyprinids 40

Comparison with esocoids 41

Comparison with Amia 41

Cephalic Lateralis Canals and Neuromasts 41

Innervation of Upper Jaw 44

Cheek Muscle Innervation 45

Correct Name for Ramus Lateralis Accessorius 45

Trunk Lateral Line Nerves 46

An External-Internal Lateral Line Canal Nerve Relationship 46

Radix Profundus 47

A Stretch Receptor Nerve to Base of Maxillary Tendon 47

Simplifying Cranial Nerve Studies 47

Summary 48

Acknowledgments 50

Literature Cited 52

Abbreviations for Figures 54

Illustrations 57

Abstract

Freihofer, Warren C. Cranial nerves of a percoid fish, Polycentrus schomburgkii (family Nandidae), a contribution
to the morphology and classification of the order Perciformes. Occasional Papers of the California Academy of
Sciences, no. 128, 78 pages, 31 figures, 1 table, 1978. — Four cranial nerves, the trigeminus, facialis, gJossopha-
ryngeus. and vagus, of Polycentrus schomburgkii (Nandidae) are described and illustrated (including muscles of
jaws and gill arches) in detail from cleared-and-stained nerve preparations of whole specimens and from serial
sections. The nerves are described in terms of their main functional components. The descriptions are intended as
a basic reference for comparative nerve studies of perciform fishes for systematic purposes. Comparisons were
made with numerous other families (85 represented as nerve preparations) for particular points such as the inner-
vation of the snout, upper jaw, cephalic lateral line canals and pitorgans. cheek musculature, and trunk lateral line
systems. In many features of its cranial nerves, Polycentrus is a moderately generalized percoid. Compared with
Roccus, Archoplites, Kuhlia, and Perca, it is more specialized in its lateral line system: the second to fourth
infraorbitals apparently are fused as are the fifth and sixth, and only one canal neuromast is in each compound bone;
there are more cephalic pitlines, and these have more organs: the trunk lateral line is reduced to one tubed scale
but there are three longitudinal rows of scales bearing free lateralis organs (pitorgans), one row each along the bases
of the dorsal and anal fins and one row halfway between the dorsal fin and the horizontal septum. These are
innervated by dorsal and ventral segmental branches from a trunk lateral line nerve pattern of the basic acanthop-
terygian type. No communis fibers from the vagus nerve join the ramus lateralis accessorius (RLA) on top of the
head; RLA is composed only of communis fibers from the facial nerve; the same observation holds for other percoids
and other groups examined. Therefore, it may be necessary to use the name ramus recurrens facialis in its place.
Comparisons with other groups, especially some percoids. beryciforms. atherinomorphs. and paracanthopterygians,
brought out specializations in these groups which made more evident the generalized state of the nerves of Poly-
centrus. Whereas Polycentrus is generalized in its innervation of the snout, the carangids, rachycentrids, cory-
phaenids, and echeneids have a shared specialization in prenasal canals and canal bones; a shared specialization
rare in teleosts, of an evident migration of an anteriormost frontal canal organ into the nasal canal occurs only in
the gadoids, ophidioids, and Stephanoberyx; a shared specialization, apparently unique to the group, of an evident
capture of a free lateralis organ by the nasal bone occurs in all berycoid families; atherinomorphs have a shared
specialization of a large general cutaneous nerve to the upper jaw, but it is present also in holocentrids; a unique
specialization of the nasal canal occurs also in Scomber and Rastrelliger; whereas the cheek-muscle innervation in
Polycentrus is not distinctive, it is in atherinomorphs and in various other groups. The pattern of innervation within
a muscle mass as well as the source of innervation to the muscle may be of systematic importance.

Of the four functional nerve-component systems, Polycentrus is specialized mostly in the lateralis system; the
communis (gustatory) system is present in one of the basic percoid patterns of the recurrent facial nerve; nothing
distinctive was observed in the motor system (gill-arch-muscle innervation was not compared) nor in the general
cutaneous system. Generalizations drawn from observations of 85 families for the innervation of the snout and
upper jaw are that (1) pitorgans on the snout and neuromasts of prenasal canals are invariably innervated from the
infraorbital, not from the supraorbital trunk, and (2) general cutaneous innervation of the upper jaw is only from the
infraorbital trunk (except in atherinomorphs and the holocentrids), not from the supraorbital trunk as might be
expected. Reasons for utilizing cranial nerves in higher category classification are given along with suggestions for
simplifying cranial nerve studies.

Introduction

In the 1960's there was a notable renewal of
interest in problems of the classification of bony
fishes at higher taxonomic levels. Numerous or-
ders were shifted into new systematic positions
(Rosen 1964; Greenwood, Rosen, Weitzman,
and Myers 1966; Rosen and Patterson 1969; Ro-
sen 1973). An increase in the number of higher
taxonomic categories was utilized to express
new and more detailed views of relationships.
Much of the new classification has been influ-
enced by the methodology proposed by Hennig
(1966) for phylogenetic systematics. The entire
classification of fishes is due for reexamination
under the impetus of new methods and renewed
interest. The largest and a most formidable
group, the order Perciformes, should receive
major attention.

One precept of an improved methodology of
systematics should be that systematic informa-
tion be drawn from several anatomical systems.
Most past studies on higher category classifi-
cation have utilized the skeletal system as the
chief source of characters. Few have included
the muscles and almost none the nerves (see
Freihofer 1963). The muscles are now being
used more extensively (Winterbottom 1974a and
1974b). The nerves, hopefully, will be also. A
large obstacle to their use, the lack of a tech-
nique for readily viewing the nerves, has been
removed. Whereas the only way to study ac-
curately the peripheral nerves has been by te-
dious methods of serial sectioning and recon-
struction, the nerves can now be seen in a whole
specimen by means of the Sihler technique.

The Sihler technique renders a whole or hemi-
sectioned specimen virtually transparent except
for the nerves, which are stained a dark purple.
Descriptive nerve studies involving little more
effort than for osteological studies are now prac-
tical. The growth of a comparative literature on
the nerves can begin. Of more immediate im-
portance for getting at the taxonomic utility of
the nerves than accumulating a nerve literature,
which will take decades, is the formation of a
reference collection of Sihler nerve prepara-
tions. Such a collection can now be assembled
relatively quickly, covering a sizeable taxonom-
ic range. Assuming that properly preserved fish-
es of numerous groups are available, an expe-
rienced technician working one year can
produce fine nerve preparations representing 50
to 100 or more families. Properly processed Sih-

ler preparations (see under "Methods" section
for use) may last 15 to 20 years and no doubt
will last longer. The reference collection, once
assembled and growing, can be used for con-
ducting surveys of promising nerve complexes.

Several nerve complexes were surveyed dur-
ing the time this descriptive account of Polycen-
trus was in progress. The results are in various
stages of completion and are planned for later
publication. The studies embrace comparisons
ranging from Amia up to callionymids. Sihler
nerve preparations representing up to 90 families
were used. Two of the nerve complexes in-
volved the innervation of lateral line canal
bones; a third was a large general cutaneous
nerve of the supraorbital trunk; a fourth in-
volved patterns of innervation to the cheek mus-
cle mass; a fifth concerned new patterns of a
gustatory nerve, the recurrent facial; and the
sixth was on trunk lateral line nerve patterns.

Each of these studies revealed nerve charac-
ters of promising systematic importance. A few
are apparently convergent in some groups. Two
attributes of nerves giving them systematic po-
tential were observed in these studies. One is
that nerves follow their end organs (taste buds,
lateral line canal organs, and muscles). The oth-
er is that, in general, each nerve innervating a
lateral line canal neuromast has a certain mor-
phological integrity connected with that bone
and organ. No other nerve to a canal neuromast
may enter through the substance of that bone
and supply a canal organ there. This observation
might be stated as a rule. As with all rules, they
are always (it seems) occasionally broken, but
there are always good reasons for their being
broken; the exceptions to the rule, if the excep-
tions are valid, should prove the rule. Important
for the systematist using nerves is the fact that
the exceptions result in new specializations
being formed. These may become characters
useful to the systematist. If nerves always fol-
lowed the rules, there would be fewer important
systematic characters.

Some examples of what nerves do that are
important to systematists come from study of
the nerves and neuromasts of the canal bones.
Not only may the total number of canal organs
be significant for a main branch of the cephalic
canal system, but the changes in the number of
organs in each canal bone may be especially im-
portant. These changes involve how canal or-
gans in a bone may increase or decrease in num-

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

her. An increase in the number of organs may
result from an original organ dividing into two
organs which subsequently move away from
each other; an organ may migrate out of its bone
into another canal bone; a canal bone may, in
effect, '"capture" an adjacent terminal free lat-
eralis organ. Unless the innervation to the canal
organs is studied, the systematic significance of
the canal bones may largely or completely es-
cape detection.

Such facts as these plus the fact that the cra-
nial nerves of more than 20,000 species of fishes
remain to be explored should make the study of
nerves of fishes a rather exciting prospect to
some systematists.

The order Perciformes, to which Polycentrus
belongs, has been divided into as many as 20
suborders (Greenwood et al. 1966) and may con-
tain up to 7,000 species. The present report is
the only detailed description of the fifth, sev-
enth, ninth, and tenth cranial nerves of a mem-
ber of this order. Accounts are needed of the
cranial nerves of representatives of the other
suborders, though descriptions need not be as
detailed as this one for Polycentrus \ Descriptive
reference studies break the ground for ensuing
comparative studies in which the mass of detail
need not be reported, but only the significant
differences between compared species. This re-
port on Polycentrus will, hopefully, serve such
a purpose for the suborder Percoidea.

Methods

The courses of the cranial nerves are de-
scribed mainly from whole specimens cleared
and stained selectively for the nerves by the Sih-
ler technique. For use of the method see Wil-
liams (1943), Freihofer (1966), Fraser and Frei-
hofer (1971), and Freihofer et al. (1977). All
myelinated nerves are stained down to very
small branches. A much more accurate and
complete picture of the distribution of the nerves
is possible by this method than can be had from
serial sections. The latter method should be used
for study of the complexes of nerves and gan-
glia, especially those inside the cranial cavity for
which it is indispensable. It is best to use both
methods. Much preliminary, exploratory work
on the nerves can be done for systematic pur-
poses, however, by use of the Sihler technique
together with the study of the basic nerve ref-
erences.

The nerves are drawn in Figures 1 through 14

as white cords as accurately as possible on the
background of the skeleton, the bones serving
as reference points for the courses of the nerves.
This seems the natural way to illustrate the
nerves for use by systematists. The major nerve
components are not drawn upon the nerves.
Usually, so many components would have to be
crowded into the space of each nerve and its
branches that the distribution of the nerves
could not be shown in the detail that they now
are. The probable components for all the nerves
and their branches are given in the text.

One serious problem with the preservation of
specimens for Sihler processing should be em-
phasized. The problem is that manufacturers of
formaldehyde now leave from 10 to 15% methyl
alcohol in it for the purpose, they say, of "pres-
ervation of the preservative," for retarding the
breakdown of formaldehyde into paraformalde-
hyde. Even reagent-grade formaldehyde has this
amount of alcohol in it. The only grade of form-
aldehyde that I have been able to obtain that can
compare with the purity of the formaldehyde I
used before 1969, which had 1% or less alcohol
content, is the grade sold as "purified formal-
dehyde." Thus far, I have succeeded in obtain-
ing it only in 55-gallon drums. Specimens pre-
served in the other grades of formaldehyde are
ruined for use in the Sihler technique. It is pos-
sible to make formaldehyde free of alcohol by
heating paraformaldehyde crystals in water, us-
ing as a catalyst a drop or two of ammonium
hydroxide solution (28% NH3).

Since the intracranial courses and ganglia of
the nerves as well as the brain are destroyed
while macerating Sihler specimens in 2 or 3%
aqueous potassium hydroxide solution, a serial-
section technique was used to study these parts
in Polycentrus . The object at the time the re-
search was planned was to use a technique that
would help clarify difficult points on ganglia and
nerve anastomoses and to rely on published ac-
counts to help resolve questions of nerve-fiber
tracts and connections. The method chosen was
Curtis's modification of Van Gieson's triple
stain (Leach 1946). It was easy to use and gave
brillantly stained and well-differentiated tissues.
It is not good for fiber-tract study.

All descriptions based on Sihler preparations
are from one specimen unless otherwise indi-
cated. The nerves for the gill arches and asso-
ciated muscles are from a second Sihler speci-
men.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

Dissections of fresh formalin specimens were
used to check against the serial sections on such
points as the intracranial courses and ganglia of
the trigeminal, facial, and vagal nerves.

Skeletal preparations cleared and stained by
the alizarin method of Hollister ( 1934) were used
for making the drawings of the cranial skeleton.
All skeletal drawings were made from one spec-
imen (CAS 12540) from Guyana.

The muscle terminology follows that of Win-
terbottom (1974a). The nerve terminology gen-
erally follows that of Herrick ( 1899). In the pres-
ent work, lateralis organs are referred to as canal
neuromasts if located in canals and as free lat-
eralis organs or pitorgans if located in skin out-
side the canals. The term pitline is used to in-
dicate a row of free lateralis organs, or even a
single organ if that is all that is present in any
area, whether or not these organs are in pits.
The term nerve is loosely used to refer to an
entire cranial nerve and its branches or to a bun-
dle of nerve fibers of any size coursing inde-
pendently outside of the brain or spinal cord.
The root or radix of a cranial nerve is the prox-
imal part or parts of the nerve inside the cranium
and close to the brain. A nerve root is either
sensory, and of a single functional component,
or motor in function.

Herrick, in his work on Menidia (1899), Gad-
us (1900), and Ameiurus (1901), used a modifi-
cation of the Weigert method for preparation of
serial sections of nerves. The modification
worked excellently for Herrick, but he found te-
leost tissues to be very brittle for sectioning (see
Herrick 1898, and Sheldon 1914). The fixatives
required a hardening time of up to 6 months and
the use of osmic acid (osmium tetroxide). Using
fiber diameter as a means of identifying the four
nerve components, Herrick was able to follow
on his serial sections the fiber bundles of the
different functional components of the nerve
roots, from the brain through the ganglia and out
to their undifferentiated endings or end organs.
His Menidia paper (1899) is still the best single
reference on the nerves of fishes.

Literature on Nerves of
Perciform Fishes

Relative to the great size of the order Perci-
formes, there are very few descriptive studies
of the nerves of perciform fishes. Stannius (1849)
and Baudelot (1883) gave observations on var-
ious cranial nerves of some perciforms. Cuvier

and Valenciennes (1828) described the cranial
nerves of Percafluviatilis from dissections. Allis
(1903) carefully described the nerves of the
mackerel, Scomber scomber , but not completely
nor in much detail. Maheshwari ( 1965) described
the cranial nerves of the spiny eel, Mastacem-
belus armatus, and Saxena (1969a) did likewise
for the nandid, Nandus nandus, but both of
these authors used only dissection methods and
omitted details in their descriptions, diminishing
the systematic usefulness of their work.

The most useful references for this study were
the papers by Herrick (1899, 1900, 1901), espe-
cially his monograph (1899) on the cranial nerves
of Menidia (family Atherinidae). His Menidia
paper pioneered the analysis of nerves of fishes
according to the major types of functional nerve
fibers they carry. The nerve components, as
Herrick called the functional types of nerve fi-
bers (see section on nerve components below),
are the best basis for analyzing, identifying, and
understanding the nerves. Other papers found
useful because they were so carefully and thor-
oughly done were those by Allis (1897, 1903,
1910) on the bowfin, Ainia calva, the mackerel.
Scomber scomber, and on Scorpaena: Norris
(1925) on the genera Acipenser, Polyodon,
Amia, and Lepisosteus: Norris and Hughes
(1920) on the spiny dogfish, Squalus acanthias;
Pancratz (1930) on the toadfish, Opsanus tau;
Manigk ( 1934) on Phoxinus; and, lastly, the most
recent study by Ray (1950) on Lampanyctus.

Since 1960 the following authors published
general descriptive accounts on some or all of
the cranial nerves of fishes: Freihofer (1963,
1970, 1972); Gilmore (1972); Gupta (1972); Ma-
heshwari (1965); Mithel (1964a, 1964b); Nara-
wane (1965): Saxena (1966, 1967, 1969a, 1969b):
Saxena and Rastogi (1968): Springer and Frei-
hofer (1976); Vashisht and Uberoi (1965). In all
these studies except my own, in which serial
sections and/or Sihler whole-nerve preparations
were used, dissection of preserved specimens
was the only technique employed.

Family Nandidae

Polycentrus schomburgkii Miiller and Tros-
chel, 1848, is a small spiny-rayed fish living in
fresh water in northeastern South America and
Trinidad. It belongs to the family Nandidae,
which is one of about 70 families of the suborder
Percoidea, probably the least specialized of the
20 recognized suborders of the order Perci-

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

formes (Greenwood et al. 1%6), with perhaps
7,000 species.

Polycentrus is specialized for stalking its prey.
Its barely perceptible swimming movements and
coloration make it look rather like a dead, float-
ing leaf when approaching its prey fish. After an
investigative forward movement, instead of
turning around and swimming away, Polycen-
trus usually swims backwards and downwards,
which it can do for some distance unobtrusively.
The lateral line shows specialization seemingly
for these ways of swimming. The large, protru-
sible jaws are adapted for suddenly engulfing the
prey. Liem ( 1970) has done a comparative func-
tional anatomical study of the feeding mecha-
nism of the Nandidae. In the rest of its mor-
phology, except for the increase in number of
dorsal and anal fin spines, Polycentrus appears
to be a generalized percoid.

The Nandidae are of special zoogeographical
interest. There are two monotypic genera (Af-
ronandus and Polycentropsis) in Africa, two
monotypic genera {Polycentrus and Monocir-
rhits) in South America, and one genus, the least
specialized (Nandus), with 2 species in India and
Southeast Asia. The ancestors of the African
and South American genera were evidently liv-
ing in the area of separation between Africa and
South America when these continents drifted
apart.

Names of Cranial Nerves

There are actually eleven pairs of cranial
nerves in fishes, not ten. The nervus terminalis,
which has the number zero, was not discovered
(Pinkus 1894) until long after the other ten pairs
had been numbered. The present terminology
for the cranial nerves may not be the best that
could be devised, but it is so well established in
the literature of vertebrates that it can hardly be
uprooted.

Cranial
Nerve
Number Name

0 nervus terminalis

1 nervus olfactorius (olfactory)
II nervus opticus (optic)

III nervus oculomotorius (oculomotor)

IV nervus trochlearis (trochlear)
V nervus trigeminus (trigeminal)

VI nervus abducens (abducent)
VII nervus facialis (facial)

Cranial

Nerve

Number

Name

VIII

IX

nervus acusticus (auditory.

acoustical)
nervus glossopharyngeus

(glossopharyngeal)
nervus vagus (vagal)

Nerve Components

Herrick (1897, 1899, 1903) used a simple func-
tional analysis in describing the cranial nerves
of Menidia. His system is followed here for the
cranial nerves of Polycentrus.

Each root of a nerve is considered to be com-
posed of one functional component. Cranial
nerves I (olfaction), II (vision). III (motor), IV
(motor), VI (motor), and VIII (acousticolater-
alis) are very simple in that each has character-
istically only one main functional component
which is either sensory or motor. The other cra-
nial nerves are more complex, containing one or
more sensory and one motor root. A sensory
root is either lateralis (acousticolateralis), com-
munis, or general cutaneous in its functional
component. These components are defined be-
low. Cranial nerve V (trigeminus) has two roots:
one motor and one general cutaneous; nerve VII
(facialis) has four roots: two are lateralis, one is
communis, and one is motor: nerve IX (glos-
sopharyngeus) has two roots in most fishes: one
motor and one communis; nerve X (the vagus
together with the lateral line nerve of the trunk)
has four roots: one motor, one lateralis, one
communis, and a small general cutaneous root.

The cranial nerve roots are easy to follow in
their courses from the brain out to the first cra-
nial nerve ganglia, but at this point inside the
cranium where most of the cranial ganglia are
located, nerves V, VII, and X begin to form an-
astomosing complexes, one of which is the tri-
gemino-facialis complex. This complex forms
intracranially near the closely spaced trigeminal
and facial foramina of the prootic bone. Four
sensory roots and their ganglia and two motor
roots are more or less intimately compacted. All
necessary fiber interchanges are made there.
Three main nerve trunks arise from the trigem-
ino-facialis complex: the truncus supraorbitalis,
truncus infraorbitalis, and truncus hyomandib-
ularis, as well as the palatine nerve.

The cranial nerves of Polycentrus are ana-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

lyzed into functional components as far as pos-
sible. In instances where the component could
not be determined directly, its identification was
made indirectly on the basis of Herrick's work
on Menidia .

Definitions of the five functional components
found variously in cranial nerves V, VII, IX,
and X are listed below. Each sensory compo-
nent is referred to as a system of similar fibers.

1. General cutaneous system. General cuta-
neous fibers innervate skin: in fishes they
do not innervate specialized sense organs;
they end only in free nerve terminations.
The cell bodies are located in the Gasserian
ganglion. Their fibers terminate in the cen-
tral nervous system in the spinal V tract or
the cells associated with it. General cuta-
neous fibers are part of the somatic sensory
system.

2. Communis system. Communis fibers inner-
vate taste buds on the lips, in the buccal
and pharyngeal cavities, and wherever
taste buds occur on the external surface of
the body (head, fins, and trunk). The cell
bodies for communis fibers are located in
the geniculate ganglion. For the vagus and
glossopharyngeus nerves, a second kind of
fiber is associated with the communis sys-
tem. These are fibers that have free, un-
differentiated endings in the mucous epi-
thelium of the pharyngeal and buccal
cavities. Communis fibers end in the brain
at a single center, the lobus vagi of the
medulla oblongata. Communis fibers may
enter this center directly through the vagus
roots or indirectly through the fasciculus
communis tract from the roots of the 9th
and 7th cranial nerves. Communis fibers
belong to the special viscerosensory sys-
tem.

3. Acousticolateralis system. Its fibers inner-
vate the lateral line organs and the internal
ear. They terminate in the tuberculum
acusticum of the medulla oblongata. The
fibers belong to the special somatosensory
system.

4. Somatomotor system. On the head, fibers
of the somatomotor system innervate the
extrinsic eye muscles (the four rectus and
two oblique muscles) and are carried in the
3rd, 4th, and 6th pairs of cranial nerves.

5. Visceromotor system. On the head, fibers
of the visceromotor system innervate mus-

cles of the jaws and gill arches and are car-
ried in cranial nerves V, VII, IX, and X.
This component in the present paper is
usually simply referred to as motor, since
only the jaw and gill-arch muscles are dis-
cussed.

Descriptions of Nerves
Radix Profundus

Closely associated at the brain with the root
of the fifth, or trigeminal, nerve, but separate
from it, is the radix profundus (Figs. 14 and 31).
The radix profundus supplies visceral sensory
innervation to muscles which move the lens and
change the diameter of the iris. This nerve di-
vides into two diverging rami, the ramus ciliaris
longus and the ramus ciliaris brevis (called the
radix longus up to the point of its contact with
the ciliary ganglion). Both rami receive major
fibers from the fifth, or trigeminal, sympathetic
ganglion and separately enter the rear of the eye-
ball.

In one specimen of Polycentrus , the radix pro-
fundus has its root origin in the medulla at the
dorsal surface of the base of the trigeminal root.
Both the profundus and the trigeminal roots
emerge from the midlateral wall of the anterior
end of the medulla, ventral to the posterior ends
of the optic lobes and a little posterior to the
root of the nervus trochlearis. The radix profun-
dus remains separate from the trigeminal root
for the rest of its intracranial course. In another
specimen the radix profundus was applied
closely to the trigeminal root for some distance
from the brain, after which the two roots sepa-
rated.

En route to its cranial exit, the radix profun-
dus lies fairly close to the nervus trochlearis,
both nerves usually being on the dorsal surface
of a large blood vessel, with the profundus me-
dial and a little ventral to the trochlearis, and
both roots being medial to the roots and ganglia
of the trigeminal and facial nerves. Not far from
its cranial exit, the radix profundus bears on its
dorsal surface a ganglion of about two dozen cell
bodies (Fig. 14). Shortly beyond its ganglion, the
profundus, now called the truncus ciliaris pro-
fundus, is crossed dorsally by the intracranial
parietodorsal branch (RLA-PD) of the ramus lat-
eralis accessorius (RLA). Shortly beyond this
point, the truncus ciliaris profundus enters the
trigeminal foramen, passing through it at the dor-
solateral corner of the foramen. The truncus is

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

pressed up against the wall of the foramen by
the large dorsal fiber mass of the truncus su-
praorbitalis. The truncus ciliaris profundus
moves down to lie ventral to the large horizon-
tally elliptical fiber mass of the fifth-seventh
complex that is pressed up against the prootic
roof of the depression (the trigeminofacialis fos-
sa of Allis) in which the external part of the fifth-
seventh complex lies. The truncus ciliaris pro-
fundus divides into two parts. The lateral divi-
sion is the ramus ciliaris longus, and the medial
division is the ramus ciliaris brevis. The ciliaris
longus receives a sizeable bundle of fibers from
the trigeminal sympathetic ganglion lying below
it. The ciliaris brevis passes ventrally and then
medially through or past the trigeminal sympa-
thetic ganglion, apparently receiving sympathet-
ic fibers from it. On the left side of the specimen,
trigeminal sympathetic nerve fibers clearly could
be seen entering the ciliaris brevis, but not on
the right side (Fig. 14). Leaving the trigeminal
sympathetic ganglion, the ciliaris brevis, which
at this point can be termed the radix longa ad
ganglion ciliare or radix longa, passes medially
over to the ventrolateral surface of the oculo-
motor nerve, which lies on top of a large blood
vessel or sinus close to the prootic wall of the
cranium. Some ganglion cells form at the point
of contact between the oculomotor and the radix
longa (Fig. 14). The radix longa courses for a
short distance with the oculomotor nerve, and
the two separate and each passes ventrally down
opposite sides of a large blood vessel, the radix
longa passing down the lateral side and the oc-
ulomotor down the medial side. About two-
thirds of the way down the lateral side and after
the formation of a few more ganglion cells in it,
the radix longa passes medially around the large
blood vessel and joins the ciliary ganglion lo-
cated on the oculomotor nerve. The ramus cil-
iaris brevis directly departs from the ciliary gan-
glion and passes anterodorsally and laterally
over to the rear of the eyeball in company with
an ophthalmic blood vessel and penetrates the
sclera close to the optic nerve and vein. Inside
the sclera the ciliaris brevis passes ventrally on
the side of a large vein or sinus reaching the
lateroventral edge of the retina where the re-
tractor lentis muscle attaches to the base of the
iris (Fig. 15). The ciliaris brevis sends a branch
anteriorly and another posteriorly along the pe-
riphery of the iris, each branch ramifying over
the ventral surface of the iris.

The remainder of the ciliaris longus is de-
scribed next. At the point where it has received
fibers from the trigeminal sympathetic ganglion,
the ciliaris longus shortly leaves the proximity
of the fifth-seventh complex and passes anter-
oventrally through the fibrous coating separating
the prootic foraminal area from the orbital cav-
ity, enters the orbital cavity in company with an
ophthalmic artery, passes laterally over to the
dorsal rear of the eyeball, and enters the eyeball
about two-thirds of the way middorsally above
the entrance of the optic nerve (Figs. 14 and 15).
The course and relationships of the radix pro-
fundus are essentially the same on both sides of
the sectioned specimen.

Fifth and Seventh Cranial Nerve Roots,
Trunks, and Rami

The trigemino-faeialis complex is the result of
six roots of the fifth and seventh cranial nerves
(each nerve root carrying fibers of one functional
component) coming together, forming ganglia if
they are sensory roots, exchanging fibers, and
then leaving again with nerve components re-
combined into the three main nerve trunks
which innervate the anterior half of the head.
These three nerve trunks are the truncus su-
praorbitalis, truncus infraorbitalis, and truncus
hyomandibularis. The truncus supraorbital
courses anteriorly from the rear of the orbital
cavity dorsal to the eye and innervates the top
of the head and the snout (Fig. 3) but not, except
rarely, the upper jaw. The infraorbital trunk
passes anteriorly from the rear of the orbital
cavity along the ventral edge of the orbit and
branches into three main rami: 1) the ramus
maxillaris trigeminus to the upper jaw; 2) the
ramus buccalis facialis to the lateral line organs
associated with the infraorbital canal and to the
adjacent skin; and 3) the ramus mandibularis
trigeminus to the muscles and skin of the cheek
and lower jaw (Figs. 1, 6-10). The truncus hyo-
mandibularis facialis leaves the cranium a little
further posteriorly than do the first two trunks
and passes ventrally along or through the hyo-
mandibular and preopercular bones and divides
into two main rami, the ramus mandibularis fa-
cialis and the ramus hyoideus (Figs. 2 and 13).
The ramus mandibularis innervates the preoper-
cular area, the anterior part of the opercular
area, and the lower jaw. The ramus hyoideus
passes down the hyoid arch innervating the skin
and muscles of the gill membrane and branchio-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGKII

stegal rays, and the posterior part of the pro-
tractor hyoidei muscle connecting the hyoid
arch to the lower jaw.

The six roots of the 5th— 7th complex of fishes
may be examined more closely. The 5th or tri-
geminal nerve consists of two nerve roots, a so-
matic sensory root carrying nerve fibers belong-
ing to the general cutaneous system and a
visceral motor root carrying motor fibers to jaw
muscles associated originally with an anterior
gill slit lost in the evolution of the jaws. The 7th
or facial nerve has four nerve roots, three of
which are sensory and one motor. The motor
root supplies visceral motor fibers to the mus-
cles of the palate, opercle, and hyoid arch —
muscles associated originally with the hyoid gill
arch which are innervated by the 7th cranial
nerve. The three sensory roots of the facial
nerve consist of two lateralis roots, referred to
as the dorsal and the ventral lateralis roots; the
third is a visceral sensory root carrying fibers
that innervate the taste buds and the mucosa of
the mouth. Each of the sensory roots of the 5th
and 7th nerves bears a large ganglion.

After leaving the posterior part (medulla ob-
longata) of the brainstem, the six roots of the
5th and 7th nerves converge anteriorly towards
their foramina in the prootic bone, but shortly
before passing through the prootic, a ganglion
forms on three of the sensory roots of the facial
nerve. In Polycentrus the Gasserian ganglion of
the sensory root of the trigeminal nerve forms
directly outside of the trigeminal foramen in the
prootic bone. In some other fishes it forms inside
the cranium. Just beyond the ganglia but still
inside the cranium, the fiber bundles in all fishes
begin to detach from the roots, the various fiber
bundles coming together forming the three nerve
trunks described above.

In Polycentrus the dorsal lateralis root of the
7th cranial nerve sends a large bundle of fibers
into the supraorbital trunk, and the remainder
of the root enters into the formation of the in-
fraorbital trunk. The rest of the supraorbital
trunk is formed by a bundle of general cutaneous
fibers from the Gasserian ganglion of the 5th cra-
nial nerve and a small bundle of communis (taste
fibers) from the geniculate ganglion of the gus-
tatory root of the 7th cranial nerve. This com-
munis bundle then leaves the supraorbital trunk
as the orbito-pectoral branch of the recurrent
facial nerve.

In addition to the large bundle of lateralis fi-

bers from the dorsal root of the 7th cranial
nerve, the infraorbital trunk receives a large
bundle of general cutaneous fibers from the Gas-
serian ganglion for the skin. It also receives the
whole of the motor root of the 5th cranial nerve.
Both of these trunks, the truncus supraorbitalis
and truncus infraorbitalis, leave the cranium
through the trigeminal foramen on the outer face
of the prootic bone and then diverge on the rear
wall of the orbital cavity, one trunk passing dor-
soanteriorly above, the other ventroanteriorly
below, the orbit.

The truncus hyomandibularis in Polycentrus
is formed by the whole of the motor root of the
7th cranial nerve, plus a large bundle of com-
munis fibers from the geniculate ganglion of the
7th cranial nerve, and by the whole of the ven-
tral lateralis root of the 7th nerve. The truncus
hyomandibularis usually contains a sizeable
bundle of general cutaneous fibers from the Gas-
serian ganglion. These fibers reach the truncus
hyomandibularis as the ramus communicans n.
trigemini ad n. facialem. This ramus passes pos-
teriorly in a chamber or lateral passageway that
lies in the wall of the prootic between the tri-
geminal and facial foramina. The ramus com-
municans turns laterally beyond the prootic
chamber and joins the truncus hyomandibularis
as this trunk enters its passageway in the hyo-
mandibular bone.

Not all of the communis fibers of the genicu-
late ganglion of the 7th cranial nerve go into the
three trunks of the 5th and 7th cranial nerves.
Some geniculate fibers form the ramus palatinus,
which passes out of the cranium into the myo-
dome and then along the medial edge of the pal-
ate next to the parasphenoid bone, innervating
taste buds and the mucosa of the palate and up-
per jaw. In many fishes there are still other gus-
tatory branches arising from the geniculate gan-
glion. These are considered together under the
terms ramus lateralis accessorius (ramus recur-
rens facialis). The branches of this ramus course
back from the head onto the trunk.

As will be seen in the detailed descriptions for
Polycentrus , both the ramus mandibularis trige-
minus of the truncus infraorbitalis and the ramus
mandibularis facialis of the truncus hyomandi-
bularis course onto the lower jaw and out to its
tip. Although the trigeminal (fifth) and facial
(seventh) nerves parallel each other in their
courses on the lower jaw, each nerve serves a
different function there. Where these rami reach

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

the lower jaw in Polycentrus and in teleosts in
general, the ramus mandihularis trigeminus car-
ries only motor fibers for muscles and general
cutaneous fibers for the skin of the lower jaw,
while the ramus mandibularis facialis carries on-
ly lateralis fibers for free lateralis organs and
canal neuromasts, and communis fibers for the
taste buds and mucosa of the lower jaw.

Roots and ganglia of nervus trigeminus

The single sensory root and single motor root
of the nervus trigeminus (V) are indistinguish-
ably bound together as they arise from the mid-
lateral wall of the medulla oblongata directly
posterior to the root of the oculomotor nerve,
anterior and ventral to the facial roots, and pos-
terior to the lateral emergence of the nervus
trochlearis (Fig. 29). The radix profundus lies on
the dorsal surface of the trigeminal root as these
two roots leave the brain. They soon separate
but remain rather close for most of their intra-
cranial courses. The trigeminal root remains un-
connected to the roots and ganglia of the facialis.
When close to its foramen, the compound motor
and sensory trigeminal root lies dorsal to the
geniculate ganglion of the facial nerve and me-
dioventral to the dorsal lateralis ganglion of the
facial nerve. The Gasserian ganglion of the tri-
geminal nerve forms outside the trigeminal fo-
ramen where the final interchanges between the
trigeminal and facial nerves occur to form the
truncus supraorbitalis and truncus infraorbitalis.

The communis root and geniculate ganglion

The communis root of the facial nerve carries
gustatory fibers to taste buds in the mouth and
to terminal buds on the body, and communis
fibers to the mucosa of the buccal cavity. Dorsal
to the facial foramen, the communis root en-
larges into a round, dense mass of large and
small ganglionic cells, the geniculate ganglion
(Fig. 31). From the geniculate ganglion arise two
ventrally directed, large fiber bundles; one is the
anterior ramus palatinus which innervates taste
buds on the palate and upper jaw, and the other
is the communis bundle which joins the truncus
hyomandibularis as this nerve passes through
the facial foramen.

Several fiber bundles leave a dorsoanterior
extension of the geniculate ganglion. One of
these is a small bundle, the parieto-dorsal
branch of the ramus lateralis accessorius (Fig.
31), which passes laterally around the ventral

surface of the trigeminal root and then dorsally
up the side of a blood vessel where it is joined
by a similar bundle from the medial side of the
geniculate ganglion. The enlarged nerve thus
formed shortly comes into contact with the in-
tracranial ganglion of the radix profundus and
then passes dorsally up to the parietal bone,
through which it passes. The further course of
the parieto-dorsal branch of the ramus lateralis
accessorius (RLA), is described in another sec-
tion. There is no fiber exchange between the
parieto-dorsal branch of the RLA and the radix
profundus. The remainder of the dorsoanterior
part of the geniculate ganglion gives rise to a
fiber mass which passes through the trigeminal
foramen, lying, as it does so, on the lateral sur-
face of a mass of trigeminal fibers. As this com-
munis bundle goes out the trigeminal foramen.
it detaches fibers that course with the ramus
oticus. These fibers of the geniculate ganglion
constitute the orbito-pectoral branch (Fig. 31,
RLA-OP) of the RLA. General cutaneous fibers
leave the Gasserian ganglion outside the trigem-
inal foramen and also join the ramus oticus. On
serial sections no fiber bundle from the genicu-
late ganglion was observed to pass into the in-
fraorbital trunk, but on a dissection a fiber bun-
dle from the geniculate ganglion appears to enter
the infraorbital trunk, and another apparently
enters the supraorbital trunk, but it could not be
definitely determined that they do.

In summary, the fiber bundles leaving the ge-
niculate ganglion and joining various parts of the
trigemino-facialis complex are as follows: (Da
large bundle of fibers that forms the ramus pal-
atinus; (2) a large bundle to the truncus hy-
omandibularis; (3) a dorsally directed intracra-
nial branch (the parieto-dorsal branch of the
RLA) to the dorsal fin; (4) a sizeable bundle that
forms the orbito-pectoral branch of the RLA to
the pectoral, pelvic, and anal fins; (5) a sizeable
bundle, probably to the infraorbital trunk, and
a small bundle, probably to the supraorbital
trunk. Herrick ( 1899: 351) states that in Menidia
such fibers in small numbers enter the supraor-
bital trunk.
Dorsal lateralis root of the facial nerve

The dorsal lateralis root forms a rather large
ganglion of from small- to large-sized, compactly
grouped cell bodies. On its course to its ganglion
(Fig. 31), the dorsal lateralis root lies on the
medial side of the internal ear and is lateral and

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1

dorsal to the trigeminal root. The ganglion is
directly posterior to the intracranial profundus
ganglion and medial to the geniculate ganglion.
The dorsal lateralis root leaves the cranium at
the dorsal corner of the trigeminal foramen. Out-
side the cranium, part of the root turns antero-
dorsally and continues against the side of the
cranium as a part of the truncus supraorbitalis.
Some fibers of the dorsal lateralis root leave it
and pass dorsally as part of the ramus oticus. A
sizeable portion, probably half of the dorsal lat-
eralis root, leaves the root as it passes out the
trigeminal foramen and crosses to the lateral
side of the trigemino-facialis complex (Fig. 31);
this portion then passes ventrally to become the
ramus buccalis facialis of the infraorbital trunk.

Gasserian ganglion of the nervus trigeminus

The Gasserian ganglion lies entirely outside
the cranial cavity in Polycentrus and is separate
from other ganglia near it except the trigeminal
sympathetic ganglion, with which it has a fiber
connection (Fig. 31). The radix profundus
(called the truncus ciliaris profundus after for-
mation of its ganglion) passes into the dorsolat-
eral part of the Gasserian ganglion and divides
into the ciliaris longus and ciliaris brevis while
inside the Gasserian ganglion. Gasserian cells fill
spaces between fiber bundles of the trigeminal
and facial roots which are effecting fiber bundle
exchanges and which form the truncus supraor-
bitalis and truncus infraorbitalis. One arm of
Gasserian cells extends dorsoanteriorly over the
anterior surface of the dorsoanteriorly ascending
truncus supraorbitalis, reaching almost as far as
the first lateralis branch of the supraorbital
trunk. A shorter, thicker arm of cells extends
along the anterior surface of the truncus infraor-
bitalis. The lateralis fibers from the intracranial
dorsal lateralis ganglion and the communis fi-
bers from the geniculate ganglion of the facialis
nerve pass anteriorly behind the Gasserian gan-
glion cells and form part of the supraorbital
trunk. The rest of this trunk is formed by fiber
bundles from the Gasserian ganglion constitut-
ing the general cutaneous component. Lateralis
and communis fiber bundles from the facial
roots, plus all the trigeminal motor fibers, and
a large number of cutaneous fibers from the Gas-
serian ganglion all join and pass ventrally behind
the Gasserian ganglion to form the infraorbital
trunk.

Roots and ganglia of the nervus facialis

The nervus facialis arises by four roots which
are fused basally giving the appearance of one
root (Fig. 29). A short distance from the medul-
la, the basal root separates into three parts
which, however, represent four facial roots, the
motor facial and the ventral lateralis facial roots
being so close together as to appear as one root
(Fig. 31). The facial roots emerge from the me-
dulla directly dorsal and a little anterior to the
anteriormost auditory root. The facial roots are
as follows, starting dorsally: the dorsal lateralis
root; the communis root, which enlarges ante-
riorly into its geniculate ganglion; the motor
root: and, most ventral, the ventral lateralis
root, which arises directly ventral or medial to
the anteriormost auditory root. A short distance
from the brain, this ventral lateralis root comes
to lie on the ventral surface of the motor root.
These two roots become indistinguishably
bound together. More anteriorly they leave the
cranium as the truncus hyomandibularis through
the facial foramen in the prootic bone. Before
joining the motor root, the ventral lateralis root
receives a ramus which is connected to the last
two auditory roots. An intracranial connection
between the auditory and facial nerves is appar-
ently common in fishes, being found in Menidia
(Herrick 1899), Lampanyctus (Ray 1950), and
Scomber (Allis 1903). All these facialis roots
near their points of origin lie over the posterior
end of the lobus inferioris of their side. All the
roots run anteroventrally to the trigemino-faci-
alis foramina, where their relationships become
complex in the formation of the supraorbital, in-
fraorbital, and hyomandibular trunks.

A few ganglion cells appear on the medial side
of the ventral lateralis root a short distance after
the ramus from the auditory roots joins its lateral
surface (Fig. 31). A little further distally the ven-
tral lateralis and motor roots join and many gan-
glionic cell bodies appear on the lateral surface
of the compound root, but they do not form as
dense and compact a mass as occurs in the ge-
niculate or Gasserian ganglia. The ganglionic
cell bodies which are most abundant on the ven-
tral half of the joined motor and lateralis roots
(Fig. 31) are part of the ventral lateralis root.
Beyond the ganglion the compound trunk of
motor facialis and ventral lateralis roots passes
medial to the intracranial flange of the prootic,
which separates the facial and trigeminal fora-

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

mina, receives communis fibers from the genic-
ulate ganglion, and, as the truncus hyomandi-
bularis, passes out the facial foramen.

Ramus communicans of the nervus trigeminus

The ramus communicans of the nervus trigemi-
nus is large in Polycentrus and forms from the
posterior end of the part of the Gasserian gan-
glion that extends into the prootic chamber (Fig.
31). The ramus communicans runs posteriorly
in this chamber, emerges close to the facial fo-
ramen, but remains separated by large blood
vessels from the truncus hyomandibularis as the
latter truncus leaves the facial foramen. The
truncus hyomandibularis and its ramus com-
municans from the trigeminal nerve pursue sep-
arate courses which converge laterally and ven-
trally at the medial side of the hyomandibular
bone, which they enter together and course in
a passageway in this bone, the ramus commun-
icans lying on the dorsal surface of the truncus
as the two go into the hyomandibular. The fibers
of the ramus communicans shortly become a
part of the truncus and cannot further be fol-
lowed separately on the serial sections. All of
the ramus communicans was observed on a Sih-
ler preparation of Liparis pulchellus (Liparidae)
to leave the proximity of the truncus hyoman-
dibularis, not having become attached to that
truncus, and to constitute almost the entire ra-
mus hyoideus. In Menidia (Herrick 1899; fig. 3)
all of the ramus communicans enters the ramus
hyoideus, none apparently entering the other
main division of the truncus hyomandibularis,
that is, the ramus mandibularis facialis. In Poly-
centrus some general cutaneous fibers continue
in the latter nerve also.

Truncus Supraorbitalis

The dorsal lateralis and communis roots of the
facial nerve together with the general cutaneous
root of the trigeminal nerve contribute to the
formation at the trigeminal foramen of the fol-
lowing nerves that constitute, or are associated
with, the truncus supraorbitalis: (1) the ramus
oticus (general cutaneous and dorsal lateralis
components); (2) the orbito-pectoral branch of
the ramus lateralis accessorius (communis fibers
from geniculate ganglion); and (3) the truncus
supraorbitalis (dorsal lateralis and general cu-
taneous fibers and possibly some communis fi-
bers). The supraorbital trunk separates into its
two main rami, the ramus ophthalmicus super-

ficialis trigeminus (general cutaneous fibers) and
the ramus ophthalmicus superficialis facialis
(lateralis fibers), shortly beyond the frontal com-
missure of the supraorbital lateralis canal.

Ramus ophthalmicus superficialis trigeminus
and ramus ophthalmicus superficialis facialis

The first branch of the truncus supraorbitalis
is the ramus oticus (Fig. 3, ROT). It is consid-
ered separately in the next section. The second
branch of the truncus, SORB 2, supplies skin
and certain scale pockets bearing free lateralis
organs on the head dorsal to the orbital rim
(Figs. 1, 3, and 5) and is assigned, therefore, to
the ramus ophthalmicus superficialis facialis, al-
though it carries some general cutaneous fibers.
It detaches from the truncus a short distance
after the orbito-pectoral branch of the ramus lat-
eralis accessorius (RLA-OP) leaves from along-
side the truncus. Branch SORB 2 runs dorsally
a short way and penetrates the alisphenoid
through a relatively large foramen. On other
specimens the foramen for SORB 2 was occa-
sionally in the sphenotic bone. Entering the cra-
nial cavity, SORB 2 rises dorsally along the in-
ner surface of the frontal bone. En route it is
crossed by SORB 3 (Fig. 5) from the truncus
supraorbitalis. SORB 3 passes through the fron-
tal bone, and after crossing SORB 2, it joins with
the parieto-dorsal branch of the ramus lateralis
accessorius (RLA-PD). SORB 3 was absent on
the other side of the specimen. Near the cranial
roof, SORB 2 detaches several minute nerves
which appear to innervate, in part, the meninges
of the brain in the region dorsal and anterior to
the anterior semicircular canal. Medial to the
supraorbital canal, but at about its dorsalmost
level, SORB 2 divides into SORB 2a and SORB
2b (Fig. 1). The smaller. SORB 2a. passes
through the midmedial roof of the cranium, turns
anteriorly, runs over the surface of the horizon-
tal myoseptum between the dorsal and ventral
cranial roof musculature, curves laterally over
to the skin, turns posteriorly underneath it, and
innervates free lateralis organs on one of the
scale pockets. Intracranially SORB 2a gives off
a tiny twig which appears to supply the men-
inges.

At the point of origin of SORB 2a, a larger
branch, SORB 2b, runs intracranially dorsoan-
teriorly and soon penetrates the frontal bone
medial to the frontal sensory canal. It curves
over the external surface of the canal and passes

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGK11

laterally to skin over the posterior corner of the
eye. Upon reaching the skin it divides into sev-
eral branches. One branch passes onto the skin
connecting the eye to the orbital rim and onto
the cornea over the dorsoposterior quadrant of
the eye (Fig. 16, COR 1). A smaller branch
passes posteriorly and innervates a row of free
lateralis organs on a scale (Figs. 5 and 17). A
larger branch of SORB 2b passes anteriorly giv-
ing off about five successive short twigs each of
which innervates a row of free lateralis organs
on the skin of one of the scales that lies above
the orbital rim, the lateralis-bearing scales form-
ing a row which extends anteriorly from near
the dorsoposterior quarter of the eye up to the
frontal canal pore located in the anterior half of
the orbital rim. The twig to the pore of the fron-
tal canal near the middle of the orbital rim in-
nervates a cluster of free lateralis organs on the
membrane covering most of the canal opening.
The main body of SORB 2, at the point where
it detaches SORB 2a and SORB 2b, continues
intracranially in a posterior and slightly dorsal
direction a little above the anterior semicircular
canal and comes in contact with the ramus lat-
eralis accessorius (RLA-PD) but is separable
from it. SORB 2 passes through the parietal
bone and through the thin flange of bone (Fig.
1) constituting the parietal ridge, breaking up in-
to four branches in the ridge. These branches
send twigs to various scale pockets, each scale
pocket bearing a line of free lateralis organs (Fig.
17), the lateralis organ-bearing scale pockets to-
gether forming a line of free lateralis organs
leading posterodorsally towards the middorsal
line and ending above the rear of the supraoc-
cipital area. It could be seen on the Sihler prep-
arations that the sprays which these twigs form
on the scale pockets are supplying specialized
sense organs rather than merely being free sen-
sory nerve endings of general cutaneous fibers
in the skin. One of the four branches sends a
twig dorsally and posteriorly, a few of its fibers
going to the two dorsal scale pockets of the ver-
tical row supplied by the ramus supratemporalis
vagi. The remaining fibers of this branch sepa-
rate into numerous small fiber groups which
cross or run for a short distance with the ramus
lateralis accessorius (RLA-PD), located beneath
skin on top of the head, but then leave this ra-
mus and innervate a few scales, each posterior
to the vertical row supplied by the ramus supra-
temporalis vagi. These few scale pockets are

much less strongly innervated than are those of
the supratemporalis row. It is doubtful that they
also bear free lateralis organs, but they could.

The remaining branches of the truncus su-
praorbitalis serve mainly the lateral line organs
of the frontal and nasal canals (from the ramus
ophthalmicus superficialis facialis) and the skin
(from SORB 5 and SORB 6 of the r. oph. sup.
trigeminus) near the canals. Especially interest-
ing are the apparently lateralis branches, one
from each of three of the four branches to the
lateral line organs. There are patches of free lat-
eralis organs where these branches (SORB 4,
SORB 8, and SORB 11a, see Figs. 3 and 17)
terminate in the skin. Each of these probable
lateralis rami detaches from one of the branches
that innervates a canal neuromast of the frontal
or nasal bone and continues, usually rather far
anteriorly, apparently to innervate free lateralis
organs mainly over the anterior end of the or-
bital roof. One of these branches, SORB 1 la
(Fig. 3), detaches from the nerve (SORB 1 1) to
the lateral line organ in the nasal bone and runs
anteriorly in the canal some distance before it
passes through the lateral wall of the canal and
innervates the overlying skin. Its terminal
branchings lie directly opposite those of a
branch of SORB 6, which is apparently a com-
pletely general cutaneous nerve. Since there is
a patch of free lateralis organs in this area and
since SORB 6 is apparently a general cutaneous
branch, it seems likely that SORB 11a is a lat-
eralis branch supplying these free lateralis or-
gans. It is probably the usual relationship that
the same lateralis branch that supplies a canal
neuromast also supplies the free lateralis organs
in the skin around the adjacent canal pore.

After giving off SORB 2, the truncus is a
broad, flat band of nerve fibers with no distinct
bundles and is pressed close against the frontal
bone in the orbital cavity. Shortly, it divides into
two groups of fibers, a medial, slightly smaller
one with many black nuclei, and a lateral, larger
one with much lighter-stained fibers. These two
divisions are the rami ophthalmicus superficialis
trigeminus and facialis, respectively. The trunk
at this point has come to lie near the medial side
of the frontal canal, as this structure lies near
the orbital rim. A lateralis branch, SORB 4 (Fig.
3), detaches from the facial part of the main
truncus, enters the bone of the frontal canal, and
bifurcates, one fork at a time entering the canal
and innervating sensory canal organs 4 and 5 of

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

the supraorbital canal. The two organs lie close
together posterior to the frontal commissure of
the supraorbital canal. The branch to each canal
organ detaches a slender ramus, which is prob-
ably lateralis or perhaps both lateralis and gen-
eral cutaneous in function. Each penetrates the
frontal bone and innervates tissue near the or-
bital rim.

The truncus supraorbitalis continues anterior-
ly and a little laterally, lying up against the roof
of the orbital cavity underneath the frontal ca-
nal, and gives off two branches (Fig. 3) of un-
even size, SORB 5 and SORB 6, which together
constitute most of the ramus ophthalmicus tri-
geminus and are general cutaneous in function.
The much smaller branch, SORB 5, curves lat-
eroanteriorly close to the edge of the orbital rim
where two small twigs detach, one of which was
lost in the skin connecting the orbital rim to the
eyeball; the other is distributed to the orbital
surface bordering the rim. The rest of SORB 5
(Fig. 16), now labeled COR 2, continues in skin
directly lateral to the orbital rim, until in the
anterodorsal quadrant of the orbit it turns to-
wards the center of the eye, giving branches to
skin connecting the eye and orbital rim; the rest
of COR 2, which is the larger part, goes to the
conjunctiva and cornea. SORB 6, which is the
major portion of the ramus ophthalmicus super-
ficialis trigeminus (r. oph. sup. tri.), and the re-
mainder of the truncus, which is equivalent to
the ramus ophthalmicus superficialis facialis (r.
oph. sup. fac; see Fig. 3), diverge rather sharply
from each other, then, after some distance, ap-
proach each other and continue to the anterior
end of the orbital roof where they leave together
and pass out onto the snout beneath the nasal
bone. The r. oph. sup. tri. courses across the
ventral surface of the frontal bone in the orbital
cavity and the r. oph. sup. fac. courses in a bony
canal beneath or to the side of the frontal canal.
Shortly before leaving the orbital rim. SORB
6 detaches SORB 6a, which passes dorsoante-
riorly up the medial side of the nasal canal and
innervates skin overlying the junctions of the
anterior end of the frontal canal and the poste-
rior end of the nasal canal. The rest of SORB 6
continues anteriorly a little below the ventral
side of the nasal canal. Two-thirds of the way
along the nasal canal and at the ventrolateral
side of it, SORB 6 gives off several branches.
The first of these is a small branch, SORB 6b,
which passes dorsally and innervates skin on the

medial side of the nasal canal. It lies directly in
front of the terminal branching of the lateralis
branch SORB 11a from the main truncus su-
praorbitalis. The next branch, SORB 6c, larger
than the SORB 6b, passes around the medial
side of the nasal bone, rises to the dorsal level
of this bone, and innervates skin medial to and
a little behind the anterior end of the nasal bone.
The remainder (SORB 6d) of SORB 6 passes to
skin in front of, and lateral to, the anterior narial
opening. Here it bifurcates, the dorsal fork pass-
ing medially around the front end of the nasal
bone to innervate skin behind the head of the
maxilla, the other fork passing anteroventrally
towards the dorsal half of the shaft of the max-
illa, where it innervates skin in front of the an-
terior narial opening and below the nasal bone.
Branches SORB 6b, 6c, and 6d are essentially
the same on both sides of the specimen. There
is no indication that these branches innervate
free lateralis organs in their vicinity. The nu-
merous free lateralis organs located near the na-
rial and nasal canal openings (Fig. 19) are most-
ly, if not completely, innervated by facialis
fibers of the infraorbital trunk (Fig. 1). Further
study is needed of the areas of the front end of
the snout and nasal and narial openings where
the truncus supraorbitalis and truncus infraor-
bitalis meet.

The rest of the truncus supraorbitalis. after
detaching SORB 6, is the ramus ophthalmicus
superficialis facialis, which carries mostly lat-
eralis fibers but apparently also some general
cutaneous fibers. The ramus, coursing in a bony
passageway in the frontal bone, curves to lie
medial to the frontal canal and gives off branch
SORB 7 that courses along the orbital roof.
SORB 7 shortly detaches branch SORB 7a that
enters the frontal bone, curves medially and dor-
sally around the frontal canal, continues cours-
ing anteriorly along the medial side of the canal
until, a short distance behind the posterior end
of the nasal bone, it rises to the skin over the
frontal canal and innervates it. It could not be
determined if this branch is general cutaneous
or lateralis or both. The rest of SORB 7 courses
anteriorly along the lateral side of the frontal
canal and divides into four diverging, anteriorly
directed branches; two of these emerge on the
dorsal surface of the head, supplying skin in
front of the anterior pore of the frontal canal,
one branch passing anteriorly across the floor of
the pore. Another of the branches continues

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

13

along the lateral side of the frontal canal and
innervates skin at the ventroanterior corner of
the anterior pore of the frontal canal. The two
other branches pass anteriorly almost up to the
end of the orbital cavity, where they penetrate
the frontal bone and pass to the skin anterior to
the frontal pore. These branches of SORB 7 all
innervate skin, none apparently innervate free
lateralis organs, as far as could be determined,
and are classed as general cutaneous branches.
Only a few scattered free lateralis organs are
found in the anterior third of the supraorbital
rim area.

The ramus ophthalmicus superficialis facialis
continues anteriorly in bone at the medioventral
side of the frontal canal. Halfway along its or-
bital course, it detaches branch SORB 8, which
innervates the third supraorbital canal organ.
Some distance further SORB 9, innervating the
second supraorbital canal organ, is detached. At
the point where SORB 6 touches it, the ramus
ophthalmicus superficialis facialis gives off
SORB 10, which rises dorsoanteriorly along the
medial wall of the frontal canal. From SORB 10
a twig is sent to skin outside the frontal canal,
the rest going dorsally to innervate skin dorsal
to the posterior end of the nasal bone. Directly
beyond this branch, a smaller branch (not illus-
trated) is sent to skin a little anterior to the pre-
ceding branch. Branch SORB 10 apparently car-
ries cutaneous fibers of the trigeminal ramus
rather than lateralis fibers of the facial nerve.
The ramus ophthalmicus superficialis facialis
next passes through the frontal bone and contin-
ues medial to the nasal canal which it penetrates
and detaches SORB 11 which innervates SO 1,
the first canal neuromast of the supraorbital ca-
nal and the only lateral line organ in the nasal
canal. Extending beyond SORB 1 1 is a thick,
straight branch, SORB 11 A, which runs antero-
laterally, penetrates the lateral wall of the nasal
canal two-thirds along its length, and ends in a
darkly stained spray of terminal fibers on the
surface of the skin on the side of the canal. Free
lateralis organs are located in this area, which
SORB 1 1 A apparently innervates.

Truncus Infraorbitalis

The truncus infraorbitalis has three main di-
visions: division IOl, the ramus buccalis faci-
alis; division 102, the ramus mandibularis tri-
geminus; and division 103 the ramus maxillaris
trigeminus. Divisions 102 and 103 are closely

bound together for some distance after leaving
the area of the trigeminal foramen.

Ramus buccalis facialis

Division IOl, the ramus buccalis facialis, car-
ries mainly lateralis fibers innervating the canal
organs of the infraorbital series of bones, these
lateralis fibers having come from the dorsal lat-
eralis root of the facial nerve. InPolycentrus the
ramus buccalis also carries a general cutaneous
component, the fibers of which come from the
Gasserian ganglion of the trigeminal nerve. They
supply the skin of the cheek area and preoper-
cular regions as well as skin on or near the in-
fraorbital bones. The lateralis fibers of the ramus
buccalis supply four canal neuromasts enclosed
within the lachrymal canal as well as a neuro-
mast enclosed in the canal of each of the second
and third bones of the infraorbital series (Figs.
1 and 3). The fourth infraorbital, that on the
sphenotic bone, has its neuromast innervated by
a branch of the ramus oticus, a nerve which is
not considered by Herrick (1899) to belong to
either the supraorbital or infraorbital trunks but
to lie in between the two. Free lateralis organs
are distributed along the lower edge of the sec-
ond and third infraorbital bones, along the pos-
terior one-fifth of the lachrymal, and on the
membrane of the second pore of the lachrymal
(Fig. 17). The ramus buccalis facialis innervates
these naked lateralis organs. The ramus buccalis
also apparently innervates free lateralis organs
medial or dorsal to the anterior and posterior
ends of the nasal bone and a patch of these or-
gans that lies in skin lateral and ventral to the
anterior and posterior narial openings (Figs. 1,
3, and 17). A patch of free lateralis organs in-
nervated by the ramus buccalis also occurs on
the anterior end of the maxilla, ventral to the
anterior nostril. Some branches to canal neuro-
masts detach a branch that innervates free lat-
eralis organs near an adjacent canal pore. An
example is the neuromast branch for the second
neuromast and second pore of the lachrymal ca-
nal (Fig. 1, I01d2).

The ramus buccalis, division IOl of the trun-
cus infraorbitalis, forms from the dorsal lateralis
root of the facial nerve and moves through the
dorsolateral corner of the trigeminal foramen
and through the trigemino-facialis complex out-
side the foramen. A fairly large contribution of
general cutaneous fibers from the Gasserian gan-
glion joins it as the ramus buccalis passes ven-

14

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

trally down the lateral side of the trigemino-fa-
cialis complex and lateral to the rest of the
truncus infraorbitalis.

The first branch is IOla (Fig. I) to the lateralis
organ in the fourth infraorbital bone (the sixth
organ of the infraorbital canal). The ramus buc-
calis shortly divides, the larger part remaining
as the ramus buccalis, the smaller part, 10 lb, in
turn divides into four branches, all being appar-
ently the general cutaneous fibers going to skin
of the cheek area. The first of these is branch lh
(Fig. 1), which passes under the posterodorsal
end of the second infraorbital bone and across
the cheek underneath skin near the sensory ca-
nal of the preopercle. Branch lh turns sharply
ventrally and innervates skin in front of and on
top of the preopercle about midlength of the ca-
nal. Branch lg passes directly posteriorly and
crosses the preopercular canal, innervating skin.
Branch If is short. It passes under the second
infraorbital and ends in skin partway across the
cheek towards the preopercle. The fourth
branch, le, after contacting a thick branch of
I02b from the ramus mandibularis trigeminus
(102), passes under the second infraorbital and
extends almost in a straight line over to the pre-
opercle, where it breaks up in skin overlying the
canal of this bone. Branch I02b of the ramus
mandibularis trigeminus is mentioned here be-
cause it should be part of the ramus buccalis
although it detaches from 102, the r. mand.
trigeminus. No comparison of this branch was
made on other specimens. Branch I02b also
passes under the second infraorbital bone about
midway along the length of this bone after hav-
ing been in contact with branch le of the ramus
buccalis. Branch I02b divides into cheek
branches lc and Id, both of which pass ventro-
posteriorly over the cheek, supplying apparently
general cutaneous innervation to skin over to
and on top of the preopercular canal.

The ramus buccalis next detaches branch
IOlc, which shortly divides into IOlcl (Figs. 1
and 3), which supplies the lateralis organ located
halfway along the length of the second infraor-
bital, and I01c2, which in turn gives off two
branches. The first branch, C0R6, innervates
conjunctiva and cornea of the posteroventral
part of the eyeball and skin connecting the eye-
ball and the second infraorbital bone. The rest
of I01c2 passes under the second suborbital,
emerges at the ventral edge of this bone, rises
to skin, and divides into branches 3b and 3c.

Branch 3b passes anteriorly, innervating a series
of four or five free lateralis organs in a row. It
anastomoses with branch 3d. Branch 3c turns
posteriorly and innervates a row of four or five
lateralis organs along the ventral edge of the an-
terior half of the second suborbital bone. The
rest of the ramus buccalis continues anteriorly
over the floor of the orbital cavity medial to the
infraorbital bones and gives off branch IOld,
which passes anteriorly giving off branches to
the suborbital bones and skin of the cheek. The
first branch of IOld (not labeled in Fig. 1) leaves
IOld near the anterior end of the second infraor-
bital and divides into three branches. Branches
la and lb pass ventrally down the cheek, inner-
vating skin below the eye and anterior to the
preopercular canal. Branches 3d and 3e both
supply a row of free lateralis organs lying at the
ventral edge of the anterior end of the second
infraorbital bone and about three or four organs
extending onto the ventral edge of the posterior
end of the lachrymal (Fig. 1). Branch 3e is not
continuous with branch 3f, although they are
shown continuous in Fig. 1. Branch 3d anasto-
moses posteriorly with 3b. The last branch of
the ramus buccalis to supply free lateralis organs
in the infraorbital row is branch 3f, which in-
nervates four organs in a row anterior to those
innervated by 3e. The four organs lie a little
above the ventral edge of the lachrymal bone
well posterior to the canal of this bone. The next
branch, I01d2. detaching almost at the same
point as branch 3f, passes anteriorly some dis-
tance and innervates the second lateralis organ
in the lachrymal as well as the membrane over
the second lachrymal canal pore. The branch
innervating the pore membrane detaches from
I02d2 inside the lachrymal canal. The next
branch of IOld is 3g (Fig. 1). which passes to
the exterior of the lachrymal bone and anteriorly
some distance, reaching the membrane over the
third pore of the lachrymal. Branch 3g inner-
vates the patch of free lateralis organs on this
membrane. Here is another example of a later-
alis branch to a canal organ detaching also a
branch to free lateralis organs on the membrane
of the adjacent canal pore. The last two branch-
es of IOld each innervate a canal neuromast lo-
cated near the third lachrymal pore and its mem-
brane.

After detaching IOld, the ramus buccalis con-
tinues anteriorly some distance and divides into
IOle and IO If about halfway along the lachry-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

15

mal (Fig. 1). Branch 10 le shortly gives off a
branch (not labeled) on either side of itself be-
fore passing to the first canal organ in the lach-
rymal. The first of these branches is a thin nerve
that passes anterolaterally medial to the lach-
rymal bone. It crosses under the branch to the
first lateral line canal organ and emerges from
under the lachrymal, where the large articulating
surface of the maxilla comes in contact with the
anteromedial surface of the lachrymal (Fig. 1).
The nerve supplies skin in this area, especially
the fold of skin that lies directly ventral to the
first indentation on the anterior leading edge of
the lachrymal bone adjacent to the articulating
head of the maxilla. The second of the two
branches of 10 le continues anterodorsally me-
dial to the lachrymal and then almost straight
dorsally near the posterior edge of the lachrymal
where it innervates the skin covering the olfac-
tory organ and olfactory chamber. From the ap-
pearance of its tiny spraylike endings as seen on
Sihler whole-mount nerve preparations, this
branch innervates free multicellular sense or-
gans located on the skin. The distribution of
such organs as seen on serial sections and from
whole formalin specimens (Fig. 19) coincides
with the location of the spraylike endings just
mentioned. The serial sections show the organs
to be free lateralis organs.

Branch 10 If, which arises at the same point
as IOle (Fig. 1), continues anterodorsally,
passes ventral to the lateral ethmoid and a little
lateral and dorsal to the palatine bone and along
the medial wall of the nasal sac. At a point about
on the same dorsal level as the first dorsal pore
of the lachrymal, 10 If 1 is detached and passes
dorsally and then anteriorly medial to the lach-
rymal. It apparently innervates only skin on the
anterodorsal part of the lachrymal. Branch IOlf
continues anterodorsally and divides medial to
the first pore of the lachrymal. One of these
branches (IOlfa; Fig. 1) passes dorsally, medial
to the posterior end of the nasal bone, and in-
nervates the membrane over the posterior nasal
canal pore and some skin anterior to it. The ter-
minal spraylike endings of these branches on
Sihler preparations indicate innervation of free
multicellular sense organs on the skin. The dis-
tribution of free lateralis organs as seen on serial
sections coincides with the distribution of the
spraylike endings of the nerves. There is little
doubt that they are innervating free lateralis or-
gans.

Branch IOlfb (Fig. 1) continues for a short
distance anterodorsally and medial to the lach-
rymal before dividing into two branches. One
branch passes anterolaterally to innervate skin
overlying the dorsal edge of the head of the max-
illa and skin ventral to the anterior narial open-
ing where there are free lateralis organs (Fig.
19). The other branch passes dorsally up the
medial side of the nasal canal and ends in skin
medial and dorsal to the anterior end of the nasal
canal. There is a patch of free lateralis organs
here, which this branch evidently supplies.

Ramus maxillaris trigeminus

The ramus maxillaris trigeminus of the trun-
cus infraorbitalis has two main branches, the
ramulus maxillaris superioris to the snout and
symphyseal area of the upper jaw and the ram-
ulus maxillaris inferioris to the upper jaw. In
Polycentrus , at least in the specimen on which
the descriptions are based, the superior ramulus
is not a separate nerve but courses, to whatever
extent it is present, with the ramus buccalis fa-
cialis. The inferior ramulus (103; Fig. 1) to the
upper jaw is moderately developed. It inner-
vates the skin of the premaxilla and maxilla. The
following description covers only the inferior
ramulus.

The ramulus maxillaris inferioris trigeminus
leaves the floor of the orbital cavity about half-
way across it and passes anterolaterally and
ventrally of the palatine bone, then across the
lateral side of the palatine but medial to the lach-
rymal, giving off as it does two small branches
(not shown in Fig. 1) which anastomose with
branch IOlf of the ramus buccalis facialis. The
next branch, I03a, leaves the inferior ramulus
maxillaris and sends a branch to skin on the
lachrymal, dorsal to the second and third pores
of the lachrymal canal. The remainder of the
I03a (Figs. 1 and 16) is branch COR 4, which
continues onto the anteroventral quadrant of the
eye, innervating skin on the edge of the eye and
then the conjunctiva and cornea.

The main part of the inferior ramulus (103)
continues anteriorly lateral to the palatine and
crosses the medial side of the alveolar shaft of
the maxilla a little ventral to the curved process
of the maxilla in which the premaxillary ascend-
ing process rides. As the inferior ramulus (103)
leaves the maxilla, it receives the main part of
the palatine nerve. The ramulus courses parallel
and ventral to the ascending process of the pre-

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

maxilla, lying between membranes of the upper
jaw (Fig. 1). The external membrane is the skin
and the internal membrane is the mucosal lining
of the mouth, both having become modified into
a stretchable, thin, tough pair of membranes.
Before reaching the premaxilla, branch I03b is
detached medial to the lachrymal as 103 passes
beyond the palatine (Fig. 1). Branch I03b also
runs between the jaw membranes, passes lateral
to the A, tendon which fastens the cheek mus-
cles to the maxilla, and runs close to the dorsal
edge of the maxilla towards its distal end. Two-
thirds along the maxilla, I03b crosses onto the
lateral surface of this bone and shortly divides
into three branches. A small branch runs an-
terodorsally into the jaw membrane anterior to
the maxilla, another ends in skin over the shaft
near the distal end of the maxilla, and the main
part of I03b continues to the distal end of the
maxilla, coursing along the ventral edge of the
ligamentous connection between the distal ends
of the maxilla and premaxilla. Branch I03b ram-
ifies in folds of skin in this region. After passing
beyond the maxilla on its way to the premaxilla,
103 receives, as mentioned, the anterior end of
the palatine nerve. The juncture of the two
nerves varies somewhat on different specimens
and on the two sides on the same specimen. On
one side, the palatine nerve crosses 103 but then
continues alongside it, the two nerves remaining
separate for some distance before joining. On
the other side, the two nerves remain separate
for some distance, except for a small branch,
until after 103 bifurcates at two-thirds of the
way toward the shaft of the premaxillary bone.
The palatine nerve then joins the dorsal fork,
I03c (Fig. 1). The dorsal fork and the palatine
nerve continue as one nerve towards the base
of the ascending process, giving off twigs at right
angles, which run in the thin membrane of the
upper jaw and innervate it. Just before I03c
passes medial to the shaft of the premaxilla, it
breaks up into two large and several small
nerves. The largest branch I03cl, passes onto
the medial side of the premaxilla, penetrates the
premaxilla at the edge of the alveolar region, and
emerges on its dorsal (external) surface and di-
vides, one branch going towards the symphysis
of the upper jaw and out onto the lip. The rest
of I03cl innervates teeth and lip tissue adjacent
to the symphysis. Branch I03cl is the main in-
nervation to the lip tissue in front of the sym-
physis. The fair-sized remainder of I03c inner-

vates the teeth and adjacent tissue of the rest of
the premaxillary. It sends a small branch to the
premaxillary oral flap and a small branch to the
premaxillary membrane (neither branches shown
in Fig. 1) and then passes across the medial sur-
face of the shaft of the premaxillary until it
reaches the alveolar region, where it turns dis-
tally and runs in the gum tissue between the
middle rows of teeth, supplying the teeth and
gums out to the end of the tooth region.

The posterior fork, I03d, formed from the
bifurcation of 103, slants anteroventrally across
the jaw membrane and reaches the lateral sur-
face of the premaxilla about one-third of the way
along its shaft, giving off en route two branches
which supply the area of the lip distal to that
supplied by the dorsoanterior fork. The rest of
the posterior fork passes in skin diagonally
across the premaxilla, giving off branches to the
upper lip; leaving the premaxilla one-third of the
way from its distal end, it innervates the pos-
terior end of the lip. Branch I03d must carry
predominantly general cutaneous fibers. Of the
three main branches of the compound 103 and
palatine nerves, the branch to the alveolar re-
gion is the smallest.

The conspicuous part of the superior maxil-
lary ramulus, the branch to the symphyseal re-
gion of the upper jaw that is apparently generally
present in many teleosts, is absent in Polycen-
trus. The rest of the superior ramulus that in-
nervates the skin of the anterior end of the snout
no doubt courses as parts of branches IOlfa and
IOlfb of the ramus buccalis.

Ramus mandibularis trigeminus

The ramus mandibularis trigeminus (102)
courses for some distance bound to the rest of
the truncus infraorbitalis. It leaves the truncus
and turns ventrally. Medial to the second in-
fraorbital bone, it detaches its first branch, I02a,
the ramus opercularis trigeminus (Fig. 1) and
continues towards the cheek muscles and the
lower jaw.

Ramus opercularis trigeminus

The ramus opercularis trigeminus, I02a,
passes posteriorly towards the hyomandibular,
curves dorsally, crosses the anterior edge of this
bone a little ventral to its anterior articulating
head, continues posteriorly close to the lateral
surface of the hyomandibular and divides en
route into a dorsal and a ventral branch. The
ventral branch breaks up to supply the levator

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

17

arcus palatini muscle near its insertion. The dor-
sal branch passes through this muscle to inner-
vate the adjacent dilatator operculi muscle. The
main arm of the dorsal branch then innervates
the dilatator fibers that pass under the dorsal end
of the preopercle (Figs. 1 and 22).

After the ramus mandibulars trigeminus (102)
has passed ventrally below the second infraor-
bital bone, it detaches I02b (Fig. 1 ), a thin nerve
that passes laterally across the floor of the or-
bital cavity. At the inner edge of the third in-
fraorbital, it anastomoses with the anteriormost,
fourth branch of IOlb of the ramus buccalis.
From the anastomosis three nerves spread out
(only 3b and 3c shown in Fig. 1) as they pass
under the infraorbital bone and run under skin
across the cheek area, as has been described in
a preceding section, giving off branches en route
and ending in skin covering the preopercular ca-
nal. These nerves do not appear to end in the
spray typical for branches that innervate free
lateralis organs. There are no free lateralis or-
gans in this area. These nerves undoubtedly be-
long to the general cutaneous system. A second
and smaller nerve, not illustrated, detaches at
the same place as I02b, diverges anteriorly from
I02b, and passes out as another cutaneous
branch down the cheek.

Innervation of cheek muscle

A fair-sized branch, I02c (Fig. 6), passes lat-
erally and a little ventrally through the adductor
mandibulae muscle mass a short distance below
the orbit. The nerve breaks up into a fairly large
posterior branch which supplies the ventrolater-
al part of the anterior half of muscle A,. How-
ever, a sizeable portion (not labeled) of I02c
rises to skin not far below the orbit where it
divides into numerous branches which pass un-
der the third infraorbital to innervate the skin in
its vicinity. One rather large branch of I02c
curves sharply ventrally (shown in Fig. 6 but not
labeled) and passes under the skin of the cheek
toward the preopercular canal, giving off what
apparently are cutaneous branches to skin. It
ends in skin over the anterior end of the pre-
opercular canal. The terminal branches in the
skin are very fine.

The next branch, I02d, arises a short distance
further, passes anteriorly, and breaks up in the
anterodorsal half of the A, portion of the adduc-
tor mandibulae muscle, which it innervates (Fig.
6). A smaller branch of I02d passes posteriorly

and shortly divides, the posterior branch sup-
plying the more posterolateral part of A,, the
anterior branch going to the more ventrolateral
part of the anterior half of A,.

The fifth branch, I02e, quite large, leaves the
ramus mandibularis trigeminus at the same point
as does I02d and passes ventroposterioriy (Fig.
6). The first branches to come off I02e ante-
riorly form a rather dense ramification on the
most medial side of the muscle mass. These
branches lie medial to the main trunk of the ra-
mus mandibularis trigeminus (102) and appear
to supply mainly the muscle fibers which insert
by way of the prearticular tendon (TA3; see Fig.
24). Branches from the posterior side of I02e
supply the more lateral and ventral fibers of the
posterior part of A, in this region, fibers which
insert on the ventral end of the maxillary tendon
(TA,; see Fig. 24). Most of the rest of I02e
passes anteroventrally towards the tendon con-
necting the mentalis (Aw) division of the adduc-
tor mandibulae, supplying en route the ven-
troanterior fibers of this muscle, that is, those
which mainly constitute A2. Some of the more
dorsolateral muscle fibers which I02e inner-
vates insert on the ventral end of the maxillary
tendon. After giving off I02d and I02e, the main
trunk of 102, the ramus mandibularis trigemin-
us, continues anteroventrally, passing between
the body of the cheek muscle mass along a rath-
er clear-cut separation between what has been
designated as divisions A, and A2 of the jaw
muscles. As the main ramus reaches the anterior
edge of the quadrate a little above its articulating
head where 102 is covered laterally by fibers of
A2, the nerve forms three large subdivisions.
The most ventral of these, the ramulus mandib-
ularis cutaneus trigeminus (I02f; see Fig. 6),
passes directly anterior to the articulating head
of the quadrate onto the lateral surface of the
posterior end of the articular bone.

Ramulus mandibularis cutaneus trigeminus

The first branch detached en route, I02fl,
passes medially around the anterior edge of the
quadrate. It ends in a dense, localized ramifi-
cation of branches (Fig. 10) in the tendinous
mucosa which lies on the inside of the mouth
directly in front of the anterior edge of the quad-
rate near the articulation head of the bone. This
tendinous mucosa fans out towards the ventral
end of the maxillary tendon. Branch I02fl may
innervate stretch receptors located in the jaw

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

membranes in this region. Just before I02f
reaches the quadrate, three branches ofI02f are
given off. One of these, I02f2, runs dorsally be-
neath the skin covering the ventral area of the
cheek (Fig. 6; only the stub of this branch is
shown) and which fastens onto the articular
bone. One twig innervates this skin. A more dor-
sal twig innervates the skin area directly poste-
rior to the ventral end of the maxillary tendon.

A second of the three branches, I02D (Fig.
6; stump only of branch shown), runs beneath
skin posteriorly, gives off a small twig to skin
lying over the articulating head of the quadrate,
and then continues dorsally a short distance,
parallel to the ventral edge of the quadrate and
bifurcates. One of the two forks extends poste-
riorly to the ventral end of the maxillary tendon
and ends in very fine branches in the skin near
the area supplied by I02fl. The other, larger
fork slants posteroventrally over the preoper-
cular canal and ends in fine branches in skin
directly dorsal to the ventral opening of the pre-
opercular canal. It innervates skin close to that
innervated by a branch of the ramus mandibu-
laris facialis of the truncus hyomandibularis,
TH16, but TH16 (Fig. 2) has terminal sprays
typical of nerves supplying free lateralis organs
in the skin, whereas for the smallest distal
branches of the larger fork of I02f3, the termi-
nations as viewed on Sihler specimens are very
delicate, widely forked twigs and apparently are
of the general cutaneous component.

The last of the three branches, I02f4 (Fig. 6),
passes anteriorly over the lateral side of the pos-
terior end of the articular, gives off a small ven-
tral branch to skin, then slants dorsally and
shortly bifurcates, with fork I02f4b passing
close to the dorsal edge of the articular. A short
distance up the articular, I02f4b gives off a
small branch that enters the fold of bone con-
stituting the dorsal edge of the articular. This
nerve passes to the end of the dorsal edge and
onto the ventral surface of the cartilaginous pad
between the posterior end of the alveolar pro-
cess of the dentary and the anterior end of the
dorsal edge of the articular. It breaks up into
tiny branches in this region. The rest of I02f4b
continues up the dorsal articular process, de-
taches a branch which passes onto the cartilag-
inous pad, and then continues in a curved course
anteriorly along the ventral edge of the alveolar
process of the dentary, gradually becoming
smaller. It is apparently a cutaneous nerve. A

second branch, which was given off at the same
time as this branch from I02f4, also passes to
the cartilaginous pad where it could not be fol-
lowed. The third branch of I02f4b curves an-
terodorsally along the lateral surface of the
broad anterior articulating shaft of the articular
bone, becomes thinner as it approaches the pos-
terior edge of the body of the dentary, and dis-
appears between the lateral wall of the dentary
and the anterior shaft of the articular.

The other fork of the general cutaneous
branch of I02f4, branch I02f4a (Fig. 6), extends
anteriorly under skin above the articular seg-
ment of the mandibular lateral line canal, giving
off occasional branches which run downward in
the skin over the canal. It becomes progressive-
ly smaller until it disappears in skin. Branch
I02f4 is apparently all general cutaneous.

Shortly after I02f passes onto the articular,
it is joined by TH16, a branch from the ramus
mandibularis facialis of the truncus hyomandib-
ularis. Branch TH16 could be carrying either
lateralis or cutaneous fibers or both. Branch
I02f from the r. mandibularis trigeminus would
be carrying general cutaneous fibers but not mo-
tor fibers. Since I02f and TH16 distribute to the
same areas and I02f carries only or mostly gen-
eral cutaneous innervation, it is not likely that
TH16 is carrying this component. More likely,
since it detaches from the r. mandibularis exter-
nus (Fig. 2) which carries lateralis fibers mainly
or only, TH16 must carry lateralis fibers, which
it supplies to free lateralis organs of the articular
and preopercular areas. The compound nerve
(TH16 + IO20, after a short distance, detaches
I02f5 (Figs. 6 and 9), which passes postero-
ventrally directly ventral to the articulating head
of the quadrate. Branch I02f5 shortly sends a
small branch which contributes to the innerva-
tion of the skin over the posterior opening of the
lateral line canal in the articular bone. Branch
I02f5 passes medial to the lateral line canal and
comes out under skin covering the posterior pro-
cess of the articular and angular bones. Here it
breaks up into several branches. Branch I02f5a
turns anteriorly beneath skin at the postero-
ventral surface of the articular, where it disap-
pears as fine branches; the other branches come
off the remainder of I02f5. Branch I02f5b (Fig.
6) divides into an anterior branch, which passes
in skin of the articular ventral to its sensory ca-
nal, and into a long, thin posterior branch which
runs posteriorly in the ligament connecting the

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

19

interopercle to the angular and articular. It
passes further onto the interopercle, where it
anastomoses with a branch from the ramus hy-
oideus and gives off en route another branch,
I02f5d (Fig. 6), which passes dorsally, medial
to the ventral end of the preopercle. Branch
I02f5d anastomoses with the r. mandibularis fa-
cialis of the truncus hyomandibularis. Branch
I02f5e passes posteriorly underneath the ventral
edge of the preopercle, giving off branches to
skin on the interopercle. A larger branch,
I02f5c, continues across the interopercle-artic-
ular ligament and onto the ventral skin covering
the articulation between the interopercle, artic-
ular, and angular bones, and the bases of the
anteriormost branchiostegal rays. Branch I02f5
is undoubtedly partly general cutaneous and
partly lateralis, since it is a branch of the com-
pound nerve formed by TH16 (lateralis) and
I02f (general cutaneous). There are free lateralis
organs in the area.

The remainder of I02f, after detaching the
above branches, enters the articular segment of
the mandibular lateral line canal and detaches
I02f6, a small branch (Fig. 9) which ends in a
dense and very finely divided network on the
surface of skin covering the articular segment of
the mandibular canal. About halfway anteriorly
along the articular, the remainder of I02f breaks
up into branches I02f7. I02f8, and I02f9.
Branch I02f7 (Figs. 6 and 9) passes postero-
medially and supplies skin over the medial ven-
tral surface of the articular. Two long anterior
branches of I02f8 course in skin over the artic-
ular and dentary canals. There is a row of free
lateralis organs in this skin and a patch of them
at the junction of the articular and dentary ca-
nals. It could be observed directly that these
branches of I02f8 innervated these free lateralis
organs. The longer branch of I02f8 ends in skin
and membrane around lateral line canal pore
number four of the dentary. No free lateralis
organs were observed in this area (Fig. 17). The
branches of I02f7 and I02f9 ending in skin over
the ventral surface of the articular and dentary
medial to the lateralis canal apparently are of a
general cutaneous component and would be
from the r. mandibularis trigeminus, not from
the r. mandibularis facialis.

The lateralis fibers for I02f8 are apparently all
from the r. mandibularis facialis of the truncus
hyomandibularis via TH16. which joins I02f
above the quadrate's articulating head. Herrick

(1899: fig. 3. V-VII.I) found with fairly good
certainty such a source of innervation for a small
number of free lateralis organs over the canal of
the articular bone in Menidia.

Returning in the description of the main trunk
of the r. mandibularis trigeminus (102) to the
point where it detaches I02f (Figs. 7, 9, and 10),
it is seen than the ramus mandibularis trigeminus
passes anteriorly medial to the muscle fibers that
insert on the A2-Aw common tendon, and onto
the medial side of the articular, crossing at about
midpoint of the posterior edge of this bone. 102
continues anteriorly and a little ventrally on the
medial surface of the articular, detaching en
route four branches rather close together which
innervate subdivisions for the mentalis muscle
(Fig. 7). The subdivisions are shown in Figures
23 and 24. Shortly beyond the branches to the
mentalis muscle, the r. mandibularis trigeminus
(102) detaches the ramulus mandibularis inter-
nus trigeminus (I02g; Fig. 7). The remainder of
102 continues anteriorly as the ramulus mandib-
ularis externus trigeminus (I02h; Fig. 8). The
internal trigeminal ramulus (I02g; Fig. 7) cross-
es Meckel's cartilage and runs forward with the
ramus mandibularis facialis of the truncus hyo-
mandibularis. Branch I02g innervates the pro-
tractor hyoidei and intermandibularis muscles,
and adjacent skin on the outside, and the mu-
cous lining on the inside of the lower jaw.

Ramulus mandibularis externus trigeminus

After detaching I02g, the ramulus mandibu-
laris externus trigeminus (I02h) continues an-
teriorly some distance and, near the teeth, it de-
taches I02hl (Fig. 10), which carries general
cutaneous fibers. I02hl is shortly joined antero-
dorsally by TH19a carrying communis fibers.
The two branches course together towards the
inner edge of the alveolar region of the dentary,
where the compound nerve divides. An anterior
branch, TH19a4 (Fig. 8), enters the dentary be-
neath the inner rows of teeth and courses to-
wards the symphysis of the lower jaw, supplying
teeth and apparently tissue surrounding the
teeth. Two posterior branches run along the in-
ner edge of the alveolar region. TH19a3 in bone
under the teeth and Thl9a2 next to the alveolar
region but in the skin (Fig. 8). The latter nerve
breaks up into several parallel branches, one of
which, a little posterior to the teeth, drops ven-
trally and innervates an area of mucosa lining
the inside of the lower jaw. A thin branch.

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

TH19al (Fig. 8), detaches from THl9a shortly
after the latter leaves TH19 and runs forward to
an area a little posterior and lateral to the sym-
physis, where it ends in skin. Shortly before it
breaks up, TH19al is joined by a long anterior
branch of TH19bl (Fig. 8). Branches of TH19
should be carrying communis fibers for taste
buds and mucosa.

After detaching I02hl, the remainder of the
ramulus mandibularis externus trigeminus (I02h)
(Fig. 8) courses anteriorly to near the end of
the dentary and detaches a fairly stout branch,
I02i, at the curve of the lower jaw. Branch I02i
goes to the anterolateral corner of the dentary,
near the symphysis, and probably carries mostly
general cutaneous fibers. It passes through the
dentary directly above the attachment of the la-
bial cartilage of the lower lip and directly divides
into three large and several small branches
which supply the lower lip. The largest of these
branches follows the curve of the labial cartilage
posteriorly, giving off branches to the posterior
half of the lip. One of these branches curves
posteriorly across the dorsal surface of the lip
and runs in skin of the lip above the teeth of the
dentary. Branches pass laterally and anteriorly
supplying the anterior half of the lip. After de-
taching I02i. the rest of I02h continues ante-
riorly as I02j (Fig. 8), which passes under the
teeth, has a connection with TH19bl, and, near
the symphysis, comes close to and probably
joins with the rest of TH19b, which carries com-
munis fibers from the r. mandibularis internus
facialis.

Ramulus mandibularis internus trigeminus

Branch I02g (Figs. 7 and 10) of the r. man-
dibularis trigeminus (102) remains to be de-
scribed. The rest of the r. mandibularis facialis
(branches TH19 through TH25) are described in
another section along with the rest of the r. man-
dibularis facialis and the truncus hyomandibu-
laris. The ramulus mandibularis internus trigem-
inus (I02g) innervates the protractor hyoidei
(geniohyoideus), the intermandibularis muscles,
and the skin of the anterior end of the lower jaw
in the area of these muscles. It carries a lateralis
contribution from the r. mandibularis externus
facialis, which innervates free lateralis organs
between the anterior ends of the dentary bones.
Just before the main trunk of the r. mandibularis
trigeminus (102) reaches the dorsal side of
Meckel's cartilage, about halfway along the ar-

ticular bone, branch I02g is detached. K)2g
passes ventrally around the cartilage and comes
to lie on the medial surface of the r. mandibularis
facialis, runs with it for some distance on the
ventral surface of Meckel's cartilage, leaves the
r. mandibularis facialis, and continues dorso-
anteriorly medial to the cartilage. After branch
TH19 is detached (Fig. 10) from the r. mandib-
ularis facialis (see section on the truncus hyo-
mandibularis for description of TH19), the re-
mainder of the r. mandibularis facialis (lateralis
fibers from the ramulus mandibularis externus
facialis) plus the trigeminal branch I02g (general
cutaneous and motor fibers) continue anteriorly
medial to Meckel's cartilage. The facial and tri-
geminal parts of this nerve cannot be separated.
En route to the muscles and skin of the floor of
the lower jaw. branches TH20 to TH24 are de-
tached. These branches mainly constitute the
remainder of the r. mandibularis externus faci-
alis, although some cutaneous innervation of the
trigeminus courses with them. Only branches
I02g2 and I02g2a (Fig. 8), which innervate the
protractor hyoidei and the intermandibularis
muscles, respectively, and overlying skin are la-
beled as deriving from I02g of the r. mandibu-
laris trigeminus. Branch I02g2 passes antero-
medially (Fig. 8) and detaches I02g2a, which
continues anteriorly and is almost contiguous at
the midventral line with a similar branch from
the opposite side, the two together innervating
the intermandibularis muscle (Figs. 8, 9, and 10).
The remainder of I02g2 enters the protractor
hyoidei muscle, courses posteriorly in it near the
medial edge of the muscle, and sends lateral
branches into the muscle. Near the point of di-
vergence of the two parts of the protractor
hyoidei where the belly of each muscle is
crossed by a myoseptum, the remainder of
branch I02g2 of each side meet. There appears
to be some crossing of the nerve fibers of each
side over to the opposite side as branch I02g2
continues posteriorly in the protractor hyoidei,
I02g2 finally overlapping, as far as could be de-
termined; the anterior extent of the ramus hy-
oideus passes anteriorly from the hyohyoideus
muscle.

Ramus Oticus

The ramus oticus forms intracranially from a
larger bundle of fibers from the dorsal lateralis
root and a smaller bundle from the ventral lat-
eralis root, both being roots of the facial nerve.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKU

21

The two bundles join, pass out the lateral side
of the trigeminal foramen, and receive general
cutaneous fibers from the Gasserian ganglion.
The compound nerve passes laterodorsally over
the surface of the orbital cavity and into a fo-
ramen in the sphenotic bone. En route to this
foramen, a branch is detached which innervates
the next-to-last lateral line canal organ of the
infraorbital series, organ 6. In Figure 1 this
branch is labeled 10 la and is shown as detaching
from the ramus buccalis facialis. Usually this
branch is associated with the ramus oticus (Frei-
hofer 1963: fig. 5). A cutaneous branch (not
shown in Fig. 1) extends from 10 la underneath
the infraorbital bone and ramifies in skin pos-
terior to this bone. Upon emergence from the
sphenotic bone, the ramus oticus (Fig. 5) lies
underneath the last infraorbital bone. It detaches
a lateralis branch innervating the single lateralis
organ in the last infraorbital, which lies over the
sphenotic, and also detaches a branch (not
shown in Fig. 1) which passes from under this
last infraorbital. It innervates skin overlying the
dilator operculi muscle. The rest of the ramus
oticus, along with the orbito-pectoral branch of
the ramus lateralis accessorius (RLA-OP),
which joins it in the porous passageway through
the sphenotic, enters a bony passageway at the
lateral side of the pterotic canal, shifts medially,
and enters the pterotic canal, where it innervates
two lateral line canal organs lying close together.
The orbito-pectoral branch of the ramus lateralis
accessorius continues on and is described in a
later section.

Ramus Palatinus

The ramus palatinus carries communis fibers
for the mucosa of the palate and its taste buds,
and for taste buds of the upper jaw. The ramus
leaves the geniculate ganglion of the facial nerve
and passes above the anterior end of the facial
foramen. Intracranially the ramus palatinus ap-
parently divides into an anterior and a posterior
ramus, this division not being discernible on se-
rial sections or on Sihler preparations. It may be
that both rami arise separately from the genic-
ulate ganglion. Two rami are identifiable outside
the cranium. The anterior ramus is the main one.
The posterior ramus leaves the cranium with the
truncus hyomandibularis as branch TH1 (Fig. 4)
to the pseudobranch area. The anterior palatine
ramus drops sharply ventrally and a little ante-
riorly, passing through its foramen in the prootic

bone, and enters the prootic chamber connect-
ing the trigeminal and facial foramina. It directly
enters the wall of the prootic and passes antero-
ventrally next to the lateral prootic wall of the
posterior myodome chamber. It courses in a
bony space outside that of the myodome. Leav-
ing the wall of the prootic, it passes through the
parasphenoid rather close to the anterior edge
of the prootic wing of this bone. It continues
next to the top edge of the parasphenoid, grad-
ually shifts ventrally, and finally comes to lie
alongside the parasphenoid directly above the
origin of the adductor arcus palatini muscle. The
first branch (not illustrated) passes anterodor-
sally in the palatal mucosa, continues halfway
anteriorly across the adductor arcus palatini,
and curves laterally. It sends several long
branches posteriorly that innervate the mucosa
of the posterior area of the palate. On the other
side of the specimen, a branch was given off
from the right anterior palatine ramus that
courses near the middle of the parasphenoid
bone for about half the length of this bone, and
innervates mucosa. The next branch, P2, is giv-
en off a little before the main ramus passes an-
teriorly beyond the end of the palatal roof (Fig.
4). Branch P2 passes laterally reaching the dor-
sal surface of the palatine bone near its anterior
end. It detaches en route a branch that courses
straight posteriorly some distance, innervating
the mucosa of the palate. The rest of P2 bifur-
cates at the palatine bone. The anterior fork
gives off several twigs; some innervate anterior
palatine teeth. One branch continues anteriorly
across the ventral surface of the palatine liga-
ment connecting the palatine and prevomer and
innervates mucosa in this area. Another branch
from P2 passes anteriorly across the ventral sur-
face of the articulation pad of the maxillary with
the prevomer and innervates mucosa in this
area. Another branch serves the prevomer area.
The posterior, larger fork of P2 courses par-
allel and medial to the palatine teeth and gives
off a small nerve at the posterior extent of these
teeth, the nerve passing anteriorly beneath
teeth. The rest of the posterior fork continues
onto the ectopterygoid bone, where branches
supply mucosa and teeth. Numerous small
branches occur in the mucosa medial to the an-
terior end of the palatine bone and dorsal to the
palatine-prevomer ligament. The rest of the an-
terior ramus palatinus, after detaching P2,
courses anteriorly, passes beneath the process

::

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

of the maxillary in which the premaxillary spine
moves, and continues parallel to the ascending
process of the premaxilla and the ramus maxil-
laris trigeminus (103; Fig. 1). The anterior pal-
atine ramus finally joins the dorsal fork of the
ramus maxillaris trigeminus (Fig. 1).

On the other side of the specimen, the anterior
ramus palatinus joins the maxillary ramus (103)
proximal to the splitting of 102 into primary
branches to the alveolar region of the premax-
illary ramus.

Truncus Hyomandibularis

All of the nerve fibers and components of the
truncus hyomandibularis are derived from the
roots of the facial nerve except the general cu-
taneous fibers which come from the trigeminal
nerve via the ramus communicans and also some
sympathetic fibers from the facial sympathetic
ganglion.

There are four main branches of the truncus
hyomandibularis. These are (1) the ramus oper-
cularis profundus: (2) the ramus opercularis su-
perficialis facialis: (3) the ramus hyoideus: and
(4) the ramus mandibularis facialis, which has
two main divisions: the ramus mandibularis fa-
cialis externus and the r. mand. fac. internus.

The ramus opercularis profundus facialis car-
ries visceral motor component fibers and inner-
vates the muscles of the palate and those moving
the hyomandibular bone and opercle. muscles
whose origin is medial to these bones.

The ramus opercularis superficialis facialis
carries lateralis and general cutaneous fibers. In
Polycentrus it innervates the dorsalmost two ca-
nal organs of the mandibulo-preopercular canal
and free lateralis organs on certain scales: one
scale near the dorsal end of the preopercle: an-
other on the opercle near the operculo-hyoman-
dibular articulation: and a third on the anterior
end of the side of the subopercle.

The ramus hyoideus facialis follows a course
mainly along the ventral edge of the hyoid arch,
ending a little beyond the anterior end of the
arch. In Polycentrus it contains all or nearly all
of the general cutaneous fibers that join the trun-
cus hyomandibularis from the Gasserian gan-
glion of the trigeminal nerve via the ramus com-
municans. It also carries visceral motor fibers
for the branchiostegal muscles. The ramus hy-
oideus apparently carries no lateralis or com-
munis fibers. Almost all of the ramus hyoideus

innervates the hyoid arch, a small part of it ap-
parently continuing into the posterior end of the
protractor hyoidei muscle, where it appears to
anastomose with a posteriorly coursing branch
of the ramus mandibularis trigeminus which in-
nervates most of the latter muscle.

The ramus mandibularis facialis contains lat-
eralis and communis fibers, but apparently none
or few general cutaneous fibers and no motor
fibers. It has three main branches. One of these
is a lateralis branch, the ramus buccalis acces-
sorius (TH 10; Fig. 2), which in Polycentrus in-
nervates free lateralis organs around some pores
of the preopercular canal, a vertical row of free
lateralis organs on the cheek in front of the pre-
opercular canal, and free lateralis organs along
the third and fourth infraorbital bones. Another
is the ramus mandibularis facialis externus,
which is a lateralis branch that separates from
the remainder of the r. mandibularis facialis at
the symplectic bone, the remainder of the r.
mandibularis facialis at this point being the r.
mandibularis facialis internus. These two rami
rejoin beyond the symplectic but remain more
or less distinct entities, componentwise, but
such distinctness is not evident externally. The
ramus mandibularis facialis externus is so
named because it courses closer to the external
surface of the lower jaw, where it supplies lat-
eralis organs in the mandibular canal and free
lateralis organs in skin on the lower jaw. The
last of the three branches is the ramus mandib-
ularis facialis internus, which courses separately
from the r. mandibularis facialis externus in the
region of the symplectic, rejoining the r. man-
dibularis facialis externus. in most but not all
fishes, medial and anterior to the symplectic. It
carries communis fibers for taste buds located
mainly at the anterior end of the lower jaw, and
those on the lower lip and gum area of the teeth.

In Polycentrus there are apparently few or no
cutaneous fibers in the r. mandibularis facialis
beyond the preopercle. Herrick (1899) found a
similar condition for the atherinid Menidia.

In the labeling of Figures 2 and 8-13, all of
the branches of the truncus hyomandibularis are
numbered consecutively, and given the prefix
TH, and occasionally a name where one is avail-
able.

In Polycentrus the ventral lateralis and motor
roots of the facial nerve pass through the facial
foramen as one combined trunk, the truncus hy-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

23

omandibularis (Fig. 31). As the truncus leaves
the facial foramen, it receives a bundle of fibers
from the facial sympathetic ganglion.

Directly after leaving the cranium, a small
nerve, TH1 (Fig. 4), the posterior palatine ra-
mus, detaches from the truncus and passes an-
teriorly and laterally at a level dorsal and ante-
rior to the pseudobranch, where it is joined by
a nerve of equal size coming from the nervus
glossopharyngeus, forming what is called a Ja-
cobson's anastomosis. Herrick (1899) used the
term ramus pretrematicus facialis for branch
TH1 in Menidia but later (1901) changed to the
noncommittal term, the posterior palatine ra-
mus. The compound facial and glossopharyngeal
nerve continues its course through the adductor
arcus palatini muscle (Fig. 26) to skin at the pos-
terior roof of the mouth in front of the pseudo-
branch, where the compound nerve breaks up
into five branches. None of these branches was
observed to course onto the hyoid arch. Nerve
fibers from the glossopharyngeus innervate the
pseudobranch (Laurant and Dunel 1966). but no
innervation of this organ, a very vascular, gland-
like structure in Polycentrus , could be observed
by the methods employed.

Ramus opercularis profundus facialis

The next two branches from the truncus, TH2
and TH3 (Figs. 2 and 4), arise together at the
same point from the truncus but course in op-
posite directions. Together they constitute the
ramus opercularis profundus of the facial nerve.
Branch TH2 courses anteriorly through the ad-
ductor arcus palatini muscle, innervating it.
Branch TH3 (Fig. 4) extends posteriorly medial
to the head of the hyomandibular bone. In pass-
ing beneath the membrane connecting the pos-
terior end of the adductor arcus palatini muscle
and the adductor hyomandibularis muscle, TH3
detaches several very small nerves which inner-
vate this membrane, which contains only a few
muscle fibers (Figs. 4 and 26). It then enters the
adductor hyomandibularis muscle near its inser-
tion and divides. One division of TH3 gives off
three small nerves which run dorsally in the ad-
ductor hyomandibularis muscle, innervating it.
The other division also contributes to this mus-
cle. The two divisions of TH3 are next con-
nected by a small branch, and immediately sev-
eral rather large branches detach and pass
dorsally in the posterior part of the adductor

hyomandibularis. The lateral of the two divi-
sions of TH3 passes through the middle of the
levator opercularis muscle, sending branches in-
to this muscle, except for two small branches
which join with branches of the vagus coursing
down the medial surface of the opercle. One of
these vagal branches apparently supplies the an-
terior part, and the other the posterior part, of
the uppermost portion of the hyoidei adductores
muscle. It has not been possible to verify this
observation. The lateral division of TH3 cross-
es, at right angles, three branches of the vagus
and continues into the body of the levator oper-
cularis muscle, where it breaks up into a dorsal
and a ventral branch of about equal size and a
middle, small branch. All run posteriorly in the
muscle.

No other branches leave the truncus before it
passes through its foramen into the hyomandib-
ular bone. As it enters this bone, the ramus com-
municans from the Gasserian ganglion joins the
tr. hyomandibularis on its posterior surface (Fig.
2: r com V).

Shortly after entering its canal in the hyoman-
dibular and turning ventrally, the tr. hyoman-
dibularis detaches the ramus opercularis super-
ficialis facialis (Fig. 2; TH4).

Ramus opercularis superficialis facialis

The ramus opercularis superficialis facialis
(Fig. 2; TH4) directly supplies the twelfth, or
last, lateral line organ of the mandibulo-pre-
opercular canal. The rest of the opercular facial
ramus sends a branch which passes directly pos-
teriorly and, just in front of the opercle and a
little below the operculo-hyomandibular joint,
divides into TH4aa and TH4bb. The ventrally
directed branch TH4bb passes onto the lateral
surface of the opercle a little below the articular
head, enters a foramen near the leading edge of
the opercle, emerges on its lateral surface, and
shortly detaches branch TH4bbl and. a short
distance further, branch TH4bb2, which soon
rejoin and supply the pocket of a large scale.
About 15 free lateralis organs were observed on
a scale in this area (Fig. 17). The rest of TH4bb
passes ventrally, crosses the anteroventral cor-
ner of the opercle, continues onto the suboper-
cle a little posterior to the interopercle. and in-
nervates free lateralis organs in the skin of this
region. There are 15 such organs at this location
(Fig. 17). Branch TH4aa passes dorsally. lateral

24

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

to the hyomandibulo-opercular articular head,
and ends in skin a little below the point where
the preopercular, pterotic, and supratemporal
canals open. The terminal twigs of this branch
appear the same as those which supply free lat-
eralis organs in the skin elsewhere. There are six
or more free lateralis organs in this area (Fig.
17). Branch TH4aa apparently supplies these
organs.

Branch TH5 leaves the hyomandibular, pen-
etrates the preopercular lateral line canal, and
after a short distance, innervates lateral line ca-
nal organ number 1 1 of the mandibulo-preoper-
cular canal.

A short distance further TH6, a thin branch,
detaches and passes posteriorly onto the ante-
rior edge of the surface of the opercle that artic-
ulates with the preopercle (Fig. 2). Branch TH6
courses down the articulating edge, sending a
branch laterally onto the opercle, where it ap-
pears to end by several tiny branches in a scale
pocket dorsal to the pocket supplied by TH4bb 1 .
It does not appear to innervate free lateralis or-
gans nor are there any at this location on six
whole, formalin-preserved specimens examined.
A tiny twig is sent from TH6 into skin over the
ligament which connects the preopercle to the
interopercle. A small cutaneous branch, TH7
(Fig. 2), was present on one side of the specimen
but not the other.

About three-fourths of the way toward the
articulation of the interhyal with the hyoman-
dibular and symplectic bones, the truncus hy-
omandibularis detaches TH8, which supplies
lateralis organ number 10 of the mandibulo-pre-
opercular canal. The truncus next directly gives
off the sizeable ramus hyoideus (TH9), which
passes down near the posterior edge of the hyoid
arch and detaches several cutaneous branches
to skin over the anteroventral ends of the oper-
cle and subopercle, and the ventral half of the
interopercle as well as branches to the hyoidei
muscles and to the branchiostegal membrane.
The rest of the truncus shortly divides into the
rami mandibularis facialis externus and interims.

Ramus hyoideus

The ramus hyoideus (TH9; Fig. 2) continues
ventrally towards the interhyal, but before
reaching this bone it leaves the hyomandibular,
turns posteroventrally paralleling the interhyal
and gives off en route a thin branch, TH9A

(Figs. 2 and 13). Branch TH9A crosses the distal
end of the interhyal and passes onto the pos-
teromedial surface of the epihyal, where it
breaks up in the mucous lining of the mouth.
The main part of the ramus hyoideus (TH9)
passes around the posterior edge of the inter-
hyal-epihyal articulation and detaches TH9B
(Fig. 2), which passes a short distance to a point
above the posterodorsal end of the interopercle,
where it divides into TH9B0 and TH9B1 (Fig.
2). Branch TH9B1 goes through the broad liga-
ment connecting the interopercle to the shaft of
the hyomandibular and shortly divides into four
branches, TH9Bla through TH9Bld (Fig. 2),
treated together, and into branch TH9Ble.
Branch TH9Bla sends long thin branches inner-
vating skin covering the joint between the inter-
opercle and opercle. Branch TH9Blb courses
up the anterior edge of the opercle and anasto-
moses with a descending branch of the vagus
and with TH6. These branches apparently sup-
ply general cutaneous innervation overlying the
anterior edge of the opercle. Branch TH9Blc
passes to skin covering the joint between the
subopercle and the opercle, one small branch
ending in this joint. Branch TH9Bld courses
posteriorly above and somewhat parallel to the
ventral end of the opercle; another branch of
TH9Bld passes over the joint and curves pos-
teriorly along the ventral edge of the opercle for
a short distance, anastomoses with a branch of
TH9B02, and detaches several twigs which pass
down over the subopercle a short distance, in-
nervating skin. The remainder of TH9B1, after
detaching branches TH9Bla through TH9Bld,
is TH9Ble, which passes along the medial side
of the dorsal edge of the interopercle, continues
antero ventrally, and turning horizontally, passes
medial to the preopercle. About midway across
the interopercle, TH9Ble curves ventrally, con-
tinues anteroventrally across the medial surface
of the interopercle, detaching as it does at least
five branches which emerge from under skin on
the lateral surface of the interopercle below the
preopercle. These branches supply the skin of
ten scale pockets on the exposed lateral surface
of the interopercle. No free lateralis organs were
observed on any of these scales on the six whole
specimens examined. The anteriormost terminal
branch of TH9Ble anastomoses with a branch
from I02f5b (Fig. 2), a general cutaneous branch
from the r. mandibularis trigeminus.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

25

The details of these branches of TH9B differ
on the two sides of the specimen, but the same
areas are served by similar branches.

Branch TH9B0 arises at the same point as
TH9B1. It passes ventrolaterally onto the pos-
teromedial surface of the interopercle where it
bifurcates. The posteroventral fork. TH9B02,
sends a branch to the anterolateral surface of
the subopercle where it innervates skin along
the ventroanterior half of the medial surface of
the subopercle. It does not supply free lateralis
organs. Another branch of TH9B02 goes to skin
covering the articulating surfaces between the
subopercle and interopercle and to skin on the
anteromedial surface of the subopercle. Branch
TH9B03 runs anteriorly on the medial side of
the interopercle and crosses the central area of
this bone, where it is joined by a branch from
TH9C of the ramus hyoideus (Fig. 13). The com-
bined nerve shortly bifurcates: fork TH9B04
continues towards the ventral edge of the inter-
opercle, supplying skin medially in this region.
It continues anteriorly near the ventral edge of
the preopercle and into skin on the ventromedial
surface of the posterior end of the lower jaw at
the junction of the interopercle, angular, and
articular bones. The other fork. TH9B05, runs
ventrally close to the ventral edge of the inter-
opercle, turns anteriorly and dorsally, and
courses beyond the interopercle onto the fold of
skin connecting the ventral edge of the lower
jaw and the protractor hyoidei muscles, which
form, in part, the floor of the mouth. The branch
innervates this skin and sends a branch towards
the angulo-interopercular joint.

Branches TH9B1 and TH9B0 apparently
should be assigned to the general cutaneous
component. The medial side of the interopercle
is supplied mainly by branch TH9B03, whereas
the lateral side of the interopercle is supplied
mostly by TH9B13.

Branch TH9C (Figs. 13 and 2), which leaves
the ramus hyoideus (TH9) beyond TH9B, in-
nervates the portion of the hyoidei adductores
muscle connecting the sixth branchiostegal ray
to the opercle (Fig. 13). Immediately after aris-
ing, TH9C detaches a thin branch, TH9C1 (Fig.
13), which passes to the medial side of the in-
teropercle, where in part it anastomoses with a
branch of TH9B0 and then continues as a small
nerve which runs forward to the articulating
head of the sixth branchiostegal ray and then

along this ray innervating apparently muscle and
skin in this area. The rest of TH9C supplies the
dorsalmost portion of the hyoidei adductores
muscle, as already mentioned. A few branches
of TH9C cross onto the medial side of the sixth
ray and into the muscle spanning the sixth and
fifth rays. A few twigs innervate the branchio-
stegal membrane spanning the distal ends of the
fifth and fourth rays.

The remainder of the ramus hyoideus (Figs.
2 and 13) continues anteriorly along the ventral
edge of the epihyal and across the medial side
of the sixth branchiostegal ray, giving off en
route a very thin, long nerve (not shown) which
runs posteriorly in the first (dorsalmost) segment
of the hyoidei adductores muscle. The tissue
was broken in this region, but the nerve appar-
ently rejoins the main branch of TH9C. As the
ramus hyoideus crosses the sixth ray, another
nerve. TH9D (Fig. 13), is given off which passes
posteriorly across the sixth, fifth, and fourth
rays, decreasing in size as it supplies the muscle
and skin connecting these rays. As it crosses the
fourth branchiostegal ray (counting the anterior-
most ray first), the ramus hyoideus divides into
TH9E and TH9F. Branch TH9E passes around
the anterior edge of the third branchiostegal ray
and into the posterior end of the protractor
hyoidei (geniohyoideus) muscle, which it inner-
vates, and then anastomoses with the posterior
end of branch I02g2 of the ramus mandibularis
trigeminus supplying the major part of the pro-
tractor hyoidei muscle. A branch (not illustrat-
ed) of TH9 in the protractor hyoidei area runs
back to the bases of the branchiostegals and ap-
pears to innervate the tendons and muscle fibers
of the hyohyoidei abductores (H AB: Fig. 25).
Branch TH9f supplies the anteriormost segment
of the hyoidei abductores (H AB) and the muscle
and skin connecting the first and second rays.
Small twigs are detached from TH9 as it crosses
the fifth to second rays, which innervate the
muscle slips of the hyoidei adductores that ori-
ginate on the ventral edge of the ceratohyal.

Ramus mandibularis facialis

The truncus hyomandibularis (Figs. 2 and 13).
after detaching TH8 and the ramus hyoideus
(TH9), is referred to at this point as the ramus
mandibularis facialis. It courses away from the
side of the preopercular canal and towards the
point where the interhyal articulates with the

26

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

symplectic, passing a little anterior to that point.
Shortly it detaches TH10, the ramus buccalis
accessorius facialis.

Ramus buccalis accessorius facialis

The ramus buccalis accessorius (Fig. 2, TH 10)
rises through the adductor mandibulae muscle
to the skin, where it bifurcates; one fork,
(TH10A; Fig. 2), turns dorsally and courses be-
neath skin up to the second suborbital bone
where, near the posterior end of this bone,
TH10A innervates a series of free lateralis or-
gans that continues posteriorly near the ventral
edge of the third suborbital (Figs. 2 and 17). The
other fork, TH10B, runs ventroanteriorly, par-
alleling the preopercular canal, and shortly gives
off branch TH10B1, a fairly large nerve which
passes anterodorsally a short distance and divides
into a dorsal and a ventral branch which together
course vertically supplying a series of free lat-
eralis organs in the skin of two large scale pock-
ets. A third scale pocket in the series is supplied
by TH10B2, which arises more ventrally from
TH10B. The free lateralis organs on these three
scales form a vertical row (PCL; Fig. 17). During
its course down the preopercle, TH10B has a
small connection with the r. mandibulars faci-
alis, crosses the anterior arm of the preopercular
canal, and detaches TH10B3 and TH10B4.
Branch TH10B4 innervates free lateralis organs
in the membrane over the pore of the anterior
end of the preopercular canal, and branch
TH10B3 innervates a cluster of free lateralis or-
gans at the second preopercular canal pore.
Branch TH10, therefore, supplies apparently
only free lateralis organs. These free lateralis
organs include those around the second pore of
the preopercular canal plus a vertical row of
about 20 organs extending dorsally up the cheek
area (Fig. 2) and some free lateralis organs ad-
jacent to the junction of the second and third
suborbital bones. Branch TH10 should be
termed the ramus buccalis accessorius. It may
be a remnant of the ramus canalis lateralis sys-
tem (Freihofer 1972). A similar nerve is present
in other percoids.

Ramus mandibularis externus facialis and ra-
mus mandibularis interims facialis

After giving off TH10, the rest of the ramus
mandibularis facialis passes directly anterior to
the proximal end of the interhyal, at which point
it detaches TH11 (Fig. 2), which innervates the

fourth canal organ of the preopercle (counting
from anteriorly), the ninth organ of the mandib-
ulo-preopercular canal. The r. mandibularis fa-
cialis next crosses the medial surface of the
proximal end of the symplectic and divides into
two parts, the r. mandibularis internus facialis
and the r. mandibularis externus facialis, the in-
ternus portion continuing anteroventrally di-
rectly in front of the symplectic and the externus
portion passing down the posterior side of the
symplectic. The r. mandibularis internus ap-
proaches the externus beyond the distal end of
the symplectic bone, the two rejoining on the
medial surface of the articular head of the quad-
rate. Halfway down the quadrate, the r. man-
dibularis internus sends a long, thin nerve,
TH12a, dorsally up the inner wall of the mouth
to the mucosa covering the anterior end of the
adductor arcus palatini, where the nerve could
not be followed. It presumably innervates taste
buds, communis fibers being the main, if not
sole, component in the r. mandibularis internus.
Further along its course, not far from where it
rejoins the r. mandibularis externus, two more
thin branches leave the r. mandibularis internus
(TH12). One branch (TH12b, not illustrated) is
soon joined by another twig also detached from
TH12. Branch TH12b passes anteriorly on the
medial surface of the quadrate to near the an-
terior edge of this bone and then turns dorsally
onto the pterygoid bone and passes among the
small patch of pterygoid teeth, where it appears
to anastomose with a branch of the palatine
nerve. Branch TH12c (not illustrated), which
arises at the same point as TH12b, passes ven-
trally and then laterally around the posterior end
of the angular and the articular bones anas-
tomoses with the posterior end of I02f
(branch I02f5d). Branches very similar to
TH12a and TH12B were observed on Sihler
preparations of several other percoid fishes. On
the opposite side of the specimen, a branch cor-
responding to TH12a detaches more proximally
along the r. mandibularis internus (TH12) and
goes to the same area of skin in the roof of the
mouth.

Some distance beyond the detachment of
TH10, branch TH13 leaves the r. mandibularis
facialis at the point of its division into the inter-
nal and external facial rami and passes towards
the preopercular canal and bifurcates at the edge
of the canal (Fig. 2); TH13a sends off one branch
which ends in the external skin near the fourth

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

27

pore of the preopercular canal; another branch
passes under the canal and divides, one fork
ends in skin at the anterior and posterior sides
of the fourth pore of the canal. The other fork,
TH13b, courses a short distance anteriorly along
the dorsal edge of the horizontal arm of the pre-
opercular canal and sends a branch laterally un-
der the canal. This branch also splits into two
branches under the canal, one branch innervat-
ing skin at the anterior side of the third pore of
the canal, the other innervating skin of the pos-
terior side of this same pore. No free lateralis
organs were observed on preserved specimens
in the vicinity of the third and fourth pores of
the preopercular canal, yet branch TH13b
should be suspected of carrying lateralis fibers
since the r. mandibularis facialis externus car-
ries mainly or only this component. The anterior
of the two branches to the third pore sends a
branch to skin at the posterior side of the second
pore of the preopercular canal. There are free
lateralis organs at this pore. TH13 also sends a
branch into skin dorsal to the canal. The small
remaining part of TH13 anastomoses with TH10.
The next two branches, TH14 and TH15, in
succession supply sensory canal organs eight
and seven of the mandibulo-preopercular canal
located between canal pores four and three and
canal pores three and two, respectively. A little
before the lateralis branch to the first preoper-
cular sensory canal organ arises, a fairly large
nerve, TH16, comes off the r. mandibularis ex-
ternus facialis. TH16 rises to the skin, passes
anteroventrally beneath the skin parallel to the
posterior edge of the quadrate, and courses
around the anterior edge of the articular head of
the quadrate, where it anastomoses with I02f of
the ramus mandibularis trigeminus (102). The
further course of TH16 is described as a part of
I02f. TH16 appears to constitute part of I02f5
and apparently carries lateralis fibers, judging
from all the other branches of TH10 (the r. buc-
calis accessorius). Branch I02f of the r. man-
dibularis trigeminus carries only general cuta-
neous fibers. The last branch of the r.
mandibularis facialis before it is joined by TH12,
the r. mandibularis facialis internus, is TH17. a
lateralis branch to the first sensory canal organ
of the preopercle (Fig. 2). After detaching TH 17,
the ramus mandibularis externus facialis contin-
ues its anteroventral course, running along the
posterior edge of the quadrate bone directly be-
neath the mucosal lining of the mouth and di-

rectly dorsal to the preopercular canal. The ra-
mus mandibularis externus passes over the
articular head of the quadrate bone and receives
the ramus mandibularis internus (TH12) as it
does so. Once again referred to as the r. man-
dibularis facialis, the compound nerve passes
onto the medial surface of the articular bone;
then keeping between the mandibular canal and
Meckel's cartilage, the ramus runs beneath mu-
cosa for about two-thirds of the way towards the
symphysis of the lower jaw, giving off several
branches en route (Fig. 10). The first branch,
TH17a, innervates the only sensory canal organ
of the articular. The r. mandibularis facialis then
passes between tendons TA2 and TA, which in-
sert the adductor mandibulae muscles on the
articular bone (Fig. 24). About halfway between
the third and fourth pores of the sensory canal
of the dentary, branch TH18 (Fig. 10) passes to
the fourth lateralis canal organ of the dentary.
A short distance further, the r. mandibularis fa-
cialis receives a large nerve, the ramulus man-
dibularis externus trigeminus (I02g). from the
ramus mandibularis trigeminus (102). Branch
I02g, carrying visceral motor and general cu-
taneous fibers, courses for some distance with
the ramus mandibularis facialis, carrying later-
alis and communis fibers, and then a number of
branches arise carrying various combinations of
these functional components to the anterior end
of the lower jaw (Fig. 10). Just before branch
TH20 leaves the compound r. mandibularis fa-
cialis and I02g, a small nerve, TH18a, appar-
ently carrying communis fibers, passes dorsally
beneath skin of the medial side of the dentary
up towards the posterior extension of the alveo-
lar process, where it innervates mucosa in this
region. Branch TH20 enters the mandibular ca-
nal and innervates the third lateralis organ of the
dentary. Before innervating this canal organ,
three nerves to the external surface of the den-
tary arise from TH20 (Figs. 8-10). The first of
these, TH20a (Fig. 8), passes posterolateral^
around the canal, emerges medial to the canal
and runs posteriorly beneath skin on the ventral
surface of the dentary. It is probably mostly, if
not completely, general cutaneous and not lat-
eralis in function. Branch TH20b curves antero-
lateral^ around the dentary canal and runs an-
teriorly and then posteriorly for some distance
under skin on the external surface of the den-
tary, medial to the canal. It also is apparently a
general cutaneous branch. The third branch.

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

TH20c, runs anteriorly on the external surface
of the dentary canal almost up to the third pore
of the dentary, where it bifurcates; the medial
fork passes around the canal and sends one
branch anteriorly and another posteriorly. The
anterior of these two branches could not be fol-
lowed, but the posterior one emerges in skin on
the ventral surface of the dentary and runs back
medial to the canal. The lateral fork likewise
runs posteriorly beneath skin but lateral to the
sensory canal. All these branches coming off of
TH20 appear to belong to the general cutaneous
system. Apparently no free lateralis organs oc-
cur in the skin over the dentary canal where
these branches terminate.

At the point of origin of TH20, the rest of the
compound r. mandibularis facialis plus I02g di-
vides into two main branches, TH19 and TH21
(Fig. 10). Branch TH19 apparently carries com-
munis fibers from the r. mand. internus facialis
that supply the taste buds on the lower lip, labial
cartilage, and gum area of the teeth as well as
other branches to the floor of the anterior end
of the mouth. Its branches are described after
those of TH21.

Branch TH21 (Fig. 10) contains the visceral
motor and general cutaneous fibers carried by
I02g from the r. mandibularis trigeminus as well
as lateralis fibers from the r. mandibularis ex-
ternus facialis for the large patch of free lateralis
organs near the tip of the lower jaw. It probably
carries few or no communis fibers. A number of
branches, TH22 to TH25, arise from TH21.
Branch TH22, containing mainly the lateralis
portion and some general cutaneous fibers of
TH21. continues forward along the medial side
of the lateral line canal of the dentary and de-
taches TH22a to the second canal neuromast of
the dentary not far from the symphysis of the
lower jaw (Figs. 8-10). The remainder of TH22,
after detaching TH22a, continues anteriorly in
skin over the ventral surface of the mandibular
canal. Halfway towards the second pore of this
canal, the remainder of TH22 bifurcates (neither
fork illustrated), one fork passing laterally and
one medially around the canal, both emerging
on the ventral surface of the dentary. The medial
fork innervates skin medial to the second pore
of the canal. The lateral fork sends a branch
anteriorly and one posteriorly, innervating skin
lateral to the canal.

Branch TH23, the next most medial branch
arising from TH21, courses some distance an-

teriorly in mucosa covering the dorsal surface
of the dentary, penetrates the bone, enters the
dentary canal, and innervates the first canal neu-
romast of the dentary. Branch TH24 passes an-
teriorly until it reaches the medial edge of the
dentary, where it detaches two thin branches,
one of which, TH24a (Figs. 8 and 9), passes up
the inner side of the dentary and innervates skin
near the dorsal edge of the first pore at the an-
terior end of the mandibular canal. The other
thin branch (TH24b: Fig. 9) passes up the ex-
ternal surface of the dentary medial to the an-
terior end of the canal and innervates skin at the
first canal pore. Branch TH24b passes between
the medial edge of the dentary and the anterior
tendons of the protractor hyoidei (geniohyoid-
eus) muscles, reaching skin on the external sur-
face of the dentary near the symphysis of the
lower jaw below the intermandibularis muscle,
where it curves toward the midventral line de-
taching small branches to skin between the an-
terior ends of the rami of the lower jaw. It then
turns posteriorly in skin over the medial edge of
the protractor hyoidei and innervates skin. The
branches of TH24 going to skin over the anterior
end of the dentary canal may be innervating
some free lateralis organs. More likely, all the
numerous free lateralis organs on the chin be-
tween the two dentary rami are supplied by
TH25, but this point could not be definitely de-
termined.

Branch TH25, the next most medial of the
branches arising from TH21, passes anterome-
dially and continues between the dentary bone
and protractor hyoidei muscle of its side,
emerges beneath the skin medial to the anterior
tendon of this muscle, and ends in branches
which appear to innervate numerous free later-
alis organs in this area (Figs. 9 and 17). Branch
I02g2, which corresponds to branch I02g from
the r. mandibularis trigeminus, innervates the
intermandibularis and protractor hyoidei mus-
cles and overlying skin. It has already been de-
scribed under the branches of the r. mandibu-
laris trigeminus.

Branch TH19 of the r. mandibularis facialis
remains to be described (Figs. 8 and 10). It prob-
ably contains cutaneous fibers of branch I02g
of the r. mandibularis trigeminus, but apparently
most of the branches of TH19 are of the com-
munis component for taste buds on the lips and
the inside of the anterior end of the lower jaw.
On Sihler preparations these communis fibers

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKll

29

could be seen to derive from branches of the r.
mandibular is facialis internus. Branch TH19
(Fig. 8) continues anteriorly on the ventral sur-
face of Meckel's cartilage some distance and
divides into branches TH19a and TH19b.
Branch TH19a is shortly joined by branch I02h
containing apparently general cutaneous fibers
from the r. mandibulars trigeminus (102). The
two branches course together to the inner edge
of the alveolar region of the dentary, where they
divide. An anterior branch, TH19a4, enters the
dentary beneath the inner rows of teeth and
courses anteriorly towards the symphysis of the
lower jaw, supplying teeth and tissue surround-
ing the teeth. Two posterior branches, TH19a2
and TH19a3 (Fig. 8), course along the inner edge
of the alveolar region, branch TH19a2 in bone
under the teeth and TH19a3 next to the alveolar
region but in mucosa. The latter nerve breaks
up into several parallel nerves, one of which, a
little posterior to the teeth, drops a little ven-
trally and innervates an area of the mucosal lin-
ing of the inside of the lower jaw. A thin nerve,
TH19al (Fig. 8), detaches from TH19a and
courses forward to an area a little posterior and
lateral to the symphysis, where it ends in mu-
cosa that may contain taste buds. Shortly before
it breaks up, TH19al is joined by part of a long
anterior branch, TH 19b 1 (Fig. 8). Branch TH 19b
departs from TH19a, continues anteriorly me-
dial to Meckel's cartilage, and divides into
TH19bl and TH19b2. TH19bl passes anteriorly
up to the posterior edge of the intermandibularis
muscle where it curves medially and connects
to I02j and TH19al by a short branch to each
one. The rest of TH19bl continues medially into
the bone of the alveolar region adjacent to the
symphysis and could not be followed. TH19b2
curves medially and detaches TH19b3, a thin,
long nerve that arches across the tendon of the
protractor hyoidei muscle and runs close to the
lateral side of the posterior end of the tendon of
the opposite side, where it could not be followed
further. A similar nerve from the opposite side
comes to lie near it. These branches are appar-
ently carrying communis fibers to the floor of
the anterior end of the buccal cavity. After de-
taching TH19b3, the remainder of TH19b2
passes posteriorly as TH19b4 and innervates the
mucosa of the buccal cavity. About halfway
along its length TH19bl detaches TH19bla that
curves posterolateral^ in the oral membrane of
the dentary giving off many fine branches to it.

Ramus Lateralis Accessorius

The ramus lateralis accessorius (RLA), also
referred to as the ramus recurrens facialis or
simply the recurrent facial nerve, has been de-
scribed in detail for Polycentrus and some other
percoids in another paper (Freihofer 1963). Only
a summary of its course is given here. The name
ramus lateralis accessorius is used in the present
paper. The nerve itself has nothing to do with
the lateral line innervation. It innervates taste
and terminal buds, both of which apparently are
basically the same kind of sense organ, the latter
being located on the external body surface (Her-
rick 1899). The nerve fibers of RLA belong to
the communis system of nerve components.

The ramus lateralis accessorius in Polycentrus
consists of two main branches, an orbito-pec-
toral branch (RLA-OP) that courses to the pec-
toral, pelvic, and anal fins, and a parieto-dorsal
branch (RLA-PD) that courses to the dorsal fin,
with some fibers apparently reaching the caudal
fin. Both these branches arise intracranially
from the geniculate ganglion (Fig. 31).

The orbito-pectoral branch (RLA-OP)

The orbito-pectoral branch of RLA arises
from a sizeable bundle of fibers leaving the an-
terior end of the geniculate ganglion anterior to
the facial foramen. The bundle passes through
the trigeminal foramen and into and through the
extracranial trigemino-facialis complex (Frei-
hofer 1963: figs. 1-4), and then dorsolateral^
over the posterior wall of the orbital cavity up
to and through the sphenotic bone from which
it emerges to lie underneath the last infraorbital
bone. RLA-OP courses the overall distance in
close proximity or contiguous with the ramus
oticus. From under the last infraorbital bone, it
passes alongside the anterior end of the pterotic
canal as far posteriorly as its midlength, where
it passes diagonally under this canal over to its
medial side and then rises to the overlying skin,
at which point it turns posteriorly and pursues
a shallow course beneath the skin, continuing
either under the ventral end of the supratem-
poral canal or between this canal and the pos-
terior end of the pterotic canal, then past the
dorsal rami of the ramus supratemporalis vagi
and the main branches of the nervus linae lat-
eralis and onto the medial side of the supra-
cleithrum. Crossing this bone, it drops sharply,
ventrally down the medial side of the cleithrum
onto the first postcleithrum, then alongside the

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

posterior edge of the second postcleithrum, and
continues more or less diagonally under skin to
near the midventral line, reaching it just poste-
rior to the anus. From this point posteriorly, it
courses next to the bases of the anal spines, ap-
parently supplying communis fibers to each
branch of a segmental ventral spinal ramus that
enters an anal spine or ray.

In its course past the pectoral fin, RLA-OP
detaches branches which innervate the pectoral
fin (for details see Freihofer 1963). A branch is
detached to the pelvic fin as RLA-OP passes this
fin.

The parieto-dorsal branch (RLA-PD)

The parieto-dorsal branch of the ramus later-
alis accessorius arises by two roots from the
large geniculate ganglion which separately pass
dorsally around the overlying dorsal lateralis
root of the facial nerve and join above it (Fig.
31). RLA-PD passes laterally over to the inside
of the cranial wall, encounters the radix profun-
dus and its ganglion, or nearly does, and then
rises to the cranial roof beneath the parietal
bone, where it is met by the intracranial dorsal
vagal ramus, which was identified on serial sec-
tions as belonging to the rami cutanei dorsales
vagi. This vagal ramus did not actually contact
RLA-PD in two Sihler preparations examined
but was seen to remain separate from it and to
pass anteriorly a short distance to innervate
skin. It was sometimes observed on Sihler nerve
preparations of several kinds of fishes not to
join with RLA-PD nor course with the latter
nerve. It seems unlikely that this vagal ramus
carries communis fibers as maintained by Her-
rick (1899).

After passing through the parietal bone, RLA-
PD continues laterally across the parietal ridge
and to the overlying skin and then posteriorly
towards the middorsal line and the dorsal fin. It
has similar relations to branches of the dorsal
spinal rami innervating the fin spines, rays, and
membrane that RLA-OP does for the anal fin.
None of the branches of the ramus supratem-
poralis vagi fuse with RLA-PD as Herrick ( 1899)
found in the atherinid Menidia.

It could not be determined by the methods
used in this study whether or not any taste buds
were innervated by the two main branches of
RLA between their cranial exit and the fins or
whether there are taste buds in these areas.

Innervation of the Gill Arches
There are four filament-bearing gill arches in
Polycentrus (Fig. 18, CB1-CB4) and a fifth gill
arch which bears no gill filaments and has only
one bone supporting it, the fifth ceratobranchial
(Fig. 18, CB5). Each of the first four arches has
two vertical rows, a medial and a lateral, of gill
filaments and a lateral and medial row of gill
rakers (Fig. 20, LGR, MGR).

Two pairs of cranial nerves, the glossopha-
ryngeus (IX) and the vagus (X), innervate the
five arches and their associated muscles (Fig.
19).

The second or third gill arch exhibits the more
complete pattern of branching of a branchial
nerve trunk to its gill arch. Typically a branchial
nerve trunk divides into two rami, a pretrematic
and a posttrematic. The pretrematic ramus of a
branchial nerve trunk passes down its gill arch
anterior to its gill slit; the posttrematic ramus
passes down the succeeding gill arch lying pos-
terior to the same gill slit. For the third gill arch,
its pretrematic branchial ramus (Fig. 19, V2PR)
innervates the area of the medial row of gill fil-
aments, and its posttrematic ramus (Fig. 19,
V2PO) innervates the lateral row of gill filaments
of the next posterior gill arch. The glossopha-
ryngeus nerve innervating the first gill arch has
a posttrematic ramus (Fig. 19, GLR) passing
down the first arch, but the pretrematic ramus
(G2) for the glossopharyngeal nerve courses an-
teriorly onto the palate, where it joins the pos-
terior ramus palatinus. The medial side of the
first gill arch and the whole second, third, and
fourth gill arches are innervated by vagal bran-
chial trunks one, two, and three, each of which
has a pretrematic and posttrematic ramus (see
symbols for each arch. Fig. 19). After passing
onto a gill arch, posttrematic rami 2, 3, and 4
each gives off a small nerve (shown diagram-
matically large in Fig. 19) that passes down the
anterior face of a ceratobranchial bone, coursing
between the lateral and medial rows of gill rak-
ers, innervating these rakers and the mucous
epithelium between them. It is referred to as the
gill raker ramus (G6, V1B, V2F). It apparently
does not innervate gill filaments. The pretrem-
atic ramus of each branchial arch nerve trunk
also has a pharyngeal ramus. Other branches of
the pretrematic or posttrematic rami innervate
the various gill arch muscles and mucous epi-
thelium on the floor of the gill arches. In Poly-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

31

centrus one gill arch muscle, the protractalis
pectoralis, is innervated by a branch that comes
from the ramus supratemporalis vagi (Fig. 19,
PRPE). Branches to the muscles of the gill arch-
es and gill filaments detach from the posttrem-
atic, not from the pretrematic rami.

Nervus Glossopharyngeus

The glossopharyngeal, or ninth pair of cranial
nerves, arises by a single root on each side a
little below the midlateral extent of the medulla
and courses posteroventrally a rather short dis-
tance to its cranial exit in the exoccipital bone
at the posterodorsal end of the swelling of the
otic bulla (Figs. 26, 29). The glossopharyngeal
foramen lies directly in front of the vagal fora-
men but separated fiom the latter. Shortly be-
yond its cranial exit, the glossopharyngeus is
joined on its ventral surface by the sympathetic
trunk. The two course closely bound together an-
teriorly three-quarters of the way across the otic
bulla at which point the petrosal ganglion forms
on the glossopharyngeus. A little before or after
the petrosal ganglion, some ganglion cells form
in what must be the sympathetic part of the com-
pound nerve. The two nerves then separate, the
glossopharyngeus continuing anteriorly. At the
anterior end of the otic bulla it detaches branch
Gl (Fig. 19), which passes anterolaterally and
innervates the levator internus II branchial mus-
cle (Fig. 18, LI2). On some Sihler nerve prepa-
rations, the glossopharyngeus itself passes
through this muscle as it innervates it. The glos-
sopharyngeus next detaches branch G2, the ra-
mus pretrematicus IX, which passes anteriorly
and then medially. Upon reaching the proximal
head of the first, or suspensory infrapharyngo-
branchial bone, G2 meets the posterior palatine
ramus (PPR, Fig. 19; TH 1 . Fig. 4) from the trun-
cus hyomandibularis. These two nerves join
forming Jacobson's anastomosis, then course
anteriorly past the pseudobranch and innervate
skin over the posterior end of the palate in the
vicinity of the pseudobranch, which is a highly
vascularized saclike structure in Polycentrus.

The glossopharyngeus, in turning laterally,
crosses the anterolateral surface of the levator
internus II (LI2; Fig. 18) and passes around the
medial and anteroventral surface of the levator
externus I (LEI) branchial muscle which it in-
nervates by branch G3 (Fig. 19). The glossopha-
ryngeus (IX; Fig. 19) continues onto the dorsal

surface of the first epibranchial bone (EP1; Fig.
18) and laterally along this bone, lying under the
bases of a lateral row of gill filaments, this part
of the glossopharyngeus being the posttrematic
branchial ramus (GLR) of the first gill slit. It
continues ventrally onto the ceratobranchial
along its posterolateral side under the lateral row
of gill filaments. Halfway down the first cera-
tobranchial, the posttrematic ramus (GLR) de-
taches a small gill raker branch that passes an-
teriorly a short distance and which, upon
reaching the anterior face of the first gill arch,
is joined by a similar gill raker branch (not la-
beled on Fig. 19) from the pretrematic first vagal
branch (not labeled) from the pretrematic first
vagal branchial ramus (VI PR). The joined
branches (G6; Figs. 19, 20) pass ventrally be-
tween the lateral and medial rows of gill rakers
innervating them. As the posttrematic ramus of
the glossopharyngeus (GLR; Fig. 19) proceeds
down the posterolateral side of the ceratobran-
chial along the bases of the lateral row of gill
filaments, a series of very small branches are
sequentially detached, each of which passes
posteriorly and join together forming a vertical
branch, G5 (Fig. 20). Branch G5 weaves in and
out between the gill filaments, apparently sup-
plying the muscles of the filaments.

The posttrematic of the glossopharyngeus
(GLR) detaches branch G7 (Fig. 19) near the
ventral end of the first ceratobranchial: G7 in-
nervates the obliquus ventralis I (OV1) muscle
(Fig. 18). The remainder of the posttrematic
(GLR, Fig. 19), continues down the lateral face
of the first hypobranchial bone and ventrally
around its anterior end and up medially and an-
teriorly to the side of the basihyal bone, along
which it courses anteriorly innervating mucosa
at the side of the tongue lateral to the basihyal.
En route past the first hypobranchial, the glos-
sopharyngeus detaches branch G8 (Fig. 19) for
the rectus ventralis I muscle (RV1, Fig. 18). A
branch is given off for the mucosa on the floor
of the mouth dorsal to the first basibranchial and
dorsal hypohyal. The last branch given off runs
posterolaterally on the dorsal surface of the dor-
sal hypohyal towards the first ceratohyal.

Nervus Vagus

The functional components of the nervus va-
gus, or tenth pair of cranial nerves are (1) vis-
ceromotor and communis fibers contained in the

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES. NO. 128

pharyngobranchial and intestinal rami: (2) gen-
eral cutaneous and possibly communis fibers in
the rami cutanei dorsales vagi: general cuta-
neous fibers in the opercular ramus: lateralis and
general cutaneous fibers in the supratemporal
ramus: and (3) visceromotor fibers in the cardiac
ramus. The intestinal and cardiac rami are not
considered further. The lateral line nerve of the
trunk of the body is considered separately from
the vagus. Herrick (1899) found the general cu-
taneous component to be very small in the vagus
of the atherinid Menidia, but he found the motor
component to be of considerable size, with the
communis component by far the largest. Similar
relative developments exist in the percoid Poly-
centrus. The cell bodies for the general cuta-
neous component are located in the jugular gan-
glion of the vagal nerve: neither this ganglion
nor its root was distinguishable from the rest of
the ganglion and common root of the vagal nerve
in Polycentrus .

According to Herrick (1899). fibers of the
communis system are of two kinds: fibers that
innervate taste buds and fibers that innervate
general visceral and mucous surfaces by the
simplest free nerve endings. The latter would be
comparable to the general cutaneous fibers of
external body surfaces.

The root of the vagus arises from the midlat-
eral side of the medulla by four rootlets on dis-
sected specimens, but these appear very close
together on serially sectioned specimens and are
not distinguishable. The vagal root passes a
short distance posteroventrally to its foramen in
the exoccipital bone, the foramen for the glos-
sopharyngeal nerve lying a short distance ante-
rior to that for the vagus (Figs. 4, 25. 28-30).
Intracranially the nervus vagus is separate from
the nervus linae lateralis (NLL). The two nerves
pass through the same foramen together, the
nervus linae lateralis a little anterior and medial
to the nervus vagus.

Intracranial dorsal vagal ramus

Two-thirds along its intracranial course, the
nervus vagus detaches a fairly large ramus. This
vagal ramus may be equivalent in part to the
rami cutanei dorsales vagi of Menidia, which
rami Herrick (1899) found to arise from the jug-
ular ganglion outside the cranium, not inside as
in Polycentrus . Part of the rami cutanei dorsales
vagi of Polycentrus does pass out the cranium
as in Menidia through the vagal foramen.

The intracranial vagal ramus in Polycentrus
passes dorsally a short distance from the root of
the nervus vagus and detaches a branch about
one-third its own size, the extracranial vagal ra-
mus, which passes towards the vagal foramen
in the exoccipital bone where the extracranial
vagal ramus forms a ganglion just before reach-
ing the foramen. This ganglion is the jugular gan-
glion of the vagal nerve, the ganglion for general
cutaneous sensory neurons. The extracranial
vagal ramus (the rami cutanei dorsales vagi, in
part) passes through the dorsolateral corner of
the vagal foramen between the nervus linae lat-
eralis and the slightly posterior root of the ner-
vus vagus. The extracranial vagal ramus was
traced on serial sections almost up to three size-
able fiber bundles lying lateral to the nervus lin-
ae lateralis as this nerve leaves the cranium. The
extracranial vagal ramus could not be traced be-
yond this point. The extracranial vagal ramus
evidently joins with the three groups of fibers
which are evidently lateralis, and together form
the ramus supratemporalis vagi. More ganglion
cells form in the supratemporal ramus as it
moves laterodorsally and anteriorly away from
the nervus linae lateralis. The further course of
the ramus supratemporalis vagi is described af-
ter the intracranial vagal ramus.

One of the three fiber bundles forming the ra-
mus supratemporalis vagi, or part of one of these
bundles, must be of motor fibers for the pro-
tractalis pectoralis muscle. Another of the bun-
dles is of lateralis fibers for the posttemporal and
supratemporal canals. The fiber bundle from the
intracranial vagal ramus must be carrying gen-
eral cutaneous fibers and possibly communis fi-
bers for taste buds, but the methods used in the
present study did not permit definite determi-
nation of the presence or absence of communis
fibers in any of these rami.

Shortly after the intracranial dorsal vagal ra-
mus detaches the extracranial ramus that evi-
dently joins the ramus supratemporalis vagi, the
intracranial division forms a sizeable ganglion.
The ramus then rises dorsoanteriorly and me-
dially in the cranial cavity up to the parietal
bone, through which it passes close to the exit
of the ramus lateralis accessorius (RLA-PD) but
medial to RLA and about on the same transverse
plane with it. Before reaching the parietal, the
intracranial dorsal vagal ramus bifurcates. Both
branches exit through the parietal, pass trans-
versely across the parietal ridge, and innervate

FREIHOFER: CRANIAL NERVES OF POLYCESTRUS SCHOMBURGKU

33

skin on the side of the head dorsal to this ridge.
The intracranial vagal ramus exiting through the
parietal is missing in Menidia (Herrick 1899). It
is absent in the atherinid Atherinops affinis
(Freihofer 1963).

It seems most probable that this intracranial
vagal ramus is not carrying communis innerva-
tion for taste buds, since RLA which does carry
such innervation passes through or close to the
area on top of the head served by the intracranial
vagal ramus. Nor would it likely be carrying lat-
eralis fibers, since the r. supratemporalis vagi,
which carries lateralis fibers, innervates the ad-
jacent area posteriorly, and SORB2 of the su-
praorbital trunk, also carrying lateralis fibers,
innervates the adjacent area anteriorly. If the
foregoing statements are correct and the intra-
cranial vagal ramus carries neither lateralis nor
communis fibers to the skin, the ramus must be
carrying general cutaneous fibers.

Rami cutanei dorsales vagi

The rami cutanei dorsales vagi comprise the
general cutaneous bundles of fibers coursing
with the nervus vagus (Herrick 1899). Branch r.
supr. 2a in Polycentrus (Fig. 5) is apparently a
cutaneous dorsal branch of the supratemporal
vagal ramus and belongs to the rami cutanei dor-
sales vagi system, but it is described in Poly-
centrus under the ramus supratemporalis vagi.

The intracranial dorsal vagal ramus described
above also apparently belongs to the general cu-
taneous system of branches comprising the rami
cutanei dorsales vagi. Although described in
Polycentrus as a separate ramus, the ramus
opercularis vagi (Figs. 11-12. and 19) is appar-
ently general cutaneous in function and also be-
longs to the rami cutanei dorsales vagi.

Ramus opercularis vagi

The ramus opercularis vagi is associated prox-
imally with the ramus supratemporalis vagi (Fig.
12). In Polycentrus the ramus opercularis vagi
arises from a thin, elongate ganglion lying out-
side the cranium and beneath the nervus linae
lateralis as this nerve leaves the vagal foramen.
The cutaneous root from which the ganglion
came could not be observed as a separate entity.
Herrick (1899) assigns the r. opercularis vagi to
the rami cutanei dorsales vagi. As seen on serial
sections, the ramus opercularis vagi is a rather
independent entity, although it lies in close
proximity to the basal part of both the nervus
linae lateralis and the ramus supratemporalis

vagi (Fig. 12). The ramus opercularis vagi leaves
the side of the ramus supratemporalis vagi near
the origin of the latter from the nervus linae lat-
eralis (Fig. 12) and detaches its first branch
(PRPE: Fig. 12). which is a visceromotor nerve
innervating the nearby protractalis pectoralis
muscle lying dorsal to the fourth gill arch. This
motor branch is not considered part of. but only
associated with, the rami cutanei dorsales vagi.
The temporal branch (r. supr. 2a) of the r. su-
pratemporalis vagi may come off as part of the
ramus opercularis vagi (Fig. 5) or as a separate
branch from the ramus supratemporalis vagi,
detaching before the ramus opercularis vagi.
The ramus opercularis vagi passes dorsally
above the adductor opercularis muscle, across
the tip of this muscle, and down its lateral side
to the dorsal edge of the opercle. where it pen-
etrates the opercle a little posterior to the hy-
omandibulo-opercular articulation at about the
level of the horizontal thickening of the bone
right at the line of insertion of the adductor oper-
culi muscle. Here it divides into three branches,
r. op. 1-3 (Fig. 12). Branch r. op. 1 appears to
go to the mucosa covering the dorsoposterior
side of the posterior wall of the last gill slit.
Branch r. op. 2 passes to skin dorsal to the oper-
cle and gives off branch r. op. 2a. which comes
close to the terminations of branch TH4AA of
the truncus hyomandibularis in the area where
a large scale bears a row of free lateralis organs
(Fig. 2). These lateralis organs are innervated by
TH4AA. not by a branch of r. op. 2a. The rest
of r. op. 2a innervates skin on the dorsoposterior
lateral side of the opercle (Fig. 11). Branch r.
op. 3 innervates most of the medial surface of
the opercle down to the subopercle (Fig. 12).
where it anastomoses with dorsally coursing
branches of TH9C (from the ramus hyoideus)
that terminate in the branchiostegal membrane.
One dorsal branch of r. op. 3 passes posteriorly
and innervates the opercular membrane both
dorsal and ventral to the opercular spine.
Branch r. op. 3 is the only branch found to ex-
tend below the opercle any distance. Where it
does extend below the opercle, it enters the
branchiostegal membrane and does not appear
to course on the subopercle. The innervation to
the subopercle is, in part, by several fine branch-
es coming down from a branch of the ramus
opercularis vagi that extends horizontally along
the line of contact between the opercle and sub-
opercle (Fig. 12) and. in part, by fine branches

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

from the ramus hyoideus coming onto it at the
anterior end of the gill cover (Fig. 2).

Ramus supratemporalis vagi

The ramus supratemporalis vagi (Fig. 5) con-
sists mainly of lateralis fibers from the root of
the nervus linae lateralis and, to a small extent,
of general cutaneous fibers. Most of the cuta-
neous fibers are apparently carried in branch r.
supr. 2a (described below) and also in branch r.
supr. lb (Fig. 5). Communis rami detaching from
the r. supratemporalis vagi and from the ante-
riormost branches of the nervus linae lateralis
were observed by Herrick (1899: fig. 3; a. r.
VII. 1, 2, and 3) to join the ramus lateralis ac-
cessorius (RLA) extracranial^ on the top of the
head and nape. No such communis rami were
identifiable in Polycentrus . The components for
the r. supratemporalis vagi in Polycentrus are
apparently only lateralis and general cutaneous
(see also under section on rami cutanei dorsales
vagi). Herrick may be wrong in his interpreta-
tion of the three rami in Menidia.

As the r. supratemporalis vagi and nervus lin-
ae lateralis move away from each another, a
ganglion forms in the ventral part of the r. su-
pratemporalis vagi, and the ramus shortly di-
vides into two main branches: branch r. supr. 1,
carrying mainly lateralis fibers innervating lat-
eralis organs in the posttemporal and supratem-
poral canals, and free lateralis organs in a ver-
tical row of scales above the supratemporal
canal, but carrying also some cutaneous fibers
for skin dorsal to these canals (Fig. 5); and
branch r. supr. 2, carrying lateralis fibers to free
lateralis organs in a vertical row anterior to the
supratemporal canal (STL; Fig. 17) as well as
some cutaneous fibers to skin of the temporal
region (Fig. 5).

Branch r. supr. 1, after separating from r.
supr. 2, passes straight laterally across the base
of the cranium and swings dorsally medial to the
cranio-pectoral-girdle muscle, the levator
pectoralis, and continues dorsally medial to the
supratemporal canal, where it detaches branch
r. supr. la, which innervates the lateralis organ
in the posttemporal canal. From branch r. supr.
la, a branch passes ventrally (shown extending
horizontally in Fig. 7) below the posttemporal
canal, where it shortly breaks up in thick skin
in front of the dorsal end of the supracleithrum.
Also detached medially of the supratemporal
canal is r. supr. lb. It innervates skin located

between the anterior, epiotic arm of the post-
temporal bone and the posterior end of the su-
pratemporal. The rest of r. supr. 1 detaches r.
supr. lc and r. supr. Id, each of which inner-
vates a lateralis canal organ in the supratemporal
canal. Branch r. supr. 1 then continues in a dor-
soanterior curve towards the middorsal line, in-
nervating three scales, each of which bears a
row of free lateralis organs that together form a
continuous, almost vertical line of organs (Fig.
17).

Branch r. supr. 2a (Fig. 5) is apparently a gen-
eral cutaneous branch and belongs to the system
of branches that Herrick (1899) calls the rami
cutanei dorsales vagi. R. supr. 2a passes dor-
sally medial to the posterior end of the pterotic
canal and medial to the anteroventral end of the
supratemporal canal where it turns anteriorly,
coursing under and innervating skin on the side
of the head dorsal to the pterotic in the temporal
area of the head. The remainder of r. supr. 2
continues dorsally and detaches another branch
that courses towards the temporal area but
passes lateral to the levator pectoralis muscle
that extends from the posterolateral corner of
the cranium back to the proximal end of the op-
isthotic arm of the posttemporal bone. Branch
r. supr. 2 curves dorsoposteriorly and innervates
the long vertical row (Fig. 17, STL) of free lat-
eralis organs lying across three consecutive
scales anterior to the supratemporal canal. En
route r. supr. 2 crosses the orbito-pectoral
branch of the ramus lateralis accessorius and
runs a short distance anteriorly along RLA-OP.

First vagal branchial trunk

The first vagal branchial trunk, VI, for the
second gill arch detaches itself from the pha-
ryngo-intestinal trunk of the vagus (Fig. 19; see
symbols for each branchial trunk) shortly after
the latter leaves the cranium at the anterior end
of the head kidney. It continues anteriorly and
then anterolaterally and ventrally, passing me-
dial to the internal and external levator branchial
muscles. Medial to these muscles the first vagal
branchial trunk detaches VIA (Fig. 19), which
innervates the levator externus II muscle (LE2;
Fig. 18). Before the detachment of VIA, a gan-
glion forms on the first branchial trunk. A short
distance further, it detaches a second branch
(not shown in Fig. 19) to the levator externus II
muscle. Before passing around the second le-
vator internus branchial muscle, the first vagal

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

35

branchial trunk (VI) divides into pretrematic
(V1PR) and posttrematic (V1PO) rami. The pre-
trematic ramus (V1PR) to the first gill arch
shortly detaches a pharyngeal ramus, VIP,
which passes ventrally directly posterior to the
cartilaginous medial process of the first epibran-
chial bone and continues medially, reaching the
mucous epithelium anterior to the second infra-
pharyngobranchial bone. Continuing antero-
ventrally from near the base of the pharyngeal
ramus (VIP) is branch VIE, here referred to as
a gill raker ramus. Branch VIE passes onto the
ventral surface of the first epibranchial where it
turns posteroventrally between the two rows of
gill rakers. Branch VIE meets a second gill raker
branch from the first vagal pretrematic ramus at
the junction of the first epibranchial and cera-
tobranchial bones. The reenforced gill raker ra-
mus continues ventrally between the two rows
of gill rakers.

The remainder, and larger part, of the first
pretrematic vagal branchial ramus (V1PR),
passes onto the posteromedial side of the first
epibranchial bone at the upper end of the medial
row of gill filaments and continues ventrally un-
derneath the filaments, following them onto the
ceratobranchial. The first pretrematic ramus de-
taches the second gill raker branch (described
above) at the junction of the epibranchial and
ceratobranchial bones of the first gill arch. This
ramus passes around the ceratobranchial to its
anterior surface and continues in the mucous
epithelium between the lateral and medial rows
of gill rakers, innervating them and the epithe-
lium to its junction with a similar gill raker
branch from the posttrematic ninth nerve (GLR:
Fig. 19). The latter branch continues ventrally
to the end of the gill raker rows on the first hy-
pobranchial bone. The remainder of the first va-
gal branchial pretrematic ramus continues under
the medial row of gill filaments to its termination
on the first hypobranchial.

The posttrematic ramus (V1PO) continues on-
to the second gill arch, passing onto the pos-
terolateral surface of the second epibranchial
bone and underneath the lateral row of gill fila-
ments, and then onto the second ceratobranchial
bone where it continues underneath the postero-
lateral row of gill filaments to the end of the
second ceratobranchial. At the junction of the
second epi- and ceratobranchials, the posttrem-
atic branch (V1PO) detaches a gill raker branch
which passes around to the anterior surface of

the second ceratobranchial, down which it con-
tinues between the two rows of gill rakers to the
end of the second ceratobranchial. The last im-
portant branch of the posttrematic ramus is
branch VIC, which innervates the obliquus ven-
tralis II (OV2) branchial muscle (Fig. 18). The
posttrematic ramus (V1PO) ends after passing
between the second cerato- and hypobranchials
where it innervates mucous epithelium at the
base of the gill arch.

Second vagal branchial trunk

After giving off the first vagal branchial trunk,
the rest of the vagus, consisting of the remaining
branchial trunks and the ramus intestinalis,
passes ventrally and gives off the second vagal
branchial trunk which innervates the third gill
arch. This trunk passes laterally a short distance
and forms the second vagal branchial ganglion.
From this ganglion (Fig. 19), the pretrematic and
posttrematic rami (V2PR and V2PO) arise and
parallel each other for some distance anteriorly.
En route to the second gill arch, the second va-
gal pretrematic ramus (V2PR) detaches the pha-
ryngeal ramus, V2P, which passes medially be-
tween the second and third pharyngeal bones,
innervating the mucous epithelium and teeth.
The rest of the pharyngeal ramus (now labeled
V2E) continues as the upper gill raker ramus for
the second gill arch onto the anterior surface of
the second epibranchial and ventrally down it
between the two rows of gill rakers. It then joins
the gill raker branch (V1B) from the posttrem-
atic of the first vagal ramus and continues onto
the anterior surface of the second ceratobran-
chial, innervating the two rows of gill rakers and
the intervening mucosa. The rest of the second
pretrematic ramus (V2PR) passes onto the pos-
teromedial surface of the second epibranchial
underneath the medial row of gill filaments, in-
nervating them to the end of the second cera-
tobranchial.

Just beyond the second smaller ganglion of
the second vagal pretrematic ramus, there are
two short connections between the two main ra-
mi of the second vagal branchial ramus. At the
first of these two connections, branch V2A
leaves the posttrematic second vagal branchial
ramus (V2PO), passes laterally and innervates
the levator posterior branchial muscle (LEP).
Closely thereafter a larger branch, V2B, detach-
es from the posttrematic and passes anterolater-
ally and innervates the large levator externus IV

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

(LE4) branchial muscle. At the site of the two
cross connections, or independently of them and
from the second pretrematic branchial ramus,
branch V2C detaches and passes anteriorly be-
tween the pretrematic and posttrematic second
vagal rami. It continues parallel to the latter and
above the obliquus dorsalis III muscle (OBD3),
detaches a branch (not labeled on Fig. 19) that
innervates this muscle and another branch,
V2D, that passes anteriorly and innervates the
transversus dorsalis II (TD2) branchial muscle.

The second posttrematic vagal ramus (V2PO)
continues anteroventrally medial to the large le-
vator externus IV branchial muscle (LE4) and
dorsal to the obliquus dorsalis III muscle
(OBD3). Then it passes onto the dorsal surface
of the third epibranchial and underneath the dor-
sal end of the lateroposterior row of gill fila-
ments of the third arch and continues under-
neath the row of filaments to its end at the base
of the third ceratobranchial bone. A gill raker
branch (V2F) is detached at the joint between
the second epi- and ceratobranchials and passes
around the arch to its anterior surface where it
meets a more dorsal gill raker branch (V3E)
from the pretrematic ramus of the fourth vagal
branchial trunk. Branch V2F passes ventrally
between the two rows of gill rakers, innervating
them and intervening mucous epithelium to the
end of the third ceratobranchial.

The remainder of the posttrematic ramus
(V2PO) of the second vagal branchial trunk, af-
ter giving off branch V2F, continues down the
third ceratobranchial at its lateroposterior side
beneath the bases of the lateral gill filaments to
the end of the row. At the base of the third cer-
atobranchial, the remainder of the posttrematic
ramus gives off branches innervating four ven-
tral branchial muscles and then ends in mucous
epithelium overlying the hypobranchial and ba-
sibranchials of the third arch. The four branches
are branch V2J to the third obliquus ventralis
muscle (OV3); branch V2H to the rectus ven-
tralis IV (RV4) muscle; a large branch, V2G, to
the rectus communis (RCOM) muscle; and a
branch (not shown in Fig. 19) to the rectus ven-
tralis V (RV5) muscle.

Third vagal branchial trunk

The third vagal branchial trunk for the fourth
gill arch separates proximally from the second
vagal branchial trunk, forms a ganglion, passes

ventrally a short distance, and detaches branch
V3A which drops ventroposteriorly and inner-
vates the retractor dorsalis (RETD) muscle, en-
tering this long muscle anteriorly near its at-
tachment to the third infrapharyngobranchial
bone. Next, the third vagal branchial trunk di-
vides into the pretrematic (V3PR) and posttrem-
atic (V3PO) rami, which continue close together
anteroventrally towards the fourth epibranchial.
The pretrematic ramus (V3PR) passes medial to
the levator externus IV muscle (LE4), crosses
the dorsal surface of the fourth and third epi-
branchials, and detaches the pharyngeal ramus,
V3P. The pharyngeal ramus passes between the
two epibranchials and gives off a medial branch
which passes beneath the mucosa towards the
third pharyngeal bone, and a lateral branch,
V3E, which passes onto the anterior surface on
the third epibranchial and then down it between
the two rows of gill rakers. The remainder of
V3E joins branch V2F at the top of the third
ceratobranchial. The pretrematic ramus (V3PR)
then continues ventrally down the third epibran-
chial and ceratobranchial to the end of the latter
underneath the medial row of gill filaments.

The posttrematic ramus of the third vagal
branchial ramus (V3PO), after departing from
the pretrematic ramus, passes ventroanteriorly
and gives off a gill raker branch V3B which
courses over the proximal end of the fourth cer-
atobranchial and onto its anterior surface be-
tween the two rows of gill rakers for the anterior
third of this bone. The rest of the posttrematic
passes the joint between the fourth epi- and cer-
atobranchials, medial to the levator posterior
(LEP) muscle. It then crosses the dorsolateral
surface of the obliquus posterior muscle (OP)
and at the top of the fourth arch detaches branch
3BC which innervates the adductor IV (AA4)
branchial muscle. The postrematic then courses
down the fourth ceratobranchial underneath the
lateral row of gill filaments, near the end of this
bone detaching branch 3BD which passes me-
dially and innervates the transversus ventralis
IV (TV4) muscle. The end of the posttrematic
branch innervates the floor of the pharyngeal
cavity at the base of the fourth gill arch. En
route down the fourth ceratobranchial, the post-
trematic detaches about six short gill raker
branches, each of which innervates a series of
gill rakers and adjacent mucous epithelium on
the anterior surface.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

37

Fourth vagal branchial trunk

After departure of the first three vagal bran-
chial rami, the vagus consists of the intestinal
and cardiac rami and the fourth vagal branchial
trunk. Only the first three esophageal rami
which detach segmentally are illustrated. The
intestinal and cardiac rami were not further
studied. The ganglion for the fourth vagal bran-
chial trunk forms on the dorsolateral surface of
the third ganglion. Near the anterior end of the
esophagus, the fourth vagal trunk separates into
pretrematic and posttrematic rami, V4PR and
V4PO. respectively. The pretrematic (V4PR) ra-
mus passes anteroventrally towards the pharynx
where, at the junction of the fourth ceratobran-
chial and fourth epibranchial, it detaches a small
branch (not labeled on Fig. 19) which passes
medially under the fourth epibranchial bone, in-
nervating the dorsal extension of the medial row
of gill filaments. The rest of the fourth pretrem-
atic ramus continues ventrally about halfway
down the fourth ceratobranchial beneath the
medial row of gill rakers. Although the gill slit
behind the fourth arch is reduced to about half
size, the medial row of filaments extends some
distance further, but the innervation to it was
not detected.

The fourth vagal posttrematic ramus (V4PO)
drops ventrally towards the dorsal end of the
fifth ceratobranchial bone, passing along the
posterior surface of the obliquus posterior mus-
cle (OP), detaching a branch to this muscle (the
upper branch of V4B), and another (the lower
branch of V4B) to the adductor V (AA5) muscle.
Just past the dorsal head of the fifth ceratobran-
chial, the fourth posttrematic vagal ramus de-
taches branch V4E, which in turn divides, one
part innervating the pharyngoclavicularis inter-
nus (PCI) and the other the pharyngoclavicularis
externus muscles (PCE). Branch V4D detaches
at the same point as V4E and divides: one
branch innervates the transversus ventralis IV
muscle (TV4) and another branch (not shown)
innervates the floor of the pharynx directly pos-
terior to the fifth ceratobranchial. The remainder
(V4C) of the fourth posttrematic ramus inner-
vates the teeth and mucous epithelium of the
fifth ceratobranchial.

Summary of Gill-Arch Muscle Innervation

Glossopharyngeal nerve innervates:

(1) Levator internus II (LIZ) by branch Gl

(2) Levator externus I (LEI) by branch G3

(3) Rectus ventralis I (RV1) by branch G8

First vagal branchial ramus innervates:

(1) Levator internus III (LI3) by branch VIA

(2) Obliquus ventralis II (OV2) by branch
VIC

Second vagal branchial trunk innervates:

(1) Levator posterior (LEP) by branch V2A

(2) Levator externus IV (LE4) by branch V2B

(3) Obliquus dorsalis III (OBD3) by branch
V2C

(4) Transversus dorsalis II (TD2) by branch
V2D

(5) Obliquus ventralis III (OV3) by branch
V2J

(6) Rectus communis (RCOM) by branch
V2G

(7) Rectus ventralis V (nerve supply not
shown on Figure 19)

(8) Rectus ventralis IV (RV4) by branch V2H

Third vagal branchial trunk innervates:

( 1 ) Retractor dorsalis (RETD) by branch V3A

(2) Adductor IV (AA4) by branch 3BC

(3) Transversus ventralis IV (TV4) by branch
3BD

Fourth vagal branchial trunk innervates:

(1) Obliquus posterior (OP) by upper branch
of V4B

(2) Adductor V (AA5) by lower branch of
V4B

(3) Pharyngoclavicularis internus (PCI) by
branch V4E

(4) Pharyngoclavicularis externus (PCE) by
branch V4E

(5) Transversus ventralis V (TV5) by branch
V4D

Ramus opercularis vagi innervates:
(1) Protractalis pectoralis (PRP) by branch
PRPE

Lateral Line Nerves of the Trunk

Herrick (1899) did not consider the nervus lin-
ae lateralis to be part of the vagal nerve. He
treated it as a separate entity morphologically,
since it has a different origin in the medulla ob-
longata and is physically separate from the va-
gus nerve, although it has a connection with the
vagus by general cutaneous fiber bundles. Some
of the latter join the ramus supratemporalis vagi
from the vagus. The origin of the lateral line

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

nerve is from the acoustico-lateralis center in
the medulla near that of the auditory nerve (Her-
rick 1899).

The terminology for the trunk lateral line
nerves follows Freihofer (1972).

The lateral line of the trunk of most fishes is
usually a linear series of scales along the side of
the body, each scale having a bony tube or canal
opening laterally by a pore onto the surface. A
relatively large lateral line canal organ lies about
midway inside the tube of each scale. In Poly-
centrus there is only one tubed lateral line scale.
It is the first scale after the posttemporal canal.
Although there is virtually no scaled or mem-
branous lateral line canal on the trunk in Poly-
centrus, the lateral line nerve on the trunk is
well developed. The branches of the lateral line
nerve innervate short vertical rows of small, free
lateralis organs located on certain scales, the lat-
eralis scales forming longitudinal rows as de-
picted in Figure 21.

Nervus Linae Lateralis

The nervus linae lateralis (NLL) arises from
the brain about halfway down the side of the
medulla oblongata and a little anterior to the root
of the nervus glossopharyngeus (Figs. 28 and
30). NLL courses posteriorly, almost horizon-
tally, close to the medulla.

As NLL continues posteriorly, it comes to lie
lateral to the emerging root of the nervus vagus
at the midside of the medulla. The two roots
proceed separately lateroposteriorly to their
common foramen in the exoccipital bone at the
top of the bulge of the wall of the otic bulla, the
nervus linae lateralis lying dorsal and lateral to
the nervus vagus (Fig. 4). A few ganglion cells
form on the dorsal surface of NLL before it
passes out through its foramen. More ganglion
cells form outside the cranium in the recess be-
tween the otic wall of the bulla and the lateral
horizontal wall of the exoccipital. Then ganglion
cells form a large swelling which continues for
some distance as NLL passes posterolaterally
through the head kidney. Shortly before leaving
the head kidney, the sizeable ramus supratem-
poralis vagi is detached (Fig. 5), passing dorsally
and a little posteriorly towards the medial side
of the supratemporal canal. This ramus is de-
scribed in a preceding section.

Immediately anterior and medial to the supra-
cleithrum, the nervus linae lateralis splits into
two large rami, NLL1 and NLL2 (Fig. 21). Ra-

mus NLL2, the dorsal longitudinal "collector"
lateral line nerve, passes dorsoposteriorly me-
dial to the shoulder girdle and detaches two
branches en route. The larger of these, NLL2a,
then gives off a relatively short branch which
can be designated the dorsal fin branch. It in-
nervates the vertical row of free lateralis organs
on a scale pocket dorsal to the posterior opening
of the posttemporal canal (Figs. 17 and 21). The
rest of NLL2a curves anterodorsally and then
posteriorly, coursing to the anterior end of the
dorsal fin where it innervates free lateralis or-
gans on two scale pockets anterior to this fin
(Fig. 21). The other branch, NLL2b, innervates
the scale pocket directly posterior to the post-
temporal canal, which is the only lateral line
scale on Polycentrus .

The main part of NLL2, the dorsal longitu-
dinal collector lateral line nerve, arches dorso-
posteriorly beneath the skin to nearly halfway
to the dorsal fin, where it levels off and contin-
ues posteriorly gradually dropping ventrally to-
wards NLL1 which it finally overlies at the pos-
terior end of the soft anal fin. En route, NLL2
detaches ten long ramuli which innervate free
lateralis organs on ten individual scale pockets
along the base of the spinous dorsal fin, and two
long ramuli which similarly innervate free lat-
eralis organs on two scale pockets near the base
of the soft dorsal fin (Fig. 21). En route it also
gives off thirteen shorter ramuli, including
NLL2b, twelve of which innervate free lateralis
organs on twelve scale pockets that lie horizon-
tally along a line one-third to one-fourth of the
way towards the dorsal fin. Ten of these branch-
es occur on the anterior half of the body. The
thirteenth ramulus innervates free lateralis or-
gans on a scale pocket a little below NLL2, not
far from the caudal peduncle. The main trunk of
NLL2 terminates by splitting into two ramuli
which supply free lateralis organs on two suc-
cessive scale pockets anterior to the caudal fin.
The branches NLL1 and NLL2 do not rejoin
posteriorly.

The other ramus, NLL1, the horizontal sep-
tum lateral line nerve of the nervus linae later-
alis, continues straight to the caudal fin. En
route it detaches three commissural or collector
branches, NLLla, NLLlb, and NLLlc, which
join and form the dorsal longitudinal collector
lateral line nerve, NLL2. Branch NLLlb de-
taches a long ramulus which passes dorsally to
innervate free lateralis organs on a scale pocket

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1

39

lying directly ventral to the sixth spine of the
dorsal fin. The commissural branch NLLlc de-
taches a ramulus that passes ventrally towards
the anterior anal spines where it splits into three
branches, each innervating free lateralis organs
on a scale pocket directly dorsal to the anal
spines. The main trunk, NLL1, next gives off
two more ramuli, each innervating a scale pock-
et and its free organs near the bases of anal
spines. The penultimate ventral ramulus divides
near the anal fin and innervates the free lateralis
organs on three more scale pockets along the
base of the fin. Lastly, a ramulus is detached
which in turn divides into three more branches
which supply free lateralis organs on three scale
pockets along the base of the soft anal fin.

The remainder of NLL1 courses posteriorly
and bifurcates near the base of the caudal fin.
The dorsal fork runs along the bases of the rays
of the dorsal half of the fin and detaches a large
ramulus which continues in the membrane be-
tween the fifth and sixth caudal rays, innervating
a long row of about 24 free lateralis organs. The
rest of the dorsal fork passes to the skin of the
dorsal surface of the caudal peduncle where it
innervates, in succession, free lateralis organs
on four small scale pockets, one of these branch-
es innervating a scale pocket at the base of the
fourth caudal ray. The ventral fork continues in
the membrane between the eleventh and twelfth
caudal rays, innervating a long line of about 24
free lateralis organs.

Discussion

Free Cephalic Lateralis Organs

Free cephalic lateralis organs (pitorgans) or
their derivatives are found in all the classes of
jawed fishes. The pitorgans are often rather
closely associated with the cephalic lateralis ca-
nals. The organs may occur in clusters or lines
or in both arrangements on the same fish. In
Polycentrus they are in clusters at the anterior
end of the head and increasingly arranged in
lines more posteriorly.

Although considerable information exists on
pitlines (see Disler 1971; Stensio 1947), there is
not much information on these organs for per-
ciform fishes. Stensio (1947) broadly homolo-
gizes six pitlines of the cheek and lower jaw in
all classes of gnathostome fishes and of amphib-
ians. The purpose here is merely to compare the
pitlines of Polycentrus with those of some other
percoids. with Menidia, and with a few lower

groups to obtain an idea of the degree of pitline
specialization in Polycentrus. Simple locational
names for various pitlines are used for conve-
nience.

Comparison with Perca fluviatilus

Perca (Disler 1971: fig. 56) has four organs
medial to the anterior end of the nasal canal and
a longitudinal row of seven or eight organs ven-
tral to the anterior and posterior narial openings.
There are three organs in the location of the an-
terior pitline of Amia (Allis 1889: pi. 42, fig. 49)
and six organs in the location of the supratem-
poral row (the posterior pitline of Amia). Lastly,
Perca has a vertical row of about six organs and
an opercular row of about eight organs. These
pitlines in Perca correspond to pitlines in Poly-
centrus having similar location and innervation.
Polycentrus has more organs at these locations.
The main differences between Perca and Poly-
centrus are that Polycentrus has, in addition to
the above lines, well-developed supraorbital, in-
fraorbital, and mandibular pitlines. Perca lacks
these lines and presumably every organ of each
line. Perca is a more generalized percoid in its
swimming and feeding habits than is Polycen-
trus. These extra cephalic pitlines in Polycen-
trus, together with the development of pitlines
on the trunk of the body and the lack of lateral
line scales, suggest that the additional pitlines in
Polycentrus are specializations.

There are indications that the ancestors of
percoids may have had a fuller development of
the pitline system than do recent species. Nu-
merous beryciforms such as melamphaeids,
trachichthyoids, and stephanoberycoids have
many free cephalic lateralis organs. Percopsi-
forms have the system very well developed. So
do myctophoids and various other protacan-
thopterygians, not to mention ostariophysans.
Pitlines are well developed in the percoid family
Apogonidae, where its elaboration is apparently
a specialization rather than a retained ancestral
condition. Inspection of nandid genera for pit-
lines shows that Nandus has the system least
developed, and the others (Afronandus, Mono-
cirrhus, and Polycentropsis) have it well devel-
oped. The lines in nandids have lengthened, but
whether a line can be completely lost (not a sin-
gle free organ present where the line should be)
and be redeveloped is uncertain. Both Polycen-
trus and Apogon may be examples in which at
least some lines redeveloped after having been

40

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

lost. One would think that as long as the facial
and vagal lateralis roots are present, any partic-
ular pitline could be completely lost and later
reformed. Detailed comparative studies of pit-
organs are needed and should prove most inter-
esting.

Comparison with Menidia

Herrick describes for Menidia some twigs of
a branch (SO. 14; Herrick I899:pl. 2, fig. 3) of
the r. ophthalmicus superficialis facialis that
supply free lateralis organs (g, h, and i) lying
between the dorsal margin of the anterior narial
opening and the anterior end of the nasal canal.
These organs correspond to a cluster of organs
in the same location in Polycentrus, but the in-
nervation is different in Polycentrus , being from
the r. buccalis facialis of the infraorbital trunk.
If Herrick is correct, Menidia stands alone
among teleosts, as far as I can determine, in its
innervation of these snout organs. Examination
of Sihler preparations of representatives of 85
families did not show any species with free lat-
eralis organs in this area innervated from the
supraorbital trunk. Herrick found other pit or-
gans on the snout of Menidia to be innervated
from the infraorbital trunk. These include three
organs (a, b, and c; Herrick 1899:pl. 2, fig. 3)
lying between the anterior and posterior nostrils
and three more organs on top of the anterior end
of the snout medial to the anterior nostril, one
organ lying quite far medially. These pitorgans
correspond in position and innervation to similar
clusters of pitorgans in Polycentrus.

In Menidia there are pitorgans lying below the
orbit in the area of the missing part of the in-
fraorbital canal that are innervated by the r. buc-
calis facialis. They presumably represent the
modified canal neuromasts from the missing ca-
nal segment. In Polycentrus there is an infraor-
bital row containing many more pitorgans than
in Menidia which are innervated by the r. buc-
calis, but in Polycentrus the canal and canal
bones are still present, although there is only
one canal neuromast in the fused second, third,
and fourth infraorbital bones. The interesting
question is, Do these pitorgans along the edge
of these infraorbitals represent modified canal
neuromasts or do they represent a proliferation
of pitorgans that were never canal neuromasts
but which formed or proliferated as the canal
neuromasts disappeared? The implication by
other authors seems to be that they presumably
are modified canal neuromasts.

Menidia also has one pitorgan at the dorsoan-
terior corner of the opercle and four at the ven-
troanterior corner, much as in Polycentrus (Fig.
2. branches TH4AA for the opercle, and TH9B02
for the subopercle; and Fig. 15), innervated by
branches of the r. opercularis facialis. Menidia
apparently has a reduced cheek pitline (either
the vertical or horizontal cheek line of Ainia; see
Allis 1889: fig. 42) innervated by branch M.VII
1 (Herrick 1899: fig. 3) supplying only one pit-
organ, which is all Herrick found. The same
branch, M.VII 1 of the r. mandibularis externus
facialis, also innervates four organs over the
horizontal arm of the preopercular canal and an-
other organ at the base of the third pore of the
preopercular canal. These four organs plus one
organ more anteriorly correspond to the man-
dibular pitline of Amia (Allis 1889: fig. 42) and
to a similar line of organs in Polycentrus (Fig.
17).

Herrick shows no pitorgans associated with
the supratemporal canal in Menidia, whereas
Polycentrus has a lower line (STL: Fig. 17) and
a higher line (two scales above the supratem-
poral canal, each bearing a row of pitorgans)
innervated by the r. supratemporalis vagi.

Comparison with cyprinids

Pitlines are well developed in Phoxinus (Man-
igk 1934: fig. 1). A number of lines correspond
in position and innervation to those in Polycen-
trus. A seemingly important difference in Phox-
inus that is not found in Polycentrus and not
noted in other fishes is the presence of lateralis
fibers in the r. mandibularis trigeminus. These
fibers supply pitorgans located in Phoxinus at
the anteroventral corner of the cheek above the
mandibular canal. In other fishes, organs in this
location would be innervated by the r. buccalis
accessorius. These pitorgans in Phoxinus could
not be homologous with part of the postmaxil-
lary or supramaxillary lines of Stensio (1947).
Another unusual innervation occurs in Phoxinus
for pitorgans lying just in front of the vertical
arm of the preopercle and along its horizontal
arm (Manigk 1934: fig. 1). These pitorgans in
Phoxinus are supplied by branches of the r. hy-
oideus. The same pitorgans and innervation oc-
curs in Parasilurus (Atoda 1936). In Polycentrus
the preopercular pitline is supplied by branches
of the r. mandibularis externus facialis. It would
seem most probable that the pitorgans in this
location in Phoxinus are an independent devel-
opment. They would not appear to be homolo-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

4!

gous with any of the six pitlines of Stensio. An-
other difference in Phoxinus is that pitorgans on
the uppermost cheek region ventral to the pter-
otic canal are supplied by the ramus oticus.
Polycentrus lacks these pitorgans.

Comparison with esocoids

Esocids and umbrids have numerous ce-
phalic pitlines (Nelson 1972), some of which lie
in gaps in the cephalic canal system. Three of
the pitlines of Polycentrus are compared with
pitlines in corresponding places in esocoids. The
lines are the subnasal, infraorbital, and supraor-
bital. In Polycentrus the infraorbital and sub-
nasal pitlines (Fig. 17) are innervated by branch-
es of the r. buccalis facialis of the infraorbital
trunk (Fig. 1, branches 3b, 3c, I02fg, and a ver-
tical branch of I01d2 that goes to pitorgans be-
low the posterior nostril) and by one branch
(TH10A; Fig. 2) from the r. buccalis accesso-
rius, which supplies pitorgans at the posterior
end of the infraorbital pitline. Nerve fibers of
the r. buccalis facialis come from the dorsal lat-
eralis root of the facial nerve (Fig. 31) and
course in the infraorbital trunk. The innervation
for these three pitlines in umbrids and esocids
is quite different from that in Polycentrus. Sihler
nerve preparations of Esox vermiculatus and
Umbra pygmaea show that these pitlines are all
innervated by a branch of the r. buccalis acces-
sorius facialis which detaches from the truncus
hyomandibularis high up on the side of the
cheek. The lateralis fibers constituting the r.
bucc. ace. fac. belong to the ventral lateralis
root of the facialis. Another pitline, the supraor-
bital, is innervated in Polycentrus by the r.
ophthalmicus superficialis facialis, the fibers of
which belong to the dorsal lateralis root of the
facial nerve, whereas in esocids and umbrids
these pitorgans are innervated by fibers derived
from the ventral lateralis root of the facial nerve.
They course in the supraorbital branch of the r.
bucc. ace. fac. These three cephalic pitlines of
esocoids, therefore, are not homologous with
pitlines in corresponding positions in Polycen-
trus or with corresponding pitlines in numerous
acanthopterygians.

Nelson (1972: 16) states that for esocoids in
which a segment of a cephalic canal has been
eliminated, the canal neuromasts may be modi-
fied into superficial pitorgans. As far as I have
been able to determine, branches of the r. bucc.
ace. fac, which innervate these pitorgans in
esocoids, never innervate canal neuromasts.

These branches appear to belong to a special
pitline system represented in part at least by the
ramus canalis lateralis facialis system seen well
developed in Lampanyctus (Freihofer 1970; Ray
1950) and to which the r. bucc. ace. fac. belongs.
It would seem worthwhile to entertain the
thought that all pitorgans are innervated by a
system of lateralis nerve fibers distinct from that
which innervates canal neuromasts. The main
difference between the two classes of lateralis
fibers, if there are two classes, may be that lat-
eralis fibers innervating canal neuromasts can
induce bone formation, whereas lateralis fibers
innervating pitorgans cannot. It would make
sense to keep the "power" of bone induction in
one system of fibers.

The esocoids appear to be an exception to the
general statement made by Nelson (1972) that
pitlines are not useful in higher category classi-
fication. The innervation of pitlines in esocoids
may be particularly useful for this purpose.

Comparison with Amia

Polycentrus has several pitlines that have the
same location and innervation as in Amia. These
are the vertical pitline of the cheek (Allis 1889:
pi. 42, fig. 49), the supratemporal (extrascapu-
lar). the mandibular, and probably the anterior
pitline. Polycentrus lacks the middle pitline (in-
nervated by the glossopharyngeus nerve in
Amia), the gular pitline, and the horizontal pit-
line of Amia. Pitlines present in Polycentrus that
are absent in Amia are the supraorbital, infraor-
bital, chin, narial, opercular, subopercular, and
preopercular pitlines. The interesting question
is still unanswered of whether or not the narial
pitlines of Polycentrus and other fishes corre-
spond to modified canal neuromasts that result-
ed from the loss of ethmoidal and antorbital ca-
nals presumably present in the ancestors of
teleosts.

Cephalic Lateralis Canals and Neuromasts

The cephalic lateralis canals and their organs
for Polycentrus are shown in Figures 1, 2, 3, 5,
10, and 17. The number of neuromasts for each
cephalic canal-bearing bone is given in Table 1
for Polycentrus , several other perciforms. Men-
id ia. Gadus, and Amia.

The head canals of Polycentrus are all en-
closed in bone. There are four separate infraor-
bitals including the lachrymal and the dermo-
sphenotic (shown missing in all nandids by Liem
1970: fig. 3). Judging from Perca. Kuhlia (Table

4:

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

Table 1. The Number of Canal Neuromasts in Each Cephalic Canal-Bearing Bone.3-7

Name of

Poly-

Para-

Archo-

Canal

cent rus*

A mia

Roccus

labrax

Kuhlia

Perca

plites

Scomber

Gad us

Menidia 5

Nasal

1

3

1

1

1

!

1

3

2

1

Frontal

4

3

4

4

4

4

4

4

3

5

Ethmoidal

-

2

-

-

_

_

_

_

_

_

Antorbital

-

4

-

_

_

_

_

_

_

_

Lachrymal

4

2

4

4

4

4

3

4

5

2

2nd Infra2

1

1

1

1

I6

1

1

1

I

3

3rd Infra2

-

1

1

1

2

1

1

1

1

_

4th Infra2

-

1

1

1

_

1

2

1

1

_

5th Infra2

1

1

1

1

1

1

1

2

1

_

6th Infra2

r

1

l1

r

1

1

1'

1'

1

_

7th Infra2

-

r

-

-

r

1'

_

_

r

I1

Pterotic

2

3

2

2

2

2

2

3

i

1

Supratemporal

2

4

3

3

3

4

3

3

3

3

Posttemporal

1

1

1

1

1

1

1 or 2

1

1

1

Preopercle

7

6

6

6

6

6

6

3

5

5

Articular

1

3

1

1

1

1

1

1

1

1

Dentary

4

7

4

3

4

6

4

4

6

6

1 This last infraorbital is the dermosphenotic.

2 Infra = infraorbital

3 It is assumed that the primitive number of infraorbitals in percoids is seven, counting the lachrymal as the first.

4 In Polycentrus the second, third, and fourth infraorbitals may have fused and also the fifth and sixth.

s The primitive number of infraorbitals for atherinids is uncertain. The second infraorbital consists of two bones (Pranasus
and Melanotaenia). There is plenty of space between the second infraorbital and the dermosphenotic for two or three missing
bones. Herrick (1899) shows for M. beryllina eight large free lateralis organs in place of the missing infraorbitals.

h The third and fourth infraorbitals have apparently fused as indicated by the presence of two canal neuromasts in the
third infraorbital.

7 The species examined are A. calva . P. clathratus. K. rupestris , Perca flavescens, Archoplites intern/plus. S. japonicus,
and M. beryllina. Two specimens were examined of Polycentrus and Kuhlia but only one for each of the other species.

1), and Lobotes, the generalized number of in-
fraorbitals for percoids appears to be seven
(counting the lachrymal as the first), but judging
from Roccus and Paralabrax, it appears to be
six. In Table 1 it is assumed that seven is the
primitive number of infraorbitals for percoids.
Polycentrus is specialized compared with Roc-
cus, Perca, Kuhlia, Archoplites , and Paralabrax
in apparently having infraorbitals 2, 3, and 4 as
well as 5 and 6 fused, and in having only one
canal organ in each compound bone. In Nandus
(Liem 1970: fig. 20) the second infraorbital is
missing, but the dermosphenotic is present. Af-
ronandus (Liem 1970: fig. 18) has only the lach-
rymal, the other infraorbitals having disap-
peared. It would be particularly interesting to
study the infraorbitals of Nandus and the other
nandid species for the varying conditions of the
canal bones, their neuromasts, and the pitorgans
associated with the infraorbitals. Some under-
standing might be gotten of the presumed evo-
lution of pitorgans from modified canal organs,
freed when their canals disappeared. Character-

istics of the infraorbitals should be useful in nan-
did taxonomy.

Polycentrus is also specialized in having one
less organ in the supratemporal, one more in the
preopercle, and one less in the pterotic than do
the above percoids. Archoplites appears more
specialized than Roccus and Polycentrus in hav-
ing one less organ in the lachrymal and one more
organ in the fourth infraorbital. Polycentrus,
therefore, is a little more specialized in the ce-
phalic canals and their neuromasts compared to
some generalized serranids and centrarchids.

Polycentrus differs from the five other per-
coids in the innervation of the two pterotic canal
neuromasts. Both of its neuromasts are inner-
vated by the ramus oticus, whereas in Roccus,
Kuhlia, Paralabrax, Archoplites , and Perca the
second organ is innervated by the r. supratem-
poralis vagi. Polycentrus appears to be special-
ized over the other percoids in the pterotic canal
organs.

Compared with the head canals of Scomber
(see Allis 1903) and Gadus (see Cole 1898), those

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

43

in Polycentrus are more generalized in several
respects. Instead of the single nasal canal organ
present in Polycentrus and many other percoids
and perciforms (in fact in most spiny-rayed fish-
es). Scomber has three and Gadus two organs
in this canal. Study of the innervation of the
nasal canal organs in Scomber and Gadus is nec-
essary for understanding the significance of
these differences in number of nasal organs.

In Scomber the anteriormost organ is inner-
vated from the infraorbital trunk (by the r. buc-
calis facialis), which fact suggests fusion of a
prenasal ossicle onto the nasal, a feat which is
very rare in teleosts, if not unique. Out of more
than 90 families of teleosts examined, the Scom-
bridae is the only one found so far with this ev-
ident condition. The other two nasal canal or-
gans are innervated from the supraorbital trunk
and are evidently derived from an original single
organ. The two rear nasal canal organs in Ras-
trelliger kanagurta are very close together and
are innervated by a branch that divides just be-
fore reaching the two organs, which suggests the
original single organ has divided.

The nasal canal bone of Gadus has an even
more interesting history than has the nasal bone
of Scomber. Study of the innervation of the
frontal and nasal canal organs in Sihler prepa-
rations of Microgadus and Merluccius (Gadi-
dae), Physiculus (Moridae), and Malacocephal-
us (Macrouridae) indicates that the anteriormost
frontal canal organ has migrated forwards over
the floor of the frontal canal and onto the rear
of the floor of the nasal canal, the original nasal
canal organ having moved onto the anterior half
of the nasal canal. Examination of the nasal and
frontal canals in many families of paracanthop-
terygian and acanthopterygian fishes for the
number of canal organs in these bones reveals
that there is always one organ in the nasal and
four in the frontal in all families examined except
in the gadoids, ophidioids, and the beryciform
Stephanoberyx. Cole's figure of Gadus (Cole
1898:pl. 22, fig. 2) shows two nasal and three
frontal canal organs located in the posterior half
of the frontal, the anterior half of the frontal
being empty of organs. The ophidioids that were
examined (Brotula, Lepophidium, Dicrolene,
and Chilara) agree with the gadoids in the num-
ber of organs in the nasal and frontal, their in-
nervation, and the lack of organs in the anterior
half of the frontal. Zoarcids have one nasal and
three frontal canal organs. Though the ophid-

ioids and gadoids share a very unusual and
rather surprising specialization of the nasal
bone, it is not unique to them. Stephanoberyx,
as already mentioned, also has it. The nasal
bone in the three groups is always spacious and
curved rather steeply downward around the an-
terior end of the olfactory organ. The original
nasal canal neuromast is located in the anterior
half of the canal about at the ventral bend in the
canal. Both nasal canal neuromasts have mi-
grated anteriorly, the original nasal neuromast
into the front end of the canal and the posterior
neuromast into the rear of the canal. Stimuli for
the nasal canal organs apparently come from a
ventral direction. Though this condition of the
nasal canal is rare, it is the result of processes
that could plausibly happen more than once in
teleosts. It surely has occurred independently in
Stephanoberyx. Whether it has or not in the ga-
doids and ophidioids remains to be seen.

Compared with other spiny-rayed fishes ex-
amined, the nasal canal and its bone in Polycen-
trus is in a generalized state, having only one
canal neuromast and almost no membranous ex-
tension anteriorly. The nasal canal of some per-
coids has an anterior membranous extension of
greater or lesser extent, and sometimes there is
a canal neuromast in it. In the latter instance,
the membranous walls are thickened (formed of
secondary cartilage from the dermis) and may
have the shape of a small infraorbital canal bone.
Examples are found in some lutjanids and po-
madasyids. There may be one prenasal bone
with a canal neuromast, as in the Toxotidae, or
there may be two separate prenasals, one mem-
branous and one bony (Carangidae), or both
bony and separate (Coryphaenidae), or both
bony and fused but separate from the nasal
(Rachycentridae and Echeneidae). These per-
coids with two prenasals (no other percoids hav-
ing two have been found) appear to share the
same specialization and very likely form a natu-
ral, related group. Nematistius also was found to
have a small, partially ossified prenasal canal unit
with a neuromast. The Sciaenidae and Polynem-
idae have a complex prenasal membranous canal
development containing neuromasts. All of the
additional prenasal canal units, whether mem-
branous or ossified, are innervated from the in-
fraorbital trunk.

The nasal canal of berycoids, compared with
that of Polycentrus, other percoids, and, in fact,
with that seen in all other Sihler-prepared spec-

44

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

imens and in all published accounts, is strikingly
different and specialized. The character consists
of two (or one) secondary canal neuromasts in
addition to the single original (primary) neuro-
mast. The secondary neuromasts lie very close
to the anterior edge of the floor of the nasal ca-
nal, one organ near each lateral corner of the
canal, and are innervated from the infraorbital
trunk. The original nasal canal neuromast lies
near the midlength of the canal and is innervated
from the supraorbital trunk.

The berycoids all have this character (at least
one species of each family examined), but the
stephanoberycoids, including melamphaeids and
gibberichthyids, do not. Polymixiids have what
appears to be an earlier development of the ber-
ycoid condition. In Polymixia there are three
free lateralis organs in a membranous canal that
passes across but just outside of the entrance to
the nasal canal. This membranous canal is con-
nected across the tip of the snout with a similar
canal on the other side of the head. Another
lateralis organ lies at the midpoint of the cross-
ing canal. The stephanoberycoids have what ap-
pears to be a still more generalized condition in
that there is a row of free lateralis organs in the
skin across the tip of the snout in place of the
membranous canal of Polymixia and a somewhat
enlarged free lateralis organ in the skin just out-
side each lateral corner of the opening in the
nasal canal in place of the canal organ inside the
nasal canal near each corner in berycoids.

The mode of formation of the secondary nasal
canal organs of berycoids is what makes this
nasal canal specialization especially different
from that in other fishes. In berycoids free lat-
eralis organs close to the nasal canal opening
have apparently been simply engulfed by the
bony nasal canal without first being formed in
a prenasal ossicle. In carangids, rachycentrids,
echeneids, coryphaenids, and other groups, the
prenasal ossicle or ossicles do not fuse onto the
nasal bone. In Scomber a prenasal ossicle un-
doubtedly has fused onto the nasal bone. In ber-
ycoids there are no indications of such fusion;
the one or two added canal neuromasts lie very
close to the anterior edge of the nasal bone,
there is no pore marking a fusion, and there is
no bend or irregularity indicating a junction of
two bones.

It appears that in the berycoids we have an
example, surely very rare, of two free transverse
organs (reduced to one organ in some berycoids)

being, in effect, "captured" (engulfed) by a na-
sal canal bone! The berycoid nasal canal bone
specialization would seemingly remove the ber-
ycoids from being considered the ancestral
source of percoids. The same statement may
hold for the stephanoberycoids which have what
appears to be an earlier stage of the polymixiid
condition. This character state in beryciforms
will be presented in a separate paper.

It may be added that beryciforms have other
specializations of the cephalic lateralis system.
In stephanoberycoids the supratemporal canal
is actually in communication with the nasal ca-
nal and the frontal canal via a large lateralis
chamber lying in the interorbital area over the
frontals. In melamphaeids the lachrymal canal
is in communication with the nasal canal. These
developments are rare or unique in teleosts.

In summary, two generalizations might be
made about the innervation of the snout region
for teleosts from conditions observed in Poly-
centrus and Sihler nerve preparations of repre-
sentatives of 85 families. The lateralis innerva-
tion of the supraorbital trunk ends with the nasal
canal bone. Any pitorgan development on the
snout will be innervated from the infraorbital
trunk. Any new canal and canal neuromasts be-
yond the anterior end of the nasal canal will also
be innervated from the infraorbital trunk. A sim-
ilar generalization applies to the general cuta-
neous innervation of the supraorbital trunk. In
most of the fishes observed, it ended about at
the anterior end of the nasal bone or a little be-
yond it. Only in the atherinomorphs and holo-
centrids did it extend significantly further, going
to the upper jaw as a large nerve.

Innervation of the Upper Jaw

In Polycentrus the upper jaw is supplied with
general cutaneous innervation by the inferior
ramulus of the ramus maxillaris trigeminus (103;
Fig. 1) and with gustatory innervation by the
anterior ramus of the palatine nerve (Fig. 1). No
other nerves go to the upper jaw, not even from
the supraorbital trunk, which itself is something
of a surprise if the upper jaw is considered a part
of the snout. Polycentrus is representative of
most teleosts in innervation of the upper jaw.
One exception is Menidia (Herrick 1899; fig. 3,
the yellow branch to the upper jaw). In Menidia
the supraorbital trunk is continued out to the tip
of the upper jaw, supplying it rather heavily with
general cutaneous innervation. The nerve is

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

45

large, as seen on Sihler nerve preparations of
various atherinomorphs. Of 85 families, only the
seven atherinomorph families examined and the
Holocentridae had the premaxillary extension of
the supraorbital trunk. In the Holocentridae the
functional component is, presumably, also gen-
eral cutaneous.

Cheek Muscle Innervation

The pattern of innervation of the cheek mus-
cle in Polycentrus (Fig. 6) reflects the partial
subdivision of the adductor mandibulae into
three parts called A,, A2, and A3 (Fig. 22),
branches I02c and I02d innervating A,, branch
I02e innervating A2, and the hatched parts of
102 innervating A3. The pattern in Polycentrus
is generalized for percoids. In fact, most of the
other percoids examined had more distinctive
patterns of innervation of the cheek muscle than
does Polycentrus, each being a little different
from the others. The sciaenids were especially
distinct, the A,/3 muscle in some species being
developed as fully as the A,/3 in percopsiforms,
including its pattern of innervation. Atherino-
morphs (7 families examined) have an innerva-
tion pattern distinct from that of all other fami-
lies studied except gasterosteids in which it is
the same. Much can be learned of systematic
interest from the cheek muscles by study of the
pattern of innervation within the muscle. Results
of a study of the Ax(3 muscle are being prepared
for a separate paper.

Correct Name for
Ramus Lateralis Accessorius

Herrick (1899: fig. 3) describes three ramuji
from the r. lateralis vagi which join the r. recur-
rens facialis to form the r. lateralis accessorius
facialis (RLA). These ramuli join RLA on the
posterior part of the head above the pharyngeal
area and on the anterior part of the trunk. Her-
rick indirectly derives these ramuli from a small
bundle of fibers (about 20) which detach from
the root of n. glossopharyngeus, this small bun-
dle joining intracranially the root of the ramus
lateralis vagi (r. lat. vagi). The fibers are of small
to medium diameter, considerably smaller than
lateralis fibers to canal neuromasts, according to
Herrick, but larger than average communis fi-
bers. Herrick could not trace these medium-
small fibers from the glossopharyngeus through
the ganglion of the r. lat. vagi. He assumed that
fibers of the same size observed leaving the oth-

er side of the ganglion were the same as the ones
observed entering it, that is, that they were from
the 20 fibers from the glossopharyngeus. He
rather confidently identifies the three ramuli
from the r. lat. vagi which appear to join RLA
as being derived from the small bundle of fibers
from the root of the glossopharyngeus. He fur-
thermore assigns them to the communis system.
Herrick's reasons, others in addition to those
just given, are not very convincing. The use of
the name ramus lateralis accessorius, therefore,
really rests upon the fact that this nerve is made
up of gustatory fibers from both the facialis and
vagus (or glossopharyngeus) nerves.

In Polycentrus no such ramuli from the r. lat.
vagi were observed to join the recurrent facial
ramus. In Polycentrus there is an intracranial
vagal ramus that passes up to the parietal bone,
and on some specimens it passes out of the cra-
nium through the same foramen as does RLA,
but on other specimens it passes through its own
foramen close to that for RLA. In the latter
specimens it was observed to pass to overlying
skin and to skin lying anterior to its cranial exit.
As far as could be determined from serial sec-
tions of Polycentrus, it was seen to be an intra-
cranial part of the rami cutanei dorsales vagi. It
would be carrying general cutaneous innervation
to the top of the head. Menidia lacks this intra-
cranial vagal ramus. Herrick equates the three
extracranial ramuli from the r. lat. vagi of Men-
idia with this vagal ramus that is present in many
other fishes (see Freihofer 1963 for examples).
It may be equivalent as Herrick thought, but
what seems quite doubtful from Herrick's dis-
cussion of these three ramuli is that they are of
the communis component and that they join
RLA and presumably course some distance with
it. On a Sihler nerve preparation of the atherinid
Atherinops affinis, no ramuli from the r. lat. vagi
were observed to anastomose with RLA. Ath-
erinops also lacks an intracranial vagal ramus to
the parietal. These three ramuli of Menidia and
the intracranial vagal ramus of Polycentrus and
other fishes need more study. If they prove not
to be communis, that is. if there is no vagal com-
munis contribution to the formation of RLA.
there would be reason for changing the name of
RLA to simply that of the ramus recurrens fa-
cialis, in recognition of its purely facial com-
munis composition. The facial part of RLA is
much larger than is the vagal in apparently all
teleosts having RLA. One disadvantage of using

46

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

the name RLA is that it implies that the nerve
is an accessory lateral line nerve of the acous-
tico-lateralis system, which it is not. The term
RLA should stand until the question of the con-
tribution of the vagal communis is resolved.

Trunk Lateral Line Nerves

The pattern of the trunk lateral line nerves of
Polycentrus (Fig. 21) is especially interesting
because it shows some ventral and dorsal seg-
mental lateral line branches which previously
have been known only in various lower, non-
acanthopterygian fishes and in a less-developed
state in zoarcids, gobiids, and mugilids (Frei-
hofer 1970, 1972). There is one basic difference
between the Polyce ntrus pattern and that of oth-
er fishes having ventral segmental lateral line
nerves. In Polycentrus as well as in the other 20
or so percoid families that have been examined,
there is a dorsal longitudinal collector lateral line
nerve. Other perciformes examined have this
collector also, but the zoarcids, gobiids, and
mugilids do not have it. The atherinomorphs all
lack it, as do other groups examined that are
classified lower than the acanthopterygians and
paracanthopterygians. Some of the paracan-
thopterygian fishes develop a dorsal longitudinal
collector lateral line nerve at least towards the
distal end of the dorsal longitudinal ramus. The
ventral segmental lateral line branches in Poly-
centrus, of which there are five, are a secondary
development on a basic percoid pattern and is
apparently associated with the specialized
swimming habits of Polycentrus . It would be in-
teresting to see the lateral line nerves of nandids
more generalized than Polycentrus, especially
Nandus. It would take very carefully preserved
specimens to provide the information, but the
distribution of free lateralis organs on the head
and trunk of all nandid genera should be deter-
mined. The results should have systematic sig-
nificance for nandid classification.

Polycentrus is a secretive fish which stalks its
prey by an extremely slow forward movement
made by the beating of its transparent soft dorsal
and anal fins, its mode of forward progress, its
coloration, and its body shape resembling a
drifting dead leaf. When startled or after attack-
ing a prey fish, Polycentrus can move quite rap-
idly backwards from its position near the surface
to its retreat near the bottom in a hole or pot.
The head and trunk lateral line system may re-
flect specializations for such swimming behav-

ior. The lateralis organs of the trunk are all free
or naked organs borne on scales, a series of
about eight organs on each such scale, the lat-
eralis-bearing scales being arranged in rows fol-
lowing the main contours of the trunk (Fig. 21).
The lateral line on the head is also specialized
in that there are large neuromasts in the head
lateralis canals as well as free organs arranged
as shown in Fig. 21.

The distribution of free lateralis organs on the
trunk of Polycentrus illustrates to what degree
lateralis organs can migrate and their nerves fol-
low them. The question arises for the zoarcids,
gobioids, and mugilids as to whether these
groups have lost all traces of the basic percoid
pattern or whether they ever had them.

The large number (20 to 25) of free lateralis
organs on the inside of the chin between the
anterior ends of the dentaries is interesting in
that a similar aggregation was observed on var-
ious other percoids. It is apparently an impor-
tant location for receiving lateralis stimuli,
which in Polycentrus may serve a prey-locating
function.

An External-Internal Lateral Line Canal
Nerve Relationship

Worthy of special note is a branching rela-
tionship observed on a number of ramuli going
to individual neuromasts of the head canals (see
branches to second and third pores of lachrymal
canal. Fig. 1 . and SORB 4. SORB 1 1 . and SORB
1 la. Fig. 3). A similar relationship was also ob-
served for lateral line scales on the trunk of vari-
ous fishes. In this relationship a neuromast ramu-
lus detaches from a main nerve ramus and
courses alone towards its canal neuromast, but
before reaching its canal neuromast. the ramulus
itself detaches a branch which curves away and
passes some distance to skin or membrane
around an adjacent canal pore. In some in-
stances, on Sihler nerve preparations this
branch to the membrane around the pore ended
in branchlets that resembled in appearance those
that elsewhere were known to be innervating
free lateralis organs. Such organs occur in the
skin along the supraorbital and infraorbital ca-
nals (Fig. 17) and elsewhere. If the ramulus were
carrying only general cutaneous innervation, it
would seem as practical, a distribution to have
such fibers course in other rami that carry the
main cutaneous innervation.

The arrangement of a canal neuromast ram-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK11

47

ulus closely associated with a ramulus innervat-
ing free lateralis organs in the skin would allow
for the reception of differences between lateralis
stimuli inside and outside the canals for each
such location. Its development mPolycentrus is
no doubt associated with this fish's very slow
swimming habits, but it was observed also in
other fishes, even for the trunk lateral line
scales. Herrick (1899) briefly described a few of
these branches on the head of Menidia but did
not comment on them.

Radix Profundus

The complex relationships of the radix pro-
fundus with the oculomotor nerve and trigeminal
sympathetic ganglion in Polycentrus (Fig. 14)
are quite similar to those of the perciform Ura-
noscopus (Young 1931: text-fig. 8). There is a
difference in Menidia that may be significant
systematically. Herrick (1899) found that a rec-
ognizable intracranial profundus root and gan-
glion are missing in this atherinid. Since the cil-
iary nerves are present in Menidia , the root and
ganglion of the profundus must be present also,
but apparently they are fused with the trigeminal
root and ganglion, a condition which may be
representative for atherinomorphs.

A Stretch-Receptor Nerve to Base of
Maxillary Tendon

Especially interesting is a branch (I02fl: Figs.
6 and 10) of the r. mandibularis trigeminus which
ends in a dense ramification of nerve fibers in
the tendinous mucosa on the inside of the
mouth, the innervation being directly in front of
the anterior edge of the quadrate near the artic-
ulation head of this bone. This tendinous mem-
brane fans out towards the ventral end of the
maxillary tendon. Branch I02fl may innervate
stretch-receptor organs in this membrane. A
similar branch was observed on a number of oth-
er kinds of fishes. It was a large branch in a
goatfish. Parupeneus porphyreus. A similar
branch occurs in Menidia, but Herrick (1899)
did not suggest any stretch-receptor innervation
for it. It should be of interest to functional anat-
omists studying jaw mechanisms.

Simplifying Cranial Nerve Studies

The fifth, seventh, ninth, and tenth cranial
nerves are the most complex in their branching
and number of nerve components, and for these
reasons they hold the most interest for system-

atists. Of these four cranial nerves, the fifth and
seventh rank above the ninth and tenth. Broader
taxonomic coverage can be had by concentrat-
ing only on the fifth and seventh nerves, or by
restricting the study even further to a certain
trunk, ramus, or even to only a single larger
branch of a ramus. The nerve chosen should be
an integral unit, complete in itself, and not parts
of two nerves or character complexes.

It is also best to chose only one nerve com-
ponent in a nerve trunk or ramus rather than
include all components with all their branches.
For example, one of the character complexes
selected for comparison with Polycentrus was
the lateralis component in the supraorbital
trunk. Only the nasal and frontal bones were
included. These seemed to form a natural mor-
phological unit for this component in this nerve
trunk.

For practical purposes comparative studies
can be made directly from Sihler nerve prepa-
rations without recourse to serial-section tech-
niques and involved neurological research. Prior
grounding in the important nerve references em-
ploying functional component analysis is, of
course, essential. A brief listing of the most im-
portant of the longer studies is given in the "In-
troduction.** There are huge gaps in the taxo-
nomic coverage in the nerve literature. The gaps
can be filled effectively by a reference collection
of Sihler nerve preparations.

The nerve components of the various trunks,
rami, and smaller branches can be worked out
with relative assurance in most instances by
study of Sihler nerve preparations and dissec-
tions of preserved specimens. The dissections
should expose the roots and ganglia of the tri-
geminus, facialis, glossopharyngeus, and vagus
nerves. The motor and lateralis components are
not difficult to determine because their end or-
gans are relatively large. Since free lateralis or-
gans may be lost in the handling and preparation
of specimens, the distribution of these organs
should be plotted from freshly and carefully pre-
served specimens (Fig. 17). Such a drawing is
useful in helping assign terminal branches in a
particular area of a Sihler preparation to the lat-
eralis component. The gustatory component is
difficult to determine unless the fibers course
more or less as independent nerves for most of
their length. Taste (terminal) buds located on the
external body surface are too small to be seen
except microscopically. Most of the gustatory

48

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

system will be represented by the distinctive
branches of the recurrent facial and palatine
nerves. Dissection of the geniculate ganglion
should disclose the presence of larger bundles
of gustatory fibers leaving this ganglion and en-
tering the supra- and infraorbital trunks, but
since these fibers disappear into the branches of
these trunks, appropriate microtechnique meth-
ods are necessary for determining their distri-
bution. For most systematic purposes gustatory
fibers entering these two trunks can be ignored.
For practical purposes the last component, the
general cutaneous, is what remains after the oth-
er three components have been determined. In
fishes, general cutaneous fibers terminate in free
nerve endings in the skin or in special tactile
elaborations of skin, such as cirri and other skin
flaps, or in barbels or barbel-like structures.

After determination of the functional compo-
nents at the periphery of the nerves, the pres-
ence of a component can be shown diagram-
matically in drawings by a distinctive symbol,
the fiber bundles of each branch being brought
together as they course centrally towards the
cranial roots and ganglia and to the brain. An
example in which these simplified approaches
were taken in a systematic study is that by
Springer and Freihofer (1976).

Short cuts such as those suggested above are
necessary if nerves are to be used in the clas-
sification of fishes. Basic, descriptive neurolog-
ical studies are still needed on numerous groups.
It may fall to the lot of some systematists to do
them. Neurologists have seemingly turned to
other tasks.

Summary

1. The courses of the trigeminus, facialis,
glossopharyngeus, and vagus cranial nerves of
a percoid fish, Polycentrus schomburgkii , are
described in detail, and the functional compo-
nents of the nerves determined as far as possible
with the methods used. The closest groups with
which Polycentrus could be compared in pub-
lished accounts were Scomber (Scombridae) and
Menidia (Atherinidae). Comparisons were also
made from Sihler preparations of numerous
groups (representatives of 85 families available)
for selected nerves.

2. Nothing unusual was noted in the olfactory
(I), optic (II), oculomotor (III), trochlear (IV),
or abducens (VI), nerves.

3. The radix profundus in Polycentrus has the
same relationships to the Gasserian ganglion.

trigeminal sympathetic ganglion, ciliary gan-
glion, and oculomotor nerves as it has in Ura-
noscopus, as far as could be determined.

4. Polycentrus was compared with five per-
coids (Roccus, Kuhlia, Perca, Paralabrax, and
Archoplites) and several other groups of fishes
for cephalic canal neuromasts and with addi-
tional groups for cephalic free lateralis organs
(pitorgans).

5. Polycentrus is more specialized than the
above percoids, both in number of pitlines and
in their size.

6. A pitline corresponding to the vertical pit-
line of Amia is present and innervated from the
truncus hyomandibularis by the ramus buccalis
accessorius. The posterior end of the infraorbital
pitline is also innervated by a branch of the r.
buccalis accessorius, which represents a spe-
cialization since the infraorbital pitline is usually
innervated from the infraorbital trunk by the r.
buccalis. This posterior part of the infraorbital
pitline may represent the horizontal pitline of
Amia that has moved up to the edge of the in-
fraorbital.

7. Some pitlines of some fishes may not be
homologous with corresponding pitlines of other
fishes. Esocoids are an example. At least three
pitlines in Polycentrus (the infraorbital, subna-
sal, and supraorbital) are not homologous with
pitlines in the same location in esocoids. These
three pitlines in esocoids are all innervated by
the r. buccalis accessorius from the tr. hyoman-
dibularis, whereas in Polycentrus the first two
are innervated from the infraorbital trunk by the
r. buccalis and the last pitline (the supraorbital)
is innervated from the supraorbital trunk.

8. Reflecting perhaps the greater develop-
ment of the infraorbital pitline is a specialization
of the infraorbital canal-bearing bones, a first
step towards degeneration of the infraorbital ca-
nals; the second, third, and fourth infraorbitals
are fused and there is only one canal neuromast
in the compound bone. In other respects the ce-
phalic lateralis canal-bearing bones are a little
more specialized (one less neuromast in the su-
pratemporal and one more in the preopercular
canals) than in Roccus, Paralabrax, Archo-
plites , and Kuhlia .

9. Various clusters and lines of cephalic pit-
organs should be useful in nandid taxonomy.

10. The innervation of the snout in fishes is an
important area for comparison in systematic
studies. The snout in teleosts is innervated from

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1

4')

two sources: the supraorbital and infraorbital
trunks. In Polycentrus the supraorbital trunk
supplies one canal lateralis organ of the nasal
canal, and the infraorbital trunk innervates ap-
parently all of the free lateralis organs on the
snout dorsomedial and ventral to the nasal bone.
In some fishes there are important differences
in this generalized condition seen in Polycen-
trus. If there are further developments of the
lateralis system on the snout, such as an exten-
sion anteriorly of the nasal canal, they are in-
nervated by the infraorbital trunk. Innervation
of the nasal canal organ or organs should be de-
termined in systematic studies because two (or
three) lateralis organs in the nasal canal may in-
dicate a fusion of the nasal canal bone (with one
or two canal organs) and a prenasal canal (with
one canal organ), the latter being innervated by
the infraorbital trunk, or it may have other sig-
nificance. An example of a group having a nasal
and two prenasals (the anterior one membranous
and the posterior one bony) is the Carangidae.
Other percoids having two prenasals with fea-
tures indicating a shared, derived specialization
with the Carangidae are the Coryphaenidae (two
bony prenasals, each separate and free from the
nasal), Rachycentridae (two bony prenasals
fused but free from nasal), and Echeneidae (same
as Rachycentridae). Some other percoids having
other specializations of an anterior extension of
the nasal canal are the Sciaenidae and Polynem-
idae (both with deep, complicated membranous
extensions); Toxotidae (a broad, bony prenasal);
and Lutjanidae (one membranous prenasal). The
Scombridae is so far unique in having a bony
prenasal fused to the nasal.

11. Compared with Polycentrus, other per-
coids, and all teleosts examined, the berycoids
have a quite different specialization of the nasal
canal. It consists of one or two nasal canal sec-
ondary neuromasts located close to the anterior
edge of the floor of the canal and innervated
from the infraorbital trunk. Polymixia exhibits
a stage that could be antecedent to that of ber-
ycoids. Stephanoberycoids have what may be the
most generalized condition for beryciforms. It
appears that in berycoids free lateralis organs
lying close in front of the opening of the nasal
canal were directly incorporated into the ante-
rior end of the nasal canal without the prior for-
mation of a prenasal ossicle that subsequently
fused onto the nasal canal bone. The "capture"
or engulfing mode of formation would be rare.

if not unique. In any event, the nasal canal spe-
cialization appears basic in berycoids. It indi-
cates that neither stephanoberycoids, polymix-
ioids, nor berycoids are the ancestral source of
perciforms. There are other striking specializa-
tions of the cephalic lateralis canal system of
beryciforms.

12. The gadoids and ophidioids have a shared
specialization of the nasal canal in which the
anteriormost frontal canal neuromast has mi-
grated into the nasal canal, giving that canal two
neuromasts and the frontal canal only three, the
usual number being four for almost all acan-
thopterygians examined. Stephanoberyx also
has this specialization but not Gibberichthys .
The zoarcids have only three frontal canal neu-
romasts, but only one nasal canal neuromast.

13. The general cutaneous component of the
supraorbital trunk in Polycentrus ends on the
snout posterior to the upper jaw, which is where
it ends in most teleosts. In all atherinomorph
fishes examined, it continues anteriorly as a
large nerve onto the upper jaw. The only other
group also found having a similar large extension
onto the snout is the Holocentridae. The pre-
maxillary extension of the supraorbital trunk
carries general cutaneous fibers in atherino-
morphs. The functional component is not yet
known for holocentrids, but it probably is gen-
eral cutaneous.

14. The pattern of branching of the ramuli
from the ramus mandibularis trigeminus into the
adductor mandibulae muscles of the cheek in
Polycentrus consists of two ramuli leaving the
ramus mandibularis trigeminus close together.
Their ramifications in the subdivisions of the
cheek muscle mass reflect the structure of the
muscle. The pattern of nerve branching in the
adductor mandibulae muscle can be important
in understanding the subdivisions of this muscle,
such as the origin of the A^ muscle. It also may
have systematic significance. An example was
discovered in comparing the pattern of Polycen-
trus with that of the atherinid Menidia. The ath-
erinomorphs as a group have a nerve pattern to
the cheek muscle different from that of all other
fishes examined except for the gasterosteids.

15. The recurrent facial ramus (RLA) is pres-
ent in one of the basic percoid patterns (referred
to as the Serranus pattern), characterized by an
orbito-pectoral and a parieto-dorsal branch.

16. There are few or no lateralis fibers in the
ramus hyoideus.

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

17. There are apparently few or no communis
fibers in the ramus mandibularis trigeminus and
r. maxillaris trigeminus.

18. The anterior ramus palatinus joins the r.
maxillaris trigeminus on the upper jaw. Some
groups of fishes lack this anastomosis (atherino-
morphs being one).

19. There is a Jacobson*s anastomosis.

20. The ramus mandibularis internus facialis
is present.

2 1 . A nerve possibly functioning mainly as an
innervation for stretch receptors in the mem-
brane and tendons associated with the base of
the maxillary tendon was observed in Polycen-
trus and some other percoids.

22. A double type of cephalic canal lateralis
innervation was observed on Polycentrus and
some other acanthopterygians. It consists of two
branches detaching from a single lateralis branch
that innervates a canal neuromast: one of the
two canal branches innervates the canal neuro-
mast, and the rest of the canal branch passes to
the membrane around the adjacent canal pore,
the membrane at least sometimes observed to
bear free lateralis organs.

23. There is an intracranial vagal ramus which
in Polycentrus is a branch of the ramus cutanei
dorsales vagi. This intracranial vagal ramus does
not course with the recurrent facial ramus. It
does not contribute to the latter ramus. No vagal
branch was seen to contribute to the recurrent
facial nerve on the nape. The question of the
intracranial ramus being of general cutaneous or
communis component should be studied in other
fishes. If the intracranial vagal ramus does not
contribute communis fibers to the recurrent fa-
cial nerve, then the name of ramus lateralis ac-
cessorius should not be used and the name of
recurrent facial nerve be used in its stead for the
entire course of the nerve.

24. The trunk lateral line nerves show a basic
acanthopterygian pattern of a so-called dorsal,
longitudinal collector lateral line nerve. In ad-
dition there are a number of dorsal and ventral
segmental branches which innervate three rows
of scales bearing free lateralis organs (pitor-
gans): a row along the base of the dorsal fin; a
row halfway between the dorsal fin and the hor-
izontal septum; and a row along the base of the
anal fin. There are two rows of free organs on
the caudal fin: one on its upper lobe and one on
its lower lobe. There is only one regular tubed
lateral line scale, the first one. Each of these

separate rows of free organs on a scale may rep-
resent a canal neuromast that has migrated to-
wards the base of a fin and subdivided into about
eight smaller free organs; or each row of free
organs on a scale may represent multiplication
of a single pitorgan originally associated with
each tubed lateral line scale. Such pitorgans
were observed, one per lateral line scale, on
some lateral line scales of other fishes. It was
not observed on the single tubed scale of Poly-
centrus. It is not known which of the possible
origins is correct for the development of such
free lateralis organs, either on the head or on
the trunk of the body.

25. Some interesting systematic problems on
the higher category classification of certain
groups of fishes were disclosed in the compar-
ative studies made between Polycentrus and
groups represented in the nerve literature and
from Sihler nerve preparations.

26. For systematic purposes the most useful
cranial nerves to study are the fifth, seventh,
ninth, and tenth, with the fifth and seventh being
the most useful, if a choice has to be made.
These cranial nerves are the most complex and
offer the most characters.

27. From a consideration of the usefulness
that nerves apparently have for studies on the
classification of fishes and the great gaps there
are in the taxonomic coverage of the nerve lit-
erature for fishes, it is apparent that at least one
basic descriptive study of the cranial nerves of
a representative of each order is definitely need-
ed. This research should be carried out by sys-
tematists. Morphologists are no longer interest-
ed in descriptive nerve studies.

28. Making the preceding recommendations
much more feasible is the Sihler technique for
staining nerves in a cleared, intact specimen.

Acknowledgments

My thanks go out to many individuals who
helped make this study possible. Dr. George S.
Myers gave the original breeding stock of Poly-
centrus and encouraged continuance of the proj-
ect. Dr. Stanley H. Weitzman helped locate
"'populations" of Polycentrus in San Francisco
aquarium stores, gave advice on techniques and
on other matters. Dr. Richard Winterbottom
kindly advised on the muscle terminology. Drs.
Stanley H. Weitzman, William N. Eschmeyer,
and Mr. Leonard J. V. Compagno critically read
the manuscript. I assume full responsibility for

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1

51

any errors or omissions still in the paper and for
the views expressed. The following individuals
all kindly sent formalin specimens for use in the
nerve processing: Dr. Gerald Allen, Mr. Eric
Anderson, Drs. Gilbert Bane, Clyde Barbour,
Gregor Cailliet, Bruce Collette, Mr. C. E. Daw-
son, Drs. Hugh De Witt, Douglas Hoese, Rich-
ard Ibara, Tomio Iwamoto, Mr. Shelley John-
son, Mr. Susumu Kato, Dr. Leslie K. Knapp,
Dr. Robert J. Lavenberg, Mr. Robert Lea, Drs.
John E. McCosker, Robert W. McDowall, John
W. Meldrim, Mr. George C. Miller, Drs. John
R. Paxton, Theodore Pietsch, John E. Randall,
Edward Raney, Richard Rosenblatt, Mr. Walter

Schneebeli, Drs. Victor G. Springer, Jon C.
Staiger, the late Mr. Franz Steiner, and Dr.
Camm Swift. The late Mary Hayes Wagner
helped greatly with all the final inking and la-
belling of the drawings. Maurice Giles of the
California Academy of Sciences contributed his
photographic skills. Leonard J. V. Compagno
again has been a patient listener and discussant.
Much of the research was done at the California
Academy of Sciences. It was begun at Stanford
University. The help and support I received are
gratefully appreciated. The research was sup-
ported in part by NSF Grant GB-30551.

52

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

Literature Cited

Ai i is. Edward Phelps, Jr. 1889. The anatomy and devel-
opment of the lateral line system in Amia calva. J. Morphol.
2(3): 463-568, 10 text-figs. + pis. 30-42 (49 figs.).

. 1897. The cranial muscles and cranial and first spinal

nerves in Amia calva. J. Morphol. 12(3): 487-808, pis. 20-
38 (64 figs.).

. 1903. The skull, and the cranial and first spinal mus-

cles and nerves in Scomber scomber. J. Morphol. 18: 45-
329, 1 text-fig., pis. 3-12.
. 1910. The cranial anatomy of the mail-cheeked fish-

es. Zoologica (Stuttgart), 57: iii + 219. 8 pis.

Atoda, K. 1936. The innervation of the cranial nerves of the
catfish: Parasilurus asotus L. Sci. Rep. Tohoku Univ., Sen-
dai 11(4): 91-113.

Baudelot, Emile. 1883. Recherches sur le systeme ner-
veux des poissons. Paris. 178 pp., 10 pis.

Cole, Frank J. 1898. Observations on the structure and
morphology of the cranial nerves and lateral sense organs
of fishes; with special reference to the genus Gadus. Trans.
Linn. Soc. Lond., ser. 2. Zool. 17(5): 17-221, pis. 21-23.

Cuvier, Georges L. C. F. D., and Achille Valen-
ciennes. 1828. Histoire naturale des poissons. 1. Paris,
xvi + 573 pp.

Disler, N. N. 1971 [I960]. Lateral line sense organs and
their importance in fish behavior. Academy of Sciences of
the U.S.S.R., Severtsov Institute of Animal Morphology.
(Transl. from Russian by H. Mills and M. Yariv. Israel Pro-
gram for Scientific Translations, Ltd. 328 pp., 57 figs.)

Fraser, Thomas H., and W. C. Freihofer. 1971. Trypsin
modification for Sihler technique of staining nerves for sys-
tematic studies of fishes. Copeia 1971(3): 574-576, 1 fig.

Freihofer, Warren C. 1963. Patterns of the ramus lateralis
accessorius and their systematic significance in teleostean
fishes. Stanford Ichthyol. Bull. 8(2): 79-189, 29 figs.

. 1966. The Sihler technique of staining nerves for sys-
tematic study especially of fishes. Copeia 1966(3): 470-475,
2 figs.

. 1970. Some nerve patterns and their systematic sig-

nificance in paracanthopterygian, salmoniform, gobioid,
and apogonid fishes. Proc. Calif. Acad. Sci., ser. 4, 38(12):
215-264, 20 figs.
. 1972. Trunk lateral line nerves, hyoid arch gill rakers.

and olfactory bulb location in atheriniform, mugilid, and
percoid fishes. Occas. Pap. Calif. Acad. Sci. 95: 31 pp., 12
figs.
, Leonard J. V. Compagno, and William Rogers.

1977. Additional notes on the use of the Sihler technique
of staining nerves of small, whole specimens of fishes and
other vertebrates. Copeia 1977(3): 587-588.

Gilmore, R. G., Jr. 1972. The cephalic nerve pattern and
lateral line system of Hyporhamphus unifasciatus and
Strongylura marina (Pisces: Exocoetidae, Belonidae). Mas-
ter's Thesis. University of West Florida. 35 pp., 7 text-figs.

Greenwood, P. Humphry, Donn E. Rosen, Stanley H.
Weitzman, and George S. Myers. 1966. Phyletic stud-
ies of teleostean fishes, with a provisional classification of
living forms. Bull. Am. Mus. Nat. Hist. 131(4): 339-456,
text-figs. 1-9, pis. 21-23, charts 1-32.

Gupta, O. P. 1972. On the origin and innervation of the
cranial and spinal nerves along with the autonomic nervous
system of the Indian Gar-fish, Xenentodon cancila (Ham.).
Anat. Anz. 131: 39-50, 4 figs.

Hennig, Willi. 1966. Phylogenetic systematics. (Transl. by

D. Dwight Davis and Rainer Zangerl.) University of Illinois

Press. 263 pp., 69 figs.
Herrick, C. Judson. 1897. The cranial nerve components

of teleosts. Anat. Anz. 13(16): 425-431.
. 1898. Experiments with the Weigert method. J.

Comp. Neurol. 8: XXVII to XLIV.
. 1899. The cranial and first spinal nerves of Menidia;

a contribution upon the nerve components of the bony fish-
es. J. Comp. Neurol. 9: 153^155, pis. 14-20.
. 1900. A contribution upon the cranial nerves of the

codfish. J. Comp. Neurol. 10: 265-316, pis. 21-22.
. 1901. The cranial nerves and cutaneous sense organs

of the North American siluroid fishes. J. Comp. Neurol. 1 1:
177-249, pis. 14-17.
. 1903. The doctrine of nerve components and some

of its applications. J. Comp. Neurol. 13: 301-312.

Hollister, Gloria. 1934. Clearing and dyeing fish for bone
study. Zoologica (N.Y.): 12(10): 89-101.

Laurent, P., and S. Dunel. 1966. Recherches sur
l'innervation de la pseudobranchie des teleosteens [in
French. English summary]. Arch. Anat. Microsc. Morphol.
Exp. 55: 633-656, 9 figs.

Leach, E. H. 1946. Curtis' substitute for van Gieson's stain.
Stain Technol. 21: 107-110.

Liem, Karel. 1970. Comparative functional anatomy of the
Nandidae (Pisces: Teleostei). Fieldiana: Zool. 56: 1-166, 66
figs.

Maheshwari, S. C. 1965. The cranial nerves of Mastacem-
belus armatus (Lacepede). Jpn. J. Ichthyol. 12(3/6): 89-98,
4 figs.

Manigk, Wolfgang. 1934. Der Trigemino-Facialiskomplex
und die Innervation der Kopfseitenorgane der Elritze
(Pho.xinus laevis). Z. Morphol. Oekol. Tiere 28: 64-106, 16
figs.

Mithel, Manorama. 1964a. The cranial nerves of the si-
sorid catfish Bagarius bagarius. Copeia 1964(4): 673-678,
2 figs.

. 1964b. The cranial nerves of Mystus seenghala

(Sykes). Agra Univ. J. Res. 13(1): 67-78, 7 figs.

Narawane, D. D. 1965. Studies on the skeleton, muscula-
ture and distribution of nerves in the caudal peduncle and
fins of Heteropneustes fossilis Bloch. (Physostomi-Siluri-
dae). J. Univ. Bombay 33(5): 64-75, 7 figs.

Nelson, Gareth J. 1972. Cephalic sensory canals, pitlines,
and the classification of esocoid fishes, with notes on gal-
axiids and other teleosts. Am. Mus. Novit. 2492: 49 pp., 23
figs.

Norris, Henry Waldo. 1925. Observations upon the pe-
ripheral distribution of the cranial nerves of certain fishes
(Amia, Lepidosteus, Polyodon, Scaphirhynchus , and Aci-
penser). J. Comp. Neurol. 39: 345-432, 12 text-figs., 7 pis.
(figs. 13-19).

, and Sally P. Hughes. 1920. The cranial, occipital,

and anterior spinal nerves of the dogfish, Squalus acan-
thias. J. Comp. Neurol. 31(5): 293-402, 53 figs.

Pancratz, D. S. 1930. The cranial nerve components in the
toadfish (Opsanus tau). J. Comp. Neurol. 50(3): 247-286,
2 pis.

Pinkus, Felix. 1894. Die Hirnnerven des Protopterus an-
nectens. Morphol. Arbeit. (Jena) 4: 275-346. 7 pis.

Ray, Dixie Lee. 1950. The peripheral nervous system of
Lampanyctus leucopsarus . J. Morphol. 87(1): 61-178, pis.
1-17.

Rosen, Donn E. 1964. The relationships and taxonomic po-

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKI1

53

sition of the halfbeaks, killifishes, silversides, and their rel-
atives. Bull. Am. Mus. Nat. Hist. 127(5): 217-268, figs. 1-
23, pis. 14-15.
. 1973. Interrelationships of higher euteleostean fishes.

pp. 397-513, 129 figs., 4 tables. //;, Greenwood, P. Hum-
phry, R. S. Miles, and Colin Patterson. Interrelationships
of fishes. Supplement no. 1 to Zool. J. Linn. Soc. 53: 536
pp.
, and Colin Patterson. 1969. The structure and re-

lationships of the paracanthopterygian fishes. Bull. Am.

Mus. Nat. Hist. 141(3): 357-474, figs. 1-74, pis. 52-78. ta-
bles 1-8.
Saxena, P. K. 1966. Cranial nerves of the common catfish.

Clarias batrachus (Linn.). Jpn. J. Ichthyol. 14(1/3): 91-98,

pis. 8-12.
. 1967. The cranial nerves of the mud ee\, Amphibnous

cuchia (Ham.). Acta Anat. 68: 306-320, 3 figs. [Summaries

in French and German]
. 1969a. The cranial nerves of Nandus nandus (Ham.)

and Xenentodon cancila (Ham.). Anat. Anz. 124(2): 142-
155, 3 figs.
. 1969b. The cranial nerves of Notopterus notopterus

(Pallas). Anat. Anz. 124(2): 198-209, 3 figs.
, and Rakesh K. Rastogi. 1968. The cranial nerves

of the flat-fish, Cynoglossus bilineatus (Lac). Annot. Zool.
Jpn. 41(2): 70-76, 4 figs.
Sheldon, R. E. 1914. Paraffine-Weigert methods for the
staining of nervous tissue, with some new modifications.
Folia Neurobiologica 8(1): 1-28.

Springer, Victor G., and Warren C. Freihofer. 1976.

Study of the monotypic fish family Pholidichthyidae (Per-

ciformes). Smithson. Contrib. Zool. 216: iv + 43 pp., 23

text-figs.
Stannius, Hermann. 1849. Das peripherische Nervensys-

tem die Fische, anatomisch und physiologisch Untersucht.

Rostock. 156 pp., 5 pis.
Stensio, E. A. 1947. The sensory lines and derma! bones of

the cheek in fishes and amphibians. K. Sven. Vetenskap-

sakad. Handl., ser. 3, 24(3): 195 pp., 38 figs.
Vasisht. H. S., and I. B. S. Uberoi. 1965. Anatomy of

Mystus seenghala (Sykes). IV. Nervous system. Res. Bull.

Panjab Univ. (new ser.) 16(1-11): 61-85.
Williams, T. W. 1943. A technique for the gross differential

staining of peripheral nerves in cleared vertebrate tissue.

Anat. Rec. 86: 189-194, 1 pi.
Winterbottom, Richard. 1974a. A descriptive synonymy

of the striated muscles of the Teleostei. Proc. Acad. Nat.

Sci. Phila. 125(12): 225-317, 56 figs.
. 1974b. The familial phylogeny of the tetraodonti-

formes ( Acanthopterygii: Pisces) as evidenced by their com-
parative myology. Smithson. Contrib. Zool. 155: iv + 201,

185 figs.
Young, J. Z. 1931. On the autonomic nervous system of the

teleostean fish Uranoscopus scaber. Q. J. Microsc. Sci.

(new ser.) 74: 491-535. 12 text-figs.

54

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

Abbreviations for Figures

A,, A2, A.j — divisions of the adductor mandib-
ulae muscle.

AA4, AA5 — m. adductores 4,5.

ADD OP — m. adductor operculi.

AAP2 — m. adductor arcus palatini anterior por-
tion.

AD HYO — m. adductor hyomandibularis.

ADD OP — m. adductor opercularis.

AN — anterior narial opening.

Anasto w — anastomoses with.

AWBl.2,3 — divisions of the mentalis muscle.

BB1, BB2, BB3— basibranchials 1, 2, 3.

br — branch.

br & vis tr of vag — branchial and visceral trunks
of nervus vagus.

CB1 to CB5— ceratobranchials 1, 2, 3, 4, 5.

CIR — a circular, roundish bundle of muscle on
top of m. transversus dorsalis.

Cor 1 to Cor 6 — branches of ramus ophthalmicus
trigeminus to cornea.

EM — longitudinal orientation of medial fibers of
the sphincter oesophagi.

EP1 to EP4 — epibranchial bones 1 to 4.

fac — facialis.

FR COM — frontal commissure of supraorbital
canal.

G — nervus glossopharyngeus (n. IX).

Gl — branch of m. glossopharyngeus to m leva-
tor internus 2.

G2 — ramus pretrematicus IX.

G3 — branch of IXth to m levator externus 1.

G5 — branch of IXth to muscles of gill filaments.

G6— branch of IXth to gill rakers.

G7 — branch of IXth to m. obliquus ventralis 1.

G8 — branch of IXth to m. rectus ventralis 1.

GAM — area of attachment of some gill arch
muscles.

GANG IX — petrosal ganglion of IXth cranial
nerve.

GG4 — ganglion of 4th vagal branchial ramus.

GLR — ramus posttrematicus of IX.

H AB — m. hyoidei abductores.

H AD — m. hyoidei adductores.

HB1 to HB3 — hypobranchial bones 1 to 3.

INFOl, 4 — canal neuromasts 1 and 4 of infraor-
bital canal.

101 to IOlflb. — branches of ramus buccalis fa-
cialis to lateralis organs (or to skin of cheek:
these branches actually belong to the r.
maxillaris inferioris trigeminus).

102 to I02f — branches of ramus mandibulars
trigeminus.

I02a — ramus opercularis trigeminus.

I02c, I02d, K)2e — to adductor mandibulae
muscle of cheek.

I02f, I02fl, 2, 3 — to tendinous mucosa near
ventral end of maxillary tendon and adja-
cent skin.

I02f4, a. b — to skin over articular and lip pad
at posterior end of lower jaw.

I02f5 thru I02f5e — to skin over articular, inter-
opercle, angular, anterior end of preopercle
and bases of anterior branchiostegal rays.

I02f6 thru I02f9 — to skin over ventral surfaces
of articular and dentary bones.

I02g, I02g2, I02g2a — ramulus mandibularis in-
ternus trigeminus (I02g) and branches to m.
protractor hyoidei and adjacent skin and
mucosa (I02g2) and m. intermandibularis
(I02g2a).

I02h thru I02j — branches of ramulus mandibu-
laris trigeminus externus (I02h) to lower
lips, labial cartilage, teeth, and skin near
symphysis of lower jaw.

103 and I03a to I03d — ramus maxillaris infer-
ioris trigeminus and its branches.

IX — nervus glossopharyngeus.

LL pore 1. 2. 3. 4 — lateral line canal pores 1 to
4 of dentary.

LEI, LE2, LE4 — m. levator externus 1, 2, 4.

LEP — m. levator posterior.

LGR — lateral row of gill rakers.

LI1 to LI3 — m. levator internus 1, 2. 3.

Lig I — palatomaxillary ligament.

Lig 4 — palatopalatine ligament connecting pal-
atine of each side across ascending process
of premaxillary.

m — muscle.

MGR — medial row of gill rakers.

MP1 to MP10 — lateralis organs 1 through 10 of
mandibulo-preopercular canal.

MTC — patch of free lateralis organs between
anterior ends of dentaries.

NLL — nervus linae lateralis vagi and some of its
branches.

NLL1 — horizontal septum lateral line nerve of
nervus linae lateralis.

NLL1 VI— 1st ventral branch of NLL 1.

NLL2 to NLL2b — the longitudinal collector lat-
eral line nerve (NLL2) and some of its
branches.

OBD3 — m. obliquus dorsalis 3.

OP — m. obliquus posterior.

OV1 to OV3 — m. obliquus ventralis 1 to 3.

P2 — branch of r. palatinus.

FREIHOFER: CRANIAL NERVES OF POLYCENTRVS SCHOMBVRGKll

55

PCI — m. pharyngoclavicularis internus.

PCE — m. pharyngoclavicularis externus.

PCL — vertical row of free lateralis organs in
front of preopercle.

PHI to PH3 — infrapharyngo-branchials 1 to 3.

PIV — pharyngo-intestinal trunk of nervus va-
gus.

PN — posterior narial opening.

POl — 1st lateralis organ of postorbital section
of cephalic lateralis canal system.

PPR — posterior palatine ramus.

PR HY — m. protractor hyoidei.

PRP — m. protractalis pectoralis.

PRPE — branch of ramus opercularis vagi to m.
protractor pectoralis.

PT1 — lateralis organ of posttemporal canal.

QTAW — quadrate tendon of mentalis muscle.

r — ramus.

RCOM — m. rectus communis.

r com v — ramus communicans from Gasserian
ganglion to truncus hyomandibularis.

RETD — m. retractor dorsalis.

r hyo — ramus hyoideus

RIN — r. intestinalis and r. cardiacus vagi.

RLA-OP — orbito-pectoral branch of ramus lat-
eralis accessorius (recurrent facial nerve).

RLA-PD — parieto-dorsal branch of ramus lat-
eralis accessorius.

r mand fac — r. mandibulars facialis.

r mand ext fac — ramus mandibulars externus
facialis.

r mand int fac — ramus mandibulars internus fa-
cialis.

r mand trig (102) — ramus mandibularis trigemi-
nus.

r op 1 thru r op 3b — branches of ramus oper-
cularis vagi to skin and mucosa of opercle
and part of subopercle.

r oper fac — ramus opercularis facialis.

r op sup fac — ramus opercularis superficialis fa-
cialis.

r oph sup fac — ramus ophthalmicus superficialis
facialis.

r ophth sup tri — ramus ophthalmicus superfici-
alis trigeminus.

r oper vagi — ramus opercularis vagi.

R SUPR 1 to R SUPR Id— branches of lateralis
portion of ramus supratemporalis vagi with
some general cutaneous fibers.

R SUPR 2 and R SUPR 2a— portion of ramus
supratemporalis vagi containing in part the
rami cutanei dorsalis vagi.

RSV — ramus supratemporalis vagi.

RV1, RV4, RV5— m. rectus ventralis 1, 4, and
5.

SIR — esophageal ramus of 4th vagal branchial
ramus.

SOI to S05 — canal neuromasts 1 through 5 of
supraorbital canal.

SORB 2 to S0RB2b— branches of truncus su-
praorbitalis to meninges, skin, and free lat-
eralis organs above orbit.

SORB3— joins RLA-PD intracranially.

SORB4 — branch of ramus ophthalmicus super-
ficialis facialis.

S0RB5 — branch of r. ophth. sup. trigeminus to
skin dorsal to orbit.

SORB6 to S0RB7 A— branches of r. ophth. sup.
trigeminus to skin of snout.

SORBS and SORB9— branches of r. oph. sup.
facialis to 1st and 2nd supraorbital canal
organs of frontal bone.

SORB 10, SORB1 1-1 la— branches of r. oph.
sup. trigeminus to skin and free lateralis
organs near nasal canal and to lateralis or-
gan of nasal canal.

ST1 — dorsalmost lateralis organ of supratem-
poral canal.

STL — vertical line of free lateralis organs in
front of supratemporal canal.

SYM TR — sympathetic trunk.

T — tendon.

TA1, TA3 — tendons of A, and A3 divisions of
m. adductor mandibulae.

TA W/33 + TA2— tendon of A2 and of AW/33 di-
visions of mentalis muscle.

TD1. TD2 — m. transversus dorsalis 1 and 2.

TH — truncus hyomandibularis.

TH1 — posterior palatine ramus.

TH2, TH3 — anterior and posterior parts of ra-
mus opercularis profundus facialis.

TH4 — ramus opercularis superficialis facialis.

TH4AA, TH4BB, TH4BB1, TH4BB2— branch-
es of r. oper. sup. fac. innervating lateralis
organs on opercle and subopercle.

TH5 — to canal organ #11 of mand.-preopercular
canal.

TH6 — to skin between opercle and interopercle.

TH7 — anastomoses with cutaneous branch from
IOlc.

TH8— to canal organ #10 of mand.-preopercular
canal.

TH9. TH9A. TH9B. TH9Bla-le. TH9B0,
TH9B02-05. TH9C. TH9C2. TH9D-TH9F.
TH10, TH10A-TH10B4, TH 11— ramus hy-
oideus and its branches.

56

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

THI2 — ramus mandibularis internus.

TH12A— TH12C — to mucosa of anterior part of
palate and to ectopterygoid teeth.

TH 13, TH 13 A-B, TH 14-15— branches of ramus
hyoideus.

TH16 — branch of ramus hyoideus anastomosing
with I02f.

TH 17-TH 17a, TH 18— lateralis branches of r.
mand. fac. to mand. preopercular canal.

TH18a — branch of combined r. mand. tri. & r.
mand. fac. to mucosa on medial side of den-
tary.

TH19, TH19a-TH19a4,TH19b-TH19b4,TH19b
4a — branches of combined r. mand.
tri. and r. mand. fac. to skin, taste buds,
gums of teeth, and mucosa of anterior part
of lower jaw.

TH20 — lateralis branch of r. mand. facialis to
mandibulo-preopercular canal.

TH20a-TH20c — to skin on ventral surface of
dentary.

TH21, TH21a, TH22— lateralis and cutaneous
branches of combined r. mand. tri. & r.
mand. fac. to mandibulo-preopercular canal
and to skin.

TH23, TH23a-b, TH24, TH24a, TH24b, TH25—
lateralis and cutaneous branches of com-
bined r. mand. tri & r. mand. fac.

tr — truncus.

TS1 — canal neuromast of first (and only) truncus
lateral line scale.

TV4, TV5 — m. transversus ventralis of the
fourth and fifth branchial arches, respec-
tively.

VI — 1st vagal branchial ramus. VI is the prefix
to all branches of this first ramus.

VIA — branch of 1st branchial ramus to levator
externus 2.

V1B — branch of 1st vagal posttrematic branchial
ramus to gill rakers.

VIC — to m. obliquus ventralis 2.

VIE — to 1st epibranchial gill rakers.

VIP — pharyngeal ramus of 1st vagal pretrematic
branchial ramus.

V1PO — 1st vagal posttrematic branchial ramus.

V1PR — 1st vagal pretrematic branchial ramus.

V2A — branch of 2nd vagal posttrematic bran-
chial ramus to m. levator posterior.

V2B — branch of 2nd vagal posttrematic bran-
chial ramus to m. levator externus 4.

V2C — branch of 2nd vagal pretrematic branchial
ramus to m. obliquus dorsalis III and m.
transversus dorsalis 2.

V2D — branch of 2nd vagal pretrematic branchial
ramus to m. transversus dorsalis 2.

V2E — branch of V2P to ceratobranchial gill rak-
ers.

V2F — branch of 2nd posttrematic vagal bran-
chial ramus to gill rakers.

V2G — branch of 2nd posttrematic vagal bran-
chial ramus to m. rectus communis.

V2H — branch of 2nd posttrematic vagal bran-
chial ramus to m. rectus ventralis 4.

V2J — branch of 2nd vagal branchial posttrema-
tic ramus to m. obliquus ventralis 3.

V2P — pharyngeal ramus of 2nd vagal pretrem-
atic ramus.

V2PO — second vagal posttrematic branchial ra-
mus.

V2PR — 2nd vagal pretrematic branchial ramus.

V3A — branch of 3rd vagal branchial ramus to m.
retractor dorsalis.

V3B — branch of 3rd vagal branchial posttrema-
tic dorsalis ramus to gill rakers.

V3E — gill raker branch of pharyngeal ramus of
3rd vagal branchial ramus.

V3P — pharyngeal ramus of 3rd vagal branchial
ramus.

V3PO — 3rd vagal posttrematic branchial ramus.

V3PR — 3rd vagal pretrematic branchial ramus.

V4A — to mucosa of roof of posterior end of
pharynx.

V4B — branch of 4th vagal posttrematic branchi-
al ramus to m. obliquus posterior and ad-
ductor 5.

V4C — branch of V4PO to teeth and mucosa of
5th ceratobranchial.

V4D — branch of V4PO to m. transversus ven-
tralis IV.

V4E — branch of V4PO to pharyngoclavicularis
externus and internus muscles.

V4PO — 4th vagal posttrematic branchial ramus.

V4PR — 4th vagal pretrematic branchial ramus.

X — nervus vagus.

la to lh — branches of ramus maxillaris trigem-
inus (coursing in ramus buccalis facialis) to
skin over cheek and part of preopercle.

3b to 3g — branches of ramus buccalis innervat-
ing free lateralis organs on orbitals and lach-
rymal.

3 BC — branch of 3rd vagal posttrematic bran-
chial ramus to m. adductores 4.

3 BD — branch of 3rd vagal posttrematic bran-
chial ramus to m. transversus ventralis 4.

fREIHOFER: CRANIAL NERVES OF POLYCENTR US SCHOMBURCK11

r maxillaris (103) 102b

inferioris v COR 6 r t

101c
I01d

I01d

I01e

I01f
I01f 1
I01f a

I01f b
r palatinus fac
IC3c 1

SORB 2b

101

101b

10

I03d
r palat

COR 4

r opercularis
trigeminus (I02a)

r mandibulars
trigeminus (102)

Figure 1. Polycemrus schomburgkii . Lateral view of branche- of infraorbital trunk to snout and suborbital regions. See
text and list of abbreviations.

58 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBVRGKI1

™ 4AA r com V

TH 5\ r op sup fac (TH 4)

tr hyomandibularis (TH)
r opercularis facialis (TH2)

TH 7 TH 10(rbuccalis accessorius)

TH 10B
TH11
TH 10B1

H 9B 1a
H 9B 1b

H 9B 1c

H 9B 1d

H 9B 1e
TH 9B 02

TH 9B 1e
TH 9B 02
TH 14

TH 9B 1e

TH 15
TH 9C

TH 10B 2

is internus
(TH 12)

mam
TH 16
TH 10B 3

anasto w I02f
TH 10B 4
anasto w I02f5 b

TH 9B 1e
TH 9B 05

TH 17

TH 9B 1e
r hyoideus

Figure 2. Polycentrus schomburgkii. Lateral view if branches of truncus hyomandibularis.

60 OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

61

S0RB 7 SORB 8 S0RB 7A C°R 2
SORB 5 \ L

RLA-OP

RAMUS
OTICUS

Tr supraorbitalis

FR COM

SORB 6B
SORB 6C

R OPH SUP FAC

R OPH SUP TRI

Figure 3. Polycentrus schomburgkii . Oblique view of supraorbital trunk looking towards roof of orbital cavity.

TH3

PREVOM

LOP

PARASPHENOID
NLL

PALATINE

tr

R PALATINUS

^SYM TR

V \\ # \\ lx

7^XUf G2 GANG IX
SYM TR
TH1
PSEUDOBRANCH

Figure 4. Polycentrus schomburgkii . View looking dorsally showing branches of truncus hyomandibularis and glosso-
pharyngeal nerves to palate and posterior floor of cranial area.

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

NLL2

RSUPRlc
RSUPRlb

RLA-PD

NLL2b

NLL1

NLL2a

RLA-OP

NLL2

RSUPRi
SUPR 2
SUPR 1
R SUPRATEMPORALIS VAGI

ROTICUS
TR INFRAORBITALS

Figure 5. Polycentrus schomburgkii . Lateral view of main divisions and some branches of supraorbital trunk, lateral line
nerves and supratemporal ramus of vagus nerve to dorsoposterior side of head.

r mandibulars
trigeminus (102)

Figure 6. Polycentrus schomburgkii. Lateral view of cheek area showing pattern of innervation to adductor arcus palatini
and adductor mandibulae muscles.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKU

63

RAMUS MANDIBULAR IS
INTERNUS FACIALIS

RAMUS MANDIBULARS TRIGEMINUS (102)
ARTICULAR-
RAMUS MANDIBULARS EXTERNUS TRIGEMINUS

RAMUS MANDIBULARS
EXTERNUS FACIALIS

angular

DENTARY RAMUS MANDIBULARS FACIALIS

RAMULUS MANDIBULARS INTERNUS TRIGEMINUS (I02G)

Figure 7. Polycentrus schomburgkii . Medial view of lower jaw showing innervation to mentalis division of adductor
mandibulae muscle.

102 j
TH19b2 ,02i\ J-1-^

TH!9b1

TH 19b3

^^I02g2

TH 20c

TH21

mand f ac ♦ 102 g
eckel s cartilage

ramulus mand ext tri (I02h)

Figure 8. Polycentrus schomburgkii. Dorsal view of branches of ramus mandibularis trigeminus and of r. mand. facialis to
anterior half of lower jaw.

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

LL pore 3 TH 20c

TH24

TH24a^

LL pore1^
TH24b
TH25

I02 g2

I02f8 r man tri (I02)
I02f
^TH16

^=V|02f5
^^^^r man fac
?M^z-- I02f5b
- I02 f5c

myoseptum

I02f5a
I02f6

myoseptum

I02f7

Figure 9. Polycentrus schomburgkii. Ventral view of branches of ramus mandibularis trigeminus and r. mand. facialis to
lower jaw.

TH19a2

102 f
TH19 ectopterygoid

I02 h / ,Q2h

TH 19b1
I02i

TH19a1

TH23-
TH 24
TH25""
102 g2a
TH 22a
TH19b

nd tri(l02)
02f1

r mand int fac
-quadrate

r mand ext fac

angular
articular

TH 17a

x Meckel's cartilage
I H 20a \dentary xTu 10

TH20c ™18

TH 20b canal pore

I02g2 TH19b4

Figure 10. Polycentrus schomburgkii. Medial view of lower jaw showing some innervation of dentary region.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

us

D ._

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

truncus hyomandibularis
r mandibularis facialis
TH 9A

r mand int fac

r mand ext fac

TH 9B

I02g2

r oper vagi

TH 8

r hyoideus (TH 9)

TH 9B 1a
TH 9B 03
TH 9B 02

Figure 13. Polycentrus schomburgkii. Medial view of hyoid arch and opercular bones showing distribution of ramus
hyoideus.

SUPERIOR RECTUS

NERVUS OPTICUS (Nil)

SUPERIOR OBLIQUE

INFERIOR 08L

INTERNAL RECTUS

CILIARIS BREVIS

NERVUS TROCHEARUS IN. IV I

CILIARIS LONCIJS

CILIARY GANGLION

GASSERIAN GANGLION

PROFUNDUS GANGLION

RADIX PROFUNDUS

NERVUS OCULOMOTOR IUS IN. Ill I

TRUNCUS CILIARIS PROFUNDUS

NERVUS ABDUCENS IN. VI )

INTERNAL RECTUS

RADIX LONGUS
EXTERNAL RECTUS

INFERIOR RECTUS

Figure 14. Polycentrus schomburgkii. Medial view of eyeball and eye muscles showing distribution of cranial nerves III,
IV, and VI, and ramus profundus.

FREIHOFER: CRANIAL NERVES OF POLYCEMTRUS SCHOMBURGKII

(.7

ciliaris longus

"ciliaris brevis

Figure 15. Potycentrus schomburgkii . Medial view of eyeball showing branches of ciliaris longus and ciliaris brevis of radix
profundus.

cor 2

cor 1

to skin

cor 6

cor 5

cor 4

Figure 16. Polycentrus schomburgkii . Lateral view of eyeball showing branches of supraorbital and infraorbital trunks
innervating skin and cornea.

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO 128

ST1

INF01

MP1

Figure 17. Polycentrus schomburgkii. Lateral view of head showing distribution of free lateralis organs (open circles),
canal neuromasts (paired triangles), and canal pores (black circles).

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

69

EUDOBRANCH

DORSAL HYPOHYAL

VENTRAL HYPOHYAL

Figure 18. Polycentrus schomburgkii. Lateral view of gill arches and pectoral girdle showing associated gill arch muscles.
Anterior to right.

-(I

OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

R OPER VAGI

V2J

Figure 19. Polycenirus schomburgkii . Lateral view of gill arches showing innervation.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGK1I

71

latera
medial gill fila

G5

al gill raker

G6

of 1st vagal branchial nerve

Figure 20. Polycentrus schomburgkii . Lateral view of ceratohranchial section of first gill arch showing details of innervation
of branches of glossopharyngeal nerve.

FREE LATERALIS ORGANS

NLLla

NLL1

NLL1 V1

Figure 21. Polycentrus schomburgkii . Lateral view showing trunk lateral line nerves.

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II. LEVATOR OPERCUL

PALATINE

MAXILLAR

RAMUS MANDIBULARS TRIGEMINUS 1102 I

Figure 22. Polycentrus schomburgkii . Lateral view of head showing opercular and superficial cheek muscles and jaw
ligaments.

/Z^RAMUS MANDIBULARS INTERNUS

RAMUS MANDIBULAR IS EXTERNUS

INTERMANDIBULARIS MUSCLE

Figure 23. Polycentrus schomburgkii. Medial view of jaws and associated bones showing tendons of jaw muscles and
mentalis (A„) muscle.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

73

1NM

-JJ

m. INTERMANDIBULARIS

MECKEL'S CARTILAGE

RAMUS MANDIBULARIS TRIGEMINUS

Figure 24. Polycentrus schomburgkii . Medial view of jaws showing insertion of adductor mandibulae muscles and tendons.

HYOIDE! A

HVOIDEI ABDUCTORES MUSCLE

Figure 25. Polycentrus schomburgkii. Medial view of opercle and hyoid arch showing hyohyoideus muscle.

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MESOPTERYGOID

ADDUCTOR ARCUS PALATINI POSTERIOR PORTION

HYOMANDIBULAR BONE
PREOPERCLE

AREA OF ORIGIN OF SOME GILL ARCH MUSCLES

m. ADDUCTOR HYOMANDIBULARIS

m, DILATATOR OPERCULI

m. LEVATOR OPERCULI

PSEUDOBRANCH
FIRST INFRAPHARYNGOBRANCHIAL

NERVUS VAGUS ( N. X )

BAUDELOT'S LIGAMENT

SYMPATHETIC TRUNK

NERVUS GLOSSOPHAKYNGEUS ( N. IX)
OTIC BULLA
PARASPHENOID
TRUNCUS HYOMANDIBULARIS

Figure 26. Polycentrus schomburgkii. Ventral view of palate and rear of cranium showing muscles of palate, hyomandibular.
and opercle.

RANCHIOSTEGAL RAY

HYOIOEI ABDUCTORES MUSCLE

Figure 27. Polycentrus schomburgkii. Ventral view of protractor hyoidei muscle, tip of lower jaw. and part of hyoid arch.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKII

75

nervus trochlears (l\l. IV

corpus cerebelli
eminentia granularis
nervus auditorius ( N. VIII )

nervus linae lateralis

NERVUS VAGUS ( N. X

olfactory organ
nervus olfactorius ( N. I )
m. superior oblique
exit from cranial cavity

cut end of anterior semicircular cana
cristae

medulla oblongata

Figure 28. Polycentrus schomburgkii. Dorsal view of brain and nerve roots.

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

.£.

FREIHOFER: CRANIAL NERVES OF POLYCENTRUS SCHOMBURGKIl

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OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES, NO. 128

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