Full text of "Journal of comparative neurology"

See other formats

pee
a eae te
veetetel,

. * 4
pk

a)
in

; Sire r
serene

4 4) £
Nf stot t : Teite es
LriTer blero. brn sl OL Lele 82 ¥LN,
steeantttttt

« +
Laie wUbaies
4 ‘

Leh
Ks

yt
*
bg!

Kage" rL9 KT
* eee ee F . “biale
C9185. 4,9) 818) Ol O14) B/S . o°4 © o[e: ‘i ra §
eee heh Ph aire te Lee i NY + of * i 4543 M Ni i it

“it - i fe ein ee ene “e j -* . 4
Leia. ¢ * . sfathtele le’

Litters:

OLS SL Fa ler are
"Er aTa el # hae.
Batt As erate ee Trelis Je tesey .
Cyr $14) $i 9) 4.4) Yoair ‘ 7 + fhe
Saab ene ta te te Se be bn 18 Oe
ee
th «
Tele

*) ri
i Sata taretareeal brace] oy “Pals “re
resseerassravefarats relegeteteteTarelateray seLtatenteert tah
* t? srerhrerey ef etelatele Alerele:

Pree
ay ye te TE ETE
PER PLPLYL

Ce oD
*
hs aeeeieesoe
eres ee ¢
arate

*
be ‘aTals ‘

e688
Hf ee 8 La * > 4 91 91F bhai q
sel eat tetatere eras eisiaee aibeeee ec ei aL
ei kly 94% 3 26 | {
Tate) neha’

ig 0 &
fala ela
(al eiela a
a nae
RTE Ce eS
1 Hs alec dee RE
pe ye a ale
Tele
*
Le
« ae @
relsc bse

eee ee ae

see
eicvet
AO

a-~e

s :
ee 4 8
Le Yl ele:

{ *

«
te. ae
> .

estetats tet

(ves

Sn, Poe ee
Aaeae?
oN

‘

= 3p

4 ald

THE JOURNAL

COMPARATIVE NEUROLOGY

EDITORIAL BOARD

Henry H. DonALDSON ApoutF MEYER

The Wistar Institute Johns Hopkins University
J. B. JoHNSTON OLIvER S. STRONG

University of Minnesota Columbia University

C. Jupson HERRICK, University of Chicago
Managing Editor

VOLUME 22

1912

PHILADELPHIA, PA.

THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY

CONTENTS

1912

No. 1. FEBRUARY

F. L. LanpacrE. The epibranchial placodes of Lepidosteus osseus and their
relation to the cerebral ganglia. Fifty-eight figures................... 1

Henry H. Donaupson. A comparison of the European Norway and albino
rats (Mus norvegicus and Mus norvegicus albinus) with those of North
America with respect to the weight of the central nervous system and
foucranial capAaciiys. SHIVE MOUTCS. sz oga02 thas <1 eke wie 5 Sool Soe bis sss ane prea 71

No. 2. APRIL

Henry O. Feiss. Experimental studies of paralyses in dogs after mechani-
cal lesions in their spinal cords with a note on ‘fusion’ attempted in
the cauda equinas or the sciatic nerves. Twenty-seven figures........ 99

EvizABETH Hopkins Dunn. The influence of age, sex, weight and relation-
ship upon the number of medullated nerve fibers and on the size of the
largest fibers in the ventral root of the second cervical nerve of the

aT OM Tal Geek BRoll OUR CS ee earn caso anes ae eaet a sce tesa Ao cata or att Sia 2 aw 131
S. WatTerR Ranson. The structure of the spinal ganglia and of the spinal
NEEVER. - Mifteen MRUTes:o).ni.s aca ee ora ees cries os Circe Serna male Si 159
Nowe. JUNE

RauteH Epwarp SHELDON. The olfactory tracts and centers in teleosts.
IDOE =tWOrPLabes.<.s 0. cis 2 sc ere uti aa tered icra, So Stee ASO lou! Seis cise « Se 177

No. 4. AUGUST

J. B. Jounston. The telencephalon in cyclostomes. Forty-one figures.... 341

ili

iv CONTENTS
No. 5. OCTOBER

Samuret C. Parmer. The numerical relations of the histological elements
in the retina of Necturus maculosus (Raf.). Twelve figures........... 405

F. W. Carpenter. On the histology of the cranial autonomic ganglia of
the sheep. Ten figures. : <<: 40.) .det steuyemn seis eee tet ree eee 447

F. L. LANDACRE AND Martz McLEeLuan. The cerebral ganglia of the em-
bryo of-Rana pipiens: Eleven figures. .2) 202). soos <li «ene re 461

No. 6. DECEMBER

S. Watter Ranson. Degeneration and regeneration of nerve fibers.
Twenty mime mapurenin. sees sec te oe ie as ily te ee ae one ke eee 487

Ezra ALLEN. The cessation of mitosis in the central nervous system of
the albinowat; * Twenty-two figures. 3.0.02. 25, Soh. feta ee eee 547

THE EPIBRANCHIAL PLACODES OF LEPIDOSTEUS
OSSEUS AND THEIR RELATION TO THE
CEREBRAL GANGLIA

F. L. LANDACRE

From the Department of Zoology, Ohio State University

FIFTY-EIGHT FIGURES

CONTENTS
TT yavi aa GC LSUC CHET NO Ni pak oe ape eet aca Paey es eeepc ro ee ME eI co dice 1
Miche rtaleee eer vty thces tee iad ceeds oy tM Senta Aho eerie: seed aki ote 2 2c on ee 4
hes Obmmyembrnyou(eenen all) Mase yeve er ci aries sels ket betel teiaielios cask oe seer 6
Rheweangliaand nerves of the: 10 mm: embryo.)..5.59. 2502. 8.525: ..4. eta: 8
SAE OLOMUIN Gus tea el ON. sepa: Mie Sere eee ema Ries cet saves cS ee, eee 9
MHcMGASseriat Mane MOMt mesos teats ney et pews oats Poe eke ee cee eee 10
pwnexdorsoclareralleyililte trae) 2s. we Seatac bCe a ah A eet a Angee re se eee 12
Pe lihesceniculaberman maar, peg is opts! dee ees Sh ences os kai’ x hs he 13
MND eee MUEO=la heb Alle VELLA. 5 seen Rees a tote cua oho. RPI ieie recited > Cnet neers Siksin wescis © 14
PCE TaniOny? GANCMOMS 2 j.2 62S see ee oe 5 oS a fe) octet Se eS 16
herstossopharyngeus: camehion, co feeu).8-ieid een eles eee SRE. Set 16
ULSD OPTIC oT I eae See |, ce) ee NS Oe RL eRe? Bree 17
Tears) ey eviah ate D ee anal ee mR dA es = Sata Ue ee Re Ons cory cere 6 ease 18
Setrecnienmchiicrie canola OP ON. cote ita) Lets Cee oC oes see 6 eokn e ocn sm OE 18
Detailed description of the epibranchial placode of VII...................... 19
Mheclater history, ofuhe epibranchiall placodevofavilly. =. +. ... 425... sso 22
he origin col thesepioranchtal, placode: of Vales... os 45 ac noe stia ss Sede Se 23
Summary of the history of the first epibranchial placode.................... 30
Mhe-epibranchialsplacodetot the LXenerveweene sss eo aon ee eee 32
Mheshrsixepibranchialaplacodexot: them xterm n er) ries seers inners 36
Rhersecconcseplbraneimmak placode ofaihnemNerees rit. poeta a eee re oe 38
The third and fourth epibranchial placodes of the X......................-- 38
Geuersisummary ind discussions: eeaweee sce. fe chee eee naee o> as 39
ImiteratwnTereited!..:<:.- ists S.A A ae eee tne chad cre Stat eae es 48
INTRODUCTION

A description of the origin and fate of the epibranchial pla-
codes of Lepidosteus was undertaken with the object of extend-
ing our knowledge of the part these placodes play in the forma-
tion of the cerebral ganglia. Ectodermic thickenings, in the

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 1

FEBRUARY, 1912

Z F. L. LANDACRE

region of the gill slits, concerned in the formation of the cerebral
ganglia, have been known for a long time through the work of
Beard (’85), Van Wijhe (’82), Froriep (’85) and others and seem
to be present in all classes of vertebrates including the higher
mammals.

The mode of origin of the placodes in many forms is such that
it is difficult to determine whether there is an actual contribu-
tion of cells by the placode to the corresponding ganglion. In
most types described, the neural crest which enters into the
composition of a given ganglion such as the VII, IX and X, comes
into contact at its ventral border with the epidermis just dorsal
and posterior to the corresponding gill pocket, and it is difficult
to determine just how far the contact is due to the lateral exten-
sion of the neural crest portion of the ganglion as contrasted with
the mesial ingrowth of the cell mass derived from the thickening
of the ectoderm or placode.

In some types such as the catfishes (Landacre, ’10), however,
the mode of origin of the epibranchial placodes is such that the
conditions are easy to interpret. The epibranchial placodes
of the VII, IX and first two branchial ganglia of the X arise free
from contact with the endodermie gill pockets and become de-
tached from the epidermis en masse and are added to the remain-
ing portions of the cerebral ganglia in such a manner that they
ean be followed with ease up to the time they become fused with
the neural crest ganglia. The last two branchial ganglia of the
X do not appear until the neural crest ganglia in their downward
growth approach the skin, and consequently do not furnish such
good evidence of the integrity and continuity of their placodes.
All these cell masses derived from the placodes, except in the
case of the IX, become indistinguishably fused with the general
visceral ganglia derived from the neural crest or its homologue
in the lateral mass.

The condition of the epibranchial placode in the [X ganglion
of Ameiurus is of the greatest importance in determining the
significance of these structures. The visceral portion of this
ganglion seems to come exclusively from the epibranchial placode

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 3

of the first true gill and the visceral portion of the ganglion is
detached from the lateralis portion. Herrick (07) found only
special visceral or gustatory fibers arising from the visceral gang-
lion so that, since the visceral portion of the ganglion is exclu-
sively placodal in origin, we are warranted in concluding that
the epibranchial placodes give rise to those ganglionic cells from
which gustatory fibers arise. This conclusion is strengthened by
a number of facts that need not be repeated here. It does not
seem an unwarranted conclusion that this is the function of the
epibranchial placodes in all classes of vertebrates, although its
demonstration in the higher vertebrates will always be a differ-
cult undertaking, owing to the fact that the relations of the pla-
code to the general visceral ganglion rarely seem to be so diagram-
matic as in Ameiurus and that it is extemely difficult to secure
a series of embryos of the higher vertebrates in stages sufficiently
close to follow all the changes, since these series must in the
lower forms, at least, be as close as four hours.

These facts emphasize the necessity of clearing the problem
up as far as possible among the lower vertebrates, where series
can be secured at sufficiently close intervals and where we should
expect to find simpler relations owing to the generalized condi-
tions. of the peripheral nervous system. Of equal importance
with the two facts just mentioned, however, is that of the hyper-
trophy of some of the components of the peripheral nerves, espec-
ially among the Ichthyopsida. This is probably the reason for
the diagrammatic simplicity of the special visceral system of
Amelurus.

While Lepidosteus was taken up primarily because it is a
generalized type, it appears that there is a beautiful example of
hypertrophy in the case of the visceral portion of the VII ganglion
as compared with the same ganglia in the IX and X. This is
probably associated with the elongation of the head and the
consequent increase in the area supplied by the VII nerve.

One of the principal difficulties encountered in the study of
the placodes in Lepidosteus arises from the fact that the endo-
dermal evagination from the pharynx is long anterio-posteriorly,

4 F. L. LANDACRE

and seems to encroach upon the territory occupied by the ecto-
dermic evagination forming the placode; at least the placode is
so closely applied to the posterior surface of the pharyngeal pocket
that it is often difficult and sometimes impossible to tell where one
ends and the other begins. Aside from this feature the condi-
tions are quite similar to those found in Ameturus with the excep-
tion that the visceral portion of the IX is not purely placodal in
origin and that the placode of the VII nerve is much larger in
Lepidosteus than in Ameiurus. In view of these facts I shall
describe the placode of the VII nerve in detail, and treat the re-
maining placodes briefly.

MATERIAL

The material consists of thirty-three stages taken at intervals
of six hours from one lot of eggs. Usually this would be too long:
an interval to follow accurately the changes in the cerebral gan-
glia but, by cutting a large number of series of any given age, it
is rare that one cannot pick out some one of a given series that
is as far advanced or even further advanced than the youngest
stage of the next older series; so that if the series are sufficiently
numerous they become practically continuous. The sections
were cut 6 uw thick and stained in bulk in Delafield’s haematoxylin
one-sixth the strength of the stock solution, for twenty-four hours.
This gave a much better differentiated stain than when sections
were stained on the slide and owing to the amount of yolk gran-
ules present is much superior to Heidenhain’s stain.

Table 1 shows the age, length and increments in age and length
of embryos of Lepidosteus osseus ranging from 100 hours after
fertilization to 272 hours after fertilization. Several series
younger than 100 hours are referred to in the body of the paper
but are not included in the table because they had not been freed
from the membranes before fixation and consequently could not
be measured accurately. They are referred to by age only.

LEPIDOSTEUS

THE EPIBRANCHIAL GANGLIA OF

29% | VIG| 96T| T6T | PST | SAT} 99T | O9T | FST) SFE} PT] LZEL} OSL | F0GE | ZIT | 9OT \OOT/ Say ur uOTQezr
| | | -[I}10} WlOIy os

tS &€ of Te | 08 66 82 13 92 SS ¥G £@ Go 1% 02 61 8T

Sa1lugs JO YaaWON |

‘woynzyrdas Lazfo SINOY BLE 07 UOY
~pzyijlaf sazfo sinoy Qo] Wwouf Bur.buns snasso snajsopidaT fo sohiqua fo yjbua) pun abp ur squawmasour pun y}bua) ‘abo ay) Buinoyy

T HTaVb

6 F, L. LANDACRE

THE 10 MM. EMBRYO (GENERAL)

Owing to the fact that the nerve components of the adult
Lepidosteus have not been worked and that there are some pecu-
liarities in the size and arrangement of the ganglia and nerves, it
will simplify the description of the placodes to give a general
account of structures and to give a rather complete account of
the gangla and nerves of some stage, for which I have selected
the 10 mm. embryo.

This stage represents an intermediate condition in theforma-
tion of the epibranchial ganglia; the placodes being completely
detached from the epidermis in the geniculate or VII ganglion,
in process of formation in the IX or petrosal and first two epi-
branchial ganglia of the X, while the two remaining epibranchial
placodes of the X are not yet present, there being only three well
defined gill bars.

The general form of the anterior end of the body is quite char-
acteristic as shown in fig. 1. The anterior end of the head has
a sharp downward flexure beginning in the region of the infun-
dibulum and ends in a prominent sucking dise. Directly over
the posterior end of the infundibulum lies the mesencephalon
which marks the highest point on the dorsal surface of the body.

The mouth is open and the pharynx has a cavity to a point
just posterior to the third gill. Neither teeth not taste buds
can be detected in the oral cavity or pharynx.

No cartilages are present at this stage, although the primordia
of both cartilaginous and muscular structures can be identified
in condensed masses of mesoderm.

The olfactory capsule has no cavity and is attached to the
ectoderm throughout almost its whole length. Both roots of
the olfactory nerve are well formed, that is, fibrillated and there
are a number of loose cells lying around the nerve that probably
develop later into the ganglion of the nervus terminalis. The
optic vesicle is large, and elongated slightly in its anterior-pos-
terior axis.

The auditory vesicle is a simple sae slightly elongated from
anterior to posterior and has a short ductus endolymphaticus.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS if

The supra-orbital, sub-orbital, mandibular and body sensory
lines are present (figs. 6, 7, 15) and well defined and the position
of some of the lateral line organs can be determined, although
they are not well differentiated and not all of them are present,
even on the head. The epidermal thickenings (figs. 8 and 9)
forming the caudal extension of the epibranchial placodes are
present and extend from the point of origin of the epibranchial
placodes of the VII and IX nerves. They can be distinguished
histologically from the primordia of the lateral lines in both the
VII and IX nerves, and in the case of the IX, lie at a lower level
than the primordia of the lateral lines.

The brain (fig. 1) at this stage shows a few of the peculiarities
that are so pronounced in the adult Lepidosteus. The three
primitive brain vesicles are still present. The telencephalon is
not sharply separated dorsally from the diencephalon; in fact,
except for arbitrary landmarks it is not possible to define the two
divisions of the primitive prosencephalon. The epiphysis and
dorsal sac are present at the boundary between the thin walled
prosencephalon and thick walled mesencephalon, but the para-
physis is not present and appears first in an embryo of 11 5 mm.
as a definite evagination, although its position can be determined
somewhat earlier as a thickened: area in the roof of the prosence-
phalon. With the appearance of the paraphysis comes the ele-
vation and broadening of the thin roof of the telencephalon which
marks it off as distinct from the diencephalon.

Ventrally the hypophysis is well developed and there is a marked
flexure in the floor of the brain directly under the mesencephalon
and directly over a point just anterior to the posterior end of
the hypophysis. The pituitary body is well developed at this
stage. The mesencephalon is well developed and rises consider-
ably above the level of the roof of the brain and consists of a large
flattened vesicle. which extends laterally over the anterior end
of the metencephalon and has uniformly thick walls (figs. 6 and
7). These lateral lobes of the mesencephalon completely con-
ceal the anterior end of the metencephalon from the dorsal sur-
face. The roof of the brain is of uniform thickness from the
region of the epiphysis to the posterior end of the mesencephalon.

8 F. L. LANDACRE

The anterior end of the metencephalon (figs. 6 and 7) consists
of two lateral lobes with thick dorsal and ventral walls but with
thin lateral walls. These, as mentioned above, are overhung by
the broad flat mesencephalon. The anterior ends of these lobes
are almost in contact with the posterior ends of the optic vesicles
(fig. 1). At a point dorsal to the posterior end of the hypophysis
they fuse on the median line and at a level with the entrance of
the root of the Gasserian ganglion their cavities become conflu-
ent with the median ventricle. The roof of these vesicles is
thick from their anterior end to a point just posterior to the pos-
terior end of the mesencephalon. These two thick walled vesi-
cles I take to be the lateral lobes of the cerebellum and the
thickened roof of the anterior end of the metencephalon, lying
under the posterior end of the mesencephalon and above the
unpaired ventricle of the brain, the middle lobe of the cerebellum
(valvula cerebelli). From the posterior end of the mesencephalon
the roof of the metencephalon has the usual character of the
medulla.

THE GANGLIA AND NERVES OF THE 10 MM. EMBRYO

Since the components of the cranial nerves in the adult
Lepidosteus have not been worked out, certain difficulties pre-
sent themselves when one attempts to identify the ganglia and
nerves of the 10 mm. embryo. Some of these difficulties will
appear in the description. For the most part, however, the iden-
tification of ganglia and nerves and even the identification of
the components can be made with ease, owing to the isolated
position of the ganglia and the solitary course pursued by com-
ponents which are later combined into mixed nerve trunks. In
the main, the position of definite ganglia is remarkably constant
among the Ichthyopsida. The most striking differences among
ganglia are three: (1) the presence or absence of the profundus
ganglion; (2) the position of the ventro-lateral lateralis of the
VII; and (3) the extent to which the branchial ganglia of the
vagus are distinct. The profundus is present in Lepidosteus.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 9

The ventro-lateral lat. is mesial to the geniculate, while it is
lateral in the Amphibia (Coghill, 702); and lastly the branchial
ganglia of the X, in contrast with the Amphibia, are fairly dis-
tinct.

The branchial ganglia of the 10 mm. embryo are in an inter-
mediate stage, as stated above, the branchial ganglion of the VII
being completely formed, or rather detached from the epidermis,
and the last two branchial ganglia of the X not yet formed owing
to the absence of the last two gills. The same statement can be
made of the ganglia as a whole. The V, VII, VIII and IX
ganglia are definitely outlined, while the posterior portion of
the X, the visceral portion, is not definitely formed.

The general visceral and general somatic ganglia which arise
from the neural crest pass through a stage when their cells are
quite loosely arranged and their boundaries are indefinite, so
that, during the early stages in the formation of neural crest
ganglia it is difficult to determine the exact limits of their bound-
aries. The general visceral X is in this condition in the 10 mm.
embryo. If one chooses an older embryo, however, in which
the X ganglia are fully formed, the V and VII ganglia are fused to
such an extent that it renders their description difficult unless
the nerve components are readily separable by differences in
size. This condition is not reached in a 6-inch Lepidosteus.
The process of fusing of ganglia is particularly true in the case of
the lateralis VII and the auditory. There is usually a brief
period during the growth of these ganglia when their boundaries
can be made out; but preceding and following this period the
general visceral VII, lateralis VII, and auditory are likely to be
more or less fused.

The profundus ganglion (ganglion mesencephali; trigeminus I)

This ganglion lies dorsal to the posterior portion of the optic
vesicle (figs. 1, 4, 5). It is an elongated cord-like mass of cells
placed diagonally in the mesoderm between the posterior portion
of the optic vesicle and the mesencephalon. ‘The anterior end

10 F. L. LANDACRE

extends dorsal to the upper border of the vesicle and the posterior
end lies at a lower level. The nerve trunk (ophthalmicus profun-
dus) which arises at the anterior end of the ganglion can
be followed forward at this stage to a point over the anterior
end of the lens where it becomes so attenuated that it cannot be
followed further.

The nerve forms a gentle curve corresponding to the dorsal
surface of the optic vesicle and maintains a constant position
over the middle of the optic vesicle. The ophthalmicus profun-
dus does not at this stage come into contact with either the
ophthalmicus superficialis VII or the ophthalmicus superficialis
V and is presumably a pure general somatic nerve, although in
the early stages of the formation of the ganglion (82 hours) there
is a pronounced contact with the epidermis, but whether this
is placodal in nature or not has not been determined. The root
of the profundus arises from the posterior end of the ganglion
and passes back and down arching under the lateral lobes of the
metencephalon which it enters from the ventral surface. The
root forms a gentle curve down and back reversing the relations
of the trunk. At the middle of its course the root comes into
intimate relations with the third nerve, and somewhat further
posterior, with the ciliary ganglion also.

The Gasserian ganglion (trigeminus IT)

This ganglion (fig. 1) in the 10 mm. embryo is a large oblong
ganglion placed diagonally in the mesoderm with its anterior end
at the side of the oral cavity and above the level of the roof of the
oral cavity. It is nowhere in contact with the epidermis. It
extends from a point just anterior to the pituitary body, where it
is located under the posterior portion of the optic vesicle, back to
a point at the level of the anterior end of the dorso-lateral por-
tion of the lateralis VII ganglion. It is not in contact with either
the profundus (trigeminus I), or the geniculate ganglion of the
VII, nor with the dorso-lateral VII. The ganglion is compact
and definitely outlined. Its root is at the posterior end and is
quite short, the ganglion cells at this point being closely attached

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS vl!

to the ventro-lateral wall of the medulla at a point opposite the
posterior end of the mesencephalic roof.

There are two well defined fibrillated nerves arising from this
ganglion at this time, a supra-orbital trunk (ophthalmicus super-
ficialis trigeminus), and an infra-orbital trunk (truncus infra-
orbitalis), which splits up into the maxillary and mandibular
trunks.

The supra-orbital trunk (fig. 1) arises from the dorsal surface
of the posterior end of the ganglion and runs upward and slightly
forward and becomes so attenuated that it cannot be followed as
far forward as the posterior border of the optic vesicle. There
is consequently no connection between supra-orbital V and the
profundus, such as we see later when these two nerve trunks come
to lie closer together.

The infra-orbital trunk is much larger and longer. It arises
from the extreme anterior and ventral end of the ganglion. It is
separated from the point of origin of the supra-orbital trunk by
the whole length of the ganglion. This condition is of course
temporary, since the Gasserian ganglion becomes shorter as it
becomes older, and the two points of origin are brought closer
together. Near its point of origin the infra-orbital trunk divides
into two branches, a dorsal, the ramus maxillaris V (figs. 4 and 5)
and a ventral, the ramus mandibularis V. The ramus maxil-
laris pursues a course forward under the optic vesicle at the level
of its point of origin and can be followed to the anterior border
of the vesicle. The ramus mandibularis V runs directly ventral
into the mandible. All the nerves arising fromthe Gasserian
ganglion, owing to their freedom from contact with other nerves
and ganglia, are at this time pure general somatic nerves.

The VII ganglion is composed, as usual among Ichthyopsida,
of three more or less distinct masses; a visceral ganglion, the genic-
ulate, and two lateralis ganglia, the dorso-lateral and ventro-
lateral. There is more or less fusion between these ganglionic
masses as well as with the auditory ganglion at various stages of
their growth and migration into the adult condition; so that it
will be easier to describe them in the order of their simplicity.

12 F. L. LANDACRE

The dorso-lateral VII

This ganglion (figs. 1, 8, 9) is an elongated rod-like mass
occupying a position at the side of the anterior end of the
medulla on a level with the floor of the medulla and between
it and the epidermis. Its anterior end reaches as far forward
as the root of the Gasserian, being situated of course more
laterally, and its posterior end reaches posterior to the anterior
end of the auditory vesicle and lies between the auditory
vesicle and the medulla. The anterior end of the ganglion lies
near the skin, while the posterior end lies near the cord, so that
on a frontal section, it has a position diagonal to the longitudinal
axis of the body. Its root enters the medulla along with the
roots of the geniculate and ventro-lateral ganglion. It main-
tains about the same level dorso-ventrally throughout its course
lying parallel with the long axis of the body. The posterior end
of the ganglion comes into close contact with the posterior end
of the geniculate and the anterior end of the auditory, the root
fibers passing dorsally from the cells along the anterior end of
the auditory ganglion.

There are three fibrillated nerves arising from this ganglion
at this stage; a supra-orbital ramus, an infra-orbital ramus,
and the ramus oticus. The first two arise from the anterior end
of the ganglion and shortly beyond their origin from the ganglion
come closely into contact with the skin, where they innervate
lateral line organs anterior to the position of the ganglion.
Neither of these rami comes into close relation with the corre-
sponding rami of the Gasserian, so that we do not have true
supra-orbital and infra-orbital trunks at this time. The supra-
orbital ramus (lateralis portion of ramus ophthalmicus super-
ficialis VII, figs. 4 to 7) arises from the dorsal portion of the ante-
rior end of the ganglion, pursues a course diagonally forward and
upward innervating lateral line organs of the supra-orbital line.
It arches over the optic vesicle and can be traced with certainty
as a fibrillated root to the anterior end of the optic vesicle. It
always occupies a position quite close to the epidermis.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 13

The infra-orbital ramus, ramus buccalis (figs. 4 to 7), origin-
ates from the ventral portion of the anterior end of the ganglion
and pursues a course downward and forward in close contact with
the skin where it can be followed as a fibrillated cord to a point
near the anterior end of the optic vesicle. It innervates lateral
line organs of the infra-orbital line anterior to the position of the
ganglion. The ramus oticus is represented by a small twig
arising midway between the anterior and posterior ends ofthe
ganglion. Itsupplies the last lateral lineorganin the infra-orbital
line. The twig runs laterally from the ganglion and passes under
the anterior end of the auditory capsule and can be followed easily
throughout its whole course at this stage.

The geniculate ganglion

The geniculate ganglion is an elongated mass of cells placed
diagonally in the body with the anterior end situated somewhat
more ventrally and lying directly on the dorsal surface of the
pharyngeal pocket (figs. 1 and 8). The anterior end of the
ganglion lies as far forward as the posterior end of the Gasserian.
The posterior end of the ganglion rises to the level of the base
of the medulla and its root enters the medulla along with those
of the dorso-lateral and ventro-lateral ganglia.

It is throughout part of its extent (fig. 9) wedged in between
the dorso-lateral ganglion and the ventro-lateral ganglion, to be
described in the next section, and its posterior end comes closely
into contact with the auditory. The geniculate ganglion is
double in composition. The posterior portion, derived from the
neural crest, 1s definitely outlined and circular in form andseems
to be purely general visceral in composition. The anterior end,
which contains cells derived from the placode, is less regular in
form and incloses or has attached to its ventral surface and
resting directly upon the endoderm of the pharyngeal pocket a
mass of cells which projects laterally giving a ‘‘comma’’ shape
to the ganglion in transverse section( fig. 8). The laterally pro-
jecting mass is derived from the epibranchial placode and can be
distinguished both by its color and position of its cells. The

14 F. L. LANDACRE

placodal cells represent the special visceral portion of the ganglion
while the remainder is general visceral. This placode is to be
followed in detail later as well as similar cells in the IX and X,
and will not be described more fully here.

Two nerves arise from this ganglion. The truncus hyoman-
dibularis arises from the ventral border of the ganglion about
one-third of its length from the anterior end and runs ventro-
laterally from its point of origin.

The truncus hyomandibularis contains lateralis fibers derived
from the ventro-lateral ganglion in addition to those derived from
the geniculate. At the level of the floor of the pharynx it divides
into two rami, the dorsal (ramus mandibularis) turning cephalad
and the ventral ramus (ramus hyoideus facialis) running directly
ventral.

A second smaller nerve (the ramus palatinus facialis) arises
from the anterior end of the ganglion and pursues the course
usual in teleosts following the roof of the pharynx and oral cav-
ity forward to the level of the olfactory capsule. It seems to
be accompanied throughout the proximal part of its course by
the motor trunk of the facialis which supplies the muscle adduc-
tor arcus palatini and the relation of the two components at
their exit from the ganglion is somewhat peculiar, in some series
the visceral fibers having the appearance of entering the lateral
line ganglion (ventro-lateral). In other series of the same age,
however, one can trace the visceral component into the anterior
end of the geniculate while the motor component passes further
caudad and enters the ganglion from the ventro-mesial side where
it joins the motor trunk running out with the truncus hyoman-
dibularis.

The ventro-lateral VII

This ganglion (figs. 1 and 9), as I have identified it, lies on
the mesial side of the anterior third of the geniculate, partially
inclosed in a crescent shaped depression of the geniculate. This
ganglion has a very characteristic appearance. The interior of
the ganglionic mass is usually free from nuclei, all the cells being
arranged radially with the small ends directed centrally (fig. 29).

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 15

The whole ganglion in embryos of 10 mm. is not usually more
than one-third as long as the geniculate, but this ratio varies,
since the ganglion is sometimes triangular with the smaller end
extending back into the truncus hyomandibularis. In older
embryos the ganglion is always triangular and the posterior end
grows posterior and ventral to the geniculate, thus simulating the
relations in Menidia (Herrick, ’99), although the greater portion
of the ganglion retains its position mesial to the geniculate. The
fibers coming from the ganglion, mentioned in the preceding
section as running out in the hyomandibular nerve, arise from
the extreme posterior end of the ganglion and run into the hyo-
mandibular on the ventral surface of the visceral fibers. The
root arises here also and arches around the mesial surface of the
geniculate ganglion and enters the medulla along with those of
the dorso-lateral ganglion.

The position of the ventro-lateral panelion in Lepidosteus
differs from the position in Menidia (Herrick, 799) and in the
embryo of Ameiurus (Landacre, 710) and in the Amphibia Cog-
hill (02 and ’06). In the embryo of Ameiurus (56 hours) the
ventro-lateral ganglion lies posterior to the geniculate, in Meni-
dia posterior and mesial, while in the urodeles it is lateral (exter-
nal) to the geniculate. There seems to be.no other case recorded
where it is directly mesial to the geniculate.

The fact that the nerve components have not been worked and
consequently one cannot trace the ganglion back to this stage
from an older series, renders the identification of this ganglion
more difficult than in such cases as the Gasserian and dorso-
lateral, where the ganglia are distinct and their nerves contain
only one component which can be traced to its peripheral dis-
tribution.

Since, however, the placodal portion of the geniculate is quite
distinct and its history can be traced, it becomes an important
factor in the differentiation of the geniculate and ventro-lateral
ganglia. Notwithstanding the rather unusual position of the
ganglion identified as ventro-lateral, the following facts seem to
warrant the identification:

(a). The two ganglia are quite distinct histologically. |

16 i F. L. LANDACRE

(b). The epibranchial placode is added to the one identified
as geniculate, or general visceral, as in the IX and four branchial
ganglia of the X.

(ec). The ramus palatinus, which does not contain lateralis
fibers in any type, arises from the geniculate.

(d). The ganglion identified as ventro-lateral seems to send
all its fibers into the hyomandibular.

(e). Inthe later stages of the ventro-lateral ganglion it assumes
a position more ventral and posterior to the geniculate as in Meni-
dia and in Ameiurus.

The auditory ganglion

The auditory ganglion (fig. 1) is a large comma-shaped mass
with the large end directed forward and the smaller end extend-
ing caudad. The large anterior end is closely attached to the
posterior end of the geniculate and to the ventro-lateral VII.
The root enters the medulla from the anterior end and a fibril-
lated trunk enters the auditory capsule at the middle region of
the ganglion.

The glossopharyngeus: ganglion (petrosal and lateralis portion)

This ganglion (figs. 1 and 10) is club-shaped with the large end
projecting forward and downward and is attached at its extreme
anterior end to a mass of cells (placode II) proliferated from the
ectoderm at the posterior and dorsal portion of the pharyngeal
pocket of the first true gill. The posterior attenuated portion
arches up around the posterior surface of the auditory capsule
and enters the medulla at a point almost directly dorsal to the
anterior end of the ganglion. Just before it enters the medulla it
passes into a well defined mass of cells. This is not a ganglion
however, since in later stages there are no ganglion cells in this
position and the thickness of the root at this point as shown in
fig. | is undoubtedly due to the exit of motor fibers and the pres-
ence of the root of the lateralis X ganglion which enters at this
point. After the lateralis X root becomes more completely

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTFUS 17

medullated the appearance of the proximal portion of the root
of the IX changes completely and there is no connection between
IX and X except through the lateralis X root which runs forward
as in Ameiurus from the lateralis X ganglion to enter near the
entrance of the IX root.

The glossopharyngeal ganglion contains three components, (1)
the general visceral, (2) the placodal (special visceral or gusta-
tory) and (3) lateralis cells. The lateralis portion of IX, in the
10 mm. stage and in preceding stages, is quite distinct in outline
from the visceral portion and occupies the dorso-lateral portion
of the IX and can be positively identified by the ramus supra-
temporalis which innervates a lateral line organ lying just lateral
to the ganglion in the same transverse level. The anterior por-
tion of the ganglion is composed of general visceral cells derived
from the neural crest, and of the placodal portion which can be
distinguished both by color and form of cells, while the posterior
portion is composed of the general visceral cells and lateralis cells.
Two nerves are present at this stage; the truncus glossopharyn-
geus, arising from the anterior end of the ganglion and running
ventrally into the first gill bar and containing probably both
general and special visceral fibers, and a lateral line nerve, ramus
supra-temporalis, arising from the middle of the ganglion and
running laterally to innervate at least one lateral line organ of
the body line which I take to be the second organ of this line.

The vagus ganglia

This complex (fig. 1) contains at this time three chief ganglionic
masses (a) the lateralis X ganglion, (b) the first branchial
ganglion and (c) a large poorly differentiated ganglion corre-
sponding to the primordia of the general visceral (nodosal) and
three remaining branchial ganglia. This last mass comes into
contact with the third gill slit and contains cells contributed by
the third placode (counting the placode of the VII as no. 1) and
its posterior end is not clearly definable. There is no definite
jugular, or general somatic, ganglion present at this time. It
can be detected first in my series in a 138 mm. embryo as a

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 1

18 F. L. LANDACRE

small ganglion lying on the root of the vagus intracranially.
At this time its ganglionic cells cannot be distinguished from
embryonic sheath cells.

The lateralis X

The lateralis X is the best defined ganglion of the vagus group.
It is an elongated cylindrical mass of cells with its anterior end
reaching the posterior end of the first branchial ganglion of the
vagus and its posterior end reaching posterior to the caudal end
of the visceral X. It is situated laterally in the body at the level
of the notochord and lies between the skin and the branchial
ganglia of the vagus. I can detect only two fibrillated nerves
arising from it at this time. The chief nerve (ramus lateralis
vagi), arises from the posterior end of the ganglion and runs
posteriorly as usual in teleosts. The second nerve is the ramus
supra-temporalis vagi which arises from the anterior end of the
lateralis X ganglion and passes directly lateral and slightly forward
to a lateral line organ apparently the third organ of the body
lateral line.

The root of this ganglion does not enter with the vagus roots
but pursues a course diagonally forward and upward to the region
of the root of the glossopharyngus with which at this stage, it
enters the medulla. In older embryos the fibrillated root of the
lateralis X passes beyond the visceral root of the IX and enters
the medulla anterior to that root.

The branchial ganglia of the vagus

The first branchial ganglion of the vagus (figs. 1 and 11) is a
visceral ganglion composed of cells derived from the neural crest
(general visceral) and of cells derived from the placode of the
second true gill (special visceral or gustatory). In shape it
resembles the glossopharyngeal but has a position more nearly
vertical in the body. The ventral end is the larger and it
curves dorsally and at this stage comes into contact at its dorsal
and posterior border with the remaining portion of the general

visceral mass of the X. It is convex on its anterior face. The

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 19

root of this ganglion enters the medulla along with the remaining
visceral roots of the X. One fibrillated nerve is present (truncus
branchialis vagi lI). It arises from the anterior ventral end of the
ganglion just behind its attachment to the placode and runs
ventrally into the second true gill bar.

The remainder of the visceral X is not differentiated into bran-
chial ganglia. It is an elongated mass of cells lying somewhat
ventrally and mesially to the lateralis X. Its posterior end as
mentioned above is ill defined. Its middle portion is attached
to the placode (placode 4) and one branchial nerve (truncus
branchialis vagi II) arises from it just posterior to its attachment
to the placode. This ganglionic mass differentiates later into
the three remaining branchial ganglia of the X having the same
composition as the first branchial of the X and consists of general
visceral cells derived from the neural crest and special visceral
or gustatory cells derived from the placodes.

The root of this ganglion passes dorsally along with that of
the first branchial ganglion and part of its fibers enter the medulla
directly over the ganglion. Many of the fibers, however, at this
stage pass further posterior forming a bundle lying near the
medulla and enter the medulla posterior to the posterior end of.
the ganglion.

DETAILED DESCRIPTION OF THE EPIBRANCHIAL PLACODE OF
THE VII IN THE 10 MM. EMBRYO

This placode is completely detached from the epidermis in
the 10 mm. embryo, as mentioned above. After describing it
in this stage its later history will be followed first, and then the
mode of origin will be taken up.

After detachment from the epidermis, the placode occupies
the anterior end of the general visceral ganglion of the VII nerve
(fig. 1). The posterior and middle portions of the geniculate
are round in transverse sections. The anterior third is indented
on its mesial side by the ventro-lateral lateralis ganglion (figs.
20, 21 and 27). The extreme anterior end varies a good deal
in shape in different series owing to the varying relations of the

20 F. L. LANDACRE

general visceral and placodal portions to each other. The gen-
eral visceral portion sometimes extends farther forward than the
placodal portion, sometimes both general visceral and placodal
portions are of equal length and the anterior end of the ganglion
is split (figs. 14, 15). In all series of this stage the anterior end
consists of a mesial rounded portion and of a lateral spur resting
on the endoderm of the hyoid gill pocket and extending somewhat
dorso-laterally toward the epidermis (figs. 16 to 20). A portion
of the median rounded mass and all of the lateral spur are derived
from the placode. The manner in which the placodal portion
joins the general visceral varies in different embryos somewhat.
The visceral cells may lie like a cap dorsal, mesial and sometimes
lateral to the placodal cells. In later stages the placodal cells
are usually surrounded by the general visceral cells in this manner,
but the condition shown in figs. 14 to 21 is the usual one in the
10 mm. stage, so that the placodal portion of the ganglion begins
at the extreme anterior end of the ganglionic mass (fig. 14)
becomes broader a few sections posterior to this point and pos-
sesses a large lateral spur (figs. 17 to 19) and disappears a few sec-
tions posterior to the anterior end of the ventro-lateral lateralis
VII.

The placodal portion of the ganglion can be distinguished
from the general visceral by the difference in staining reaction,
the placodal portion usually being much darker (fig. 26) and
can be distinguished further, by the arrangement of the cells,
the placodal cells being elongated in the direction in which they
have moved into the ganglionic mass. The most uniform and
most easily recognized characteristic is that of color (figs. 26, 28,
30, 31).

Posterior to the placodal portion of the geniculate ganglion
we find the general visceral and ventro-lateral and dorso-lateral
portions only (fig. 27). The ventro-lateral ganglion lies mesial
and quite close to the geniculate and usually imbedded in it. It
is a short round ganglionic mass with its cells usually arranged in
a rosette with the nuclei situated peripherally. The geniculate
ganglion has a totally different appearance, consisting of a rather
dense mass of cells irregularly arranged and having very indefin-

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 21

ite cell boundaries (figs. 26, 27, 28). Posterior to the ventro-
lateral lateralis ganglion, the geniculate is uniform in structure
and passes dorsally and posteriorly toward the medulla accom-
panied by the root of the ventro-lateral ganglion. The posterior
end of the geniculate ganglion is closely attached to the audi-
tory ganglion, and near its entrance into the medulla, is joined
by the root of the dorso-lateral lateralis ganglion; so that all the
roots of the VII ganglion come into contact with the medulla
near the same point and quite close to the entrance of the root
of the auditory. The ganglionic complex of the VII has in gen-
eral an arrangement quite characteristic for the Ichthyopsida
(Herrick, ’99, Landacre, ’10) with the exception that it is quite
easy at this stage in the development of Lepidosteus to separate
the placodal or special visceral component from the neural crest
or general visceral portion of the geniculate.

The relation of the placodal portion of the VII ganglion to
the endoderm of the hyoid gill pocket is of the greatest importance
in forming a clear conception of the mode of origin and detach-
ment of the placode. The hyoid gill pocket as it approaches the
ectoderm gives off at this stage two solid processes of cells neither
of which come into contact with the epidermis (figs. 14 to 16),
but from an early stage up to the 8.8 mm. stage both these proc-
esses are in contact with the epidermis. As they withdraw from
the epidermis there appears a rather dense mass of mesoderm
between the two processes and in the area between the processes
and the ectoderm (fig. 19). This mass of mesoderm later devel-
ops into the hyomandibular cartilage and muscles associated
with this cartilage and the ear capsule. The dorsal process lies
farther forward, considerably anterior to the anterior end of the
geniculate ganglion. At the anterior end of the geniculate it
has the appearance shown in figs. 14, 15, 16. The primordium
of the hyomandibular cartilage lies between the hyoid pocket and
the epidermis in a recess formed by the dorsal and ventral pro-
longations of the endoderm and extends forward from this point.
Four sections posterior to fig. 14 the ventral prolongation becomes
detached and seems to disappear later, at the same time the dor-
sal prolongation becomes shorter and seems to detach a mass of

2? F, L. LANDACRE

cells which also disappear later. The placodal portion of the
ganglion always rests upon the dorsal endodermic prolongation
and in earlier stages is in continuity with the ectoderm at the pos-
terior end of the dorsal endoderm process and abuts against it
as shown in model (fig. 33). In the 10 mm. embryo where the
placode is no longer in contact with the ectoderm and is separ-
ated from it by the primordium of the hyomandibular cartilage
it still rests upon this dorsal pocket. The later history of the
placodal cells is closely associated with this pocket.

THE LATER HISTORY OF THE PLACODE OF THE VII

The later history of the placode may be summarized briefly
as consisting of (a) the withdrawal from the epidermis and incor-
poration into the geniculate ganglion, and (b) the reduction in
number and the metamorphosis of the numerous compact pla-
codal cells into ordinary ganglion cells that cannot be distinguished
from cells of the geniculate ganglion derived from the neural
crest. As to the withdrawal from the epidermis, a comparison
of figs. 22, 23, 24, 25, with figs. 17, 18, 19 will show that the pla-
codal spur of the geniculate ganglion nowhere approaches so
closely to the epidermis as in the earlier stage. Fig. 25 shows
also that the posterior end of the lateral spur extends caudad
from the ganglion and lies, as an elongated mass of cells, small
and dark staining like the placode, upon the endoderm of the
hyoid pocket. The appearance of the posterior extension of
cells is usually like that in fig. 25. The appearance of the caudal
prolongation changes slowly. It is gradually withdrawn into
the ganglionic mass of the geniculate. Fig. 30 illustrates the con-
dition at the middle of the placodal mass and fig. 29 illustrates
the condition five sections caudad where there are no placodal
cells in the ganglion but the posterior spur is present (12.4 mm.).
In stage 13.5 mm. there is no longer any posterior projection of
placodal cells although the placodal cells reach the ventral sur-
face of the ganglion (fig. 31).

The later history of the placodal cells is rather peculiar. They
are the most striking feature of the facialis complex. The cells

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 23

as mentioned above stain a deep blue and in addition are quite
small and closely packed. In a24 mm. embryo they can be iden-
tified still, although reduced in numbers, and they seem to be
represented in a 44 mm. and even in a 6-inch Lepidosteus. That
they should remain so long undifferentiated is striking, but there
ean be no doubt as to the continuity of this mass of cells and that
they are derived from the placode. That they are gradually
transformed into ganglion cells seems evident from the conditions
in the older series where they are of various sizes and some of
them are evidently ganglion cells.

In a 24 mm. embryo the number of undifferentiated placodal
cells is much reduced and there are groups of similar small cells
in the posterior portion of the Gasserian, so that the minute cells
are not peculiar to the placodal ganglion. The process of differ-
entiation seems to take place on the periphery of the placodal
cells where they are in contact with the normal ganglion cells.
Since some placodal cells remain undifferentiated up to the 6-inch
stage, it is possible that they may never be converted into normal
cells, although this is improbable. The transformation of these
placodal cells into ganglion cells is roughly correlated with the
relative time of appearance of the placodal ganglia. They are
the last ganglia to be formed and it is not surprising that they
should transform into normal cells much later, but it is a little
surprising that they should be delayed so long in their transfor-
mation.

THE ORIGIN OF THE EPIBRANCHIAL PLACODE OF THE VII

The determination of the exact time of appearance of the
epibranchial placode of the VII nerve is rendered difficult by
the presence of three associated structures, viz; the preauditory
placode, the thickening of the epidermis at the point where the
hyoid endodermie gill pocket joins the epidermis, and lastly the
presence of the anterior end of the geniculate ganglion which
ends at the point where the epibranchial placode is formed,
rendering difficult the identification of detached groups of cells
lying in this immediate region.

a ey F, L. LANDACRE

The preauditory placode is the first of these to appear and con-
sists, as in Ameiurus (Landacre, 710), of a forward continuation
of the thickening of the epidermis which forms the auditory ves-
icle. This thickening (including preauditory placode, auditory
vesicle, and post-auditory placode) in its early stages is much
longer than the auditory vesicle which is formed in its middle
region and its anterior end can be traced forward in the epider-
mis as a thickened column of cells to the region of the hyoid gill
pocket. As in Ameiurus, this preauditory placode is modified
in its anterior end and seems to disappear as a preauditory pla-
code, but the posterior portion of it persists to a relatively late
stage and is closely associated with, although probably not
genetically related to, the epibranchial placode of the VII nerve.
Before the appearance of a placode, or at least before the prolif-
eration of cells begins to form the epibranchial placode, the pre-
auditory placode seems to be continuous at its anterior end with
the thickening of the epidermis at the point of contact of the endo-
derm of the hyoid gill pocket with the ectoderm. The preaudi-
tory placode (which is presumably the earliest trace of the dorso-
lateral placodes of the authors) seems to be continuous with
the ectodermic thickening of the gill pocket up to 82 hours, but
no thickening of either gill pocket or preauditory placode extends
beyond the hyoid gill pocket.

The preauditory placode shows, in its posterior part particu-
larly, an arrangement of its cells characteristic of early stages in
the auditory vesicle and of lateral line organs. The cells are
radially arranged but the placode does not show these charac-
teristics as it approaches the hyoid gill pocket (fig. 35).

The thickening of the epidermis at the point where the endoderm
of the hyoid gill pocket joins the ectoderm is the most conspicu-
ous feature of the hyoid region up to the time that the epi-
branchial placode appears (fig. 34). The significance of this
thickening is uncertain. It may be due simply to the stimulus
furnished by the contact of the endoderm. with the epidermis,
but is much more pronounced than in Ameiurus and consequently
obscures the early differentiation of the epibranchial placode as
well as renders it difficult to determine the exact relation of the

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS pas 5)

preauditory placode to both the epibranchial placode and the
supra- and infra-orbital lines.

The cell arrangement of this thickening presents certain defi-
nite histological characters, the most conspicuous of which is
the fact that it can be distinguished readily from the endoderm
by the darker stain taken by the ectoderm, apparently due to the
smaller size of the cells, the more compact and irregular arrange-
ment, and the earlier loss of definite cell boundaries. These
characters make it easy to trace the line of demarkation in most
preparations between endoderm and ectoderm.

The third structure that must be constantly kept in mind in
tracing the history of the placode is the position of the anterior
end of the general visceral (geniculate) portion of the VII gan-
glion. This mass of cells, indefinite in outline as are all neural
crest ganglia in their early stages, lies at the level of the hyoid
gill pocket between the posterior end of this structure and the
auditory vesicle and extends forward from the auditory vesicle
to the posterior portion of the endodermic gill pocket. It is
thus seen to be a mass of cells whose anterior end is wedged into
the pocket formed by the withdrawal of the posterior end of the
gill pocket from the ectoderm, and it is at this exact point that
the ectoderm proliferates cells mesially to form the placode;
so that the difficulty that has been found to exist in the
interpretation of the relation of placodal cells to neural crest
cells in other types occurs here with the exception that one can
be certain that the neural crest portion of the VII (general vis-
ceral ganglion) does not form a contact with the epidermis. The
difficulty arises in determining if a given group of cells which one
finds in the anterior end of the geniculate came from the forward
extension of the geniculate or from the placode. When these
cells come off en masse and are numerous, no difficulty is presented
but the determination of the source of small groups of cells, as in
fig. 37, does present a difficulty. In the later stages of the for-
mation, the placodal cells are detached from the epidermis in a
large compact cluster, which can be distinguished from neural
crest cells, so that the tracing of their ancestry is easy; but in
the early stages of the formation of the geniculate ganglion this

26 F, L. LANDACRE

is not true owing to the indefinite outlines of both the placode
and general visceral ganglion.

Since the placode begins by the proliferation of cells mesially
at the posterior end of the hyoid gill pocket and at the anterior
end of the preauditory placode, it can be seen readily that it is
only when the process of prolification has reached a somewhat
advanced stage that the placode can be definitely identified.
Conditions in Ameiurus are somewhat simpler (Landacre,’10).
There the preauditory placode does not persist in the region of the
hyoid pocket up to so late a period and there is a definite histo-
logical change in the region of the pocket before the process of
proliferation begins, and further there is no such marked thick-
ening of the epidermis in the region of contact of ectoderm and
endoderm as in Lepidosteus. However, aside from the presence
of pronounced sensory lines, the primordia of the lateral lines,
there is no striking difference between the two types, the per-
sistence of the anterior end of the preauditory placode and the
great thickness of the ectoderm being minor differences.

A fourth structure, the posterior extension of the epibranchial
placode, should be mentioned in connection with the three just
described. In the case of the IX and Xth ganglia it presents
no difficulties, since the posterior extension of the epibranchial
placode lies at a lower level and is quite distinct from the dorso-
lateral placode or primordia of the lateral lines.

In the VII, however, this is not true. The posterior extension
of the epibranchial placode lies in the same plane approximately
as the preauditory placode. In the early stages of the epibranchial
placode the preauditory placode extends forward to the hyoid
gill. Later, as the preauditory placode recedes toward the ear,
the epibranchial extends backward toward the ear in the same
plane as that occupied by the preauditory.

The most probable interpretation of the relation of the preaudi-
tory placode to the ectodermic thickening of the gill pocket,
and of the epibranchial placode to both of these, is that the
preauditory placode extends forward into the thickening of the
ectoderm in the hyoid region and before the disappearance of the
preauditory placode and during the maximum development of the

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 26h

ectodermic thickening the epibranchial placode appears. The
later history of all three structures almost precludes the inter-
pretation that their relations to each other involves more than
juxtaposition.

The first probable trace of the appearance of the epibranchial
placode is found in a 94-hour embryo. A section taken through
the extreme posterior end of the contact of the hyoid endodermic
gill pocket with the ectoderm (fig. 36) shows that the ectodermic
thickening extends further mesially than it does anterior to this
point and farther than in preceding stages. One section posterior
to this (fig. 37) the endoderm has withdrawn completely from the
ectoderm but the thickening is present and is continuous with
an irregular mass of cells lying between the placode and endoderm.
The proliferated mass of cells is continuous posteriorly with
the neural crest (general visceral) portion of the VII. Mitotic
figures are numerous between the cell mass and the placode in-
dicating its origin from the placode. If this is true, however, the
anterior end of the geniculate consists almost exclusively of cells
derived from the placode since there is added to these cells later,
the large body of cells that comes off en masse and is much more
definite in outline.

In a 7.8 mm. embryo the epibranchial placode has reached a
stage in its development such that it can be positively identified
as the structure that later becomes detached en masse and added
to the general visceral portion of the VII, since there is no break
in its continuity from this stage up to the time of its detachment
from the ectoderm. The ectoderm in the region of the placode
is definitely differentiated into the primordia of the sensory
lines, placode, and the thickening of the ectoderm at the attach-
ment of the endodermic pocket. Throughout the length of the
attachment of the endodermic pocket, and dorsal to the thicken-
ing of the ectoderm associated with this pocket, there is a second
thickening incorporated more or less with the ventral thickening
but distinguished from it by its rounded contour and by the
arrangement of its cells. This dorsal thickening (fig. 38) is the
primordium of the sensory lines anterior to the hyoid gill pocket.
This line at this stage extends somewhat anterior to the hyoid

28 F. L. LANDACRE

gill pocket and also extends posterior to this point (figs. 39, 40);
so that it extends backward past the point of origin of the placode.

The dorsal sensory line shown in figs. 39 and 40 extends one-
half of the distance from the hyoid gill pocket to the auditory
vesicle, while the thickened area on which the placode forms
extends two-thirds of this distance. This series is unusual,
since in later series I cannot find a dorsal sensory line extending
posterior to the placode and lying dorsal to it.

The form and position of the placode is shown’ in fig. 39. It
consists of a well defined mass of cells projecting mesially and
lying just ventral to the dorsal sensory line. Fig. 40 is taken
four sections posterior to fig. 39 and shows the posterior exten-
sion of both the sensory line and the thickening which represents
the posterior extension of the epibranchial placode and is contin-
uous with the preauditory placode. The anterior end of the gen-
eral visceral VII is more definite in outline than in the preceding
stage figured, and comes into contact at its anterior end with
the placode, although there is no difficulty in separating the two
structures owing to the definite outline of the placode. There
is the doubt, however, as to the composition of this extreme
anterior end of the general visceral ganglion mentioned above.

The changes in an 8 mm. embryo are not marked, consisting
chiefly in the increase in size of the mass of cells proliferated
mesially in the placode. It should be borne in mind that the
anterio-posterior extent of the placode is usually not over three
or four sections (24u) thick, so that in transverse sections one
passes from the endodermic prolongations of the hyoid pocket
directly into the ectodermic prolongation of the placode.’ This
thickness in the anterio-posterior extent of the placode seems
to be due to its being apposed so closely to the posterior surface
of the gill pocket and gives the placode when seen cut through its
greatest transverse dimension, the appearance of being much
larger than it is.

In fig. 41 the endoderm of the gill pocket characterized by its
pale color and large cells with definite walls abuts directly against
the dark staining small celled ectoderm so that the boundary
line is quite definite. In fig. 41 the continuity of the gill pocket

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 29

and ectoderm is not broken but at least half of this is formed of
ectoderm and the ectodermic cells at the base of the proliferated
mass are in active mitosis.

In fig. 42 the endodermic pocket has withdrawn from the ecto-
derm and the placodal mass projects freely into the mesoderm.
One section posterior to this point the placodal mass is shorter
and posterior to this is present as a slight ridge in the ectoderm.
The condition just described, i.e., a thin flat placodal prolifera-
tion of cells closely apposed on its anterior surface to the posterior
wall of the hyoid gill pocket and usually extending through not
more than four sections, is so constant that it is unnecessary
to follow it in detail further than to give sections through the
placode at its maximum size. Between the 7.3 mm. stage and
the 8 mm. stage the general visceral portion of the VII has grown
forward as shown in fig. 42 until it lies upon the dorsal surface
of the posterior end of the hyoid gill pocket. This change in
position of the anterior end of the ganglion carries the ganglion
anterior to the point at which the placode originates; so that
the placodal cells are added in such a manner that they work
their way into the general visceral mass or are surrounded by
the visceral cells; at any rate they are incorporated into the gen-
eral visceral ganglion.

In the 8.3 mm. stage (fig. 43), both the placode and the anterior
end of the general visceral VII have increased in size. ‘The gen-
eral visceral ganglion is irregular in outline and it is difficult in
this particular series to tell how much of the complex is placodal.
Mitotic figures are numerous both in the ganglion and in the
placode. The dorso-lateral VII ganglion is present in fig. 43
but the section is taken just anterior to the ventro-lateral VII.

The changes in the placode, aside from its darker color, are
almost imperceptible between the 8.3 mm. stage and the 9.5
mm. stage (figs. 32 and 33). The general visceral portion of the
geniculate, however, becomes more definite in outline and com-
pared with the placodal portion of the ganglion, is much lighter
in color and the cells are larger and more loosely arranged. Be-
tween the 9.5 mm. stage and the 10 mm. stage which has been
fully described, the placode becomes completely detached from

30 F. L. LANDACRE

the ectoderm in most series. In the process of becoming detached
the placode seems to break near the epidermis and does not leave
the epidermis of normal thickness at the point of detachment.
The presence of loose masses of mesoderm cells in the region of
the placode and particularly the presence of the primordium of
the hyomandibular cartilage and associated muscles render it
difficult to determine the exact time of detachment even though
it were constant. The thickening of the epidermis after the
placode is completely detached extends from the posterior end
of the placode to the level of the anterior border of the auditory
capsule. While this thickening does not confuse the relation
in the hyoid region during the later stages of the placode, it
is of the greatest importance to determine its early history and
exact anatomical relations with reference to the dorso-lateral
sensory lines.

SUMMARY OF THE HISTORY OF THE FIRST EPIBRANCHIAL
PLACODE

The epibranchial placode of the VII nerve in Lepidosteus
can be identified first as a definite structure whose history can
be followed consecutively, at about the age of 94 hours after
fertilization. It appears as a mesial proliferation of cells from
the ectoderm just posterior to the endodermic pocket of the hyoid
gill to whose posterior surface it is closely attached. The pla-
code appears to be the posterior portion of the ectodermic thick-
ening with which the endodermic hyoid pocket comes into con-
tact. It is also apparently continuous posteriorly with a thick-
ened ridge of cells, the preauditory placode, extending back to
and in early stages being continuous with the anterior end of
the auditory vesicle. Both the preauditory placode and hyoid
ectodermic thickening are present before the placode appears
and they are continuous with each other. As the placode grows
mesially it comes into contact with the anterior end of the gen-
eral visceral portion of the geniculate ganglion, with which it
fuses, sometimes being attached on the lateral portion of the
geniculate, sometimes'to the ventral portion, and sometimes being

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS ot

surrounded by general visceral cells. After growing mesially
and coming into contact with the general visceral ganglion
at about the age of 94 to 100 hours, it becomes detached
from the ectoderm when the embryo is somewhat less than 10 mm.
in length. At the point of detachment there is left a cell mass
which extends backward to the region of the ear.

Preceding and for a long time after detachment, the placodal
cells are sharply differentiated from the remainder of the genic-
ulate cells. As late as the 44 mm. stage and probably as late
as the 152 mm. stage some of the placodal cells are differentiated
by their small size and intense dark color. The number is con-
stantly reduced, however, and similar small dark staining cells
can be detected in other ganglia particularly the Gasserian, so
that the fact that one can trace the history of these cells to so
late a period is probably due to their late differentiation into
normal ganglion cells.

Just how much of the geniculate ganglion at any stage after
the detachment of the placode and after the metamorphosis
of the small placodal cells into normal ganglion cells, may be
general visceral and how much may be special visceral cannot
be determined, but the late differentiation of these placodal cells
enables one to locate them and follow their history before meta-
morphosis much more completely than in any type described.

The relation of the early stage of this placode to the dorso-
lateral sensory lines needs a more careful study than can be given
the question in connection with the later history of the placodes.
The presence of definite sensory lines resembling those of the sea
bass (Wilson, 791) shows that the lateral line system, at least in
its earlier stages, resembles Serranus much more closely than
Ameiurus, but whether these sensory lines are continuous with
the anterior end of the auditory thickening (preauditory placode
of Ameiurus, Landacre, ’10) or not must be taken up separately.
The presence of epidermal thickenings or sensory lines, lying at
the same level as the preauditory placode or dorso-lateral sensory
line, but not identical with it, as a study of the epibranchial
placodes of the IX and X nerves shows, emphasizes the necessity
of exercising caution in order not to confuse these dorso-lateral

ae F. L. LANDACRE

sensory lines with ventro-lateral sensory lines when they lie
at the same level and apparently are continuous the one with the
other.

THE EPIBRANCHIAL PLACODE OF THE IX NERVE

The placode of the [X nerve resembles the placode of the VII
in its mode of origin, detachment, and incorporation into the
general visceral ganglion. It is much smaller, however, and
occupies less time in the transition from ectoderm into ganglion
cells. The difficulty in determining the time of appearance of
the placode of the IX is in part the same as that encountered
in the VII. Owing to the angle at which the gill meets the roof
of the pharynx, the ectodermic invagination in the region of the
IX is more extensive and projects further caudad relatively than
in the VII and until there is some structural or color differentia-
tion in this mesially projecting mass, the identification of the
placode is almost impossible. The relation of the general vis-
ceral IX to the placode is exactly like that in VII. The general
visceral ganglion projects cephalad to the point where the placode
forms, and ends in most series between 8.8 and 9.9 mm. Just at
the mesial tip of the placode; sometimes, however, it projects
farther cephalad as it always does in series older than 9.9 mm.
and its anterior end rests upon the ectodermic invagination.

The difficulty found in the VII in regard to the relation of the
sensory line to the placode does not exist here. The post-hyoid
sensory line (dorso-lateral) extends beyond the anterior end of
the IX ganglion but does not reach, as a definitely differentiated
column of cells, the posterior end of the auditory vesicle. This
sensory line lies dorsal to the placode and entirely detached from
it so that there can be no doubt that the two structures are quite
distinct and the condition here strengthens the opinion expressed
in discussing these conditions in the VII, that the relation of the
preauditory to the epibranchial placode was one of contiguity
only and due to the fact that in the forward growth of the pre-
auditory placode it occupies the same level as the epibranchial
placode. This conclusion is still further strengthened from the
study of Ameiurus (Landacre, ’10) where the degeneration of

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS ao

the anterior end of the preauditory placode could be followed
preceding the appearance of the epibranchial placode. The rela-
tive position of the placode, general visceral IX, and ecto-
dermic wall of the gill, are shown in text-figs. 1, 2, and 3 (p. 34).

The first positive trace of the placodal cells was found in an
8.8 mm. embryo. This is shown in fig. 44. It differs somewhat
from the early condition usually found, in that the ectodermic
invagination of the gill pocket extends mesially to the placode
and some cells projecting from the ectoderm in the region of the
anterior end of visceral IX do not stain like placodal cells and
are not genetically continuous with placodal cells. The reason
for the greater extent of the ectodermic invagination in the IX,
as well as in the first two branchial X, is the more acute angle
at which the gill joins the roof of the pharynx.

The placodal cells are usually found immediately posterior
to the ectodermic invagination of the gill pocket. However,
there are ectodermic cells not belonging to the placode situated
mesially to the placodal cells. The ectodermic gill invagination
forms a curved mass reaching from in front of the placode to the
mesial side of the placode of the IX. The placodal cells seem to
have pushed their way into the posterior end of the ectodermic
gill invagination. One section anterior to fig. 44 the placodal
cells are absent and one section posterior to this point the section
passes through into the general visceral ganglion which is barely
in contact with the epidermis. It is thus seen that at this stage
the placode in its anterior-posterior extent is quite thin, as are
all the placodes in Lepidosteus. Between the 8.8 mm. and the
9.9 mm. embryo this mass of placodal cells cannot be identified
always but in the 9.9 mm. embryo they become permanently
established and their continuity can be traced up to the time they
become detached from the ectoderm and incorporated into the
general visceral IX.

In a 9.7 mm. embryo (fig. 45) we find the usual form of the
placode. It consists of a mass of cells projecting mesially from
the epidermis with the thickest portion of the placode lying ventral
to the point of attachment. Mitotic figures are numerous in
both the placode and the epidermis. On its anterior surface it

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, no. 1

34 F, L. LANDACRE

1X0 PISO

Text figures 1, 2 and 3 are camera tracings through the region of the IX gill
from a 9.7 mm. embryo of Lepidosteus.

Fig. 1 passes through the point of contact of the first true gill with the roof of
the pharynx.

Fig. 2 passes through the aati gill shelf (ec.) seven sections posterior to
fig. 1

Fig. 3 passes through the epibranchial placode of the IX and through the ante-
rior end of the general visceral IX. The resemblance stucturally between the
ectodermic gill shelf and the placode is striking. The placode can be recognized
by its darker color.
Aud.V., auditory vesicle; Aud., auditory ganglion; B.V. blood vessel; Br.A,
branchial “artery ; ; E.P.IX, epibranchial placode of IX; Hc., ectoderm of ea shelf;
G.V.IX, general visceral ganglion of IX; Met., Metencephalon; No., notochord;
Pr.L.L., primordium of lateral line.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 515)

abuts against the ectodermic gill invagination and on its posterior
surface it abuts against the anterior end of the general visceral
IX. It is thus wedged in between the ectodermic gill invagination
and the general visceral portion of the IX. From the 9.9 mm.
stage on, the anterior end of the IX grows forward so that it
rests upon the shelf formed by the ectodermic gill invagination.
In some embryos younger than the 9.9 mm. stage, cells are found
on this shelf but it is a constant feature of the ganglion from
this stage on.

In the 10 mm. stage, the ganglion has assumed the comma
shape (fig. 46) consisting of a rounded mesial portion and a lateral
projection extending toward the epidermis and resting upon
the extreme posterior end of the ectodermic gill invagination.
This lateral projection is not continuous with the epidermis,
but one section posterior to the one figured it is continuous.
It is not possible at this stage to distinguish accurately by color
differentiation between the placode and the ganglion cells pre-
sumably of neural crest origin. Since, however, the placode is
not yet completely detached from the epidermis, one can trace
the derivative of the placode by the form of the cells and their
continuity with the epidermis.

After the detachment of the placode from the epidermis the
placodal cells become, as in the VII, sharply differentiated in
color from the remainder of the ganglion. The general form of
the placodal mass is quite similar to that of VII, consisting of
a central core more or less incorporated into the general visceral
and projecting laterally and caudally (figs. 47, 48). This spur
of cells is incorporated into the ganglion and cannot be detected
in the 13 mm. stage, but is present in the 12.4mm. stage. The
remnant of the mass of placodal cells can be found in the 24 mm.
stage and similar small dark staining cells can befound in the ante-
rior tip of lateralis X indicating, as suggested in the discussion
of the similar condition in the trigemino-facial complex, that
there is a delayed development of these cells and that in Lepi-
dosteus, if the cells retarded in development happen to be aggre-
gated, the appearance described above is found, since it occurs in
both the Gasserian and lateralis X and is always found in the pla-

36 F. L. LANDACRE

codal ganglia. As in the case of the VII, the number of undif-
ferentiated placodal cells is apparently greatly reduced in the
later stages of my series and one can find cells lying at the
periphery of the incorporated placodal cells and consequently in
contact with general visceral cells, intermediate in size between
the small and large size of ganglion cells. The late differentia-
tion of these cells is apparently correlated with the late appear-
ance of the ganglia and taste buds as stated above.

THE FIRST EPIBRANCHIAL PLACODE OF THE X

There are four epibranchial ganglia on the X nerve, as is usual
among the Ichthyopsida. They are smaller than that on the
VII and correspond closely in size and position to the IX. There
is, however, owing to the differences in size and position of the
general visceral ganglia, to which the special visceral ganglia
are added, considerable variation in shape. The difference in
position of the last gills alters also the appearance of the placode,
particularly its relation to the ectodermic invagination.

Reference to fig. 1 will show that the first branchial ganglion
of X resembles the IX in general form, being an elongated mass
of cells placed nearly vertical in the body with its dorsal extension
joining the large body of cells which constitutes the larger portion
of general visceral X. This large mass of cells which contains
the remaining three branchial ganglia of X is not so definitely
formed into branchial ganglia as in Menidia. There is, however,
at the point where each placode is formed a mass of cells pro-
jecting ventrally, to which the placodal cells are added, so that,
while the presence of branchial* divisions is indicated, the bulk
of the general visceral cells is contained in one large general vis-
ceral ganglion.

The size of general visceral X and the fact that the branchial
divisions are less marked give an appearance to the placodes
that lends itself to the older interpretation of these structures,
i.e., that they are epidermic thickenings with which the neural
crest ganglia come into contact, but a careful examination of a
series of embryos taken at close intervals shows that they resem-

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 37

ble closely the conditions already described for VII and IX
nerves and consist of proliferations of cells derived from the ecto-
derm and added en masse to the neural crest ganglia.

The first placodal ganglion of the X appears in a 10 mm.
stage (fig. 49). It projects mesially from the ectoderm at the
extreme anterior end of the general visceral X, of which it forms
the most anterior portion. No portion of the first branchial
X lies upon the ectodermic shelf at this stage. It also abuts
against the posterior end of the ectodermie gill shelf, from which
it can be distinguished by its color and the arrangement of its
cells as well as by the fact that it becomes detached later.

The relation of the epibranchial placode to the dorso-lateral
sensory line is similar to the condition in the IX. The dorso-
lateral sensory line lies somewhat dorsal to the placode and quite
distinct fromit. This placode is continued as in the [X posterior
to the point of detachment by a thickened column of cells which
disappears before reaching the next placode. Evidently the dorso-
lateral sensory line and caudal prolongation of the placode are
quite distinct structures in both [X and first branchial X and must
be reckoned with in the case of the VII also if one is to interpret
correctly the structures lying in the region of the first epibranchial
placode.

In the 10.9 mm. embryo the placode is attached to the ectoderm
by a slender cord of cells only, the lateral prolongation described
in the VII and IX. This lateral prolongation extends backward
also. In the 11.5 mm. stage (fig. 50) the placode is completely
detached from the ectoderm, although both the placodal cells
and the general visceral cells of the ganglion are in contact with
the ectoderm; in fact, the ganglion rests upon the lateral roof
of the pharynx. Before the placode is detached from the ecto-
derm the color differentiation between placodal and general
visceral cells is marked and continues to be marked in all my
series up to the 24 mm. stage without so apparent a reduction
in the number of placodal cells as is shown in the VII and IX.
The later differentiation of the placodal cells here and in the
remaining placodes of the X is to be expected on account of their
later appearance as compared with the VII.

38 F. L. LANDACRE
THE SECOND EPIBRANCHIAL PLACODE OF THE X

The second epibranchial placode appears first in my series
in a 10 mm. embryo (fig. 51). As in the case of the first epi-
branchial placode of the X, it lies at the anterior end of the corre-
sponding general visceral branchial ganglion (fig. 1) and at the
posterior end of the ectodermic shelf of the third true gill. It
lies below the fundament of the lateral line and it is continued
caudad in a thickening of the epidermis which does not reach the
next gill and is throughout its course entirely distinct from the
fundament of the lateral line. Fig. 52 shows the condition of
the placodal portion of this ganglion in a 10.9 mm. embryo.
It is completely detached from the epidermis laterally but still
rests upon the epidermis and has both the lateral and caudal
prolongations. The later history of this placode parallels those
already described and the placodal cells can be readily detected
in my oldest series (24 mm.)

THE THIRD AND FOURTH EPIBRANCHTIAL PLACODES OF THE X

The third epibranchial placode of the X appears first in my
series in a 10.9 mm. embryo (fig. 53). It differs from those
already described in being less pronounced both as to size and
color differentiation. In some stages succeeding the 10.9 mm.
the placodal cells are difficult to detect, although they can always
be found if the approximate location of the placodal cells is de-
termined with reference to the corresponding gill bar.

The appearance of this placode after detachment from the
ectoderm and before complete incorporation into the general
visceral ganglion and while still possessing the lateral and caudal
spurs, is shown in fig. 54. The fundament of the lateral line
is not present at the level at which this section is taken, owing
apparently to the absence of a lateral line organ at this point,
but slightly posterior to this point it is present and occupies a
level above the epibranchial placode. The thickening of the epi-
dermis running caudad from the point of origin of the epibran-
chial placode is not pronounced but is present. The later history
of the placode, including its incorporation into the general vis-

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 39

ceral ganglion, offers no new features. It can be detected in the
24 mm. stage.

The fourth epibranchial placode of the X appears first in a 12.9
mm. embryo (fig. 55). The posterior surface of the fourth gill
bar of the X does not become detached from the ectoderm but
this does not alter the relations greatly. There is no ectodermic
. shelf and I can detect no thickening of the epidermis extending
caudad from the point of origin of the epibranchial placode.
The fundament of the lateral line in this region lies far dorsal at
the level of the lateral line nerve of the X. ‘This nerve lies on a
level with the middle of the notochord. The later history of
this placode duplicates the history of the preceding placodes
described. The lateral- and caudal prolongations are less pro-
nounced but it becomes incorporated into the last general visceral
branchial ganglion and can be located in the 24 mm. series.

GENERAL SUMMARY AND DISCUSSION

1. The epibranchial placodes of Lepidosteus osseus arise as
proliferations of the ectoderm at the dorsal and caudal border of
the corresponding gill bar. They project mesially and finally
become detached en masse and fuse with the general visceral
portions of the VII, IX and four branchial ganglia of the X nerve.
The point on the general visceral ganglion at which the placodal
cells join it is always near its anterior end, sometimes in such a
manner as to form the extreme anterior tip of the corresponding
ganglion, sometimes, however, joining it laterally and ventrally
in such a manner as to be partly surrounded by the general vis-
ceral cells.

2. Preceding the detachment of the epibranchial placodes their
history can be followed, owing to their continuity with the ecto-
derm, from which they differ both in color intensity and in his-
tological character. In the earlier stages, however, especially in
the case of the VII nerve whose epibranchial placode is by far
the largest and most conspicuous of the series, difficulties arise
because of the presence of othef thickenings in the ectoderm, i.e.,
(a) the primordia of the lateral sensory lines, (b) the thickening

40 F. L. LANDACRE

of the epidermis at the point where the pharyngeal endodermic
pocket joins the ectoderm, (c) the anterior extension of the audi-
tory vesicle (the preauditory placode of Ameiurus, Landacre,
’10, the branchial sense organ of Wilson, ’91), (d) the thickening
of the epidermis extending caudad from the point of origin of the
epibranchial placode.

In all the epibranchial placodes there is a thickening of the
epidermis at the point where the endodermic gill pocket joins the
ectoderm and this always lies anterior to the point of origin of the
placode. The epibranchial placode always arises at the poste-
rior endof this thickening and while in Lepidosteus the placodes are
unusually long in their transverse axis they are thin from anterior
to posterior and abut against the posterior border of the ecto-
dermic gill invagination. In all the placodes except the VII,
and sometimes here, there is a sharp color differentiation as well
as histological differentiation between the two structures and one
can be quite sure of this distinction in the later stages of the
placode, although the two structures are continuous, when one
reads the sections from the ectodermie gill shelf into the placode.

The primordia of the lateral sensory lines can be differentiated
from the epibranchial placodes with equal ease except in the case
of the VII. They lie at a different level, much above the placodes
in IX and X, but in VII the supra-orbital, sub-orbital and man-
dibular sensgry lines converge at the hyoid gill rendering it diffi-
cult to differentiate between primordia of lateral sensory lines
and the early stage of the epibranchial placode. Much the same
difficulty exists in the VII with reference to the preauditory pla-
code. This structure in its anterior extension drops to the level
of the hyoid gill and seems in the earlier stages, before the appear-
ance of the epibranchial placode, to become continuous with the
ectodermic gill thickening in this region although it changes
its histological characters at the anterior end. To add to these
difficulties in the case of the VII, each epibranchial placode in
Lepidosteus is continued caudad by a thickening of the epider-
mis, which in the case of the IX and X ganglia lies at a lower
level than the fundament of the lateral lines and of course in these
cases cannot be confused with the dorso-lateral placodes.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 41

In the VII the column of cells extending caudad from the epi-
branchial placode and persisting after the detachment of the
placode occupies the same level in the epidermis as that previously
occupied by the preauditory placode. There can be no doubt,
however, from an examination of the epibranchial placodes of
IX and X that this is a different thickening from either the pre-
auditory placode or the primordia of the dorso-lateral sensory
lines. I interpret all these as distinct structures, including the
epibranchial placode and its posterior extension in the epidermis,
the preauditory placodes and primordia of the sensory lines and
the ectodermic thickening at the point where the endoderm of the
hyoid gills joins the ectoderm, on evidence furnished by the
study of similar structures in the IX and X ganglia; and I con-
clude that they are simply contiguous in the VII. As to the exact
relation of the sensory lines to the preauditory placode, there is
some degree of uncertainty in view of the conflicting evidence
furnished by Wilson (91) on Serranus and my own work on
Ameiurus.

The significance of the posterior extensions of the epibranchial
placodes is problematical also. They are certainly not closely
related to the fundament of the lateral lines in the IX and X,
being, in fact, entirely distinct from them. The whole situation
emphasizes the extreme caution that must be exercised in mak- '
ing statements in regard to the relations of sensory lines lying in
the region of the VII either epibranchial or dorso-lateral, and in
particular in regard to the relation of the preauditory placodes
to the supra-orbital, sub-orbital and mandibular sensory lines,
since the point at which the preauditory placode is supposed to
split up into sensory lines is in the region of the epibranchial
placode of the VII. The hyoid gill region becomes the focal
point in the differentiation of all these structures. The easiest
of all these structures to follow is the epibranchial placode of the
VII after it once becomes established, although it is difficult to
locate in its early stages. The growth of all the placodes, includ-
*ing the VII, can be followed with ease to the time when they
reach their maximum size. Both their structural and color dif-
ferences are sharp. The placodes take a darker stain than either

42 F. L. LANDACRE

the epidermis or the general visceral ganglia and their cell arrange-
ment is characteristic, the cells being closely packed with numer-
ous mitotic figures. The body of the placode is apparently de-
rived from the deeper nervous layer of the ectoderm ventral to
the point of attachment. The ectoderm dorsal to the point of
attachment of the placode is always thin.

3. During the time of detachment and throughout their later
history the placodal cells can be followed for the same reasons;
in fact, the placodal cells during their later history and up to the
time they become metamorphosed into ordinary ganglion cells
are more sharply differentiated from general visceral cells than
in their earlier stages and present a striking feature in the gan-
glia of which they are components. ‘The ease with which these
placodal cells can be followed in Lepidosteus seems to be unique
among the Ichthyopsida so far studied.

Immediately after the epibranchial placodes become detached
from the epidermis and during the earlier stages of their incor-
poration into the general visceral ganglia they occupy the ven-
tral or ventro-lateral portion of the corresponding ganglion and
alwayshave aspur of cells projecting laterally toward the epidermis
at the point at which the placode became detached. This spur
of cells always except in the case of the fourth branchial ganglion
of the X projects caudally also.

In the later history of each ganglion this spur becomes incor-
porated into the larger mass of placodal cells which at first, while
being largely surrounded by general visceral cells, always reaches
the external boundary of the ganglion at its ventral surface.
Still later in the history of each ganglion the placodal cells are
found completely surrounded by general visceral cells or cells
of the same type. At the boundary between the incorporated
placodal cells and the surrounding general visceral cells there are
found in embryos of 12.4 to 24 mm., especially in the VII ganglion,
cells varying in size from that of the minute dark staining pla-
codal cells to that of the ordinary visceral ganglion cells. This
indicates that the placodal cells are gradually transformed into
ordinary ganglion cells indistinguishable from general visceral
ganglion cells. Some of these small dark staining cells persist

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 43

in the oldest of my series and there are such cells found in a 44
mm. embryo and even in a 152 mm. fish at approximately the
point where the placodal cells should be, although my series are
not continuous up to these older stages.

The fact that the history of the placodal cells can be followed
so definitely seems to depend upon two things; first, the late
appearance of the placodal ganglia as compared with the general
visceral ganglia and the retarded development of the gustatory
organs of Lepidosteus as compared with such a form as Ameiurus.
This sets the immature placodal ganglion off in sharp contrast
with the older and more mature general visceral ganglia. As the
placodal cells become transformed into normal ganglion cells, they
can no longer be distinguished from the general visceral cells.

In the second place, the identification of the placodal cells
seems to depend upon the fact that in the ganglia of Lepidosteus
the histological distinction between immature ganglion cells and
mature ganglion cells is unusually sharp, so that if the immature
ganglion cells happen to be aggregated they become, owing to
their small size and dark staining properties, quite conspicuous.
Such masses of cells can be found in a 24 mm. embryo in both
the Gasserian and in the lateralis X ganglion but not in the earlier
stages of these ganglia. Since there are no epibranchial placodes
on these ganglia, these masses of cells are to be interpreted as
immature cells. Such immature cells are usually found in gan-
glia but become especially prominent when collected in definite
masses. The nerve fibers arising from ganglia containing both
placodal cells and neural crest cells are not sufficiently different
from each other in the oldest specimen examined (152 mm.) to
enable one to trace the gustatory and general visceral fibers to
their respective ganglion cells and peripheral terminations, so
that for the present the reason for the classification of the pla-
codal cells as special visceral cells must rest on the evidence
offered in a later paragraph. ;

4, The explanation suggested in the body of the paper, that
the observed difference between the placodal cells and the re-
maining cells of the general visceral ganglia of the VII, IX, and
X nerves is due to the relatively late appearance of the gustatory

44 F. L. LANDACRE

organs, finds confirmation in a comparison of the relative time of
appearance of the placodes and taste buds in Lepidosteus and
Ameiurus (Landacre, ’07).

Approximately the same time, five days, intervenes between the
fertilization of the eggs and the time of hatching in Lepidosteus
and Ameiurus. If we compare the size at any given age, and rate
of growth for any given period, Lepidosteus is found not only to
be longer but to grow faster than Ameiurus. At the age of 113
hours Ameiurus is 5.73 mm. long, while at the nearest correspond-
ing age, 112 hours, Lepidosteus is 8 mm. long. Between the ages
of 113 hours and 199 hours, Ameiurus increases 2.77 mm. in length,
while Lepidosteus between the ages of 112 hours and 196, my
nearest corresponding series, increases in length 5 mm.—a total
difference in growth of 2.23 mm. in favor of Lepidosteus. Dur-
ing this period Ameiurus increases 43.3 per cent while Lepidos-
teus increases 62.5 per cent.

If now we compare the more rapid rate of growth in Lepidos-
teus with the time of appearance of preauditory placodes, the
length of time intervening between the appearance of the first
placode and the appearance of.the last, the time at which taste
buds first appear, and lastly the total number of taste buds at
any given age, we shall find all these processes beginning earlier
and being completed earlier in Ameiurus, which is the slower
growing form.

The first epibranchial placode appears in Ameiurus preceding
the 49-hour stage and the last placode appears at 105 hours.
In Lepidosteus the first placode appears at 94 hours and the last
at 191 hours. There is a difference of 45 hours between the time
of appearance of these structures and a difference of 41 hours in
the time intervening between the appearance of the first and the
last placode, the placodes appearing earlier and consuming less
time in their formation in Ameiurus which measured by length
grows slower than Lepidosteus. The first taste buds appear in
Lepidosteus at 191 hours, 97 hours after the appearance of
the first placode while in Ameiurus the first taste buds appear at
115 hours, 74 hours after the appearance of the first placode.
So that here again the taste buds appear later and more time

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 45

intervenes between the appearance of the placode and the
appearance of the taste-buds in Lepidosteus than in Amelurus,
which is the slower growing form. Of more significance still,
is the relative number of taste buds present at a stage when
both types have them developed fully enough so that they can
be counted with certainty. Two series fulfil these conditions
closely, Lepidosteus at 214 hours and Ameiurus at 213. At the
age of 214 hours, Lepidosteus has 32 taste buds distributed on the
roof of the oral cavity and pharynx, and on all five gills. Owing
to the large number of mucous glands on the outer surface of the
body and the presence of the adhesive disc on the head where
external buds are most likely to be found, it is not possible to
determine the number in the skin.

In Ameiurus at 213 hours there are 146 taste buds in the oral
cavity, 352 in the pharynx and gills and 117 situated externally
on the skin of the head chiefly. This gives a total of 615 taste
buds in Ameiurus as compared with 32 for Lepidosteus for a
corresponding age. The later appearance and slower rate of
growth of ganglia and limited number of taste buds in Lepidos-
teus as compared with Ameiurus of the same age seem to offer,
when we consider the different rate of growth in the two types,
strong evidence that the gustatory system of Lepidosteus is
retarded in development as compared with other structures in this
form and that this retardation is indicated in the histological
differences between placodal and neural crest cells and offers a
satisfactory explanation of the retarded metamorphosis of the
special visceral cells into normal ganglion cells.

5. The assumption that cells derived from the epibranchial
placodes, after their metamorphosis into ganglion cells, are the
cells giving rise to fibers supplying taste buds and consequently
designated as special visceral ganglia, rests upon indirect evidence
but evidence of such a character as to warrant the assumption
in view of the extreme difficulty of demonstrating its truth or
falsity. Epibranchial placodes are found in all types of verte-
brates, even among mammals, including man. Among the lower
vertebrates where their history can be followed in series taken
at close intervals, they can be shown in some cases to con-

46 F, L. LANDACRE

tribute cells to the neural crest portions of the corresponding
ganglia. In other types where the placodes are less prominent
an actual contribution of cells to the neural crest portion of the
corresponding ganglia has not been shown to take place, but a
contact is formed between the neural crest ganglia and the epi-
dermis in all cases. In view of the reduced character of the gusta-
tory system in many forms as compared with the fishes, it is not
surprising that the actual contribution of cells by the epibran-
chial placode should not be large and might take place during
the period of contact and still be difficult to demonstrate. There
seems to be no other adequate explanation for the formation of
this contact between the neural crest ganglia and the ectoderm in
such types that would harmonize with the known conditions in
Ameliurus and Lepidosteus.

In all types epibranchial placodes occur on those nerves and
those only, VII, IX and X, which contain gustatory fibers.
Whenever, as is usually the case among the Ichthyopsida, the
ganglia of these nerves are complex, containing lateralis, cutaneous
and visceral components, the placodal cells join only the visceral
ganglia, never the lateralis or general cutaneous ganglia. These
visceral ganglia give rise to fibers supplying general visceral sur-
faces and taste buds only. In Ameiurus and Lepidosteus the
various components of the ganglia are so distinct in the embryos
that this conclusion can not be doubted and the problem resolves
itself into the effort to differentiate special visceral or gustatory,
and general visceral ganglia. Ganglia such as the profundus and
Gasserian which do not contain visceral fibers of either type and
have no epibranchial placodes, can be eliminated. With equal
certainty we can eliminate all lateralis and general cutaneous
ganglia in VII, [X and X, since they give rise to no visceral fibers
of either type and have no epibranchial placodes.

An examination of the visceral ganglia of Ameiurus shows that
the VII ganglion, which in the adult supplies a large number of
taste buds, has a large placode, while the last branchial ganglion
of the X which supplies in most types a limited number of taste
buds, has a small placode. The visceral portion of the [X seems
to be exclusively placodal in origin and seems in the adult to give

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 47

rise to gustatory fibers only. So that in general there is a close
correspondence between the size of the epibranchial placode and
the number of gustatory fibers to which the ganglion gives rise
in the adult.

A study of Lepidosteus, in addition to furnishing a confirmation
of the conclusion reached from a study of Ameiurus, shows in
addition that the placodal ganglia maintain their integrity for
a long time, although embedded in the general visceral ganglia,
and that the late appearance of the epibranchial placodes and their
slow metamorphosis into ganglion cells is closely correlated with
the retarded appearance of the gustatory organs. This correla-
tion, when taken in conjunction with the fact that only those
ganglia having placodal cells give rise to gustatory fibers and in
proportion to the size of the placodes and that all ganglia having
epibranchial placodes give rise to gustatory fibers and particularly
that a ganglion that is apparently exclusively placodal is also
apparently exclusively gustatory, seems to warrant the assumption
that placodal ganglia are special visceral ganglia.

AS F. L. LANDACRE

LITERATURE CITED

Brarp, J. 1885-1886 The system of branchial sense organs and their asso-
ciated ganglia in Ichthyopsida. A contribution to the ancestral his-
tory of the vertebrates. Quart. Jour. Micr. Sci. (n.s.), vol. 26, pp.
95-156.

Brookover, CHarLes 1910 The olfactory nerve, the nervus terminalis and
the pre-optic sympathetic system in Amiacalva. Jour. Comp. Neur.,
April.

Cocuitt, G. E. 1902 The cranial nerves of Amblystoma tigrinum. Jour.
Comp. Neur., vol. 12.
1906 The cranial nerves of Triton taeniatus. Jour. Comp. Neur.,
vol. 16.

Froriep, A. 1885 Ueber Anlagen von Sinnes-organs am Facialis, etc. Archiv
fiir Anat. und Phys.

Herrick, C. J. 1899 The cranial and first spinal nerves of Menidia. A con-
tribution upon the nerve components of the bony fishes. Jour. Comp.
Neur., vol. 9, pp. 153-455.

1907 A note on the distribution of the IX nerve in author’s paper
(07), p. 55.

Lanpacre, F.L. 1908 On the place of origin and method of distribution of taste
buds in Ameiurus melas. Jour. Comp. Neur., vol. 18, no. 6.

1910 The origin of the cranial ganglia in Ameiurus. Jour. Comp.
Neur., vol. 20.

Witson, H. V. 1891 The embyrology of the sea bass (Serranus atrarius). Bull.
of U. S. Fish Com., vol. 9, Washington.

Wie, J. W. van 1882 Ueber die Mesodermsegments und iiber die Entwickel-
ung der Nerven des Selachier-Kopfes, Amsterdam.

ABBREVIATIONS
Aud. V., Auditory vesicle. Ec., Ectoderm
Aud., Auditory ganglion En., Endoderm

Br. IX, Branchial nerve of the [Xth Epi., Epiphysis
Br. X,, First branchial nerve of the Xth #. P., Epibranchial placode (poster-

Br. X2, Second branchial nerve of the Xth lor extension)
Br. X;, Third branchialnerveof theXth EF. P. VII, Epibranchial placode of
Br. Xs, Fourth branchial nerve of the the VII

Xth E. P. IX., Epibranchial placode of
Br. A, Branchial artery the IX
Bv., Blood vessel E. P. X,, First epibranchial placode of
Bu., Ramus buccalis VIT the X
D. L. VII, Dorso-lateral ganglion of | EZ. P. X2, Second epibranchial placode

the VII of the X

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS

HE. P. X;, Third epibranchial placode
of the X

E. P. X4, Fourth epibranchial placode
of the X

Gass., Gasserian ganglion

Gen., Geniculate ganglion, general and
special visceral

G. Cil., Ciliary ganglion.

. IX, Glossopharyngeus ganglion

. V. VII, General visceral portion

of the VII

V. IX, General visceral portion of

the IX

V. X, General visceral portion of

the X

V. X1, General visceral portion of

1st branchial of X

V. X2, General visceral portion of

2nd branchial of X

V. X3, General visceral portion of

3rd branchial portion of X

V. X4, General visceral portion of

4th branchial of X

Hyo., Hyomandibular cartilage

Hyo. VII, Truncus hyomandibularis

L. IX, Lateralis ganglion of the IX

L. X., Lateralis ganglion of the X

Mand. V, Truncus mandibularis V

Maz. V, Truncus maxillaris V

Met., Metencephalon

Mes., Mesencephalon

N. III, Oculomotor nerve

No., Notochord

O. VII, Ramus oticus VII

Olf., Olfactory capsule

De Re Ss oa aS

Opt., Optic vesicle

O. Pro., Opthalmicus profundus nerve

O. S. V., Ramus opthalmicus superfi-
cialis V

O. S. VII, Ramus ophthalmicus super-
ficialis VII

Pros., Prosencephalon

Pro., Profundus ganglion

Pal. VII, Ramus palatinus VII

Pr. L. L., Primordia of lateral lines

Aud., Root of auditory nerve

. VII, Root of facialis

. V, Root of trigeminus

. L. VII, Root of lateralis VII

L. X, Root of lateralis X

V. I, VIRoot of visceralis VII

. V. X, Root of visceralis X

St. IX, Ramus supratemporalis IX

St. X, Ramus supratemporalis X

Sup. L, Supra-orbital lateral line

Sub. L, Sub-orbital lateral line

S. V. VII, Special visceral ganglion
of VII

S. V. IX, Special visceral ganglion of [X

S. V. X, Special visceral ganglion of X

S. V. Xi, Special visceral portion of 1st
branchial of X

S. V. Xe, Special visceral portion of 2nd

fi}

by oy by bo

branchial of X

. V. X3, Special visceral portion of 3rd
branchial of X

. V. X4, Special visceral portion of 4th
branchial of X

. L. X, Truncus lateralis X

THE JOURNAL OF COMPARATIVE NEURGLOGY, VOL. 22, No. 1

PLATE 1

A flat reconstruction of the brain, sense organs and sensory components of
V, VII, VIII, IX and X cerebral ganglia of a 10 mm. embryo of Lepidosteus osseus.

General cutaneous ganglia are indicated by horizontal shading and this compon-
ent is found at this stage in the profundus (trigeminus I) and the Gasserian gan-
glion (trigeminus II). The jugular ganglion of the X is not present at this stage;
when it becomes organized it lies on the root of the X near the entrance of the root
into the brain.

The special cutaneous ganglia are indicated by cross hatching and are found in
the VII (dorso-lateral and ventro-lateral lateralis ganglia of the VII), in the VIII,
IX and X.

General visceral ganglia are indicated by vertical lines and are found in the
VII (geniculate), IX (petrosal), and X (nodosal).

The special visceral ganglia are indicated by stipple and are found in the VII,
IX and X, there being only two of the four epibranchial ganglia of the X found at
this stage. Aside from the hyomandibular nerve, all the nerve trunks are pure,
i.e., contain only one component. The absence of the last two branchial ganglia
and the lack of fusion in nerve. trunks, which takes place later, are the chief dif-
ferences between this embryo and older stages.

The scale at the side of the figure indicates the serial numbers of the sections
from which the reconstruction was made.

PLATE 1

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS

LANDACRE

Ov OS O9 OL

os oO6 OO!

Olt O@t O€L Ol

Osi

i pe 2X A's

‘ot xX |

O91, OLL O8l O61 OO Ole O¢e OE? Ove OSe O92 OLe

PLATE 2

A series of camera tracings of transverse sections of the head of Lepidosteus
of 10 mm. length. The numbers following the number of the section indicate
the level at which the section falls, as indicated on the scale over fig. 1. The
sections are slightly diagonal, the right side of figure being further anterior.

Fig. 2 is taken at the level of the olfactory capsule and nerve.

Fig. 3 passes through the anterior portion of the qptic vesicle and the epiphysis
and dorsal sac.

Fig. 4 lies just posterior to the lens and passes through the anterior end of the
profundus ganglion.

Fig. 5 passes through the third nerve, on right side of figure, and the posterior
end of the profundus ganglion. The anterior end of the hypophysis is cut in this
section.

Fig. 6 passes through the posterior end of the Gasserian on right side of figure
and the anterior end of the lateral lobes of the medulla.

Fig. 7 passes through the root of the Gasserian ganglion on right side and the
posterior end of the mesencephalon.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 2
F. L. LANDACRE

2=72X50

5=//2X 50,

4=/02xs0.
° T=/97-X SO.

PLATE 3

A continuation of figures of plate 2. All references are to the right side of
figures.

Fig. 8 passes through middle of dorso-lateral VII and through the geniculate
ganglion at the point where the placode was attached to the epidermis. The
area blocked out in this figure lies in the middle of the series of figures on succeed-
ing plate (fig. 18).

Fig. 9 passes through the posterior end of dorso-lateral VII and through the
middle of ventro-lateral VII. The geniculate is cut posterior to the placodal
ganglion.

Fig. 10 passes through the middle region of the auditory capsule and through the
IX ganglion at the point of origin of its visceral trunk.

Fig. 11 passes through the epibranchial placode of the first branchial ganglion
of X and the root of the lateralis X ganglion.

Fig. 12 passes through the middle of the lateralis X ganglion and through the
visceral X just anterior to the epibranchial placode of the second branchial gan-
glion of X. The visceral root of X is cut in this section.

Fig. 13 passes through the posterior end of the lateralis X ganglion posterior
to the posterior end of visceral X. The visceral root of X is cut in this section
quite close to the medulla.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 3
F. L. LANDACRE

11=230Xx350,

12=24 4X 50.

13=264X510:

PLATE 4

Figs. 14 to 21 are a series of camera tracings of transverse sections of the 10
mm. embryo extending from the anterior end of the geniculate ganglion to the pos-
terior end of the placodal portion of this ganglion. The anterior third of the
ventro-lateral VII is included in the last two figures (20 and 21). Lateralis com-
ponents are indicated by cross hatching, general visceral by vertical lines, and
special visceral by stipple.

Fig. 18 corresponds to the area blocked out in fig. 8 of the preceding plate.

These figures were sketched from the same series as that from which the first
reconstruction was made, fig. 1, and numbers of sections indicate position on
scale of fig. 1. The figures are from consecutive sections. These figures show
clearly the part the placode plays in the composition of the geniculate ganglion
after the placode has become detached from the ectoderm.

Fig. 14 lies at the extreme anterior tip of the geniculate ganglion. See fig. 26
for detail of fig. 19, and fig. 27 for detail two sections posterior to fig. 21.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 4
F. L. LANDACRE

18=/6/ x/o0.

1Q=/62.x/00,

I. S.V.\V/]|

21-164 100,

PLATE 5

Figs. 22 to 25 from a 10.9 mm. embryo, are camera tracings to show the character
of the placodal spur of the VII projecting laterally and caudally. Components
are indicated as in preceding plate and in fig. 1. Lateralis or special cutaneous
cross hatched; general visceral vertical lines; placodal or special visceral, stipple;
figs 23, 24 and 25 are from consecutive sections. Two sections lie between figs. 22
and 23. The portion of this ganglionic complex shown in stipple is that which can
be positively identified as placodal in origin. That more of the geniculate or
general visceral should be shown as derived from the placode is possible, if the
placodal cells have metamorphosed into ganglion cells. See fig. 28 for detail of
fig. 23.

Fig. 26 shows the histological detail of the general visceral and placodal gan-
glia in fig. 19. The color differentiation due to size and density of cells is well
shown in this figure. Length of embryo 10 mm.

Fig. 27 shows the detail of dorso-lateral, ventro-lateral and geniculate ganglia
posterior to the placodal portion in a 10 mm. embryo. This section lies two
sections posterior to that shown in fig. 21.

Fig. 28 shows the detail of the geniculate ganglion and the ventro-lateral
ganglion in a 10.9 mm. embryo. This figure gives the histological detail of fig.
23 minus the dorso-lateral VII. Fig. 28 should be compared with fig. 26, since they
are taken through approximately the same region of the geniculate ganglion of
embryos differing nearly 1 mm. in length. The constancy in appearance of the
placodal ganglion is striking.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 5
F. L. LANDACRE

26 x 350.

22x/00

23 X/00.

PLATE 6

Fig. 29 from a 12.4 mm. embryo, is taken from approximately the same position
in the VII ganglionic complex as fig. 25, which is from a 10.9mm. embryo. There
are no placodal cells present in this section except the caudally projecting spur.
This is soon incorporated into the geniculate ganglion. The close resemblance
histologically between the dorso-lateral and the geniculate, and the distinct
character of the ventro-lateral which are so noticeable in this figure, can be detec-
ted in. all earlier stages.

Fig. 30 is taken from the same embryo (12.4 mm.) as that from which fig. 29
was taken and lies five sections anterior to fig. 29. Only the anterior tip of the
ventro-lateral ganglion shows and the dorso-lateral has been omitted on account
of its size. The placodal ganglion projects somewhat from the ventro-lateral
surface of the geniculate.

Fig. 31 shows the same relations in a13.5mm.embryo. The placodal ganglion
is almost completely incorporated into the geniculate. The distinction shown
here between unaltered placodal cells and the normal ganglion cells of the geni-
culate is fairly representative for all later stages in which placodal cells can be
detected.

Fig. 32 shows the detail of the epibranchial placode of the VII in a 9.5 mm.
embryo and illustrates the relation of the placode to the ectoderm above and below
its point of attachment. This figure corresponds to the middle of the placode
shown in fig. 33.

Fig. 33 is a sketch of a wax reconstruction of the epibranchial placode of VII
and associated structures in the ectoderm and endoderm. The model rests on its
anterior surface and is seen from the ventral surface. The ectoderm with its
attached epibranchial placode is detached from the endoderm and that portion
of the ectoderm lying anterior to the placode. The hyoid gill pocket lies to the
right and is closely fused with the ectoderm back to the point of origin of the pla-
code. If the two portions of the model are placed together it will be seen that the
anterior surface of the epibranchial placode rests upon the posterior surface of
that portion of the hyoid gill pocket that comes into contact with the ectoderm.
The length of the embryo from which the model was reconstructed was 9.7 mm.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 6
F. L. LANDACRE

30 x30.
CHATTY

‘SS.V.V II

31 X35 0:2

PLATE 7

Fig. 34 from an 82 hr. embryo is taken through the posterior portion of the thick-
ening of the ectoderm at the point where the endoderm of the pharyngeal gil |
pocket joins it. The ectoderm is easily distinguished by its color.

Fig. 35 from an 82 hr. embryo is taken through the thickening in the epidermis
just posterior to the hyoid gill pocket and is presumably the anterior extension of
the preauditory placode and, although it is not detached from the auditory ves-
icle, it shows none of the histological characters of the preauditory placode. Fig.
35 les three sections posterior to fig. 34.

Fig. 36 from a 94 hr. embryo, is taken at the extreme posterior limit of the con-
tact of the pharyngeal gill pocket with the ectoderm. The nuclei of the ectoderm
are closely packed and the cell walls are indefinite or absent, showing distinctly
that it is related to the epibranchial placode rather than to the preauditory pla-
code. ;

Fig. 37 from a 94 hr. embryo is taken just posterior to the contact of the hyoid
gill pocket with the ectoderm and shows the proliferation of cells to form the epi-
branchial placode. Fig. 37 is the next section posterior to 36. -

Figs. 36 and 37 show the absence of any primordium of the lateral lines in the
region of the placode up to this age.

Fig. 38 from a 7.3 mm. embryo is taken at the posterior limit of the contact
of the hyoid gill pocket with the endoderm. In addition to the ectodermice gill
thickening there is a dorsal thickening (primordium of lateral line).

Fig. 39 from a 7.3 mm. embryo is taken just posterior (two sections back of fig.
38) to the contact of the hyoid gill pocket with the ectoderm. It shows three
thickenings; most dorsal, the primordium of the lateral line; most ventral the prob-
able remnant of the preauditory placode. The middle thickening is the epi-
branchial.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 7
¥. L. LANDACRE

35 x3<50.

Eo===

De.

2 Eer Oi Naa!

Be EP \yiII

PLATE 8

Fig. 40 is from a 7.3 mm. embryo. The section passes through the posterior
extension of the epibranchial placode of VII and the posterior extension of the
primordium of the sensory line lying dorsal to it. Thissection contains the an-
terior end of the geniculate ganglion and lies four sections posterior to fig. 39.

Fig. 41 from an 8 mm. embryo, passes through the extreme posterior portion of
the contact of hyoid gill pocket with the ectoderm. It shows in addition to the
differentiation between ectoderm and endoderm the fact that the geniculate gan-
glion sometimes extends forward over the phyarngeal gill pocket. The primordium
of the sensory line lies well dorsal to the ectodermie gill thickening.

Fig. 42 from an 8 mm. embryo, shows the first section posterior to the point
where the hyoid gill pocket withdraws from the ectoderm. The epibranchial
placode is cut through its anterior end. The small mass of cells lying between
placode, endoderm, and geniculate ganglion may belong either to the placode or
to the ganglion since the ganglion has a rather indefinite outline.

Fig. 43 from an 8.3 mm. embryo, shows the maximum size of the placode at this
age. The indefinite outline of the geniculate ganglion at this stage renders the
line of separation between the placode and the geniculate ganglion difficult of
determination.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 8
F. L. LANDACRE

41 x350

GV.VIL-29

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 1

PLATE 9

Fig. 44 from an 8.8 mm. embryo shows the earliest trace of cells in the IX that
would ordinarily be identified as placode. Succeeding series do not show it to be
continuous and it differs from other placodes in having the ectodermic shelf extend
mesially to the placodal cells.

Fig. 45 from a 9.7 mm. embryo shows, in the IX, the earliest trace of the placode
that can be followed continuously in later series up to the time of its detachment.

Fig. 46 from a 10mm. embryoshows the ‘comma’ stage of [IX immediately after or
during its detachment from the epidermis. The placode is not sharply differen-
tiated from the general visceral, but includes at least all of the ventro-laterally
projecting mass. The whole ganglion rests upon the ectodermic shelf.

Fig. 47 from a 12.4 mm. embryo passes through the anterior end of the placodal

“mass of cells of [IX and is almost surrounded by the general visceral cells.

Fig. 48 from a 12.4 mm. embryo passes through the point where the lateral spur
of placodal cells is present and the remainder of the placodal cells are only partially
incorporated and occupy the ventral side of the ganglion. Fig. 48 lies three sec-
tions back of fig. 47. ;

Fig. 49 from a 10 mm. embryo shows the early stage of the epibranchial placode
of the first branchial ganglion of X still attached to the ectoderm.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 9
F. L. LANDACRE

S AAx370
Seti 5 Go

ND eee ee

PLATE 10

Fig. 50 from a 11.5 mm. embryo is taken through the ‘comma’ stage of the pla-
code of the first branchial ganglion of X and shows the relation assumed by the
placodal and general visceral cells in a ganglion where they are approximately
equal in number.

Fig. 51 from a 10 mm. embryo shows an early stage of the epibranchial placode
of the second branchial ganglion of the X at a stage where it is still attached to
the ectoderm.

Fig. 52 from a 10.9 mm. embryo shows a late stage in the second epibranchial
ganglion of X. The incorporation of placodal cells is not complete, there being
a ventro-lateral spur of placodal cells and, contrary to the usual rule, the placodal
cells lie chiefly on the lateral portion of the general visceral ganglion.

Fig. 53 from a 10.9 mm. embryo shows an early stage before detachment of the
epibranchial placode of the third branchial ganglion.

Fig. 54 from a 11.5 mm. shows the process of incorporation of the third epibran-
chial placode into the ganglion of the X. The lateral spur is still present.

Fig. 55 from a 12.9 mm. embryo shows. an early stage in the formation of the
fourth epibranchial placode of the X. The general visceral cells are so numerous
that the relation seems to be one of contact only but later series show that there is
an actual contribution by the placode of the ganglion.

THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS PLATE 10
F. L. LANDACRE

51 x350
oleae

4
&
¥

=
E of "@ at
: x

4x30

A COMPARISON OF THE EUROPEAN NORWAY AND
ALBINO RATS (MUS NORVEGICUS AND MUS. NOR-
VEGICUS ALBINUS) WITH THOSE OF NORTH
AMERICA IN RESPECT TO THE WEIGHT OF THE
CENTRAL NERVOUS SYSTEM AND TO CRANIAL
CAPACITY

HENRY H. DONALDSON

The Wistar Institute of Anatomy and Biology

FIVE FIGURES

In a paper recently published (Donaldson and Hatai, ’11) the
fact that the domesticated albino rat (Mus norvegicus albinus)
of our laboratory colony has a relatively smaller central nervous
system than the wild Norway (Mus norvegicus) from which it
is derived, has been presented and examined in some detail.
This difference between the two forms has been known to us for
several years and ever since it was first appreciated we have been
in search of a satisfactory explanation for it.

In the paper just cited, the conclusion is reached that this
difference represents one effect of domestication on the albino
rat, but in order to justify this conclusion, it will be necessary not
only to analyse domestication into its main factors, but also to
test other explanatory suggestions which have been made.

One such suggestion is to the effect that the small relative
weight of the central nervous system in the domesticated Albino
is due to the fact that the Albino has been derived from a strain
of the wild Norway in which the central nervous system was
also relatively small. It was to test this suggestion that the
present study has been made.

At the same time we recognize that this question represents
one aspect only of the larger problem of the possible variations

72 HENRY H. DONALDSON

which the Norway rat has undergone in its migration across
Europe and over seas to the Americas.

From our experience with the wild Norways of North America,
as found in Chicago and Philadelphia, there is no reason to think
that such an established strain exists in the United States, al-
though there appear to be slight differences characteristic for the
rats from different stations, and in one instance the rats from a
restricted locality near Philadelphia showed a brain weight
decidedly lower than that of our standard series. We do not
look on this latter group however as representing an established
strain.

It was thought possible nevertheless that such a strain might
be found in western Europe and I decided therefore in the summer
of 1909 to test the matter by collecting both Norway and albino
rats from Vienna, Paris and London in order to compare these
in respect to their central nervous systems with specimens of
both forms as observed in Philadelphia.

Historically, nothing is known of the albino variety of the
Norway rat, not even whether the Albinos found in Europe and
those in North America have had a common origin.

Concerning the wild Norway rat, we are a trifle better informed.
Mus norvegicus is reported by Pallas to have entered Europe by
way of southern Russia about the beginning of the eighteenth
century. It arrived in England, by ships, about 1728-1729 and
in Paris about 1758, but of its first arrival in Vienna, I have found
no mention. The date of its arrival on the eastern seaboard of
the United States was about 1775 (Lantz, ’09). Thus the wild
Norway rat has been in Europe for nearly two hundred years, and
in the eastern United States for about a hundred and thirty-five
years. It seems most probable that the albino variety has been
established since the appearance of the wild Norway rat in Europe.

For the opportunity to make these studies on the rat at the
several European stations, I was indebted to the courtesy of
colleagues in each city, and it is a pleasure to present here my
thanks to all of them for their unfailing kindness and interest.

At Vienna, Professor Obersteiner obtained for me a table in

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 73

the Physiological Institute directed by Professor v. Exner.
Through Dr. Przibram, Director of the Biologische Versuchsan-
stalt, arrangements were made to get Norway rats and ultimately
Dr. Przibram, beside presenting me with some of his own Albinos,
kindly allowed his assistant, Dr. Megusar, to make for me the
collection and first measurements of the animals needed to com-
plete the Vienna series. My thanks are specially due to Dr.
Megusar for the precision and care with which this work was
done.

In Paris, Professor Lapicque obtained for me-a table in the
Physiological Laboratory at the Sorbonne, and in every way
alded my plans.

Finally, in London, Sir Victor Horsley courteously allowed
me to work in his own laboratory and through his assistants
arranged for the supply of animals.

It may be noted in passing that rats in these several cities are
most readily obtained through local dog fanciers who usually
control a supply used for the higher education of their terriers.

Norway rats were hard to get in Vienna. Possibly the war of
extermination waged against them about 1898, when public inter-
est was aroused by a laboratory outbreak of plague, has served to
check their increase.

In Paris the rats were easier to obtain, but bore evidence of
having been caught in rather unsavory surroundings. In London
they were very numerous. I was offered a thousand in three
days, and moreover Mus rattus alexandrinus and Mus rattus,
the old English black rat, were also to be had—both kinds in
large numbers.

The general plan of this investigation was the following: To
collect at each of the three foreign cities about one hundred Nor-
way rats—and a smaller number of Albinos; to record the body
weight and body length of each individual, and in a few cases to
remove and weigh the central nervous system on the spot. In
the majority of cases however, it was planned to preserve the
heads only.

Later the skulls were to be prepared in this laboratory, the
cranial capacity determined and the data from the several series

74 HENRY H. DONALDSON

as thus obtained, used as a basis for determining the relative
weight of the brain.

Moreover, corresponding series of animals from Philadelphia
were to be prepared by a like technique and these data in turn
used as standards with which to compare the European records.
This plan was carried out, and the results furnish the material
for the discussion which follows.

The constitution of the several series of specimens is shown in
tables 1 to 11 inclusive. These tables give by series the number
of individuals and the range in body weight for each sex separately.

TABLE 1

Mus norvegicus from Vienna

HPemales:....2 2. MP ek 8s, a Ae es x Ae 46 | 86-389

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 75

TABLE 4

Mus norvegicus from Paris. Used for direct determination of the weight of the cen-

tral nervous system

NUMBER RANGE IN BODY WEIGHT
Z 7 grams
IIS See SRO BO ES es SMe I <n a DP | 7 183-328
Ae TIn GS erento eee Spare ote aw Reet <i heads Poe Oe | 2 154-234

TABLE 5

Mus norvegicus albinus from Paris

NUMBER RANGE IN BODY WEIGHT
grams
INTIS sentacidGe he SRE C COA Bans Ml oe an eee 8 86-203
~ arene ea ate eae eee Caines en, Oe 2 94-109

TABLE 6

Mus norvegicus from London

NUMBER
VIG Carrer wary to aes Senin wipe tk) 2a. see aa ok iS Cee 51
JOINS 5 SACs vpn Rend Shae ean, Suen cen ee 45

RANGE IN BODY WEIGHT

grams

72-385
88-382

TABLE 7

Mus norvegicus from London. Used for the direct determination of the weight of the

central nervous system

NUMBER RANGE IN BODY WEIGHT
grams
SM DEH PSS) aI tg oe em Mao NB i Po Ge S| 5 157-305
MG TAL GS a5 fs. ccp aoe net ee le ee de tee 4 173-215

TABLE 8

Mus norvegicus albinus from London

NUMBER RANGE IN BODY WEIGHT
~|
grams
NMialestans=- eeeeers APY ey ee ee Pee ei ie. d 5 106-286
STV S ce ee ees ch orchid she ERE Alico ec ee 5

150-250

76 HENRY H. DONALDSON

TABLE 9

Mus norvegicus from Philadelphia

NUMBER RANGE IN BODY WEIGHT
7 : : grams
Males ch) Se occ Ae oe eee | 49 104-533
Menmialess si «2a ye soe ee rh 46 75-457

TABLE 10
Mus norvegicus albinus from Philadelphia. Prepared in 1910-11

NUMBER RANGE IN BODY WEIGHT
F : grams
Ma eS ee A. aes See en ats or ea mee eee 9 101-194
Hemaless 4.335 errr eae ee dee 11 72-124

TABLE 11

Mus norvegicus albinus from Philadelphia and Chicago. Material prepared in
1907 by Dr. Hatai

NUMBER RANGE IN BODY WEIGHT

| grams
Ninleceeee es Nee | bet a ee eae | 41 | 112-292

Females tee es a a eee Ce | 35 108-253

An examination of the data for the four longer series—namely
those for the wild Norways—used in the determination of cranial
capacity (tables 1, 3, 6 and 9) suggests several comments. In
collecting these series no selection by either size or sex was made
by me, and yet the proportion of the sexes is rather similar in all
four. In the three European series, the range in body weight is
also similar, while distinctly heavier rats are found in the Phila-
delphia series. It may be remarked that in this latter case we
received every animal caught, while it is just possible that in the
case of some of the European series, the dealers reserved the
very largest animals for their own use, and in this way modified
the range in body weight. However that may be, the data as
they stand show that the several series were taken from rat popu-
lations which were similar in their general composition.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 77
TECHNIQUE

In all cases the rats were brought alive to the laboratory, killed
with chloroform, weighed and the body length taken (see Don-
aldson, ’09).

Then, either the central nervous system was removed and
weighed, according to the usual technique (Donaldson and Hatai,
11) or the head cut off. This latter was marked with a num-
bered metal tag and preserved in 60 per cent alcohol, pending the
preparation of the skull. As all the series were treated in the
same manner, the effects of the 60 per cent alcohol in modifying
the capacity of the cranium should be similar, provided of course
that the composition of the skull bones was also the same.

The skulls were cleaned by immersion for from 5 to 6 hours at
a temperature of 90° C. in 100 ee. of a 2 per cent watery solution
of commercial ‘gold dust washing powder.’! The very young
skulls required less time and a half strength solution.

The softened tissues were removed with a bone scraper. The
skull was then marked with water proof ink, dried in the air, and
the foramina at the base plugged with a minimal quantity of
universal cement to prevent the escape of the shot later used for
determining the cranial capacity.

To determine the capacity of the dried cranium? it was filled
with new number eleven shot. These shot are 0.06 of an inch
in diameter and weigh individually from 0.0203 to 0.0215 grams
and therefore run from 47 to 49 to the gram, with a mean of 48.

In filling the cranium the following method was used: The
cranium was held vertically between the thumb and forefinger of
the left hand with the ventral side towards the observer. The
shot was poured from a small aluminum beaker into the cranium
through the foramen magnum until it was nearly filled, then trans-
ferring the cranium to the right hand, and holding it vertically
between the thumb and middle finger with the index finger closing

1 “Gold dust washing powder’ consists of about 45 per cent sodium carbonate,
30 per cent soap powder and 25 per cent water.

2 Departing from the strict anatomical nomenclature, and following the usage
of the anthropologists, we shall here employ the term ‘‘cranium’’ for the skull
without the mandible (see Cunningham, ’09, p. 103, note 1).

78 HENRY H. DONALDSON

the foramen magnum, the right hand was gently struck three
times against the left. This was done to pack any shot which
might have been caught on irregularities within the cranium.°

The cranium was then transferred to the left hand again and
held as before while more shot were poured in. These were
packed with a small spatula and finally pressed down with the
forefinger of the right hand. ‘The filling was such that the shot
was slightly heaped in the center of the foramen so as to rise a
little above the level of its edge. When thus filled, each cranium
was placed vertically, nose down, in a small weighing bottle, so
that no shot should be lost through accidental jarring.

The filled cranium was next weighed to the tenth of a milli-
gram and the weight of the shot computed by subtracting from
the weight of the filled cranium the weight of the empty cranium
as previously determined. The cranium was then emptied and
again filled and weighed, and if the two weights of the shot were
within one per cent of one another, they were deemed satisfac-
tory. In 84 per cent of the cases two weighings only were neces-
sary. When the discrepancy was greater than 1 per cent in the
first instance, and more than two weighings were required, the |
two determinations in closest agreement were selected for aver-
aging, and the number thus obtained was that recorded. In this
connection it may be noted that in the nine series of crania meas-
ured in the course of this investigation, the mean difference be-
tween the two weighings of shot which were used as the basis for
the averages, was 0.6 per cent. This corresponds to a mean dif-
ference of from three to five shot according to the total weight of
the shot required to fill the cranium.

3 As serving to illustrate the pitfalls besetting the determination of cranial
capacity by the use of shot, I may call attention to the fact that when a container
has been filled, it does not always follow that any disturbance of the contained
shot will decrease its volume. For example: if a glass measuring cylinder gradua-
uated to hold 10 ce. and having an internal diameter of 1 cm. is exactly filled to the
upper limit of the graduation with number 11 shot, poured into it in a steady
stream, so that the filling requires about fifteen seconds, and then the mouth of
the cylinder is closed with the thumb and the cylinder once inverted, the shot hav-
ing a run within the cylinder of about 5 em., it is found that the volume of the
shot is increased by this treatment about 0.5 cc. or 5 per cent. If the cylinder be
now gently tapped on the bottom eight or ten times, the volume of the shot again
diminishes to its original value.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 79

This technique is essentially that which was used by Hatai (07)
but has been given here in detail because in the determination of
cranial capacities, concordant results can be obtained only by the
strictest adherence to a uniform procedure.

The various measurements made by the foregoing methods have
been recorded and tabulated in detail and the individual records
are on file at the Wistar Institute where they are at the service
of other investigators. In the presentation which follows how-
ever, we shall use only mean values, grouping the records for
each series by mean body weights within weight groups differing
by 50 grams. The smallest weight group includes the individuals
betsveen 51 to 100 grams in body weight, and the largest those
between 351 to 400 grams. The higher body weights appearing
in the Philadelphia Norway series have not been considered be-
cause there are no European records with which to compare them.

BODY FORM

Before taking up the records touching the central nervous sys-
tem, it is important to know whether the several series to be
examined are composed of animals having a like body form. The
most general test for likeness in form is the relation of body length
to body weight. The data for such a test are contained in tables
12and13. For our present purpose therefore we select from these
tables the records giving the mean body weights and mean body
lengths for each weight group of each series.

In chart 1 these data for body length both for the Norways and
Albinos are entered in relation to the standard curves for body
length based on Philadelphia material (Donaldson ’09 and Don-
aldson and Hatai, 711). A study of chart 1 shows that the Euro-
pean series of both forms agree fairly with the standard records
as represented by the continuous curves in the chart.

The records for the European Norways run somewhat below
the standard. This is especially noticeable in the case of the
Vienna and Paris series. The records for the European Albinos
agree very closely with the standard curve based on the Phila-
delphia Albinos. On the whole, the accordance between the

SO HENRY H. DONALDSON

BODY LENGTHmm.
2505

250
240 240
| 230
220+ STANDARD CURVE 9 STANDARD CURVE 4220
An a ae ALBINO oi
200} i 200

190
180
170
160
150
140

CHART 1. 130
ee BODY WEIGHT ems.

60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

Chart 1, giving the body length in millimeters for each of the three European
Norway series separately in relation to the standard curve for the body length of
the Philadelphia Norways. Also giving the*body length for the three European
albino series combined, in relation to the standard curve for the body length of the
Philadelphia Albinos. Norways: © = Paris series, & = London series, V =
Vienna series. Albinos: X = European series (combined).

European series and the standards is close. Hence we conclude
that in body form, the European Norways are similar to one
another and to the Philadelphia standard, and that the same rela-
tions are true for the European and Philadelphia Albinos.

Since the completion of this manuscript, a paper by Chisolm
(11) has appeared in which he compares the body length of tame
albino and piebald rats of London with those of the Philadelphia
Albinos as given by me in an earlier paper (Donaldson, ’09).

Chisolm’s measurements agree with mine very well up to about
100 grams of body weight and from there on fall steadily below
the Philadelphia records with a maximum deficiency of about 5
per cent. It seems probable however that this difference is mainly
due to the difference in the method of taking the body length.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED S8I1

TABLE 12

Giving for each body weight group of Mus norvegicus the mean values for all the indi-
viduals from each of the four stations. Below each weight group is also given the
mean for the European series alone.

Records from Philadelphia = A; Paris = P; London = L; Vienna = V

NUMBER OF

CASES BY SEX = | | MEAN
WEIGHT GROUP coal | Cseceam aaa | coe
M. || °F: |
grams mm. | cc.
A 0 1 74.9 157 I SCKD)
iy de 1 2 19.3 142 1 G83
1 t=3100,0)- 25 Oi ker eee eee lees A 87.8 156 1509
[ore I) 8 4 80.6 | 148" 7) Sie 567
Mean of European series.........| .. Senor 82.5 149 1.536
Agial) g2snedie |) 128-2." |) 170m ainingas
P 10 MEO SiG Mealy |) ales
TIDY 1 U5 OES fo ter ater eer eer are ore cena L Sl ae 196 1 179 1.653
WU 4 |) 5 126.0 178 | 1.694
Mean of European series.........|...... eae Bree cscs 127.4 178 1.714
ASP 5) | SE aetOro 9 |) - 194°. |) 12. 897
Ls janie 122 3 10°) 173.8 | 195 | 1.894
PION ce ate sams re ae oe
Cl Vee Sin 20m aia. |) 103 1.788
Mean of Huropeanseries.........)......|...... pera 174.1 | 196 1.860
(} A 11 6 2,226.2 214 | 2.000
TLS eee er | eh eee ee?) «| 2002
L 14 8 224.7 | 214 1.980
V OW esl4 es 223608 4 21a 1.936
MeamonBunepedn series: ...1hs.0|...2-|2 28 oa eee 223.4 211 1.972
A 5 8 28279) {| 225 PAB
SIS EO Tae ee te a a een P| 5 | 10 | 277.8 | 224 | 2.129
L 12 13 272.3 224 2.053
V 8 en | DOs. 221 1.978
Meaniof Huropean series... «2. <2 ..|a1.se\aaeeee nea. _ 270.6 223 2.053
| RS eden is | S266 2! 1 237° | 2! 210
TCS ee ee, ee P | 7 | 5 | 322.2 | 234 | 2.205
L 8 5 320.7 | 234 2.090
V 2 A 22:00) || 250 2.154
Mean of Hurapesn Series.:).. 5 <. slaeeeelies ve line ee ok | 321.9 234 | 2.149
ee 13 2 BME 0 ZAG) | 2.285
SAN 0, 5 i oe ae | P 3 3 377.6 238” Aes
eels 3 1 Sy) 3) 246 2.318
a's 4 ie SCR 245 2 225
Mean of Kuropeanseries. ..... 022 |fcs, <:\o0. ee. Roe eee: 377.0 243 | 2.264

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 1

TABLE 13

HENRY H. DONALDSON

Giving for each body weight group of Mus norvegicus albinus the mean values for all

the individuals from each of the four stations.

Below each weight group is also

given the mean for the European series, so far as represented in the group.

Records from Philadelphia =

AC Paris) — sb London —

L; Vienna = V

NUMBER OF |
WEIGHT GROUP SERIES aia i ais liga Raa onANTAT
M. F. ‘
| grams mm. CC.
A OMe 87.8 5G 1.364
S100. hs ee P yt 90.0 | 158 | 1.443
L
Vv
IRATISSCRIeS: eae eee one ee neo 2, | PLSPNtnbet eeat es 90.0 158 1.443
A LO ts WAY 8) 173 1.524
i - ef land |
101-150 ERS |. ton ee bale a 12 oO 1 117 6 175 | 1.560
L 1 1 128.0 7A 1.494
Hy OW 0 2 145.5 | 174 1.497
Meanofpunopeamiseriess..4-.4<.clusaearle: «one ae 130.4 174 iba ly
A 19 B) || gGb 193 1.661
PO eee Se, P 1} 0 | 173.0 ) 194 | 1.671
L 0 De 184.0 196 1.646
V 1 3 160.2 184 | 1.688
Meamormmunopeaniseriess. ce. o024| hearers: |p cea peers 172.4 191 1.652
A 13 Dy 218.6 1.748
DLP Oe et OMe a Od eal eee eee 208 [ee
L eae ll 234.7 | 209 1.758
V 1 1 | 213.5 199 | 1.704
Mean of European series....... Allee ioc an ete echoed [ease ea 217.1 204 1.761
A if 1 210.9 1.768
251-300 s |
aes Fi. CARRERE con tL | (3) fs 27606 || ois” aieens
V 2 OD) S280) Ara ee | 1.916
Mean of London and Vienna
NGO. Jo) Se nate aCe ee Alicea ile. lems ri ef 283 .0 220 | 1.860

Chisolm used the posterior margin of the symphysis pubis,
while I used the anus, as the caudal limit of the measurement and
thus my measurements must give slightly greater values than were

found by him.

When correction is made for this difference in

method, the two series of records agree nicely and give a welcome

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 83

confirmation of the statements just made concerning the similar-
ity of the albinos on the two sides of the Atlantic.

In this case of body length, as in that of the other data on the
weight of the brain and spinal cord and on cranial capacity, to be
presented later, the records are for the two sexes combined, since
the differences according to sex are so small as to be negligible for
the present investigation (Donaldson and Hatai, ’11).

WEIGHT OF THE CENTRAL NERVOUS SYSTEM

The establishment among the several series of the similarity in
body form clears the way for the study of the weight of the central
nervous system in these same series. The method of direct
weighing is the simplest and, as it has turned out, the most satis-
factory method of attacking the problem before us. Had I to
repeat this investigation I should make only direct determinations
on the weight of the brain and spinal cord and omit those on
cranial capacity, but when the investigation was begun, it was
thought that the longer series of cranial capacity determinations
would be more valuable than a shorter series of direct weighings,
which require withal more time to make; and my time was limited.
Nevertheless I had planned from the first to make direct weighings
of the central nervous system for very short series of the Norways
at each of the European stations. This was not done at Vienna
because specimens for the purpose could not be obtained during
the period of my stay there, but it was done for both the Paris
and the London Norways. It is these latter records which are
now to be considered. The data are given in tables 14 and 15.

When these data for the weight of the brain and the weight of
the spinal cord are entered in relation to the corresponding stand-
ard curves for brain weight based on body weight (Donaldson and
Hatai, ’11) as given in chart 2, it is plain that both the European
series closely agree with the respective standards for brain and
spinal cord. The mean percentage deviation of the values as
observed, from those of the standards, are given in table 16, A.

For comparison and control we have also given in table 16, B,
the mean percentage deviation of the values as observed from

84 HENRY H. DONALDSON

values for the brain weight when based on the body length (Don-
aldson and Hatai, ’11, tables 5 and 8). It will be noted that
the two series of results agree very well.

BRAIN WEIGHT CHART 2.
2 gms. 24
oO
2.3 STANDARD CURVE se
NORWAY
oO
29 2.2
© a
21 eas 21
zo STANDARD CURVE Ae
ALBINO
1.9 i 1.9
18 1.8
SPINAL CORD WEIGHT
0.9 gms. 0.9
©
08 aT 08
STANDARD CURVE
NORWAY
07 0.7
0.6 STANDARD CURVE 0.6

ALBINO
BODY WEIGHT gms,

0.5 0.5
160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330

Chart 2, brain and cord weight of Paris and of London Mus norvegicus, entered
in relation to the respective standard curves for the Philadelphia data. For fur-
ther control, the corresponding standard curves for the Philadelphia Albinos are
also given on the chart. O = Paris series. O = London series.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 85

TABLE 14
Mus norvegicus, Paris. Weight of brain and spinal cord

NUMBER OF CASES BY | ; Se oe hae
wetous nour |____ nee eee eee) UTE

M. F. Brain | Spinal cord

a i | grams mm. grams | grams

HELE BOONES Af ae 1 ate 1686 Piet, (1/2) 1410 0804s

PAOINAPAS( U2 Siete heer citer 3 il EY atl 219 2.2028 | 0.6838
PAS} 0, Ue Ree eee eee eee 1 0 293 .0 230 2.3514 | 0.8630*

BOI SOU sae ceeras Oee tere 2 0 317.0 227 2.2133 | 0.7785

TABLE 15
Mus norvegicus, London. Weight of brain and spinal cord

NUMBER OF CASES BY
andan Clea ces Bone Cheon |e lids as saan
M. F. Brain Spinal cord
Pz grams mm. | grams | grams
POY os ts ese, Be va ae 173.0 197 2.0959 0.5815
PADIS). ee tacee Seen | 1 3 208.5 210 | 2.1404 | 0.6328
OM ck soca ate os | | |
UO DU ane Se) 6 es ound Sd nce | 1 0 305.0 237 | 2.2440 | 0.8031

*As this record for the spinal cord, which is correct, is also exceptional and is
based on a single case only, the record is not used in computing the percentage
deviations given in table 16.

TABLE 16
Mus norvegicus. Mean percentage deviation of the weight of brain and spinal cord
in the Paris and London series from the standard values for the Philadelphia

Norways

A. Comparison on the basis of body weight, as given in table 2

MEAN PERCENTAGE DEVIATION

B. Comparison on the basis of body length

PAE S ase gE NS hes sos ay oo vse ohiad in Po eR +2.9 | +4.5

LOIN Git; Stee Aha ee nm a La le —0'2 | +0.9
PATER A aD N ee B) . 8 1S Seige SOOM Se | | a! | Sei

Average Ol. bOun Aw andsbasye ads aceee ae +1.2 | +2.4

86 HENRY H. DONALDSON

The average of the deviations as given in tables 16, A and 16,
B, is the figure used in the subsequent discussion.

According to these determinations, it is plain that both the
Paris and London Norways have central nervous systems (brain
and spinal cord) slightly heavier than that of the standard Phila-
delphia Norways. The deviations of the European forms from
the standard are so small however, even in the case of the Paris
series, that they are probably not significant. It is possible to
conclude therefore that the Paris and London rats do not have
central nervous systems of less relative weight than those found in
the Philadelphia Norways, while as the records stand, the relative
weight is really slightly higher. Although, as has been explained,
the corresponding data for the Vienna Norways are lacking, we
shall see further on that the true cranial capacity of the Vienna
Norways is compatible with a brain weight about equal to that of
the Philadelphia series or a trifle below it—but probably not
deviating to any significant degree.

Although the data for the percentage of water in the brain and
spinal cord are not presented here because the determinations
could not be made abroad with all the desired precautions, yet the
data as they stand agree well with those for the American Norway
as previously determined (Donaldson and Hatai, *11). In this
respect then the European and American Norways are again in
agreement.

The foregoing determinations are highly important for the
control and interpretation of the data on cranial capacity since
these latter, as we shall see, cannot be taken at their face value,
but must be corrected for shrinkage, which varies not only accord-
ing to age, but also according to other less evident conditions.
The characters of these crania, so far as they are indicated by
weight, have been discussed elsewhere (Donaldson ’12).

CRANIAL CAPACITY

In determining the cranial capacity by the methods given earlier
we obtain in the first instance the weight of the shot necessary to
fill the cranium. It was found that one cubic centimeter of the

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 87

shot used weighed 6.354 grams + 0.020, hence the observed
weight in grams is transformed into volumes in cubic centimeters
by dividing the weight of the shot by 6.354. In tables 12 and 13
the data on the cranial capacity in cubic centimeters are presented
for each one of the entries.

Taking the entries in table 12, which refer to the wild Norways,
we wish in the first instance to learn how the cranial capacities
of the several European series are related to that of the Phila-

9. 4CRANIAL CAPACITY OF
NORWAY RATS 24

Cc,
23

2.2

2.1 — PHILADELPHIA 24
xe RECORDS

CHART 3.

BODY WEIGHT gms.
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

Chart 3, showing the cranial capacity in cubic centimeters for the four Norway
series. The values for the Philadelphia series are represented by a curve com-
puted from formula (1). The values for the European series are entered sep-
arately. O = Paris series, 0 = London series, V = Vienna series.

delphia series taken as a standard. To show this, the European
data have been plotted by groups on chart 3, while the Phila-
delphia records are represented by a continuous line showing the
computed values. For the formula for this line, I am indebted
to Dr. Hatai.

The relation between the computed and the observed values in
the Philadelphia series is close. Except for the second entry
at 128.2 grams, which entry is a trifle high, the observed data for
the cranial capacity of the Philadelphia Norways show an orderly

88 HENRY H. DONALDSON

increase. Assuming then that the terminal values are correct,
that the second entry is aberrant and that the intermediate values
are approximately normal, Dr. Hatai determined the formula
for the curve which fits the observations. This formula is as
follows:

y = 0.00105 x + 0.548 log x + 0.476.......... (1)

where x equals the body weight and y the cranial capacity in cubic
centimeters.

Examination of chart 3 shows at once that the three series of
the European records do not run exactly with the line representing
the Philadelphia series. Inspection shows that the order of the

TABLE 17

Mus norvegicus. Showing the mean percentage deviation in cranial capacity for
each of the three European Norway series from the Philadelphia series taken as a
standard

mean values from highest to lowest is Philadelphia, Paris, London
and Vienna. If then we compute the mean deviation from the
Philadelphia records for each of the European series given on the
chart, we obtain the values entered in table 17.

As table 17 shows, the average of the mean deviations for the
cranial capacity of the European Norway series combined is —2.1
per cent. It thus appears that all the European series for the
Norway rat exhibit a smaller cranial capacity than the Philadel-
phia series and that the most marked deviation occurs in the case
of the London and Vienna series where the deficiency is 2.5 and
3.3 per cent respectively. ,

For the Albinos, the Philadelphia series are also taken as the
standard. The curve is represented by the continuous line in

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 89

chart 4. This is calculated from formula (2). The observed
value for the smallest weight group of the Philadelphia series
was considered normal (see table 13) but that for the largest
weight group was taken midway between the value for the Vienna
series and that observed for the Philadelphia series. The inter-
mediate determination, at a body weight of 175 grams, was also
taken midway between the observed Philadelphia record and the
corresponding record for the London series—which is here low.

go PANIAL CAPACITY OF

2. ALBINO RATS 20
Gic:

1.9 ye 1.9
— PHILADELPHIA B ae

18 RECORDS u : 18

7 ee 7

16 16

15 15

CHART 4.

14 14

/) BODY WEIGHT gms.

0 100 120 140 160 180 200 220 240 260 280 300 "=

Chart 4, showing the cranial capacity in cubic centimeters for the four albino
series. The values for the Philadelphia series are represented by a curve com-
puted from formula (2). The values for the European series are entered separ-
ately. O = Paris series, 0 = London series, VY = Vienna series.

Using these three points, Dr Hatai has kindly devised the follow-
ing formula:

y = 1202 log z= 0:00027) 2 = 0.596.428 bens. (2)

where x is the body weight and y the cranial capacity.

The curve thus obtained is the one entered in chart 4 and used
as the standard from which to compute the deviations of the
records for the European series.. The European albino records
follow in about the same order as the records for the Norways,
1.e., the Paris series give the highest mean value, being above the
standard, while the London and Vienna series are slightly below
it.

These relations suggest that the conditions in the three Euro-
pean stations which act to modify ultimately the cranial capaci-

90 HENRY H. DONALDSON

ty of the dried crania also act in a like manner on both the wild
Norways and the domesticated Albinos. Calculation shows that
the combined records for the European Albinos run somewhat
above those for the Philadelphia Albinos. The figures are given
in table 18.

These results suggest for consideration several important ques-
tions. As is seen in table 17, the mean cranial capacity of the
Paris Norway series is 0.4 per cent less than that of the Phila-
delphia series, while from table 16, we see that the Paris brain
weight is about 2.5 per cent greater. It would appear from this
that the Paris crania had shrunk about 3 per cent more than the
Philadelphia crania. Again table 17 shows the capacity of the

TABLE 18
Mus norvegicus albinus. Showing the mean percentage deviation in cranial capacity
of each of the three European albino series from the Philadelphia series taken as a
standard

SERIES MEAN PERCENTAGE

DEVIATION
Parisien oak Ne BO os en aGeam endo Pe a oes oh eee eeeee +4.9
i Wravave (OLnT. 329 sey tee eR eee i ene Ni he Se ea —0.1
\VAT( a anal tes Alpe eh SI hag RIE, Sor ers ar Pd ah —0.1
IA VERA ONE EM cise. ioe Ohta Abie a ne ete Mi cs ores ee eae ce +1:6

London crania to be about 2.5 per cent less than that of the Phil-
adelphia crania while the brain weights are nearly identical;
once more a greater relative shrinkage in the London series. The
same thing has probably happened in the case of the Vienna
series, but for this series the brain weight determinations are
lacking.

The albino records must also represent crania which have suf-
fered more or less shrinkage characteristic for the series to which
they belong, but as table 18 shows, two of the series run close to
the Philadelphia standard, though slightly below it, while one,
the Paris series, is clearly above it. As the preparatory treatment
of all the skulls was the same, these variations in the amount of
shrinkage must find their explanations in variations in the com-
as represented by the amount of

position of the skull bones

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 91

water, organic matter and salts in them and by their thickness.
Watson (’06) has shown that the constitution of the osseous sys-
tem of the rat can be significantly modified by diet.

In the meantime it is clear that we cannot infer that the brain
weights in the several Norway series are related precisely as are
the cranial capacities.

CRANIAL CAPACITY CHART 5 oy
24 Ge: ] .
23 23

NORWAY Bs
— ——— PHILADELPHIA RECORDS °
24 e EUROPEAN RECORDS 2.1
2.0 2.0
Bs 19
18 18
nf 17
6 ~ ALBINO. ig
—— PHILADELPHIA RECORDS
5p x EUROPEAN RECORDS — 415
14h 1.4

BODY WEIGHT gms.

3
80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 S

Chart 5, cranial capacity based on European series only. Showing the cranial
capacity in cubic centimeters of the Europeanseries of Norways all combined,
contrasted with the computed value (formula 1) for the Philadelphia records and
similarly of the European series of Albinos all combined, contrasted with the com-
puted value (formula 2) for the Philadelphia records. @ = European series—
Norway. X = European series—Albinos.

However, bearing in mind that the cranial capacities of the
three European Norway series combined are probably as much as
2.1 per cent too low, and that so far as the tables 13 and 18 and
chart 4 show, the capacities of the combined European albino
series are slightly (1.6 per cent) above those for the Philadelphia
Albinos, it is possible to make a general comparison between the
two forms as found in Europe, in respect to their cranial capacity.

The data for this comparison are found in tables 12 and 13
and the averages for the European series there given are plotted

92 HENRY H. DONALDSON

in chart 5. In making these averages, the mean values for each
series are taken as they stand in the tables and are not weighted
for the number of cases to which each applies.

When the records for the European albino cranial capacity are
thus compared with those for the European norway, it is evident
that there are considerable differences between the two. The
approximate values of these differences can be determined in the
following way: .

If we take as the standard the body weight values of the Euro-
pean albinos as given in each body weight group in table 13 and

TABLE 19

Showing the percentage values of the differences in cranial capacity between the Euro-
pean Albinos and the European Norways of like body weights. See chart 5. The
values in the fourth column have been read from chart 5

| MEAN CRANIAL CAPACITY

Albinos Norways BUSH ANON AAS
> | grams | 2 y 7

SCO ae Cee o dk shee 90.0 | AAS 1570 | (8.8)
LOIS VO Siren ese c ; 130.4 i ok 1.725 3A; 0
Dy 2 OO Peeters ones, cw 172.4 1.652 1.860 12.6
PDO AS DAR Rats eeoteasye ole oetechs PAL SII iL. “oul 1.960 | Wt.
P25 e100). ae Boece rere 283 .0 1.860 2.070 11.3
US Co ay ae ee A RRL REN ei -c: Hic Gos NG Ge oO otic 12.2

* There is in this weight group only the Paris record, see table 13 and chart 4.
The Paris record, which runs high, raises this value and hence diminishes the per-
centage difference given in the last column, thus slightly diminishing the general
average. Hence the record for the 51-100 grams body weight group is omitted in
making the final average.

enter also for these the cranial capacity as observed, and then
read from chart 5 the corresponding observed values for the cran-
ial capacity of the European Norways, and enter these readings
also in table 19, we have before us the numbers which make it
possible to compute the percentage differences between the albino
and the Norway records (see table 19).

Table 19 shows the average difference between the combined
European Albino and the combined European Norway records
to be 12.2 per cent.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 93

From the foregoing data on cranial capacity, we therefore con-
clude that there is no evidence that any of the European Norway
series represent a small brained strain which might have been the
source of the Albino variety.

The studies on the cranial capacity lead then to the same con-
clusion as was reached from the direct determinations of the
weight of the central nervous system and thus the particular
suggestion which we proposed to test is shown to be without
support. There remain however some minor aspects of these
results on cranial capacity which require further consideration.

TABLE 20

Showing the percentage values of the differences in brain weight between the Phila-
delphia Albinos and the Philadelphia Norways of like body weight—using the
body weights for the European Albinos as given in table 19. Data in column 3
are calculated from the formula for the albino brain weight based on body weight
(Donaldson ’08). Datain column 4 are calculated from the formula for the Norway
brain weight based on body weight (Donaldson and Hatai, ’11)

| MEAN BRAIN WEIGHT | fA a
WEIGHT GROUP poe a = TIGUHIgREANOENGR
_ Albinos | Norways EUS) RRC
SOO Rew. et eet: hese 90.0 * 1.640 | 1.827 | (114) *
NOES SO Mes ae ake hc 130.4 1.740 1.965 12.9
HIL—PA0 ORS ean lapere se eer 172.4 1.814 2.068 14.0
PAU SPAS 0) Sa en en 217.1 1.873 2.152 14.9
Dol UO maria Maire as oe 283 .0 1.941 2.249 | 13 om
CE Rc VRE. AOR Pi ys Ss I NAR Rec OR CSE cree hee | 4. fe

* This entry omitted in making the final average so that this BERNE may be
directly compared with the final average in table 19.

Before it was recognized that the amount of shrinkage of the
skulls in the different series was dissimilar, I had expected to find
the percentage differences between the cranial capacities of the
European Norways and European Albinos approximately equal
to the percentage differences between the brain weights of the
Philadelphia Norways and Philadelphia Albinos.

The data on brain weight which should be used for such a com-
parison are given in table 20.

94 HENRY H. DONALDSON

This table was formed by using the same body weights as are
given in table 19, but in place of the records for cranial capacity,
entering those for brain weight. The average percentage differ-
ence in the brain weight is seen to be 14.4 per cent or 2.2 points
higher than the corresponding value for the cranial capacity—
which is 12.2 per cent.

We have already found that according to the data in table 17,
the crania of the European Norways have shrunk 2.1 per cent more
than those of the Philadelphia Norways, and those of the Euro-
pean Albinos 1.6 per cent less than those of the Philadelphia
Albinos. Therefore if the average observed difference in the
cranial capacity (12.2 per cent) were corrected for the excessive
shrinkage of the European Norway crania, and the deficient
shrinkage of the European Albino crania (1.e., 2.1 + 1.6 = + 3.7
per cent) it would give a value of (12.2 + 3.7) 15.9 per cent as
that for the anticipated average difference in brain weight.

From table 20 the observed difference is seen to be 14.4 per
cent. It is to be remembered however that this last is based on
the brain weights of the Philadelphia forms and that we have
already found, table 16, the brain weight of the European Nor-
ways (Paris and London series) to be 1.2 per cent greater than
that of the Philadelphia Norways. If we use this as a correction,
then the average difference in brain weights becomes (14.4 + 1.2
per cent) 15.6 per cent, or very close to the difference found (15.9
per cent) when the cranial capacities are corrected for the varying
amounts of shrinkage shown by the several series.

Neither the nature of the data nor the method of comparison
will justify us in pushing this argument in detail, but the general
relations thus determined, clearly support the view that the dif-
ference in cranial capacity here found—when corrected for the
unequal shrinkage of the crania in the two forms of the Kuropean
rats, and for the slight excess in the brain weight of the Huropean
Norways, approximates the difference in brain weights which we
should expect to find between the two European forms if the
European and American rats were nearly alike in the relative
weight of their central nervous systems.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 95

There is still to be noted another dissimilarity between the
percentage differences of the cranial capacities (table 19) as com-
pared with the corresponding differences in brain weight (table 20).
This dissimilarity also is due to the manner in which the cranium
shrinks—in this instance according to age. It will be seen by
looking at table 20 that the percentage difference in the brain
weight increases regularly with increasing body weight. On the
other hand, the corresponding records for cranial capacity in table
19 indicate a decrease with increasing body weight. Here again
we should have expected the cranial capacity records to behave
in the same way as the brain weight records, but they do not. We
find the explanation for this disagreement in the shrinkage of the
crania as influenced by age. The argument is as follows:

As is well known, in any series of crania those from the younger
animals contain a larger proportion of water as well as more
organic matter and have thinner bones and hence shrink rela-
tively more when dried than do the crania from the older ani-
mals. We assume then that in any series of crania, loss of water
and thickening of the bones increases with advancing age, and
concomitantly, shrinkage on drying decreases with advancing age.

In the heaviest body weight group of the albinos (table 19)
the crania are the more mature and so shrink less than the crania
of the Norways of like body weight—which are somewhat less
mature. This statement is based on the fact that the Norway
rat, although it has probably the same span of life as the Albino
(Donaldson and Hatai, 711) has nevertheless a much greater range
in body weight and hence in general for a given body weight it
must be younger than the corresponding Albinos, although the
difference in the relative shrinkage for the heaviest body weight
groups may be absolutely small. It follows from what has been
said about the range of body weight in relation to the span of life
in the Norways that an equal diminution in mean body weight,
say 50 grams, implies a greater diminution in age for the Albino
than for the Norway. According to the foregoing reasoning, this
should be followed by a relatively increasing shrinkage in the
albino crania, and this is the interpretation of the values given in
the last column of table 19.

96 HENRY H. DONALDSON

To bring together the observations and comments on cranial
capacity which have just been presented, it appears that while
the European Norways areshown to be distinct from the European
Albinos as regards their cranial capacity, yet the interpretation of
the direct observations is necessarily so modified by the shrinkage
of the crania that in the case of any particular series, we can infer
only in a general way from the cranial capacity to the brain weight.

CONCLUSIONS

1. In the case of the wild Norway rat, which entered western
Europe about the beginning of the eighteenth century, and the
eastern United States about 1775, the observations on the con-
stitution of the populations, the general body form, the weight of
the central nervous system and the cranial capacity, show that
‘it is at the present time essentially similar in these respects in the
two continents.

2. The observations on the albino rat from different stations
indicate that this variety is also essentially similar in the two
continents. Therefore there is no evidence to support the view
that the Albino was derived from a strain of the Norway hav-
ing a relatively small central nervous system.

3. Logically this result does not preclude the possibility of such
an origin, but it does indicate on the other hand the absence of
present evidence in favor of it.

4. That the Norway rats from the three stations in Europe are
very similar to the Philadelphia Norways, despite the difference
in station and the wandering of those that have crossed the sea,
is probably due to the fact that the series of rats which have here
been compared represent those which kept close to man, and all
of which lived among food conditions and other surroundings
characteristic of large cities; conditions and surroundings which
are much the same in western Europe and eastern America.

A like explanation applies also to the similarity found among the
Albinos from these two regions, and perhaps even more forcibly,
as the treatment of these caged animals probably represents a
still more uniform environment than that which the Norways
experience in their wild life.

BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 97

At some future time it will be of interest to examine the Nor-
ways of still other countries—those from India for example—
where we should expect the food conditions to be quite different
from those obtaining in western Europe and North America.

5. The capacity of the dried cranium of the rat is modified
by age and by the amount of calcification to such an extent
that the data for capacity cannot be transformed into those for
brain weight without making correction for several fluctuating
conditions.

6. The constancy of the foregoing characters in the rats (both
Norway and Albino) from western Europe and easter America
indicates that for the purpose of further general studies, the two
populations may be considered as essentially similar.

LITERATURE CITED

Cuisotm, R. A. 1911 On the size and growth of the blood in tame rats. Quart.
J. of Exper. Physiol., vol. 4, no. 3, pp. 207-229.

CunnincHaM, D. J. 1909 Text book of anatomy. 3d edition. William Wood
and Co., New York.

Donaupson, H. H. 1909 On the relation of the body length to the body weight
and to the weight of the brain and of the spinal cord in the albino rat
(Mus norvegicus var. albus). Jour. Comp. Neur., vol. 19, no. 2, pp.
155-167.

Donaupson, H. H. and Harai,S. 1911 A comparison of the Norway rat with the
albino rat in respect to body length, brain weight, spinal cord weight
and the percentage of water in both the brain and the spinal cord.
Jour. Comp. Neur., vol. 21, no. 5, pp. 417-458.

Donatpson, H. H. 1912 On the weight of the crania of Norway and albino

rats from three stations in western Europe and one station in the
United States. Anat. Record, vol. 5, no. 2.

Harat, S. 1907 Studies on the variation and correlation of skull measurements
in both sexes of mature albino rats (Mus norvegicus var. albus). Am.
Jour. Anat., vol. 7, no. 4, pp. 423-441.

Lantz, Davip E. 1909 The brown rat in the United States. U.S. Department
of Agriculture, Biological Survey, Bull. no. 33, pp. 9-54.

Watson, CHALMERS 1906 The influence of an excessive meat diet on the os-
seous system. Proc. Roy. Soc. Edin., 1906-7, vol. 27, part 1, (no. 1).

EXPERIMENTAL STUDIES OF PARALYSES IN DOGS
AFTER MECHANICAL LESIONS IN THEIR SPINAL
CORDS WITH A NOTE ON ‘FUSION’ ATTEMPTED
IN THE CAUDA EQUINAS OR THE SCIATIC NERVES

HENRY O. FEISS

From the H. K. Cushing Laboratory of Experimental Medicine, Western Reserve
University

TWENTY-SEVEN FIGURES

CONTENTS

[trot PRO CIO ta A ia igsG ah we bab Bhar ba aE ere ic ah Big es Gea chs oh ae san gts oe eu iene ag erica 100
JRGRINCIMEL NOI HCV) TROSTOCUAClN ay nc Gus oe Da oe Pe ae aadre cues dato ememenduE Sooner 100
SEDER WLOCUCTIONAO! une Le SION wey Ne Aso eer Abe Ghani: sish-ceyt acai 101
Method of studying the surviving aMintals). 2.092 44sec cu soo gore 101
SEMA Gre aIlt OPS WTA A LEI Al cr ped Oe, cha he cea ott ete eels ah 4 fae ancients eae 102

Part 1. Clinical improvement after the production of the lesion in relation
‘0 the histological findings at different stages....* ..4.........---+--5---:- 102
Gharacversotche clinicalmmprovementemen=.— oes eee eee aac 103
Espolomical simamanyan ces. 2. 2: «- Se e an e em etnies aeerero or eles, 2 103
limerencesmirommoheEaboOviesteuecn |... eeeece conce are hia os =o 104
Bearings of above inferences on infantile paralysis..................... 105
Part 2. The localization of centers in the lumbo-sacral cord. .............. 106
IM etdavarel @n Siiioly Bune) REAR ONIN bbs o6 ccc uSsucnoaeuosuboubobonouHuoUOOEC 106
Inferences from the individual experiments: summary............-.-.+-- 107
Correlation of data derived from individual experiments................ 109
AEE Controlcos(OMlsetRCeteT a: ae eer aera eer ee ees sys mera 109
i Bicgel <0i Lev (ol 0 se cage ae ene A 2°? 22! Si ee eRe 109
GO Sensationes - ca toee oe he ee ree nas OME Ok pawns esa plan 109
Dae Atriailiene Hex si75 sn ne. aces a eee elie sks ce nomen 109
BeControlyot sphimcters.< 4.5, yas r pa sete orate ne ny eae 109
Ha CON CIUSTONE see src Aer eR Re Ne Bisce, Spc n nse Oise 110
Comparison of inferences with current views on the subject............ 110
Significance of cell-groups in grey matter of the spinal cord............ 113

Part 3. Nerve fusion attempted in the caudas and the sciatic nerves in ani-
mals paralyzed by mechanical lesions in the cord......................++ 113
RTE inns OLAUHeT PLOCE GUILE: pcr. to nO Ebr renee 2 ec cr2 sSar).a: « raves oo Sle Sieh 113
We MME NL AMC a GALe a. n10e Wace parse een eee oie te See cuca soe Bis iw a coleta ace Sibel 114
IDASOUS ORS SS Cte se SOE AE SOS 115 ble bot dhowma gt G0 /c..5 cho nerd aes caer pearl Oi Pesan thee 117

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2
APRIL, 1912

100 HENRY O. FEISS

INTRODUCTION
Reasons for the research

The present series of experiments was begun in the spring of
1908 with the production of mechanical lesions in the lumbar
spinal cords of dogs. The object was to bring about distinct
motor paralyses. After the animals had reached permanent
stages in the paralysis, so that there was no question about degen-
eration in the roots and peripheral nerves, it was planned to
attempt to distort the nerve-patterns in these structures, using for
this purpose a method heretofore apparently untried. This
method is referred to as nerve ‘fusion,’ and consists simply in
uniting two or more nerves by tying them together with absorb-
able ligatures.

In carrying out the plan given, it early became apparent that
the subject of nerve ‘fusion’ was a research in itself, requiring
many special experiments. Fusions were therefore attempted
on normal nerves where no central lesions had been produced.
A preliminary report of this work has already appeared', and
we have been able to offer some evidence that after nerves are
united by this method, a certain amount of distortion of pat-
tern may take place.

However, even if changes in nerve-pattern are obtainable by
the union of nerves which are normal, it does not follow that the
same changes may be expected where there has been a central
lesion. Fatty degeneration takes place in the paralyzed muscles
and in the nerve trunks themselves, the degenerated tracts close
up and become replaced by new connective tissue.

Therefore, the original design of producing central lesions and
later trying nerve fusions has been carried out. In the course
of this research two other issues have developed which proved to
be of equal if not greater interest. It was shown that after a
lesion was produced in the spinal cord by the method which will
be outlined, a very characteristic spontaneous recovery took
place similar to the early recovery often seen in infantile

| Feiss: Boston Medical and Surgical Journ., May 11, 1911.

PARALYSES IN DOGS 101

paralysis, and it was found that the material furnished data for
adding to the precision of our knowledge on the localization in
the lumbo-sacral cord certain nuclei of the pelvic viscera and of
the muscles of the hind limb and tail.

This report may therefore, be divided into three parts; in the
first part attempting to account for the clinical improvement
occurring after the lesion, in the second part showing the rela-
tion of the autopsy findings to the peripheral and visceral palsies
produced, and in the third part discussing the subject of fusion
and giving a brief account of some experiments in which, some
months after the lesion, this procedure was attempted.

The production of the lesion

The lesions were made subdurally through a single trephine
opening, usually at the 4th or 5th lumbar spine. The instru-
ment for the purpose (fig. 1) was L-shaped, the longer arm form-
ing the handle and the shorter shaped into a thin blade. This
was entered through the dura in the median line and then moved
laterally with sufficient force to crush the cord substance. Both
unilateral and bilateral lesions were attempted. The operations
were done under complete ether anesthesia with the usual precau-
tions forasepsis. All told, lesions were attempted in some seventy-
five animals, but of course, on account of various causes, including
an epidemic of distemper, the majority of animals were lost.

Method of studying the surviving animals

Observations were made from day to day and notes were made
on the changes. At intervals of 2 or 3 months, each dog was
studied more systematically, according to the following routine:

Attitude

Gait. Nature of limp if present

Active movements: runip, hips, knees, ankles, paws and tail

Passive movements: rump, hips, knees, ankles and paws

Response to stimulation; sharp point applied to skin of various parts of limb
Response of paw to heat with immersion in hot water (heat-pain sense)
Temperature of skin between toes

SE EM Bee Sh

102 HENRY O. FEISS

8. Measurements. Circumferences above paw, ankle and knee

9. Reflexes: knee jerks; anal reflex (observed by inserting glass rod into anus)
10. Control of sphincters (based on ordinary clinical observations)

11. Response to faradism; applied to various parts of limb

12. Remarks

13. Photograph

In a few of the dogs data bearing on spinal localization could
be obtained by direct stimulation of peripheral nerves, which
was done at the time of the secondary operations of nerve fusion.

Study of autopsy material

The spinal cords were studied in twenty of the cases. In six
of them proper identification of the roots could not be made,
owing to scar. The other fourteen were each mounted on card-
board, and the roots spread out, stitched down, and properly
numbered. The count was made from the thirteenth, using the
last rib as a land-mark. Each mounted specimen was sketched
and placed in Miiller’s fluid.

The boundaries of the cord segments were usually estimated
by means of their relations to dural root exits, this relationship
having been based on a number of dissections of normal cords.

After proper hardening, the cord was cut transversely into a
number of pieces without attempting to remove the dura, so as
not to disturb the rootlets within. The exact location of each
of these cuts in relation to dural root exits was indicated on the
sketch. The pieces were cut 2 to 3 mm. thick and imbedded in
celloidin. Sections from each piece were stained by at least three
methods, Hematoxylin-eosin, Van Gieson and Weigert-Pal.

PART 1. CLINICAL IMPROVEMENT AFTER THE PRODUCTION OF
THE LESION IN RELATION TO THE HISTOLOGICAL
FINDINGS AT DIFFERENT STAGES

This portion of the research is based on the studies of twenty
dogs and their spinal cords. The important points are summa-
rized in table 1. Glancing at this, it is seen that after such a
lesion as described, almost all the animals showed more or less
clinical improvement. It is further seen that this improvement

CLINICAL IMPROVEMENT

TABLE 1

HISTOLOGICAL CONDITION

Spinal cord

ment

Roots and nerves

Mass of débris including broken down myelin and blood, which is entered by granulation tissue from pia and dura. This
granulation tissue more dense toward periphery. In the interior there are young fibro blasts with elongated nuclei.
Also many new capillaries. Compound granular cells, small round cells and leucocytes also present. Areas of beginning

Granulation tissue denser than above. Many myelin droplets

left. Some fibroblasts and compound granular cells. Less débris than in above. Leucocytes and round cells in new
connect. tissue. Little repair in grey matter. Some ant. horn cells swollen and pale.

Dense scar with small cavities adjoining. These contain a little débris and a few myelin drops small in size. Some small
nerve fibers, perhaps new, entering cavities. Many round cells.

Zone of dense scar from dura. Nextazone of less well organized connect. tissue containing in its meshes compound granu-
lar cells and myelin drops. Next a zone of a relatively few fibro blasts and myelin drops, débris in large amounts and
old blood. Finally normal cord substance. Some ant. horn cells are bloated.

One main large cavity, which is lined by thin layer of new connect. tissue. Ant. horn cells show bloating and chromatolysis.

Many leucocytes and new vessels.
Much dense sear. Two large cavities still containing the remains of myelin in small amounts.

Large cavity, which tends to follow outline of grey matter.

Ant. horn cells pale and bloated, having lost their polygonal shapes.
Broken down tissue in grey matter.

Cavities.
Light connect. tissue and areas of partial necrosis in grey matter. Some dense scar with cavities.

Dense scar.

When first noticed One month after lesion Two wee after Biante Aes
No improvement
necrosis in neighboring grey matter.
Distinct improvement Similar to above.
noted on 5th day
Distinct improvement | Improvement Marked formation of cavity divided into compartments.
noted on 5th day
Distinct improvement | Improvement Similar to above.
noted on 6th day
Distinct improvement | Improvement Similar to above.
noted on 11th day
Distinct improvement | Improvement Similar to above.
noted on 9th day
No improvement No change No change
Distinct improvement | No change No change
noted on 9th day
Gradual improvement | Improvement No change
Gradual improvement | Improvement Improvement Slight improve- | Dense scar with large patches of round cells.
ment
Gradual improvement | Improvement Improvement Slight improve-
ment Distortion of grey matter.
Ant. horn cells often bloated and show chromatolysis.
Distinct improvement | Improvement Slight improve- | No change Much dense scar.
: ment Distortion of grey matter. Vacuolation of ant. horn cells.
Distinct improvement | Improvement Improvement No change Much dense scar containing cavities.
noted on 13th day
Gradual improvement | Improvement Improvement No change Dense scar and cavities.
Vacuolation of ant. horn cells.
Gradual improvement | Improvement Improvement No change Dense scar containing cavities.
Gradual improvement | Improvement Slight improve- | Slight improve- | Dense scar, débris and light connective tissue.
ment ment Distortion of grey matter.
Distinct improvement | Improvement Slight improve- | No change
noted on 6th day ment
Distinct improvement | Improvement Slight improve- | No change 2 large cavities, one of which follows outlines of grey matter.
noted on 6th day ment
Gradual improvement | Improvement Improvement Slight improve- | 1 large cavity. Thick scar in dura.
ment
Gradual improvement | Improvement Slight improve- Slight improve-

Dense and light scar, one cavity, débris and remains of myelin.
Areas of necrosis in grey matter.

Ant. horn cells often swollen, bloated and pale.

Marked degeneration
in some of the fibers

Similar to above

Complete or almost
complete degen. of
some of the fibers

Similar to above

Some remains of bro-
ken down myelin in
fibers

Some beginning regen-
eration

Some fibers show signs
of degeneration.
Others suggest new
regeneration

Similar to above

Increase in connect. tis-
sue in nerve trunks
Similar to above

Similar to above

Signs of new regenera-
tion in roots

Good regeneration of
many fibers

Similar to above

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No, 2

gee ee .

“

7
rete ew
App ne

< a “
ic. sat al Be

) dtecterotdati Suonteeth

i LAD oe Sud teer. ie
: ; 5 a ee
; Ji Hee LM) PASTY Let rar “iireTel he
meV «2b gi to baton, ¢.
cake coke i ee
2 by, 1g Seay
on a et !
‘
; Aisi hs
et
:
E f o
‘i ae { A ty |
'
.
> ‘
APR P "honey oigans baat?
1 ®
{hh ic . hero ign baat

fail | iv (icone) denial
- f is fs
rs a fly git ane ede
uct? . Rr aa ee
¢t iss ]
YAN AD Aa Paar.

2 ‘ w - | +
~~ » * e — = +2 aaa p0oy anny
- * ; > & ) . '
: “ e ND, OR, I OY saatins h- 08,

PARALYSES IN DOGS 103

fell into two stages, (1) a sudden improvement occurring in the
first or second week, and (2) a slow improvement continuing for
three or four months.

Character of the clinical improvement

The paralysis immediately following the operation was often
a complete paraplegia, sometimes of one leg only, and rarely of the
tail and sphincters. The dog lay in the kennel, seemingly stunned
and not caring for food. He appeared feverish and _ thirsty.
After a day or two, in spite of the paralysis, he made some attempt
to get over the ground, with but partial success. The sudden
improvement in the first or second week was often very marked,
a paraplegia sometimes changing into a mere turning of one paw.
Figs. 2, 3, 4 and 5 show characteristic changes in two of the dogs.
Whether or not the improvement began suddenly, there was
always a period of gradual recovery ending in a permanent state
of residual paralysis.

The question is, how much of the improvement is based on
changes which are histologically demonstrable? The table (table
1) indicates what the chief histological changes were (the topog-
raphy of ten of the lesions is studied in Part 2).

Histological summary

In the early autopsies the location of the lesion was evidenced
by a mass of débris, including broken down myelin in drops,
leucocytes and round cells in clumps. A mass of granulation
tissue had formed along the dura, at the place of injury. This
entered the mass of débris. In this stage, cavities were not
apparent, but in the neighboring grey matter were small areas
of beginning necrosis.

In animals autopsied at the end of one month, the most note-
worthy thing was the appearance of cavity-like spaces. These
were formed of connective tissue bands some of which had become
well defined owing to the partial removal of the tissue débris.
By this time the sear connected with the dura had become ‘quite
dense.

104 HENRY O. FEISS

At the end of two to three months, the sections showed the per-
manent histological characteristics of the lesion. These were
either cavity spaces or scar, or both. The cavity spaces were
sometimes sharply circumscribed, and occasionally their outlines
corresponded to the original outlines of the grey matter. In gen-
eral, it seemed that the amount of scar depended on the amount
of direct injury to the pia and dura, and the size of the cavity-
spaces on the extent of the original destruction of cord substance,
although of course, the extent of the original cavities could not
be completely judged on account of tissue repair. In some places
the grey matter showed marked distortion of outline, suggesting
contraction.

As to signs of nerve regeneration in the cord, one occasionally
saw among the débris and granulation tissue small fibers with
faint coats of myelin. But of course, there was no way of telling
whether these indicated repair; if they ‘did it could have been
slight only.

In all stages, one saw striking changes in the ganglion cells of
the gray matter, near the lesion. These consisted in alterations
in size, shape and staining, reactions as well as chromatolysis and
vacuolation.

Inferences from the above

Judging from the histological condition one could divide the
anatomical appearances into two stages, roughly corresponding
to the two stages in the clinical improvement. It seemed likely
that the early improvement was partially due to the removal of
tissue débris, because the cavities became apparent about that
time. Also as shown clinically, by the swelling about the wound,
there was at first marked fluid exudate, the absorption or escape
of which was undoubtedly a factor in that improvement.

As to the more gradual improvement that supervened in most
of the cases, disregarding the anatomic evidence of repair of nerve
tissue in the cord itself, as being too slight to explain the marked
restoration of function, there are four other explanations to be
considered: (1), actual regeneration of nerve fibers in roots and
peripheral nerves; (2), vicarious activity of nerves and muscles

PARALYSES IN DOGS 105

(including employment of other paths in the cord); (3), failure
of many of the neurones originally pressed on by the exudate to
degenerate completely, so that with removal of the exudate they
recovered their functions; (4), changes in subjective state in the
animal as brought about by lessened discomfort. (The last two
explanations might also apply to the early improvement.) We
cannot say which of these factors were most important—in fact,
it is possible that all of them had a share in explaining the clin-
ical change for the better.

Previous researches on the subject

That marked restoration of power may occur after lesions in
the central nervous system is well known. This applies both
to cortical extirpations,? and to hemisections in the cord.* The
fact that there is also considerable restoration of power after
complete section would seem to indicate that there might be
regeneration across the scar. This has been actually observed
in some of the lower animals.4. Brown-Sequard noted it in fishes
and Fraisse in amphibians. But in higher animals it has not been
observed,* and for this reason, in cases of hemisection restoration
of the clinical state has been said to be partially due to the em-
ployment of paths on the contralateral side. Be that as it may,
it is not necessary to base the restoration of function on nerve
repair across the scar because the clinical improvement seemed
practically as great in our cases where, on account of the extent
of the lesion, conditions for nerve repair were not favorable and
where, moreover, signs of such repair were scarcely to be made out.

Bearing of above inferences on infantile paralysis

The spontaneous restoration of power noted in our dogs is
very similar to that often observed in infantile paralysis. This
applies both to the early and late improvement. The former,

2 Sherrington: Integrative action of the nervous system, 1906, p. 277.
3 Weiss: Sitz. d. Akad. d. k., Wissensch., Wien, 1879, Bd. 80.

¢ Bechterew: Functionen der Nerven Centra, 1908, vol. 1, p. 652.

5 Schiefferdecker: Virchow’s Archiv, Bd. 67.

106 HENRY O. FEISS

also in that disease, is at least partially due to the removal of
inflammatory material, somewhat as in the conditions described
above, where the exudate is dependent only on simple mechani-
eal lesions, although part of the recovery in infantile paralysis
may be related to cell changes which take place as a result of
the expulsion or neutralization of specific toxines. As regards
the later improvement in that disease, one is just as much in
doubt as to which of the factors above mentioned is of greatest
significance.

It is plain, however, that the spontaneous recovery observed
in infantile paralysis is perhaps an attribute less characteristic
of the disease than of the anatomical structures which the dis-
ease attacks. Whether it is a clean section, or a crushing lesion
or an inflammation set up by some virus, there are certain suc-
ceeding manifestations that seem to be common to all these ante-
cedents, and these manifestations are exhibited with striking
clearness simply because of the fact that in the central nervous
system, a relatively small anatomical change affects an extremely
large physiological sphere.

PART 2. THE LOCALIZATION OF CENTERS IN THE LUMBO-
SACRAL CORD

Method of study and reasoning

This part of the research is based on ten of the experiments.
The study of data furnished by this material is summarized in
tabular form (table 2) and each experiment is illustrated with a
photograph, and a diagram based on the sketch made at the
autopsy. In these diagrams only direct involvements due to
the lesions are indicated. The degenerations were partly due
to secondary operations, and are therefore best omitted, because
under the circumstances they throw no light on the localization.

in handling the data, each case is analyzed for itself and the
inferences individually derived are collated according to the impor-
tant clinical and physiological headings under which each was
studied. The cord segments were numbered according to the
roots, calling the root issuing beneath the last rib, the 13th.

CONTROL OF JOINTS

TABLE 2

Paralysis of dorsal flex. of left paw Poor on

and ankle
Direct stimulation evoked no re-
sponse in left E. P.

Paralysis of dorsal flexion of right
paw and ankle.
of rt. hip and knee

Direct stimulation evoked no re-
sponse in right E. P.

Paralysis of rt. paw and ankle and
of dorsal flex. of left paw and
ankle. Weak extension of rt.
hip and knee and some weakness
of It. hip and knee

Direct stimulation evoked no re-
sponse in either E. P. and very
slight (of toes only) in rt. I. P.

Slight weakness in dorsal flex. of
rt. paw and ankle

Paralysis of entire left leg except
for flex. of hip. Weak extension
of knee and weak flex. of hip on
right

Weakness of gluteals and hamstrings
on rt. hip flexed and knee straight
and stiff

Paw paralyzed and flaccid

Spastic loss of control of hind parts
from pelvis down.
erector spinae, glutei and quadri-
ceps. Hamstrings fairly good

Flaccid paralysis of hind parts from
pelvis down,
Paralysis of tail and slight weakness,

in dorsal flex. of rt. paw.

Paralysis of tail

masronne oF | arte tor —— oe
oo. (pax) Knee jerk Anal Anus | Bladder
No test Absent on | Sluggish N N
both legs left
Poor on Poor on Absent on | Sluggish N N
Weak extension rt. leg right right
Poor on Poor on Absent on | Sluggish N Weak
rt. leg right right
Weak on
left
N N N Sluggish N N
Poor on No test Absent on | Sluggish N N
left left
Weak on
right
Poor on Poor on Absent on N N N
right right right
Poor on N N N N N
Weakness of left
Poor on No test Absent on | No test Weak Weak
both both
Poor on Poor on N Sluggish Weak Weak
tail tail
On legs
N
Poor on Poor on N Sluggish N Weak
tail tail

CORD AND ROOT INVOLVEMENT
(See diagrams)

POSITIVE CONCLUSIONS FOR INDIVIDUAL

In upper 7th L. seg. post. horns and cols. on both sides.

On left, lat. col. and upper 7 of ant. horn. In Ist S. seg.
cent. part of grey matter on left. In 5th, 6th, 7th and Ist
S. seg. postero-mesial col. 5th and 6th post. roots.

In mid. 4th L. seg., lower part of rt. ant. horn and adjoining
col. Inhigh 5th L. seg., entire rt. ant. horn and adjoining
col. In low. 5th L, seg., entire rt. half of cord except ant.
mesial col. In mid. 6th L. seg., whole cord except ant.
cols. and lower part of lt. lat. In upper 7th rt. ventro-
mesial col. very narrow 4th, 5th and 6th rt. ant. roots.

In upper 5th L. seg., rt. side of cord except pyram. tract, also
It. ant. horn. In low. 5th L. seg. rt. sideofcord. Inmid.
6th whole cord except It. ant. col. and small part of It.
ant. horn. In upper 7th inner } of rt. ant. horn.
5th and part of 6th rt. and lt. ant. and post. roots and 4th
rt. ant. root.

In mid. 6th all of grey matter and dorsal and ventral cols.
which are partly spared on left. In upper 7th rt. ant.
horn, rt. lat. col., both ant. cols. and lower ¢ of It. ant.
horn. 6th rt. post. and 6th and 7th rt. ant, roots.

In upper 6th whole left of cord, and dorso- and ventro-mesial
cols. and inner part of grey matter onrt. In low. 6th lt.
ant. horn and It. antero-lat. col.; also inner part of rt. ant.
horn. In low.7th outer part of It. ant. horn and It. antero-
lat. col. In 2d Sac. grey matter about central canal. 5th
6th, 7th and 1st It. ant. roots; 5th and 6th It. post. roots;
6th rt. ant. root.

In mid. 6th dorsal cols. and inner part of base of rt. post.
horn. In upper 7th rt. side of cord and dorsal col. and
inner part of grey matter onlt. In 1st Sac. rt. side of cord
and inner part of It. ant. horn. 6th and 7th rt. post. horns.

In mid. 4th rt. ant. horn. In upper 5th It. post. and all of
antero-mesial cols. rt. ant. horn, most of lt. grey matter. In
mid. 5th all of cord except rt. post.horn. Inlow.5th whole
cord. Inhigh 6th lt. of cord. In mid. 6th ant. cols. and lower
part of ant. horns. 4th, 5th, and part of 6th rt. and It.
ant. roots 4th It. post. root.

In mid. 5th, base of dorsal cols. part of rt. ant. root. In
low. 5th, all of grey matter and dorsal and vent. cols. ex-
cept left post. horn and small part of vent. col. adjoining.
In mid. 6th all of grey matter and rt. ventral and lat. cols.
In mid. 7th rt. ant. horn and inner part of lt. grey matter.
5th, 6th and part of 7th rt. It. ant. roots, rt. 5th post. root.

In mid. 6th dorso-mesial col. In mid. 7th rt. side of cord,
dorso- and ventro-mesial cols. and inner part of lt. grey
matter. In low Ist Sac., whole of cord (conus). 5th and
6th rt. ant. and post. roots.

In upper 7th, all of grey matter except It. post. horn; also
vent. cols. and lower part of rt. lat. col. and rt. dorsal
col. In lower 7th entire cord (conus).

Dorsal flexion of paw and ankle (E. P.), in dorsal part of
ant. horn of upper 7th L.

Dorsal flexion of paw and ankle (E. P.)—in lower 6th L.

1. P. control lower (in 7th)

Extens. of hip and knee in 5th

Gap between centers of lower and upper leg, perhaps con-
taining centers of hamstrings

Dorsal flex. of paw and ankle (E. P.) in mid. 6th

Plantar flex. of paw and ankle (I, P. ) in inner dorsal part of
ant. horn of upper 7th

Extens. of hip and knee in 5th

Dorsal flex. of paw and ankle (E. P. ) partly in upper 7th.
Gap between centers of lower and upper leg

Control of most of leg in 5th seg. and those below
Point sensation passes through 5th post. root

Sciatic centers in 7th L. and Ist Sac.

Some crural and gluteal centers in upper 5th. Hamstrings
below mid. 6th

Transection in lower 5th cuts off brain control of lower leg

Point sensation passes through 4th post. root

Heat-pain sensation above mid. 5th

K.J. anal reflex, control of sphincters below upper 6th

Control of hind parts including sensation, K.J.’s and sphinc-
ters in 5th to 7th inclusive

Control of motion and sensation to point and heat-pain in
tail in 7th L. and Ist S.
Anal reflex and control of sphincters in 7th L. and Ist Sac.

Control of motion and sensation to point and heat-pain in
tail in 7th L.
Anal reflex and control of bladder in 7th L.

Letter N = normal.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL, 22, No, 2

E. P, = external popliteal. I. P. = Internal popliteal

—

vl
,
aT 1
\
I
‘
'
:
:
°
:
te
iS o0

= 7 v
we 4 daa seen 5 lan ad 4. oe

aa
HY
fet
’ wa
‘ ? f
, A
\ fi E
pee ,
i
: 4
@ \
:
‘> Poa
i 4 “ee
5 i
: sib entice acusten
ata brag
? \
' ay ee oie seit hed
dd hy ‘xen bie sor 8
-
ad
‘as Dod
t
Awe
, ge f
+
» whe
a boi
“~~ Di

PARALYSES IN DOGS 107

Unfortunately, the ribs themselves were not counted, so that
the possibility of variation must not be lost sight of, as a source
of error.

The most pertinent information is that obtained in the individ-
ual case by comparing rights and lefts. Other things being equal,
one may in certain cases, ascribe a unilateral effect toa correspond-
ing unilateral lesion. In the same way by proper elimination,
bilateral effects may sometimes be ascribed to bilateral lesions.
It will be apparent that the collation of all the evidence according
to numerical segments offers less exact conclusions than those
which can be derived in the same individual and more especially
with reference to the relative position of centers. But by com-
paring relationships and detecting correspondence, certain infer-
ences of significance may be obtained. Aside from the assump-
tion that the upper leg centers are, generally speaking, higher
than those of the lower leg, no further assumptions were used,
except, of course, such as are based on the classical conceptions
of the functions of anterior and posterior roots and of the white
and grey matter of the spinal cord.

Inferences from individual experiments: summary

Experiment 64. (Figs. 6 and 7.) External popliteal paralysis on
left not accounted for by slight anterior root damage as there was simi-
lar damage on right where there was no paralysis. Therefore the exter-
nal popliteal centers must be in the upper 7th lumbar segment, and by
comparing right and left anterior horns, they must be in the dorsal two-
thirds of the horn. Loss of left knee jerk accounted for by involve-
ment of 5th and 6th posterior roots. If internal popliteal centers are
at the level of or below the external popliteal centers (see Experiments 78
and 86), paths for voluntary control seem to run in the anterior column.

Experiment 78. (Figs. 8 and 9.) Weakness of right knee and hip
best explained by involvement in 5th lumbar segment and anterior
root filaments attached. As lesion in grey matter of middle 6th lumbar
leg is bilateral and left leg seemed good, it could not account for paraly-
sis of right external popliteal, which is consequently traceable to damage
of right anterior roots attached to lower 6th and upper 7th lumbar seg-
ments. Both internal popliteals being good, their centers must be lower
than external popliteal centers, for they could not be higher on account
of bilateral lesion just above, which les.on also suggests a possible gap
between upper and lower leg centers. Extinction of right knee jerk
explained by 5th and 6th anterior root involvement. Voluntary dor-

108 HENRY O. FEISS

sal and plantar flexion of left paw and ankle, and plantar flexion of right
seems possible with only anterior columns open.

Experiment 86. (Figs. 10 and 11.) External popliteal paralysis on
both sides due to damage in middle 6th and lumbar segments and roots
attached. Almost complete paralysis of internal popliteal on right
and not on left corresponds to lesion in upper 7th lumbar segment.
Loss of point and heat-pain sensation on right and not on left explained
by lesion in right half of cord in 5th lumbar segment. The difference
in damage to grey matter in lower 6th and upper 7th lumbar segments
must account for preservation of left knee jerk. As internal popliteal
is good on left and its centers are in upper 7th lumbar segment, impulses
from the brain to its synapses must have passed through the marginal
portion of the anterior column in the segment above.

Experiment 69. (Figs. 12 and 13.) The difference between the right
and left anterior horn involvement in the upper 7th might explain the
weakness of the right external popliteal. Lesion in 6th lumbar segment
suggests a gap between upper and lower leg centers. This lesion seems
to have had no effect on either knee jerk or on sensations, suggesting
that these latter must have entered through upper 6th rootlets or higher.
As the centers presiding over control of right paw may be presumed to
be below the 5th lumbar segment, the extent of the lesion might denote
that such control was cut off on that side. Therefore, as the dog used
the paw quite well (except for the external popliteal weakness mentioned)
it is possible that impulses crossed from the other side, where the lat-
eral column was good.

Experiment 65. (Figs. 14 and 15.) The extensive paralysis of the
left leg and paw together with loss of knee jerk, best accounted for by
severe root involvement, while the weakness in the right upper leg is
accounted for by damage to anterior horn in lower 6th lumbar segment
and some of the 6th anterior root filaments.

Experiment 75. (Figs. 16 and 17.) Here permanent flexure of right
hip and stiffness of knee, perhaps due to weakness of gluteals and ham-
strings respectively, caused by damage of 5th, 6th and 7th anterior
roots. The lower leg paralysis explained by Jesion in 7th lumbar and
lst sacral segments. Loss of right knee jerk explained by damage to
6th posterior root.

Experiment 70. (Figs. 18 and 19.) The lesion in lower part of 5th
lumbar segment involved entire cord, practically acting as a trans-sec-
tion. This accounts for loss of control and spasticity of hind parts,
and places most of leg centers below that segment. It is likely that
preservation of knee jerk, anal reflex and control of sphincters is due to
sparing of centers below middle 6th lumbar segment (the anterior roots
being also destroyed above that level).

Experiment 72. (Figs. 20 and 21.) The lesion in upper 5th, 6th and
7th lumbar segments, with the corresponding anterior root damage ac-
counts for loss of control of hind parts, including point sensation, knee
jerks and sphincters.

Experiment 68. (Figs. 22 and 23.) Impairment of control of motion,
point and heat-pain sensation of tail, together with impairment of anal

PARALYSES IN DOGS 109

reflex and sphincteric control, all accounted for by lesion in 7th lumbar
and Ist sacral segments. Slight paralysis of right paw also explained
by damage to right anterior roots.

Experiment 78. (Figs. 24 and 25.) Impairment of control of motion,
point and heat-pain sensation in tail, together with impairment of anal
reflex and bladder control, all accounted for by lesion in the 7th lumbar
segment.

Correlation of data derived from individual experiments

A. Control of joints. Upper leg centers are mostly in the
5th and 6th lumbar segments, that is, about the level of the 4th
dural root exit. Lower leg centers are in the lower 6th and the
7th lumbar segments, that is, at the level of the 5th dural root
exits. Nuclei of the external popliteal, the internal popliteal
and the tail are somewhat circumscribed and relatively isolated,
and the nucleus of the external popliteal is, as a whole, higher
than that of the internal popliteal. There may be some over-
lapping of nuclei, but in one portion of the cord, namely, the mid-
dle 6th lumbar segment, there seem to be relatively few centers,
the nuclei of the upper and lower leg seeming to be respectively
above and below this apparent gap. (Possibly the hamstring
centers lie here.)

It is suggested that the anterior columns contain fibers from
the brain which convey volitional impulses.

B. Knee jerks. Its extinction or weakening is consistent with
corresponding damage to either the roots or grey matter of the
5th and 6th lumbar segments.

C. Sensation. As to point sensation of the whole leg, the 4th
and 5th posterior roots seem important links in the afferent chain.

As to heat-pain sensation of the paw (studied by immersion in
hot water), the test was omitted in three of the experiments and
was always accompanied by loss of point sensation. In one case
however (Experiment 70), point sensation was lost without
corresponding impairment of heat-pain sensation in paw.

D. Anal reflex. This test was omitted in one case, found
impaired in seven and normal in two.

E. Control of sphincters. Their centers lie below the 6th
lumbar segment. It is suggested by comparison of two cases

hg HENRY O. FEISS

(Experiments 68 and 73) that the bladder centers are higher than
the anal centers. Sphincteric centers are very close to tail cen-
ters (5th dural exit).

F. Conclusion. Inferences cannot be drawn for every point
investigated, but there is significance to certain isolated facts,
such for example, as pertains to the relative isolation of the exter-
nal popliteal and internal popliteal centers, suggesting perhaps
that these nerves, which on account of their individual spheres
of distribution control the best codrdinated joint movements, have
their nuclei relatively best defined. The main suggestion is that
the grouping of cells seems to correspond at least roughly to the
gathering of fibers in individual peripheral nerves.

Comparison of above inferences with current views on the subject

As regards the cases where preservation of voluntary control
in certain muscles seemed to depend on paths in the anterior
columns, which alone were open, other experiments are on rec-
ord,® which show that in dogs and other animals, these columns
do convey motor fibers from the brain. There is also the possi-
bility of the employment of paths on the contralateral side (cf.
Part 1) and in one of our cases (Experiment 69) this seems to
be the only explanation for preservation of control of the paw, for
the lesion had blocked all the homolateral paths higher up.

With reference to the knee jerk our localization in the 5th and
6th lumbar segments corresponds to Sherrington’s more accurate
findings.7

As to sensations, anal reflex and relative warmth of the paws,
our findings are too few to be entitled to colligation with those
of others.

The most important question that we have to consider is the
significance of the cell-groups in the grey matter of the cord.
Three methods have been previously used to investigate this
point, the first being that of direct stimulation of spinal roots.
The findings depend on the presumption that the cells of origin

6 Bechterew: Functionen der Nerven Centra, 1908, vol. 2, p. 667.
7 Sherrington: Schaefer’s Text-book of Physiology, 1900, vol. 2, p. 874.

PARALYSES IN DOGS aha

of the fibers in a given root are about on a level with the super-
ficial origin of that root from the cord. Sherrington’ has advanced
some evidence for this, which evidence is based partly on the
fact that after section through the cord just above a given ante-
rior root, very little degeneration is to. be seen in the fibers of that
root, and partly on the results of direct stimulation of roots above
and below the place of section. Besides Sherrington’s contribu-
tion important reports on the results of direct stimulation of roots
have been made by Bikeles and Gizelt,? Langley,!® and Risien
Russel.4! The subject has been studied in connection with the
formation of the lumbo-sacral plexus. The results agree fairly
well, the fibers constituting the main nerve trunks being said to
arise from the cord in the following descending order: crural,
obturator, gluteal, sciatic, tail and sphincters. The internal
popliteal fibers are, as a whole, placed higher than the external
popliteal. There is supposed to be considerable overlapping of
nuclei. Further than this longitudinal relationship, little infor-,
mation is obtainable by the method. Our results conform fairly
well to the above order except as regards to relative height of the
external popliteal and internal popliteal.

A second method is based upon the pathological findings in
human beings in such conditions where definite motor paralysis
were clinically under observation” (infantile paralysis, tumors of
the cord, etc.). The observations are, however, very fragmentary.

The third method consists either in the amputation of limbs
or parts of limbs, or in the excision of peripheral nerves, and
later studying the ganglion-cell changes to be observed in the
spinal cord. Valuable contributions have been those by Sano,"
Van Gehuchten and Nelis,“* Flatau,!* Marinesco,'* Bruce,!? and

§ Sherrington: Journ. of Physiol., vol. 13, 1892, p. 621.

* Bikeles and Gizelt: Pfliiger’s Archiv, 1905, vol. 106, p. 43.

10 Langley: Journ. of Physiol., 1891, vol. 12, p. 347.

41 Risien Russel: Proceed. Royal Soc., 1894, vol. 54, p. 243.

Wickmann: Die Riickenmark-nerven und ihre Segment-beziige, Berlin, 1901.

8 Sano: Les localizations des functions motrices de la moelle épiniére, 1908.

4 Van Gehuchten and Nelis: Jour. de. Neurol., 1898, p. 301.

16 Flatau: Archiv f. Anat. u. Physiol. Physiol. Abt., 1898, p. 112.

16 Marinesco: Revue Neurol., 1898, p. 483.
‘7 Bruce: Topographical atlas of spinal cord. 1901.

12 HENRY O. FEISS

Knape.'’ Knape is practically the only one of these who leans
toward the theory that cell groups represent collections of fibers
in peripheral nerves. Even he does not describe sharply cireum-
scribed nuclei as representing these nerves. He let his animals
run a long time after excising the nerves, and before he studied
the cords, in several cases allowing an interval of almost five
years to intervene. His nuclei extend over more segments than
our own.

As to previous observations on sphincteric control, reliance
has usually been placed upon the stimulation of roots.1® Accord-
ing to most observers?® 24 22 the nerve supply affecting control
of micturition in dog and cat comes from two sources in the cord,
an upper from the 3d, 4th and 5th lumbar roots, and a lower
from the 2d and 3d sacral roots. Nerve fibers are sorted out
in the hypogastric plexus before they finally pass to the bladder
itself. According to Bechterew,?? Sherrington,24 Langley and
Anderson,”> and others, the lower source is especially important.
This does not conform to our localization for bladder control in
the 7th lumbar or 1st sacral segments.

Very much like the bladder, the rectum receives its nerve-supply
from two sources,”° and from about the same spinal nerves. More-
over, as in the case of that organ, the sacral nerves are much more
important than the lumbar. Masius,2”7 and Ott,?8 like ourselves,
place the center higher than the lower source given by the others.

18 Knape: Ziegler’s Beitrage. 1901, vol. 29, p. 251.

‘9 Langendorff: Nagels Handbuch der Physiologie, vol. 4, 1st half, p. 350.

20 Nawrocki and Scabitschewsky: Pfliiger’s Archiv, 1891, vol. 48, p. 335, vol.
49, p. 141.

*t Budge: Zeitsch. f. rational med., 1864, vol. 21, pp. 1 and 174.

22 ©. C. Stewart: Amer. Jour. of Physiol., 1899, vol. 2, p. 182.

** Bechterew: Functionen der Nerven Centra, 1908, vol. 1, p. 292.

*4 Sherrington: Schaefer’s Text-book of Physiology, 1900, vol. 2, p. 874.

*» Langley and Anderson: Jour. of Physiol., 1895, vol. 19, p. 71.

°° Starling: Schaefer’s Text-book of Physiology, 1900, vol. 2, p. 336.

*7 Masius: Bull. Acad. Royal de Belgique, pp. 67, 68.

*6 Ott: Jour. of Physiol., 1879, vol. 2, p. 54.

PARALYSES IN DOGS tS

The significance of cell-groups in the grey matter of the spinal cord

According to different authors, the cell-groups in the gray matter
of the cord are variously supposed to represent muscles, peripheral
nerves, primary metameres or movements (as in the cortex).
After a rather careful.scrutiny of some of the literature, beside
that mentioned above, we feel that in the present state ofour
knowledge, there is not sufficient evidence for any of these explan-
ations. It is by no means certain that these cell-groups have
any physiologic significance whatever. According to Knape, as
above shown, and according to our own experiments, the findings
seemed to point somewhat toward the peripheral nerve theory.
Another piece of evidence for this theory is the fact that some of
the cranial nerves have their cells of origin grouped in fairly well
circumscribed nuclei. But neither is this analogy, nor the other
evidence which we have cited, of sufficient weight to carry con-
viction. If the grouping of cells in the cord is ever susceptible
of explanation, much further investigation will be required.

PART 38. NERVE FUSION ATTEMPTED IN THE CAUDAS AND THE
SCIATIC NERVES IN ANIMALS PARALYZED BY MECHAN-
ICAL LESIONS IN THE SPINAL CORD

This part of the research is based on eight cases, the only ones
in which the animals survived both the original spinal lesion and a
secondary ‘fusion’ done some time after they had reached per-
manent states in their paralyses.

~The aim of the procedure

Nerve fusion, it has been stated, consists simply in uniting two
or more nerves by tying them together with absorbable ligatures.
In the preliminary report?? the theoretical basis for this procedure
is given, the important point being that the direction of fibers
regenerating in scar is governed by conditions offered by the mass
of proliferated cells and nuclei which are here formed. As these
are laid down in all directions the new fibers which develop in
the interstices of the cells must grow accordingly. Therefore it

29 Feiss: Boston Medical and Surgical Journ., May 11, 1911.

114 HENRY O. FEISS

may be hoped that permanent changes in nerve pattern might
result, and if two or more nerves are joined, that the mechanical
attributes of the scar might cause fibers from fascicles of one
nerve to pass into those of another. Besides, as shown by
Perroncito,*®® Bethe*! and others, one might even hope for branch-
ing of some of the regenerating fibers, so that if certain tracts,
previously emptied by the paralysis, are entered by the new
branches, there might result not only a change in nerve pattern
but perhaps also a relative increase in the number of fibers. The
purpose of the ligature is thus seen—it not only brings the nerves
into physical apposition, but it also crushes them so as to cause
the scar to form. Being absorbable (cat-gut) it disappears of
itself. Compared with the older method of nerve crossing by
suture, the theoretical advantages are: (1), that no division of
nerves may be necessary; (2), that as many nerves as are in phys-
ical proximity may be included in the fusion; and (3), that change
of nerve pattern may be hoped for in the individual nerve, even
if no other unites with it.

Of special interest is the fact that in the cauda, at the region of
the interspace between the dural exits of the 5th and 6th lumbar
roots (dog) one may intradurally gather all the roots which supply
the hind limb and tail into a compact bundle, and fuse them in
the manner suggested above. In fact, by retracting the sensory
roots, the motor roots alone may be thus joined together.

Below are given summaries of experiments in which fusions
were attempted either in the cauda or in the sciatic nerves, some
months after primary lesions were produced. These lesions have
already been described (Part 2). The essential facts in the
secondary fusions are given in table 3.

Experimental data*?

Experiment 64. Lesion, January 18, 1910. On April 27, 1910, resid-
ual paralysis (fig. 6) chiefly of left external popliteal. On this date,
following operation, left sciatic exposed, and after faradic stimulation*

30 Perroncito: Ziegler’s Beitrige, 1907, vol. 42, p. 354.

1. Bethe: Pfliiger’s Archiv, 1907, vol. 116, p. 385.

82 All exposures of roots and nerves were made under full ether anaesthesia.

%¢ Tn all the experiments a du Bois coil with 10,000 windings of the secondary
and a two-pint Daniell cell in the primary current, were used.

PARALYSES IN DOGS i 5)

determining that there was no response in the external popliteal the two
popliteals (sciatic) crushed with haemostat and tied together with three
eat-gut ligatures one-quarter inch apart. On August 19 (114 days
after fusion), same nerves exposed, and firm neuroma found at place of
fusion. Faradic stimulation of external popliteal showed flexion of
toes, but no extension. Internal popliteal responded normally. On
November 6 (193 days after fusion) similar responses and animal sac-
rificed. No clinical improvement noted.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2

116 HENRY O. FEISS

Anatomic report (In this and the following experiments, sections were
stained by Weigert-Pal and general methods): Left sciatic above scar
showed normal fibers and some unusual patches of connective tissue.
Sections through midst of neuroma showed many small, and partially
myelinated fibers some in bundles and others scattered among the cells
of the scar. Scar dense and contains numerous nuclei. Popliteals
below scar show scattered fibers with large interspaces and myelination,
although not complete further advanced than in sear. Some large
areas where no fibers appear suggesting that sheaths emptied by lesion,
have not been filled.

Experiment 65. Lesion, January 19, 1910. On April 28, 1910,
residual paralysis (fig. 14) chiefly of left leg. On this date, following
operation: 6th and 7th arches removed, dura opened, cauda exposed.
Sensory roots lifted aside and such motor roots as lay in the field stim-
ulated. No response except in tail. Motor roots fused with one cat-
gut ligature and crushed with haemostat. Dura sewed. Wound closed
tight. No clinical improvement noted after operation. On September
26, 1910, stimulation of roots attempted with doubtful results. Ani-
mal sacrificed.

Anatomic report: Partial disappearance of anterior roots at region
of fusion. Some scar with only a few nerve fibers interwoven in it.
Roots peripheral to scar show greater numbers of fibers and myelination
further advanced.

Experiment 68. Lesion, March 17, 1910. On June 10, 1910, resid-
ual paralysis (fig. 22) chiefly of tail and slight weakness of dorsal flex-
ion of right paw. On this date following operation: 6th lumbar arch
removed and all sacral and coccygeal roots (both anterior and posterior)
constituting cauda at this region, fused with two cat-gut lgatures.
No change noted after operation till in September or October, when tail
seemed to be moved better (figs. 26 and 27). Thereafter but little gain.
On November 30, 1910 (173 days after fusion), all roots divided and stim-
ulated peripheral to fusion-neuroma and found to evoke tail movements.
Animal sacrificed.

Anatomic report: Place of fusion shows dense and knotty scar with
large numbers of cells running in all directions. Among these, small
and partially myelinated nerve fibers have formed. Roots peripheral
to scar contain fibers better myelinated, some almost normal.

Experiment 69. Lesion, March 17, 1910. On July 18, residual par-
tial paralysis (fig. 12) of muscles supplied by right external popliteal.
On this date following operation: right sciatic divided above bifurca-
tion and immediately resutured. Then popliteals fused by usual method
with two cat-gut ligatures. (The object of the division was to promote
fibrillation at the cut end of the central stump, before the fibrils entered
the region of fusion.) Clinically dog became worse after the operation.
On December 19, 1910, nerves investigated under ether and the cut ends
of the sciatic were found ununited. Yet stimulation of popliteals below
neuroma evoked responses. Animal sacrificed.

Anatomic report: Popliteals in fair states of regeneration.

PARALYSES IN DOGS Likes

Experiment 70. Lesion March 18, 1910. On July 20 residual spas-
tic paralysis (fig. 18) of both legs. On this date operation similar to
that done on dog 65. The immediate result was flaccidity of homolateral
paw. December 8, 1910, all roots which were involved in the fusion
sear divided and stimulated under ether. Leg movements evoked on
side of fusion, similar to those on other side. Popliteals stimulated and
responded to weak currents. Animal sacrificed.

Anatomic report: At region of fusion dense sear containing partially
myelinated fibers. Peripheral to sear, roots show myelination better
advanced.

Experiment 73. Lesion March 19, 1910. On July 8, 1910, residual
paralysis (fig. 24) confined to tail. On this date operation similar to
that done on dog 68. In September dog was wagging tail pretty well
and seemed to have more strength in it. On December 20, 1910, all
roots below fusion divided and stimulated, under ether, and tail responses
evoked. Animal sacrificed.

Anatomic report: Region of fusion showed dense, knotty scar infil-
trated with nuclei, also a few fascicles of good fibers and some partially
myelinated fibers interwoven among the cells. At more caudal levels
regeneration quite advanced.

Experiment 75. Lesion April 12, 1910. On July 12, residual spastic
paralysis (fig. 16) of right leg, except for paw which was flaccid. On
this date operation on right anterior roots similar to those done in dogs
65 and 70. Clinical result completely negative. Death by accident,
November 20, 1910.

Anatomic report: In region of fusion, dense scar containing some faintly
myelinated fibers.

Experiment 78. Lesion April 15, 1910. On August 22, 1910, resid-
ual paralysis (fig. 8) chiefly of right external popliteal. On this date
following operation: external popliteal divided and fused to internal
popliteal low down. Dog found dead, October 10, 1910.

Anatomic report: Right sciatic above fusion contained increased con-
nective tissue spaces. At region of fusion dense scar with numerous
nuclei. New nerve fibers among these running in all directions. Some
regeneration in nerves below fusion.

Discussion

In the three dogs (Experiments 64, 78 and 69), in which the
popliteals were fused, there was no functional gain, although
there was anatomically some regeneration in all the nerves below
the scar. In one of these (78) death occurred before any func-
tional result could be expected. In dog 69 where the sciatic was
sectioned higher up and the stumps failed to unite, the peripheral
stump must have made new central connections through small
fibers injured in the wound during the operation. The stim-

118 HENRY O. FEISS

ulation tests in Experiment 64 could not be said to be positive
for the external popliteal. As to the other five dogs, the three
which had their anterior roots fused on one side could not be said
to show any functional gain, although two (Experiments 65 and
70) showed some response to faradic stimulation in the roots
below the fusion. Anatomically again, there was some regener-
ation.

The only animals in which functional improvement was sug-
gested were dogs 68 and 73, both of which had paralyzed tails,
and therefore had the fusion done so as to inelude all the roots,
taking part in the innervation of that appendage.** In both of
these, there also were signs of good regeneration, from the ana-
tomical and physiological points of view. However, one could
not be positive that the functional return of power was due to
the fusion, because it took place so soon after. To help settle
this point we performed similar operations in the cauda of three
normal dogs. In these cases the tails were pretty well restored
in power by the end of three months. It is likely that this early
improvement 1s owing to the shortness of route between the nerve-
collectors of the tail and the roots from which these are formed.

As regards the whole question of the fusion of nerves, it is not
desirable, at the present time, to discuss it further on a basis of
the experiments above described, but, at some future time, after
becoming acquainted with conditions of regeneration after the
fusion of normal nerves, it is likely that these experiments will be
alluded to again.

In closing, I wish to acknowledge the assistance of Dr. R. H.
Bishop in the conduct of many of the experiments, and of Dr.
David Marine in the preparation and interpretation of anatomical
material. I am especially indebted to Professor George N.
Stewart, Director of the Laboratory. He has made many impor-
tant suggestions in the plan and details of the work, as well as
in the preparation of the manuscript.

Cleveland, Ohio.

94 Schiimacher: Anat. Hefte Beitrage zur Anat. und Nntwickelungsgeschichte,
120 Heft., 1909.

PARALYSES IN DOGS 119

Instrument used to produce lesions.
Experiment 90; two days after lesion.
Experiment 90; five days after lesion.
Experiment 100; two days after lesion.
Experiment 100; twenty-one days after lesion.

----+ ee

Scar in Dura-

Fig. 6 Experiment 64; ninety-four days after lesion. Left, no dorsal flexion
of paw and ankle; direct stimulation of nerves showed L. P. practically all involved.

Fig. 7 In this and the following diagrams, the topography of the cord lesions
is indicated; fine stipple represents cavity; parallel line shading represents broken
down tissue; cross-hatching represents dense scar from dura; the heavy shading
in the circles, which represent roots, indicates the extent of involvement at the
level shown; degenerations are not represented. [K. P.and I. P. = internal and
external popliteals respectively. |

120

Right, no

the lesion.

one days after

ty-

nine
aw; weak extension of hip and knee; direct stimula-

)

Experiment 78;

and 9

S
dorsal flexion of an

Figs.

kle and p

P. (right) all involved.

tion of nerves showed

Figs. 10 and 11 Experiment 86; seventy-one days after lesion; condition little
changed two to three months later, viz.: right, no dorsal flexion of paw and ankle;
weak plantar flexion of toes; knee quite weak in extension; hip usually held flexed
and also weak, left, stronger than right; dorsal flexion of paw and ankle gone;
hip and knee slightly weak. Before killing, direct stimulation of nerves showed

tight, J. P., slight response in toes; no movement in ankle. /. P., no response;
left, J. P., good response in toes; good response in ankle; 4. P., no response.
122

(a0)
pales

Right, dorsal

xperiment 69; eighty-five days after lesion.

—
4
4

Figs. 12 and 13
flexion of paw and ankle weak.

123

Figs. 14 and 15. Experiment 65; ninety-three days after lesion. Left, bad
control of paw and ankle; knee flexed; hip contracted and extension lessened.
tight, flexion of hip weak (so that she occasionally drags leg); weak power in

extension of knee.

124

held

s
ind hamstrings weak; quadriceps partially gone but contracted.

Right, no con-

aralyzed and i

; ninety-four days after lesion.

Experiment 75
knee and ankle held straight and stiff; paw probably p

Figs. 16 and 17
trol except in flexion of hip; leg held under her, being flexed and adducted at

hip

€
«

flaccid; glutei

125

Root 5 y

Exper. 70

Figs. 18 and 19 [experiment 70; one hundred and twenty-three days after
lesion. Poor control of pelvis, hips, knees, ankles and paws, but for the most part,
not an atonic, flaccid paralysis. All joints are held permanently flexed to about
normal angles, except the hips which are more extended than usual; spine bent
convexly backward. On both sides erector spinae, glutei and quadriceps all weak;
hamstrings fairly good; paws turn under occasionally; drags legs in position

deseribed.

126

no control

ally

s after lesion. Practic

y day

Ss.

Figs. 20 and 21 Experiment 72; sixt
of paws, ankles, knees, hips and pelvi

127

Tail, mostly

lesion.

ifter

xion of p

Lys

; sixty-two d

nt 6S
in root.

Experime

Figs. 22 and

uk.

«
«

1w we

‘
«

ght, dorsal fle

some powe

aralyzed;

Tail, mostly para-

ays after lesion.

sixty d

135

xperiment

~
}

Figs. 24 and 25
lyzed; moves root a little.

129

Fig. 26 Experiment 68; one hundied and thirty-nine days after lesion; fifty-
four days after fusion. Practically no control of tail.

Fig. 27 Experiment 68; two hundred and nine days after lesion; one hundred
and twenty-four days after fusion; showing extent of control of tail in lifting at

this date.

THE INFLUENCE OF AGE, SEX, WEIGHT AND RELA-
TIONSHIP UPON THE NUMBER OF MEDULLATED
NERVE FIBERS AND ON THE SIZE OF THE LARGEST
FIBERS IN THE VENTRAL ROOT OF THE SECOND
CERVICAL NERVE OF THE ALBINO RAT

ELIZABETH HOPKINS DUNN
From the Hull Laboratory of Anatomy, The University of Chicago

Six FIGURES

So much has been published regarding the growth of the medul-

* lated nerve fiber that an explanatory word may be permissible

on offering a paper which duplicates in many particulars the
findings of other investigators.

The collection of the data presented here was suggested in
1903 by an examination of the control, or normal, material used
by Dr. S. W. Ranson for his study of the spinal ganglion. Of the
sectioned material, that for five rats of the thirty-one here re-
ported was generously furnished by Dr. Ranson. In examining
that material the salient feature was, to me, the increase in size
of the medullated nerve fibers in the older rats, and it seemed
desirable to ascertain if possible what conditions other than age
might influence the size of these fibers. This point seems to
have attracted other interest, since in 1906 Dr. Boughton
published important data regarding the increase in size with age
and weight of the medullated nerve fibers of the oculo-motor
nerve in the albino rat and in the cat from a mixed series of males
and females.

While the chief point of my inquiry was so admirably elucidated
by Dr. Boughton’s paper, there seemed to be place for the more
extended study with defined categories which I had undertaken.
Inquiry was made before continuing the work as to the existence

131

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2

132 ELIZABETH HOPKINS DUNN

of any further duplicating studies. When it was learned later
that Mrs. M. H.S. Hayes had a considerable series of counts of the
ventral root nerve fibers of the second cervical nerve for the albino
rat, postponement of publication was made for more than two
years, but as her material has not been published it has seemed
expedient to present my own findings with all due. apologies to
others.

With age as the constant factor in each group it seemed wise
to vary the other factors which might determine the size of the
largest nerve fibers. The additional factors selected were sex,
body size as shown by extremes of weight within the limits of
health, and relationship as shown by conditions within the same
litter or in different litters. To these ends seven groups of rats
were selected ranging in age from seven days to two hundred and
seventy days, or nine months. These two limits were determined
upon, the first because technical difficulties made accuracy in
measurement among younger rats rather uncertain and the
second because it had been found difficult to maintain good health
and normal weight among laboratory rats after nine months of
life. Each one of these seven groups was made up of four rats
of the same age but of as widely varying weights as could be
secured among healthy animals. The emphasis was laid upon the
selection of light and heavy females, light and heavy males, thus
including two females and two males in each group. Further
information concerning conditions within and without the litter
was secured by selecting certain groups from one litter and other
groups from scattered individuals. The four rats of seven days,
three of fourteen days and the one rat of one hundred and thirty-
eight days are of one litter. The four rats of the group at thirty-
six days are of one litter. The three rats of seventy-five days are
of one litter. The four rats of the group at two hundred and
seventy days are of one litter.

To this series of seven groups was added a group of aged rats,
three males, of widely varying weights but not in good health.
These rats were about six hundred and forty days of age.

As previously stated, the medullated nerve fibers of the ventral
root of the second cervical nerve were selected for study and for

SECOND CERVICAL NERVE OF THE RAT 133

the purpose of uniformity the fixed point of section was opposite
the spinal ganglion and central to the fusion of the two roots.

The methods of preparation of the material were those used for
the enumerations and measurements in the leopard frog, (Dunn,
00, ’02, 09) and differed but slightly from those of Boughton,
(06) Donaldson and Hoke (’05) and those of other investigators
with whose findings comparison will be made. The nerve roots,
ganglion and a portion of the nerve were fixed and stained unsep-
arated in a one per cent solution of osmic acid, imbedded in par-
affin, cut to a thickness of 4 micra and mounted serially.

The counts were made by the aid of an ocular net, and the
measurements with an ocular micrometer, using an oil immersion
lense at a magnification such that ten of the subdivisions of the
ocular micrometer equalled one of the stage micrometer, or one
one-hundredth of a millimeter. One division equalled 1 micron.
This magnification facilitated greatly the final computations which
were at best very tedious and required the closest control to elim-
inate the chances for error.

In selecting the nerve fibers for measurement, the entire sec-
tion was surveyed and the largest fibers methodically selected.
Each fiber was measured in two diameters, and its axis cylinder
immediately measured in the same diameters.

The counting was done in daylight and the measurements taken
under an oil immersion lense by the aid of an electric microscopic
bulb of thirty-two candle power.

It was at first intended to select a variable number of nerve
fibers for measurement, making the number proportional to the
number of medullated nerve fibers in the section. But this plan
was abandoned in favor of that of a fixed number which showed
more accurately the increase in size at successive ages. The
number fixed upon was ten. The results of this examination are
found in tables 1 and 2.

Table 1 shows individual by individual, the age, the sex, the
weight in grams, and the number of medullated nerve fibers in
the ventral root of the second cervical nerve. Then for the ten
largest medullated nerve fibers, the average diameter in micra,
and the average area ‘in square micra for the fibers, and the

134 ELIZABETH HOPKINS DUNN

TABLE 1

Records from measurements on the ten largest nerve fibers in the ventral roots of the
second cervical nerve in a number of albino rats

TEN LARGEST FIBERS

THEIR AXIS-

eC | 22 | CYLINDERS Bo
a | Ss | Ba | A A | Aver- | og
| 2 = & | .Average | verage ver- | Pt

Belcan 1) (8 S| BF | diameter | “sa jase de| Amos | 3
| Grams ORs | | : :
TAC i 7 | Female | 8.25 | 368 4.60 UGG I Ba | 10.18 rh Bales}
AC.) | Henvale 8.93 368 4.75 UO) | Bers |) Mal wo 1 62;
AM .| 7 | Male | 8.90 | 372 5.05 19.95 4.05 | 12.82 1b Sika fais)
Ae 7 | Male | F754) 1360 5.60 24.63 | 4.55 15.07 1S als (ahs
A...| 14 | Female} 19.98 | 518| 7.05 | 38.93 |4.85) 18.40 | 1:2.06
185 5 ih re} Female | ZAKS ue 0G 6.95 38 .04 4.75 719) leet:
A | 14S Viale 20.73 | 536 6.60 34.13 | 4.50 | 15.90 1B OAL
14 | Male | 21.98 | 594 6.35 31.59 4.30 14.52 Lov 2ale
iC 36 | Female | 39.17 | 651 9.35 68.81 5.80 | 26.42 1 227388
(6 36 Female | 45.30 | 654 10.55 87.58 (S745) |) Stay) 1 :2.44
C 36 Male 31.20 | 536}. 10.36 84.30 6.50 | 33), 18) 1S)
@ 36 Male 52.65 689 | 9.90 76.98 6.20 30.19 ee 4 5)
IDES si 753 Female 130.31 505 | 12.15 Sate 7.90 | 49.01 13 sata)
Diaieto Female | 143.10 | 615 12.10 114.99 8.00 | 50.26 ly etze29
D 75 | Male 149.40 | 609 122 5115) 116.13 8.20 | 52.81 e220)
E 74 | Male | 189.70 | 726 12825 117.67 8.20 | 52.81 19.93.98)
lee gl) ies} | Female | 161.00 | 634 | 12.70 126.68 8.25 | 53.58 1218
G...| 183 | Female | 167.51 | 731 13.60 145 .27 9.10) 65.03 22
AY 2a 1Sss Male 260 .00 | 680 13.16 133 .96 | 8.84 61.37 IPF ils)
H...| 132 | Male 274.00 | 569 13.70 148.04 | 9.10 | 65.03 UA 7;
L250\ 280, Female 200.00 | 510 | 14.55 166.50 9.80 75.43 Li 2e20
J...| 180 | Female | 225.00 526 14.75 IAL ill 9.85 76.36 15 See
K...| 180 | Male 227 .60 | 546 15.45 187 .23 10.65 88.91 1h 9274140
L...| 180 | Male 302.00 | 6627) 16750 215.38 11 MOWIO ol 1 :2.00
M ..| 270 Female | 165.85 | 698] 18.20 | 260.16 13.10 | 134.78 1:1.94
Vie 270, Female 187.96 | 853 18.25) ZolcSr Wil2s05 | 131-92 L298
M ..| 270 Male 330.68 | 576| 16.25 | 207.65 /11.30 | 100.28 3/206
M..| 270 | Male 349.41 658 16.95 | 225.91 {12.05 | 113'.85 1 1.98

| | | | 5

N!..;Aged| Male | 210.00 | 901 | 14.85 | 173.43 |10.50| 86.59 ee
©O!..|Aged| Male | 379.40 934 15.00 | 176.69 |10.00 | 78 . 54 L 22.25
P! ..|;Aged| Male | 414.00 758 | 14.35 | 161.96 9.40 | 69.40 ae

1 These aged rats were about 640 days old.
1907.

They were killed in 1903, 1904 and

SECOND CERVICAL NERVE OF THE RAT 135

average diameter and the average area for their axis cylinders;
and, in the final column, the ratio of the area of the axis cylinder
to the area of the entire fiber.

TABLE 2

Averages for the enumerations and measurements for the groups of albino rats
specified in table 1

136 ELIZABETH HOPKINS DUNN

Table 2 introduces the averages for the groups of rats, first
according to sex, and finally as a whole. It shows the average
weight, the average number of medullated nerve fibers, the aver-
age areas of the largest nerve fibers in square micra, the average
areas of their axis cylinders, and the ratio of these averages.

It may be of interest to show how the individual rats of the
selected series differ from such averages as have been established
already for the weight-age complex. In a joint paper by Donald-
son, Watson, and Dunn (’06) certain averages and extremes of
weight by age were published, upon which I have drawn for a
series comparable with the present series. These data are pre-
sented in table 3 and are followed in table 4 by a compilation of
the ages and weights of the rats of the present study.

TABLE 3
MALES FEMALES
DAYS SA Was a a r — a — a), Ao
Lightest Heaviest Average Lightest Heaviest | Average
|
7 73 12.7 9.2 ee sls Dee a Sez
149/74 490 17.6 15.2 13.5 18 a ereRG
37 28.5 48.0 37.8 29.8 47.4 | 39.5
76 89.8 157.5 121.3 89.6 131.6 | 2 104
131 132.4 249.2 202.5 151.2 DAG 1°. | 7 eee
178 167.9 291.2 239.4 153.0 915.0 “| “aol
256 190.5 310.0 265.4 |
TABLE 4
MALES FEMALES
DAYS ¢ r —s es
Lightest Heaviest | Lightest Heaviest
|
=a = | = —— ———
7 8.90 9.75 8.25 8.93
14 | 20.73 21.93 19.98 | 21.85
36 31.20 52.65 39.17 45.30
75 149.40 189.70 130.31 143.10
132 | 260.00 274.00 161.00 167.51
180 227 .60 302.00 200.00 225.00
270 330.68 | 349. 41 165.85 187.96

SECOND CERVICAL’ NERVE OF THE RAT Lae

A comparison of the records for the approximate ages shows
that, while the individuals of the present inquiry, are not the
lightest or the heaviest which might be obtained, they vary in a
satisfactory degree from the averages given for males and females
of comparable ages. I am not able to state the relationships of
the Watson groups of rats but in my own groups of the younger
rats a number of litters was included for each age.

The young of any given litter tend at birth to be of like weights
and, so far as the argument can be drawn from records of the
members of one litter, such related rats if differing initially in
weight tend to approach each other in weight as growth goes on,
if the conditions of growth are favorable (Dunn, ’08).

Donaldson (08, p. 353) says, ‘“‘It is a familiar fact that rats
even of the same litter and reared together grow very differently
and therefore at the same age may have widely different body
weights.’’ Unfortunately we have no published data to show the
initial body weight for related rats which differ so greatly at
maturity. It appears, however, that unrelated rats and those
reared under different conditions exhibit less uniformity of growth.
The present findings suggest that these variations from the aver-
age may make themselves apparent in the nervous system as
well as in the body weight. ‘This is shown in the group at one
hundred and eighty days of unrelated rats which, while fitting
into the scheme for body weight, give numbers of fibers which are
less than might be expected.

In all the findings which refer to weight the females must be
considered separately from the males, at least after sexual matur-
ity, since the growth curves for body weight differ greatly. For
the curves showing this, reference may be made to Donaldson’s
papers, chiefly the collaboration with Watson and Dunn (’06).
The body weight for the male rat increases for a longer period than
that for the female and the average body weight for the adult
male is considerably greater than that for the adult female of the
same age.

The findings for this series of albino rats group themselves under
two heads, first, the factors influencing the number of medullated
nerve fibers, and second, those influencing the size of the nerve

138: ELIZABETH HOPKINS DUNN

fibers. The records for the individual rats are to be found in
table 1. For the group averages table 2 must be consulted. Of
the figures fig. 1 gives in Ca curve based upon the averages of the
groups for the body weight-age comparison, and in curves B and
A the comparison of age with the size of the largest fibers and of
their axis cylinders. Fig. 2 gives two curves related directly to
the number of medullated nerve fibers. Curve D has been plotted
for the fiber-age complex, and Curve H for group-weight averages
and number of fibers. Both curves of fig. 2 show considerable
irregularity in the later stages of growth. There is shown, how-
ever, a tendency for the number of medullated nerve fibers to in-
crease in relation to both age and weight. The curves for the
two are quite different, since the increments of age are daily
periods, while the body weight is laid on chiefly during early life,
as is shown by Curve C, fig. 1, by which two-thirds of the maxi-
mum average body weight is found to be present at one hundred
and eighty days of life.

THE NUMBER OF MEDULLATED NERVE FIBERS

It is a difficult matter to estimate the direct relation of the num-
ber of medullated nerve fibers in the ventral root of the second
spinal nerve in the albino rat to the body weight if the attempt to
do so is made to the exclusion of the age factor. Especially is
this true in the present series in which the extremes of weight at
definite ages have been selected. So the attention has been direc-
ted to the variations to be observed within the group of one age.
This number-weight relation must be considered for the sexes
separately. If this is done the statement may be made that of
two female rats of the same age or two male rats of the same age
the heavier rat tends to have the greater number of medullated
nerve fibers. This is especially noticeable when the compared
rats are of the same litter. Unrelated rats are more likely to vary
from this rule. This finding in regard to weight corroborates that
of Mrs. M. H. 8. Hayes in her unfinished work quoted by Hatai
(08, p. 154) with the added statement that this rule applies to
the sexes separately.

139

SECOND CERVICAL NERVE OF THE RAT

‘Udye} WOM GF PUR P 10]

SplOdo1 OY} YOTYM WOIJ S}YVI OY} IOJ OAIND YYMOIB Apoq oy} st ‘sout] Usyorqg ut “yD *Z e]qQuy ‘(V) StopurpAo SIX¥ ITIY} JO OZTS VSR.IIAG
dy} pus (G) S1oqY 4SoBiv] OY} JO ozIs oBV.AOAV oy} ‘SOB SNOTIVA 4B 8}VA ANOJ Jo sdnoAd oy} IJ ‘MOYsS 0} poyjotd ow g— puR py TBA

shop 0+9

fies

Li----

Le----
9¢----

O0L | hema

SL of at Z

19---

Bl aj a

18---
10 00L
Siten-

Oel---F

Bel--4

[Ll --
S8L---
00g

Wo
6£2 --

ha
E
ae

eer |e
ene? |

\
\
\

7
-

ee \ ae ka

eae Sea
ee eee eee

a
s

i
aaste

Seal i,
be 4 al

swp.b

----8S1

---B8S2

\
QD
ie)
N

= ee ek
a

[Bi

be
Seen
tes aaa
Pole aibales| als

ae
ese ek

Ea
i
Ee
el
ie
ics
ie
i
E
ie
fia So See

258---

239--

eS
a

153 ---

~-135

fiber rs 367 fibers 554 504 is dssiss 637 as fibers

lig. 2 D is plotted to show the averages of the number of fibers for the four
rats of each group, at the ages studied. JF is plotted to show the same averages
of numbers in relation to the averages of body weight at the same ages.

140

SECOND CERVICAL NERVE OF THE RAT 141

Our findings seem to show that age has more influence on the
number of medullated nerve fibers than has weight. In this
regard our records disagree with the conclusion of Boughton (’06)
for the oculomotor nerve of the albino rat. Reference to individ-
ual records in table 1 shows very definitely that there is no such
relationship between body weight and the number of medullated
nerve fibers that two rats of different ages but the same body
weight will be more likely to have the same number of medullated
nerve fibers in the ventral roots of the second spinal nerve than
those of the same age but different body weights.

The statement also seems justifiable that rats of like age and of
one litter tend to have the same number of medullated nerve fibers.

Curve E, fig. 2, has been plotted to show the relation of the aver-
ages for groups of rats of given ages to the averages for the num-
ber of their nerve fibers, but as this curve introduces the age factor
in addition to that of weight, it will be discussed in the following
section.

A considerable increase in the number of medullated nerve
fibers occurs during the early life of the albino rat. This was
noted by Hatai (03) for the ventral roots of the sixth cervical,
the fourth thoracic and the second lumbar spinal nerves, and by
Boughton (’06) for the oculomotor cerebral nerve. In the second
spinal nerve the increase seems to be checked at an earlier period
than in the regions mentioned by Hatai. After the thirty-sixth
day of our series, (table 2 and fig. 2) there is no uniform increase
in the number of medullated nerve fibers, although the increments
of age are considerable.

Hatai (’03) using the criterion of body weight, argued that the
increase in number among the ventral root fibers continued to a
later period. His maximum of weight was 264.3 grams, which
might correspond to that of one of our one hundred and thirty-
two day rats. Hatai’s conclusions were based on the findings
from one rat of each weight, age and sex not noted.

Boughton (’06) while noting age, weight and sex in his series
for the oculomotor nerve, did not select his material systematically
with respect to these factors. He obtained the maximum num-
ber of medullated nerve fibers in a male of one hundred and thir-

142 ELIZABETH HOPKINS DUNN

teen days and with a body weight of 278 grams. However, his
curve immediately drops to a number not exceeding by one fiber
the record for a male of seventy-seven days and 213 grams body
weight. Tozer and Sherrington (710) argue that the oculomotor
is a mixed nerve.

Ranson (’08) made a few records for the number of ventral
root medullated nerve fibers of the second cervical nerve in the
albino rat in order to show the ratio of ventral to dorsal root
nerve fibers. While his records for the dorsal roots begin with
twelve day rats his counts for the ventral root fibers are only for
seventy-two day and six month rats. The level of the count, the
weight and sex of the rat are not stated.

His records for the dorsal root fibers give no stage between
twelve and seventy-two days but show a marked increase in
number at the later age. Of the ventral root fibers the average
number of fibers for four seventy-two day rats is six hundred
and thirty-two while that for two six month rats is seven hundred
and thirty-six fibers. My own averages for seventy-five day rats
and nine month rats give six hundred and fourteen fibers for
seventy-five days against six hundred and ninety-seven fibers
for the nine month rats.

Ranson’s records then are comparable with those presented
now and together they show that in regard to the second spinal
nerve of the albino rat the number of medullated nerve fibers in
both the dorsal and ventral nerve roots increases during the life
of the individual but that the greatest increase occurs before the
sexual maturity or so-called puberty of the animal.

More than this, if comparison between Ranson’s records for
the dorsal roots and my own records for the ventral roots of other
individuals is permissible, the statement is possible that the in-
crease in number is relatively greater and extends over a longer
time among the dorsal root nerve fibers than among the ventral
root nerve fibers. The functional significance of this finding is
not so great as it would be if the counts for the dorsal root fibers
had been made peripheral to the ganglion when the fibers directly
innervating sensory elements would have been counted. As it
is, the records are for processes central to the ganglion and ending

SECOND CERVICAL NERVE OF THE RAT 143

in the central nervous system. More than this they are upon
individuals other than those from which the ventral root fiber
records were made. Comparable records may yet be secured for
the material upon which the present report is made. The plane
of the section which was necessary to make measurements on the
ventral roots peripheral to the ganglia reliable made similar
measurements upon the dorsal roots unreliable. If some control
for the measurements can be devised, the counts will also be made.
Whatever may be the significance of the presence of the added
fibers the determination of the time and manner of their appear-
ance must be of importance.

The albino rat becomes sexually mature about the beginning of
the third month of extra-uterine life, or‘about the seventieth day,
but its increase in body weight may continue, to the end of the
second year of life. According to the present records the average
daily increase in weight between the ages of seven and fourteen
days is 1.74 grams, and the average daily fiber increase is twenty-
seven fibers. The average daily increase between fourteeen days
and thirty-six days is 0.95 grams and 3.6 fibers. The incre-
ments of age and weight are too great to establish these averages
as final, but they undoubtedly show the general growth relations.

The rate of increase in the number of medullated nerve fibers,
in essential agreement with Hatai (03) and Boughton (06)
diminishes with age. In our series the fourteen day period marks
the greatest increase. :

That such an increase in the number of medullated nerve fibers
occurs in other animals has been shown by Boughton (’06) for
the cat and suggested by Willems (11) for the rabbit. Boughton
(06) used a mother cat and her five kittens, two males and three
females. An increase in the number of medullated nerve fibers
of the oculomotor nerve is shown among the kittens from one day
to one hundred and eighty-two days, with the exception of the
female at ten days, but the mother cat at thirteen years has a
number of fibers not quite equal to that of the kitten of fifty-six
days.

Willems’ records (’11) were offered to show the relation of large
and small nerve fibers in the portio minor of the fifth cerebral

144 ELIZABETH HOPKINS DUNN

nerve and its branches in various adult rabbits but, unfortunately
for comparison with other records, do not state the age or sex of
the animal. There is shown however in his table 4 (p. 143) a
variation in the total number of medullated nerve fibers in the
motor portion of the fifth cerebral nerve which might indicate the
influence of an age factor.

It would seem from the present more extended series from albino
rats that the increase in the number of medullated nerve fibers
practically ceases with the attainment of the adult condition and
that the presence of an individually greater number after that
period is dependent upon some factor determining the number to
be supplied to the adult body and is not likely to be due to the
maturing of immature elements in the nervous system as it seems
to be at the earlier ages.

This increase in number of medullated nerve fibers with the
increase in weight and age may have several interpretations.
When it appears as a condition most marked during the period of
rapid growth, it may well seem to be associated with the increase
of the number of body elements which must be innervated. Dur-
ing the same period, or more naturally later, it may be dependent
upon an increased innervation of already innervated material.

Our data as regards the number of innervated peripheral ele-
ments either sensory or motor are extremely limited.

Intimately bound up with this question is that of the splitting
of peripheral nerve fibers, and no absolute correlation between the
number of nerve fibers in the spinal roots and the number of
peripheral innervated elements can be made with our existing
knowledge.

It would appear in general that the increase in size of the imma-
ture body is accomplished by the increase in both number and
size of the individual elements, while that of the mature body is
rather due to increase in size of the already formed elements.

Boughton’s (’06) findings lead him to state that after the initial
laying down of nerve fibers the added fibers never attain the size
of the earlier formed fibers, and the added fibers must be small
fibers. Under this interpretation size is determined by age and

SECOND CERVICAL NERVE OF THE RAT 145

these additional fibers whatever their function are determined
by the time of their appearance to be small fibers.

This phase of the significance of the added fibers is so bound up
with the discussion of size that we may consider it more readily
under that topic.

SIZE OF THE MEDULLATED NERVE FIBERS

If the period preceding puberty marks the time of the chief
increase in the number of medullated nerve fibers, it has no such
notable relation to the increase in size of the medullated nerve
fibers, which continues at least to the ninth month. This is
clearly indicated in table 2, which gives the average areas in
square micra for the ten largest fibers of four individuals in each
group. In this table, and in fig. 1, curve B, an unbroken increase
occurs for our averages from the seven day group to the two hun-
dred and seventy day group. A somewhat similar increase
occurs in the areas of the axis cylinders of the same fibers, showing
that the integral portion of the nerve cell increases in size during
health with increasing age at least to the ninth month of life.

The ratio of the average for the axis cylinder and for the entire
fiber (table 2) gives some interesting information as to the growth
of the medullary sheath. Using the average area of the axis
cylinder as the unit, at seven days the area of the entire fiber is
about one and one-half times that of the axis cylinder, that is the
medullary sheath has half the area of the axis cylinder. At the
succeeding stages of body growth to the two hundred and seventy
day period the medullary sheath is thicker than the axis cylinder.
The greatest relative thickness of the medullary sheath appears
in our series at the thirty-sixth day when, contrasted with the
unit area of the axis cylinder, the area of the medullary sheath
is 1.47. From this age there appears a readjustment in the growth
of the two, until at nine months the ratio is 1:0.99 or the one to
one relation of the normal adult (Donaldson and Hoke, ’05).

Among the members of our group of aged and infirm male rats
the nerve fiber is affected in both axis cylinder and medullary
sheath. The average area of the entire fiber and of the axis cylin-

146 ELIZABETH HOPKINS DUNN

der is considerably decreased. The axis cylinder is the more
affected so that the ratio approximates that of a fourteen day rat
or a hundred and eighty day rat, in which the medullary sheath
has a slightly greater area than has the axis cylinder.

The curves for the averages have been plotted in fig. 1, Curves
A and B. At seven days Curve A begins at 12 square micra and
Curve B at 17sq remicra. As age increases the curves diverge
until at two hundred and seventy days the fiber is twice the size
of the axis cylinder. In old age, six hundred and forty days, the
axis cylinder has an average area of 78 square micra, while that of
the entire fiber is 171 square micra, showing a distinct shrinkage
in both axis cylinder and medullary sheath. ‘

The comparison of the curves for the nerve fiber and for its
axis cylinder with the curve for the body weight of the same ani-
mals is full of interest. Curve C has been plotted in the same
figure to show the relation of the body weights of the groups to
their age.

From this comparison we see that the size of the largest nerve
fibers increases more rapidly than the weight of the body until the
thirty-sixth day. From the thirty-sixth to the seventy-fifth day
or until puberty the body growth is very rapid, overshadowing
that of the nerve fiber. This disporportional growth of the body
continues until about the one hundred and thirty-fifth day. At
that age the body has acquired two-thirds of its ultimate size,
while the largest nerve fibers have acquired only a little more than
one-half of their ultimate size. The growth of the nerve fibers
from the one hundred and thirty-fifth day is more rapid than the
body growth, so that the curves approach one another at the two
hundred and seventieth day. At six hundred and forty days, or
old age, the curves are widely separated, due both to the increased
weight of the body and to the decreased size of the nerve fibers.

It may be well to discuss more fully the question of size as
related to all the nerve fibers.

Measurements have been made upon the largest nerve fibers
for convenience and for accuracy. ‘To those who have made the
attempt, the difficulty of making such measurements with the
ocular micrometer need not be emphasized. The difficulty of this

SECOND CERVICAL NERVE OF THE RAT 147

series was considerably increased by the handling of very young
material.

These measurements prove the increase in the size of the largest
medullated nerve fibers, but that the increase is not confined to
the largest fibers is evident to one making even a casual study of

Oo 09 od oe
02 9000 i 0 os 2D. 00
°0 oP 8 ob ve oO LOO
Bo Me2310 RoE O 0°60
SO Sig 8 508 oO 0
A B Cc

Fig. 3 Camera lucida drawings by A. B. Stredain at table level, ocular 8, objec-
tive 8, Zeiss, showing typical areas from the ventral roots of the second cervical
nerve of three male rats of one litter. A at seven days, body weight 8.9 grams;
B at fourteen days, body weight 21.93 grams; C at one hundred and thirty-eight
days, body weight 260 grams.

“0
8

oO Be
96 OQ: 200 00

D E

Fig. 4 Camera lucida drawings, at same magnification as those of fig. 3, show-
ing typical areas from the ventral root of, the second cervical nerve of two male
rats. Dat 270 days, body weight 349 grams; E at 640 days, body weight 414 grams.

the material. Fig. 3 was drawn by camera lucida to include
typical areas from the ventral roots of the second cervical nerves
of three male rats from one litter. A at seven days, B at fourteen
days and C at one hundred and thirty-eight days. Fig. 4 gives
drawings at the same magnification from two additional male rats,
D at two hundred and seventy days, and # at six hundred and

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2

148 ELIZABETH HOPKINS DUNN

forty days. ‘The variation in size is too obvious to need further
comment. EH shows the decrease in size among the old rats.
The increase in size is apparent among the majority of the fibers
and may include all the fibers. Nevertheless some of the medul-
lated nerve fibers may appear early and not continue their growth
over the usual time or may grow more slowly. Small fibers may
be destined to be small fibers from their first appearance.

Boughton (’06) made an attempt to classify the medullated
fibers of the oculomotor nerve into ‘large’ fibers and ‘small’
fibers. One is somewhat puzzed regarding his method. Accord-
ing to his table 1, Boughton entered all the fibers present at eleven
days as ‘large’ fibers, noting the addition of ‘small’ fibers at later
ages. In his discussion of method (p. 156) he states that all his
sections were photographed at the same magnification and only
those fibers distinctly recognizable at that magnification were
entered as ‘large’ fibers. If the material was at all comparable
to that of the present investigation a magnification which would
show all the fibers at the youngest period would show all the fibers
at all the other periods. Our fig. 3 proves this.

The oculomotor nerve carries a considerable number of small
medullated nerve fibers as viscero-motor fibers to the ciliary
ganglion (Apolant, ’96, p. 664). The presence of such fibers
may account for the large number of small fibers found by Bough-
ton (’06) in the oculomotor nerve of the albino rat. In such a
group of nerve fibers, which plainly differs functionally from the
somatic fibers, a distinct difference in size would be difficult to
interpret alone from the standpoint of age of the fibers. All
viscero-motor medullated nerve fibers have been recognized as
small fibers. This was early stated by Gaskell (’86) and Langley
(96) and corroborated by mahy more recent investigators. It
is possible that these fibers are later in medullation than those
passing to the body muscles, but they may not grow so rapidly
as do the somatic motor fibers.

Further, if we have in the third nerve which has been considered
a purely motor nerve, a mixed nerve as Tozer and Sherrington
(10) have argued, the interpretation of Boughton’s findings has
an added complication as both efferent and afferent fibers would

SECOND CERVICAL NERVE OF THE RAT 149

be included. Such an interpretation has been given to the func-
tion of the ventral roots by Kidd (11) and others. I have
unpublished a note on the presence of medullated nerve fibers
in the ventral roots of the spinal nerves in the leopard frog, which
from the direction of their degeneration seem to have their cells
of origin in the dorsal root ganglia. It may be then that in no
nerve or spinal root are we dealing with unmixed fibers. The
relative number of efferent fibers seems greater in the second
cervical nerve than in any of those previously considered. Roth
(05) states as an argument in proof of the visceral character of the
eleventh cerebral nerve that in the rat the ventral roots above the
sixth cervical have a small number of small medullated nerve
fibers, and that the second cervical nerve has in its rami communi-
cantes few or no small medullated nerve fibers.

Willems (11) has discussed the question of the size of medul-
lated nerve fibers quite fully giving prominence to three theories
and introducing one of his own based on the differences in size
found among the branches distributed to various muscles from the
efferent portion of the fifth cerebral nerve in the rabbit. Quoting
from page 203, ‘‘ Nous pensons done que l’individualité des nerfs
a son origine principalement dans la différente valeur de l’accrois-
sement secondaire pour chaque muscle.”’

It has seemed to the writer that the propounders of these so-
called theories as set forth by Willems have not attempted to put
forth an all embracing theory, but have each one been attempting
to define factors which may influence the size of the medullated
nerve fiber. Each one has noted conditions which have run paral-
lel with size and have been piling up evidence bit by bit. At the
present moment it seems most probable that the size of the medul-
lated nerve fibers must be interpretated finally as due to a com-
bination of causes, and I anticipate that all the bits of information
will be wrought into a complex mosaic when the final illuminating
word can be said. One can readily see that in regard to size the
neurones may appear in successive crops so that the earlier crop
may have a greater size, according to Boughton’s and Donald-
son’s attractive theory, while at the same time these successive
crops have definite functional values which in turn may be influ-

150 ELIZABETH HOPKINS DUNN

enced by the richness of the fiber branching, by the size of the
innervated elements, by the frequency of their use, or possibly,
if neurofibrils are the conducting elements, by the number or size
of the neurofibrils. However this may be, we must be grateful
for every attempt to delimit the problem, while admitting that
much further information is desirable.

Increase in size is indeed a matter of growth, and it is extremely
confusing to the problem that age plays so large a part in deter-
mining the actual and possibly the relative size of the medullated
nerve fibers. It would appear that the next step in the interpre-
tation involves the accumulation of a mass of data regarding the
direct relation of the size of the nerve fibers to the tissues inner-
vated and much further information as to the relation of these
successively appearing fibers to the peripheral structures. The
latter involves a study of the axonic relations to the periphery and
the time of medullation of these axones.

My own findings (Dunn, ’02 and ’09) on the distribution of the
medullated nerve fibers to the segments of the leg of the leopard
frog suggest that difference in time of outgrowth from the central
nervous system is not sufficient to account for the appearance of
the largest medullated nerve fibers in each instance in the segment
nearest to the body. A peripheral factor seems to be present
here.

At the moment it is sufficient to inquire as to the information
regarding the factors determining the size of the medullated
nerve fibers which may be drawn from the present investigation.

It has been pointed out that, unlike the oculomotor nerve, the
number of medullated viscero-motor fibers is small, and that the
number of very small medullated nerve fibers is much less in the
adult than in a rat of seven days.

Among the possible influences upon the size of the medullated
nerve fibers has been mentioned the size of the animal. Dhéré
(03) has shown that the extraction of myelin is greater among
mammals of greater size than among those of less size. It will
be interesting to inquire as to the influence of weight among the
individual groups of white rats. Comparing females with females
and males with males, table 1, in each group of fixed age, the

SECOND CERVICAL NERVE OF THE RAT ail

heavier individual tends to have the larger average size of the
largest nerve fibers. To this law there are a few exceptions, but
in each instance the individual of greater weight but with the
smaller nerve fibers was found to have a greater number of nerve
fibers in this spinal root.

The correlation, then, is not between body weight and size of
the nerve fibers, but between body weight on the one hand and
number and size of the nerve fibers on the other hand. Of the
two factors, the size of the fiber is more affected by the body
weight than by the number of fibers. The larger fibers may be
found with greater body weight and greater number but when less
size of fibers is found with greater body weight the compensating
factor is the increased number of nerve fibers. This relation
appears to be an argument in the establishment of a definite
relation between the amounts of innervated and innervating mate-
rial.

Size of the fibers appears to have little relation to the body
weight when the sexes are considered together. There are but
slight deviations in size of the largest medullated nerve fibers in
males and females of the same age but of widely diverse weights.

Body weight without regard to age is misleading when used for
a.criterion of the size of nerve fibers. Selecting at random from
table 1 a male and a female of a weight less than 200 grams, one
might chance upon a female of 187.96 grams weight and a male
of 189.70 grams weight. ‘The male however is seventy-four days
old, the female two hundred and seventy days of age. The male
has seven hundred and twenty-six medullated nerve fibers in the
ventral root of the second cervical nerve, the female eight hundred
and fifty-three fibers. The average area of the ten largest medul-
lated nerve fibers in the male is 117.67 square micra and of their
axes 52.81 square micra, while for the female the average area
for the fibers is 261.87 square micra and for their axes 131.92
square micra. This may be analogous to the condition found in
the spinal cord by Donaldson (’08, p. 371). In those findings, in
rats of the same body weight without regard to age, female rats
were found to have heavier spinal cords than the males. The

15 4 ELIZABETH HOPKINS DUNN

amount of medullation and size of the fibers might increase the
weight of the cord.

A further step in the comparison of males and females of the
same ages but of different weights is the recognition of the fact
that among mature rats, the females, which rarely attain the
weight of the males, must have a mass or bulk of the peripheral
nervous system much greater in proportion to the body weight

550

300

200

100

Fig.5 F is plotted to show the body growth for the female rats of each group
and G the curve for the male rats of the same groups. These curves are to be con-
trasted with those in fig. 6, which show the curves for the growth of the largest
nerve fibers.

than that of the males. Increased weight in the spinal cord in
the female has been interpreted as due to the richness of visceral
innervation, especially of the pelvic organs. But in this second
cervical nerve an excess over the males is found with very few or no

SECOND CERVICAL NERVE OF THE RAT 153

viscero-motor medullated nerve fibers, so that the proportional
greater pathway for impulses is furnished by the somatic motor
system. An interpretation of this condition is difficult, since there
seems to be nothing in the bodily functions of the muscles to
require or explain richer somatic innervation in the females of a
given age. In plotting the curve for the number of rats used in
this investigation there seems to be no association between the

300

200

150

100

50 -
OV

.~ Fig.6 4H is plotted to show the growth curve of the largest nerve fibers for the
female rats of each group, and J for the male rats of each group (table 2).

early checking of body growth in the female and the growth of
the nerve fiber. The latter goes on as rapidly or more rapidly
in the female after the checking in rapidity of body growth as it
does in the male with a more prolonged growth. A comparison
of fig. 6 with fig. 5 makes this clear. Fig. 5 gives the curve for
body growth for the two males (G) and the two females (/) of
each group. Fig. 6 gives the curves for the nerve fiber growth of
the same rats, H for the females and J for the males.

154 ELIZABETH HOPKINS DUNN

In the interpretation of all investigations on the albino rat
much gratitude is due to Professor H. H. Donaldson now of The
Wistar Institute of Anatomy and Biology at Philadelphia, for
his preliminary studies upon the rat. Growth questions in gen-
eral are of especial value to us with reference to human young.
Professor Donaldson over a long period of years, more than ten
to my knowledge, has been inspiring a series of studies of a more
and more critical nature upon the albino rat as preliminary and
comparative studies to those on the human body. An outline
of some of his plans accomplished and projected is to be found in
the President’s address before the Philadelphia Neurological
Society (Donaldson, 711).

While the present investigation was undertaken independently,
it owes much for its interpretation to the solid and illuminating
researches just mentioned. It is interesting to find a laboratory
animal which in so short a lifetime as three years so conveniently
reproduces many of the conditions found in the human being.
because of this recapitulation, growth conditions in the peripheral
nervous system of the albino rat have the added value of aiding
in the interpretation of anatomical and functional conditions in
the human body.

CONCLUSIONS :

During the period of rapid growth, shown in the albino rat in
the accompanying tables from the seventh to the thirty-sixth
day, there is a parallel increase of the number of medullated nerve
fibers in the ventral root of the second cervical nerve. When the
sexes are considered separately, the heavier individual at each
age has the greater number of medullated nerve fibers. Neither
of these relations is so definitely marked among the adult rats.

In this series of observations there is found a continuous in-
crease in the size of both the medullated nerve fibers and their
axis cylinders to nine months of age. Among the old rats about
six hundred and forty days of age, there is a noticeable decrease
in size from that of the nine month rat both in the nerve fiber
and its axis cylinder.

SECOND CERVICAL NERVE OF THE RAT 155

The growth of the medullary sheath as compared with that of
the axis cylinder is emphasized in this series. At seven days the
area of a cross section of the axis cylinder is noticeably larger
than that of the medullary sheath. After that age the medullary
sheath grows more rapidly than the axis cylinder, at fourteen
days having a greater area than the axis cylinder. At thirty-six
days it has one and one-fourth times the area of the axis cylinder.
From thirty-six days the axis cylinder grows more rapidly until
at nine months there exists the one-to-one relation of the adult
which has been found in many vertebrates including the albino
rat. In old age there is a relatively greater loss in the axis than
in the medullary sheath, so that the area of the medullary sheath
is the greater.

While male and female rats may be grouped together in the
study of the influence of age upon the size of the medullated nerve
fibers, accuracy demands their separation when the influence of
weight is to be considered. The growth curve for the two sexes
appears to be different for the individual elements of the nervous
system, as it has been shown to be for the central nervous system
and for the body.

Usually for both males and females of a fixed age the greater
average area of the largest medullated nerve fibers of the ventral
root fibers of the second cervical nerve is found with the greatest
body weight. But if the less fiber area is found with greater
body weight the number of fibers is always greater. Greater
number may be found with greater area and greater body weight.
This correlation between the body weight and the size of the med-
ullated nerve fibers is an argument in favor of the theory of a
certain relation between the amount of tissue to be innervated and
the caliber of the innervating pathway.

In the later periods of growth among both males and females the
size of the medullated nerve fiber runs more closely parallel with
the body weight than among the more immature individuals,
that is, growth processes in the individual nerve elements are more
rapid and also more variable among the immature than among
more mature individuals.

156 ELIZABETH HOPKINS DUNN

The comparison of mature males with mature females shows
that, while the body weight of the females may be much less than
that of the males of the same age, there is no marked difference
in the size of the largest nerve fibers, so one may say in general
that the largest nerve fibers in mature females are much larger in
proportion to the body weight than are those of mature males
of the same age, that is, the efferent pathway is greater in the
female than in the adult male of the same age.

LITERATURE CITED

Apouant, H. 1896 Ueber die Beziehungen des Nervus oculomotorius zum Gan-
glion ciliare. Arch. f. mikr. Anat., Bonn, Bd. 47, 8. 655-668.

Bovuauton, THomas Harris 1906 The increase in the number and size of the
medullated fibers in the oculomotor nerve of the white rat and of the
cat at different ages. Jour. Comp. Neur., vol. 16, pp. 153-165.

Duférh, CuHaRLtEs 1903 Sur l’extension de la myéline dans le névraxe chez des
sujets de différentes tailles. Comptes rendus de la Société de biologie,
t. 55, pp. 1158-1160.

Donatpson, Henry H. 1908 A comparison of the albino rat with man in respect
to the growth of the brain and the spinal cord. Jour. Comp. Neur.,
vol. 18, pp. 345-390.

1911 President’s address. Journal of Nervous and Mental Disease,
vol. 38, pp. 257-266.

Dona.pson, Henry H. and Hoxsr, G. W. 1905 On the areas of the axis cylinder
and medullary sheath as seen in cross sections of the spinal nerves of
the vertebrates. Jour. Comp. Neur., vol. 15, pp. 1-16.

Dona.pson, H. H., Watson, J. B., and Dunn, E. H. 1906 A comparison of the
white rat with man in respect to the growth of the entire body. Boas
Memorial Volume, New York.

Dunn, Exizaseta Hopkins 1900 The number and size of the nerve fibers inner-
vating the skin and muscles of the thigh in the frog (Rana virescens
brachycephala, Cope). Jour. Comp. Neur., vol. 10, pp. 218-242.

1902 On the number and on the relation between diameter and distri-
bution of the nerve fibers innervating the leg of the frog (Rana vires-
cens brachycephala, Cope). Jour. Comp. Neur., vol. 13, pp. 297-328.

SECOND CERVICAL NERVE OF THE RAT ia

1908 A study in the gain in weight for the light and heavy individuals
of a single group of albino rats. Anat. Rec., vol. 2, pp. 109-111.

1909 A statistical study of the medullated nerve fibers innervating the
legs of the leopard frog, Rana pipiens, after unilateral section of the
ventral roots. Jour. Comp. Neur., vol. 19, pp. 685-720.

GASKELL, W.H. 1886 On the structure, distribution and function of the nerves
which innervate the visceral and vascular system. Journal of Physi-
ology, vol. 7, pp. 1-80.

HatTal, SHINKISHI 1903 On the increase in the number of medullated nerve fibers
in the ventral roots of the spinal nerves of the growing white rat. Jour.
Comp. Neur., vol. 18, pp. 177-183.

1908 Preliminary note on the size and condition of the central nervous
system in albino rats experimentally stunted. Jour. Comp. Neur.,
vol. 18, pp. 151-155.

Lana.ey, J. N. 1896 Observations on the medullated fibers of the sympathetic
system and chiefly those of the grey rami communicantes. Journal of
Physiology. vol. 20, pp. 55-76.

Ranson, 8S. WALTER 1908 The architectural relations of the afferent elements,
entering into the formation of the spinal nerves. Jour. Comp. Neur.,
vol. 18, pp. 101-119.

Rotu, A. H. 1905 The relation between the occurrence of white rami fibers and
the spinal accessory nerve. Jour. Comp. Neur., vol. 15, pp. 482-498.

Tozer, Frances M. and SHERRINGTON., C. S. 1910 Receptors and afferents of
the third, fourth and sixth cranial nerves. Proceedings of the Royal
Society of London, Series B, vol. 82, pp. 450-457.

Wiutems, Epovarp 1911 Localisation motrice et kinesthesique. Les noyaux
masticateur et mesencephalique du trijumeau chez le lapin. Le Nev-
raxe, t. 12, pp. 1-220.

THE STRUCTURE OF THE SPINAL GANGLIA AND OF
THE SPINAL NERVES

S. WALTER RANSON

Northwestern University Medical School!

FIFTEEN FIGURES

The application to the spinal ganglion of the reduced silver
method of Cajal has brought to light many new facts (Cajal, ’05)
and the renewed interest in this subject has found expression in a
number of investigations including that of Dogiel (08). The pres-
ent paper is concerned, in part, with a confirmation of these newer
observations and in part with observations which, though touched
upon by Dogiel and Cajal, escaped serious consideration by either
of them.

For this work the largest spinal ganglia (L vi, vii, § 1) in large
dogs were subjected to the pyridine-silver (modified (Cajal)
technique, an account of which has already been published (Ran-
son, 711). Pieces of fresh nerve are placed for two days in abso-
lute alcohol containing 1 per cent of concentrated ammonia;
washed one to three minutes in distilled water; placed in pyridine
for twenty-four hours, after which they are washed in many
changes of distilled water for twenty-four hours. They are then
placed in the dark for three days in a 2 per cent aqueous solution
of silver nitrate at 35° C.; then rinsed in distilled water and placed
for one day in a 4 per cent solution of pyrogallic acid in 5 per
cent formalin. Sections are cut in paraffin and after mounting
are ready for examination. With fresh pure chemicals, abso-
lutely clean utensils, and a reasonably constant temperature this
method can be relied upon to give uniform results.

1 The work upon which this paper is based was done in the Anatomische Anstalt,
Freiburgi. Br. My thanks are due to Professors Wiedersheim and Keibel,through
whose courtesy it was possible for me to carry on the investigation.

159

160 S. WALTER RANSON

The ganglia were cut into sections 18 thick. It is difficult
to make use of thicker sections because the silver method, unlike
the intra-vitam use of methylene blue, brings out all the nerve
elements so that very thick sections are confusing. On the other
hand it is difficult except in thick sections to follow the axons
to their bifurcation.

Types of spinal ganglion cells according to external form

1. The simple unipolar cell. From the body of a cell of this
type arises a single axon, which after a longer or shorter, straight
or convoluted course divides dichotomously into a thin fiber
directed toward the spinal cord and a much thicker fiber running
into the nerve. These represent, according to my observations,
the great majority of the cells in the spinal ganglia of the dog.
In sections 18, thick it is only in a small proportion of the axons
that the entire course from cell body to bifurcation can be seen.
For the most part it is possible to follow the axons for only a limited
distance before they leave the level of the section. Many axons
can be seen dividing but these can rarely be followed back to
their cells of origin. Nevertheless this connection is so well
established that it needs no confirmation.

In the case of (a) the large cells, the axon is usually much
convoluted in the immediate vicinity of the cell and within its
connective tissue capsule, but in some cases the coil is wanting.
In other cases the axon is very short and divides almost imme-
diately after leaving the cell. These axons acquire a myelin
sheath and stain by the pyridine silver method a light yellow.

(b) All of the small cells and some of the medium sized ones
present a different picture (fig. 1). The axon (whose thickness
varies with the diameter of the cell) is thin and stains a dark
brown or black. These axons seldom make complicated coils
about the cells, but run more or less directly toward the central
fiber bundles of the ganglia. Here these fibers can be seen in
large numbers dividing in the manner of a 7 or Y into a very
fine centrally directed fiber and a somewhat thicker one running
toward the nerve (fig. 2). These branches together with others

THE STRUCTURE OF THE SPINAL GANGLIA 161

of similar origin and appearance form bundles of fine black fibers
which can be followed into the dorsal root on the one side and
into the peripheral nerve on the other. These axons are devoid
of a myelin sheath (or according to Dogiel, some of them may
present a thin and interrupted coat of myelin similar to that
which is seen on some sympathetic fibers).

The axons in fig. 1 show about the average amount of coiling;
but while in many cases they are almost straight, in a few the
winding is as pronounced as that of the axon of any large cell.
It is of interest to compare the bifurcation of these fibers with
that of the medullated axons (fig. 2). These latter branch at a
node of Ranvier and show a marked constriction both of the
main stem and the two branches at the point of bifurcation. In
none of the dividing non-medullated fibers is such a constriction
to be seen. Instead there is a broad triangular area at the point
of the bifurcation. These fibers differ then from the medullated
in their small size, in the intensity with which they stain with
silver, in the absence of a surrounding unstained ring of myelin,
and in the manner of their bifurcation.

The description which is here given of the small cells and their
axons is in no sense new. JDogiel in 1897 gave a very satisfactory
account of them, which was confirmed by Cajal (’07) and later
again by Dogiel (’08, p. 33). Dogiel found on some of these
fibers very fine myelin sheaths which disappeared and reappeared
from stretch to stretch along the fiber. It is strange that neither
author gave any further consideration to these axons, apparently
overlooking the fact that they outnumber the medullated fibers
by as much as the small cells outnumber the large. We will
return to the significance of these observations in another part
of this paper.

2. Cells whose axons have collaterals ending in end bulbs. Do-
giel’s type 11, Cajal’s type vi. The peculiarity of these cells lies
in the fact that the axon gives off fine collaterals, which after
a course usually of no great length, end in characteristic swellings,
which according to their location may be divided into three sub-
groups: (a) In the majority of the cases the collaterals are given
off from the axon before it has left the connective tissue capsule

162 - S. WALTER RANSON

which surrounds its cell of origin. The collateral is usually short
and directed toward the surface of the cell but may be long and
coiled in its course. It ends in a bulb which lies upon the surface
of the cell from the axon of which it arose (fig. 3). The terminal
swelling may be very large in proportion to the size of the col-
lateral, and in some cases the latter increases in thickness as it
approaches the end-bulbs. These bulbs take only a light stain
with silver, appearing bright yellow. They lie upon the surface
of the cell beneath the connective tissue capsule and produce as a
rule a depression of the cell surface. (b) Sometimes the collateral
is given off from the axon at some distance from its cell of origin—
and piercing the connective tissue capsule of another cell ter-
minates in an end bulb which lies upon the surface of this second
cell (fig. 4). (¢) Still other collaterals run in the connective tissue
of the ganglion and end there in bulbs surrounded by a special
capsule. Sometimes two or three such bulbs lie together in a
felt-work of fine fibers and the whole mass is surrounded by a
capsule.

Huber (’96) was the first to describe these structures but saw
only those that fall under subhead (a). Both Cajal and v. Len-
hossék considered that some of these fibers were fine dendritic
branches arising directly from the cell body. On this point
my observations agree with those of Dogiel for in every case
where the origin could be determined they arose as collaterals
from axons and never as fine dendrites. According to Cajal and
Dogiel the axons of cells of this group, after having given off
the collaterals just described, end by dividing after the manner of
a T or Y into central and peripheral fibers.

3. The axon of a cell of this type splits up into a number of
branches which with or without further branching are finally
reassembled into a single axon. In sections 18 thick it is not
possible to see in their entirety such complicated structures
of this sort as were seen by Dogiel in his thicker sections and
whole mounts; but the simpler forms are often included within a
single section. A relatively common arrangement is seen in fig.
5. The axon divides into two fibers which may or may not be
of equal size and which soon reunite. A somewhat more compli-

THE STRUCTURE OF THE SPINAL GANGLIA 163

cated form is shown in fig. 6. Here the axon breaks up into a
number of fibers which unite with each other to form a plexus
out of which a single axon is again formed. Sections through
much more complicated networks formed by splitting axons can
often be seen.

4. In another variety, closely related to those just described,
the axon arises from the cell by two or more roots, each of which
has the appearance of an axon and forms a conical expansion at
the point of origin from the cell. Each of these roots may branch
repeatedly. These branches then reunite with each other form-
ing a more or less complicated network, out of which a single axon
arises (fig. 7).

Groups 3 and 4 are closely related in that the cells of the latter
differ from those of the former only in the fact that the splitting
involves the initial portion of the axon. In both cases it is rare
to find a-myelin sheath on the fine fibers forming the plexus.
These two groups correspond to Dogiel’s types v and vi taken
collectively, but the basis of separation into the two groups is
different. It is quite bewildering to read Dogiel’s description of
types v and vi with their subvarieties and try to determine
what the basis of classification of his seven subvarieties into these
two major groups might have been. For this reason it has
seemed best to adopt as a basis of classification the more obvious
and apparently more fundamental difference in the hehe of the
axon by a single or by a number of roots.

According to Dogiel the axons of both types, after exhibiting
their peculiar plexiform arrangements course as single axons for
some distance and finally divide in the manner of a 7 or Y into
central and peripheral fibers, a point which could not be verified
in the relatively thin sections with which I worked. It was, how-
ever, chiefly the origin of the axon from several roots, the split-
ting of the axon or itsroots, and the formation of plexuses in its
course which most needed confirmation; the final division of the
axon as described by Dogiel agrees so well with our former knowl-
edge of the ganglion that it may safely be accepted. The cells
included in groups 3 and 4 are fully as numerous as those in
group 2; and if one might be permitted to make a very rough

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 2

164 S. WALTER RANSON

estimate they might be said to represent together about 3 per
cent of the total number in the spinal ganglia of the dog. In the
horse, according to v. Lenhossék, they are very much more
numerous.

5. Cajal’s ‘fenestrated’ cells are characterized by the presence
of excavations in their substance. These are most commonly
found in the neighborhood of the origin of the axon, where they
often cause a U-shaped mass of protoplasm to be raised from
the surface of the cell. The axon usually arises from the sum-
mit of such a loop. Fig. 8 shows a simple cell of this kind and
fig. 9 a more complicated one. These excavations are filled with
small cells, ‘subcapsular or satellite cells.’ It is only in the poorer
of the pyridine silver preparations, however, that these satellite
cells are stained. Dogiel was unable to find the fenestrated cells
in his preparations—and concluded that Cajal had seen and
wrongly interpreted certain cells of our type Iv.

Indeed it seems that among his fenestrated cells Cajal has
figured and described some which more properly belong with the
cells of the preceding variety. There is, however, a group to
which the term ‘fenestrated’ properly applies, such as those seen
in figs. 8 and 9. In these the network is formed by protoplasmic
loops, while in figs. 5, 6 and 7 the axon is itself broken up to form
the network. In the fenestrated cells the axon is usually smaller
than the protoplasmic loops from which it arises, while in the
other varieties the size of the fibers forming the network is always
smaller than that of the axon and depends upon the number of
such fibers into which the axon has been split.

In addition to the cells of the varieties just enumerated, one
bipolar and two multipolar cells were seen in the sections of the
spinal ganglia of the dog. Fig. 10 represents a multipolar cell
with short, club-shaped processes, and fig. 11 a cell of Dogiel’s
type x1, which, according to his more complete pictures, possesses
many medullated processes which divide repeatedly, breaking
up into fine branches with expanded ends.

According to Nageotte (07) the fibers ending in end bulbs
resemble those seen in large numbers in transplanted ganglia and
are therefore to be regarded as being the product of regenerative

THE STRUCTURE OF THE SPINAL GANGLIA 165

activity in the neurone. Cajal (07) accepts this interpretation
and Bielschowsky (’08) extends it to the fenestrated cells and to
the cells whose axons have plexuses intercalated in their course.
On this hypothesis one would expect to see an increase in the
number of such cells after the division of the associated nerve.
With this in mind the left sciatic nerve was cut in four dogs and
after one month the associated spinal ganglia were prepared by
the pyridine silver technique. The results of these experiments
were entirely negative. There was no increase in the number of
fine fibers ending in end bulbs nor were any other of the peculiar
cell types seen in the normal ganglia increased in number.
Since the division of the axons might be expected to be as efficient
as any stimulus in producing regenerative changes in the neurone,
these experiments, so far as they go, speak against the interpre-
tation of these new cell types as the expression of a slow regen-
eration constantly going on in the normal ganglia. Other
experiments are in progress with the purpose of making a more
complete test of the hypothesis of Nageotte.

The axons of the small cells

In concluding his section on the cerebro-spinal ganglia in
‘Plasma und Zelle,’ Heidenhain (’11) says:

Es wirde gewiss fiir die Physiologie von grosser Bedeutung sein
wenn wir behaupten kénnten, das wir mit der Anatomie der cerebrospin-
alen Ganglien im reinen sind. Dies ist jedoch nicht der Fall. Erstlich
ist der Ursprung der erwaihnten afferenten sympathischen Fasern leider
nicht néher bekannt .. . Und zweitens befindet sich nach
den Zihlungen von Gaule und Lewin, ebenso von Biihler in den Gan-
glien eine ausserordentliche Ueberzahl von Zellen deren Fortsitze wir
noch nicht kennen.

It is with this second problem that we wish now to deal. The
numerical excess of spinal ganglion cells over medullated afferent
fibers is well established as table 1 shows, although in most cases
it is not so great as that found by Gaule and Lewin in the 32d
spinal nerve of the rabbit.

Hatai (02) by a separate enumeration of the large and small
cells of the (tv C, rv T and 11 L) spinal ganglia of the white rat,

166 S. WALTER RANSON

TABLE I
Ratio of spinal ganglion cells to dorsal root fibers

YU 9
NUMBER OF AMOR CO)

AUTHOR ANIMAL | NERVE eel pti

NERVE FIBERS
Gaule and Lewin (’96)..°... Rabbit 1 Coe. 20,361 3,173
laa (OZR tte Lk teeta oe White rat v1 C 12,200 4,227
pth aly COZ ES. ae. ern oe eee White rat at Abs 9,442 1,644
Ranson iOS) ssa yee se White rat ue (©; The 2,472

showed that the small cells constitute about 60 per cent of the
total number, while Warrington and Griffith (’04) working with
the 1 C. spinal ganglion of the cat estimated the small cells as
constituting 70 per cent of the total number. Now we have
shown in a former paragraph that the axons of these small cells
are non-medullated and it is therefore clear that they could not
be taken into consideration in the enumeration of the afferent
fibers represented in table 1 based as it was in every case upon a
differential myelin sheath stain. It is to these non-medullated
fibers, the axons of the small spinal ganglion cells, that we are to
look for the explanation of the discrepancy between the number
of spinal ganglion cells and medullated afferent fibers. If a count
of the afferent axons were made, the number would probably
closely approximate that of the spinal ganglion cells.

We have shown in fig. 1 how these non-medullated fibers arise
from the small cells, in fig. 2 how they divide dichotomously
into a thin fiber directed toward the dorsal root and a slightly
thicker one directed toward the nerve. These branches unite
themselves into bundles of fine black fibers which course longi-
tudinally through the ganglion—along with the medullated ‘fibers
having an analogous origin from the large cells. These bundles
of non-medullated fibers can be followed into the dorsal root to
which they give an appearance wholly different from that of the
ventral root. Similar bundles of non-medullated fibers can be
followed into the nerve. Fig. 12 shows the point of union of the
ventral and dorsal roots to form the mixed nerve. It cam be seen
at a glance that the composition of the dorsal root (a), as it streams
out of the spinal ganglion to unite with the ventral root (6b) differs

THE STRUCTURE OF THE SPINAL GANGLIA 167

markedly from the latter because of the bundles of fine black fibers
which it contains. One can see this contrast in a striking way
where the bundles from the two roots decussate as fibers from the
ventral root run into the dorsal ramus (d) and others from the
dorsal root into the ventral ramus (c). Fig. 18 represents a por-
tion of this decussation under higher magnification. In the
center is a pure bundle of medullated fibers derived from the
ventral root, while the fibers taking the other direction are derived
from the dorsal root, and of these some are medullated but more
are non-medullated.

It has not been possible to show that no non-medullated fibers
run into the nerve from the ventral root, but if present they are
in very small number. The majority of such fibers seen in the
nerve can be directly traced into the spinal ganglion. Nor has
the contribution of the ramus communicans to the non-medul-
lated fibers of the nerve been investigated, but even this must be
small compared to the enormous numbers coming through the
dorsal root.

As to what ultimately becomes of these fibers, there are as yet
no observations. That the central branches of the non-medul-
lated axons enter the spinal cord, there can be no doubt, but their
distribution within it has not yet been investigated. That their
peripheral branches run for long distances in the nerve has been
shown in a previous paper. They have been demonstrated in
the sciatic nerve of man, dogs, cats, rabbits and rats (Ranson,
11). Figs. 14 and 15 have been drawn with the aid of a camera
lucida from adjacent sections of the same human sciatic nerve,
the one (fig. 14) prepared according to the Pal-Weigert technique
and the other (fig. 15) by the Cajal silver method. The magnifi-
cation is the same in both instances. Great care was exercised
not to decolorize any medullated fibers in differentiating the Pal-
Weigert preparations and the field from which fig. 14 was drawn
was chosen because it exhibited the maximum number of small
medullated fibers. In the Cajal preparation (fig. 15) the color-
less rings represent the myelin sheaths, within which are lightly
stained axons. In the interspaces between these medullated fibers
are enormous numbers of small black axons directly imbedded

168 S. WALTER RANSON

in the connective tissue from which they are only separated by a
thin neurilemma. The number of axons medullated and non-
medullated which can be seen in the Cajal preparation far exceeds
the number of myelin sheaths demonstrated by the Pal-Weigert
method.

In summing up this point it may be said that the small cells
of the spinal ganglion exceed in number the large cells, that their
axons are non-medullated and divide after the manner of a T
or Y into a central and a peripheral fiber. The former runs into
the spinal cord and the latter can be followed for long distances
in the spinal nerves, but the ultimate distribution of neither the
centrally nor peripherally directed branch has yet been deter-
mined.

BIBLIOGRAPHY

Brecscuowsky, M. 1908 Uber den Bau der Spinalganglien unter normalen
und pathologischen Verhaltnissen. J. f. Psychol. u. Neurol., Leipz.,
Bd. 11, pp. 188-227.

Casa, S. R. 1905-06 Trab. del Laborat. de Investig. Biol., vol. 4. Ref. Rev.
Neurol. and Psych., vol. 4, p. 124.
1907 Die Structur der sensiblen Ganglien des Menschen und der Tiere.
Anat. Hefte, Zweite Abt., Bd. 16, p. 177.

Doatet, A. S. 1897 Zur Frage tiber den feineren Bau der Spinalganglien.
Internat. Monatsschr. fir Anat. u. Physiol., Bd. 14, p. 73.
1908 Der Bau der Spinalganglien des Menschen und der Siugetiere.
Jena.

GauLe and Lewin 1896 Uber die zahlen der Nervenfasern u. Ganglienzellen
des Kaninchens. Centralbl. f. Physiol., H. 15 u. 16.

Havat, SHinkrsHt 1902 Number and size of the spinal ganglion cells and dor-
sal root fibers in the white rat at different ages. Jour. Comp. Neur.,
vol. 12, p. 107.

HeipENnHAIN, M. 1911 Plasma und Zelle. Jena, 1911.

Huser, G. Cart 1896 The spinal ganglia of Amphibia. Anat. Anz., Bd. 12,
p. 4)7.

Lennosshx, M. v. 1907 Zur Kenntnis der Spinalganglienzellen. Arch. f.
Mikrosk. Anat., Bd. 69.

THE STRUCTURE OF THE SPINAL GANGLIA 169

Levi, G. 1905 Beitrige zur Kenntnis der Structur des Spinalgangliens. Anat.
Anz., Bd. 27.

Marinesco, G. 1906-07 Quelques recherches sur la morphologie normale et
pathologique des cellules des ganglions spinaux et sympathiques de
Vhomme. Névraxe, Louvain, vol. 8, pp. 7-38.

Naaerotrs, J. 1907 a Deuxiéme note sur la greffe des ganglions rachidiens’
Comp. Rend. Soc. Biol., Paris, vol. 62, p. 289.
1907 b Recherches experimentales sur la morphologie des cellules et
des fibres des ganglions rachidiens. Rev. Neurol., Paris, vol. 15, p. 357.

Ranson, S. W. 1908 The architectural relations of the afferent elements enter-
ing into the formation of the spinal nerves. Journ. Comp. Neur., vol.
tSempe 1 O1e
1911 Non-medullated nerve fibers in the spinal nerves. Am. Jour.
Atmiaiters viOle We O7/.

WARRINGTON, W. B., AND GrirritH, F. 1904 On the cells of the spinal ganglia
and on the relationship of their histological structure to the axonal
distribution. Brain, vol. 28, p. 297.

PLATE 1

EXPLANATION OF FIGURES

The drawings are, with the exception of figs. 14 and 15, free hand sketches from
pyridine silver preparations of the spinal ganglia of dogs. Figs. 14 and 15 are
camera lucida tracings from a human sciatic nerve, the section from which fig.
14 was drawn having been prepared by the Pal-Weigert method, and that from
which fig. 15 was drawn by the Cajal method.

1 Small and medium sized cells with non-medullated axons. Non-medul-
lated fibers black, medullated fibers gray.

2 Bifurcation of a medullated fiber and four non-medullated fibers. The
latter are fine and black with a triangular expansion at the point of bifurcation,
the former is large and grey (in the preparation light yellow) with a constriction
at the point of bifurcation.

3-4 Collaterals ending in end bulbs.

5-6 Cells whose axons are split to form a plexus.

7 <A cell whose axon arises by three roots which form a plexus out of which
the axon is formed

8-9 ‘Fenestrated’ cells.

10 Multipolar cell.

11 Cell of Dogiel’s type xt.

170

THE STRUCTURE OF THE SPINAL GANGLIA PLATE 1
S. WALTER RANSON

171

PLATE 2

EXPLANATION OF FIGURES

12 Nerve just distal to spinal ganglion; a, dorsal root just outside the
ganglion; b, ventral root; c, ventral ramus of nerve; d, dorsal ramus of nerve; e,
an arrow points to a central bundle of ventral root fibers running into the dorsal
ramus.

13 Higher magnification of the central portion of fig. 12. The central
bundle is derived from the ventral root and contains only medullated fibers; the
fibers passing in the other direction are from the dorsal root. A large part of these
are non-medullated.

172

PLATE 2

THE STRUCTURE OF THE SPINAL GANGLIA

S. WALTER RANSON

PLATE 3

EXPLANATION OF FIGURES

14 Humansciatic nerve in cross section. Myelin sheaths as black rings.
15 From same nerve as fig. 14, axons black, myelin sheaths colorless.
Non-medullated fibers in the interspaces between the medullated ones.

174

THE STRUCTURE OF THE SPINAL GANGLIA PLATE 3
S. WALTER RANSON

THE .OLFACTORY TRACTS AND CENTERS IN
TELEOSTS

RALPH EDWARD SHELDON

Assistant Professor of Anatomy, the University of Pittsburgh Medical School
From the Hull Laboratory of Anatomy of the University of Chicago

ONE HUNDRED AND FORTY-TWO FIGURES

CONTENTS
Temple (RO CU CHVOMS AAS Ne See scores acl swe Sad, ele TT hrs en ee: 178
ILLS VAN OIRE WILY 60 epee een ae Cn aR Re PN Tus Cae AS NN Re Fut ee 182
iPeeeripueral, olfactory Apparatus, : <s 24 kolie, peels betes nulls heute 183
a wOMActOryaGapSUles:: Sk. 5h. 5 0 skeen eee tke ac toe ae 183
baeihexolfactoryanervel so). <\./ san as eRe eee oe OR ek ee 185
c. The ganglion of the nervus terminalis. .)....5.....5..0....0. 186
2. The telencephalon ............... Ro aS ek ieee ae Smee 186
an eroliactorsyaoulllo nan Gy CUS ae ete ene ee te 186
b, hencerebralhemispheres!:... sic yen eee ene a en a ate 189
Gi) eiGrossamornpbolo gy: .\ sau .5 eee ae eee one ae ae 189
(GA cIN TUE Lei toy ee Mee Se Le oat 2 one ane sya
Beubhexdiencephalontesse pene. sees Benet a Bn es Oe ee ker 198
aRostralelimatence rac... Lt eae an ene enn MmEn Sh ete ry 198
bb: (Gross: morpholomy.-..° i): {eee ee) a 199
(1)! vEpithialamusgy:s)) 1) 30.) eee eer ve oo oye Oe
(2). 2 Dilwale oso 02. 2s See ee ORE eg cet ce cee 201
(Se-Hypothalamustss os eee ee eee eee 204
A ane DC LEG ACUS iar cheno Se reo TLC ET ne eee 207
Ae AC EUT ALL ACHS: oo Uecker ee | Re oe ee One oe ote Wnt aae 207
() peizactusoliactortussaterallisi eee ete ee eres 209
(2) Tractus olfactorius medialis ie myar se... 4. cr. oe, 20
@)e NervusiGerminailiss cen ee ee eet ee te 5 ene s 212
(4) Distribution secondary olfactory fibers in forebrain... 212
bauthelantertorcommissunes: 0) --e eee eee oe oe eee 213

LWPS

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3
JUNE, 1912

178 RALPH EDWARD SHELDON

ce. Diencephalieg connections =. 4-0-0)... ase eee 214

(1) . Tractus olfacto-shabenulariss. =). 9442-5 72 214

(2)? (Fascreultismretroflexuss: 45 jt. oo eee 217

(3) Tractus habenulo-diencephalicus..................... 217

(4) Posthabenular preoptic connections. ................. 218

(5)... Epiphysealiftbers’: co. ).)....'. Uae eee eee 218

(6) Fasciculus medialis hemisphaerii..................... 219

(7) Fasciculus lateralis hemisphaerii..................... 222

(8) The nucleus preopticus and its connections........... 227

5. The conduction pathways tron... 6.00.5 ic eee ee ee 231

6. The morphological areas of the forebrains)... . {.....024- sone 238

LED. Discussionyy.2 Sere. 5 2 eRe ee otc Le A alk Are to)
TVs: Literature icrtedseon: |.) 6.8 eee ee seh thee gh evened a 248
Vio, eres: Oe ete Bie Mc. ok SRI N cane occ Se 254

I. INTRODUCTION

The information here added to that heretofore existing in the
literature is derived largely from a study of the olfactory apparatus
in the carp, Cyprinus carpio (L). The olfactory apparatus is
highly developed in the eyprinoids which, therefore, lend them-
selves readily to its study. For the elucidation of difficult points,
however, comparison has been made with Weigert and Golgi
sections of the brains of the pike, Lucius lucius (L), the gold-
fish, Carassius auratus (L) and the catfish, Ameiurus nebulosus
(Le Sueur).

I am indebted to Prof. C. Judson Herrick for helpful sugges-
tions and criticism in every phase of the work, together with the
opportunity to use his unexcelled neurological library and his
personal material. Prof. R. R. Bensley likewise placed at my
disposal all the facilities of the department, including the services
of the artist, Miss Katharine Hill, who has drawn, with the most
painstaking care, the larger portion of the figures. Through the
kindness of Prof. Charles Brookover, of Buchtel College I have
been able to examine preparations of the brain of Amia calva and
to secure well preserved material for most of the Ramén y Cajal
impregnations. Acknowledgments should also be made to Prof.
B. G. Wilder of Cornell University, at whose suggestion this re-
search was undertaken, and to Prof. 8. H. Gage of Cornell Uni-
versity and Prof. FE. L. Mark of Harvard University, in whose
laboratories important parts of this investigation were conducted.

OLFACTORY CENTERS IN TELEOSTS 179

MATERIAL AND METHODS

_ The material used consists of the following eighty-three series
of sections of the carp brain.

I. Wewgert method

Inasmuch as the method used varies somewhat from that usu-
ally followed, and since it is very successful, it will be briefly out-
lined here. The fish are killed in a mixture of ether and water, the
brain removed immediately and placed in 4 per cent formalde-
hyde for at least forty-eight hours. It is then washed in running
water for a few hours and placed in Miiller’s fluid at a tempera-
ture of 40° C. for from eight to fourteen days. The fluid is
changed every second day during this period. The brain is next
washed, dehydrated, cleared in carbol-xylene and embedded in
paraffine. After the removal of the paraffine from the mounted
~ sections the slides are placed for twelve hours in a half-saturated
solution of copper acetate, stained three to four hours in Wei-
gert’s hematoxylin, and differentiated in 24 per cent potassium
ferricyanide with the addition of 2 per cent borax. Pal’s
modification was tried but rejected, as it was found that sections
on the slide could not be evenly differentiated; moreover, the
method outlined gives rather better results for the work in ques-
tion, as it brings out the unmedullated tracts and the cell groups,
which the Pal modification does not. There were stained accord-
ing to this method:

Two series transverse sections of the entire brain.
Two series sagittal sections.

Two series frontal sections.

Six series through the olfactory bulbs and crura.

All of these were from carp 35 to 60 cm. in length and were cut
at 15 micra. In addition there were prepared one transverse
and one frontal series through the entire head of carp of 3 em.
in length. The method followed in this case is as follows; the
fish are placed in Miiller’s fluid, changed every second day, for a
month, and then decalcified for another month in Flemming’s

180 RALPH EDWARD SHELDON

stronger fluid, changed each week. From this point on the
method is similar to the one first outlined; viz., dehydration, clear-
ing, embedding in paraffine, etc. Medullated fibers and nerves
stand out very distinctly after the use of thismethod. Other
methods of decalcification were tried but, as Herrick (’97) points
out, the Weigert method will not ‘take’ after any of the ordinary
processes of decalcification. Professor Herrick was kind enough
to loan me, in addition, a series of transverse sections through the
adult carp brain, stained by the Weigert-Pal method.

IT. Chloral hematoxylin and eosin method

Entire carp, 1 em. in length, decalcified.
Two series transverse sections.
Three series sagittal sections.
Two series frontal sections.

ITI. Toluidin blue method

The only fixing agent which gave uniformly good results with
this stain was Graf’s chrom-oxalic for twelve hours. This method
was used for the differentiation of areas and the cytological struc-
ture of the nerve cells.

One series transverse sections.
One series sagittal sections.
One series frontal sections.

IV. vom Rath method

This was used for the unmedullated tracts, particularly in the
olfactory bulbs, where two series of transverse sections were made.
The method followed is that given by vom Rath (’95). This
consists of fixation in the following solution for three days; satu-
rated aqueous solution of picric acid, 200 ec., 10 per cent platinie
chloride, 10 ce.; 2 per cent osmic acid, 25 cc.; glacial acetic acid,
2 cc. Next the specimens are placed in methyl alcohol for 15
minutes, 0.5 per cent aqueous solution of pyrogallic acid for two
days, dehydrated for two weeks in the dark, cleared in carbol-

OLFACTORY CENTERS IN TELEOSTS 181

xylene, embedded in paraffine and sectioned at 5 micra. This
method is of particular value in tracing the course of the nervus
terminalis.

V. Gold chloride method

This was used to bring out the unmedullated fibers, particu-
larly in the olfactory bulbs; it is not of great value, however, owing
to its low penetrating power. The method of fixation in formalin
as given in Hardesty’s ‘Neurological technique,’ was followed with
the best results. Two series of sections of the bulbs were pre-
pared by this method.

VI. Golgi method

Individuals two to five centimeters in length.
Five series transverse sections.
One series frontal sections.
Individuals twenty-five to forty centimeters in length.
Six series transverse sections.
One series sagittal sections.
Nine series cut in various oblique planes.
Fourteen series of the olfactory bulbs cut in various
planes.

Two different methods were followed, both of which gave good
results. With most of the Golgi material the fish were killed, the
brains removed and placed for three to five days in a mixture of
two parts of 3 per cent aqueous solution of potassium dichromate
and one part of 1 per cent aqueous solution of osmic acid. Next
they were rinsed in a ? per cent solution of silver nitrate in which
they may remain indefinitely but are ready for dehydration and
embedding in celloidin after two to four days. The second method
was used for brains fixed in 4 per cent formaldehyde.

After fixation for forty-eight hours the brains were washed in
running water for twenty-four hours and then placed in a 3 per
cent aqueous solution of potassium dichromate at a temperature
of 40° C. for six to ten days. They were next placed in the
osmium-dichromate mixture and treated as outlined for the first

182 RALPH EDWARD SHELDON

method. In addition to the series noted above, Professor Herrick
very kindly loaned me ten series of the brains of young carp cut
in various oblique planes. The Golgi method was used chiefly
for the study of the different neurones and the course, with par-
ticular reference to the direction, of the fiber tracts.

VII. Ramén y Cajal method

Two series transverse sections.

Three series frontal sections.

Five series sagittal sections, two of these partly
oblique.

Some difficulty was experienced in getting good preparations,
the following method giving the best results. Whole brains are
fixed in 95 per cent ethyl alcohol, washed for two hours in running
water, placed in a 1 per cent aqueous solution of silver nitrate
at a temperature of 35° C. for three to five days, washed in dis-
tilled water, transferred to a 1 per cent aqueous solution of hydro-
quinone for twenty-four hours, washed inrunning water for twenty-
four hours, dehydrated, cleared in cedar oil, mounted in paraffine
and cut at ten to fifteen micra. Fixation in neutral or acid for-
malin gave poor results.

II. ANATOMY

The names applied to the different fiber tracts and cell areas
have, so far as is consistent with their morphology, been taken
from the literature. In a few cases such terms have been used
in a sense slightly different from that assigned them by the orig-
inal authors; whenever such is the ease the fact has been noted.
In several cases inappropriate terms of long use have been
retained owing to their familiarity and common use. Where,
however, a term is lacking in the literature, or where a previ-
ously used term is greatly at variance with the morphology, a
new name has been selected. In this case the endeavor has been,
as far as possible, to make such new name descriptive of the rela-
tionships involved, or else suggestive of a homologous structure

OLFACTORY CENTERS IN TELEOSTS 183

in the nervous anatomy of higher forms. In the case of fiber
tracts the customary methods of neurological nomenclature have
been followed, viz., the application of a term which will include in
itself full information as to the origin and termination of the
fibers as well as their direction; as for example, the tractus inter-
medio-habenularis, originating in the nucleus intermedius and
terminating in the habenula.

1. PERIPHERAL OLFACTORY APPARATUS

a. The olfactory capsules

The olfactory apparatus in the carp consists of the olfactory
capsules with their lamellae, open to the exterior through two
apertures; the olfactory nerves, bulbs, crura, centers in the cere-
bral hemispheres, epithalamus, medithalamus and hypothalamus,
to which may be added the motor connections common to the
olfactory and gustatory senses, etc. These latter will not be
considered in this article.

Gross morphology. The two external apertures of the capsules
are in close. proximity, one rostro-medial of the other. They are
separated by a grooved flap of skin so shaped that in forward
movement water will be driven into the more rostral aperture.
The lateral aperture opens caudally for the exit of water from the
cup. Inside the capsule, and running caudo-laterally from the
rostro-medial aperture, is a median ridge from which the lamellae
radiate on either side and at its caudo-lateral end.

Microscopic anatomy. The lamellae are covered by the epi-
thelium of the olfactory mucous membrane, consisting of the
typical nervous olfactory cells, and the supporting cells. Goblet
cells are particularly numerous in the epithelium of the central
ridge, which is also slightly thicker than that of the lamellae
(fig. 5). It resembles closely the respiratory epithelium of the
Schneiderian membrane of mammals, as distinguished from the
olfactory portion. It is probable, therefore, that there are found
here two varieties of epithelium, similar to the condition in higher
forms; an olfactory, concerned with smell and a respiratory,
concerned, in this case, with the water current.

184 RALPH EDWARD SHELDON

Innervation. From the olfactory cells arises the unmedullated
fibers which, passing through the lamellae, form the olfactory
nerve. Medullated fibers penetrate the central ridge, ending
immediately underneath the epithelium (fig. 5). Such an inner-
vation has been described in no other anamniote (Sheldon,
’08 b), although it has long been known that in mammals, partic-
ularly in man, such fibers take part in the innervation of the
nasal mucous membrane.

In 1903 Rubasehkin demonstrated their presence in birds.
Practically all Amphibia and many fishes have been studied with
reference to this point, but in no case have medullated fibers been
demonstrated beyond doubt, although Aichel in 1895 believed that
he found something of the kind in embryo teleosts. In six Wei-
gert series through the olfactory capsules, bulbs and crura of the
adult carp it has been possible to demonstrate the presence of
medullated fibers in the tunica propria of the Schneiderian mem-
brane, part of which evidently distribute to the epithelium, as
they can be traced to the membrana propria itself. These latter
probably end in free nerve terminations, as there are no special
organs developed. Part of the fibers entering the tunica pro-
pria join the bundles of unmedullated fibers and apparently run
to the mucous membrane of the lamellae with them. The re-
mainder of the medullated fibers innervate the skin about the
nasal capsule.

All of these medullated fibers are derived from the supra-
orbital trunk, which is made up of general cutaneous fibers from
the Gasserian ganglion (nervus ophthalmicus superficialis tri-
gemini) and sensory fibers from the facial (nervus ophthalmicus
superficialis facialis). This latter nerve is composed partly of
fibers from the dorsal lateralis ganglion, and partly of visceral
sensory fibers from the geniculate ganglion. The fibers entering
the tunica propria are certainly not acustico-lateral, since no canal
or pit organs are developed in connection with the epithelium;
the fibers are also smaller than are the lateralis fibers. They
may, therefore, be either general cutaneous or visceral sensory,
with the preponderance of evidence in favor of the former. This is
due, in part, to the fact that in birds and mammals such innerva-

OLFACTORY CENTERS IN TELEOSTS 185

tion is trigeminal and partly because the weight of evidence in the
teleosts is against the supposition that visceral sensory fibers
are present in this region. Part of the branch entering the tunica
propria goes to the skin, as already noted; the number of general
cutaneous fibers in the supra-orbital trunk is much greater than
the number of visceral sensory. If there are visceral sensory
fibers going to the mucous membrane, they must be unspecialized,
as there are.no taste buds present; there is not the slightest evi-
dence, however, that such fibers are here present. In their course
from the supra-orbital trunk to the tunica propria the.medullated
fibers pass partly between the two bundles of the olfactory nerve
and partly directly laterad into the median ridge.

Young gold fish and cod were studied with reference to the
presence of medullated fibers in the mucous membrane, but none
could be demonstrated. This may have been due, particularly, in
the case of the gold fish, to the fact that the individuals were
immature, as such fibers could not be found in young carp.

As the main current of water would be forced along the ridge
thus innervated by general cutaneous fibers, it is probable that
their function is that of tactile response for solid substances in the
water or else with respect to the strength of the water current
or both (see also Kappers, with respect to the ‘Oralsinn,’ and
Sheldon, ’09 b, on ‘Chemical Sense’).

b. The olfactory nerve

The olfactory fibers gather from the different lamellae in two
main bundles. In general, the medial bundle is derived from
the more rostral lamellae, while the lateral is derived from the
more caudal. The fibers of the two bundles distribute to all
parts of the rostral and lateral surfaces of each bulb, the lateral
bundle causing a protuberance on the dorso-lateral surface of each
bulb as shown in figs. 1, 6 (a). There is a quite general crossing
of the fibers of the two bundles before they reach the bulb so that
fibers from each reach all parts of the bulb (fig. 123). Apparently,
however, the lateral bundle is more especially associated with the
tractus olfactorius lateralis and to a somewhat less extent with the

186 RALPH EDWARD SHELDON

tractus olfactorius ascendens, while the medial bundle is most
closely associated with the tractus olfactorius medialis. The
olfactory bulb is closely applied to the caudo-mesal face of the cap-
sule so that the nerve itself is very short, although individual
fibers may be of some length.

c. Ganglion of the nervus terminalis

Lying between the two bundles of the olfactory nerve from the
lamellae to the bulb are a number of large scattered ganglion cells
forming the ganglion of the nervus terminalis. In the adult carp
these cells are most numerous near the bulb and are apparently
about a hundred in number. This is less than is the case in Amia
as described by Brookover (’08, ’10). Neurites from these cells
run mesad to form a bundle of fibers on the mesal aspect of each
bulb (figs. 7, 123, 124).

2. THE TELENCEPHALON

a. Olfactory bulb and crus

The olfactory bulb is ellipsoid in shape, about 1.5 mm. long and
1 mm. thick, in a 40 em. carp. Rostrally and laterally it is cov-
ered by a mass of olfactory nerve fibers as noted above. At the
rostral end of the bulb a circular constriction appears externally,
separating the bulb proper from the olfactory nerve proper, which
rostro-lateral to the constriction spreads out over the olfactory
capsule. Caudally the bulb tapers down to the small, elongated:
crus on which it is borne in the cyprinoids. This is from three to
four centimeters long in a 40 em. carp, extending from the bulbs to
the cerebral hemisphere (fig.1). In young fry the bulbs are closely
apposed to the hemispheres; but since the cranium grows faster
than the brain as a whole, the crura elongate. Each crus is a
hollow tube, the base of which is formed by the tracts connecting
the bulb and hemisphere (figs. 2, 22, 23). Dorsally is an epithe-
lial roof, a rhinotela, which is simply a rostral prolongation of
the tela, or so-called pallium of the hemispheres, consisting ofa
layer of ependyma and one of pia. This covering arches over the

OLFACTORY CENTERS IN TELEOSTS 187

solid base of the crus at its caudal end as shown in fig. 23, gradu-
ally decreasing in extent rostrad (fig. 22) until it forms only a
roof for the trough-like cavity below. This cavity is morpho-
logically a part of the ventricle of the hemispheres, extending, even
a short distance into each bulb, as is the case with most verte-
brates (Wiedersheim, ’02).

Internal to the layer of olfactory nerve fibers occurs the for-
matio bulbaris, formed chiefly by the glomeruli. The glomeruli
are of the usual type, consisting of the terminal end-brush of
olfactory nerve fibers, mingled with the dendrites of mitral cells,
chiefly. The central and mesal portion of the bulb is made up of
a mass of cells, the nucleus olfactorius anterior, the lobus olfac-
torius anterior of Goldstein.

According to Golgi preparations, neurones of several differ-
ent types are found in the olfactory bulb. The most conspicu-
ous are the large cells with short, thick, many branched dendrites,
the mitral cells (figs. 8 to 12). These are irregular in form and
are situated largely in the peripheral portion of the bulb, with
their long axes approximately parallel with the surface as figured
by Johnston, Catois, ete. The mitral cells are very irregular in
form; pyramidal, stellate and goblet shapes being the most nu-
merous. The dendrites of these cells, as already mentioned, break
up in the glomeruli and there come into relation with the terminals
of the olfactory nerve fibers. ‘Their neurites form the majority
of the centripetal fibers of the tractus olfactorius lateralis and
tractus olfactorius medialis. A dendrite of a mitral cell will
often enter, also, into relation with one of the cells of the nucleus
olfactorius anterior, usually a fusiform or stellate cell. The
smaller cells of the bulb are more nearly central in position and
make up most of the nucleus olfactorius anterior. Fusiform and
stellate cells are the most numerous of these, with occasionally a
pyramidal or goblet-shaped cell (figs. 13 to 20). The stellate
cells, particularly of the types shown in figs. 14 and 17, are the
most common, and are situated near’the center of the bulb, with
their many processes extending fan shaped toward the periphery,
where many of them enter glomeruli (Johnston, ’98, fig. 1).
Other processes of these cells enter into relation with other cells

188 RALPH EDWARD SHELDON

of the nucleus olfactorius anterior. It is certain that a few of the
stellate cells send their neurites into the hemispheres, but such
could not be demonstrated with certainty for all. Many fusi-
form cells of the type shown in fig. 13 lie near the center of the
bulb with two processes extending to either margin. These cells
likewise send their neurites to the hemispheres (fig. 21). Cells
of the types shown in figs. 15, 16, 18, 20 may be found in any part
of the nucleus olfactorius anterior, with their processes extending
nearly equally in all directions. Small granule cells, of the type
shown in fig. 19, are common in the center of the bulb, where they
apparently function as association cells, as no neurites entering
the crura could be demonstrated. The mitral cells undoubtedly
correspond with the mitral cells of all other vetebrates, so far
as studied; there is some question, however, regarding the com-
parative morphology of the smaller cells throughout the verte-
brate series. Apparently, as is shown also by Johnston, the stel-
late cells in lower vertebrates are connected with the glomeruli
and hemispheres, much as are the mitral cells; as an ascent is made
in phylogeny, however, these cells may either disappear or may
metamorphose into mitral cells. The typical stellate cells of the
carp as shown in figs. 14, 17, are undoubtedly similar to the stel-
late cells of the granular zone of Acipenser, as described by John-
ston; there is the same relation to the glomeruli, the position in
the bulb is the same, and the central processes take the same
course. Fusiform cells of the type shown in fig. 13 are probably
the homologues of Johnston’s spindle cells of the granular zone,
although no neurites were traced from these cells into the crura.
The type found in figs. 15 and 20 probably corresponds to John-
ston’s cells with short neurites, Golgi type II cells. Cells of Cajal
were not identified with certainty. The granule cells of the carp
are apparently simply intrinsic association nerve cells, differing,
therefore, from the granule cells of Acipenser.

The fiber tracts of the olfactory bulb will be taken up later, in
connection with the fiber systems of the cerebral hemispheres.

OLFACTORY CENTERS IN TELEOSTS 189

b. The cerebral hemispheres

(1) Gross morphology. The cerebral hemispheres are of the typi- .
cal teleostean type (figs. 1 to 4). They consist of paired solid basal
lobes which contain chiefly the secondary olfactory centers, con-
tinuing caudo-ventrally over the optic chiasma as the pedunculi
thalami, or praethalamus of C. L. Herrick. Dorsally and later-
ally, these are covered by a membranous roof, the so-called pal-
lium, composed of adjacent layers of ependyma and pia. This
tela is continuous rostrally with the membranous roof of each
olfactory crus, the separation into two parts occurring just at
the rostral margin of the basallobes. This tela is attached at the
ventro-lateral margin of each hemisphere, at which point its pia
becomes continuous with that of the base of the brain, while its
ependyma is reflected over the basal lobes (figs. 1, 2, 3, 4, 34).
Immediately mesal to the attachment of the tela occurs a fis-
sure, the fissura endorhinalis (figs. 4, 24, 25, etc.). This is the
sinus rhinalis of Kappers (’06), the fovea endorhinalis externa of
Kappers and Theunissen (’08), the fovea limbica of Goldstein
and Edinger, the fissura ectorhinalis of Owen (’68), the fissura
endorhinalis of many authors. This fissure holds a constant posi-
tion throughout the vertebrate series, separating in the higher
forms the basal olfactory centers from the pyriform lobe; it like-
wise bears a constant relation to the tractus olfactorius lateralis,
as will be noted later.

The ventricle of the forebrain consists of the open space between
the tela and the basal lobes. This forms a large, but shallow
cavity, excepting between the two basal lobes where it is of some
depth (figs. 24, 34, 35, etc.). It extends caudally to the velum
transversum. Caudal to this velum, occurs a much convoluted
epithelial sac extending rostrally over the tela proper; this is
the dorsal sac, and is an evagination of the membranous wall of
the diencephalon (fig. 68). Ventral to the velum transversum, the
forebrain ventricle passes over into the third ventricle or dien-
cephalic cavity.

Each basal lobe is separated by ependymal sulci on the dorsal,
lateral and mesal surfaces into regions with characteristic internal

190 RALPH EDWARD SHELDON

structure and fiber connections (figs. 2 and 3). The deepest of
these is the sulcus ypsiliformis, which arises from the ventro-
lateral border about three-fourths of the distance back from
the rostral pole of the basal lobe, ascends to the dorsal surface and
here divides into an anterior and a posterior limb, which enclose
a central eminence. This eminence contains the palaeostriatum
and the primordium hippocampi, the latter covering the dorsal
surface of the palaeostriatum, especially on its mesal border.
The posterior limb separates the posterior pole from the rest of the
hemisphere; the anterior limb separates the central eminence from
the tuberculum anterius and the tuberculum laterale, these com-
prising a part of the nucleus olfactorius lateralis. The remainder
of the lateral olfactory nucleus is the nucleus pyriformis of the
posterior pole.

The anterior limb of the sulcus ypsiliformis corresponds fairly
closely with the sulcus palaeopallio-epistriaticus of Thynnus and
the fovea endorhinalis interna of Amia, as described by Kappers
and Theunissen (08).

On the mesal aspect of each basal lobe, extending for almost the
whole length of the lobe is a well defined sulcus of great morpho-
logical importance which has been ignored by other writers on
the brains of fishes. It forms the dorsal boundary of the precom-
missural body and has some points of resemblance with the fis-
sura limitans hippocampi (C. Judson Herrick, ’10) in Amphibia
and Reptilia, the fovea septocorticalis (Kappers and Theunis-
sen) in Rana, and the fissura arcuata of Gaupp, with which, how-
ever, it is not fully homologous, as will appear beyond. It will
be designated sulcus limitans telencephali.

Ventrally of this furrow lies the corpus precommissurale, termed
the epistriatum by Kappers (’06), the lobus olfactorius posterior,
pars medialis, by Goldstein, ete.

An examination of fig. 4 shows that the fissura endorhinalis
on the ventral surface of the hemispheres forms an open V._ It
first appears rostrally at the point where the olfactory tract joins
the hemispheres (fig. 24), gradually extending laterally until the
base of the sulcus ypsiliformis is reached, whence it turns medially
again. For the whole of its extent the tractus olfactorius lateralis

OLFACTORY CENTERS IN TELEOSTS 191

lies immediately dorsal, giving off fibers to the nucleus olfacto-
rius lateralis and nucleus pyriformis. Lateral to the caudal end
of the fissura endorhinalis lies the nucleus teniae of Edinger,
Kappers and Goldstein.

(2) Nuclei. The basal lobes are entirely separate, excepting
ventrally, where they are joined by the lamina terminalis, which
runs rostrally from the region of the optic chiasma. At a point
approximately two-thirds distant from the rostral margin of the
hemispheres, there lies embedded in the lamina terminalis, the large
anterior commissure, connecting both lobes (figs. 34 to 61).
Rostrally, the lobes overhang the olfactory tracts for a short dis-
tance (fig. 24), while caudally the hemispheres, spreading later-
ally over the optic tracts, are partly covered by the optic lobes
(fig. 76).

The basal lobes contain, in teleosts, the secondary olfactory
centers, one or more tertiary centers and the so-called corpus
striatum, here designated the palaeostriatum. In the carp this
receives, throughout most of its extent, secondary olfactory fibers.

(a) Corpus precommissurale. Extending from the rostral end
of the hemispheres caudally into the diencephalon is a column of
cells, bordering the medial cavity on either side. Its dorsal
limit is indicated by the sulcus limitans telencephali and it is
bounded laterally, throughout most of its more caudal portion, by
the palaeostriatum.

This is the corpus precommissurale; the area olfactoria posterior
medialis and epistriatum of Kappers, ’06, but not of Kappers, ’08,
where this name is applied to the primordium hippocampi; the
lobus olfactorius posterior, pars medialis of Goldstein; ‘vordere
nucleus,’ partly, of Bela Haller. At the rostral end of the hemi-
sphere this nucleus is largely ventral (fig. 25); toward the anterior
commissure, however, it increases in dorso-ventral extent cover-
ing practically all the mesal surface of each hemisphere (fig. 35).
The interposition of the fibers of the commissure separates the
nucleus into two parts, a dorsal passing above the commissure,
and a ventral composed of cells lying between its fiber systems
(figs. 35, 36, 38, 55, 56, 61). Caudally of the anterior commissure,
these two divisions of the nucleus remain distinct, one continuing

192 RALPH EDWARD SHELDON

ventrally, close to the median cavity, while the other remains
dorsal, meeting the lateral olfactory area in the polus posterior
of the hemisphere, and then continuing caudally under the haben-
ula. This forking column of cells is, as will be brought out more
clearly later, the morphological equivalent of the precommissural
body or paraterminal body of Elliot Smith in mammals and rep-
tiles, and is, therefore, here termed the corpus precommissurale.
The rostral portion of the nucleus corresponds morphologically
to the rostral part of the ganglion mediale septi of Gaupp, or the
area precommissuralis septi of Kappers and Theunissen in the
frog, and is called, therefore the nucleus medianus (fig. 25).

The portion of the nucleus extending into the commissure is
simply the bed of the anterior commissure of Elliot Smith in
reptiles and mammals and is called, therefore, the pars commis-
suralis. The arm of the precommissural body arching over the
commissure presents points of resemblance to the pars fimbrialis
septi of Kappers and Theunissen in the frog. It is here called the
pars supracommissuralis (figs. 35, 36, 38, 55, 56, 61). Its exten-
sion caudad behind the commissure joining the lateral olfactory
area is named the pars intermedia (figs. 66,67, 68, 70). Thecom-
missure bed passes immediately caudad into a nucleus of small
cells, bordering the ventricle, which is here termed the nucleus
preopticus (figs. 61, 66, 67, 68, 70, 73, 76, etc.). This is composed
of several different cell groups which will be taken up in greater
detail later.

All parts of the corpus precommissurale appear very discrete
in toluidin blue preparations. In the nucleus medianus, the
cells are closely packed, but are arranged in groups or islands
(figs. 25, 26). (See Calleja, 93.) Usually a clear zone of few
cells surrounds the precommissural body particularly dorsally
and laterally (fig. 38). In the pars supracommissuralis the cells
are less closely packed (figs. 38, 46, 56), and have lost the island
arrangement. The grouping in the pars commissuralis, is largely
dependent on the position of the fiber bundles of the anterior com-
missure; the cells are, however, fairly evenly distributed (figs.
38, 56).

OLFACTORY CENTERS IN TELEOSTS 193

In the rostral part of the commissure bed is found the group
of cellsin which terminate the fibersof the nervus terminalis. The
pars intermedia of the corpus precommissurale consists of a
narrow column of cells, fairly closely packed and forming a dis-
tinct band across the ventral portion of the posterior pole of the
hemisphere (figs. 66, 67, 68, 70). Its morphological relationships
are obscure.

In Golgi preparations of different parts of the precommissural
body some of the cellular relations are brought out more fully.
In the nucleus medianus the cells are fairly large, fusiform, pyra-
midal or ellipsoid in shape, with almost all of their processes com-
ing from the ends of the perikaryon as shown in figs. 28 to 31.
A large proportion of these cells give rise to the fibers of the
tractus olfactorius ascendens. The neurites are very delicate,
possessing granular enlargements along their course. Smaller
cells with a number of short, root-like dendrites and a single long
neurite extending into the palaeostriatum, are not uncommon
(fig. 43). Several varieties of small cells, apparently functioning
as association cells, are found also in the nucleus medianus;
these are chiefly stellate, or irregularly rounded (figs. 41, 42).
In the pars supracommissuralis the cells are smaller; also rather
more of the association cells of the type shown in figs. 41, 42 are
found. Cells of type shown in fig. 48, sending fibers to the palaeo-
striatum, are more common than in the nucleus medianus. Many
of the cells of this nucleus send their neurites into the tractus
olfacto-thalamicus medialis. Such a cell is shown in fig. 40. Small
stellate and small pyramidal cells are rather more common than
the type illustrated.

(b) Primordium hippocampi. Dorsad of the sulcus limitans
telencephali, appearing with especial distinctness rostrally, lies
the primordium hippocampi, or nucleus olfactorius dorsalis.
Between it and the corpus precommissurale may be seen a slight
clear area, devoid of cells. The cells of the primordium hippo-
camp1 are rostrally slightly smaller than those of the nucleus medi-
anus, while dorsal to the pars supracommissuralis they are very
similar to those of the latter nucleus (fig. 46). Many of them
resemble the dorsal cells of the nucleus olfactorius lateralis (figs.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

194 RALPH EDWARD SHELDON

48, 49, 56). The primordium hippocampi receives secondary
olfactory fibers from the tractus olfactorius medialis and a few
commissural fibers associated with the commissura corporium
precommissuralium. The neurites of its cells descend partly
with the tractus strio-thalamicus and partly with the tractus
olfacto-thalamicus medialis, pars dorsalis. No tertiary olfactory
fibers could be traced, in Golgi preparations, either from the
lobus pyriformis or the corpus precommissurale to the primordium
hippocampi. In Ramén y Cajal preparations, however, mingled
with the fibers of the commissura corporium precommissuralium
rostrally are a number of unmedullated fibers connecting the
nucleus medianus with the primiordium hippocampi. From the
conditions in amphibians, reptiles and mammalsit seems extremely
probable that these represent the tractus area-hippocampalis rectus
of Kappers and constitute an association path between the pre- .
commissural body and the primordium hippocampi. The mor-
phology of this region will be considered more in detail further on.

(ec) Nucleus olfactoriuslateralis. Laterally, extending from the
extreme rostral end of each basal lobe to the extremity of the
polus posterior, lies the lateral olfactory area; the area olfactoria
of Edinger, the lobus olfactorius posterior, pars lateralis of Gold-
stein, area olfactoria posterior lateralis of Kappers (’06), area
olfactoria lateralis of Kappers and Theunssen (’08). The nucleus
olfactorius lateralis is here divided into itwo parts, both rostral
to the sulcus ypsiliformis, and consisting of rather evenly dis-
tributed, somewhat scattered cells. The more rostral appears
externally as the tuberculum anterius (figs. 2 and 3), while the
more caudal presents superficially the tuberculum laterale. The
nucleus olfactorius lateralis covers as a cap the entire rostro-
lateral surface of each basal lobe. At the extreme rostral pole it
is restricted to the lateral aspect but passing caudally it gradually
spreads dorsally covering the dorso-lateral aspect of each lobe, at
the level of the sulcus ypsiliformis (figs. 25, 38).

The lobus pyriformis, so named since it is closely related to the
pyriform lobe of mammals, consists dorsally and caudally, of
evenly distributed scattered cells very similar to those of the nu-
cleus olfactorius lateralis (figs. 38, 56, 66,67). Ventrally, imme-

OLFACTORY CENTERS IN TELEOSTS 195

diately lateral to the fissura endorhinalis, a portion of the nucleus
pyriformis is specialized to form the nucleus teniae of Kappers,
Goldstein, Edinger, the caudal portion of the hypostriatum of
Catois, nucleus occipito-basalis of C. L. Herrick. This is a com-
pact nucleus of rather small cells (fig. 57). Caudally it meets the
pars intermedia of the corpus precommissurale, both being covered
dorsally by the unspecialized cells of the lobus pyriformis (figs.
30,.00, 66,67, 70).

In preparations by the Golgi method, this region is plainly
marked. Throughout the whole lateral olfactory area, near the
periphery of the lobes, one finds cells of the same general type,
with fine processes, lightly spiny, and with small sized perikarya
(figs. 52, 33, 48, 49, 52, 53). The perikarya vary considerably
in shape, flask-shaped cells being most numerous, as shown in
figs. 32, 33, from the rostral portion of the lateral area, figs. 48,
49 from the dorso-lateral part. Occasionally, small pyramidal
cells of the type shown in fig. 53 may be found. Flask-shaped
cells are particularly numerous close to the periphery of each lobe,
with the rounded margin of the perikaryon directed toward the
periphery and most of the processes arising from the mouth of the
flask. A cell of this type is shown in fig. 52. Part of these proc-
esses extend laterally along the ventricular margin, while the
neurite enters the basal forebrain bundle.

The cells of the nucleus teniae vary somewhat from the general
type of the lateral olfactory area neurone but are recognizably
similar. Many of the cells, as shown in figs. 59, 60, possess peri-
karya more nearly ovoid than flask-shaped; the processes are
fine and bear inconspicuous spines, however, as do the other cells
of the lateral olfactory area. Fig. 58 shows a cell nearly pyra-
midal in shape.

(d) Palaeostriatum. In the central part of each basal lobe is
a region called by practically all writers on the teleostean brain
the corpus striatum, here termed the palaeostriatum (figs. 25, 38,
56). It is bounded mesially by the precommissural body, dor-
sally by the primordium hippocampi and on the other sides by the
lateral olfactory nucleus. Practically all parts of it receive
olfactory fibers of the second order and it is largely, therefore, a

196 RALPH EDWARD SHELDON

portion of the mesal and lateral olfactory areas. The cells of the
central part of this area are very large and conspicuous (fig. 44)
and are quite scattered as compared with the cells of other areas of
the basal lobes. In series stained by cytological methods, such as
toluidin blue or thionin, it is easy to demonstrate that there is a
gradual transition from these conspicuous cells to those typical
of the lateral olfactory area.

According to the Golgi method, neurones of the central portions
of the palaeostriatum appear very large, with comparatively
enormous perikarya, and with long, thick, very thorny dendrites
(figs. 50, 51). In shape, the perikarya vary from short, flask-
shaped to pyramidal (fig. 45).

There is shown in Golgi preparations the same transition
between the area olfactoria lateralis and the palaeostriatum, as
in toluidin blue or thionin preparations. One may note a gradual
change, in passing from the periphery centrally, from the small,
flask-shaped cells with rather inconspicuous thorns, to the large
cells, with enormous perikarya and thick, thorny processes; more-
over, now and then, a cell of the palaeostriatal type will be found
close to the periphery, or a small lateral area cell found in the palae-
ostriatum. A large proportion of the cells of both the lateral
olfactory area and the palaeostriatum send their neurites into the
basal forebrain bundle, the different parts of which will be taken
up later. The neurites of the cells of the nucleus teniae, however,
enter the tractus teniae. Many of the cells of these two areas are
apparently association cells, functioning not only to bring differ-
ent parts of the same area, but also adjacent areas, such as lateral
olfactory area, palaeostriatum and corpus precommissurale, into
relation. Such is apparently the function of some of the cells of
the type shown in figs. 50, 51.

The word ‘palaeostriatum’ is not used in quite the same sense
as it is used by Kappers, as will be noted from the preceding dis-
cussion. Kappers believes that the palaeostriatum is closely con-
nected with the olfactory apparatus, but receives no somatic sen-
sory connections from the thalamus, which it probably does receive
in the teleosts. The term as here used indicates that astructure is
found in the teleosts, closely related to the secondary olfactory

OLFACTORY CENTERS IN TELEOSTS 197

centers, and morphologically related to a part, at least, of the cor-
pus striatum of higher forms.

(e) Nucleus commissuralis lateralis. Situated in the ventro-
medial portion of each basal lobe, in the region of the anterior
commissure, at either end of the commissure is a small compact
nucleus of fairly large, closely packed cells (figs. 38, 56). No
references to it in the literature have been noted; it has, therefore,
beens termed the nucleus commissuralis lateralis, owing to its
location, laterally at the level of the anterior commissure.

(f) Nucleus preopticus. Immediately caudal to the anterior
commissure there appears ventrally the recessus preopticus of the
third ventricle (fig. 56). Surrounding this, on either side, and
passing rostrally insensibly into the pars supracommissuralis,
is the nucleus preopticus. This nucleus is composed of cells of
two types; at the level of the caudal margin of the hemispheres is a
dense mass of cells bordering the median ventricle; its cells are some
of the largest in the brain (fig. 71), and are flask-shaped with their
bases directed toward the ventricle and most of their processes
extending laterally and ventro-laterally (figs. 67, 70,71). This is
here termed the pars magnocellularis of the nucleus preopticus.
Rostral to this nucleus, continuous with the pars supracommis-
suralis, is a nucleus of small cells (fig. 64). This group of cells
extends caudally, lateral to the pars magnocellularis, gradually
curving around it caudally, thus enclosing the nucleus magnocel-
lularis on three sides. In contradistinction to the nucleus mag-
nocellularis this is called the pars parvocellularis of the nucleus
preopticus. To the portions rostral, lateral and caudal to the
pars magnocellularis are assigned the suffixes, anterior, lateralis
and posterior, respectively (figs. 64, 66, 67, 70, 78). This nucleus
extends caudally to the region of the fibrae ansulatae.

In Golgi preparations the pars parvocellularis shows cells of
several types, resembling closely the various kinds of small cells
of the corpus precommissurale.

The nucleus preopticus was recognized by C. L. Herrick in 1892.
Herrick saw both the large and small cells and applied the name
nidulus praeopticus to the larger portion of the nucleus; it is
probable, however, that his nucleus postopticus contains a por-

198 RALPH EDWARD SHELDON

tion of the cells here included under the name nucleus preopticus.
Bela Haller noted the same group of cells and termed it the
nucleus posterior of the forebrain. Johnston (’98) and (01) found
a nucleus bordering the recessus preopticus and termed it the
nucleus thaeniae owing to the fact that he observed fibers passing
from it to the habenula, and that, therefore, it is (98) ‘‘a nucleus
corresponding to the nucleus occipito-basalis of (C. L.) Herrick
and the nucleus thaeniae of Edinger” in reptiles. This view is
untenable as will be pointed out later. Johnston probably recog-
nized the fact, as he terms it nucleus praeopticus in his ‘Nervous
System’ (06). Kappers noted the large cells and, following Her-
rick, named the group, nucleus praeopticus. Goldstein, follow-
ing the descriptions of Edinger for the brains of reptiles and birds,
applied the names magnocellularis and parvocellularis strati grisei
to the two components of the nucleus.

(g) Nucleus entopeduncularis. Appearing immediately cau-
dal to the nucleus commissuralis lateralis is a group of very small
cells (fig. 65), lying embedded in the basal forebrain bundle (figs.
66, 67, 68, 70). This is the nucleus entopeduncularis of Gold-
stein.

3. THE DIENCEPHALON

a. Rostral limits

The division of the vertebrate brain into transverse segments,
with a clear definition of their limits, is a matter of considerable
difficulty, particularly since, as Johnston and C. J. Herrick have
pointed out, most of the important morphological centers and
fiber connections are arranged in longitudinal columns. The
question of the caudal boundary of the telencephalon ventrally
is still unsettled, some authors considering the pedunculi thalami,
caudal to the anterior commissure, part of the diencephalon,
others placing the rostral limits of the ’tween-brain behind the
optic chiasma in the adult. Dorsally the caudal margin of the
velum transversum has long been considered the limit of the fore-
brain. Johnston recently (’09) has taken up the subject in some
detail and his interpretation is here followed; according to which

. OLFACTORY CENTERS IN TELEOSTS 199

the caudal limits of the forebrain include the velum transversum |
and the optic chiasma. The pedunculi thalami, the praethalamus
of C. L. Herrick, are included in the telencephalon, and their cen-
ters have already been described (nucleus preopticus and nucleus
entopeduncularis).

Most writers on the brains of fishes have, however, included
these structures in the diencephalon; in fact even under the inter-
pretation here followed, the pars parvocellularis posterior of the
nucleus preopticus extends into the diencephalon, since it reaches
caudally to the level of the fibrae ansulatae.

b. Gross morphology

The diencephalon in the carp is of the typical teleostean type.
Immediately caudal to the velum transversum, the diatela is
thrown into a convoluted folded epithelial sac, extending ros-
trally over the membranous pallium of the hemispheres, forming
the saccus dorsalis, post-velar arch, or Zirbelpolster (figs. 68, 73).
This is an extremely vascular structure, formed by the covering of
pla mater and a lining, continuous with the ependyma of the third
ventricle. Arising immediately caudal to the saccus dorsalis,
with the caudal wall of the one practically adherent to the rostral
wall of the other, is the epiphysis or pineal body. This is a small
elongated tubular organ extending rostrally, suspended in the
folds of the dcrsal sac. Its epithelium, while an extension of that
of the ependyma, is glandular in type. Lying embedded in the
membranous wall between the dorsal sac and the epiphysis, is
found the commissura habenularum, or commissura superior. At
the caudal base of the epiphysis is found the commissura posterior,
between it and the tectum opticum.

The diencephalon is commonly subdivided into epithalamus,
_ hypothalamus and thalamus. The latter has been divided by

_C. J. Herrick (10), followimg Ramén y Cajal, into pars dorsalis
(sensory correlation centers) and pars ventralis (motor correlation
centers). The epithalamus of the carp is distinct; the other parts
are so confused that further embryological study will probably be
necessary to effect this separation; and the assignment of the differ-

200 A RALPH EDWARD SHELDON

ent nuclei and fiber tracts to these regions in this paper must be
regarded as provisional, particularly with respect to the centers
lying within, and immediately dorsal to, the lateral parts of the
inferior lobes.

The inferior lobes consist of an unpaired pars medialis, which is
clearly hypothalamic, and paired partes laterales, the lateral
lobes, which apparently belong chiefly to the pars ventralis
thalami.

The lobi laterales are widely separated rostrally by the inter-
posed lobus medius, while they meet one another caudal to it.
Caudally a furrow appears onthe ventral aspect of the lateral lobes,
the suleus mammillaris of Goldstein (fig. 4). The prominence of
the lobes mesal to the two sulci, is due to the development dor-
sally of the corpora mammillaria of Goldstein (fig. 117). Later-
ally, each inferior lobe shows several lobes and sulci, varying some-
what in different individuals. Rostrally the great size of the
nucleus prerotundus and nucleus rotundus causes the development
of a slight protuberance, appearing on the outside of the lobe (fig.
3). Further caudally the nucleus cerebellaris hypothalami gives
rise to a similar enlargement (fig. 3). The lobus medius consists
of the tuber cinereum rostrally, and the pars infundibularis
caudally.

Extending ventro-rostrally from the tuber is found the hypo-
physis, consisting of the two conspicuous solid lobes, separated by
a circular constriction; a rostral pars glandularis and a caudal
pars nervosa. Ventrally these are separated into symmetrical
parts by a longitudinal median furrow (fig. 4). Extending cau-
dally from the caudal margin of the pars i.fundibularis of the lobus
medius is a narrow, thin, glandular, men.branous sac, the saccus
vasculosus, opening into the infundibular cavity (fig. 4).

The median cavity of the forebrain extends caudally and ven-
trally between the two pedunculi thalami and thalamus proper,
giving rise to diverticula which penetrate the lateral lobes. (For
a more detailed account of the ventricles of the teleostean infe-
rior lobes see Goldstein (’05), pp. 189-195, figs. 13-19; Edinger
(08), fig. 171.)

OLFACTORY CENTERS IN TELEOSTS | 201

(1) Epithalamus. The epithalamus of the carp is easily defined,
consisting of the saccus dorsalis and epiphysis and the habenular
centers, including the two habenular ganglia, the habenular decus-
sation, or commissure and the nucleus posthabenularis, together
with their connections.

The ganglia habenularum are very conspicuous in the carp,
protruding for half their diameter into the median cavity (figs.
78, 81). Their cells are small and evenly distributed but thrown
into groups or islands by the fibers of the tractus olfacto-habenu-
laris and the fasciculus retroflexus (figs. 78, 81). As seen in Golgi
preparations, the cells are very characteristic, of the type normal
throughout the vetebrate series (fig. 75).

Nucleus posthabenularis. Immediately ventral to the habenu-
lar ganglia, the cells of the one continuous with the cells of the
other, les the nucleus posthabenularis, ‘das posthabenulare
Zwischenhirngebiet’ of Goldstein, the ‘posthabenulare Zwisch-
enhirngegend’ of Bela Haller, Meynert’s nucleus of reptiles
(figs. 78, 81). Rostrally, it becomes continuous with the nucleus
intermedius (fig. 70), while caudally it extends beyond the level
of the commissura posterior (fig. 84) always holding a position close
to the median ventricle and ventral to the fasciculus retroflexus.

(2) Thalamus. At the level of the habenulae, there appear on
either side, immediately ventral to the arch of the tectum, the
corpora geniculata lateralia. Mesal to the lateral geniculate
body les the nucleus anterior thalami of Goldstein (figs. 78, 81).
This is easily recognized, owing to its large size and its character-
istic appearance, showing a ring of cells about its periphery (fig.
81).

Nucleus rotundus and associated centers. One of the most
important. parts of the thalamus, and at the same time one of the
most difficult to understand in all its relations, is the region of
the nucleus rotundus. Owing to its prominence, it has been noted
by nearly every writer on the teleostean brain. It was described
by Fritsch and called by him the nucleus rotundus; Bellonci used
the same term, while C. L. Herrick termed it the nucleus ruber.
Goldstein assigns the name nucleus ventralis thalami to this

202 _ RALPH EDWARD SHELDON

whole region, although he shows both in his figures and descrip-
tions that it contains different groups of cells with different char-
acteristics. Kappers (’06) pointed out that the center previously
described as nucleus rotundus is really made up of several char-
acteristic eroups of cells. That

situated most dorsally, proximally and laterally, is the nucleus praero-
tundus. This group . . . .. gradually passes backward into a
much larger group situated under and lateral to the level of the nucleus
rotundus and ending where the real nucleus rotundus has its largest
size. This latter group, which belongs entirely to the lobi inferiores,
I shall distinguish as the nucleus subrotundus from the nucleus rotundus
proprius, as it extends in part under the real nucleus rotundus so that
the com. horizontalis, before it enters the lower border of the latter, lies
for some distance over it and between it and the nucleus rotundus pro-
prius.

This separation of the nucleus rotundus of the earlier authors
into three different components is a matter of considerable mor-
phological importance, as will be brought out later. Kappers’
description applies in a general way to the’relations in the carp,
with some important modifications.

At the level of the rostral margin of the lateral lobes, the nucleus
prerotundus appears ventro-laterally immediately ventro-lateral
to the commissura transversa (fig. 78). It consists here of a
fairly compact mass of irregularly shaped cells of medium size.
A short distance further caudally this nucleus lies wedged in
between the lateral lobe and the commissura transversa. Dorso-
laterally it forms a small protuberance on the lateral surface of
the brain (fig. 81). From this point the nucleus prerotundus
extends caudo-mesially to the region of the nucleus posterior
tuberis. It may be compared in shape to the caudate nucleus in
the human brain, with a large and conspicuous head rostrally,
gradually diminishing in size caudo-mesally (figs. 84, 89, 103, 106).

The nucleus rotundus proprius is by far the largest and most
conspicuous nucleus of the thalamic region. It appears rostrally
at about the rostral margin of the commissura posterior and ex-
tends caudo-mesally, lateral to the nucleus prerotundus, almost’
to the commissura ansulata, meeting the corpus mammillare
ventro-mesially (figs. 84, 89, 103, 106, 117).

OLFACTORY CENTERS IN TELEOSTS 203

Ventrally of the nucleus rotundus, extending caudo-laterally
from the level-of the nucleus posterior tuberis, to the level of the
caudal margin of the corpus mammillare, lies the nucleus subro-
tundus (figs. 106, 117).

When the three components of the nucleus are considered to-
gether, it is noted that the nucleus prerotundus forms a cap over
the rostro-mesal surface of the nucleus rotundus (fig. 84), decreas-
ing in transverse diameter as the latter increases in size (fig. 89).
At approximately the level where the nucleus prerotundus ends,
the nucleus subrotundus is beginning to appear, embedded in the
nucleus rotundus ventro-laterally (fig. 106). Further caudally
(fig. 117), since the nucleus rotundus extends caudo-mesally
while the nucleus subrotundus extends caudo-laterally, the two
come to lie approximately in the same horizontal plane, one lateral
to the other, the nucleus rotundus merging into the dorsal margin
of the corpus mammillare; the nucleus subrotundus’ similarly
ending in the nucleus cerebellaris hypothalami and losing its
typical shape and appearance (see figs. 136-140, for a horizontal
projection of these nuclei).

In addition to their conspicuous size, the nuclei rotundi show
a characteristic structure, hardly fully brought out in any of the
drawings. The nucleus prerotundus throughout most of its
extent is composed of rather large scattered cells, together with
small numbers of various smaller sized cells (fig. 85) showing
faintly between them. Severalof thecells from Golgi preparations
are shown in figs. 86 to 88. The cells of the nucleus rotundus
are smaller and more nearly of the same size. They are always
scattered in groups or islands, giving a characteristic appearance
to the nucleus (fig. 90). Figs. 91 to 94 show several from Golgi
preparations. The nucleus prerotundus and rotundus combined
form the ‘kleinzellige’ portion of the nucleus ventralis thalami of
Goldstein. The most easily recognizable of these nuclei is the
nucleus subrotundus, owing to its extremely characteristic appear-
ance near its rostral end, or head. There, as shown in figs. 106 and
107, it presents a circular appearance in transection, with its cells
grouped in the center and surrounded by a clear peripheral area.
The cells average larger than those of the remaining two nuclei

204 RALPH EDWARD SHELDON

and are noticeably so in its caudal part, where they become large,
spindle shaped or pyramidal, as the nucleus cerebellaris hypo-
thalami is approached. This nucleus corresponds to the ‘gross-
. zellige’ portion of the nucleus ventralis thalami of Goldstein.
By the Weigert or Ramon y Cajal methods the nucleus prero-
tundus and rotundus show a peculiar blotched appearance, due
to the presence of small bundles of fine fibers scattered between
the islands of cells; fig. 102 brings this out fairly well.

Nucleus posterior thalami. Lateral to the nucleus rotundus,
at the level of the nucleus posterior tuberis, is a nucleus of very
large ganglion cells, the nucleus posterior thalami, the ‘ Vereins-
gebiet’ of Bela Haller (figs. 103, 106, 117). This gradually in-
creases in size caudally finally disappearing in the nucleus cere-
bellaris hypothalami. Its cells are particularly large as shown in
fig. 109 from a toluidin blue preparation and figs. 110 to 113 from
Golgi preparations.

Nucleus ruber tegmenti. Dorso-mesal to the caudal part of
the nucleus posterior thalami, and dorsal to the nucleus subro-
tundus is a nucleus of extremely large cells, the nucleus ruber
tegmenti of Goldstein (fig. 117).

The remaining centers of the thalami are omitted from con-
sideration in this article as they have no special connection with
the olfactory apparatus and are not necessary for purposes of orien-
tation. This includes the nucleus dorsalis of Goldstein, the nucleus
corticalis of Kappers, the nucleus praetectalis, and nucleus inter-
medius of Goldstein.

(3) Hypothalamus. The hypothalamus consists of the lobus
medius and part of the lobi laterales of the inferior lobes (figs.
3, 4), together with their included centers and connections, and
the hypophysis. The lobus medius consists rostrally of the tuber
cinereum and caudally of the pars infundibularis. Ventro-ros-
trally, as previously noted, is given off the hypophysis, while
extending caudally from the pars infundibularis, is found the
saccus vasculosus.

Nucleus anterior tuberis. A single group of cells, the nucleus
anterior tuberis, makes up the larger part of the rostral portion
of the lobus medius (figs. 81, 84, 89). This is composed of smaj]

OLFACTORY CENTERS IN TELEOSTS 205

cells, appearing as a core in the center of the nucleus (figs. 84,
89). Rostrally, the nucleus anterior tuberis is continuous past the
fibrae ansulatae, Herrick’s commissure, ete., into the nucleus
preopticus, pars parvocellularis posterior. Caudally, the nucleus
ends at the level of the lateral ventricular diverticula, leading to
the lobi laterales (figs. 100,101). See also Edinger (’08), fig. 171;
Goldstein (05), text-fig. 16.

Nucleus posterior tuberis. Dorsad of the diverticula the nu-
cleus anterior tuberis passes caudally into the nucleus posterior
tuberis, immediately ventral to the tuberculum posterius (Hau-
benwulst) (fig. 103). This is a nucleus of small cells, similar in
appearance to those of the nucleus anterior tuberis, although its *
celis are more evenly distributed.

Nucleus ventralis tuberis. Appearing rostrally, immediately
ventral to the commissura horizontalis, is a nucleus of enormous
cells, not hitherto described in the literature, which is here termed
the nucleus ventralis tuberis (fig. 78). It continues for a short
distance caudally, lying close underneath the median ventricle
and gradually diminishing in size (figs. 81, 84). .

Nucleus lateralis tuberis lLaterally, appearing immediately
caudal to the commissura horizontalis, at the ventro-lateral mar-
gin of the nucleus anterior tuberis, occurs a closely packed group
of large cells, the nucleus lateralis tuberis (fig. 84). This is found
only for a short distance at the level of attachment of the hypo-
physis. .

Nucleus ventricularis. Close to the median ventricle, parti-
cularly as far caudal as its diverticula, may be seen a layer of
densely packed cells close against the ependyma. Similar cells
may be noted adjacent to the median ventricle rostrally, even
before the anterior commissure. The same condition holds
also for the walls of the lateral diverticula into the lobi laterales.
It is noticeable that wherever these cells are found the ependyma
consists of higher columnar cells than in other regions. These
probably belong to the apparatus, described by Johnston, for
the regulation of blood pressure in the brain.

Nucleus diffusus lobi lateralis. Throughout the peripheral
portion of the lobi laterales, particularly laterally and ventrally,

206 RALPH EDWARD SHELDON

is an evenly distributed area of small cells, forming the nucleus
diffusus lobi lateralis of Goldstein, the substantia grisea lobi infe-
rioris of Kappers, who divides it into a pars anterior and a pars
posterior (figs. 78, 81, 84, 89, 103, 106, 117). The cells, as shown
in Golgi preparations, possess elliptical or flask-shaped perikarya,
with many finely spiny dendrites, resembling somewhat the undif-
ferentiated cells of the area olfactoria lateralis. A number of the
cells are shown in figs. 95 to 99. This undifferentiated area is
evidently the primitive structure of the lateral lobes from which
its nuclei have been gradually evolved. (Compare the condition
of ganoids, according to Johnston.)

Nucleus cerebellaris hypothalami. Appearing rostrally, at
approximately the middle of the longitudinal extent of the lateral
lobes, occurs a nucleus of large evenly distributed, scattered cells,
the nucleus cerebellaris hypothalami of Goldstein (fig. 89). This
extends caudally and laterally,’ gradually increasing in size until
it occupies a large part of the transverse diameter of each lateral
lobe (figs. 89, 103, 106, 117). It extends practially to the caudal
part of each lobe, laterally. A small area, under high power, is
shown in fig. 108.

Corpus mammillare. The only remaining center of importance
in the lobi laterales is the ganglion mammillare of Goldstein.
Rostrally and dorsally it meets the tail of the nucleus rotundus;
thence it extends caudally, always adjacent to the median wall
of the caudal portion of each lobe (fig. 117), practically to the tip
of the lobes. It is composed of very small, closely packed, evenly
distributed cells of characteristic form (figs. 118, toluidin blue;
119 to 121, Golgi). Where this nucleus comes into contact with
the nucleus rotundus the two may be easily distinguished by the
difference in the size and arrangement of the cells.

In Weigert preparations the corpus mammnillare is easily dis-
tinguished, owing to the large number of fine medullated fibers
found in it, giving it a finely reticular appearance.

A number of the cell groups here introduced will not be fur-
ther considered but have been mentioned in order to give an
accurate understanding of the relations of the different centers.

bo
=)
“I

OLFACTORY CENTERS IN TELEOSTS
4. THE FIBER TRACTS

a. Crural tracts

The olfactory neurones of the first order from the olfactory
mucous membrane to the olfactory bulbs and their connections
at that point have already been described. The connections
between the bulbs and hemispheres will next be considered. It
has long been known that the fibers of the olfactory tracts pass
between the bulbs and olfactory lobes in two bundles; Bellonci
was the first to divide the tracts into a medial and a lateral.
C. L. Herrick in 1891 brings out clearly the morphological rela-
tions of these two tracts, which he ealls the radix lateralis and the
radix mesalis. He points out that the radix lateralis passes
directly from the bulbs to the caudo-lateral part of each basal
lobe, which he terms hippocampus, and that the radix mesalis
decussates in the anterior commissure. Edinger (’96) figures a
horizontal projection of the basal lobes of the carp, in which he
traces the lateral tract, called by him the tractus bulbocorticalis,
into a region termed the area olfactoria, while the median olfac-
tory bundle, or tractus bulbo-epistriaticus, ends partly in the epi-
striatum of the same side, and partly decussates in the anterior
commissure. Catois (’01) identifies the same two bundles as
‘Le faisceau externe’ and ‘Le faisceau interne.’ Catois is the
first to point out that the medial tract consists of both centri-
petal and centrifugal fibers. He agrees with Edinger that it is
partly crossed and partly uncrossed. Bela Haller likewise identi-
fies the two tracts. Goldstein (’05) has worked out the relations
of the bundles in more detail than his predecessors, and finds that
the lateral tract, ‘laterale Riechstrahlung,’ originates in the lobus
olfactorius anterior and ends, largely uncrossed, in the lobus
olfactorius posterior, pars lateralis, while a few fibers decussate
in the anterior commissure to end in the same area on the opposite
side. The ‘mediale Riechstrahlung’ is formed, according to
Goldstein, entirely from centripetal fibers, which run in several
distinct bundles. The more lateral originates in the lobus olfac-
torius anterior, and decussates in the anterior commissure to

208 RALPH EDWARD SHELDON

end in the lobus olfactorius posterior, pars lateralis, of the oppo-
site side. The remaining two bundles originate from the formatio
bulbaris; the more medial forms the commissura olfactoria inter-
bulbaris, while the more lateral ends in the lobus olfactorius
posterior, pars medialis, in which are confused the precommissural
body and the epistriatum of Edinger. Kappers (’06) observes two
different conditions in the teleosts examined by him. The lateral
tract, or radix olfactoria lateralis, always ends inthe area olfactoria
posterior lateralis (area olfactoria of Edinger) ; in Gadus, Thynnus
and Lophius it ends on the same side, however, while in Salmo
it decussates in the apterior commissure to end in the opposite
side. Kappers also finds that the medial tract is composed of
two parts, a medial tractus olfacto-lobaris medialis and a lateral
radix olfactoria medialis propria. He finds that both sets of
fibers decussate and that most of them end in the area olfactoria
posterior medialis, here termed epistriatum, although a few in
Salmo may end in the lateral area.

In none of the previous work on these tracts in fishes have all
of the connections been brought out. This is undoubtedly due,
in part, to the lack of a detailed study of the olfactory bulb and
in part to a failure to learn the direction of the different compo-
nents by the use of the Golgi method. —

The olfactory crura in the carp, as previously noted, are very
long and in transections at different levels, the apparent number
of tracts varies considerably. In some sections only one or two
bundles will appear, while in others ten or twelve may be seen.
In order to determine the number and relations of these bundles,
plots were made of several complete series of serial sections of the
crura, showing the number of bundles appearing in each section
and their relation to one another. Micrometer measurements
were used to determine the relations in all doubtful cases; that is
to say, whenever in one section two bundles were found, and
in the next section three, measurements were taken if there was
any doubt as to which of the two gave rise to the third. In this
way, it is possible to determine the number of important fiber
bundles in the crura and by tracing them to their origin and ter-
mination, learn their relation to the centers of the bulbs and basal

OLFACTORY CENTERS IN TELEOSTS 209

lobes. Thus it is shown that instead of a radix medialis and a
radix lateralis there are nine distinct fiber bundlesrunning through-
out the crura (figs. 123, 124,22, 23)?

(1) Tractus olfactorius lateralis. The lateral tract, the trac-
tus olfactorius lateralis, consists of three bundles, a pars lateralis,
pars intermedia and pars medialis. These are composed entirely
of centripetal fibers, arising largely from mitral cells of the lateral
part of each bulb. A few fibers, however, arise from stellate
cells more centrally placed (fig. 124). The tractus olfactorius
lateralis, pars lateralis originates, chiefly in this way, from stel-
late cells of the nucleus olfactorius anterior, a few of its fibers
arising, however, from peripheral mitral cells (figs. 124, 137).
The tractus olfactorius lateralis, pars intermedia is the largest
and most important of the three. Part of its cells of origin lie
in the nucleus olfactorius anterior, while the larger proportion
are mitral cells from the lateral portion of the bulb rostrally and
dorsally (fig. 6). One small bundle of fibers originates from the
mesal part of the bulb, crossing dorsally to join the main tractus
olfactorius lateralis, pars intermedia (fig. 6). The tractus olfac-
torius lateralis, pars medialis is small but extends throughout
almost the entire length of the bulb, arising partly from mitral
cells and partly from stellate cells of the nucleus olfactorius
anterior (figs. 6, 124). The fibers of all three portions of the
tractus olfactorius lateralis pass through the crura (figs. 22, 23),
and gradually spread out above the fissura endorhinalis (figs. 24,
35) to end, without decussating, in the lateral olfactory area
of the basal lobes (fig. 137), including all parts of the nucleus
pyriformis and nucleus teniae. Fibers end throughout almost
the entire length of the area, the fibers ending farthest rostrally
arising from the tractus olfactorius lateralis, pars lateralis. All
three tracts, however, give off fibers to all parts of the nucleus
olfactorius lateralis, rostrally of the sulcus ypsiliformis. <A larger
proportion of the fibers of all three bundles end farther caudally,
however, in the nucleus pyriformis, beyond the sulcus ypsili-
formis, and in the nucleus teniae. Golgi preparations show that
in all cases the fibers bend abruptly dorsad usually branching
at their termination. The termination of the lateral tract in the

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

210 RALPH EDWARD SHELDON

basal lobes of the carp is similar, therefore, to its’ending in the
majority of other teleosts; it has been possible, however, to dem-
onstrate fibers from the tractus olfactorius lateralis in the dorsal
and dorso-lateral region of the basal lobes, called by Johnston
(06) the epistriatum. This area is, therefore, simply a part of
the lateral olfactory area.

(2) Tractus olfactorius medialis. The medial olfactory, de-
scribed by the earlier workers as a single tract, and by the most
recent as two, is really composed in the carp of five bundles of
widely varying relationships (figs. 22, 23, 124, 186, 137).

Tractus olfactorius ascendens. The tractus olfactorius ascen-
dens described by Kappers, in Salmo, Gadus, ete. (radix olfactoria
medialis propria) as a centripetal tract is, in the carp, as shown by
Golgi preparations, a centrifugal bundle, originating from cells
in the nucleus medianus (figs. 27 to 31). Catois described the
more medial portion of the medial tract as centrifugal, but other
authors have been unanimous in considering all excepting a few
commissural fibers as centripetal. The fibers of the tractus
olfactorius ascendens gather from all parts of the nucleus medianus
and extend rostrad.to the bulb in two bundles which occupy the
middle or intermediate portion of the base of each crus (figs. 24,
23, 22). On reaching the olfactory bulb the fibers gradually
spread out, and end in the nucleus olfactorius anterior (figs. 124,
136).

Tractus olfactorius medialis. Medially in the bulb and crus
is found the tractus olfactorius medialis. This originates almost
entirely from mitral cells and contains the neurites from practi-
cally all the mitral cells far rostrally in the bulb; it may be traced
much farther rostrally than any: of the other tracts of the crus.
Throughout most of the bulb three bundles, belonging to this
tract may be identified (for two of them see fig. 6); near the caudal
margin of the bulb, however, these three join to form two, which
may be traced separately to their termination in the basal lobes.
The two lateral bundles originate almost entirely from cells at
the extreme rostral end of the bulb, joining to form the tractus
olfactorius medialis, pars lateralis. This can be distinguished
from the tractus olfactorius medialis, pars medialis throughout

OLFACTORY CENTERS IN TELEOSTS on kal

the entire extent of the crura; for a short distance at the rostral
end of the basal lobes the two are so closely joined, however, that
it is difficult to identify them (figs. 24, 34). As they come into
proximity to the anterior commissure they again separate, the
tractus olfactorius medialis, pars lateralis holding a_ position
dorsal to its smaller companion tract (fig. 34). From this point —
caudad it extends slightly laterad until the anterior commissure
is reached, when it largely decussates at about the middle of the
commissure, to end in the lobus pyriformis of the opposite side
(figs. 35,.36, 55, 137). This agrees with the more lateral por-
tion of the ‘mediale Riechstrahlung’ of Goldstein but differs
from the conditions observed by Kappers, excepting for a few
fibers in the brain of Salmo. A small number of fibers, however,
as shown by Golgi preparations, leave the tract before its decussa-
tion to end in the nucleus preopticus (fig. 137) and the pri-
mordium hippocampi. The tractus olfactorius medialis, pars
medialis originates from mitral cells of the medial surface of the
bulb, and extending to the basal lobes, decussates ventral to and
slightly rostral to, the tractus olfactorius medialis, pars lateralis
(figs. 34, 35, 186). This forms the commissura olfactoria inter-
bulbaris of Goldstein, the commissural fibers connecting the
two olfactory bulbs, which have been described by many writers.
In Weigert preparations it appears as if these fibers actually form
a commissure, but when the crossing is examined in Golgi and
Ramon y Cajal material, it is found that a large part of the fibers
decussate in the commissure and then end almost immediately,
while a few terminate at the commissure, without decussation.
Many fibers terminate, also, in the pars anterior of the nucleus
medianus, the pars supracommissuralis of the corpus precommis-
surale and possibly in the primordium hippocampi of the same
side. It can not be stated with certainty that no fibers pass
around to the opposite bulb; commissural fibers have, therefore,
been indicated on the diagram (fig. 124). Kappers, Edinger,
‘Bellonci and others have noted fibers belonging to the medial
olfactory tract, and ending: in the hypothalamus. Such an
appearance is likewise common in Weigert preparations, as the
fibers of the tractus olfactorius medialis, pars lateralis appear

212 RALPH EDWARD SHELDON

to continue in the tractus olfacto-thalamicus medialis. Such a
condition is deceptive, however, as no such fibers could be demon-
strated in Golgi or Ramon y Cajal preparations. It is evident
that the Weigert preparations, which fail to show the fine fibers
as they approach their termination, are, therefore, unreliable in
a study of the origin and termination of tracts, or the relations of
two closely associated bundles.

(3) Nervus terminalis. Earlier agroup of ganglion cells belong-
ing to the nervus teminalis was described. As shown in fig.
124 the neurites of these cells pass mesad, lying for a distance
between the two bundles of the olfactory nerve, along the mesal
surface of the bulb. This has been demonstrated in Golgi prep-
arations. In Weigert and vom Rath preparations, an unmedul-
lated tract, undoubtedly formed by the central processes of these
ganglion cells, extends from the same region to the hemispheres
(Sheldon, ’09, Sheldon and Brookover, ’09). Rostrally this
tract hes embedded in the tractus olfactorius medialis, pars medi-
alis (fig. 6), on the medial aspect of the bulb. As it passes caudad
throughout the crus, it still holds approximately the same position
with reference to the tractus olfactorius medialis, pars medialis
(figs. 22, 23). When the rostral part of the basal lobe is reached,
the nervus terminalis gradually turns dorso-laterad through the
tractus olfactorius medialis to lie between that and the tractus
olfactorius ascendens (fig. 24). As the anterior commissure is
reached, the unmedullated fibers separate from their companion
tracts and decussate in the rostral part of the commissure, end-
ing in the rostral portion of the pars commissuralis of the corpus
precommissurale, as described for the nervus terminalis of sela-
chians by Locy, and in Amphibia by Herrick (figs. 35, 136).

(4) Distribution of secondary olfactory fibers in the forebrain.
It will have been noted that secondary olfactory fibers end in a
very large part of the basal lobes. Fibers of the lateral olfactory
tract end throughout the lateral, dorsal and latero-ventral por-
tions of the basal lobes from the rostral end to the lobus pyri-
formis and nucleus teniae of the,polus posterior. These fibers
extend, also, into a large part of the central area formerly called
striatum. The mesal tract, the tractus medialis, carries centri-

OLFACTORY CENTERS IN TELEOSTS Pg Ne

petal fibers tothe nucleus medianus; nucleus supracommissuralis,
nucleus preopticus and the primordium hippocampi, probably
also to the nucleus commissuralis lateralis (¢r. olf. med.) ; in addi-
tion to further fibers for the lobus pyriformis. The only portions
of the basal lobes which do not receive secondary olfactory fibers
are the nucleus entopeduncularis and, possibly, a small area in the
center of the palaeostriatum. It can not be said with certainty,
however, that this latter area receives no olfactory fibers of the
second order; simply that such were not demonstrated.

b. The anterior commissure

The olfactory areas of the two basal lobes are connected by
four sets of commissural fibers, crossing in five bundles. In the
most rostral part of the anterior commissure are found numbers of
fine fibers, partly medullated and partly unmedullated, bending
sharply dorsad. The unmedullated fibers connect the mesal
portions of the two primordia hippocampi, while the medullated
join similar parts of the partes supracommissurales of the corpus
precommissurale (Sheldon, ’09 a, fig. 6). A short distance
caudad, accompanied by unmedullated fibers, is.a small commis-
sure of medullated fibers connecting the lateral portions of the
partes supracommissurales and nuclei dorsales or primordia
hippocampi (figs. 35, 36). This latter bundle, as it presents
points. of resemblance with the commissura pallii anterior of
reptiles, and the rostral portion of the commissura pallii or com-
missura dorsalis of Amphibia, is termed on the plates, commis-
sura dorsalis. Morphologically, however, the fibers mentioned
thus far are divisible into a commissura hippocampi, pars anterior,
and a commissura corporium precommissuralium, each bundle
consisting partly of each kind of fibers (fig. 138).

At the caudal part of the anterior commissure a few unmedul-
lated fibers pass across to connect the rostral ends of the nuclei
preoptici of the two lobes. This is termed the commissura nu-
cleorum preopticorum (fig. 138).

The commissura dorsalis is closely associated with the decussa-
tion of the tractus hypothalamo-olfactorius medialis and also with

214 RALPH EDWARD SHELDON

a fourth commissure, entirely unmedullated, connecting the
ventral parts of the two nuclei pyriformes, and here termed the
commissura hippocampi, pars posterior. Its fibers are closely
intermingled with those of the decussating tractus olfactorii
mediales, partes laterales, distinguishable in Weigert preparations
owing to their lack of medullary sheaths (fig. 138). See also
Goldstein, Taf. 11, fig. 7; Goldstein terms this the commissura
olfactorii internuclearis. This commissure is shaped like a bow,
with either end bent caudally to terminate inthe nuclei pyriformes
(figs. 36, 37, 55). This is the hippocampal commissure of C. L.
Herrick, probably also the commissura interolfactoria of Kappers.
This commissure offers points of resemblance with the fibers of the
commissura dorsalis, which connect the two occipital poles in the
frog and with a part of the commissura pallii of Kappers in the
frog.

It will be noticed that.the anterior commissure complex con-
tains two bundles connected with the primordium hippocampi,
and one with the nucleus pyriformis, all of which are probably
represented in the commissura dorsalis, or commissura hippocampi
of amphibians. The morphological significance of the regions
thus connected will be considered later.

These comprise all of the connections of the basal lobes except-
ing those bringing them into relation with the diencephalon,
together with a few praethalamic connections which will be taken
up later.

c. Diencephalic connections

(1) The tractus olfacto-habenularis. In 1892 Edinger described
for selachians a tract between the basal lobes and the ganglia
habenularum which he called the tractus ganglii habenulae ad
proencephalon, stating, however, the possibility that its fibers
might run in the opposite direction. Such a connection was also
indicated by C. L. Herrick, in the same year under the name of
taenia thalami. All recent writers have observed these fibers,
and have shown that they are largely ascending, from the basal
lobes to the habenular ganglia of the epithalamus. Catois
traces the fibers of his tractus olfacto-habenularis from the caudal

OLFACTORY CENTERS IN TELEOSTS 215

part of the hypostriatum (nucleus teniae) to the habenulae;
Kappers and Goldstein make similar observatiqns. Johnston,
however (98, 01, 702) in Acipenser and Petromyzon finds that
the larger proportion of the fibers ascending to the habenulae arise
from the nucleus preopticus, called by him the nucleus thaeniae
(98, ’01, 702) and nucleus praeopticus (’06). Some fibers in Aci-
penser are traced from the nucleus postolfactorius ventralis and
nucleus postolfactorius lateralis, corresponding largely to the
corpus precommissurale and the area olfactoria lateralis, respec-
tively. It will thus be noted, as Johnston himself pointed out,
that the tractus olfacto-habenularis of Acipenser and Petromyzon
is not the equivalent of that in teleosts, selachians, amphibians,
reptiles and mammals. The conditions as observed in the carp
explain this discrepancy, as in this form the tractus olfacto-
habenularis is equivalent to both the tractus olfacto-habenularis
of Edinger, etc., and of Johnston (figs. 140, 141, 142).

The tractus olfacto-habenularis of Catois, Edinger, Kappers,
etc., the taenia thalami of Goldstein, appears conspicuously as a
small, heavily medullated bundle, arising from the nucleus
teniae, lateral to the fissura endorhinalis, at the level of the caudal
margin of the anterior commissure. ‘This is here termed the trac-
tus teniae (fig. 55) and corresponds morphologically to the tractus
cortico-habenularis lateralis of C. Judson Herrick in the Amphi-
bia (10).

It extends iatero-caudad, dorsal to the bundles of the basal
forebrain bundle (figs. 61, 68), where it receives a few unmedul-
lated fibers from the nucleus intermedius, the tractus intermedio-
habenularis, pars anterior (figs. 140, 141, 142), possibly homologous
to the tr. septo-habenularis of Herrick. Slightly caudal to this
point the tract receives a small number of unmedullated fibers
from the nucleus entopeduncularis, extending dorsad from the
praethalamus. This is termed the tractus entopedunculo-haben-
ularis (fig. 72), and is probably the morphological equivalent
of the lateral praethalamic portion of the taenia thalami of
amphibians and reptiles. A large part of these fibers may be
descending, corresponding to the tr. habenulo-thalamicus of Her- °
rick (710). Quite a number of fine unmedullated fibers arise

216 RALPH EDWARD SHELDON

from the nucleus preopticus, pars parvocellularis anterior, to
join the main ,tract (figs. 73, 141, 142), termed the tractus pre-
optico-habenularis, pars anterior. Where the nucleus intermedius
becomes continuous with the nucleus posthabenularis, it gives off
a few unmedullated fibers to the tractus olfacto-habenularis, the
tractus intermedio-habenularis, pars posterior (figs. 141, 142).
The pars magnocellularis gives rise to two sets of fibers for the
habenulae, both unmedullated, a diffuse fiber connection extend-
ing dorsad, close to the median ventricle, the tractus preoptico-
habenularis, pars medialis (fig. 73), and a small compact tract,
which passes lateral to the basal forebrain bundle, the tractus
preoptico-habenularis, pars lateralis (figs. 74, 141, 142). Further
caudally tracts join the main bundle from the pars parvocellu-
laris, pars posterior, of the nucleus preopticus, the tractus pre-
optico-habenularis, pars posterior; and from the nucleus post-
habenularis, the tractus posthabenulo-habenularis (figs. 141, 142).
Part of this may also be descending and, therefore, homologous
with the tractus habenulo-thalamicus of Herrick.

All of these fibers make up the tractus olfacto-habenularis.
It will be noted that the only medullated bundle is the tractus
teniae; this is likewise the most conspicuous of the different fiber
systems which probably explains why it is the only one previ-
ously described in teleosts. The habenular ganglia, then, receive
fibers from practically all parts of the caudal portions of both the
lateral and medial olfactory columns. Laterally, fibers pass up
from the nucleus teniae of the lobus pyriformis, medially from the
nucleus preopticus, nucleus intermedius, nucleus entopeduncularis
and nucleus posthabenularis. The lateral connection is the one
observed by Edinger, Catois, Kappers, Goldstein, ete., while the
medial is that found chiefly in Acipenser and Petromyzon by
Johnston. Apparently the largest bundle in Petromyzon cor-
responds with the tractus preoptico-habenularis, pars lateralis,
in the carp.

Practically all of the fibers of the tractus olfacto-habenularis
decussate in the commissura habenularis, the commissura superior
of many writers (figs. 76, 141, 142). It is possible that a few fibers
end on the same side. It is likewise possible that there are a few

OLFACTORY CENTERS IN TELEOSTS AA

commissural fibers connecting the two nuclei teniarum, taking
this course, and running in the tractus teniae (Edinger (’08) fig.
231), as in the Amphibia. Such fibers would be comparable with
the commissura pallii posterior (commissura aberrans) of lizards.

Several different fiber systems arising from cells in the habenular
ganglia have been described. As indicated above, Edinger, in
his earlier work, believed that the tractus teniae arosein the haben-
ulae, the tractus ad proencephalon. He also describes in sela-
chians a tract to the midbrain roof, the tractus ganglia habenulae
ad mesocephalon dorsalis; a tract to the midbrain base, the trac-
tus descendens ganglii habenulae, in addition to the long known
Meynert’s bundle, or fasciculus retroflexus, more recently de-
scribed. by Goldstein, Edinger, etc. under the name ‘tractus haben-
ulo-interpeduncularis.’ Beia Haller observed fibers arising in
the habenulae and entering the optic apparatus, ‘Habenular-
wurzel des Opticus;’ also a tract extending ventrad into the dien-
cephalon, ‘Hauben-Zwischenhirnbahn.’

(2) Fasciculus retroflecus. The fasciculus retroflexus in the
carp is a strong, chiefly unmedullated tract, originating partly
from cells of the habenulae (fig. 75) and partly from the nucleus
posthabenularis, as pointed out earlier by Bela Haller and Gold-
stein (figs. 141, 142). From this point it extends caudad to the
corpus interpedunculare, as described by practically all writers
on the habenular connections (figs. 77, 79, 80, 82, 83, 100, 101, 102,
114, 115, 116, 122). As noted by Goldstein, it is surrounded by
medullated fibers caudally. These originate from the nucleus
posthabenularis and pass caudad to the commissura ansulata,
which they appear to enter, turning laterad. Goldstein simply
figures these fibers, giving no description of their connections.

(3) Tractus habenulo-diencephalicus. This tract arises in the
habenulae and, descending into the more ventral diencephalic
regions, 1s easily identified in the carp, as it is heavily myelinated.
Haller traces it into the nucleus posthabenularis, while Gold-
stein thinks that it ends farther ventrally, possibly in his nucleus
dorsalis. The tract, according to the conditions in the carp,
contains both ascending and descending fibers and extends ventro-
caudad from the habenular ganglia practically to the nucleus.

218 RALPH EDWARD SHELDON

posterior tuberis. (Tractus habenulo-diencephalicus, figs. 77,
79, 80, 82, 83, 100, 101.) Excepting its most rostral part, it is
closely associated with the medial forebrain bundle dorsally,
which probably accounts for the rarity with which it has been
reported. Apparently most of its fibers decussate in the habenu-
lar commissure, but such could not be demonstrated with cer-
tainty. ;

The tractus habenulae ad prosencephalon of Goldstein, the trac-
tus ad proencephalon of Edinger, was not identified. Of course,
it is quite possible that some of the fibers of the tractus olfacto-
habenularis are ascending, as Goldstein believes.

No optic connections with the habenulae could be found, as
Bela Haller describes. Large numbers of cells lying in the nu-
cleus posthabenularis, particularly near the median ventricle,
give rise, however, to fibers which pass directly laterad to enter,
apparently, the optic apparatus as Haller notes (figs. 76, 77, 79,
83). These require further study. Considering the intimate
relation between the nucleus posthabenularis and the ganglia
habenularum, an optic connection, such as Haller describes, not
improbably exists in some forms.

(4) Posthabenular-preoptic connections. In addition to the
connections already described with the fasciculus retroflexus and
the. optic apparatus, the nucleus posthabenularis is placed in
relation with the nucleus preopticus through three sets of diffuse
unmedullated fibers, a tractus preoptico-posthabenularis, pars
anterior from the nucleus magnocellularis to the nucleus post-
habenularis; a tractus preoptico-posthabenularis, pars posterior
from the nucleus parvocellularis posterior, and the tractus post-
habenulo-preopticus from the nucleus posthabenularis to the
nucleus parvocellularis posterior (fig. 140).

It is evident from its position and connections that the nucleus
posthabenularis is closely related with the habenulae. ‘The two
are evidently a morphological entity, the habenular ganglia devel-
oping as specialized portions of the dorsal lamina of the thalamus.

(5) Epiphyseal fibers. Along the caudal wall of the epiphysis
runs a small medullated bundle, which extends caudad to the
posterior commissure. It is possible that it gives off fibers to the

OLFACTORY CENTERS IN TELEOSTS , 219

habenular ganglia as it passes them, but such could not be dem-
onstrated with certainty.

(6) Fasciculus medialis hemisphaerii. This was observed first
by Bellonci in Anguilla, and by him considered to be an olfactory
tract of the second order from the olfactory bulbs to the nuclei
rotundi. The question of the presence of such fibers in the carp
has already been discussed. Edinger similarly traced a part
of the fibers of the medial olfactory tract to the diencephalon,
the tractus ad lobum inferiorem. C. L. Herrick identified the
tract, but states that it originates in the mesaxial lobe (nucleus
medianus and nucleus supracommissuralis of the corpus pre-
commissurale), decussates as the axial commissure (anteriorcom- .
missure), and then extends to the infundibulum. Herrick calls
the rostral end the ‘basal cerebral fasciculus,’ while the dien-
cephalic part he terms the fornix tract. Johnston (’98) describes
the bundle as the tractus strio-thalamicus ventralis, passing cau-
dad, without decussation, to end in the inferior lobes. In 1901
he points out that these fibers are largely descending, originating
chiefly from the nucleus postolfactorius ventralis and to a less
extent from the nucleus preopticus. It also contains ascending
fibers from the corpus mammillare, most of which decussate in
the anterior commissure to end in the epistriatum of the opposite
side. Kappers describes the bundle in the teleosts as originating
in his epistriatum (corpus precommissurale) and ending uncrossed
immediately lateral to the nucleus rotundus. Goldstein gives
the same origin for the fibers, but states that they decussate in the
nucleus posterior tuberis. He notes also that the tract consists
of more than one bundle, but fails to observe any difference in
the connections of the different components.

A careful study of this tract in the carp shows that, instead of
being a simple, single tract, it is really a complex of six fiber bun-
dles each with a distinct course and connections. It likewise
becomes apparent that Kappers, Goldstein, Johnston, ete.,
observed only a part of these components, which accounts for
the differences in the course and connections of the tract as
described by them.

220 : RALPH EDWARD SHELDON

The medial forebrain bundle first appears rostrally at the level
of the anterior commissure, on either side of the mid-line. Im-
mediately dorsal to the commissural fibers appears the tractus
hypothalamo-olfactorius medialis, made up largely of fine, medul-
lated fibers, between which are found many unmedullated in
character (fig. 37). All of the fibers of this bundle are ascending,
originating in the nucleus posterior tuberis (figs. 102, 104). Part
of them decussate almost immediately, as shown in fig. 102, while
the majority pass up on the same side to decussate in the anterior
commissure, closely associated with the fibers of the commissura
hippocampi, pars posterior and commissura dorsalis. Both sets
of fibers terminate in the corpus precommissurale, largely in the
pars supracommissuralis. This tract is that observed by Gold-
stein caudally, and called by him a descending tract.

Ventral to the fibers of the anterior commissure, at its level,
may be seen another component of the median forebrain bundle,
the tractus olfacto-thalamicus, pars ventralis (figs. 36, 37). The
fibers making up this bundle appear very similar to those of the
tractus hypothalamo-olfactorius medialis. They originate from
the corpus precommissurale, largely in the pars supracommis-
suralis, and run caudo-ventrad, in a diffuse bundle, to terminate
in the nucleus rotundus and the nucleus posterior thalami.

At the caudal margin of the anterior commissure a third com-
ponent, the tractus olfacto-thalamicus, pars dorsalis, appears.
This is a rather diffuse bundle, made up of fine medullated and
intermingled unmedullated fibers, which originate largely in the
supracommissural part of the precommissural body and terminate
in the nucleus subrotundus. This bundle, together with the pars
ventralis, was noted by Goldstein, rostrally (Taf. 11, fig. 7).
He points out that one passes dorsal and one ventral to the tractus
olfactorius medialis, pars lateralis, and that both originate in the
medial olfactory nucleus. Apparently, however, he failed to
follow all the fibers caudad, as in the more caudal region he ob-
served only the tractus hypothalamo-olfactorius medialis, which
tract he had not seen farther rostrally. The two parts of the
tractus olfacto-thalamicus form the tractus olfacto-hypothalami-

OLFACTORY CENTERS IN TELEOSTS PA |

cus medialis of Kappers, who failed to note the bundle from the
nucleus posterior tuberis.

A short distance caudal to the anterior commissure, the medial
forebrain bundle has increased largely insize (figs. 68, 69), dueto the
presence of a large number of short fibers, most of which are
unmedullated. These are present throughout most of the extent
of tract and are both ascending and descending, connecting and
placing in relation the different parts of the precommissural
body, nucleus preopticus and diencephalon. ‘These fibers form
the tractus olfacto-thalamicus, pars intermedia and tractus thal-
amo-olfactorius, pars intermedia (fig. 136).

Another factor in the increase in size of the median bundle
consists in the addition to it of a few medullated fibers arising
from the dorso-lateral part of the nucleus magnocellularis, form-
ing the tractus preoptico-tuberis. These pass caudad mingled
with the median forebrain bundle and end, apparently, partly
in the nucleus posthabenularis, and partly in the nucleus posterior
tuberis. These fibers may correspond to the ‘Liangsbiindel’
of Goldstein.

Slightly caudal to the level of the habenulae a seventh tract
becomes closely associated with the median bundle, appearing to
be a part of it. This is the tractus habenulo-diencephalicus of
Goldstein and has already been described in connection with the
habenular tracts (fig. 77).

When a careful study of the median bundle at different trans-
section levels is made, it is a simple matter to identify its com-
ponents. Their relations rostrally have already been noted; as
the tract is followed caudad it will be seen that there is a tendency
for the longer components to arrange themselves in more compact
bundles, with the more recently acquired fibers scattered about
them (figs. 73, 74, 76). For some distance there is little change in
the bundle (figs. 79, 80, 82). At the level shown in fig. 83, how-
ever, it will be noted that the fibers of the tractus olfacto-thalami-
cus, pars intermedia and tractus thalamo-olfactorius, pars inter-
media, are decreasing in number. The remaining bundles of the
complex are, at this point, separating from one another, all, how-
ever, turning ventrad (figs. 100, 101). The tractus habenulo-

222 RALPH EDWARD SHELDON

diencephalicus can be traced only a short distance caudal to the
level shown in fig. 101, where it ends mesal to the nucleus rotun-
dus at the level of the nucleus posterior tuberis. The tractus
hypothalamo-olfactorius medialis holds a position near the median
line at this point, while the tractus olfacto-thalamici, pars dor-
salis and pars ventralis are looping ventro-laterally, to pass below
the nucleus rotundus (fig. 101) to their termini in the nuclei sub-
rotundus and posterior thalami, respectively (figs. 115, 116, 122,
139). )

(7) Fasciculus lateralis hemisphaerii. This has been known
from the time of the first workers on the microscopic anatomy of
the teleostean brain. It has been called by various names since
the time of Stieda: pedunculus cerebri, by the earlier workers,
‘basale Vorderhirnbiindel’ by Edinger, ‘faisceau basal’ by Catois,
‘tractus strio-thalamicus’ by Johnston, Goldstein, Kappers, ete.
In practically all forms it consists almost entirely of unmedul-
lated fibers, although it is one of the largest and most constant
bundles of the brain. Earlier workers considered that it was made
up exclusively of descending fibers from the cells of the corpus
striatum, ending in the diencephalon. Edinger (’88) states
simply that the fibers originate in the ‘Stammganglion’ and end
in the ventral part of the ‘Zwischenhirn.’ He thinks it very likely
that part of the fibers decussate in the anterior commissure.
C. L. Herrick (’91 and ’92) divides the basal forebrain bundle
into two parts, both descending, a ventral peduncle arising from
the rostral part of each basal lobe and ending in the caudal part
of the hypoaria, and a dorsal peduncle originating in the caudal
part of each lobe, and ending largely in the nucleus ruber and sub-
thalamicus (nucleus rotundus, sensu lato). Johnston (’98) iden-
tifies three sets of fibers in the bundle, a tractus strio-thalamicus
medialis, lateralis and ventralis. Johnston here includes under
the name tractus strio-thalamicus ‘‘all fibers connecting the fore-
brain with the ventral portion of the diencephalon.” His tractus
strio-thalamicus ventralis is evidently a part of the medial fore-
brain bundle, as is also a portion of the tractus strio-thalamicus
medialis, consisting of ascending fibers from the thalamus to the
epistriatum, decussating in the anterior commissure. John-

OLFACTORY CENTERS IN TELEOSTS Da

ston’s tractus strio-thalamicus lateralis arises from cells of the nu-
cleus postolfactorius lateralis, while the larger part of the tractus
strio-thalamicus medialis arises from the striatum proper. In
1901 Johnston modifies these descriptions somewhat. He says
that the ventral bundle is composed of ascending fibers, as noted
above, which end in the epistriatum of the opposite side, together
with descending fibers from the nucleus preopticus. He further
~ adds that most of the ascending fibers arise from the dorsal and
lateral walls of the mammillary bodies, and run in the medial
bundle. Van Gehuchten (’94) also describes ascending fibers in
the tractus strio-thalamicus, stating that the bundle is made up
of two kinds of fibers, those which originate in the basal ganglia
and end in the inferior lobes, and vice versa. Catois observed
these same two fiber groups one of which is formed by ‘fibers
motrices descendantes,’ the other by ‘fibres sensitives ascen-
dantes.’ Catois states that the descending fibers lie external and
dorsal to the ascending. The descending fibers he traces largely
into the nucleus rotundus, and also farther ventrally, while a few
fibers extend into the basal portion of the mesencephalon. The
ascending fibers are traced by Catois from the region of the infun-
dibulum, chiefly from the more rostral part. Catois includes
here the medial forebrain bundle as a part of the tractus strio-
thalamicus. Kappers traces the tractus strio-thalamicus from
all parts of his striatum into the pedunculi thalami, ending un-
crossed partly in the nucleus rotundus, but chiefly in the nucleus
subrotundus. Kappers has, however, identified a tract aris-
ing chiefly from the lateral olfactory area, the tractus olfacto-
hypothalamicus lateralis, which has been included with the tractus
strio-thalamicus by other authors. This passes caudad, lying
immediately dorsal to the tractus strio-thalamicus, and ending
after decussation inthe ventral portion of theinferior lobes. Gold-
stein has worked out the connections of the tractus strio-thalami-
cus in considerable detail and finds that it originates from all
parts of the striatum and that part of its fibers decussate in the
anterior commissure, as Edinger suggested in 1888. Goldstein
states that the crossed fibers lie mesal to the uncrossed, and that
the more dorsal fibers in the praethalamic part of the tract contain

224 RALPH EDWARD SHELDON

chiefly fibers from the more rostral part of the striatum. He
traces strio-thalamicus fibers into the nucleus anterior thalami,
nucleus dorsalis thalami, nucleus ventralis thalami, nucleus pos-
terior thalami, nucleus anterior tuberis, nucleus lateralis tuberis,
nucleus diffusus lobi lateralis. The tractus strio-thalamicus. of
Goldstein includes the tractus olfacto-hypothalamicus lateralis
of Kappers. Johnston (’02) in Petromyzon states that the trac-
tus strio-thalamicus is formed from the neurites of the cells of the ©
striatum which end in the central gray of the thalamus. He
also identifies fibers from the lateral olfactory centers, forming a
part of his tractus olfacto-lobaris, which correspond to the tractus
olfacto-hypothalamicus lateralis of Kappers.

As described here, the lateral forebrain bundle consists of the
tractus strio-thalamicus, tractus thalamo-striaticus, tractus olfac-
to-hypothalamicus lateralis and tractus hypothalmo-olfactorius
lateralis (fig. 139). Rostrally distributed through the central part
of each lobe, almost at the tip of the basal lobes, may be seen
in Weigert preparations many bundles of unmedullated fibers.
Caudally, near the level of the anterior commissure, these bundles
pass gradually ventrad, lying dorsal to the fissura endorhinalis
(fig. 34). Thence these turn slightly mesad (fig. 35), constantly
increasing in size through the accession of new fibers, until at the
caudal level of the commissure the lateral forebrain bundle appears
as a powerful tract containing many large bundles of mixed medul-
lated and unmedullated fibers (fig. 36). As a usual thing the
medullated fibers either form a sheath for the unmedullated or
else form separate bundles, the two kinds of fibers being rarely
intermingled in the same bundle. A large part of the fibers, as
Goldstein describes, decussate in the caudo-ventral part of the
anterior commissure (figs. 36, 37). Caudal to the commissure,
the different bundles become more compactly arranged and extend
through the pedunculi thalami close against their lateral margins
(figs. 55, 61, 68).

The components of the tract, as it passes through the pedunculi
thalami, are shown in fig. 139. It will be noted that the fibers
are both ascending and descending and that the several bundles
have somewhat different connections. In general it may be stated

OLFACTORY CENTERS IN TELEOSTS 225

that the fibers connected with the more rostral part of the basal
lobes lie ventrally and medially; that those belonging to the mid-
portion of each lobe hold an intermediate position, while the more
caudal fibers appear dorsally in the praethalamic bundle. It
will be noted, also, that those which decussate in the anterior
commissure are among the more caudal fibers, while those of the
extreme caudal tip of the basal lobes occupy the extreme dorsal
position and form the lateral hypothalamic tracts (figs. 36, 37,
55, 61, ‘68, 69,.72; 73).

The lateral forebrain bundle receives from, or sends fibers to,
all parts of the basal lobes excepting the corpus precommissurale,
nucleus medianus, nucleus supracommissuralis, primordium hip-
pocampi, and possibly the nucleus preopticus. The fibers from
the caudal part of the lopes belong to the nucleus pyriformis
chiefly, although a few fibers are undoubtedly in connection with
the lateral part of the nucleus intermedius; they, therefore, form
a tract corresponding to the tractus olfacto-hypothalamicus later-
alis of Kappers. Kappers, however, described this as a descend-
ing tract, while it here contains both ascending and descending
fibers, which reach all parts of the nucleus pyriformis (figs. 69,
Gene

A large part of the fibers of the tractus strio-thalamicus, or
remaining portion of the lateral forebrain bundle, are ascending
and are distributed to all parts of the palaeostriatum, nucleus
olfactorius lateralis, including the dorso-lateral area of the basal
lobes, called epistriatum by Catois and by Johnston (’06). Many
of these ascending fibers enter into relation with large association
cells of these areas, their neurites enclosing the perikarya of the
cells (figs. 49, 50,51). Other ascending fibers reach the peripheral
area and branch dichotomously to form tangential fibers (fig. 39),
here coming into relation with the association cells and their
processes. Descending fibers of the tractus strio-thalamicus arise
from cells found in all parts of the same areas, palaeostriatum,
nucleus olfactorius lateralis, etc., already described. The nucleus
olfactorius lateralis, and most, if not all of the palaeostriatum
receive secondary olfactory fibers, while the palaeostriatum
receives also processes from association cells of the corpus pre-

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

226 RALPH EDWARD SHELDON

commissurale (figs. 39, 139, fib. precom. str.). So far as the fiber
connections are concerned, therefore, a definitely limited corpus
striatum in the basal lobes can not be found, thus agreeing with
the relations as shown by a cytological study. .

In the pedunucli thalami, as was noted earlier, the fibers of the
lateral forebrain bundle enclose the nucleus entopeduncularis,
giving off collaterals to it (figs. 68, 69, 72, 139).

Throughout the extent of the pedunculi thalami little change
takes place in the bundle; as it passes over the chiasma its com-
ponents extend slightly ventrad, however, and now cover all of
the lateral surface of the peduncles (figs. 73, 76). At the rostral
margin of the lateral lobes the more ventral bundles become
closely massed against the commissura transversa (figs. 77, 79),
caudal to which they bifurcate, a few fibers entering the nucleus
anterior tuberis (fig. 80), while many turn into the nucleus pre-
rotundus (figs. 80, 82, 83, 100). The larger proportion of these
two sets of fibers are ascending as Catois states (figs. 104, 105),
although a part are certainly descending. Farther caudally the
intermediate fibers of the bundle likewise turn ventro-laterad and
enter the caudal part of the nucleus prerotundus, passing through
it to distribute along the rostro-mesal aspect of the nucleus rotun-
dus and to the ventral part of the nucleus diffusus lobi lateralis
(fig. 83). Part of the nucleus prerotundus fibers are ascending,
but a definite statement can not be made regarding those of the
nucleus rotundus. In the latter case there is no doubt but that
most of them are descending as C. L. Herrick, Catois and others
describe, although the intermediate bundles certainly contain
some ascending fibers. The fibers break up in the nucleus pre-
rotundus and rotundus in a very characteristic manner, noted by
the earlier workers on the teleostean diencephalon (see C. L.
Herrick (92), nidulus ruber). This was mentioned earlier and is
shown in fig. 102. The dorsal bundles distribute caudally a few
fibers to the nucleus subrotundus, nucleus posterior thalami,
nucleus cerebellaris hypothalami and a large number to the nu-
cleus diffusus lobi lateralis, ventrally and caudally. The tractus
olfacto-hypothalamicus lateralis has practically the same dis-
tribution excepting that it sends no fibers to the nucleus subro-

OLFACTORY CENTERS IN TELEOSTS PAT

tundus. These fibers are both ascending and descending, although
most of the ascending fibers apparently arise from the nucleus
diffusus. It is difficult to make positive statements regard-
ing the cells of origin of the dorsal ascending fibers of the basal
forebrain bundle owing to rather poor Golgi impregnations of
adult brains in this region (fig. 139); there is no question as to
their presence, however, as many such fibers can be seen leaving
these bundles rostrally. In Golgi preparations of the brains of
young carp fibers may be traced, nevertheless, from a nucleus
apparently corresponding to the nucleus cerebellaris hypothalami
into the tractus strio-thalamicus.

No strio-thalamicus fibers could be traced into the nucleus dor-
salis, nucleus anterior thalami or nucleus lateralis tuberis, as Gold-
stein found in the forms studied by him. It is probable that the
fibers which Goldstein traces into the nucleus lateralis tuberis really
arise from the nucleus magnocellularis, as will be shown later. It
willthus be seen that the lateral forebrain bundle contains through-
out, both ascending and descending fibers connecting all of the
lateral and intermediate portions of the basal lobes with practi-
cally all of the lateral and intermediate regions of the thalamus
and hypothalamus, and also a part of the medial centers. It is
not, therefore, the simple tract described by the earlier writers,
but a complicated connection of paramount importance to the
nervous mechanism.

(S) The nucleus preopticus and its connections. The fiber
connections of this nucleus have been little understood by the
different writers on the brains of the lower vertebrates. John-
ston (98), as noted earlier, traced fibers from it to the habenular
ganglia; he also believed that secondary olfactory fibers termi-
nate therein, although he could not demonstrate their presence.
Johnston also observed fibers passing caudad, but could not
trace them to their destination. In 1901 he observed fibers from
it entering the tractus strio-thalamicus ventralis (tractus olfacto-
thalamicus, probably pars intermedia). C. L. Herrick (’92)
describes unmedullated fibers from the pars magnocellularis
(nidulus praeopticus), which pass laterad into the optic tract
region. Kappers notes similar fibers, which he traces ventro-

228 RALPH EDWARD SHELDON

laterad, and thence caudad into the tuber cinereum, and terms
the tractus praethalamo-cinereus. Goldstein traces fibers from
the pars magnocellularis caudo-dorso-laterad into ‘Das _ post-
habenulire Gebiet,’ the ‘Liangsbiindel des grosszelligen Kerns
des zentralen Hoéhlengraues.’ From the pars parvocellularis a
few fibers decussate ventrally to enter the nucleus of the opposite
side, the ‘Commissur des kleinzelligen Kerns,’ evidently the fune-
tional equivalent of the commissura anterior, pars preoptica,
previously described (fig. 188). He also finds other fibers
which turn caudo-lateral, dorsal to the chiasma and postoptic
commissures and end among the cells of the caudal portion of the
nucleus in the rostral part of the hypothalamic wall. These
fibers lie lateral to the fibers from the pars magnocellularis, and
mesal to the lateral forebrain bundle. Goldstein believes that
they constitute “‘ein Lingscommissur der einzelnen Abschnitte
des kleinzelligen Kernes des zentralen Hohlengraues.”’ He like-
wise believes that these fibers are identical with the tractus prae-
thalamo-cinereus of Kappers and the caudal fibers of Johnston in
Acipenser. Bela Haller finds a part of these fibers, but believes
that they are connected with the optic apparatus.

It was pointed out earlier that in the carp there are four differ-
ent habenular connections from the nucleus preopticus, corre-:
sponding partly to the connections described by Johnston in Aci-
penser and Petromyzon. Olfactory fibers of the second order
may be traced into both the pars parvocellularis anterior and pars
magnocellularis, from the tractus olfactorius medialis, pars later-
alis, just before its decussation. This agrees with Johnston’s
conjecture (figs. 137, 139, 141). Unmedullated fibers arising from
cells in the nucleus medianus and pars commissuralis of the pre-
commissural body respectively also extend caudad, placing these
two areas in relation with the different parts of the nucleus preop-
ticus (fig. 140, tr. med. preopt. pars ant. and tr. med. preopt., pars
post.). The fibers of the tractus mediano-preopticus, pars ante-
rior pass caudad, ventral to the crossing bundles of the anterior
commissure (figs. 37,54). From it and from the tractus mediano-
preopticus, pars posterior fine fibers pass ventrad to end in either

OLFACTORY CENTERS IN TELEOSTS 229

side or ventral to the recessus preopticus (figs. 54, 61). These
are probably homologous with the ‘Lingsfasern des kleinzelligen
Kerns’ of Goldstein and are, perhaps, concerned with the move-
ment of cerebro-spinal fluid.

Immediately ventral to the recessus preopticus Goldstein fig-
ures and describes a small tract (Taf. 11, fig. 7), the connections
of which he was unable to identify. Fig. 62 shows a parasagittal
section in which the relations of this tract are clearly shown (fr.
preopt. sup.). It is entirely unmedullated and arises from small
stellate cells (fig. 63) immediately ventral to the recessus preop-
ticus, terminating partly in the nucleus parvocellularis posterior
and partly in the nucleus magnocellularis.

The most important longitudinal caudal connection of the
nucleus preopticus is the large unmedullated tractus praethalamo-
cinereus. This originates largely from the nucleus magnocellu-
laris as described by C. L. Herrick and Kappers, the fibers extend-
ing latero-ventrad (figs. 72, 73, 76). A part of the fibers, however,
originate from cells of the nucleus intermedius and nucleus par-
vocellularis anterior (figs. 69, 72), while a few arise in the nucleus
parvocellularis posterior (fig. 76). At first, the tract lies near
the median line (figs. 69, 72, 73) but it gradually turns ventro-
laterad (fig. 74) to lie ventral to the lateral forebrain bundle
(figs. 76, 77, 79). As it is unmedullated and, therefore, of the
same color as the tractus strio-thalamicus fibers, it is easily mis-
taken for a part of that tract and was undoubtedly so considered
by the earlier authors. Immediately caudal to the postoptic
commissures it bends ventro-mesad, entering the nucleus lateralis
tuberis (fig. 80), where undoubtedly some of its fibers terminate,
and where it probably also receives accessions. Goldstein de-
scribes and figures this tract but apparently considers it a part of
the tractus strio-thalamicus, as he traces the latter tract, but not
the former, into the nucleus lateralis tuberis. From this nucleus
the tract extends ventrad into the nucleus ventralis tuberis (fig.
80) where it doubtless undergoes the same change as in the nucleus
lateralis tuberis, thence passing on into the hypophysis, of which
it forms the chief innervation, to terminate particularly in the

230 RALPH EDWARD SHELDON

pars glandularis (figs. 80, 82). Kappers traces this tract, as was
previously noted, only as far as the region of the nucleus lateralis
tuberis, which he fails to identify.

The ‘‘ Lingsbiindel des grosszelligen Kerns des zentralen Hohl-
engraues”’ of Goldstein could not be identified with certainty. In
sagittal sections a few medullated fibers arising from the dorso-lat-
eral cells of the nucleus magnocellularis could be observed to pass
caudad, closely associated ventrally with the medial forebrain bun-
dle as was noted earlier, apparently ending in the nucleus posterior
tuberis and the nucleus posthabenularis (figs. 136, 140, tr. preopt.
tub.). Medullated fibers extending latero-caudad as Goldstein
describes were not found. It is possible, however, that the un-
medullated fibers of the tractus preoptico-posthabenularis, pars
anterior may correspond to Goldstein’s tract.

In addition to its longitudinal and habenular connections, the
nucleus preopticus possesses a number of important short trans-
verse, or dorso-ventral connections, all of which are composed of
unmedullated fibers. Rostrally there are short connections,
running in both directions between the nucleus parvocellularis
anterior, and both the nucleus intermedius and nucleus commis-
suralis lateralis, the tractus preoptico-intermedius, pars anterior;
intermedio-preopticus, pars anterior; preopticus lateralis; later-
alis preopticus (figs. 68, 69, 140). Further caudally are found con-
nections between the nucleus magnocellularis and the nuclei inter-
medius and entopeduncularis. The nucleus intermedius connec-
tions include a double tract medially (figs. 72, 137, 140, tr. preopt.
intermed., pars med. and tr. intermed. preopt., pars med.) and an
ascending tract passing dorsad, lateral to the lateral forebrain
bundle, the tractus preoptico-interniedius, pars lateralis (figs.
69, 72, 137, 140). The short entopeduncular connections are
shown in figs. 69, 72, 140, tr. preopt. entoped. and tr. entoped. pre-
opt. Caudally the nucleus parvocellularis posterior and the nu-
cleus magnocellularis are related to the nucleus posthabenularis
through ascending fibers to the nucleus posthabenularis from both
these nuclei, and descending fibers from it to the nucleus parvo-
cellularis posterior (fig. 140, tr. preopt. posthab., pars ant. and pars
post. and tr. posthab. preopl., pars ant.).

OLFACTORY CENTERS IN TELEOSTS nA |

There are also ascending and descending unmedullated fibers
running between the nucleus posthabenularis and the nucleus
intermedius (tr. intermed. posthab. and tr. posthab. intermed.).
Connections between the nucleus entopeduncularis and the
nucleus intermedius may likewise be found (tr. intermed. entoped.
and entoped. intermed.).

All of these latter short connections contain few fibers and in
many cases form little more than a reticular network between
different parts of closely related regions; they can not be demon-
strated by means of Weigert preparations, but come out only
in the silver methods, particularly the Ram6én y Cajal. They are
chiefly important in emphasizing the intimate relation between
all parts of the brain, and particularly, closely related morpholog-
ical areas, through the formatio reticularis.

This covers all of the direct olfactory connections which could
_ be identified, but does not include the further connections of the
different tertiary thalamic centers with other points in the dien-

cephalon, mesencephalon, cerebellum, medulla and spinal cord. ©

Some of these are shown, however, in the Weigert transections.
It is expected that an article will appear later in which the mor-
phological relations and functions of the different diencephalic
centers will be taken up in detail, in which these further connec-
tions will be brought out. Until that time, it is not deemed wise
to discuss in detail the morphological bearing of the thalamic
olfactory connections, although some points will be taken up
later in the interpretation of results.

5= THE CONDUCTION PATHWAYS

At this point it may be well to point out the different pathways
which an impulse of a given character may follow. Of the vari-
ous possible, anatomically demonstrated paths open to a given
impulse, the one chosen under given conditions can be unques-
tionably accepted only when physiological evidence can be offered
in support. Nevertheless, impulses must follow conduction paths,
and we may, therefore, plot out anatomically extensive impulse
pathways with an exceptional degree of accuracy, as is shown in
the cases where a physiological check has been used.

232 RALPH EDWARD SHELDON

Descending pathways

Nervus terminalis. In this case an impulse may travel from
the periphery to ganglion cells situated among the olfactory nerve
fibers and thence to a decussation among the rostral cells of the
bed of the anterior commissure. Its further course is not known.

The olfactory neurones of the first order end throughout the
lateral, rostral and rostro-medial face of the bulb. Fibers from
all three areas form the tractus olfactorii lateralis, and medialis,
pars lateralis, for the nucleus olfactorius lateralis and nucleus
pyriformis of the basal lobes (fig. 137). From the lobus pyri-
formis originate the tractus teniae for the habenula of the opposite
side, and the tractus olfacto-hypothalamicus lateralis for the
nucleus cerebellaris hypothalami and the nucleus diffusus lobi
lateralis of the same side (fig. 137).

The corpus precommissurale stands in relation, chiefly, with
the more medial portion of the bulb, through the tractus olfacto-
rius, pars medialis and pars lateralis, which terminate largely in
the nucleus medianus of the same and opposite side, in the com-
missure bed, and in the pars supracommissuralis of the same side.
The pars lateralis, after decussation, sends also a few fibers to the
nucleus intermedius (fig. 137).

From the corpus precommissurale there are, likewise, two great
pathways open. In one case cells with short neurites, forming
the fibrae precommissurales striatici, transfer the impulse to
the palaeostriatum, whence it is carried by the tractus strio-
thalamicus to the nuclei anterior tuberis, prerotundus, rotundus,
subrotundus, posterior thalami, cerebellaris hypothalami and dif-
fusus lobi lateralis of the same side; and the nuclei rotundus,
subrotundus, and diffusus lobi lateralis of the opposite side (fig.
139). The other connection is through the median forebrain
bundle, which places the nucleus supracommissuralis chiefly,
but other parts of the corpus precommissurale as well, in relation
with the nuclei rotundus, subrotundus and posterior thalami.
A third connection, less prominent but of considerable morpho-
logical importance, is with the nucleus preopticus. This receives
twosmall bundlesfrom the nucleus medianus, the tractus mediano-

OLFACTORY CENTERS IN TELEOSTS 233

preoptici and also secondary olfactory fibers from the tractus
olfactorius medialis, pars lateralis, before its decussation (fig. 136).
It thus receives both secondary and tertiary olfactory fibers.

Very similar to the precommissural, and of great morphological
significance, are the descending connections of the primordium
hippocampi. The latter receives secondary olfactory fibers from
the tractus olfactorius medialis, pars medialis, and gives rise to
fibers for the tractus olfacto-thalamicus, pars dorsalis, for the
diencephalon.

The important descending pathway from the nucleus preopti-
cus is the tractus praethalamo-cinereus from the nucleus magno-
cellularis to the hypophysis, together with the nuclei lateralis and
ventralis tuberis. Besides this there is the tractus preoptico-
tuberis from the same nucleus to the region of the nucleus pos-
terior tuberis and the nucleus posthabenularis. Both of these
are probably neurones of the fourth order.

Important neurones, chiefly of the third order, connect the
nucleus preopticus with the habenulae, originating from all parts
of the nucleus (figs. 141, 142).

Neurones of the fourth order originate in the habenular ganglia
and pass caudo-ventrad, the fasciculus retroflexus for the corpus
interpedunculare, and the tractus habenulo-diencephalicus for the
formatio reticularis in the region of the nucleus posterior tuberis _
(figs. 141, 142).

It will be noted, then, that the olfactory neurones of the first
order, or olfactory nerve, carries impulses to all parts of the lateral,
rostral and mesal aspects of the bulb. From the lateral part of the
bulb, chiefly, but also from the mesal, impulses are carried by
neurones of the second order to the lateral area of the basal lobes.
Thence neurones of the third order carry the impulse either to the
habenula, or else to the nucleus posterior thalami, or the diffuse
cellular area of the caudal part of the inferior lobes. From the
mesal portion of the bulb impulses are carried to all parts of the
mesal olfactory area, or corpus precommissurale and primordium
hippocampi, by neurones of the second order, which also reach the
nucleus preopticus, further caudally. From the mesal area im-
pulses may travel by neurones of the third order to the palaeostria-

234 RALPH EDWARD SHELDON

-tum, and thence by quaternary fibers of the tractus strio-thalami-
cus to practically all the nuclei of the thalamus and hypothalamus.

Or impulses will more usually take a tract of the third order,
the median forebrain bundle, for the region of the nuclei rotundus,
subrotundus, posterior thalami. Other impulses may continue
into the nucleus preopticus with fibers of the third order, the
tractus mediano-preoptici, or may reach the more rostral parts of
the nucleus by means of fibers of the second order. Neurones of
the third order, largely, carry impulses from all parts of the
nucleus preopticus to the habenular ganglia. It is, therefore,
probable that the nucleus preopticus stands in much the same rela-
tion to the habenulae as does the nucleus pyriformis. From the
nucleus preopticus fibers of the fourth order reach the nucleus pos-
terior tuberis and hypophysis, while from the habenulae such fibers
pass to the corpus interpedunculare and the medial thalamus.

Motor correlation probably takes place through two connections;
one of these is by.means of the corpus interpedunculare, which sends
fibers, according to Ramon y Cajal and Edinger, to the nucleus
dorsalis tegmenti in higher forms, from which fibers undoubtedly
pass into the great bulbar and spinal descending tracts for the
transmission of somatic motor impulses. Other connections may
also develop when this nucleus and its relations are more thor-
oughly worked out. Another connection is by way of the tractus
thalamo-bulbares et spinales from the thalamus to the medulla
and cord (Johnston, ’06). In teleosts the more usual motor
pathway for the simple direct olfactory impulses is probably by
way of the corpus interpedunculare. This pathway is the more
definitely laid down and involves the more direct connections.
An impulse may pass to any part of the bulb, practically, from
the olfactory mucous membrane, thence to the lateral olfactory
area, thence by the definite, medullated tractus teniae to the
habenular ganglia, thence by the powerful fasciculus retroflexus
to the corpus interpedunculare and thence to the tegmental region
of the mesencephalon, whence it may come into relation with the
motor areas of the midbrain, medulla and spinal cord.

The olfactory connection with the thalamus is not so simple
and direct. An impulse must pass from the corpus precommis-

OLFACTORY CENTERS IN TELEOSTS 235

surale by way of the comparatively few fibrae precommissurales -
striatici to the palaeostriatum and thence through the tractus
strio-thalamicus, or else from the corpus precommissurale by
way of the descending fibers of the medial forebrain bundle. In
neither of these cases do we find so definite and compact a path-
way as that first outlined, wherefore we may conclude that the
first is the more usual path for the direct olfacto-motor reflexes.
Another possible motor connection is through the preoptico-
habenularis fibers to the habenular region, and thence through the
fasciculus retroflexus, as above indicated. This is probably a
very unusual pathway as the connections just mentioned are
very diffuse and are undoubtedly simply the vestiges of a once
powerful pathway, now of less functional importance (ef. Acipen-
ser). The functions of these latter pathways will be considered
lovers

It is quite probable that there exist also somatic fibers connect-
ing the epithalamic with the visual centers, although such were not
demonstrated (Herrick, ’10b, pp. 468-469). The relation between
the ventral hypothalamic region and the visceral (gustatory)
pathways in teleostean fishes will be brought out later (see also
the discussion in the above mentioned paper of Herrick).

Ascending pathways

There is no evidence for the existence of centrifugal fibers in
the olfactory nerve bundles. Ascending fibers from the dien-
cephalon include fibers from the lateral and ventral portions of the
inferior lobes to the nucleus pyriformis (tractus hypothalamo-
olfactorius lateralis); fibers from the ventro-lateral part of the
inferior lobes, the nucleus prerotundus and nucleus anterior
tuberis especially, and possibly the nucleus rotundus to the palaeo-
striatum and nucleus olfactorius lateralis by way of the tractus
thalamo-striaticus; and the fibers from the nucleus posterior
tuberis to the corpus precommissurale. From the corpus pre-
commissurale, nucleus medianus, fibers pass to the nucleus olfac-
torius anterior in the tractus olfactorius ascendens (figs. 136, 137).

236 RALPH EDWARD SHELDON

C. Judson Herrick traces the gustatory fibers of the fourth
order into the caudal portion of the inferior lobes; it is likewise
probable that tactile and other general sensory fibers reach the
dorsal thalamic region through the medial lemniscus fibers. It
is, therefore, probable, as Johnston and Herrick have already
pointed out, that the ascending fibers from the pars dorsalis of
the thalamus and from the hypothalamus are in the nature of
general somatic and visceral sensory forebrain connections, respec-
tively. The relations of the nucleus posterior tuberis need to be
better understood, however, before the function of this ascending
tract can be stated positively. It may be a connection for the
transmission of visceral and somatic sensory impulses to the olfac-
tory bulbs through the tractus olfactorius ascendens.

Association connections

Cajal and Golgi preparations show that practically all parts of
the brain are permeated by a closely meshed reticulum of fine
fibers, the ‘Punktsubstanz’ or formatio reticularis. In certain
preparations it is almost impossible to identify individual cells,
so close is the fibrous mesh. All parts of closely related regions,
such as the different nuclei of the corpus precommissurale, are
also placed in relation by means of large numbers of short con-
nections. The same holds true with respect to regions derived
from, the same morphological structure. This explains the con-
nections between the nucleus intermedius and the nucleus post-
habenularis, both of which are probably parts of the same dorsal
olfactory column. It was noted earlier how the nucleus medianus
separatesinto dorsal and ventral columns; how the dorsal continues
caudo-laterad as the nucleus supracommissuralis, nucleus inter-
medius, nucleus posthabenularis and habenulae; and how the
ventral continues as the pars commissuralis, nucleus medianus
and the nucleus preopticus. It is, therefore, to be expected, after
what has been said regarding the close connection of associated
regions that these two dorsal and ventral columns would possess
short association connections. Such is the case and, while these
fibers have been given the name of tracts, they are really all a

OLFACTORY CENTERS IN TELEOSTS emi.

part of the same set of association fibers. The connections include
all the nucleus preopticus-nucleus intermedius, posthabenularis,
ganglia habenularum, nucleus commissuralis, nucleus entopedun-
cularis connections (fig. 140). Such connections also exist between
the corpus precommissurale and the primordium hippocampi.

Commissural connections

These include the commissura interbulbaris between the two
olfactory bulbs (?); the commissura hippocampi, pars anterior
connecting the two primordia hippocampi or nuclei dorsales;
the commissura hippocampi, pars posterior, Joining the lobi pyri-
formes; the commissura corporium precommissuralium, between
the partes supracommissurales; and the commissurae nucleorum
preopticorum, all present in the anterior commissure. The pyri-
form lobes may also be connected through the superior or haben-
ular commissure forming a commissura aberrans.

The formatio reticularis

In any discussion of the different pathways it must never be
forgotten that the fine, reticular network of the formatio reticu-
laris type is of great functional importance. In the past the
tendency has been to consider only the tracts laid down in definite
bundles. It is probable that in the phylogeny of a fiber tract the
heavily myelinated bundle is the latest stage. In early stages,
different areas are connected by a diffuse network of unmedul-
lated fibers, through which impulses may take many courses. As
phylogenetic development proceeds, impulses tend to take more
and more definite paths through the maze of the reticulum;
thus the diffuse unmedullated fiber connection is formed. Next
this diffuse connection becomes more compact and usually myelin-
ated. It should not be implied that the myelinated tract is more
efficient for all connections, as it probably comes into existence
chiefly when there is necessity for a stereotyped reflex; to prevent,
possibly, ‘loss of current’ through diffusion, to use an electrical
analogy. In spite of this, there is no question but that the more
diffuse connections are of the utmost importance in putting into

238 RALPH EDWARD SHELDON

relation different parts of the nervous system, and in causing it to
react as one correlated, organic whole.

6. THE MORPHOLOGICAL AREAS OF THE FOREBRAIN

On the basis of the facts brought forward in the previous
discussion, the forebrain of teleosts may be divided into morpho-
logically distinct centers, according to the following table:

Telencephalon.
Bulbus olfactorius
Nucleus olfactorius anterior
Pars lateralis hemisphaerii (pars dorso-lateralis, Herrick)
Nucleus olfactorius lateralis
Tuberculum anterius
Tuberculum laterale
Lobus pyriformis
Nucleus teniae
Pars medialis hemisphaerii (pars ventro-medialis, Herrick)
Corpus precommissurale
Nucleus medianus
Pars commissuralis
Pars supracommissuralis
(Nucleus intermedius, in part, at least)
Primordium hippocampi, or nipelene olfactorius dorsalis (pars dorso-medi-
alis, Herrick)
Palaeostriatum (pars ventro-lateralis, Herrick)
Nucleus commissuralis lateralis
Nucleus entopeduncularis
Nucleus preopticus
Pars parvocellularis
Pars magnocellularis

Johnston (711) has made an important contribution to the mor-
phology of the forebrain of fishes in his analysis of the ‘somatic
area’ of selachians. This paper came into my hands after the
present contribution was ready for the press, and I have not had
an opportunity to make a thorough inquiry into the teleostean
homologies of this selachian area. Pending further study of
this question, I may say that it now seems probable that some
or all of the following regions of the carp brain correspond with
the selachian somatic area of Johnston: palaeostriatum, nucleus
teniae, nucleus intermedius of the precommissural body, nucleus

OLFACTORY CENTERS IN TELEOSTS 239

commissuralis lateralis and nucleus entopeduncularis. The fiber
connections of several of these nuclei are still very imperfectly
known and their morphological interpretation should therefore
be considered purely provisional until this knowledge is extended.!

III. DISCUSSION

The structural plan of the teleostean diencephalon and telen-
cephalon is very different from that of any other vertebrate type
excepting the higher ganoids (notably Amia); but as we follow
down the phylogenetic series through the lower ganoids to the
generalized fishes, we approach progressively nearer to the com-
mon vertebrate type. When the development of the teleostean
brain is more fully known it will probably prove easy to follow
here also the sequence of form changes from a generalized type.

It is generally accepted that the primitive form of the verte-
brate central nervous system was a simple epithelial tube and that
from its rostral end two pairs of lateral vesicles were evaginated.
One of these comes from the diencephalon to form the optic ves-
icles: the other comes from the telencephalon to form the cere-
bral hemispheres. The telencephalon must be defined, as taught
by His and Johnston, as the rostral segment of the neural tube,
including the hemispheres evaginated from it, and not as the hemi-
speres alone, as in the BNA tables.

There is the greatest diversity in different vertebrate types
in the relative amounts of the telencephalic segment which are
evaginated into the hemispheres, but in no case is the whole of
this segment represented in the hemispheres. Accordingly,
we subdivide the telencephalon into telencephalon medium and

! Johnston’s still more recent paper on the telencephalon of ganoids and tele-
osts (Jour. Comp. Neur., vol. 21, no. 6, December, 1911), appeared while this con-
tribution was in press. His results differ in some matters of fact and in several
matters of interpretation from my own. So far as these concern the somatic or
non-olfactory connections, they do not fall within the scope of this article. Some
of his morphological conclusions J] think rest upon an incomplete knowledge of
the anatomical facts; but since the homologies of the telencephalic and dien-
cephalic centers in the carp and other lower vertebrates will be fully discussed in a
forthcoming paper, Johnston’s conclusions will not be further considered at this
time.

240 RALPH EDWARD SHELDON

cerebral hemispheres, and recognize that in general the hemis-
pheres increase at the expense of the telencephalon medium as we
ascend the phylogenetic series. For further discussion of this
question, see Johnston (’09) and Herrick (10 b). The latter
author, on the basis of the examination of a series of embryonic
and adult brains of different vertebrates, has studied the method
of evagination of the cerebral hemispheres in relation with the
functional connections of the different parts of the neural tube
involved in this process and has devised a schematic picture of
the probable relations of the functional subdivisions of the neural
tube in a primordial vertebrate whose optic and cerebral vesicles
were still in the unevaginated condition (’10 b, fig. 72). See
also Johnston (’11), fig. 82.

In such an ancestral type the sulcus limitans, terminating in the
preoptic recess, separates the ventral lamina of the neural tube
(Bodenplatte or hypencephalic region of His) from the dorsal
lamina (Fliigelplatte or epencephalic region). The ventral lamina
therefore, ends in the chiasma ridge and all of the diencephalon
and telencephalon dorsal and rostral to the sulcus limitans be-
longs in the primary dorsal lamina, i.e., to the sensory or recep-
tive region. The chief sensory function of this region was, in the
telencephalon, primitively, olfaction. The tissue in the ventral
part of this region, which lies in contact with the ventral (effer-
ent) lamina behind, secondarily assumed the function of motor
correlation tissue, this part being usually above fishes separated
from the dorsal part by a sulcus, the sulcus. medius (suleus Mon-
roi of authors), which in higher forms extends caudad from the
interventricular foramen. By a process of further differentia-
tion the part above the sulcus medius becomes divided into epi-
thalamus and pars dorsalis thalami, and the part below the sulcus
medius into pars ventralis thalami and hypothalamus, the latter
extending forward beyond the chiasma ridge into direct continu-
ity with the preoptic nucleus.

The relations just described are preserved in the diencephalon
of adult brains of many of the Ichthyopsida and are visible
in embryos of many higher vertebrates. A transection taken
through the rostral end of the diencephalon, accordingly, in these

OLFACTORY CENTERS IN TELEOSTS 241

lower vertebrates shows, in addition to the membranous median
plates in the roof and floor, four longitudinal columns or laminae
on each side, viz., the epithalamus, pars dorsalis thalami, pars
ventralis thalami and hypothalamus (fig. 128). The last two
contain motor correlation tissue, with somatic and visceral ele-
ments, respectively, predominating.

In the primordial vertebrate these four columns probably
extended forward into the telencephalon without fundamental
change. In all existing vertebrate types variable amounts of this
telencephalic tissue are evaginated to form the cerebral hemi-
spheres. The olfactory bulb clearly formed the initial center of
evagination. In cyclostomes the hemisphere is composed of
olfactory bulb, with part of the secondary olfactory nucleus (these
coming from the telencephalic extension of the pars dorsalis
thalami), and a very small corpus striatum, this being an extension
of the pars ventralis thalami. In the lower elasmobranchs the
olfactory bulb is fully evaginated and the telencephalon medium
greatly elongated, with great thickening and a very slight evagina-
tion of its rostral end. In the higher sharks the telencephalon
medium is shortened in correlation with an increase in the thicken-
ing of the tissue about the lamina terminalis and the further eva-
gination in this region of the secondary olfactory centers.

The Dipnoi show a very different line of specialization. The
olfactory bulbs are in all cases fully evaginated. The telen-
cephalon is not greatly elongated (except in adult Ceratodus) and
its lateral walls are uniformly thickened and more or less com-
pletely evaginated to form the cerebral hemispheres, whose form
and structure, especially in the case of Lepidosiren, are very close
to those of Amphibia.

The morphology of the amphibian cerebral hemisphere has
been fully discussed in the paper cited (Herrick, ’10 b), the author
showing that it is naturally divided into four parts (exclusive of
the olfactory bulb), viz., (1) pars dorso-medialis (primordium
hippocampi), (2) pars dorso-lateralis (primordium of the pyri-
form lobe), (3) pars ventro-lateralis (primordium of the corpus
striatum) and (4) pars ventro-medialis (precommissural body and
septum). He shows further that these four parts are the telen-

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

242 RALPH EDWARD SHELDON

cephalic extensions respectively of (1) the epithalamus, (2) the pars
dorsalis thalami, (3) the pars ventralis thalami and (4) the hypo-
thalamus and tissues surrounding the preoptic recess. The cere-
bral hemispheres of amniote vertebrates are modifications of this
fundamental pattern.

The teleostean forebrain conforms neither to the selachian nor
to the dipnoan and amphibian type. Further analysis of the series
of ganoidean types and of the ontogeny of the teleosts will doubt-
less shed light upon the steps by which the teleostean pecularities
have been acquired. The study of the form and fiber connections
of the adult brain, together with the available data bearing on
its phylogeny and ontogeny, suggests the following interpretation.

It is evident that the teleostean olfactory bulbs are completely
evaginated and that they have earried out with them a small
amount of secondary olfactory tissue, the nucleus olfactorius ante-
rior. The remainder of the telencephalon remains unevaginated
as the telencephalon medium, which is, moreover, considerably
elongated. The failure of any considerable part of the telen-
cephalon, except the olfactory bulbs, to evaginate laterally is the
basis of its difference from that of the Dipnoi and Amphibia.
The fact that the increase in its tissue takes place uniformly
throughout its length or somewhat more at its caudal end instead
of at its rostral end is the basis of its difference from the elasmo-
branchs.

The increase in the mass of the telencephalon occurs under
the influence of two chief factors: (1) olfactory impulses coming
in by way of the olfactory bulbs, (2) non-olfactory sensory im-
pulses coming in for correlation purposes from the thalamus and
hypothalamus. The correlation sought in the lower forms was
exclusively with the olfactory apparatus; olfacto-somatic in the
case of the thalamic tracts, and olfacto-visceral in the case of the
hypothalamic tracts. In higher vertebrates the non-olfactory
systems effect correlations inter-se thus giving rise to the neopal-
lium; but little, if any of this sort of correlation occurs in fishes.

In the teleostean brain, as has been pointed out earlier, the
arrangement of the telo-diencephalic centers in the form of
longitudinal columns, is plainly evident. At the rostral end of

OLFACTORY CENTERS IN TELEOSTS 243

the basal lobe the ventro-medial column appears in its primitive
relations, forming here the nucleus medianus of the precommis-
sural body. Passing caudad the nucleus medianus bifurcates
at- the anterior commissure into the dorsal pars supracommis-
suralis and the ventral pars commissuralis or commissure bed. -
The latter is directly continuous with the nucleus preopticus,
which in turn grades almost insensibly into the hypothalamic
nuclei. The pars supracommissuralis becomes continuous cau-
dally withthe nucleus intermedius. The cells of the latter nucleus
likewise grade over into those of the nucleus posthabenularis and
habenula, but this connection is probably secondary, as will be
brought out later.

The other diencephalic columns are interrupted at the level
of the velum transversum save for the fiber tracts of .the basal
forebrain bundles. Dorsal to the ventro-medial column lies the
primordium hippocampi rostrally, immediately above the corpus
precommissurale. This, the dorso-medial column of Herrick, is
probably the telencephalic extension of the epithalamic habenula
and nucleus posthabenularis of the diencephalon.

The nucleus entopeduncularis probably belongs to the same
column as the pars ventralis thalami, the pars ventro-lateralis
of Herrick, which expands rostrally to form the palaeostriatum.
In the evaginated hemispheres of the Dipnoi and Amphibia the
striatal complex is carried outward into the ventro-lateral wall
of the hemisphere vesicle. In teleosts the wall as a whole does
not evaginate in this way; but the striatum complex, with the
associated lateral forebrain tract, moves outward within the
solid basal lobe away from the ventricular surface and toward the
lateral surface of the brain, a movement which has been carried
to a greater extreme in the ‘somatic area’ of elasmobranchs
(Johnston, ’11). The precommissural body and the palaeostria-
tum are tobe regarded as extensions of the hypothalamus and ven-
tral part of the thalamus respectively and, therefore, as equiva-
lent to the pars basalis, or pars subpallialis, of the amphibian
hemisphere. The remainder of the basal lobe is the extension
of the epithalamus and dorsal part of the thalamus and, there-
fore, is the equivalent of the pars pallialis of the amphibian brain.

244 RALPH EDWARD SHELDON

The olfactory crus is attached to the rostral end of the basal
lobe by two systems of tracts, a medial and a lateral. The former,
as in Amphibia, connects chiefly with the precommissural body
(tractus olfactorius medialis) and in smaller measure with
the dorso-medial part of the basal lobes termed primordium
hippocampi in this paper, this relation being in principle similar
to that of Amphibia and higher forms. The closely associated
nervus terminalis and tractus olfactorius ascendens have been
discussed in another connection. The tractus olfactorius lateralis
connects chiefly with the lateral part of the basal lobe, the
nucleus olfactorius lateralis and the nucleus pyriformis. These
nuclei correspond ina general way with the dorso-lateral part of the
amphibian hemisphere, or primordium of the lobus pyriformis.
Like the palaeostriatum, they tend to move laterad away from the
ventricular and toward the lateral surface of the basal lobe.

In vertebrates with evaginated hemipheres the two dorsal
parts (pars pallialis) lie on opposite sides of the lateral ventricle
and in later phylogenetic stages become respectively the hippo-
campus and the pyriform lobe. In the teleosts these parts are
very imperfectly separated, especially at the rostral end of the
basal lobe; here both are parts of a common secondary olfactory
nucleus. Incident to the progressive enlargement of the:telen-
cephalon without the evagination ofits walls, the thickened second-
ary olfactory nucleus moves laterad, carrying with it the taenia,
or line of attachment of the membranous roof, which accord-
ingly becomes dilated laterally. (See figs. 126 to 134 illustrating
the arrangement of these parts and the process of eversion.)

It will be observed that the teleostean form has not been
reached by a simple process of eversion of the whole wall such as
that suggested by Mrs. Gage (’92; see fig. 185); for that would
bring the primordium hippocampi, which borders the taenia in
Amphibia, far ventro-laterally in the teleosts. This appears not
to be the case, but a portion of the dorsal secondary olfactory
nucleus retains its dorso-medial position with reference to the
other massive structures, in spite of the lateral movement of the
taenia. 'The movement in question is not, in fact, a simple lateral
bending of the whole wall at the sulcus limitans telencephali,

OLFACTORY CENTERS IN TELEOSTS 245

but rather a gradual plastic movement of the material, such that,
while the precommissural body and the medial part of the dorsal
olfactory nuclei remain in the original position, the intervening
portions of the lateral wall move toward the lateral part, thus
bringing the dorsal olfactory nucleus and the precommissural
body into contact at the sulcus limitans. The palaeostriatum
moves laterad only a short distance, coming to occupy the middle
of the basal lobe. Buta portion of the dorsal olfactory nucleus
and the whole of the lateral nucleus move to the extreme ventro-
lateral margin, carrying the taenia with them, thus forming at the
‘rostral end of the basal lobe the tuberculum laterale, and at the
caudal end the nucleus pyriformis.

The tuberculum anterius, tuberculum laterale, and nucleus
dorsalis are parts of the undifferentiated secondary olfactory
nucleus. The precommissural body and pyriform nucleus are
more highly differentiated parts of the secondary olfactory nu-
cleus which have developed under the influence of ascending fibers
of the medial and lateral forebrain tracts respectively. The
palaeostriatum has become an efferent correlation center rela-:
tively free from direct olfactory connections. It is interesting
to note that the termination of the lateral hypothalamic tract
caudally in the teleosts has brought about the development of the
nucleus pyriformis at that point, while in the selachians the more
rostral ending of this connection (tractus pallii) has induced the
formation of the nucleus olfactorius lateralis and primordium
hippocampi in a correspondingly different position.

The selachians exhibit a considerably more highly differentiated
condition of all of the forebrain centers than is found in the tele-
osts (ef. Johnston, ’11). The selachian ascending tract from the
hypothalamus to the primordium hippocampi (tractus pallii),
in teleosts is probably represented in the tractus hypothalamo-
olfactorius lateralis, a condition which resembles that of amphi-
bians (Herrick, ’10, p. 444).

The nucleus olfactorius dorsalis or primordium hippocampi
receives some fibers from the tractus olfactorius medialis, and this
connection is probably the reason why this portion of the undiffer-
entiated secondary olfactory nucleus retains its dorso-medial

246 RALPH EDWARD SHELDON

position during the lateral eversion of the remainder of this
nucleus. The adult configuration is such as to suggest that the
nucleus dorsalis is homologous with the amphibian primordium
hippocampi and the sulcus limitans telencephali with the fissura
limitans hippocampi of Herrick (fissura arcuata of Gaupp).
The latter homology is however, manifestly incomplete, for the
fissura limitans hippocampi is a total fissure involving the whole
wall of an evaginated hemisphere, while the teleostean sulcus
limitans is an ependymal groove within the ventricle of the telen-
cephalon medium. The two sulci in question separate homol-
ogous parts of the brain and are as nearly homologous as the
topographic relations of these two types of telencephalon permit.

Some justification may be found for the homology of the
nucleus olfactorius dorsalis with the primordium hippocampi of
Amphibia, although the apparent resemblance in position is an
argument rather against it than for it. It must not be for-
gotten that the nucleus dorsalis occupies a dorso-median position
below the telencephalic ventricle, not above it, as in Amphibia.
In the process of eversion, to which reference was made above, the
whole of the dorsal nucleus might be expected to follow the taenia
in its lateral movement. The fact that a part of this nucleus
retains its position at the dorso-medial border of the basal lobe
has been already explained as due to its connection with the trac-
tus olfactorius dorso-medialis. This is a primary connection of
the primordium hippocampi; cf. fig. 125 with C. J. Herrick (710 b),
figs. 72, 73, 83 and 84, the nucleus olfactorius dorsalis or primor-
dium hippocampi of the teleost being the functional equivalent
of Herrick’s dorso-medial ridge in spite of its position far removed
from the taenia. Nevertheless, the nucleus dorsalis shows few
other resemblances with the primordium hippocampi. It has
not been shown to receive large numbers of olfactory fibers of the
third or higher orders; it sends very few fibers to the anterior
commissure complex to form a commissura hippocampi and no
clearly defined columna fornicis fibers appear to arise from it,
though possibly the medial forebrain bundle may contain fibers
of this type.

OLFACTORY CENTERS IN TELEOSTS 247

It is concluded, therefore, that the materials found in the am-
phibian primordium hippocampi are not completely separated in
the teleosts from the other elements of the secondary olfactory
nucleus, being represented chiefly in the nucleus olfactorius dor-
salis or primordium hippocampi and to a less degree perhaps in
the nucleus olfactorius lateralis and nucleus pyriformis.

The term ‘epistriatum’ has not been used in this article in the
description of the telencephalic nuclei, owing to the fact that it
has been applied by different authors, with resulting confusion,
to morphologically different structures. It was originally used
by Edinger (96), to designate a structure found dorsal to the stria-
tum in the lateral wall of the reptilian forebrain. Its connections
here show clearly that it is morphologically a lateral structure.
corresponding to the nucleus sphaericus of students of reptiles.
The epistriatum of birds, as described by Edinger, is likewise a
lateral structure. Turning to the so-called epistriatum of the
anamniotes, a different condition is immediately noted. Edinger
(06a) and Kappers (’06) describes as epistriatum in teleosts a
medial area reached by the tractus olfactorius medialis which
seems to include a part of our precommissural body, but in their
later works this name is applied to our nucleus olfactorius dor-
salis. Catois uses the term for the dorsal portion of the
palaeostriatum. Johnston (’06) places the epistriatum of teleosts
on both the medial and lateral parts of each basal lobe, although
these two areas belong to morphologically different structures. It
is difficult to see how the term can continue in use without con-
stantly increasing confusion. Even if all workers had clearly in
mind the morphological characteristics of the different varieties
of epistriatum, it would seem unwise to use the same name, even
with a modifying adjective, as does Kappers in his later work,
for such morphologically different structures.

From the preceding discussion it is clear that the localization of
function in the telencephalon of teleosts has not advanced so far
as in Amphibia and Dipnoi with more fully evaginated hemi-
spheres. This is probably the explanation of the fact that the
diencephalic regions are also far less clearly analyzed than in Am-
phibia, and that nearly all parts of the basal lobes seem to be

248 RALPH EDWARD SHELDON

connected with both hypothalamic and thalamic centers. But
the discussion of these relations can be taken up more profitably
after the connections of the diencephalic nuclei are more fully
analyzed and particularly, after their embryological development
has been studied.

Some comment should be made on the bearing which the data
given in this article make with respect to the morphology of the
forebrain tela. It is clear from the facts presented that the fore-
brain of the teleostean fishes contains primordial pallium and
also the primordium of all important morphological structures
found in the forebrain of higher vertebrates. The pallium of
Rabl-Riickhard, then, is not the morphological equivalent of any
portion of the wall of the forebrain of higher vertebrates but is
simply a tela, derived from the Deckplatte of His. In fact there
is no evidence anywhere in the phylogeny of the vertebrate brain
that the Deckplatte gives rise to a nervous structure. The evi-
dence which has been offered, then, gives additional support to
the views of Studni¢ka, already accepted by Kappers, Johnston,
Edinger and Herrick.

Anatomical Laboratories,
The School of Medicine,
University of Pittsburgh.

LITERATURE CITED

All papers cited have been consulted, excepting those marked with an asterisk
(*). The subject matter of articles so indicated was ascertained through reviews.

Arcue., Orro 1895 Kurze Mittheilung iiber den histologischen Bau der Reich-
schleimhaut embryonaler Teleostier. Sitzungsber. d. Gesellsch. f.
Morphol. u. Physiol. i. Miinchen, Bd. 11, Hft. 2 u. 3, pp. 73-78.

BeLtoncr, Gruserre 1880 Ricerche comparative sulla struttura dei centri
nervosi dei Vertebrati. Mem. d. r. Accad. d. Lincei, Cl. se. F., ser.
3, vol. 5, pp. 157-182, figs. 1-58.
1885 Intorno all’ apparato olfattivo-ottico (nuclei rotondi, Fritsch)
del cervello dei Teleostei. Ibid., ser. 4, vol. 1, pp. 318-323, pl. 1.

Brookover, CHarutes. 1908 Pinkus’s nerve inAmiaand Lepidosteus. Science,
N.S., vol. 27, pp. 913-914.
1910 The olfactory nerve, the nervus terminalis and the preoptic
sympathetic system in Amia calva, L. Jour. Comp. Neur., vol. 20, pp.
49-118, pls. 1, text figs. 32.

OLFACTORY CENTERS IN TELEOSTS 249

BurckHarpDT, R. 1892 Das Centralnervensystem von Protopterus annectens.
Eine vergleichend-anatomische Studie. Berlin, Friedlander u. Sohn,
Taf. 1-5, pp. 1-64.

CauuEsA C. *1893: La region olfatoria del cerebro en los urodelos. Madrid.

Catois, E. H. 1902 Recherches sur l’histologie et l’anatomie microscopique
de lV’encéphale chez les poissons. Bull. scientifique de la France et
de la Belgique. Tom. 36, pp. 1-166, pls. 1-10.

Epincer, L. 1888 Untersuchungen iiber die vergleichende Anatomiedes Gehirns.
1. Das Vorderhirn. Abhdlg. d. Senckenberg. Naturf. Gesellsch., Bd.
15, pp. 91-122, pls. 1-4. ;

1892 Untersuchungen iiber die vergleichende Anatomie des Gehirns.
11. Das Zwischenhirn. Erster Teil. Das Zwischenhirn der Selachier
und der Amphibien. Ibid., Bd. 18, pp. 1-55, pls. 1-5, text fig. 1.

1893 Vergleichend-entwickelungsgeschichte und anatomische Studien
im Bereiche der Hirnanatomie. 111. Riechapparat und Ammonshorn.
Anat. Anz., Bd. 8, pp. 305-321, text figs. 6.

1894 Vergleichent-anatomische und entwickelungsgeschichtliche Stu-
dien im Bereiche der Hirnanatomie. iv. Die Faserung aus dem Stamm-
ganglion Corpus striatum. Vergl.—anat.u.exp. Untersucht. Verhandl.
der Anat Gesellsch., pp. 53-60, figs. 1-4.

1896 Untersuchungen iiber die vergleichende Anatomie des Gehirns.
111. Neue Studien iiber das Vorderhirn der Reptilien, Abhdlg. d. Senck-
enberg. Naturf. Gesellsch., Bd. 19, pp. 313-387, pls. 1-4, text figs. 14.

1896 a Vorlesungen iiber den Bau der nervésen Zentralorgane. Auf. 5.
Leipzig.

1899 Untersuchungen iiber die vergleichende Anatomie des Gehirns.
Iv. Studien iiber das Zwischenhirn der Reptilien. Ibid., Bd. 20, pp.
161-197, pls. 1-3.

1908 Vorlesungen iiber den Bau der nervésen Zentralorgane des Men-
schen und der Tiere. Bd. 2, Auf. 7, pp. 12, 334, figs. 283. Leipzig.

Fritscu, G. 1878 Untersuchungen tiber den feineren Bau des Fischgehirns.
Berlin pp. 15, 94, pls. 1-13.

GaGeE, SusANNA PoEetps 1893 The brain of Diemyctylus viridescens from larval
to adult life. Wilder Quarter Century Book, Ithaca, N. Y., pp. 259-
314, pls. 1-8.

Gaupp, Ernst 1899 A. Ecker’s und R. Wiedersheim’s Anatomie des Frosches.
Zw. Abth., Lehre vom Nerven- und Gefiasssystem. Zw. Auf., Braun-
schweig, pp. 12, 548, figs. 146.

GoupstEIN, Kurr 1905 Untersuchungen tiber das Vorderhirn und Zwischen-
hirn einiger Knochenfische. (Nebst einigen Beitrigen iiber Mittelhirn
und Kleinhirn derselben). Arch. f. mikr. Anat u. Entw., Bd. 66, pp.
135-219, pls. 11-15, text figs. 23.

250 RALPH EDWARD SHELDON

Hauuer, Beta 1898 Vom Bau des Wirbelthiergehirns. 1 Thiel. Salmo und
Seyllium. Morph. Jahrb., Bd. 26, pp. 345-641, pls: 12-22.

Harpesty, 1. 1902 Neurological technique, pp. 12, 183, Chicago.

Herrick, C. Jupson 1897 Report upon a series of experiments with the Wei-
gert methods, with special reference for use in lower brain morphology.
State Hospitals Bull., Utica, N. Y., vol. 2, pp. 1-81.

1909 The nervus terminalis (nerve of Pinkus)in thefrog. Jour. Comp.
Neur., vol. 19, pp. 175-190, figs. 1-10.

1910 a The morphology of the cerebral hemispheres in Amphibia.
Anat. Anz., Bd. 36, pp. 645-652, figs. 1-3.

1910 b The morphology of the forebrain in Amphibia and Reptilia.
Jour. Comp. Neur., vol. 20, pp. 413-547, figs. 1-84.

Herrick, C. L. 1891 a The commissures and histology of the teleost brain.
Anat. Anz., Bd., 6 pp. 676-681, figs. 1-3.

1891 b Contributions to the comparative morphology of the central
nervoussystem. 1. Topography and histology of the brain of certain
reptiles. Jour. Comp. Neur., vol. 1, pp. 14-27, pls. 3, 4, 9.

1891 e Contributions to the morphology of the brains of bony fishes.
11. Studies on the brains of some American fresh-water fishes. A. Topo-
graphy. Ibid., pp. 228-245, pls. 19-21.

1891 d Contributions to the morphology of the brains of bony fishes.
ir. Studies on the brains of some American fresh-water fishes. (Con-
tinued.) B. Histology of the rhinencephalon and prosencephalon. Ibid.,
pp. 333-358, pls. 24-25.

1892 a Additional notes on the teleost brain. Anat. Anz., Bd. 7, pp.
422-431, figs. 1-10.

1892 b Contributions to the morphology of the brain of bony fishes.
11. Studies on the brain of some American fresh-water fishes. (Contin-
ued.) C. Histology of the diencephalon and mesencephalon. Jour.
Comp. Neur., vol. 2, pp. 21-72, pls. 4-12.

1892 ec Notes upon the anatomy and histology of the prosencephalon
of teleosts. Am. Nat., vol. 26, pp. 112-120, pls. 7-8.

Jounston, J. B. 1898 The olfactory lobes, fore-brain and habenular tracts of
Acipenser. Zool. Bull., vol. 1, pp. 221-241, figs. 1-5.
1901 The brainof Acipenser. Zool. Jahrb., Abth.f. Anat. u. Ont., pp.
59-260, pls. 2-13.
1902 The brain of Petromyzon. Jour.Comp. Neur., vol. 12, pp. 1-86,
pls. 1-8.
1906 The nervous system of vertebrates. Pp. 20, 370, figs. 1-180,
Philadelphia.

OLFACTORY CENTERS IN TELEOSTS PAT

JOHNSTON, J. B. 1909 The morphology of the forebrain vesicle in vertebrates.

KAPPERS,

Jour. Comp. Neur., vol. 19, pp. 457-539, figs. 1-45.

1910 The evolution of the cerebral cortex. Anat. Ree., vol. 4, pp.
143-166, figs. 1-20.

1911 The telencephalon of selachians. Jour. Comp. Neur., vol. 21
pp. 1-114, figs. 1-85.

C. U. Ariens 1906 The structure of the teleostean and selachian
brain. Jour. Comp. Neur., vol. 16, pp. 1-112, pls. 1-16.

1907 Untersuchungen iiber das Gehirn der Ganoiden Amia calva und
Lepidosteus osseus. Abhdlg. d. Senckenberg. Naturf. Gesellsch., Bd.
30., pp. 449-500, pl. 18, text figs. 1-6. ;

1908 a (Mirwirkung von W. F. Theunissen) Die Phylogenese des
Rhinencephalons, des Corpus striatum und der Vorderhirncommissuren.
Folia Neuro-Biologica, Bd. 1, pp. 173-288, pls. 1-3, text figs. 1-5.

1908 b Weitere Mitteilungen iiber die Phylogenese des Corpus stria-
tum und des Thalamus. Anat Anz., Bd. 33, pp. 321-336, figs. 1-6. °

1908 ec Eversion and inversion of the dorso-lateral wall in different
parts of the brain. Journ. Comp. Neur., vol. 18, pp. 433-436, figs. 1-5.

1909 The phylogenesis of the palaeo-cortex and archi-cortex compared
with the evolution of the visual neo-cortex. Archives of Neurol. and
Psychiat., vol. 4, pp. 1-18, pls. 1-4.

C. U. A., AND THEUNISSEN, W. F. 1907 Zur vergleichenden Anatomie
des Vorderhirns der Vertebraten. Anat. Anz., Bd. 30, pp. 496-509,
figs. 1-10.

Kogruuiker, A. 1896 Handbuch der Gewebelehre des Menschen. 6 Auf., Zw.

Locy, W.

Bd., Nervensystem des Menschen und der Thiere, pp. 8, 1-874, figs.
330-845. Leipzig.

A. 1899 New facts regarding the development of the olfactory nerve.

Anat. Anz., Bd. 16, pp. 273-290, figs. 1-14.

1903 A new cranial nerve in selachians. Mark Anniversary Vol., pp.
39-55, pls. 5-6.

1905 On a newly recognized nerve connected .with the forebrain of
selachians. Anat. Anz., Bd. 26, pp. 33-63, 111-123. .

OweEN, RicHarp 1868 Anatomy of vertebrates, vol. 3, Mammals, pp. 10, 915,

figs. 1-614. London.

RaBi-RiickHarD, H. 1882 Zur Deutung und Entwickelung des Gehirns der

Knochenfische. Arch. f. Anat. u. Physiol., Anat. Abth., pp. 111-138,
pls. 6-7. ;

1883 Das Grosshirn der Knochfische und seine Anhangsgebilde.
Ibid., pp. 279-322, pls. 12-18.

252 RALPH EDWARD SHELDON

Rasi-RitickHarp, H. 1884 Das Gehirn dés Knochenfische. Biol. Centralbl.,
Bd. 4, pp. 499-510, 528-541, figs. 1-11.

1893 Das Vorderhirn der Cranioten. Eine AntwortanF. K. Studniéka.
Anat. Anz., vol. 9, pp. 536-547, figs. 1-16.

1894. Noch ein Wort an Herrn Studniéka. Anat. Anz., Bd. 10, p. 240.

RaM6n, PepRo *1894 Investigaciones micrograficas en el encéfalo de los Batra-
ceos y Reptiles. Zaragoza.

1896 L’Encéphale des amphibiens. Bibliographie anatomique, T.
4, pp. 232-252, figs. 1-15.

Ramo6n ¥ Casa, 8. 1894 Notas preventivas sobre la estructura del'encéphalo
de los Teléosteos. Anal. d. 1. Soc. Esp. d. Hist. Nat., Madrid. ser. 2,
iia:

1899 Textura del sistema nervioso del hombre y de los vertebrados.
T. 1. pp. xi, 566, figs. 1-206. Madrid.

1904 Ibid., T. 2, pp. 1-1209, figs. 207-887. Madrid.
Ratu, O. vom 1895 Zur Consirvirungstechnik. Anat. Anz., Bd. 11. pp. 280-288.

Rusascuin, W. 1903 Uber die Beziehungen des Nervus trigeminus zur Reich-
schleimhaut. Anat. Anz., Bd. 22, pp. 407-415, figs. 1-4.

Supetpon, R. E. 1908a An analysis of the olfactory paths and centers in fishes.
Anat Rec., vol. 2, pp. 108-109.

1908b The participation of medullated fibers in the innervation of the
olfactory mucousmembrane of fishes. Science, N.S., vol. 27, pp. 915-916.

1909 a The nervus terminalis in the carp. Jour. Comp. Neur., vol.J9,
pp. 191-201, figs. 1-7.

1909 b The reactions of the dogfish to chemical stimuli. Ibid., pp.
273-311, figs. 1-3.

Suextpon, R. E. anp BrooxovEer, CuHarLEes 1909 The nervus terminalis in
teleosts. Anat. Rec., vol. 3, pp. 257-259.

Smiru, G. Exuior 1895 The connection between the olfactory bulb and the
hippocampus. Anat. Anz., Bd. 10, pp. 470-474, figs. 1-2.

1903 On the morphology of the cerebral commissures in the vertebrata,
with special reference to an aberrant commissure found in the fore-
brain of certain reptiles. Trans. Linn. Soc.. London, 2d Ser. Zool.,
vol. 8, pt. 12, pp. 455-500, figs. 1-36.

1908 ‘The cerebral cortex in Lepidosiren, with comparative notes on
the interpretation of certain features of the forebrain in other verte-
brates. Anat. Anz., Bd. 33, pp. 513-540, figs. 1-18.

OLFACTORY CENTERS IN TELEOSTS 253

SterziI, Grusepre 1907 II sistema nervoso centrale dei vertebrati. Ricerche
anatomische ed embriologiche, vol. primo, Ciclostomi, pp. 731, figs.
194. Padova.

1909 Ibid., vol. 2, Pesci, Lib. 1, Selaci, Pt. 1, Anatomia. pp. 986, figs.
385. Padova. : ,

Stiepa, L. 1868 Studien iiber das centrale Nervensystem der Knochenfische.
Zeit. f. wiss. Zool., Bd. 18, pp. 1-72, pls. 1-2.

1870 Studien tiber das centrale Nervensystem der Wirbelthiere. Zeit.
f. wiss. Zool., Bd. 20, pp. 1-184, pls. 17-20.

1873 Uber die Deutung der einzelnen Thiele des Fischgehirns. Zeit.
f. wiss. Zool., Bd. 23.

Stupnriéka, F. K. 1893 a Zur Loésung einiger Fragen aus der Morphologie des
Voderhirnes der Cranioten. Vorliufige Mitteilung. Anat. Anz., Bd.
9, pp. 307-320, pls. 2-3.

1893 b Eine Antwort auf die Bemerkungen R. Burckhardt’s zu meiner
vorliufigen Mittheilung iiber das Vorderhirn der Cranioten. Ibid.,
pp. 691-693.

1894 Zur Geshichte des ‘Cortex cerebri.’ Verh. d. Anat. Gesellsch.,
8. Vers. Strassburg, pp. 193-198, fig. 1.

1895a Bemerkungen zu dem Aufsatze: ‘Das Vorderhirn der Cranioten’
von Rabl-Riickhard. Anat. Anz., Bd. 10, pp. 130-137.

1895b Beitrage zur Anatomie und Entwickelungsgeschichte des Vor-
derhirns der Cranioten. Erste. Abth., Sitzungsber. d. Kénigl. Bohm.
Gesellsch. d. Wissensch., math.-naturw. Klasse, pp. 1-42, pls. 1-7.

1896 Ibid., Zw. Abth. pp. 1-82, pls. 14

1898 Noch einige Worte zu meinen Abhandlungen iiber die Anatomie
des Vorderhirns. Anat. Anz., Bd. 14, pp. 561-569.

VAN GEHUCHTEN, A. 1890 Contributions 4 l’étude de la muqueuse olfactive
chez les mammiféres. La cellule, T. 6, fase. 2, pp. 395-409, pl. 1.

1894 Contribution 4 |’ étude du systéme nerveux des téleostéens (com-
munication préliminaire). Ibid., T. 10, pp. 253-296, pls. 1-3.

1906 Anatomie du systéme nerveux de homme. 4th Edit., pp. 15,
999, figs. 1-848. Louvain.

WIEDERSHEIM, RoBERT 1902 Vergleichende Anatomie der Wirbelthiere. 5 Auf.,
pp. 19, 686, figs. 379. Jena.

EXPLANATION OF FIGURES

All drawings are made from the brain of the carp, Cyprinus carpio L. The
individual specimens from which these are made range from 15 to 30 cm. in length
for the Golgi preparations; 25 to 40 em. for those prepared with toluidin blue and
the method of Ramén y Cajal, and 35 to 60 cm. for the Weigert preparations.
Figs. 1 to 4 were drawn with the use of a dissecting microscope; for all others there
were used a camera lucida and Zeiss microscope with the following objective and
ocular combinations: compensating ocular 4*, objective A*; compensating ocular
8, objective A*; ocular 2, objective AA; ocular 4, objective AA; ocular 6, objec-
tive AA; compensating ocular 6, objective AA; compensating ocular 4, apochro-
matic objective 16 mm.; compensating ocular 4*, apochromatic objective 8 mm. ;
compensating ocular 18, apochromatic objective 4 mm.

On all figures from longitudinal sections an arrow (—) is placed always pointing
rostrad. Where a double pointed arrow (<~—) appears after the name of a tract
it signifies that the tract in question contains both ascending and descending fibers ;
the name used on the figures is, however, always that of the descending tract.
All figures from the Weigert or toluidin blue method are from transections; in
the case of the latter every cell appearing in the section is drawn in with a camera
lucida in order to obtain the proper grouping.

The eight diagrams, figs. 125, and 136 to 142, consist in each case of a basal dia-
gram, the same in figs. 125 and 141, and in figs. 136 to 140, 142; to which is added in
one or more different colors, the fiber connections. The two different basal dia-
grams are made from series of adjacent sections by the Weigert method, sagittal
in the case of figs. 125 and 141, frontal in figs. 136 to 140, 142. These are drawn
with tke aid of a camera lucida, a Zeiss comp. oc. 4*, and objective A*, and are
superimposed in such a way as to bring as many as possible of the structures to be
considered into one figure. The relations are not, of course, accurate for any one
givenplane. The fiber tracts are represented by simple lines showing the course
of each tract and its connections. The tracts so represented, are not, of course,
equal in respect to number of fibers; some, such as the lateral forebrain bundle,
are composed of an enormous number, while others, such as the tr. preoptico-
habenularis, pars posterior, contain only a few.

255

PLATE 1
EXPLANATION OF FIGURE

1 Dorsal aspect of the brainof the carp. X 2.

a, dorsal-lateral protuberance on the surface of the olfactory bulb caused by the
entering fibers of the olfactory nerve; bulb. olf., bulbus olfactorius; cbl., cerebellum;
’ crus olf., crus olfactorium; gang. bas., ganglion Basale of the cerebral hemispheres;
lob. fac., lobus facialis or tuberculum impar; lob. vag., lobus vagi; mesotela, mem-
branous roof of the mesencephalon; rhinotela, membranous roof of the cavity of
the olfactory crus, the rhinocele; sac. dors., saccus dorsalis, enclosing the corpus
pineale; sp. cord. spinal cord; tela., membranous roof of the fourth ventricle;
tectum, tectum mesencephali; torus long., torus longitudinalis; valvula, valvula
cerebelli, showing through the membranous mesotela.

256

OLFACTORY CENTERS IN TELEOSTS PLATE 1

RALPH EDWARD SHELDON

a, ——— ee

OWN, CMW =

rhinotela.
tela.

Bang. bas.

DOC GGiss as

Veeluim: 0

torus. lon¢ ;
mesotela. _ if
VEIN ea 4

1 KATHARINE HILL, DEL.

raaT|

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

PLATE 2

EXPLANATION OF FIGURES

2 Dorsal aspect of the rostral end of the brain. Xx 4. The optic lobes sre
removed and the tela of the cerebral hemispheres, the so-called pallium, is torn
from the dorsal surface, exposing the basal ganglia.

3 Left lateral aspect of the rostral end of the brain. X 4. Optic lobes and
tela as in fig. 2.

crus olf., crus olfactorium; hyp., pars gl., hypophysis, pars glandularis; hyp.,
pars. nerv., hypophysis, pars nervosa; lob. inf., lobus inferior or hypoarium; NV.
ITT, nervus oculomotorius; 7”. opt., nervus opticus; n. cbl., protuberance caused by
the development of the nucleus cerebellaris hypothalami of Goldstein; n. prerot.
+n. rot., protuberance caused by the development of the nucleus prerotundus
and nucleus rotundus centrally; s. ypsil., sulcus ypsiliformis of Goldstein,
the rostral prolongation of which corresponds morphologically to the fovea
endorhinalis interna of Kappers and Theunissen (’08); tela, this indicates the torn
edge of the tela or pallium which covers the basal ganglia, extending rostrally
over the olfactory tracts to the olfactory bulbs, and caudally between the two
halves of the tectum, over the valvula; tr. olf. lat., tractus olfactorius lateralis, the
radix olfactoria lateralis of Kappers; tr. olf. med., tractus olfactorius medialis,
including also the tractus olfactorius ascendens and nervus terminalis; the cor-
responding tracts, according to Kappers are, tractus olfacto-lobaris medialis and
radix olfactoria medialis propria; he failed to note the nervus terminalis; ¢wb. ant.,
tuberculum anterius; due chiefly, to the presence underneath, of the rostral end of
the nucleus olfactorius lateralis ; lub. dors., tuberculum dorsale, enlargement due
to the development of the nucleus olfactorius dorsalis; tub. lat., tuberculum lat-
erale, caused by the development of the nucleus olfactorius lateralis; twb. post.,
tuberculum posterius, due to the development of the nucleus pyriformis.

258

OLFACTORY CENTERS IN TELEOSTS PLATE 2

RALPH EDWARD SHELDON

Gris, Olt.
tr olf. med
tr olf.
WMIMeGcele
rninotela
tub. ant
tub. dors.

=
ine
=
eB

ub DOSt
lob. Inf
ING

<FALS; Che

En, Ope

hyp., pars. ¢l.
tub. ant.

Yi.

yp. pars nerv.
tub. dors.

Roy. eae

alley.
ie Gp sos
! 2 post.

tuber

_n. prerot. +
alee tO

iar CO.

selon Wage

KATHARINE HILL, DEL.

PLATE 3
EXPLANATION OF FIGURES

4 Ventral aspect of the rostral end of the brain. > 4.

5 Transection through the median ridge of the olfactory mucosa to show its
innervation by trigeminal nerve fibers. Weigert method. 64. In adjacent
sections the medullated fibers may be seen reaching the membrana propria. Note
that the epithelium of the median ridge differs from that of the remainder of the
Schneiderian membrane, particularly in the large number of goblet cells present.
This is also a characteristic of the respiratory epithelium of mammals as distin-
guished from the olfactory epithelium, which lacks almost entirely the mucus
secreting cells.

chias., optic chiasma; c. mam., corpus mammillare of Goldstein; fib. trig.,
fibrae trigemini; f. end., fissura endorhinalis, the sulcus rhinalis of Kappers (’06),
the fovea endorhinalis externa of Kappers and Theunissen (’08), the fovea
limbica of Goldstein, the fissura ectorhinalis of Owen; go. cells., goblet cells;
hyp., pars gl., hypophysis, pars glandularis; hyp., pars nerv., hypophysis, pars
nervosa; /am., lamella; lob. inf., lobus inferior; lob. lat., lobus lateralis hypo-
thalami; lob. med., lobus medius hypothalami, of which the rostral part is the
tuber or tuber cinereum and the caudal the pars infundibularis; memb. olf., mem-
brana olfactoria, or olfactory portion of the Schneiderian membrane; memb. resp.,
membrana respiratoria, the respiratory part of the Schneiderian membrane;
m. opl., nervus opticus; sac. vasc., saccus vasculosus; s. mam., sulcus mammillaris
of Goldstein, separating the region of the corpus mammillare from the remainder
of the lobus lateralis; tub. post., tubereulum posterius.

260

OLFACTORY CENTERS IN TELEOSTS PLATI

RALPH EDWARD SHELDON

261

PLATE 4
EXPLANATION OF FIGURES

6 Transection through the middle of the right olfactory bulb. Weigert method.
< 31. Most of the stippled periphery is filled with the unmedullated fibers of the
olfactory nerve which are ending in glomeruli in this region. An especially prom-
inent mass of such fibers appears dorso-laterally, forming the protuberance ‘a,’
as shown in fig. 1.

7 Ganglion cell of the nervus terminalis. Golgi method. X 93. See fig. 124
for the position of this cell.

Sto12 Mitral cells of the olfactory bulb. Golgi method. ™X 93. In the cells
from transverse sections an arrow points toward the center of the bulb; in sagittal
or horizontal sections the arrow points diametrically away from the olfactory
crus and toward the center of the bulb. Figs. Sand 9 are from transverse sections,
figs. 10 and 12 from longitudinal section of the bulb.

13. Fusiform cell from nucleus olfactorius anterior. Longitudinal section.
Golgi method. »X 93. Arrow as in figs. 8 to 12. This neurone extends diagon-
ally across the bulb, one end entering a glomerulus.

14 Stellate cell from nucleus olfactorius anterior. Transverse section. Golgi
method. 93. Arrow asin figs.8to12. Large numbers of these cells are found,
most of which are connected with glomeruli; some of these glomeruli contain mitral
cell dendrites, while many are small and are, apparently,formed only by stellate
cell and olfactory nerve processes.

15 to 17 Neurones from the nucleus olfactorius anterior. Golgi method.
« 93. Arrow placed as in figs. 8 to 12.

15 Stellate cell, connecting with a mitral cell glomerulus. From longitudinal
section.

16 Stellate cell from longitudinal section. Shows one dendrite in connection
with a glomerulus, while the neurite extends toward the center of the bulb.

17 Fusiform cell from longitudinal section.

dend., dendrite; n. term., nervus terminalis; neur., neurite; olf. nerve, olfactory
nerve, fibers of which are scattered about the periphery at the points noted; (r.
olf. lat., pars intermed., tractus olfactorius lateralis, pars intermedia; (7. olf. lat.
pars. med., tractus olfactorius lateralis, pars medialis; tr. olf. med., pars lal., tractus
olfactorius medialis, pars lateralis; tr. olf. med., pars. med., tractus olfactorius
medialis, pars medialis.

OLFACTORY CENTERS IN TELEOSTS PLATE 4

RALPH EDWARD SHELDON

Xr.olf. lat. Ss

265

PLATE 5
EXPLANATION OF FIGURES

18 to 20 Neurones from the nucleus olfactorius anterior. Golgi method.
xX 93. Arrow placed as in figs. 8 to 12.

18 Goblet shaped cell from longitudinal section.

19 Fusiform granule cell from longitudinal section.

20 Stellate granule cell from longitudinal section.

21 Fusiform cell from sagittal section of the olfactory bulb, showing neurite
entering the crus. Golgi method. X 93.

22 Transection through the middle of the right olfactory crus. Weigert
method. »% 33. Thissection was drawn to show, particularly, the nervus term-
inalis; the remaining fiber pathways do not come out so clearly as in other series.

23 Transection through the caudal part of the right olfactory crus, immediately
rostral to the cerebral hemispheres. Weigert method. X 33.

24 Transection through the rostral portion of the cerebral hemispheres. Wei-
gert method. ™ 17. This section shows the relation to the hemispheres, of the
tracts of the crura.

bulb. olf., bulbus olfactorius; crus olf., crus olfactorium; f. endorh., fissura
endorhinalis; . term., nervus terminalis; newr., neurite; tr. olf. asc., tractus
olfactorius ascendens, the radix olfactoria medialis propria of Kappers; tr. olf.
asc., pars lat., tractus olfactorius ascendens, pars lateralis; tr. olf. asc., pars.
med., tractus olfactorius ascendens, pars medialis; tr. olf. lat., pars intermed.,
tractus olfactorius lateralis, pars intermedia; tr. olf. lat., pars lat., tractus
olfactorius lateralis, pars lateralis; tr. olf. lat., pars. med., tractus olfactorius
lateralis, pars medialis; tr. olf. med., pars lat., tractus olfactorius medialis,
pars lateralis; tr. olf. med., pars med., tractus olfactorius medialis, pars medialis.

OLFACTORY CENTERS IN TELEOSTS PLATE 5
RALPH EDWARD SHELDON

ak epithelial roof
oer | ii Olf med
\ pars med.
3 It olf mec
} pars ‘al : tic olf lal
: pars la
: \ nes ic ee tr olf. laf. pars
r LP iG jars, med. < Vie Se ea
\ | \trolf asc. eee” Tr Of. lal pars med.
, pars lat. Se
fa 22

pars lat,

# tr olf lat pars
intermed

frolf lat.
pars med,

ae ol mea

Pe olf.asc.

te olf. lat., pars.med.

\ : YOlf. Jar, pars. inyefmed,
\ & 7 he oy \ as NGS: + olf. lat pays. lat.
20 \ 24

265

PLATE 6
EXPLANATION OF FIGURES

25 Transection through the rostral portion of the left cerebral hemisphere,
slightly caudal to fig. 24. Toluidin blue method. 46.

26 Cells of the nucleus medianus. Toluidin blue method. X 575. From
transection. This nucleus is characterized by the arrangement of the cells in
small, closely packed groups as shown in the figure. Compare fig. 25.

27. Oblique longitudinal section through the hemispheres showing the origin
of the centrifugal fibers of the tractus olfactorius ascendens. Golgi method.
x 9. The section is much nearer the frontal than the sagittal plane, as is shown
by the inclusion of both olfactory crura, a portion of both optic nerves and much
of the anterior commissure.

com. ant., Commissura anterior; corp. precom., n. med., corpus precommis-
surale, nucleus medianus, this latter is the rostral end of the group of cells called
‘lobus olfactorius posterior, pars medialis’ by Goldstein; ‘areaolfactoria posterior
medialis’ and ‘epistriatum’ by Kappers (’06); ‘area praecommissuralis septi’
by Kappers and Theunissen (’08); ‘ganglion mediale septi’ by Gaupp (’99) and
‘paraterminal body’ by Elliot Smith (’03); crura olf., erura olfactoria; f. endorh.,
fissura endorhinalis; hyp., hypophysis; n. opt., nervus opticus; mucl. olf. dors.,
nucleus olfactorius dorsalis; nucl. olf. lat., nucleus olfactorius lateralis; palaeostr.,
palaeostriatum; s. lim. tel., sulcus limitans telencephali; s. ypsil., fur. ant., suleus
ypsiliformis, furea anterior, the fovea endorhinalis interna of Kappers; tr. olf.
asc., tractus olfactorius ascendens; tr. olf. med., tractus olfactorius medialis.

266

PLATE

Y TELEOSTS

RALPH EDWARD SHELDON

“

OLFACTORY CENTERS

ndorh.

€
|

267

PGA Bey,

EXPLANATION OF FIGURES

28-30 Cells of origin of the fibers of the tractus olfactorius ascendens. Golgi
method. X93. These cells lie in the rostral portion of the precommissural body,
in the nucleus medianus (see fig. 27). They are taken from a sagittal series and
show the branching of the dendrites among the cells of the nucleus. The neurites
terminate in the nucleus olfactorius anterior of the olfactory bulb.

31 Association cell of the nucleus medianus. Golgi method. 93. From
sagittal section.

32-33 Cells of the rostral part of the nucleus olfactorius lateralis. Golgi
method. X93. The neurite of fig. 32 enters the tractus strio-thalamicus, while
that of fig. 33 apparently ends in the ventro-lateral portion of the hemisphere.
The cells are taken from a sagittal series and occupy a position about midway
between the dorsal and ventral surfaces of the hemisphere.

34 Transection through the cerebral hemispheres immediately rostral to the
anterior commissure. Weigert method. X 17. The nervus terminalis is, at this
level, separated from the tractus olfactorius medialis, preparatory to its decussa-
tion; the two components of the tractus olfactorius medialis likewise appear dis-
tinctly.

com. interbulb., Commissura interbulbaris; f. end., fissura endorhinalis; 7.
ferm., nervus terminalis; s. ypsil., ant. limb, sulcus ypsiliformis, anterior limb;
tr. olf. lat., tractus olfactorius lateralis spreading in the form of a crescent to end
in the nucleus olfactorius lateralis, tr. olf. med., pars lat., tractus olfactorius med-
ialis, pars lateralis; tr. olf. med., pars med., tractus olfactorius medialis, pars med-
ialis; ¢r. strio-thal., tractus strio-thalamicus; bundles appearing here are made up,
mainly, of fibers which do not decussate.

268

PS ceimeaites,

OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON

(

) |

i 2) }

iter

eae \

as
VG Were
\ es o
) Hoses
\ is
\ time
aa | @

\
oS

f-com_) rerlrulls—s

DPS 3
"Os,

PLATE 7

7 5-4psilNant limb

ye leete sttiothal”
Lee Ae

oe caeeee J

PLATE 8

EXFLANATION OF FIGURES

35 Transection through the hemispheres at the rostral margin of the anterior
commissure. Weigert method. > 17. This section shows particulaily the de-
cussation of the nervus terminalis (see also Sheldon ’09, figs. 6 and 7); also the
commissura dorsalis, partly made up of fibers connecting the two partes stpra-
commissurales of the precommissural body, partly of fibers connecting the two
nuclei olfactorii dorsales (commissura hippocampi, pars anterior). The relaticn
of the corpus precommissurale to the anterior commissure is brought out cleaily,
the pars commissuralis or commissure bed of Elliot Smith appearing ventrally
and the pars supracommissuralis dorsally.

36 Transection through the middle of the anterior commissure. Weigert
method. 17. Shows especially the decussation of the tractus strio-thalamicus
cruciatus and of the tractus olfactorius medialis, pars lateralis; also the commis-
sura hippocampi, pars posterior, presenting points of similarity, morphologically,
with the commissura dorsalis of Elliot Smith in amphibians, reptiles and mammals,
the commissura pallii of Kappers and Theunissen in amphibians, the commissura
pallii posterior of Edinger in reptiles, the commissura olfactorii internuclearis of
Goldstein, and connecting the nuclei pyriformes of the two sides. This section
also brings out several of the components of the medial forebrain bundle, the trac-
tus olfacto-lobaris medialis of Kappers (’06). Dorsally, mingled with the fibers
of the commissura dorsalis are the fibers of the tractus hypothalamo-olfactorius
medialis. These are ascending fibers, part of which decussate in the anterior
commissure and part in the region of the nucleus posterior tuberis (see figs. 102,
104, 105). This is the tractus olfacto-hypothalamicus medialis of Goldstein.

com. ant., Commissura anterior; com. dors., commissura dorsalis; com. dors.+
dec. tr. hyp. olf. med., commissura dorsalis plus decussatio tractorum hypo-
thalamo-olfactoriorum medialium ; com. hipp., pars post., commissura hippocampi,
pars posterior; com. interbulb. (tr. olf. med., pars. med.), commissura interbulbaris
(tractus olfactorius medialis, pars medialis, the fibers of the tract forming the com-
missurainterbulbaris (aut); corp. precom., pars com., corpus precommissurale, pars
supracommissuralis; dec. tr. olf. med., pars lat., decussation of the tractus olfac-
torii mediales, partes laterales; dec. tr. strio-thal. cruc., decussation of the tractus
strio-thalamici cruciati; n. olf. lat., nucleus olfactorius lateralis; . opt., nervus
opticus; 7. pyr., nucleus pyriformis—this, together with a part of the nucleus olfac-
torius lateralis, corresponds to the lobus olfactorius posterior or area olfactoria
posterior lateralis of Kappers (06), the lobus olfactorius posterior, pars lateralis
of Goldstein, the lobus olfactorius of Edinger (08), the area olfactoria lateralis
of Kappers and Theunissen; 7. term., nervus terminalis; palaeostr., palaeostria-
tum;s.lim.tel., sulcus imitans telencephali; s. ypsil., fur. ant., suleus ypsiliformis,
furea anterior; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; (r.
olf. lat., tractus olfactorius lateralis; tr. olf. med., pars. lat., tractus olfactorius
medialis, pars lateralis; tr. olf. thal. med., pars vent., tractus olfacto-thalamicus
medialis, pars ventralis—this latter component of the medial forebrain bundle is
descending and made up of uncrossed fibers (see fig. 136), which, with the pars
intermedia, and pars dorsalis, form the tractus olfacto-lobaris medialis or tractus
olfacto-hypothalamicus medialis of Kappers; lr. strio-thal., tractus strio-thal-

‘imicus.

270

OLFACTORY CENTERS IN TELEOSTS PLATE 8
RALPH EDWARD SHELDON

eas - palaeostr
we “tr strio-thal.

ay Aes precom.,

. ‘pars. Supracom.
oa ee /
at ea ty olf, lat.

com. dors.

1% a “ow hod OT ee | ars.
: hash eae

: n.term.

Corp! precom,pars.

‘com, inter bulb, Higeehee
Z med spars. med]

Sis com.ant
A -ant.
— Lee

~~ palaeostr
~- corp. precom.,
pars. supracom.

tt hyp. olf. med.

£ com. dors. + dec.

tr hyp. olf. med.

com. hipp., pars post

tr olf. thal. med.

pars vent.

dec. tr olf. med.
= pars at.

vos dec. tr strio-thal.

Grice.

a corp. precom.,

> pays \com.

com.ant.

-n.opt

PLATE 9
EXPLANATION OF FIGURES

37 Transection through the anterior commissure. Ramén y Cajal method.

< 46. Shows particularly the decussation of the tractus strio-thalamicus crucia-
tus.
38 Transection through the anterior commissure. Toluidin blue method.
< 46. Shows with great clearness the limits of the pars supracommissuralis of
the corpus precommissurale, the sulcus limitans telencephali, the nucleus olfac-
torius dorsalis and the bed of the anterior commissure, the pars commissuralis of
the precommissural body.

corp. precom., pars com., corpus precommissurale, pars commissuralis; corp.

precom., pars supracom., corpus precommissurale, pars supracommissuralis; dec.
tr. hyp. olf. med. + com. hipp., pars post., decussatio tractus hypothalamo-olfac-
torii medialis plus commissura hippocampi, pars posterior; dec. tr. strio-thal.
cruc., decussatio tractus strio-thalamici cruciati; necl. com. lat., nucleus com-
missuralis lateralis; nucl. olf. dors., nucleus olfactorius dorsalis; nucl. olf. lat.,
nucleus olfactorius lateralis; nucl. pyr., nucleus pyriformis; nucl. teniae, nucleus
teniae, the nucleus taeniae of Edinger, Kappers and Goldstein; palaeostr., pal-
aeostriatum; rec. preopt., recessus preopticus; s. lim. tel., sulcus limitans tel-
encephali; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; tr. olf.
med., pars. lat., tractus olfactorius medialis, pars lateralis; tr. olf. med., pars
lat. + com. hipp., pars post., tractus olfactorius medialis, pars lateralis plus com-
missura hippocampi, pars posterior; tr. olf. that. med., pars. vent., tractus olfacto-

thalamicus medialis, pars ventralis; tr. med. preopt., pars. ant., tractus mediano-
preopticus, pars anterior; (r. strio-thal., tractus strio-thalamicus; ¢r. strio-thal.
incruc., tractus strio-thalamicus incruciatus.

OLFACTORY CENTERS IN TELEOSTS PLATE 9
RALPH EDWARD SHELDON

median cavity.

Se > tr hyp. olf. med.

sdec. tr hyp. olf.med.+com. hipp.,pars post
tr olf. med, pars lat.

tr olf. thal.med, pars vent.

dec. tr strio-thal. cruc.

tr strio-theal.

tr med. preopt., pars. ant.

tr. strio-thal. incruc.

rec. preopt.

nie vols

nucl. olf. dors.
Sa Uieeele
palaedstr.

EOD ice eComs
pars supracom.

WElRO ewe

pars. lat. +
com. hipp.,
pars post.

Say apes (COM
Tomnucl. teniae

4Cnucl. com. lat.

Mew

273

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

PLATE 10

EXPLANATION OF FIGURES

39 Sagittal section through the hemisphere. Golgi method. x 9. Shows
cells of the corpus precommissurale sending axones, the fibrae precommissurales
striaticae, into the palaeostriatum. Both ascending and descending fibers of the
tractus strio-thalamicus are shown; note especially the dichotomous branching
of the ascending neurites to form tangential fibers.

40 Cell of origin of the tractus olfacto-thalamicus medialis from the nucleus
medianus. Golgi method. 94. From sagittal section.

41-42 Association cells of the nucleus medianus. Golgimethod. 93. From
sagittal section.

43 One of the neurones of the nucleus medianus, the neurite of which forms one
of the fibrae precommissurales striaticae. Golgi method. X 93. (See fig. 39.)
From sagittal section.

44 Cells of the palaeostriatum. Toluidin blue method. > 575. From trans-
verse section.

45 Neurone from cerebral hemisphere. Golgi method. X 93. From sagittal
section, neurite directed caudad, into tractus strio-thalamicus. Thisneurone can
hardly be assigned to a definite region, as it lies about midway between the typical
cells of the palaeostriatum and those of the area olfactoria lateralis. It will be
noted that its perikaryon is larger than that of typical cells of the area olfactoria
lateralis but that its dendrites do not show the conspicuous thorns of the typical
palaeostriatal neurones.

46 Cells of the dorsal portion of the corpus precommissurale, pars supracom-
missuralis. Toluidin blue method. From transection. X 575.

47 Cells of the nucleus pyriformis. Toluidinbluemethod. From transection.
oe Hylae

48 Neurone from the nucleus olfactorius lateralis. Golgi method. X 93.
From sagittal section. This cell is found in the dorsal portion of the hemisphere,
adjacent to the nucleus olfactorius dorsalis, but in the region called epistriatum by
Johnston; its neurite enters the tractus strio-thalamicus.

49 Neurone from the nucleus olfactorius lateralis. Golgi method. xX 93.
From sagittalsection. This is found in the rostro-lateral portion of the hemi-
sphere; it comes into association with the ascending fibers of the tractus thalamo-
striaticus as shown also in figs. 50 and 51.

fib. precom. str., fibrae precommissurales striatici; hab., habenula; tr. strio-
thal., tractus strio-thalamicus; tr. thal. striat., tractus thalamo-striaticus.

274

OLFACTORY CENTERS IN TELEOSTS PLATE 10
RALPH EDWARD SHELDON

oa thal. striat
LOSES

/ ve a Ni

Apa Ss 47 6 OR

iw)
N
Or

PLATE 11
EXPLANATION OF FIGURES

50-51 Neuronesof the palaeostriatum. Golgi method. 185. From sagittal
sections. About the perikaryon of each neurone is a network formed by the
terminal arborization of the neurites of the ascending fibers of the tractus strio-
thalamicus. The larger portion of the cells of the palaeostriatum are very thorny,
as shown in the cells drawn; a number of the neurones, however, particularly
those giving rise to descending fibers of the tractus strio-thalamicus, resemble
more closely fig. 45, with less conspicuous thorns and a larger perikaryon. The
cells shown in figs. 50 and 51 are evidently association cells; their processes extend
over a very large area, bringing different parts of the hemispheres into relation
with one another, with the thalamus and hypothalamus, and with the olfactory
apparatus through the precommissural body.

tr. thal. striat., tractus thalamo-striaticus.

OLFACTORY CENTERS IN TELEOSTS PLATE 11
RALPH EDWARD SHELDON

277

PLATE 12

EXPLANATION OF FIGURES

52 Neurone from the nucleus olfactorius lateralis. Golgimethod. 93. From
sagittal section. This cell is found in the dorso-lateral portion of the hemisphere,
its neurite enters the tractus strio-thalamicus.

53 Neurone of the nucleus pyriformis. Golgi method. 93. From sagittal
section. Most of the neurites from cells of this character and location enter the
tractus olfacto-hypothalamicus laterals.

54 Transection through the region of the recessus preopticus. Ramdén y Cajal
method. 46.

55 Transection through the caudal part of the anterior commissure. Weigert
method. X 17.

corp. precom., pars supracom., corpus precommissurale, pars supracommis-
suralis; n. opt., nervus opticus; nucl. com. lat., nucleus commissuralis lateralis;
rec. preopt., recessus preopticus; tr. hyp. olf. med., tractus hypothalamo-olfactorius
medialis; tr. med. preopt., pars ant., tractus mediano-preopticus, pars anterior,
consisting of fibers originating in the anterior part of nucleus medianus and
terminating about the recessus preopticus; tr. med. preopt., pars post., tractus
mediano-preopticus, pars posterior, consisting largely of fibers originating in
the commissure bed and ending about the third ventricle in the region of the
nucleus preopticus; tr. olf. med., pars lat. +c. hipp., pars post., tractus olfactorius
medialis, pars lateralis plus commissura hippocampi, pars posterior; tr. olf. thal.
med., pars dors., tractus olfacto-thalamicus medialis, pars dorsalis ; this component
of the medial forebrain bundle appears in this section for the first time in the draw-
ings; tr. olf. thal. med., pars vent., tractus olfacto-thalamicus medialis, pars ven-
tralis; tr. strio-thal. cruc., tractus strio-thalamicus cruciatus; tr. strio-thal. incruc.,
tractus strio-thalamicus incruciatus; tr. fen., tractus teniae, the tractus olfacto-
habenularis of Kappers, Goldstein, etc.

278

OLFACTORY CENTERS IN TELEOSTS PLATE 12
RALPH EDWARD SHELDON .

edian cavity.

=)
SE StreeStic tina lncie:

med. preopt., pars ant.

tr med. preopt., pars post,

corp. precom.,
pars supracom.

2% tr ten.
tr olf. thal.med.pars dors.
tx hyp. olf. med.

ErApps pois sDOSsE-

x a tr. olf. thal. med, pars vent.
“> tre strio-thal. cruc.

= te strio-thal. incruc.

nucl. com. lat.

Ale (Gh ole

279

PLATE 13

EXPLANATION OF FIGURES

56 Transection through the caudal part of the anterior commissure. Toluidin
blue method. X 46.

57 Cells of the nucleus teniae. Toluidin blue method. From transverse
section. X 575.

58-60 Neurones of the nucleus teniae. Golgimethod. X93. From oblique
sections, about midway between sagittal and transverse.

corp. precom., pars com., corpus precommissurale, pars commissuralis; corp.
precom., pars supracom., corpus precommissurale, pars supracommissuralis;
nucl. com. lat., nucleus commissuralis lateralis; nucl. olf. dors., nucleus olfactorius
dorsalis; nucl. pyr., nucleus pyriformis; nucl. ten., nucleus teniae; palaeostr.,
palaeostriatum; s. lim. tel., sulcus limitans telencephali.

280

OLFACTORY CENTERS IN TELEOSTS PLATE 13
RALPH EDWARD SHELDON

MUCH Oli- Gl @ics:

5.lim. tel.

palacostr

COrp. PreCcom. pars.
Ssupracom.

“COP One com:
pars. com.

nucl.com. lat.

PLATE 14
EXPLANATION OF FIGURES

61 Transection through the caudal part of the anterior commissure. Weigert
method. X 17.

62 Sagittal section slightly to one side of the median line, showing the tractus
preopticus superior. Golgi method. X 46. The location of the different parts
of the nucleus preopticus is indicated by broken lines.

63 Neurone of the tractus preopticus superior. Golgi method. X 938. From
sagittal section. (See fig. 62).

64 Cells of the nucleus preopticus, pars parvocellularis anterior. Toluidin
blue method. 575.

65 Cells of the nucleus entopeduncularis. Toluidin blue method. X 575.

corp. precom., pars com., corpus precommissurale, pars commissuralis; corp. pre-
com., pars supracom., corpus precommissurale pars supracommissuralis; fasc. med.
hem., fasciculus medialis hemisphaerii; n. opt., nervus opticus; nuwcl. preopt., pars
parvocell., nucleus preopticus, pars parvocellularis; opl., optic chiasma; pars mag-
nocell., pars magnocellularis of the nucleus preopticus; pars parvocell. post., pars
parvocellularis posterior of the nucleus preopticus; rec. preopt., recessus preopti-
cus. tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; fr. olf. thal. med.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med.,
pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. med. preopt.,
pars ant., tractus mediano-preopticus, pars anterior; tr. preopl. sup., tractus
preopticus superior; the connections of this tract are fully shown in the figure;
it is apparently, Goldstein’s tract * (Taf. 11, fig. 7); tr. strio-thal. ineruc., tractus
strio-thalamicus incruciatus; (r. fen., tractus teniae.

OLFACTORY CENTERS IN TELEOSTS PLATE 14
RALPH EDWARD SHELDON

“corp. precom., pars
SuUpracom
tr. ten.

“str. olf. thal.med, pars.
7 VET.

sie tr. olf. thal. med., pars
ae AOS.
22), hyp. olf. med.
a Weccorp. precom., pars.com
rv. stt10-thal. incruc,

tr med. preopt, pars.
ant

nucl preopt pars.
parvoce}].

n. opt.

LL F fasc. med. hem.

Yi fe

g GZ Z 4

GSS opt
iS SS —S SSS
? SSS = SS
SSS SS
SSSSssaacca[c
wx, SS
SS

PLATE 15

EXPLANATION OF FIGURES

66 Transection through the cerebral hemispheres caudal to the anterior com-
missure. Toluidin blue method. 46.

67 Transection through the cerebral hemispheres slightly caudal to the level
shown in fig. 66. Toluidin blue method. X 46. Shows particularly the rostral
portion of the pars magnocellularis of the nucleus preopticus and its relation to the
pars parvocellularis.

corp. precom., pars intermed., corpus precommissurale, pars intermedia; this,
the caudal prolongation of the pars supracommissuralis, meets the nucleus pyri-
formis at the posterior pole of the hemisphere, it likewise comes in close contact
with the extension of the pars commissuralis caudally and ventrally, the pars par-
vocellularis of the nucleus preopticus; fasc. lat. hem., fasciculus lateralis hemi-
sphaerii, the lateral forebrain bundle; consisting of the tractus strio-thalami-
cus, tractus thalamo-striaticus, tractus olfacto-hypothalamicus lateralis and
tractus hypothalamo-olfactorius lateralis; fasc. med. hem., fasciculus medialis
hemisphaerii, the medial forebrain bundle; nucl. entoped., nucleus entopeduncu-
laris; nucl., preopt. pars magnocell., nucleus preopticus, pars magnocellularis ;
nucl. preopt., pars parvocell., nucleus preopticus, pars parvocellularis anterior;
nucl. pyr., nucleus pyriformis; nucl. ten., nucleus teniae; s. lim. tel., sulcus limitans
telencephli; s. ypsil., fur. ant., sulcus ypsiliformis, furca anterior.

284

OLFACTORY CENTERS IN TELEOSTS PLATE 15
RALPH EDWARD SHELDON

PVA Sle WO beresger

San lsimences

coyp. precom.
pos. intermed.

INCKEE Monee

Oplticus:

Corp. pr@com.,pars. intermed.

fasc.med.hem.

nucl. pyr
cl.preopt.,pars. parvocell.
nucl. ven.

fasc. lat. hem.

nucl. entoped.

cl.preopt., pars. magnocell.

cl. preopt.,pars. parvocell.

PLATE 16
EXPLANATION OF FIGURES

68 Transection, at the level of the chiasma. Weigert method. X 17.

69 Transection at approximately the same level as shown in fig. 68. Ramé6n y
Cajal method. x 46.

corp. precom., pars intermed., corpus precommissurale, pars intermedia; fasc.
lat. hem. ——, fasciculus lateralis hemisphaerii; fasc. med. hem. <——, fasciculus
medialis hemisphaerii; nucl. entoped., nucleus entopeduncularis; nucl. preopt.,
pars magnocell,, nucleus preopticus, pars magnocellularis; nuecl. preopt., pars
parvocell., nucleus preopticus, pars parvocellularis; uel. pyr., nucleus pyriformis;
sac. dors., saccus dorsalis; s. ypsil., fur. post., sulcus ypsiliformis, furca poste-
rior; tr. hyp. olf. med., tractus hypothalamo-olfactorius medialis; tr. olf. hyp. lat.
<——, tractus olfacto-hypothalamicus lateralis; tr. olf. thal. med., pars dors.,
tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med., pars vent.,
tractus olfacto-thalamicus medialis, pars ventralis; tr. opt., tractus opticus;
ir. praeth. cin., tractus praethalamo-cinereus of Kappers; tr. preopt. entoped.
<——, tractus preoptico-entopeduncularis; tr. preopt. inlermed., pars ant. ——,
tractus preoptico-intermedius, pars anterior; (r. preopt. intermed., pars lat.,
tractus preoptico-intermedius, pars lateralis; tr. strio-thal. cruc. <——, tractus
strio-thalamicus cruciatus; tr. strio-thal. incruc. <-—, tractus strio-thalamicus
incruciatus; tr. ten., tractus teniae.

286

OLFACTORY CENTERS IN TELEOSTS PLATE 16
RALPH EDWARD SHELDON

NUck pyic

Pen:
tr. olf. thal. med, pars iin a
fr: hyp. olf. med.
Liealf. se ae par, Nent.
IASemat ‘hemes
nucl. entoped,

nici, preopt., pars magnocell.
\\

tr. preopt. intermed., pars lat.

nucl. preopt., p ¥S parvocell.

aa 2 es

NS : . Ee Opt Zs
S aeRO a

bo. ee oe

Ge ali, Wyp: lat<

tr preopt intermed., pars.
ant<=

asc. med. hem<>

tr otrio-thal. cruc.<>
nucl. entoped. <>

| tr preopt entoped
tr strio-thal. incruc<>
( tr preopt. intermed.,
\ pars lat.
Upreoecth: cin
A ee

287

PLATE 17
EXPLANATION OF FIGURES

70 Transection through the posterior pole of the hemisphere and the nucleus
magnocellularis. Toluidin blue method. x 46.

71 A group of cells of the nucleus magnocellularis. Toluidin blue method.
x 575.

72 Transection slightly caudal to the level shown in fig. 69. Ramén y Cajal
method. X 46.

fase. med. hem. <——, fasciculus medialis hemisphaeril; nucl. entoped., nucleus
entopeduncularis; mnucl. intermed., nucleus intermedius; nucl. preopt., pars
magnocell., nucleus preopticus, pars magnocellularis; nucl. preopt., pars parvocell.
lat., nucleus preopticus, pars parvocellularis lateralis; tr. entoped. hab., tractus
entopedunculo-habenularis; tr. olf. hyp. lat. <-—, tractus olfacto-hypothala-
micus lateralis; tr. praeth. cin., tractus praethalamo-cinereus; tr. preopt.
entoped. <——, tractus preoptico-entopeduncularis; tr. preopt. intermed., pars
lat., tractus preoptico-intermedius, pars lateralis; tr. preopt. intermed., pars med.
<———, tractus preoptico-intermedius, pars medialis; tr. strio-thal. cruc. <——,
tractus strio-thalamicus cruciatus; tr. strio-thal. incruc. ——, tractus strio-tha-
lamicus incruciatus; tr. ten., tractus teniae.

288

OLFACTORY CENTERS IN TELEOSTS PLATE 17
RALPH EDWARD SHELDON

Sea
Well. interméd.
Ye

a nucl. entoped.

ucl. preopt.,pors magnocell.

in cl.preopt., pars parvocell. lat.

ih fh
ee

sy /

“Ss'’<tr praeth. cin.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

PLATE 18

EXPLANATION OF FIGURES

73 Transection at the level of the commissura transversa. Weigert method.
lie

74 Transection through the same region as is shown in fig. 73. Ramén y Cajal
method. 46. Shows particularly the tractus preoptico-habenularis, pars
lateralis. In Petromyzon, according to Johnston (02), alarge portion of the fibers
of his tractus olfacto-habenularis (my tractus preoptico-habenularis) take this
course; as is also the case, but to a lesser extent, in amphibians and reptiles (Her-
rick, 710'b).

75 Cells of origin of the fasciculus retroflexus, or Meynert’s bundle. Golgi
method. 93. One of the cells possesses a long neurite which may be traced into
the fasciculus retroflexus.

com. trans., commissura transversa; fasc. lat. hem. <——, fasciculus lateralis
hemisphaeril; fasc. med. hem. <——, fasciculus medialis hemisphaeri; fasc. med.
n. opl., fasciculus medialis nervi optici; hab., habenula; nucl. preopt., pars
magnocell., nucleus preopticus, pars magnocellularis; pol. post. hem., polus
posterior hemisphaerii; tr. hyp. olf. med., tractus hypothalamo-olfactorius
medialis; tr. olf. hab., tractus olfacto-habenularis; tr. olf. thal. med., pars dors.,
tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med., pars
intermed. <——, tractus olfacto-thalamicus medialis, pars intermedia; ¢r. olf.
thal. med., pars vent., tractus olfacto-thalamicus medialis, pars ventralis; (r. opt.,
tractus opticus; tr. praeth. cin., tractus praethalamo-cinereus; tr. preopt. hab.,
partes ant. et med., tractus preoptico-habenularis, partes anterior et medialis;
tr. preopt. hab., pars lat., tractus preoptico-habenularis, pars lateralis; tr. preopt.
hab., pars post., tractus preoptico-habenularis, pars posterior ;lr. preopt.intermed.,
pars. lat., tractus preoptico-intermedius, pars lateralis.

290

OLFACTORY CENTERS IN TELEOSTS PLATE 18
RALPH EDWARD SHELDON

pol. post. hem.

tr. olf hab

ie pLeopL hab,
partes ant. et med

Wa hype oli-med:

tr olf. thal. med.,
pars intermed.

tr olf. thal. med.,
pars dors.

a
— thal. med,

ars vent

Se : nu cl) preopt.,
Se ars magnocell.
~ 4 lat. hem.

\. tr opt.
(tr praeth. cin.
tr preopt. intermed,
jj} pars lat.
77~te. praeth. cin.
= i See fasc. med. n. opt.
Tielke ae a com. trans.

ab
olf. fra:
yeopt. hab., pars post.
c. med. hem. <>
Glave Wem >

PLATE 19

EXPLANATION OF FIGURES

76 Transection through the ganglia habenularum. Weigert method. 17.

77 Transection at the level of the commissura horizontalis. Weigert method.
x ite

a, fibers, originating largely in the nucleus posthabenularis and apparently
entering the optic tract (described as an optic connection by Bela Haller); com.
hab., commissura habenularis, containing also decussating fibers of the two tractus
olfacto-habenulares; com. Herrick, commissura Herricki; com. horiz., commissura
horizontalis of Fritsch; com. trans., commissura transversa; corp. gen. lat., corpus
geniculatum laterale; fasc. lat. hem. <-—, fasciculus lateralis hemisphaerii; fasc.
med. n. opt., fasciculus medialis nervi optici; fasc. retr., fasciculus retroflexus ;
fib. tect. n. opt., fibrae tectales nervi optici (centrifugal); hab., habenula; lob. inf.,
lobus inferior; nucl. preopt., pars parvocell. post., nucleus preopticus. pars parvo-
cellularis posterior; nucl. prerot., nucleus prerotundus; nucl. vent. tub., nucleus
ventralis tuberis; tr. hab. dien .<——, tractus habenulo-diencephalicus; this is the
‘tractus habenula ad diencephalon’ of Goldstein; tr. hyp. olf. med., tractus hypo-
thalamo-olfactorius medialis; ¢r. olf. hab., tractus olfacto-habenularis; tr. olf.
thal. med., pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf.
thal. med., pars intermed. <—-—, tractus olfacto-thalamicus medialis, pars inter-
media; tr. olf. thal. med., pars vent., tractus olfacto-thalamicus medialis, pars ven-
tralis; tr. opt., tractus opticus; tr. praeth. cin., tractus praethalamo-cinereus.

292

OLFACTORY CENTERS IN TELEOSTS PLATE 19
RALPH EDWARD SHELDON

tectum.

com. hab.

hab.

Fon

fibetect a. Opt:

tr hyp olf. med.

tie Olf, thal) med:
pars dors.

tr olf. thal. med,
pors intermed<->

tr olf. thal. med.
pars vent.

fasc. lat. hem.<>s

fase. med. n opt.

a SS = : Ui procth. cin:
St = A com. trans.
76 ee
ee = a ee =
; corp gen. lat.
ae \ Arav.
/ fase. rete. »
\ . : fib. tect-m—opt. ; —

ie Olin nab:

ee Ml

~ hh, b. dien. <>

hyp. olf, med.

opt.

olf. thal. med, pars dors

olf. thal. med, pars intermed <>

. olf, thal. med, pars vent.
fase, Tat hema
nucl. preopt., pas 2) parvocell, post.

fasc. med. n. opt,
7 com, PerimcK.

ie. te, praeth. cin./

com. trans. -
COMmMe WOwlzs. =.
lob. inf. oe
peg eee
25 Yuxrcl. vent. tub.

293

PLATE 20
EXPLANATION OF FIGURES

78 Transection through the ganglia habenularum. Toluidin blue method.
x 46.

com. horiz., commissura horizontalis; corp. gen. lat., corpus geniculatum
laterale; fib. ans., fibrae ansulatae; hab., habenula, showing characteristic arrange-
ment of cells; hyp., hypophysis; lob. inf., lobus inferior; nucl. ant. thal., nucleus
anterior thalami of Goldstein; nucl. posthab., nucleus posthabenularis, ‘Das
posthabenulare Zwischenhirngebiet’ of Goldstein, ‘Die posthabenulare Zwischen-
hirngegend’ of Bela Haller; nucl. preopt., pars parvocell. post., nucleus preopticus.
pars parvocellularis posterior; nucl. prerot., nucleus prerotundus; nucl. vent. tub.,
nucleus ventralis tuberis.

294

OLFACTORY CENTERS IN TELEOSTS PLATE 20
RALPH EDWARD SHELDON

cig
.

MEANUCI. preopl., pars.

. - : 5

ucl. vent. tub.

PLATE 21

EXPLANATION OF FIGURES

79 Transection slightly caudal to the level shown in fig. 77. Weigert method.
ye lee

80 Transection through the nucleus anterior tuberis. Weigert method. > 17.

a, see fig. 76; com. Herrick., commissura Herricki; com. horiz., commissura hori-
zontalis; com. post., commissura posterior; com. trans., commissura transversa;
corp. gen. lat., corpus geniculatum laterale; fasc. lat. hem.<——, fasciculus later-
alis hemisphaerii; fasc. med. n. opt., fasciculus medialis nervi optici; fasc. retr.,
fasciculus retroflexus; fib. ans., fibrae ansulatae; fib. tect. n. opt., fibrae tectales
nervi optici; hab., habenula; hyp., hypophysis; lob. inf., lobus inferior; nucl. ant.
thal., nucleus anterior thalami; nwel. ant. tub., nucleus anterior tuberis; nucl. lat.
tub., nucleus lateralis tuberis; nucl. prerot., nucleus prerotundus; nucl. vent. tub.,
nucleus ventralis tuberis; tectum, tectum opticum; for. long., torus longitudinalis;
tr. hab. dien.——, tractus habenulo-diencephalicus; tr. hyp. olf. med., tractus
hypothalamo-olfactorius medialis; tr. olf. thal. med., pars dors., tractus olfacto-
thalamicus medialis, pars dorsalis; tv. olf. thal. med., pars intermed.<——, tractus
olfacto-thalamicus medialis, pars intermedia; tr. olf. thal. med., pars vent., tractus
olfacto-thalamicus medialis, pars ventralis; tr. opt. tractus opticus, tr. praeth, cin.,
tractus praethalamo-cinereus; tr. strio-thal. incruc.<——, tractus strio-thalami-
cus incruciatus; tr. tub. dors., tractus tubero-dorsalis; valvula, valvula cerebelli.

296

OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON

‘corp. 73en tat
tb. tect mont

hab. : dien.< >
hyp. olf. med

+ olf. thal. med, pars
. Olf. thal. med., pars dors
. olf. thal. med. pars vent

Ope

fasc. lat. hem.<>
com. Herrick.
fasc. med. n. opt.
ti praeth. ein
com. trans.

_ com. horiz,

~« dob. inf.
eee Srey nase! prerot.

79 i = ~nuchvent.t Tb \

= fase. retr

: tr. opt.
ss 4 tr: hab. dien. <>
“i hyp. olf. med.

_ nucl. ant. thal.
, corp. gen. lat.

PLATE 21

intermed. <>

a tr olf. thal. med.,pears dors.

com. trans.
fib. ans.

lob, inf.
Wee
nucl. Sea.

tx. olf. thal. med., pars
¥ olf. thal. med, pars vent.

intermed..<>

) a Strio+thal. incruc. <>

PLATE 22
EXPLANATION OF FIGURES

81 Transection through the nucleus anterior tuberis. Toluidin blue method.
X 46.

com. trans., Commissura transversa; corp. gen. lat., corpus geniculatum lat-
erale; hab., habenula; hyp., hypophysis; lob. inf., lobus inferior; mucl. ant. thal.,
nucleus anterior thalami; nucl. ant. tub., nucleus anterior tuberis; nucl. posthab.,
nucleus posthabenularis; nucl. prerot., nucleus prerotundus; nucl. vent. tub.,
nucleus ventralis tuberis; fr. opl., tractus opticus.

298

PLATE 22

OLFACTORY CENTERS IN TELEO
RALPH EDWARD SHELDON

com. trans.

nucl. prerot.

ucl.ant.tub.

uci. vent. tub.

81
hyp.

299

PLATE 23

EXPLANATION OF FIGURES

82 Transection slightly caudal to the level shown in fig. 80. Weigert method.
elie

83 Transection through the rostral end of the nucleus rotundus. Weigert
method. X 17. Shows particularly the connections between the fasciculus later-
alis hemisphaerii and the nuclei prerotundus, rotundus and diffusus lobi lateralis.

a, (see fig. 76); corp. gen. lat., corpus geniculatum laterale; com. horiz., commissura
horizontalis; com. post., commissura posterior; com. trans., commissura transversa;
fase. retr., fasciculus retroflexus; fib. ans., fibrae ansulatae; fib. tect. n. opt., fibrae
tectales nervi optici; hyp. hypophysis; lob. inf., lobus inferior; nucl. ant. thal.,
nucleus anterior thalami; nucl. ant. twb., nucleus anterior tuberis; nucl. lat. tub.,
nucleus lateralis tuberis; nucl. prerot., nucleus prerotundus; nucl. rot., nucleus
rotundus; nucl. vent. tuwb., nucleus ventralis tuberis; tr. cbl. tect. + com. horiz.,
tractus cerebello-tectalis plus the commissura horizontalis; tr. hab. dien.——,
tractus habenulo-diencephalicus; tr. hyp. olf. med., tractus hypothalamo-olfac-
torius medialis; ér. olf. hyp. lat. + tr. strio-thal. cruc., tractus olfacto-hypothalami-
cus lateralis plus the tractus strio-thalamicus cruciatus; tr. olf. thal. med., pars
dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med., pars
intermed.<——>, tractus olfacto-thalamicus medialis, pars intermedia; (r. olf. thal.
med., pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. opt.,
tractus opticus; tr. praeth. cin., tractus praethalamo-cinereus; tr. rot. lent., trac-
tus rotundo-lentiformis (Kappers); tr. strio-thal. incruc.<-—, tractus strio-
thalamicus incruciatus; shows particularly the fibers innervating the nucleus
diffusus lobi lateralis; tr. thal. mam., tractus thalamo-mammillaris (Goldstein) ;
tr. thal. sp., tractus thalamo-spinalis (Kappers); tr. tub. dors.,tractus tubero-dor-
salis.

300

OLFACTORY CENTERS IN TELEOSTS PLATE 23
RALPH EDWARD SHELDON

Com. post.
fasc.rvetr
nucl. ant. thal.
orp. gen. lat.
tr hab. dien. <>
tr hyp. olf. med.
tr olf. thal. med. pars. intermed.>
tr olf. thal. med.,pars. dors.
tr. Opt.
tr. olf. thal.med,pars. vent.
com. trans.
fib. ans.
tx strio-thal. incruc.<—>
Com: Nerz.
nucl. prerot.
ta ta bedorxs:
AUCL ants Ub:
tr strio-thal. incruc. <3
enucl. lat. tub.
Ra Wty. eth. cin.
: 1eleve@»nt. tub:

Lob atate
82 hyp.
tr col. tect.4 com -norviz

f
|

tr thal. mam.
3 ir thalssp:

ZA ty. opt.

=) com. trans.

tr hab.dien <>

tr hyp.olf. med.

tr olf. thal.med,, pays. dors.

tr olf. hyp lat.+ tr strio-thal. cruc.
4\ tx olf. thal. med, pars. vent.
4\\nucl. prerot.

A}stx strio-thal.incruc. <>

Pe: on you.

com. horiz.
Ga able) son esr

: a é lob. inf

301

PLATE 24
EXPLANATION OF FIGURES

84 Transection through the rostral end of the nucleus rotundus. Toluidin
blue method. 46.

85 Cells of the nucleus prerotundus. Toluidin blue method. » 575. From
the right nucleus. Shows the scattered arrangement of the cells and their differ-
ence in size.

86 Neurones of the nucleus prerotundus. Golgi method. X93. From sagit-
tal section.

b, cells adjacent to the recessus lateralis hypothalami (see fig. 87); com.
trans., commissura transversa; fasc. retr., fasciculus retroflexus; nuel. ant. tub.,
nucleus anterior tuberis; nucl. dif. lob. lat., nucleus diffusus lobi lateralis;
nucl. lat. tub., nucleus lateralis tuberis; nucl. posthab., nucleus posthabenularis ;
nucl. prerot., nucleus prerotundus; nucl. rot., nucleus rotundus ; nucl. vent. tub.,
nucleus ventralis tuberis.

OLFACTORY CENTERS IN TELEOSTS PLATE 24
RALPH EDWARD SHELDON

Inuwel. rot.

hucl. ant.
tub.

alrenerelealinits
lob. lat.

PLATE 25

EXPLANATION OF FIGURES

87-88 Neurones of the nucleus prerotundus, Golgimethod. X93. From sag-
ittal sections.

89 Transection immediately caudal to the level of the commissura posterior.
Toluidin blue method. X 46.

90 Cells of the nucleus rotundus. Toluidin blue method. ™X 575. Shows the
typical arrangement of the cells in scattered groups.

com. post., commissura posterior; fasc. retr., fasciculus retroflexus; nucl. ant.
tub., nucleus anterior tuberis; nucl. cbl. hyp., nucleus cerebellaris hypothalami;
‘nucl. dif. lob. lat., nucleus diffusus lobilateralis; nucl. prerot., nucleus prerotundus ;
nucl. rot., nucleus rotundus; rec. lat. hyp., recessus lateralis hypothalami.

304

OLFACTORY CENTERS IN TELEOSTS PLATE 25
RALPH EDWARD SHELDON

nucl.dif.
lob. lat.

305

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. ¢

PLATE 26

EXPLANATION OF FIGURES

91-94 Neurones of the nucleus rotundus. Golgi method. X93. From sagit-
tal sections.

95-99 Neurones from different parts of the lobi laterales. Golgi method. X
93. From sagittal sections. Fig. 95 is taken from the caudal angle of the lobe,
fig. 96 from the ventro-medial area, fig. 97 from the latero-medial, figs. 98 and 99
from the ventral area proper.

100 Transection at approximately the same level as that shown in fig. 89.
Weigert method. X 17.

com. horiz., commissura horizontalis; com. post., commissura posterior; com.
trans., commissura transversa; fasc. retr., fasciculus retroflexus; nucl. ant. tub.,
nucleus anterior tuberis; nucl. dif. lob. lat., nucleus diffusus lobi lateralis; nucl.
prerot., nucleus prerotundus; nucl. rot., nucleus rotundus; tr. cbl. tect. + com.
horiz., tractus cerebello-tectalis plus commissura horizontalis; tr. hab. dien.
<——, tractus habenulo-diencephalicus; tr. hyp. olf. med., tractus hypothalamo-
olfactorius medialis; tr. olf. thal. med., pars dors., tractus olfacto-thalamicus
medialis, pars dorsalis; tr. olf. thal. med., pars vent., tractus olfacto-thalamicus
medialis, pars ventralis; tr. rot. lent., tractus rotundo-lentiformis; tr. strio-thal.
cruc.+ tr. olf. hyp. lat., tractus strio-thalamicus cruciatus plus tractus olfacto-
hypothalamicus lateralis; tr. thal. mam., tractus thalamo-mammillaris; tr. thal.
sp., tractus thalamo-spinalis.

306

OLFACTORY CENTERS IN TELEOSTS PLATE 26
RALPH EDWARD SHELDON

= tr rot: lent.

100 oI ee — tr ebl, tect. + com, horiz.
com. post.
fasc.retr
te. thal. mam.
3 | Waltell MS ioe

“com. trans.
We hab. dien.<>
y ants hyp. olf.med.
; nucl. prerot,

tk strio-thal. cruc.+tx olf.

3 hyp. lat.
om tr olf. thal.med., pars dors.
| tr. olf. thal.med. pors’ vent.
ee nucl. ‘rot.
com. horiz.

gp nucl. pA. tub.

nucl. dif. lob. Jat.

PLATE 27
EXPLANATION OF FIGURES

101 Transection slightly caudal to the level shown in fig. 100. Weigert
method. X 17.

102. Transection through the decussation of the tractus hypothalamo-olfactoru
mediales. Ramon y Cajal method. X 46.

com. horiz., commissura horizontalis; com. post., commissura posterior; com.
trans., commissura transversa; dec. tr. hyp. olf. med., decussatio tractorum olfac-
toriorum medialium; fasc. retr. fasciculus retroflexus; lob. lat. hyp., lobus lateralis
hypothalami; lob. med. hyp., lobus medialis hypothalami; nucl. dif. lob. lat.,
nucleus diffusus lobi lateralis; nucl. prerot., nucleus prerotundus; nucl. rot.,
nucleus rotundus; nucl. subrot., nucleus subrotundus; rec. lat. hyp., recessus
lateralis hypothalami; tr. cbl. tect. + tr. rot. lent. + com. horiz., tractus cerebello-
tectalis plus tractus rotundo-lentiformis plus commissura horizontalis; tr. hab.
dien.<——, tractus habenulo-diencephalicus; tr. hyp. olf. med., tractus hypo-
thalamo-olfactorius medialis; tr. olf. thal. med., pars dors., tractus olfacto-tha-
lamicus medialis, pars dorsalis; tr. olf. thal. med., pars vent., tractus olfacto-
thalamicus medialis, pars ventralis; tr. rot. lob., tractus rotundo-lobaris; tr. strio-
thal. cruc. + tr. olf. hyp. lat., tractus strio-thalamicus cruciatus plus tractus
olfacto-hypothalamicus lateralis; ¢r. thal. mam., tractus thalamo-mammillaris; tr.
thal. sp., tractus thalamo-spinalis (KKappers).

308

OLFACTORY CENTERS IN TELEOSTS PLATE 27
RALPH EDWARD SHELDON

Gom)) post
ty. cbl tect +tr rot. lent. +
com. horiz.
A fasc, retr.
4 / tr. thal. sp.
tr. thal. mam.
com. trans.
nuc]. prerot.
tre hyp. olf. med.
~~ tr. Strio-thal. cruc.
ae = tr. olf. hyp. lat.
Ze tr hab. dien. <>
*~nuc). rot.
tr olf. thal. med. pars dors.
Sa Ste olf thal. med., pars vent.
com. hor1z.

hy tx ¥ot. lob.
Re ec late ny:
; Job, iat. hyp.

—. Fe lob.med. hyp.
SH) <snuerl, dif. lob. lat.
Pi SS

Zar: 3

_fasc/ retr

nucl. prerot.

wel Lot:

PLATE 28

EXPLANATION OF FIGURES

103. Transection through the nucleus posterior tuberis. Toluidin blue method.
x 46.

104 Oblique longitudinal section showing the origin of the tractus hypothal-
amo-olfactorius medialis. Golgimethod. 9.

105 Neurone of originof the tractus hypothalamo-olfactoriusmediahs. Golgi
method. 93. Taken from same section as fig. 104.

chiasma, optic chiasma; corp. precom., corpus precommissurale; crus olf., crus
olfactorium; n. opt., nervus opticus; nucl. cbl. hyp., nucleus cerebellaris hypo-
thalami; nucl. dif. lob. lat., nucleus diffusus lobi lateralis; wwel. post. thal., nucleus
posterior thalam1i; nucl. post. tub., nucleus posterior tuberis; nucl. prerot., nucleus
prerotundus; nucl. rot., nucleus rotundus; rec. lat. hyp., recessus lateralis hypo-
thalami; sac. vasc., saccus vasculosus; tela, membranous roof of forebrain; tr.
cbl. hyp., tractus cerebello-hypothalamicus; tr. hyp. olf. med., tractus hypothal-
amo-olfactorius medialis; tr. opl., tractus opticus; tr. strio-thal., tractus strio-
thalamicus; ¢r. thal. str., tractus thalamo-striaticus; valoula, valvula cerebelli.

310

OLFACTORY CENTERS IN TELEOST
RALPH EDWARD SHELDON

PLATE 28

nu¢l. cbl. hyp.

re¢. lat. hyp.

nicl. dif. lob.
lat.

Wel post
tub. P

valvula. neurite.

tr hyp. olf. med

hnucl. post tub

thal. str

104

31]

PLATE 29
EXPLANATION OF FIGURES

106 Transection through the Haubenwulst. Toluidin blue method. X 46.

107 Transection through the nucleus subrotundus. Toluidin blue method.
x47. Detail cells. X 575. Shows the characteristic grouping of the cellsin the
center of the nucleus (see fig. 106). From right side.

108 Cells of the nucleus cerebellaris hypothalami. Toluidin blue method.
% 575. Shows typical scattered arrangement of the cells (see figs. 103 and 106).

nucl. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. lat., nucleus
diffusus lobi lateralis; nucl. fasc. long. med., nucleus fasciculi longitudinalis
medialis; nucl. post. thal., nucleus posterior thalami; nucl. prerot., nucleus
prerotundus; nucl. rot., nucleus rotundus; nucl. subrot. nucleus subrotundus;
rec. lat. hyp., recessus lateralis hypothalami.

312

OLFACTORY CENTERS IN TELEOS

RALPH EDWARD SHELDON

PLATE 29

’ long.

108

313

PLATE 30

EXPLANATION OF FIGURES

109 Cells of the nucleus posterior thalami. Toluidin blue method. 575.

110-113 Neurones of the nucleus posterior thalami. Golgi method. 93.
From sagittal sections. As will be noted, the cells of this nucleus are very large.
They appear larger in sagittal than in transverse sections, both in toluidin blue
and Golgi material.

114 Transection at approximately the same level as that shown in fig. 106.
Weigert method. X 17.

com. horiz., commissura horizontalis; com. post., commissura posterior; com.
trans., commissura transversa; fasc. retr., fasciculus retroflexus; nucl. dif. lob. lat.,
nucleus diffusus lobi lateralis; nucl. post. twb., nucleus posterior tuberis; nucl.
prerot., nucleus prerotundus; nucl. rot., nucleus rotundus; nucl. subrot., nucleus
subrotundus; sac. vasc., saccus vasculosus; tr. cbl. tect. + tr. rot. lent. + com.
horiz., tractus cerebello-tectalis plus tractus rotundo-lentiformis plus commissura
horizontalis; tr. cbl. hyp., tractus cerebello-hypothalamicus; tr. olf. thal. med.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med.,
pars vent., tractus olfacto-thalamicus medialis, pars ventralis; tr. rot. lob., tractus
rotundo-lobaris; tr. thal. mam., tractus thalamo-mammillaris; tr. thal. sp., tractus
thalamo-spinalis (Kappers).

314

OLFACTORY CENTERS IN TELEOSTS

PLATE 30
RALPH EDWARD SHELDON

oo 111

iis

S 2) | tr. cbl. tect+ tr rot. lent.+com. horiz
Pa com. post.
a a fASc. retr
rates ome tx thal. sp.
# =*-com,. trans.
ee: oe SERRE a LN + tr thal. mam.
—= SF GER yas een serra at zsh | nucl, prerot.
tt Gb hyp:
if nucl. sot.
com. horiz.
tr olf. thal. med., pars vent.
tr olf. thal. med, pars dors.
nucl. Subrot.
apetr, FOr. lob.
A ‘Nuci. post. tub.

315

PLATE 31

EXPLANATION OF FIGURES

115 Transection slightly caudal to the level shown in fig. 114. Weigert method.
< ee

116 Transection slightly caudal to the level shown in fig. 115. Weigert method.
alive

com. horiz. + tr. rot. lent., commissura horizontalis plus tractus rotundo-
lentiformis; com. trans., commissura transversa; corp. mam. (@), corpus mammil-
lare, the ganglion mammillare of Goldstein; fasc. retr., fasciculus retroflexus ;
nucl. dif. lob. lat., nucleus diffusus lobi lateralis; nucl. post. thal., nucleus posterior
thalami; nucl. post. tub., nucleus posterior tuberis; nucl. prerot., nucleus prero-
tundus; nucl. rot., nucleus rotundus; nucl. subrot., nucleus subrotundus; sac. vasc.,
saceus vasculosus; tr. cbl. tect., tractus cerebello-tectalis; tr. cbl. tect. + tr. rot.
lent. + com. horiz., tractus cerebello-tectalis plus tractus rotundo-lentiformis plus
commissura horizontalis; tr. cbl. hyp., tractus cerebello-hypothalamicus; tr. olf.
thal. med., pars. dors., tractus olfacto-thalamicus medialis, pars dorsalis; its con-
nection with the nucleus subrotundus comes out with great clearness in these
figures; tr. olf. thal. med., pars. vent., tractus olfacto-thalamicus medialis, pars
ventralis; in fig. 116, immediately lateral to the nucleus rotundus, is shown the
termination of this tract; tv. rot. lob., tractus rotundo-lobaris; tr. thal. mam..,
tractus thalamo-mammillaris; tr. thal. sp., tractus thalamo-spinalis (Kappers.)

316

PLATE 31

OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON

peesicanng id nee Ns. tr. col. tect+tx vot .lentscom. horiz.

gh eee Gtr. thal. sp.

See meets | ~6COmM. trans.

tx thal. mam.

COM. MOM Zar tie cot, lent:

AUG IOS. inal:

nucl. prerot.

tr olf. thal. med, pars vent.

Nucl you

WS: tr olf. thal.med., pars dors.
Ste Ot. loeb:

Swell Supe

MUvela Bost. «cul:

ENC asp.

“nuch dif. loeb. lat.

gts HbAC~VASCG.

Peale tr, cbl. tect.
pee: : a« fasc. retr
en ee ix. thal. sp.

tr. olf. thal. med, pars vent.
nucl. xot.
tx. ¢cbl. hyp:

trolf.thal. med, pars dors.
nucl. subrot.

tr. rot. lob.

Orp. mam. G).

PLATE 32

EXPLANATION OF FIGURES

117 Transection through the corpus mammillare, the ganglion mammillare of
Goldstein. Toluidin blue method. X 46.

118 Cells of the corpus mammillare. Toluidin blue method. 575.

119-121 Neurones of the corpus mammillare. Golgi method. 93. From
sagittal sections. It will be noted from figs. 117 to 121 that the cells of the corpus
mammillare are very small and closely packed.

corp. mam. (G@), corpus mammillare, the ganglion mammillare of Goldstein;
nucl. cbl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. lat., nucleus
diffusus lobi lateralis; nucl. fasc. long., nucleus fasciculus longitudinalis medialis;
nucl. post. thal., nucleus posterior thalami; nucl. prerot., nucleus prerotundus ;
nucl. rot., nucleus rotundus; nucl. rub. (@), nucleus ruber of Goldstein; nucl.
subrot., nucleus subrotundus; s. mam., suleus mammillaris of Goldstein; tr. cbl.
tect., tractus cerebello-tectalis.

318

OLFACTORY CENTERS IN TELEOSTS PLATE 32
RALPH EDWARD SHELDON

Tl Sng
ésQjons. med.
a.

‘

"tx ebl.tect,

\ nucl. subsot.

lob. lat.

319

PLATE 33
EXPLANATION OF FIGURES

122 Transection through the corpus mammillare. Weigert method. > 17.

123 Diagram showing the two parts of the right olfactory nerve, and the rela-
tions of their fibers to the cells of the bulb and to the fibers of the olfactory tract.

124 Diagram of a horizontal projection of the right olfactory bulb showing the
connections, in the bulb, of the different tracts of the crura.

corp. mam. (G), corpus mammillare (of Goldstein); fasc. retr., fasciculus
retroflexus; fil. olf., filaolfactoria; g.n.term., ganglion cell of the nervus terminalis;
gran. cell, granule cell of the nucleus olfactorius anterior; mitr. cell, mitral cell;
nucl. chl. hyp., nucleus cerebellaris hypothalami; nucl. dif. lob. lat., nucleus dif-
fusus lobi lateralis; n. olf. ant., nucleus olfactorius anterior; 7. olf. lat., nervus ol-
factorius lateralis, consisting largely of fibers from the lamellae of the caudal and
lateral portion of the olfactory capsule; n. olf. med., nervus olfactorius medialis,
formed largely from fibers originating chiefly in the rostral and medial portion of
the capsule; n.term.,nervusterminalis; nucl. prerot., nucleus prerotundus ;nucl. rot.,
nucleus rotundus; nucl. subrot., nucleus subrotundus;s. mam., sulcus mammillaris;
tr. cbl. tect., tractus cerebello-tectalis; tr. olf. asc., tractus olfactorius ascendens,
composed of centrifugal fibers from the corpus precommissurale, pars medianus;
tr. olf. asc., pars lat., tractus olfactorius ascendens pars lateralis; tr. olf.
asc., pars med., tractus olfactorius ascendens, pars medialis; tr. olf. lat., trac-
tus olfactorius lateralis, composed of the following three tracts, all centri-
petal, and practically all terminating, in the carp, in the nucleus olfactorius
dorsalis and nucleus pyriformis of the same side; fr. olf. lat., pars. intermed., trac-
tus olfactorius lateralis, pars intermedia; tr. olf. lat., pars lat., tractus olfactorius
lateralis, pars lateralis; tr. olf. lat., pars med., tractus olfactorius lateralis, pars
medialis; tr. olf. med., tractus olfactorius medialis, the mesal part of the medial
olfactory radix of authors, divided into the following; tr. olf. med., pars lat.,
tractus olfactorius medialis, pars lateralis, terminating, after decussation in the
anterior commissure, in the nucleus pyriformis of the opposite side; tr. olf. med.,
pars med., tractus olfactorius medialis, pars medialis, forming the commissura
interbulbaris of most authors which, as indicated in figs. 136 and 138, is largely
a decussation and not a commissure; tr. thal. sp., tractus thalamo-spinalis
(Kappers).

320

OLFACTORY CENTERS IN TELEOSTS
RALPH EDWARD SHELDON

PLATE 33

Spee. el tect,

ae fasa retr
= ti thal: sp:

nucl, prerot
PMULSIen Acts

L nucl. subrot,
--nucl. cbl. hyp,
‘corp. mam. G)

= nucl. dif. lob. lat.
smam.

n_olf. med.

Ten@ uheelietes
@.n.term.
lane lite
eran. cell
n.olf ant.
mitr cell.
n.term.

tr. olf. med.
tr. olf. asc.
Taz Olie latte

123

LIZ OlEASes PaiSulat
tr olf. asc., pars med.
tr olf. med., pars lat.
tr olf. med. pars med.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 3

PLATE 34
EXPLANATION OF FIGURES

125 Diagram of a projection of the olfactory centers on a parasagittal plane,
near the meson, showing the levels at which figs. 127 and 128 are taken and the
relation of the different centers to the four primitive columns. X II.

1, pars dorso-medialis hemisphaerii and epithalamus; 2, pars dorso-lateralis
hemisphaerii and pars dorsalis thalami; 3, pars ventro-lateralis hemisphaerii and
pars ventralis thalami; 4, pars ventro-medialis hemisphaerii and hypothalamus;
tr. olf. lat., tractus olfactorius lateralis; tr. olf. med., tractus olfactorius medialis.

(For other abbreviations see explanation of fig. 141.)

PLATE

OLFACTORY CENTERS IN TELEOSTS

RALPH EDWARD SHELDON

‘¥ep HO 44

HO ‘qinq

Geol

TH cred

a4au s#ed

‘sis AUdodAy

1d ~d4i0d

/
?
ena a ae a

4
4

“Q]N ATCA

Foy YP Tonu

323

PLATE 35
EXPLANATION OF FIGURES

126 Diagram of a transection through the hemispheres of an embryonic teleost,
showing the relations of the four primitive columns.

127 Diagram of a transection through the hemispheres of an adult teleost,
showing the changes which have taken place through rearrangement of these
columns. For approximate level see fig. 125

128 Diagram of a transection through the diencephalon of an embryonic tele-
ost, showing the relations of the same columns. Practically the same conditions
hold in the adult. (For level see fig. 125.)

129-134 Diagrams of transections through the cerebral hemispheres of Ameiu-
rus, at the level of the anterior commissure, showing the shifting which takes place
with the gradual eversion of the tenia. Figs. 129 to 133 are camera lucida drawings
obtained through the kindness of Dr. James M. Wilson, of Washington, D. C.
Fig. 129, 5 mm. stage; fig. 130,6mm. stage; fig. 131, 9mm. stage; fig. 132, 10 mm.
stage; fig. 133, 12-13 mm. stage; fig. 134, adult.

135 Transection through the cerebral hemispheres of Amia calva in the region
of the anterior commissure, to illustrate the eversion of the hemisphere wall,
after Mrs. Susanna Phelps Gage (793).

1, pars dorso-medialis hemisphaerii and epithalamus; 2, pars dorso-lateralis
hemisphaerili and pars dorsalis thalami; 3, pars ventro-lateralis hemisphaeri
and pars ventralis thalami; 4, pars ventro-medialis hemisphaerii and hypo-
thalamus; epithal., epithalamus; hypothal., hypothalamus; pars dors. thal., pars
dorsalis thalami; pars vent. thal., pars ventralis thalami; s. lim. tel., sulcus
limitans telencephali; sulc. dien. dors. suleus diencephalicus dorsalis; sulc. dien.
med., suleus diencephalicus medialis; sule. dien. vent., sulcus diencephalicus
ventralis.

OLFACTORY CENTERS IN TELEOSTS PLATE 35
RALPH EDWARD SHELDON

134

PLATE 36

EXPLANATION OF FIGURES

136 Diagram of a horizontal projection of the olfactory centers showing in
blue the connections of the corpus precommissurale, together with the fiber com-
ponents of the fasciculus medialis hemisphaerii and associated tracts. X 12.

bulb. olf., bulbus olfactorius; c. mam., corpus mammillare, ganglion mammil-
lare of Goldstein; corp. precom., corpus precommissurale, consisting of the pars
medianus, pars commissuralis, and pars supracommissuralis; crus olf., crus
olfactorium; ent., nucleus entopeduncularis; fib. precom. str., fibrae precommis-
surales striatici, running from the precommissural body to the palaeostriatum ;
hab., ganglion habenulae; hyp., hypophysis; m., pars magnocellularis of the nu-
cleus preopticus; n. ant. tub., nucleus anterior tuberis; n. cbl. hyp., nucleus cere-
bellaris hypothalami of Goldstein; n.c./., nucleus commissuralis lateralis ; 7.
dif. lob. lat., nucleus diffusus lobilateralis; n. int., nucleus intermedius; ”. lat. tub.,
nucleus lateralis tuberis; n. olf. lat., nucleus olfactorius lateralis; n. posthab.,
nucleus posthabenularis; n. post. thal., nucleus posterior thalami of Goldstein;
n. post. tub., nucleus posterior tuberis; n. preopt., nucleus preopticus; n. prerot.,
nucleus prerotundus; 7. pyr., nucleus pyriformis; n. rot., nucleus rotundus; n.
subr., nucleus subrotundus; n. ten., nucleus tenlae; n. lerm., nervus terminalis;
p.a., pars parvocellularis anterior of the nucleus preopticus; paleostr., palaeostria-
tum, the striatum of most authors; pars. com., pars commissuralis of the corpus
precommissurale; pars. med., pars medianus or the nucleus medianus of the corpus
precommissurale; p.p., pars parvocelluiaris posterior of the nucleus preopticus; p.
sup. com., pars supracommissuralis of the corpus precommissurale; sac. vasc., sac-
cus vasculosus; lela, the so-called pallium; tr. hyp. olf. med., tractus hypothalamo-
olfactorius medialis; tr. med. preopt., pars ant., tractus mediano-preopticus, pars
anterior; tr. med. preopt., pars post., tractus mediano-preopticus, pars posterior;
tr. olf. asc., tractus olfactorius ascendens; tr. olf. asc., pars lat., tractus olfactorius
ascendens. pars lateralis; tr. olf. asc., pars med., tractus olfactorius ascendens,
pars medialis; tr. olf., med., pars lat., tractus olfactorius medialis, pars lateralis;
tr. olf. med., pars. med., tractus olfactorius medialis, pars medialis; tr. olf. thal. med.,
pars dors., tractus olfacto-thalamicus medialis, pars dorsalis; tr. olf. thal. med.,
pars intermed., tractus olfacto-thalamicus medialis, pars intermedia (short des-
cending association fibers); tr. olf. thal. med. pars vent., tractus olfacto-thalamicus
medialis, pars ventralis; tr. opl., tractus opticus; tr. preopl. tub., tractus preoptico-
tuberis; tr. thal. olf. med., pars intermed., tractus thalamo-olfactorius medialis,
pars intermedia (short ascending association fibers).

326

OLFACTORY CENTERS IN TELEOSTS PLATE 36
RALPH EDWARD SHELDON

————~_—

te Clase, Pato: (Ot
tr olf. asc., pars. med
t+. olf. med., pars med.
Stenm:

tx. olf, med., pors. lat.

tr. olf. asc.

D\ precom. str

ned. preopt., pars ant.

. olf. thal. med. pars vent.
+/olf. tha). med. pars dors.
. hyp, olf. med.

tr. med. preopt., pars post.
tia preopt, twp:
tr olf. thal. med. pars intermed

tr thal. olf. med., pars inlermed.

PLATE 37

EXPLANATION OF FIGURES

137 Diagram of a horizontal projection of the olfactory centers showing the
connections of the nucleus pyriformis, nucleus teniae, nucleus olfactorius later-
alis, and nucleus intermedius. On the right side are shown the tracts terminat-
ing in these nuclei, on the left side the tracts originating in them. X 12.

com. hab. (red), com. habenularum; tr. entoped. intermed. (red), tractus ento-
pedunculo-intermedius; tr. hyp. olf. lat. (blue), tractus hypothalamo-olfactorius
lateralis; tr. intermed. entoped. (red), tractus intermedio-entopeduncularis; ¢r.
intermed. hab., pars ant. (red), tractus intermedio-habenularis, pars anterior; ¢r.
intermed. hab., pars post. (red), tractus intermedio-habenularis, pars posterior;
tr. intermed. posthab. (blue), tractus intermedio-posthabenularis; tr. intermed.
preopt. pars ant. (ved), tractus intermedio-precopticus, pars anterior; tr. inter-
mod. preopt., pars med. (red), tractus intermedio-preopticus, pars medialis; fr.
olf. hyp. lat. (blue), tractus olfacto-hypothalamicus lateralis; tr. olf. lat. (blue),
tractus olfactorius lateralis; tr. olf. lat., pars intermed. (blue), tractus olfactorius
lateralis, pars intermedia; tv. olf. lat., pars med. (blue), tractus olfactorius later-
alis, pars medialis; tr. olf. med., pars lat. (blue), tractus olfactorius medialis, pars
lateralis; tr. posthab. intermed. (blue), tractus posthabenulo-intermedius; ¢r.
praeth. cin. (blue), tractus praethalamo-cinereus; tr. preopt. intermed., pars ant.
(red), tractus preoptico-intermedius, pars anterior; tr. preopt. intermed., pars
lat. (red), tractus preoptico-intermedius, pars lateralis; tr. preopt. intermed.,
pars med. (red), tractus preoptico-intermedius, pars medialis; tr. ten. (red), trac-
tus teniae, the tractus olfacto-habenularis of Kappers, Goldstein, ete. (For
other abbreviations see explanation of fig. 136.)

328

OLFACTORY CENTERS IN TELEOSTS PLATE 37
RALPH EDWARD SHELDON

tr. olf. lat., pars lat

tr olf, lat, pars intermed.
tr. olf lat. pars med

tr. olf med.,pars lat.

tela.

ie Olflat

Fk ten

intermed preopt., pars ant.
termed. hab., pars ant.
termed. preopt., pars med.
termed. entoped.

nucl. olf, lat.
palaeostr.

t Intermed. hab., pars post.
VA Ly practh. icin:
7—~tr precpt. intermed., pars med.
tx preopt. intermed., pars ant.
tr entoped. intermed.
tr preopt. intermed., pars Jat.
com. hab,
tr posthab. interred.

. hyp. olf. Jat.
tr\ of hyp Jat.

PLATE 38

EXPLANATION OF FIGURES

138 Diagram of a horizontal projection of the olfactory centers, showing the
fibers entering into the composition of the anterior commissure, together with
their connections. X 12.

com. corp. precom. (green), Commissura corporium precommissuralium; com.
dors. (green), commissura dorsalis; com. hipp., pars ant. (green), commissura
hippocampi, pars anterior; connecting the two nuclei olfactorii dorsales or
primordia hippocampi; com. hipp., pars post. (green), commissura hippocampi,
pars posterior, the commissura internuclearis of Goldstein; com. interbulb., (dec.
tr. olf. med., pars med.) (blue), commissura interbulbaris (decussation of the
tractus olfactorii mediales, partes mediales); com. nucl. preopt. (green), commis-
sura nucleorum preopticorum; dec. n. term. (blue), decussatio nervorum termina-
lium; dec. tr. olf. med., pars lat. (blue), decussation of the tractus olfactoru
mediales, partes laterales; gang. n. term. (blue), ganglion cell of the nervus
terminalis; 7. term. (blue), nervus terminalis; tr. hyp. olf. med. (red), tractus
hypothalamo-olfactorius medialis; tr. olf. med. (blue), tractus olfactorius medialis ;
tr. olf. med., pars lat. (blue), tractus olfactorius medialis, pars lateralis; tr. olf.
med. pars med. (blue), tractus olfactorius medialis, pars medialis; tr. strio-thal.
cruc. (red), tractus strio-thalamicus cruciatus (shown only on one side); tr.
thal. str. cruc. (ved), tractus thalamo-striaticus cruciatus, (shown only on oneside).
(For other abbreviations see explanation of fig. 136.)

330

OLFACTORY CENTERS IN TELEOSTS PLATE 38

RALPH EDWARD SHELDON
—————-__

gong. n. term.

bulb. olf.

n. term
te oli med> pass med:
tr olf. med., pars Jat.

oO
Vv
at)

tr olf. med.

com. corp. precom.

+4 bi

a ie n. term.

Ke) be om. hipp., pars ant.

y oe ; . Interbulb., dec. tr olf. med.,

pars med)
—/gom. dors.
7~+te. hyp. olf. med.

SSS
: ow / com. hipp., pars post.
He ms dec. tx olf. med, pars lat.

€:! | tr. strio-thal. cruc.
if \ Nt thal. sti cruc.
Z com. nuc]. preopt.
. f=

138

PLATE 39

EXPLANATION OF FIGURES

139 Diagram of a horizontal projection of the olfactory centers showing
in blue the pathways of the fibers entering into the composition of the fas-
ciculus lateralis hemisphaerii. The ascending fibers are shown on the right, the
descending on the left. > 12.

fib. precom. str., fibrae precommissurales striatici; ér. olf. hyp. lat., tractus
olfacto-hypothalamicus lateralis; tr. strio-thal. cruc., tractus strio-thalamicus
cruciatus; tr. strio-thal. incruc., tractus strio-thalamicus ineruciatus; tr. thal. str.
cruc., tractus thalamo-striaticus cruciatus; tr. thal. str. incruc., tractus-thalamo-
striaticus incruciatus. (For other abbreviations see explanation of fig. 136.)

302

OLFACTORY CENTERS IN TELEOSTS PLATE 39
RALPH EDWARD SHELDON

tela.

precom. str

hal. str. cruc.
. /strio-thal. cruc.
. strio-thal. incruc.
* thal. str incruc.
tr olf. hyp. lat.

“

Wc). olf, Jat.

139

333

PLATE 40

EXPLANATION OF FIGURES

140 Diagram of a horizontal projection of the olfactory centers showing the
connections of the postecommissural olfactory nuclei, with the exception of the
habenular fibers shown on fig. 142. Fibers which terminate in these centers are
shown on the right, while those which originate from them appear on the left.
<lZ:

com. nucl. preopt. (red), commissura nucleorum preopticorum; tr. entoped.
preopt. (red), tractus entopedunculo-preopticus; tr. intermed. preopt., pars ant.
(red), tractus intermedio-preopticus, pars anterior; tr. intermed. preopt., pars med.
(red), tractus intermedio-precpticus, pars medialis; tr. lat. preopt. (red), tractus
lateralis preopticus;tr. med. preopt., pars ant. (blue), tractus mediano-preopticus,
pars anterior; tr. med. preopt., pars post. (blue), tractus mediano-preopticus, pars
posterior; tr. olf. med., pars lat. (blue), tractus olfactorius medialis, pars lateralis
(see fig. 186); tr. posthab. preopt. (red), tractus posthabenulo-preopticus; ¢r.
practh. cin. (blue), tractus praethalamo-cinereus: tr. preopt. entoped. (red),
tractus preoptico-entopeduncularis; tr. preopt. intermed., pars ant. (red), tractus
preoptico-intermedius, pars anterior; tr. preopt. intermed., pars lat. (red), tractus
preoptico-intermedius, pars lateralis; tr. preopt. intermed., pars med. (red), tractus
preoptico-intermedius, pars medialis; tr. preopt. lat. (red), tractus preoptico-
lateralis; tr. preopt. posthab. pars ant. (red) tractus preoptico-posthabenularis,
pars anterior; tr. preopt. posthab., pars post. (red), tractus preoptico-posthab-
enularis, pars posterior; tr. preopt. tub. (blue), tractus preoptico-tuberis. (For
other abbreviations see explanation of fig. 136.)

334

OLFACTORY CENTERS IN TELEOSTS PLATE 40

RALPH EDWARD SHELDON

6
ov
WY

tr olf. med., pars Jat.

tr med. preopt., pars ant.

tr. preopt. intermed., pars ant.
fi, preopt. lat.

mn. nucl. preopt.

ntermed. preopt., pars ant.
lat. preopt.

nucl]. olf, Jat.
palaeostr

+. Intermed. preopt., pass med.

tr preopt. intermed., pars med.

preopt. entoped.
; entoped.preopt.

. preopt. intermed.,, pars lat.

. preopt. posthab., pars post.

\tr posthab. preopt.
ses preopt. posthab., pars ant.
tx praeth. cin.

140
tx preopt. tub.

PLATE 41
EXPLANATION OF FIGURES

141 Diagram of a projection of the olfactory centers on a para-sagittal plane
near the meson, showing the components of the tractus olfacto-habenularis, and
their connections, in black (cf. Goldstein, Taf. 11, fig.7). 12.

chias., optic chiasma; com. corp. precom. + com. hipp. pars ant., commissura
corporium precommissuralium plus commissura hippocampi, pars anterior; com.
hab., commissura habenularum; com. Herrick, commissura Herrick1; com. horiz.,
commissura horizontalis; com. interbulb. (dec. tr. olf. med., pars med.) commissura
interbulbaris (decussation of the tractus olfactori mediales, partes mediales) ; com.
nucl. preopt., commissura nucleorum preopticorum; com. trans., commissura trans-
versa; corp. mam., corpus mammillare; corp. pin., corpus pineale; corp. precom.,
corpus precommissurale; crus olf., crus olfactorium; dec. n. term., decussatio
nervorum terminalium; dec. tr. hyp. olf. med. + dec. tr. olf. med., pars lat. + com.
dors. + com. hipp., pars post., decussation of the tractus hypothalamo-olfactoril
mediales, plus decussation of the tractus olfactorii mediales, partes laterales, plus
commissura dorsalis, plus commissura hippocampi, pars posterior; fasc. retr., fas-
ciculus retroflexus; fib. ans., fibrae ansulatae; hab., ganglion habenulae; n. ant. tub.,
nucleus anterior tuberis; 7. opt., nervus opticus; n. post. tub., nucleus posterior
tuberis; nucl. dif. lob. lat., nucleus diffusus lobi lateralis; nucl. posthab., nucleus
posthabenularis; nucl. preopt., nucleus preopticus; nucl. rot., nucleus rotundus;
pars gland., pars glandularis of the hypophysis; pars med., pars medialis of the
corpus precommissurale; pars nerv., pars nervosa of the hypophysis; pars p.c.
post., pars parvocellularis posterior of the nucleus preopticus; p.m., pars magno-
cellularis of the nucleus preopticus; p. p. c. ant., pars parvocellularis anterior of
the nucleus preopticus; p. suwpracom., pars supracommissuralis of the corpus pre-
commissurale; tectum, tectum mesencephali; fela, so-called pallium; tr. dien. hab.,
tractus diencephalo-habenularis; tr. entoped. hab., tractus entopedunculo-haben-
ularis; tr. hab. dien., tractus habenulo-diencephalicus; (7. intermed. hab., parsant.,
tractus intermedio-habenularis, pars anterior; ¢r. intermed. hab., pars post., trac-
tus intermedio-habenularis, pars posterior; tr. olf. hab., tractus olfacto-habenu-
laris; tr. posthab. hab., tractus posthabenulo-habenularis; tr. preopt. hab., pars
ant., tractus preoptico-habenularis, pars anterior; tr. preopt. hab., pars lat.,
tractus preoptico-habenularis, pars lateralis; tr. preopl hab., pars med., tractus
preoptico-habenularis, pars medialis;tr. preopt. hab., pars post., tractus preoptico-
habenularis, pars posterior; tr. strio-thal. cruc., decussation of the tractus strio-
thalamici cruciati; tr. leniae, tractus tenlae; valvula, valvula cerebelli. (See
also fig. 125.)

336

PLATE 41

‘DUIS sArd ‘AAaU o4ed

aces

fips was ;
: “APs, Gn} 4UeU\\ gn}, “Wew 40d.
Sy. 460d : » Aye+ ose
| [ saed “geU ’ ydoend # “$3
C : ie i, OF OnWw Ss
qdo-u Np . smeeg lS erp -gean
: Lily won 4 — - S
que saed “qey-ydoasd 47 asoftod aaa ae iat Se ela ma
‘JOGA \ ‘pow cred ~ A SITET. qeuysod +43
a \ ‘WAST U Sone mews i “JSsod BS ded Meese 44
poi nee Mae Pee ae
{ Mes ‘wWose4dned
maker “Sepuay AY
ie ored ‘ “ey IESE or

viet ~~ _‘qey wos
. Q[NAIRA

22. NOw a

337

OLFACTORY CENTERS IN TELEOSTS

RALPH EDWARD SHELDON

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL,

PLATE 42

EXPLANATION OF FIGURES

142 Diagram 0° a horizontal projection of the olfactory centers showing, in
red, the components of the tractus olfacto-habenularis and their connections.
x 12.

com. hab., commissura habenularum, or commissura superior; fasc. relr.,
fasciculus retroflexus, Meynert’s bundle, tractus habenulo-peduncularis; ¢r.
dien. hab., tractus diencephalo-habenularis (a portion of the tractus habenulo-
diencephalicus of Goldstein) ; tr. entoped. hab., tractus entopedunculo-habenularis;
tr. hab. dien., tractus habenulo-diencephalicus; tr. intermed. hab., pars. ant.,
tractus intermedio-habenularis, pars anterior; tr. intermed. hab., pars post.,
tractus intermedio-habenularis, pars posterior; (tr. olf. hab., tractus olfacto-
habenularis (under this name are included all the fiber systems which ascend
into the habenula of either side); tr. posthab. hab., tractus posthabenulo-
habenularis; ir. preopt. hab., pars ant., tractus preoptico-habenularis, pars
anterior; tr. preopt. hab., pars lat., tractus preoptico-habenularis, pars lateralis;
tr. preopt. hab., pars med., tractus preoptico-habenularis, par medialis; tr. preopt.
hab., pars post., tractus preoptico-habenularis, pars posterior; tr. ten., tractus
teniae (the tractus olfacto-habenularis of Kappers, Goldstein, etc.). (For other
abbreviations see explanation of fig. 136.)

338

OLFACTORY CENTERS IN TELEOSTS PLATE 42
RALPH EDWARD SHELDON

I
Vv
~

nucl.olf. lat.
palaeostr

----psup.cony

Se tr intermed. hab., pars ant.
: tr preopt. hab., pars ant.
tr ten.

tr. entoped. hab.

tr preopt. hab., pars med.

tx intermed. hab. pars post.
Ole. Nab:

preopt. hab., pars post.

Tie MELON A aT,
= ii
/§

. preopt. hab., pars lat.
+. posthab. hab,

fasc. retr

tr dien. hab.

tr hab. dien.

339

THE TELENCEPHALON IN CYCLOSTOMES!

J. B. JOHNSTON

From The Institute of Anatomy, University of Minnesota

FORTY-ONE FIGURES

The telencephalon of cyclostomes presents in many ways more
primitive conditions than are known in other vertebrates. Cyclo-
stomes are therfore important in the effort to trace the phylogeny
of various structures in the cerebral hemispheres. The discussions
regarding the interpretation of the lateral lobes, the pallium and
the ventricles (Ahlborn, Rabl-Riickhard, Studnicka, Edinger)
together with the contributions by Sterzi (09) and the writer
(02a), have made clear the significance of most parts of the telen-
cephalon at least in Petromyzonts. The lateral lobes are true
hemispheres,? containing lateral ventricles connected with the
third ventricle by wide interventricular foramina. The hemis-
pheres are pushed back against the sides of the diencephalon by
pressure from the buccal apparatus. The bulbar formation occu-
pies the broad rostral wall of the hemisphere and does not project
forward as a bulbus olfactorius. In addition to this bulbar forma-
tion the hemisphere walls include secondary olfactory centers
. and a basal-central area heretofore known as corpus striatum.
The bulbar formation and secondary olfactory centers are sepa-
rated by a groove which represents the olfactory peduncle.

The anterior portion of the third ventricle is closed above and
rostrally by a membrane which is thickened in two places by
commissures (figs. 5. 6). Rostral to the extraordinarily thick

1 Neurological Studies from the Institute of Anatomy, University of Minnesota,
No. 16.

2 The writer here uses the term hemisphere as synonymous with the lateral lobe
or evagination of the telencephalon, accepting in this the suggestion of Professor
Herrick (710, p. 492). .

341

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 4
AuGusT, 1912

342 J. B. JOHNSTON

chiasma ridge the lamina terminalis extends from the preoptic
recess to the recessus neuroporicus, rostral to the interventricular
foramen. The position of the recessus neuroporicus was first
clearly established by Sterzi (07). The lamina terminalis is
thickened by the anterior commissure. Above the recessus neuro-
poricus the roof of the ventricle is thickened by the so-called
dorsal olfactory commissure or decussation. This thickened
lamina should be called the lamina supraneuroporica (Burck-
hardt 94 b, ’94 ¢, ’07, Johnston, ’11b). <A short distance caudal
- to this lamina occurs a small fold in the membranous roof which
was shown by Sterzi (’07) to be the velum transversum. Caudal
to this a long dorsal sac extends to the superior commissure and
habenular bodies. This dorsal sac is covered dorsally by the
parapineal body and epiphysis, which depress the sac in various
degrees.

Upon the general morphology of the petromyzont telencephalon
thus far there is general agreement among workers. There are,
however, disputed questions regarding the relations of the telen-
cephalon and diencephalon, and the location of the primordium
of the cortical area of higher vertebrates.

The writer has reviewed the preparations previously studied
and has examined new preparations of the same and other species
of petromyzonts. The writer wishes to express his sincere thanks
to Professor Gage for a very generous supply of ammocoetes and
adults of both Lampetra and Petromyzon dorsatus. Other speci-
mens of Lampetra have been obtained from Professor Reighard’s
laboratory both while the writer was located there and later
through the kind assistance of Dr. L. J. Cole. The writer is —
deeply indebted to Professor Charles Brookover for the loan of
the series of sections of Ichthyomyzon which is described beyond.
Thanks are also due to Professor Reighard for the loan of a series
of sections of a new dwarf lamprey not yet described. Through
the kindness of Mr. W. F. Allen of this laboratory I have had the
opportunity to section and study several stages of the ammocoetes
of the Pacifie coast lamprey, Entosphenus.

THE TELENCEPHALON IN CYCLOSTOMES 343

The di-telencephalic boundary

The writer has attempted (’09) an accurate definition of the
boundary in question, upon the basis of selachian, amphibian,
avian and mammalian embryos. The result was to show that
the optic chiasma belongs to the telencephalon, the boundary
being defined by the velum transversum above and the caudal
surface of the chiasma ridge below. It was shown that the telen-
cephalon includes, in addition to the hemispheres, a median por-
tion surrounding the rostral part of the third ventricle. The
floor of this telencephalon medium is occupied by the optic
chiasma. Its roof (roof plate of His) is made up of the lamina
terminalis, lamina supraneuroporica and tela chorioidea. The
telencephalon constitutes a complete brain ring or segment as
His contended, although shorter than His thought. The hemis-
pheres are lateral evaginations of this telencephalon medium. In
the series of vertebrates, as in the stages of the ontogeny, a pro-
gressively larger part of the telencephalon is evaginated into the
hemispheres, until in man only the chiasma ridge and the small
region between it and the lamina terminalis remains as the telen-
cephalon medium.

This definition of the di-telencephalic boundary has been
accepted by Herrick (’10), Kappers and Carpenter (711), and others,
and its substantial correctness will be assumed for the purposes
of this paper. If the di-telencephalic boundary is to be deter-
mined in cyclostomes in the same way as in other vertebrates,
it becomes necessary only to describe the velum transversum in
cyclostomes accurately and completely, since the chiasma ridge
is already well understood.

The recognition by Sterzi of the small fold behind the dorsal
decussation as the homologue of the velum transversum of higher
forms was a valuable contribution to the interpretation of the
cyclostome brain. The velum was recognized, however, only in
median sections and the postition of the velum in the median
plane does not define the boundary between the telencephalon and
diencephalon. The writer has shown at length elsewhere (11 a,
"11 b) the errors and inconsistencies which arise from taking into
account only the.position of the velumin the median plane. It

344 J. B. JOHNSTON

is the point of attachment of the velum to the massive walls which
determines the boundary between telencephalon and diencephalon.
The velum transversum is a fold of the tela chorioidea having the
form of an arch whose pillars rest on the massive lateral walls.
This point of attachment is the meeting place of the taenia thalami
and taenia fornicis. The position of the velar arch in the median
plane depends upon the form of the tela chorioidea of the third
ventricle as affected by the general form of the brain and the
pressure or traction exerted upon the tela by surrounding struc-
tures. Thus in the selachian brain the velum is nearly transverse
and vertical in position (fig. 1) and is attached to the lateral walls
just in front of the habenular bodies. In certain ganoids, on the
other hand, the velum is a very deep fold which is inclined for-
ward at an angle greater than 45 degrees. The pillars of the
velum are attached to the lateral walls just rostral to the habenu-
lar bodies exactly as in selachians (fig. 2). The point of attach-
ment of the velum to the lateral walls may be more sharply defined
with reference to the internal structure of the massive wall. It
is just at the point of attachment of the velum that the several
categories of fibers which make up the stria medullaris converge
into a compact bundle to ascend to the habenular nucleus and
commissure (commissura superior Osborn). In amphibians and
reptiles this portion of the lateral wall, to which the velum is
attached and which is traversed by the stria medullaris, Herrick
(10, p. 419) has ealled the eminentia thalami. This low eminence
is clearly seen in figures 1 and 2, but is not lettered.

A careful study of the velum transversum in Lampetra shows
that it is attached as in fishes and amphibians immediately rostral
to the habenular bodies and that its point of attachment is the
dorsal border of the eminentia thalami.

As is well known, the right habenular body is very much larger
than the left, and each is bounded ventrally by a deep groove, the
sub-habenular sulcus (figs 8, 5, 6). At its rostral end this deep
sulcus leads into the dorsal sac. Here it meets with a vertical
suleus which descends in the brain wall and curves forward to
enter the interventricular foramen. (figs.5,6,suleus limitans hippo-
campi). The common space formed by the union of these two

THE TELENCEPHALON IN CYCLOSTOMES 345

deep sulci where they join in the caudal and lateral angle of the
dorsal sac is a very deep and narrow cleft which may be called
the recessus praehabenularis (figs. 14, 18). This deep recess has
been formed probably by the crowding together of the brain due
to pressure from in front. Below the habenular body two nearly
vertical ridges are seen (figs. 5, 6) in the side wall of the thalamus.
The more caudal one is occupied by the tractus habenulo-pedun-
cularis (figs. 21, 22). It is much more prominent on the right,
owing to the greater size of the nucleus habenulae and the fiber
tract on the right side. The more cephalic ridge is about equally
developed on the two sides and contains the stria medullaris (figs.
20, 21). This I shall call the eminentia thalami. It is bounded
in front by the sulcus limitans hippocampi and extends up in the
recessus praehabenularis as a narrow ridge (figs. 20, 26, 27). The
groove separating the two ridges corresponds to the sulcus b of
the selachian brain (Johnston 711 a) and to the sulcus diencephal-
icus medius of Herrick (’10) in amphibians.

The dorsal ridge in front of the habenular body is large in
Lampetra and presents a slight but distinct eversion similar to
that in the teleost brain (figs. 7, 30, 31). To this ridge the writer
formerly (02 a) gave the name epistriatum. In anticipation of
the results of the following pages, we may call it here the primor-
dium hippocampi. It extends forward over the interventricular
foramen where it becomes continuous with the roof of the lateral
evagination.

In order to determine whether this ridge belongs to the telen-
cephalon or diencephalon we must discover the point of attach-
ment of the velum transversum to the massive walls. This point
is difficult to determine in most petromyzonts because the velum
is very rudimentary and is recognizable only near the median line.
This is true of the adults of Petromyzon dorsatus and Lampetra
which the writer has examined, of Ichthyomyzon studied by Herrick
and apparently of the forms studied by European authors. In
the ammocoetes of Petromyzon dorsatus, however, the velum is
better developed and appears as a fold which extends across the
whole width of the tela so that the attachment to the massive
walls can be determined.

346 J. B. JOHNSTON

In order to demonstrate the pillars of the velar arch in this
form the writer has made a plate reconstruction of the dorsal
part of the telencephalon and diencephalon. Owing to the com-
pression of the dorsal sac by the epiphysis and parapineal body the
velum shows to best advantage in sagittal sections and the recon-
struction was made from these (fig. 8). The model was made
from the left side of the brain and included the recessus neuropori-
cus in front and a part of the nucleus habenulae behind. In
order to see as much of the velum as possible the model has been
drawn from a medio-ventro-caudal direction. This figure should
be compared with figure 3, which shows the left half of the fore-
brain from a model of another specimen of Petromyzon dorsatus
(ammocoetes). The cut surface along the upper border of the
figure corresponds very nearly to the median sagittal plane. In
this plane is seen the fold described by Sterzi as the velum trans-
versum. Extending caudo-laterally from this above the primor-
dium hippocampi is a fold of the tela which continues without
interruption into the extreme caudo-lateral angle of the dorsal
portion of the ventricle. The deep cleft in which the velum is
seen in the figure is the recessus praehabenularis described above.
In the depth of this recess the lateral pillar of the velar arch is
attached to asmall ridge which is identified as the eminentia
thalami by the presence in it of the stria medullaris. As the
model is viewed from an unusual angle, the relations will perhaps
be more clear by comparison with figures 23 to 27, which represent
five sections of the series from which the model was constructed.
The relations of the recessus praehabenularis and of the eminentia
thalami in Lampetra are shown in figures 14 to 22. Here the
sulcus praehabenularis is narrower than in the ammocoetes
because of the enlargement and crowding of the surrounding parts.
The disposition of the velum transversum in Petromyzon dorsatus
is essentially the same as that in ganoids and teleosts. The
velum is not only inclined far forward as in the latter fishes, but
owing to the depression of the dorsal sac by the overlying epiphy-
sis, its middle part is pressed down far below the plane of attach-
ment of its pillars. The whole course of the velum is diagram-
matically represented in figure 28 as it might be seen in the dorsal

THE TELENCEPHALON IN CYCLOSTOMES 347

aspect of the brain. As indicated inthis figure, that portion of
the dorsal ventricular space which les above the velum transver-
sum is properly called the dorsal sac, while the portion below the
velum belongs to the telencephalic portion of the third ventricle.

This description of the velum transversum makes it possible
to define clearly the boundary between the telencephalon and dien-
cephalon. It is marked, as shown in figures 5 and 6, by a line
running from the attachment of the velum transversum upon the
dorso-rostral border of the eminentia thalami to the caudal surface
of the chiasma ridge. 7

The ventricular sulci in diencephalon and telencephalon

Attention has been called above to the sulcus limitans hippo-
campi, the dorsal or sub-habenular sulcus and the suleus 6} or
sulcus medius. In figure 5 are to be seen three other important
ventricular grooves, the sulcus limitans of His, the sulcus hypo-
_thalamicus and a sulcus connecting the recessus praeopticus with
the foramen interventriculare. The presence of the last named in
embryos and adults of other classes of vertebrates has been pointed
out (ll a). The further study of slightly evaginated brains
(cyclostomes, ganoids and teleosts) makes it necessary to with-
draw the view stated earlier (in 711 a, p. 45) that the sulcus arising
in the preoptic recess is the continuation of the sulcus limitans
hippocampi.

The sulcus hypothalamicus is seen a short distance behind the
interventricular foramen diverging ventrally from the sulcus limi-
tans hippocampi. It grows deeper and descends into the hypo-
thalamus as a crescentic groove. Discussion of the question
whether this sulcus or any part of it is comparable to the sulcus
hypothalamicus of the human brain is reserved. The name is
used here ina purely descriptive sense and is evidently appropriate.
The sulcus is the same as Herrick’s sulcus diencephalicus ventralis.
This name has not been adopted because the sulcus in all lower
vertebrates is a transverse rather than a longitudinal sulcus.

The sulcus limitans of His traverses the midbrain in the same
position as in other vertebrates and meets the sulcus hypothalami-
cus over and in front of the tuberculum posterius. It can not be

348 J. B. JOHNSTON

traced forward to the preoptic recess, apparently owing to the
great prominence of the chiasma-ridge and the supra-optic nucleus.

Professor Herrick has given an account of the sulci in Ichthyo-
myzon which differs from the above account in important respects.
With Professor Herrick’s kind permission I reproduce his figure
73 as figure 29 of this paper. Comparison of this with my figure
5 representing the model of the Lampetra forebrain shows that
Herrick has given the name sulcus diencephalicus medius to a
part of my sulcus hypothalamicus and that he has described the
lower end of this sulcus hypothalamicus as a separate sulcus under
the name of the sulcus diencephalicus ventralis. He recognizes
also a suleus subhabenularis and sulcus diencephalicus dorsalis.

As it was impossible to harmonize this description with the
condition in Lampetra, I have secured for study at Professor
Herrick’s suggestion the identical series of sections from which
his drawings were made. The sections are fifteen microns thick
and with the exception of a single broken section the series is
perfect. A model has been made at a magnification of 100 diame-
ters, the right half of which is drawn from the ventricular surface
in. figure 6. The model when finished was a trifle longer than it
should be, in the proportion of 94 to 90.

Referring to Herrick’s figures 74 to 81, it should be noted that
Professor Herrick viewed the sections from in front, so that the
right side of the brain appears in the left side of his figures. Thus
the right nucleus habenulae, which is the larger, appears on the
left side in figures 80 and 81. From this it follows that the recon-
struction in figure 73 (figure 29 of this paper) represents the
ventricular surface of the right half of the brain as if it were the
left half. This is mentioned only to show that the model figured
is properly to be compared directly with Herrick’s reconstruction.

The model shows the following points. The primordium hippo-
campi is not so large as in Lampetra but has the same form and
relations. The nucleus habenulae projects rostrad somewhat
over the primordium hippocampi. The sulcus limitans hippo-
‘ampi and sulcus hypothalamicus very closely resemble those in
Lampetra. The eminentia thalami is better marked than in
Lampetra, being a prominent ridge near the nucleus habenulae.

THE TELENCEPHALON IN CYCLOSTOMES 349

Behind the eminentia thalami isa ridge extending from the nucleus
habenulae to the interpeduncular region and occupied by the
tractus habenulo-peduncularis. Between this ridge and the emi-
nentia thalami is a sulcus diencephalicus medius which is some-
what more regular than in Lampetra. The sulcus limitans of His
is somewhat less pronounced than in Lampetra.

Professor Herrick thought that he found in Ichthyomyzon con-
ditions which supported his theory regarding the division of the
diencephalon and the telencephalon of amphibians into four lon-
gitudinal columns. In amphibians (Herrick, ’10,p. 419) the sulcus
medius forms the dorsal boundary of the eminentia thalami and
runs caudally toward the tuberculum posterius. The statement
that this sulcus and the sulcus ventralis “converge anteriorly to
the interventricular foramen’ is evidently without foundation,
since the sulcus medius is situated dorso-caudal to the eminentia
thalami and the velum transversum, and can not reach the inter-
ventricular foramen. In the amphibians studied by the writer
(Amblystoma, Necturus, Cryptobranchus, Rana, Bufo) the suleus
medius runs up into the dorsal sac and has no relation to the inter-
ventricular foramen. This fact is clearly shown also in Herrick’s
figures 5, 18, 19, 22, 33 and 34.

In Herrick’s Ichthyomyzon figures 78, 79 and 80, the s.m. cor-
responds to my sulcus limitans hippocampi, while in figure 81
and on the right side of figure 80, s.mm. is the sulcus hypothalamicus.
Consistent with his indentification of this with the sulcus medius,
Herrick labels the area below it as the pars ventralis thalami and
compares it with the eminentia thalami of amphibians (’10, p.
471). This interpretation is obviously untenable, since the
eminentia thalami of amphibians is caudo-dorsal to the inter-
ventricular foramen, immediately adjacent to the nucleus habe-
nulae, is bounded below by the sulcus diencephalicus ventralis
and is traversed by the compact stria medullaris just before this
bundle enters the nucleus habenulae. See Herrick’s figures 17—
to 22. The true position of the eminentia thalami in Ichthyomy-
zon 1s Clear from Herrick’s figures 80 and 81 in which the compact
stria medullaris is about to enter the nucleus habenulae. These
figures show that the eminentia thalami lies as in amphibians at

350 J. B. JOHNSTON

the dorsal border of the brain near the nucleus habenulae. This
is more clear from my figure 9 which is drawn from a section
between the two drawn in Herrick’s figures 80 and 81. In this
section the stria medullaris is seen in the eminentia thalami. In
Herrick’s figure 81 the stria medullaris has bent laterad into the
outer portion of the nucleus habenulae and the tractus habenulo-
peduncularis is coming down near the ventricle. Having thus
identified the eminentia thalami, it is evident that the groove in
Ichthyomyzon which corresponds to the suleus medius of amphi-
bians is the groove so lettered in figure 6.

Professor Herrick has completely overloooked the greater part
of the suleus limitans hippocampi in Ichthyomyzon, probably
because the greater part of its course lies more or less parallel
with the plane of the transverse sections. For the same reason
he failed to recognize that his s.m. and s.v. were the two ends of
one and the same crescentic groove. The model clearly shows
the true relations in both cases, and readily explains how natural
Professor Herrick’s interpretation was in the absence of models.

In dealing with the relations of the telencephalon and dience-
phalon in the dorsal region, Professor Herrick (’10, pp. 473-4)
says,

On account of the very small degree of evagination of the cerebral hem-
isphere in cyclostomes the di-telencephalic fissure is shallow and the pars
dorsalis thalami passes over without interruption into the lateral wall
(lobus olfactorius) of the hemisphere. Moreover this fissure does not
extend upward to the mid-dorsal line and thus the dorso-median ridge
is able to pass continuously from one segment to the other. In higher
vertebrates this fissure extends dorsally up to the site of the velum trans-
versum and it is so deep as to interrupt the continuity of both the ridge

and all other massive tissue of the pars dorsalis thalami with their telen-
cephalic representatives.

It is necessary to define clearly what is meant by the di-telen-
cephalic fissure. In the human and mammalian brain there
is a great groove or fissure between the posterior part of the
hemisphere and the thalamus, midbrain and cerebellum. Near
the bottom of this is the chorioidal fissure of the hemisphere.
Dorsally the fissures of the two sides join in the great longitudinal
fissure. ‘Taken together these constitute in a true sense a margi- |

THE TELENCEPHALON IN CYCLOSTOMES Se

ginal or limiting fissure of the hemispheres. It owes its existence
to the fact that the evagination of the hemisphere causes an angle
or fold between its wall and the wall of the brain stem. The
whole fissure may therefore be referred to under the descriptive
term, stem-hemisphere fissure. When lower vertebrates are
examined it is seen that the stem-hemisphere fissure is well-
marked in reptiles and amphibians, but in true fishes is only a
broad shallow groove or constriction. In Petromyzonts, one of
the most striking features is the sharp separation between hemis-
phere and brain stem (fig. 7). In a previous paper (’09) the
writer has shown that this is not the line of division between telen-
cephalon and diencephalon. The groove seen in figure 7 running
from near the median line in front outward and backward is the
stem-hemisphere fissure. It marks the boundary between the
hemisphere and the telencephalon medium, not only in cyclostomes
but in all classes of vertebrates. When the hemispheres expand
and lie apposed to each other in the median plane, this forms the
great longitudinal fissure and its lateral extension between the
posterior pole of the hemisphere and the brain stem.

Obviously this stem-hemisphere fissure can not be called a
di-telencephalic fissure. The writer has suggested (’09, p. 516)
that the di-telencephalic fissure owes its origin to the withdrawal
of tissue to form the optic vesicle. In this Professor Herrick
concurs (’10, p. 467). The di-telencephalic fissure les at the
junction of the telencephalon medium and diencephalon, while the
hemisphere evagination takes place some distance farther rostrad,
and the two are entirely independent. That this is so is perfectly
clear from cyclostomes, selachians and other fishes. The evagina-
tion of the hemispheres has, therefore, nothing to do with the
di-telencephalic fissure or the continuity of diencephalon and
telencephalon. Further, the di-telencephalic fissure is dorsal in
position from the start and does not extend farther dorsally in
higher vertebrates. What does happen is that in higher verte-
brates more and more of the telencephalon medium comes to be
evaginated into the hemispheres until the stem-hemisphere fissure
gradually approaches the di-telencephalic fissure.

352 J. B. JOHNSTON

In cyclostomes the di-telencephalic fissure is as clearly present
as in other vertebrates. It is marked by the eminentia thalami
to which the velum transversum is attached. In the ammocoetes
of Petromyzon dorsatus, at least, the di-telencephalic boundary is
further marked by an external groove (fig. 4). Professor Herrick
is in error in his speculations regarding the continuity of the dorsal
part of the thalamus and the telencephalon in cyclostomes (pp.
474 and 477-8). The di-telencephalic fissure is slightly masked
in eyclostomes because of the crowding back of the telencephalon
against the diencephalon but the sulcus medius comes to the dorsal
border here precisely as in amphibians and if the dorsal column
is interrupted by the di-telencephalic fissure in amphibians, it is
interrupted in just the same way in cyclostomes.

Herrick states (p. 472) that he has indicated in figure 73 by a
dotted line (s.d.) ‘a somewhat arbitrary boundary’ between his
dorso-median ridge (my primordium hippocampi) and his pars
dorsalis thalami. This dotted line does not correspond to the
suleus limitans hippocampi or to any thing that I can find in
Lampetra, Petromyzon dorsatus, Entosphenus or Ichthyomyzon.
The dotted line is lettered sulcus diencephalicus dorsalis while in
the text (p. 470) the dorsal is spoken of as synonymous with the
sub-habenular sulcus. In amphibians (Herrick ’10, 431 and fig.
22) the subhabenular and dorsal sulci are distinct but are regarded
as two parts of a sulcus which separates the epithalamus from the
dorsal part of the thalamus. In amphibians the dorsal is the more
caudal segment of the common sulcus. In the Ichthyomyzon
diagram the positions are reversed. In amphibians neither of
these sulci has even a remote relation with the interventricular
foramen, and both lie wholly within the diencephalon. In the
Ichthyomyzon diagram the line s.d. is connected with the foramen
and lies wholly within the telencephalon. This arbitrary line in
Ichthyomyzon has therefore no relation to the suleus dienceph-
alicus dorsalis of amphibians.

Herrick regards the groove which extends rostrad from the
foramen as a continuation of the suleus diencephalicus dorsalis.
In this position there are two grooves in Ichthyomyzon and in
Lampetra. One extends forward from the dorsal angle of the

THE TELENCEPHALON IN CYCLOSTOMES 308

foramen, the other from the ventral angle, and the two converge
into the neuroporic recess. The lower one of these grooves is the
one designated by Herrick as the telencephalic extension of the
sulcus dorsalis (Herrick ’10, figs. 75, 76). The dorso-median ridge
(my promordium hippocampi) ends rostrally in the sections which
contain the so-called dorsal olfactory commissure. As seen in the
model, it is very abruptly reduced in dorso-ventral thickness at
the foramen and extends over the foramen only as a slender strand
of cells (which appears in Herrick’s fig. 77) in close connection
with the commissure. Rostral to the foramen this slender ridge
disappears entirely and the larger ridge which Herrick calls the
dorso-median ridge in his figures 75 and 76 contains glomeruli and
olfactory fibers and belongs to the formatio bulbaris. Of the
two sulci extending rostrally from the foramen, the upper one
separates the dorso-median ridge (primordium hippocampi) from
the formatio bulbaris, the lower one separates the formatio bulbaris
from the medial olfactory nucleus. —

In the ammocoetes of Petromyzon dorsatus (figs. 3, 8) there is
only one groove extending from the foramen to the neuroporic
recess. This sulcus separates the primordium hippocampi from
the medial olfactory nucleus and there is no formatio bulbaris
in this position . Lampetra presents an intermediate condition.
The two grooves are nearer together and the area of formatio
bulbaris which abuts on the ventricle isless than in Ichythyomyzon.
These facts show that in Ichthyomyzon and Lampetra the evagi-
nation of the hemisphere has not completely carried out the formatio
bulbaris, but that-a part of this formation remains in the telen-
cepbalon medium and forms part of the wall of the median ventri-
cle rostral to the foramen. In Petromyzon dorsatus the evagina-
tion of the formatio bulbaris is complete. Consequently, the
two sulci in Ichthyomyzon and Lampetra may be regarded as
merged into one sulcus in Petromyzon dorsatus. This one sul-
cus begins in the neuroporic recess and passes into the rostral
wall of the lateral ventricle, separating the primordium hippo-
campi from the medial olfactory nucleus. The position of this
sulcus is the same as that of the medial zona limitans (hippocampi)
in selachians (Johnston, ’11 a).

304 | J. B. JOHNSTON

The brain of Professor Reighard’s dwarf lamprey presents
larger hemispheres with wider lateral ventricles than I have seen
in any other petromyzont. In the form and size of the primor-
dium hippocampi and in the disposition of the ventricular sulci
it agrees well with Lampetra.

The primordium hippocampi

The description of the ventricular sulci has made clear the
definite ventral boundary of this body on the ventricular side.
Externally a very deep groove separates it from the caudal pole -
of the hemisphere (fig. 7). At the interventricular foramen the
primordium hippocampi bends through the roof of the foramen
to become directly continuous with the roof of the hemisphere.
Caudally, the sulcus limitans separates this body sharply from the
eminentia thalami and nucleus habenulae internally, but on the
external surface there is no visible boundary in adult Lampetra.
In the ammocoetes of Petromyzon dorsatus the external surface
shows a vertical groove which marks the caudal boundary of the
telencephalon (fig. 4).

The neurones of this body belong to a special type which is
found nowhere else in the brain of Lampetra. The same type of
neurone is characteristic of the primordium hippocampi of ganoids
and amphibians. As far as the writer’s studies have gone, these
neurones are as truly characteristic of the primordium hippocampi
as are the Purkinje cells of the cerebellum, and are much more
highly differentiated in cyclostomes than are the Purkinje cells.

In a fomer paper (02 a, p. 40) these neurones as they appear in
Golgi preparations were discribed as follows:

The cells of the epistriatum are arranged in two to four rows adjoining
the cavity. The larger end of the pyramidal cell body is next the cavity
and a large dendrite which arises from the apex divides into two or more
large branches which expand in the fiber layer. The dendrites bear
numerous small spines which are knobbed at the end (fig. 26) in the
manner characteristic of the epistriatum, inferior lobes, and tectum of
Acipenser. These peculiar spines are found nowhere in the brain of
Petromyzon except on the epistriatum cells. These cells are so closely
similar to the epistriatum cells of Acipenser that it would be impossible
to mistake their identity.

THE TELENCEPHALON IN CYCLOSTOMES SH

The pyramidal body and the dendrites studded with knobbed
spines are so characteristic of these neurones that the resemblance
to the hippocampal cells in Acipenser, Amia and Rana is at once
striking and unequivocal. Examples of these cells in each of the
forms named are shown in figures 30 to 34, for comparison with the
cells in Lampetra. The bodies of the neurones in Lampetrastand
near the ventricle and their dendrites divide into a few relatively
straight branches which traverse the thickness of the wall, often
reaching the outer surface (figs. 30, 31).

When we look for the boundary between the primordium
hippocampi and the epithalamus, the internal structure as seén in
horizontal sections seems to furnish the necessary data. First,
there is no difference in the internal structure of the whole dorso-
median ridge bounded by the foramen and the sulcus limitans
hippocampi. Everywhere it is filled by the peculiar type of
neurones just described and nowhere is there any change of finer
structure which would lead us to say that any two or more parts
of it represent different functional centers. However, the moment
the sulcus limitans hippocampi is passed in any direction we come
upon neurones of types wholly different from those of this ridge.
This can not be accidental; it must be the expression of functional
differentiation.

The neurones of the so-called striatum have been described and
figured in my earlier paper (’02 a, figs 18, 19). They are bipolar
or multipolar cells with irregularly curved and branching dendrites
free from spines. The neruones of the nucleus habenulae have
also been figured (02 a, fig. 16; this paper, figs. 17 to 20). They
are, like those in Acipenser, small cells with short very irregular
dendrites often with enlarged tips bearing tufts of small branches.
The subhabenular region is broadly continuous with the primor-
dium hippocampi but the boundary line is very distinct in Golgi
sections. The type of neurones peculiar to the primordium hip-
pocampi stops abruptly along a line drawn latero-caudad from
the sulcus limitans hippocampi (see figures of horizontal sections,
18, 19, 20). At the same time along this same line end abruptly
the parallel fibers coursing lengthwise through this ridge. At
this line the fibers are cut off in horizontal sections because they are

356 J. B. JOHNSTON

turning up into the nucleus habenulae, as is seen in the most
dorsal sections. Compare figures 15, 16 and 19, 20. Behind the
line mentioned there is a wholly irregular tangle of nerve fibers and
farther back the fibers of the optic tract. Scattered among the
tangled fibers are bipolar and multipolar neurones with long sinu-
ous dendrites devoid of spines. The type of structure of the two
bodies as a whole is as strikingly different as are the individual
neurones found in them.

In transverse sections, owing to the direct contiguity and the
oblique overlapping of the primordium hippocampi and the epi-
thalamus, the boundary is of course not so clear, but there is a
very abrupt transition from one type of neurones to the other
which strongly suggests the distinctness of the two centers.

Tretjakoff (09) gives a very imperfect description of the ‘prae-
thalamus’ without figures. He states that its cells are much
like those of the thalamus and that the only afferent or efferent
tract connected with the praethalamusis constituted by the fibers
from the parapineal organ. These reach the praethalamus after
crossing in the habenular commissure. The praethalamus serves
as a rudimentary perception center for the parapineal eye. ‘‘ Eine
andere Bedeutung des Prithalamus lasst sich bei Ammocoetes
kaum vermuten, da ungeachtet der grossen Zahl der Zellen der
Praithalamus von Ammocoetes, nach meinen Untersuchungen,
keine eigenen aus- oder zu fiihrenden Bahnen hat.’? The author
was evidently impressed with the inadequacy of the parapineal
tract to account for so large a center with a great number of cells.
This impresses us much more when we remember that the para-
pineal organ and tract exist only on the left side. According
to Tretjakoff’s description the fibers cross in the commissure to
enter the (right) praethalamus. Hence the left ‘praethalamus’
is wholly devoid of afferent fibers according to this author, and
we are led to suppose that a large center, rich in highly developed
cells exists in Ammocoetes totally without function. The writer
has found no evidence in his preparations that the parapineal
tract enters the ‘praethalamus’.

Schilling (’07) is inclined to the opinion that the ‘praethalamus’
belongs to the telencephalon (p. 431; Herrick cites him erroneously

THE TELENCEPHALON IN CYCLOSTOMES aad

on p. 473) and points out that it is separated from the nucleus
habenulae by a deep ventricular sulcus. He did not distinguish
the characteristic cells of the ‘praethalamus,’ but describes the
passage through it of the bundles of the taenia thalami which
give off collaterals to it.

None of the authors who have studied the petromyzont brain
have used methods adequate to the differentiation of the types of
cells characteristic of the so-called praethalamus and the parts
adjacent to it. No method is so well adapted to this purpose as
the Golgi method and the description of this region given by the
writer in 1902 stands as the most complete heretofore given. That
description gave, however, a very incomplete account of the facts
shown in my preparations and the deficiency is to some extent made
up in the figures accompanying this paper. The ‘praethalamus’
of authors is sharply distinguished from the epithalamus’ and
thalamus not only by the ventricular sulci but by the well marked
characteristics of its cells and by the course of fibers which traverse
it.

Between this body and the roof of the hemisphere there is in
the same way a clear difference in the type of cells. This has .
been sufficiently illustrated earlier (’02 a) and there is no dispute
among authors upon this point.

The fiber tracts related to the primordium hippocampi

These fiber tracts have been very imperfectly understood.
Both Schilling (’07, p. 482) and Tretjakoff (’09, p. 731) state that
no tracts connected with this nucleus were seen.

The stria medullaris is perhaps less complex in petromyzonts
than in the higher fishes, but at least four bundles related to the
telencephalon are present. (Fibers connecting the epithalamus
with other parts of the diencephalon will not be considered here).
One of these bundles comes from the medial olfactory nucleus,
enters the primordium hippocampi near its rostral end above the
foramen and seems to pass over the dorsal ventricular surface of
this body to enter the nucleus habenulae (figs. 14 to 1G 2b, 26;
35). It is by no means certain that this is a continuous tract.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 4

358 J. B. JOHNSTON

A tract from the medial olfactory nucleus over the foramen inter-
ventriculare to the nucleus habenulae is not known in other verte-
brates. The fibers passing up from the medial olfactory nucleus
as far as the primordium hippocampi occupy the same place as
the tractus olfacto-corticalis septi in selachians and amphibians.
If these fibers end in the primordium hippocampi, then what
appears to be the continuation of them to the nucleus habenulae
must be classed as cortico-habenular fibers. A second bundle
comes from the lateral and caudal walls of the hemisphere, passes
up behind the foramen through the inner and lower part of the
primordium hippocampi to join with the first as it enters the
nucleus habenulae (figs. 17, 18, 19). This is the tractus olfacto-
habenularis of authors. A third bundle comes from the preoptic
region and joins the first two (fig. 35). These three bundles unite
into a large compact bundle which traverses the eminentia thalami
at the bottom of the prehabenular recess and enters the nucleus
habenulae (figs. 19, 26, 27). The fourth component of the stria
medullaris is very diffuse and comes from the whole thickness of
the primordium hippocampi. Axones arising from the cells of
the primordium are seen in many cases passing at first peripherally
among the dendrites of these cells and then turning to run toward
the nucleus habenulae through the substance of the primordium
hippocampi. It is these fibers in addition to the first and second
bundles above described that give a longitudinal striation to the
whole of this body. At the caudal end of the primordium these
fibers enter the nucleus habenulae caudal and somewhat dorsal
to the compact bundle of the stria medullaris (figs. 16, 17).
The left nucleus habenulae is very small in Lampetra and nearly
all the left stria medullaris enters the superior commissure. In
the preparations from which figures 14 to 22 were drawn no fibers
were seen ending in the left nucleus. The view expressed in the
writer’s paper on Acipenser (’01, p. 115) that the larger size of
the right nucleus is correlated with the ending of a larger por-
tion of the tractus olfacto-habenularis in the right nucleus is
strongly supported in Lampetra. The superior commissure pre-
sents two main divisions, a more rostral, compact bundle and a
more caudal portion made up of several strands (figs. 17, 18).

THE TELENCEPHALON IN CYCLOSTOMES 359

The rostral bundle is composed of fibers fromthe first bundle
described above and its fibers seem to end in the fiber-mesh of the
right: nucleus (figs. 18, 19). The corresponding bundle of the
right side meets with the left and seems to end with it in the right
nucleus.

The strands of the more caudal division of the commissure are
made up of fibers of the remaining three bundles intermingled.
Many of these fibers end in the fiber mesh of the right nucleus
but many others pass through the nucleus without ending. This
is especially evident in such horizontal sections as those drawn in
figures 17 to 20. At least a part of these fibers clearly appear to
be those which arise in the primordium hippocampi. If so, it is
probable that these fibers end in the corresponding body on the
other side and are homologous with the posterior pallial commis-
sure which is prominent in selachins, ganoids, teleosts and amphi-
bians.

The fibers in the caudal division of the commissure which end
in the right nucleus may include those parts of the tractus olfacto-
habenularis which in other fishes arise in the lateral olfactory
nucleus and in the nucleus praeopticus. These may also include
fibers from the primordium hippocampi which would belong to
the tractus cortico-habenularis.

It seems reasonably certain from the study of these Golgi sec-
tions that the stria medullaris contains the equivalent of the
tractus olfacto-habenularis lateralis and posterior, and the com-
missura palli posterior as described in the selachian brain. Nearly
all of these fibers from the left side cross in the superior commis-
sure.

The writer has described (’02 a, pp. 38, 40) two afferent tracts
ending in the primordium hippocampi; one ascending from the
hypothalamus and one coming from the formatio bulbaris. The
former has since been called tractus pallii in all fishes and is re-
garded as the ascending gustatory tract entering the telencephalon
for: the sake of correlation of gustatory with olfactory impulses.
This tract decussates in the post-optic commissure and ascends
over the internal face of the tractus opticus to enter the primor-
- dium hippocampi from below and behind.

360 J. B. JOHNSTON

The fibers which enter the rostral end of the primordium hippo-
campi from the formatio bulbaris are of course part of the olfactory
tract. In the previous description (’02a, p. 40) it was stated that
these come chiefly from the opposite side, crossing in the olfactory
decussation. The contribution of the commissure to the fiber
bundle entering the primordium hippocamp? is illustrated in figure
24. Further study, both of the preparations used at that time
and of new preparations, has shown, however, that a much larger
number of direct fibers are present than was previously thought.
These fibers are soon mingled with the fibers of the first and second
bundles of the stria medullaris mentioned above and can not be
distinguished with certainty. It is clear, however, that many
fibers which enter from in front break up into end branches in
the primordium hippocampi. Since we know of no other animals
in which olfactory tract fibers run without relay to the nucleus
habenulae, the presumption is strong that these olfactory tract
fibers end in the primordium hippocampi. This is the more prob-
able in view of the fact that in selachians corresponding fibers are
present which end in the primordium hippocampi in part on the
same side and in part after crossing inacommissure situated above
the neuroporic recess.

Schilling and Tretjakoff both state that the fibers of the tractus
olfacto-habenularis give collaterals to the ‘praethalamus.’ Such .
endings would represent a rudimentary tractus olfacto-corticalis.
On comparative grounds the presumption is strong that those
fibers mentioned above which run up form the medial olfactory
nucleus rostral to the interventricular foramen to enter the pzim-
ordium hippocampi must constitute a tractus olfacto-corticalis.

The efferent tract from the primordium hippocampi has thus
far been very imperfectly understood. The writer described fibers
descending to the ‘striatum’ and these have been confirmed by
Tretjakoff. These fibers are fine and do not appear in sufficient
numbers in my preparations to warrant the conclusion that they
represent the chief or only efferent path of this highly differen-
tiated nucleus. Neither is it clear that they end in the ‘striatum’.
It is possible that they pass through the ‘striatum’ but are not
impregnated beyond. Other fibers may descend in the tractus
pallii, as this tract in selachians and ganoids contains descending

THE TELENCEPHALON IN CYCLOSTOMES 361

fibers. The pathway by which the fornix columns run in all
higher classes is occupied by a broad bundle of fibers connecting
the medial olfactory nucleus with the primordium hippo¢ampi
(see above). If any fibers descend through this to reach the
hypothalamus, they would represent the fornix columns. We
must await further investigations upon these points.

We may now summarize the evidence for the interpretation of
this ‘praethalamus’ or ‘dorso-median ridge,’ which has been
assumed in using the name primordium hippocampi.

(a) Its caudal end is just in front of the eminentia thalami to
which the velum transversum is attached. It is therefore wholly
within the telencephalon.

(b) It contains highly developed and specialized cells of a type
which is characteristic of the primordium hippocampi in selachians
ganoids, teleosts and amphibians.

(c) It is bounded by a ventricular sulcus which agrees closely
in position with the sulcus limitans hippocampi of selachians,
ganoids and teleosts.

(d) Along the line of this sulcus there is a sudden change from
the characteristic cells to cells of very different formin the thalamus,
epithalamus and hemisphere. This abrupt change of structure is
comparable to the zona limitans of fishes and amphibians.

(e) It is traversed by a part of the tractus olfacto-habenularis
as in ganoids and teleosts.

(f) It has true commissural fibers passing through the superior
commissure as in fishes and amphibians(commissura pallii pos-
terior).

(g) It receives from in front fibers of the olfactory tract, direct
and crossed, comparable to those in selachians and in part to
those of ganoids and amphibians.

(h) It receives a tractus pallii ascending from the hypothalamus
as inallfishes. The center is therefore to be regarded as anolfacto-
gustatory correlation center.

(i) It appears probable that there is a tertiary olfactory tract
ending in this body (tractus olfacto-corticalis).

Admitting such uncertainty as exists in the present state of our
knowledge regarding the posterior pallial commissure and the
tertiary olfactory connections, we have here a body of evidence

362 J. B. JOHNSTON

which leaves no reasonable ground for doubt that the body in
question is the homologue of the primordium hippocampi as
described in fishes and amphibians.

There is no ground whatever for Professor Herrick’s assumption
(10, p. 473) that the greater part of this body belongs to the epi-
thalamus, while a smaller rostral portion represents the primordium
hippocampi.

The fact of greatest interest regarding this body is, perhaps,
that the primordium of the visceral cortical complex of higher
animals (hippocampus, fornix, and related structures) remains in
cyclostomes in the telencephalon medium. As has been pointed
out in previous papers (710 ¢, ’11 a) the hemisphere evagination in
vertebrates involves at first only the primary olfactory centers and
it is only in later stages of phylogeny that the cortical substance
is evaginated.

Anterior pallial commissure

This has been known as the dorsal olfactory decussation, the
dorsal part of the anterior commissure, and by other names.
Schilling speaks of this as the anterior commissure and makes
only minor mention of the true anterior commissure. Schilling
recognizes in this dorsal commissure fibers connecting the formatio
bulbaris of the two sides and fibers connecting each formatio bul-
baris with the opposite lobus olfactorius. The writer has described
fibers connecting the lobus of one side with the opposite primor-
dium hippocampi. In addition, there are to be mentioned fibers
which come to the commissure from the area of union of the caudal
wall of the hemisphere with the telencephalon medium (fig. 22).
A certain determination of the nature of these fibers depends
on the further study of the region from which they arise. ‘They
may correspond to the fibers in selachians to which the writer has
given the namé corpus callosum. ‘The matter of greatest moment
in this connection is the existence in the lowest order of verte-
brates of a commissure located in the lamina supraneuroporica.
The writer has shown elsewhere that the corresponding commissure
in selachians is large and important, and must reiterate the view
that this dorsal or supraneuroporic commissure is primitive and

THE TELENCEPHALON IN CYCLOSTOMES 363

fundamental in vertebrates. A further examination of the pallial
commissures in reptiles and mammals with reference to this is in
progress (see 710 ¢).

Anterior commissure

This commissure is rather small in cyclostomes. It lies in the
lamina terminalis in front of the preoptic recess as in all verte-
brates. Its constitution is not at all clearly known. Its fibers
probably come from the basal (lateral) olfactory area and the
so-called ‘striatum.’

The ‘striatum’

The region to which the naine striatum has been applied includes
the supraoptic portion of the telencephalon medium and an
adjacent part of the hemisphere (figs. 5, 6, 22). It is clear that
this corresponds roughly to the striatum of other fishes. The
writer has shown (’02 a, p. 41) that the descending fibers from the
‘striatum’ go to the thalamus and not to the hypothalamus.
From this region fibers pass through the anterior pallial commis-
sure, as noted above. These facts suggest that the striatal region
corresponds to or contains the equivalent of the somatic area of
selachians. Any decision on this point must await further study.

Mode of evagination of hemispheres. Zona limitans

The cyclostomes taken in comparison with higher forms -give
clear evidence of the principle announced by the writer (710 ¢,
"11 a) that the hemispheres are lateral evaginations of the telen-
cephalon which have gradually involved the formatio bulbaris,
the lobus olfactorius and the pallium in the order named. The
comparison of the cyclostomes with selachians and amphibians
with reference to the mode by which the more fully evaginated
brains have come to have their present form, is very important
for the interpretation of these higher brains.

If attention be given to the models shown in figures 5, 6 and 7,
it will be seen that the further evagination of the hemisphere
involves the turning out of the primordium hippocampi and the

364 J. B. JOHNSTON

striatal area through the foramen into the caudal portion of the
hemisphere. Somewhat more than the rostral half of the hemis-
phere is occupied by formatio bulbaris. The further evagination
would enlarge the caudal part of the hemisphere until it became
larger than the rostral part. At the same time the hemisphere
is drawn forward by: the elongation of the rostrum, the olfactory
bulb becomes separated form the caudal part of the hemisphere
and a longer or shorter tractus olfactorius or olfactory peduncle is —
established.

The relations of the primordium hippocampi to the roof of the
enlarging hemisphere are especially interesting. We have pointed
out that there is an abrupt change of structure between the prim-
ordium and the roof of the hemisphere which may be called a zona
limitans. As the primordium hippocampi pushes out into the-
roof of the hemisphere this zona limitans would be placed suc-
cessively farther and farther laterad in this roof. In selachians
(11 a) this zona limitans runs from the olfactory peduncle back-
ward along the dorso-lateral wall of the lateral ventricle. For
a long time in the phylogeny there remains a portion of the primor-
dium hippocampi in the telencephalon medium extending along
the dorsal border of this region to the point of attachement of the
velum transversum to the eminentia thalami. In this position,
where the whole of the primordium is located in cyclostomes,
there exists in Chimaera (’10 d) and selachians (’11 a) a slender
ridge of gray matter accompanied by the fibers of the posterior
pallial commissure. In ganoids and teleosts (’11 b), where the
evagination of the hemispheres has been arrested, the primordium
has retained in the caudal part of the telencephalon essentially
the relation which it holds in cyclostomes and has taken part in
the eversion of the forebrain. In amphibians the evagination has
gone farther than in selachians, the primordium hippocampi occu-
pying the roof portion of the hemisphere and the zona limitans
being carried farther down in the lateral wall. There is still left
in the telencephalon medium, however, a small part of the primor-
dium hippocampi corresponding to that in selachians, although
shorter (Johnston, 06). Herrick (’10, p. 476). has endeévored to
show that this structure belongs to the eminentia thalami. It

THE TELENCEPHALON IN CYCLOSTOMES 365

is of course directly adjacent to the eminentia thalami and Pro-
fesssor Herrick hasapparently thought that more was to be included
in the unevaginated primordium hippocampi than the writer
intended. This structure is the continuation of the fimbria-
border of the hemisphere into the dorsal border of the telencephalon
medium until it meets the eminentia thalami. This small rem-
nant of the primordium is seen in a model of the forebrain of
Necturus standing vertically rostral to the eminentia thalami and
separated from the latter by a groove. Figure 36 will show more
clearly the relations of this structure. Deep fibers related to the
cells of this unevaginated body enter the hippocampal commissure
as already described.

As the evagination proceeds the caudal part of the hemisphere
soon extends rostrad beyond the level of the interventricular
foramen and the lamina terminalis. This is already true in selach-
ians and in amphibians and reptiles the hemisphere protrudes far
rostrally (fig. 37). In selachians, it has already been pointed out
that the sulcus limitans hippocampi continues rostrally beyond
the laterally placed olfactory peduncle and encircles the rostral
wall of the hemisphere to end at the neuroporic recess (figs. 38,
39). This portion of the sulcus was called the medial sulcus
limitans hippocampi. As compared with cyclostomes, the con-
dition in selachians has resulted from the continued evagination
which has carried the olfactory bulbs far laterad and has brought
the greater part of the primordium hippocampi into the roof of
the hemisphere. The region of the medial olfactory nucleus has
bulged forward beyond the lamina terminalis, and the sulcus which
separates the primordium from the medial olfactory nucleus in
front of the interventricular foramen in Petromyzon comes in:
selachians to lie in the medio-rostral wall of the hemisphere. In
both classes it runs from the neuroporic recess into the lateral
ventricle and marks the line of separation of the same structures.
It is properly called the sulcus (or zona) limitans medialis. In
amphibians the conditions are essentially the same (fig. 37).

Professor Herrick’s view as to the evagination of the hemispheres
and the relation of his four columns to them is summarized in
the following paragraph (’10, p. 477):

366 J. B. JOHNSTON

The roof plate and floor plate converge into the lamina terminalis,
where of course they end. The four massive columns on each side con-
verge into the interventricular foramen, and in larvae with wide fora-
mina and adult urodeles they may be followed through the foramina
into the evaginated hemispheres. Bearing in mind the fact that during
development the roof plate and floor plate retain permanently their
primitive attachments to the lamina terminalis, and that it is only the
massive lateral columns which are evaginated into the hemispheres, it
clearly follows that these columns of the diencephalon are continued into
the hemispheres in the form shown by the accompanying diagram (fig.
84), the zona limitans lateralis representing the locus of the sulcus medius
and the zona limiants medialis the line of union of the dorsal and ventral
columns in the lateral evaginations rostral to the fusion of the roof plate
and floor plate in the lamina terminalis.

It has been noted elsewhere (’11 b, p. 540) that the assignment of
the lamina terminalis in this paragraph to the floor plate was an
error of inadvertance. It has been shown also (711 b, pp. 534,
535 and in this paper) that the sulcus diencephalicus medius has
no relation with the interventricular foramen or the zona limitans
lateralis either in amphibians, fishes or cyclostomes.

The conception of the folding over of the lateral walls of the
diencephalon illustrated in Professor Herrick’s figures 83 and 84,
such that the dorsal and ventral borders fuse in the medial zonae
limitantes to form two tubes extending forward (the hemispheres),
seems to the writer to be without basis in fact.

In figure 72 Herrick (10) has given a diagram of the forebrain
in a hypothetical vertebrate ancestor. In this the representation
of the sulcus dorsalis issubject to the criticisms made above (p. 352).
No ground is given for the assumption that the retinal area does
not involve the dorsal border of the brain, except the erroneous
supposition that there is no di-telencephalic fissure in cyclostomes.
The suleus medius is represented as a horizontal sulcus ex-
tending caudad from the site of the interventricular foramen,
whereas in all lower vertebrates it runs nearly vertically up into
the dorsal sac. The sulcus ventralis should lead to the site of
the interventricular foramen as it does in cyclostomes, selachians
and amphibians. The terminal ridge is represented as an inde-
pendent thickening rostral to the chiasma ridge, whereas the ter-
minal ridge in all vertebrate embryos itself becomes the bed for
the optic chiasma (Johnston ’09).

THE TELENCEPHALON IN CYCLOSTOMES 367
SUMMARY

The evagination of the hemispheres is at a low stage in petro-
myzonts. In Ichthyomyzon and Lampetra the formatio bulbaris
is not all evaginated. The fact that a part of the wall of the third
(median) ventricle in these forms is made up of formatio bulbaris
ought to be convincing evidence, if any further evidence is needed,
that a part of the third ventricle belongs to the telencephalon. A
large part of the secondary olfactory centers is evaginated, but
a relatively much larger portion of these centers remains in the
telencephalon medium than in the case of selachians. The prim-
ordium hippocampi remains wholly in the telencephalon medium.
The exact relations of the somatic area await further study.

The di-telencephalic boundary is marked by the attachement
of the velum transversum to the eminentia thalami as in selachians
ganoids and amphibians. The eminentia thalami is a well-marked
ridge just rostral to the nucleus habenulae, bounded by the sulcus
medius and by the sulcus imitans hippocampi, and traversed by
the stria medullaris.

The telencephalon medium, which is relatively larger than in
higher vertebrates, stands as a wedge-shaped mass between the
hemispheres. Its massive nervous walls are connected with one
another by the lamina terminalis, lamina supraneuroporica and
tela chorioidea. The membranous roof plate (His) in the telen-
cephalon of petromyzonts connects the two simple unevaginated
lateral walls of the neural tube as in any other segment. The
hemispheres are evaginations of restricted areas of these lateral
walls. The foramen is roofed over by the massive primordium
hippocampi and there is no extension of the tela chorioidea into
the roof of the hemispheres.

The primordium hippocampi is represented by the ‘praethala-
mus’ of previous authors (the epistriatum of my earlier paper, ’02
a). Itisalarge body having a highly developed and characteristic
finer structure which already presents most of the relations of the
primordium hippocampi of higher forms (see text). The two
primordia converge forward to form a bed for the anterior pallial
commissure in the lamina supraneuroporica. The primordium
is separated from the epithalamus, thalamus, hemisphere and the

368 J. B. JOHNSTON

medial olfactory nucleus by a sulcus limitans hippocampi. Along
the line of this sulcus is a sudden change of structure which may
be compared with the zona limitans of fishes and amphibians.

In vertebrates above cyclostomes the primordium hippocampi
is gradually evaginated into the hemisphere, the process being
complete in the reptiles. It is only as the hippocampus is carried
into the medial border of the hemisphere that the tela chorioidea
comes to form the roof of the interventricular foramen and to
extend into the roof of the hemisphere.

The expansion of the hemisphere carries both the primordium
hippocampi and the medial olfactory nucleus rostrad beyond the
lamina terminalis where they form the medial hemisphere wall.
The sulcus limitans hippocampi which separates these two nuclei
in the telencephalon medium in petromyzonts becomes the sulcus
limitans medialis hippocampi in the hemisphere of selachians,
amphibians and reptiles.

The relation of the primordium hippocampi to the lamina supra-
neuroporica in which the anterior pallial commissure lies is funda-
mental in vertebrates and must be taken into account in seeking
the interpretation of higher brains.

The reader is referred to the extended discussion of forebrain
morphology contained in the writer’s paper on selachians (711 a,
p. 37, especially pp. 47-52). The features of the evolution of the
forebrain upon which the cyclostome brain throws light especially
are briefly the following.

(a) The hypertrophy, rising dorsad and eversion of the olfacto-
gustatory correlation center. The same thing occurs in the vis-
ceral receptive column in the medulla oblongata of many fishes
and the nucleus habenulae commonly.

(b) The presence originally of the whole olfactory central appara-
tus in the wall of the medial ventricle. Hemispheres are formed
by the evagination first of formatio bulbaris, then secondary
olfactory centers, and last the visceral and somatic correlating
centers which furnish the materials for the development of the
cortical structures. |

(¢c) From a condition like that of cyclostomes the selachian
telencephalon has been derived by the evagination chiefly of the

THE TELENCEPHALON IN CYCLOSTOMES 369

medial olfactory nucleus and the primordium hippocampi. In
(Chimaera), ganoids and teleosts the evagination has been arrested
and the eversion of the primordium hippocampi seen in cyclostomes
is greatly increased. The formatio bulbaris actually bounds the
median ventricle near the foramen and the apparent folding out of
of the striatal or somatic area in cyclostomes is absent in ganoids
and teleosts (see 711 b).

(d) The primitive relations of the hippocampal primordium
and of its commissure in the lamina supraneuroporica are splendidly
clear and instructive in cyclostomes. The selachians present
essentially the same relations in evaginated brains. In ganoids
and teleosts (11' b) the extreme eversion has abolished the primi-
tive supraneuroporic commissure, except in a few forms. In the
amphibians the commissures are similar to those of ganoids. In
reptiles and mammals the cyclostome and selachian condition
reappears.

(e) The view of the general morphology of the telencephalon
previously expressed (710 c, 711 a, ’11 b) receives the strongest
support from these most primitive brains. The functional columns
of the brain described by the writer (’02 b) extend forward to the
telencephalon. The ventral columns are represented only by cor-
relating tissue adjacent to the terminal ridge or optic chiasma.
The dorsal columns constitute the overwhelming part of the telen-
cephalon, are greatly hypertrophied and become flexed in conse—
quence. The dorsal and ventral columns meet in the preoptic
recess where the sulcus limitans of His ends. The telencephalon
in petromyzonts ts not elongated parallel with the long axis of the
fish, but owing to its flexure, is longer dorso-ventrally.

The olfactory nerve and sac on the one hand and the formatio
bulbaris on the other are closely related to the neuroporic recess
and illustrate clearly the principle (711 a, p. 39) that the neuroporic
recess owes its existence to the attachment of the olfactory nerve
to the dorsal lip of the neural tube at this point. The evagi-
nation of hemispheres began here close to the dorsal border at
some distance from the anterior end of the brain tube. This
point lies at about the middle or height of the forebrain flexure.

370 J. B. JOHNSTON

Caudal to this middle point of the forebrain the visceral recep-
tive column forms the olfacto-gustatory correlation center or
primordium hippocampi. From the study of other fishes (11 a
and ’11 b) I have shown reason to think that the somatic correla-
tion center, or primordium of the somatic cortex has been formed
by eversion and migration of neuroblasts from the dorsal border of
the telencephalon in this caudal part.

The cephalic part of the forebrain comes to be ventrally placed
owing to the flexure, and is constituted chiefly or wholly of the
medial and lateral secondary olfactory centers and preoptic
nucleus. The formatio bulbaris arises from tissue nearest the
olfactory nerve root at the middle part of the dorsal column and
in higher forms is carried out upon a peduncle. In some petromy-
zonts it actually retains its relation to the median ventricle.

An understanding of the fundamental morphological and func-
tional relations in the forebrain must be built upon the central
fact of the forebrain flexure. The conception of a curved axis of
the telencephalon ending at the preoptic recess, and of the olfac-
tory nerve entering the dorsal border at the height of the curve
must never be lost sight of. These are fundamental facts, not
hypotheses, and all forebrain morphology becomes confused unless
these facts are held firmly in mind.

In forms above the cyclostomes the rostrum elongates, the olfac-
tory sae shifts forward, the bulbar formation follows it and becomes
pedunculated. At the same time the evagination of hemispheres
progresses rapidly and the hemispheres elongate. Now the ceph-
alic and caudal portions of the visceral receptive column are
sharply flexed on one another in the form of a letter U (figs. 40,
41). The olfactory tract enters the curve of the U. The cephalic
limb, containing the secondary olfactory centers is ventrally placed
and ends at the preoptic recess. The caudal limb (primordium
hippocampi) is dorsally placed and ends at the eminentia thalami.
The two limbs are separated by the interventricular foramen and
by the medial and lateral zona limitans as already explained.

Owing to the eversion and migration of the neuroblasts of the
somatic correlating center down upon the lateral surface of the
telencephalon this primordium of the general cortex comes to lie

THE TELENCEPHALON IN CYCLOSTOMES Bll

between the limbs of the U. In this position it enters into rela-
tions with the lateral olfactory nucleus which lead to the formation
of the pyriform lobe as an olfacto-somatic correlation center
(cortex). Within the somatic primordium there develop also com-
plex correlation systems between the cutaneous, musculo-sensory,
auditory and visual fiber tracts which probably reach this center at
an early stage in the phylogeny (see 710 c¢, and ’11 a). This com-
plex correlating organ is the general cortex. As it develops it
pushes in between the primordium hippocampi and the pyriform
lobe, assuming the characteristic postion of the general cortex
in mammals. The expansion of the general cortex pushes the
hippocampal formation to the medio-dorsal border of the hemis-
phere and the pyriform lobe down to the ventral surface.

LITERATURE CITED

BurckHaArpt, Rupotr 1894b Die Homologien des Zwischenhirndaches bei Rep-
tilien und Végeln. Anat. Anz., Bd. 9.
1894 ec Zur vergleichenden Anatomie des Vorderhirns bei Fischen.
Anat. Anz., Bd. 9.
1907 Das Zentral-Nervensystem der Selachier. I. Teil: Einleitung
und Scymnus lichia. Abhdl. der Kais. Leop.-Carol. Deutsch. Akad.
Naturf., Bd. 73. Halle.

Herrick, C. Jupson 1910 b The morphology of the forebrain in Amphibia and
Reptilia. Jour. Comp. Neur., vol. 20.

Jounston, J. B. 1901 The brain of Acipenser. Zool. Jahrb., Anat., Bd. 15.
1902a The brain of Petromyzon. Jour. Comp. Neur., vol. 12.
1902 b An attempt to define the primitive functional divisions of the
central nervous system. Jour. Comp. Neur., vol. 12.
1906 Nervous system of vertebrates. Philadelphia, Blakiston.
1909 b The morphology of the forebrain vesicle in vertebrates. Jour.
Comp. Neur., vol. 19.
1910 c The evolution of the cerebral cortex. Anat. Rec., vol. 4.
1910 d A note on the forebrain of Chimaera. Anat. Anz., vol. 36.
1911 a The telencephalon of selachians. Jour. Comp. Neur., vol. 21.
1911 b Telencephalon of ganoids and teleosts. Jour. Comp. Neur.,
vol. 21.

Kappers, C. U. Arriins AND CARPENTER, F.W. 1911 Das Gehirn von Chimaera
monstrosa, Folia Neuro-Biologica, Bd. 5.

ScHILLinG, K. 1907 Ueber das Gehirn von Petromyzon fluviatilis, Abhdlg. d.
Senekenb. Naturf. Ges., Bd. 30.

Srerzi, G. 1907 Il sistema nervoso centrale dei vertebrati. Vol. 1, Ciclostomi.

Tretsakorr, D. 1909 Das nervensystem von Ammocoetes. II Gehirn. Archiv
Mik. Anat., Bd. 74.

J. B. JOHNSTON

REFERENCE LETTERS -

b.o., bulbus olfactorius, formatio bul-
baris.

c. a., commissura anterior

ch., chiasma opticum.

c.hipp., commissura hippocampi.

c.p., commissura posterior.

c.p.a., commissura pallii anterior.

C.p.p., commissura pallii posterior.

c.sup., commissura superior (Osborn).

dienc., diencephalon.

di-tel., di-telencephalic boundary.

d.p., decussatio postoptica.

e., epiphysis.

em.th., eminentia thalami.

fi., foramen interventriculare.

f.olf., fila olfactoria.

f.p.p., fibers from the parapineal body.

g., olfactory glomeruli.

hem., hemisphere.

hy., hypophysis.

hyp., hypothalamus.

l.o., lobus olfactorius (secondary cen-
ters).

l.s., lamina supraneuroporica.

l.t., lamina terminalis.

l.v., lateral ventricle.

m., caudal margin of lamina supraneu-
roporica.

mesenc., mesencephalon.

n.h., nucleus habenulae.

n.olf., nervus olfactorius.

nuc.olf.med., nucleus olfactorius medi-
alis.

par., paraphysis.

p.c.b., precommissural body.

p.h., primordium hippocampi.

p.p., parapineal body.

pt., pretectal region.

rec.ph., recessus praehabenularis.

r.m., recessus mammillaris.

r. n.,recessus neuroporicus.

r.p., recessus praeopticus.

r.po., recessus postopticus.

s.d., saceus dorsalis.

s.l., suleus limitans hippocampi.

s.l.H., suleus limitans of His.

s.m., stria medullaris.

s.m.1, first bundle of stria medullaris

s.med., sulcus diencephalicus medius of
Herrick.

s.hy., sulcus hypothalamicus.

sub.hab., subhabenular region.

t.c., tela chorioidea.

tel.m., telencephalon medium.

t.f., taenia fornicis.

thal., thalamus.

t.p., tuberculum posterius.

tr.c-h., tractus cortico-habenularis.

ir.h-p., tractus habenulo-peduncularis.

tr.o-h., tractus olfacto-habenularis.

ir.op., tractus opticus.

tr. pall.,tractus pallii.

v. tr., velum transversum.

Fig. 1 The medial surface of the right half of the brain of Mustelus to show

the position of the velum transversum in selachians.
eminentia thalami which is not lettered.

Medial view of the right half of the telencephalon and diencephalon of
The olfactory bulb is not drawn.

Fig. 2
an adult Acipenser.

It is attached to a slight

The velum transversum is

a very deep fold of the tela chorioidea which is nearly horizontal in position. It
is attached to the eminentia thalami as in selachinas, amphibians and others.

THE TELENCEPHALON IN CYCLOSTOMES 318

Nucleus habenulae J!ectum mesencephali
Velum transversum Ge
Epiphysis pee ie —
Paraphysis Sy ie Es < Cerebellum
Telencephalon >
Lob. lin. lat.

Tub acust.

= { %, a: - Com. infima
Yu Sac. vasc. Lobus visceralis
Rec. neurop.

Rec. praeop. | Lobus inferior

Optic chiasma 1

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 4

374 J. B. JOHNSTON

Fig. 3 Petromyzon dorsatus, ammocoetes. Medial view of a model of the
left half of the forebrain.

Fig. 4 Lateral view of the model shown in figure 38. The hemisphere is divided
by a vertical sulcus into a rostral portion containing the bulbar formation and a
caudal portion containing the secondary olfactory centers. About opposite the
caudal pole of the hemisphere appears a vertical sulcus in the wall of the brain
stem. This corresponds in position to the di-telencephalic boundary line as deter-
mined by other data and is to be regarded as a di-telencephalic sulcus or fissure.

THE TELENCEPHALON IN CYCLOSTOMES BH (5)

mesenc. —

376 J. B. JOHNSTON

Fig. 5 Lampetra wilderi. Medial view of the right half of a model of the

telencephalon and diencephalon. 50.

THE TELENCEPHALON IN CYCLOSTOMES

uo
ba |
“J

Fig. 6 Ichthyomyzon concolor. Medial view of the right half of a model of
the telencephalon and diencephalon. % 66. The slender groove rostral to the
sulcus medius is apparently due to one or two sections being less stretched in mount-
ing than the adjacent ones.

378 J. B. JOHNSTON

Fig. 7 Lampetra. Dorsal view of the model shown in figure 5. This is pre-
sented chiefly to illustrate the stem-hemisphere fissure and the wedge-shaped
telencephalon medium. The attached border of the tela chorioidea is drawn.
Its caudo-lateral angle is the upper end of the recessus praehabenularis. In
Petromyzon dorsatus the eminentia thalami comes up nearly to this point and the
velum transversum is attached to it. The broken line running caudo-laterad
from this point corresponds to the plane of sudden transition in internal structure
from the primordium hippocampi to the pretectal and subhabenular region.

THE TELENCEPHALON IN CYCLOSTOMES 379

vent. III

Fig. 8 Petromyzondorsatus, ammocoetes. Model of the dorsal portion of the
left half of the forebrain, drawn as seen from the medio-ventro-caudal direction.
The model was carefully constructed on a large scale in order to determine whether
the velum transversum really formed a continuous fold from the median line to
the lateral attachment of the tela (i. e., the taenia). This drawing should be com-
pared with figures 23 to 27. d.m.c., dorsal sac.

380 J. B. JOHNSTON

Fig. 9 Ichthyomyzon concolor. A transverse section through the nucleus
habenulae and eminentia thalami of the right side. The section cuts the eminen-
tia thalami at its most prominent part, where it is bounded by the sulcus limitans
hippocampi below and the sulcus subhabenularis above, as seen in figure 6.

Fig. 10 Petromyzon dorsatus, adult. Transverse section through the inter-
ventricular foramen. The primordium hippocampi is not so large as in Lampetra.
At the lip of the foramen it is continuous with the wall of the hemisphere.

Fig. 11 Same series as figure 10, section through the eminentia thalam1.

Fig. 12 Entosphenus, ammoccetes of 35 mm. Transverse section through
rostral part of foramen interventriculare. The section is quite oblique so that
on the right side it passes considerably rostral to the foramen. The primordium
hippocampi is small but occupies the same position as 1n other forms. The section
falls at the Junction of the parapineal body and the left nucleus habenulae.

Fig. 13 Same series as figure 12, section through the eminentia thalami and
the habenular nuclei. Note the great size of the right nucleus habenulae. On
the right side the primordium hippocampi is cut.

THE TELENCEPHALON IN CYCLOSTOMES 381

382 J. B. JOHNSTON

Figs. 14-22. Lampetra. Nine sections of the habenular and hippocampal
region drawn from a series of horizontal sections prepared by the Golgi method.
The figures were drawn at a magnification of 200 diameters and are reduced to one-
third. Figure 22 is at a somewhat lower magnification.

Fig. 14 The first section through the dorsal part of the left primordium hippo-
campi. The section shows the epiphysis and its stalk. The four fibers in the left
nucleus habenulae come from the parapineal body. The bundle s.m.1 is the first
part of the stria medullaris of which it is uncertain whether it is a tractus olfacto-
habenularis or tractus cortico-habenularis.

Fig. 15 The second section of the same series. The first bundle of the stria
medullaris is passing through the left nucleus habenulae.

383

THE TELENCEPHALON IN CYCLOSTOMES

384 J. B. JOHNSTON

Cine
_

Fig. 16 The third section of the same series. Note the extreme difference
in size between the two nuclei habenulae and the passage of the first stria medul-
laris fibers as a compact bundle over to the right nucleus. The prehabenular
recess is narrow in Lampetra and the eminentia thalami does not appear as a dis-
tinct ridge in these dorsal sections. This is due to the large size of the primordium
hippocampi in Lampetra as well as to the crowding together on account of the
pressure of the buccal funnel. A section through the brain of Ichthyomyzon or
Petromyzon dorsatus at this same level would show a distinct eminentia thalami.
Compare figures 6 and 9.

THE TELENCEPHALON IN CYCLOSTOMES 385

ie : ne AM
We, \wh

Fig. 17. The fourth section of the same series. Note the several divisions of
the commissura superior (Osborn). The next three figures show that the great
majority of the left stria medullaris decussates and that a large number of fibers
pass through the nuclei habenulae to the opposite primordium hippocampi.

386 J. B. JOHNSTON

lbFEZZ Fr Cy
ZS Wi: EG ‘k

tr o-h

Fig. 18 The fifth section of the same series. The right primordium hippocampi
shows the first stria medullaris bundle. On the left the tractus olfacto-habenu-
laris comes up through the lower part of the primordium hippocampi and the

eminentia thalami.

THE TELENCEPHALON IN CYCLOSTOMES 387

Ss
>s

Fig. 19 The sixth section of the same series. On both sides the fibers of the
tractus olfacto-habenularis lateralis and posterior appear as definite bundles which
in the next sections clearly lie in the eminentia thalami.

388 J. B. JOHNSTON

Fig. 20 The seventh section of the same series. In the rostral part cf the
e axone is directed toward the

right primordium hippocampi is seen a cell whos
nucleus habenulae. Note the sharpness of the structural boundary between the

primordium hippocampi and the pretectal region.

THE TELENCEPHALON IN CYCLOSTOMES 389

Fig. 21 The ninth section of the same series. Note the difference between
the cells in the primordium hippocampi and those in the subhabenular region.
The tractus olfacto-habenularis occupies a position in the eminentia thalami
which is quite typical for vertebrates generally. The great number of longitudi-
nal fibers in the primordium hippocampi are only indicated by a few lines.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 4

390 J. B. JOHNSTON

Fig. 22 The thirteenth section of the same series drawn at a lower magnifica-
tion. The section passes through the anterior pallial commissure and above the
interventricular foramen. The heavy broken line shows the outline of the next
section ventrad, in which the sulcus limitans hippocampi passes forward to enter
the foramen. Note that the primordium hippocampi is followed caudally by the
eminentia thalami and this by the ridge containing the tractus habenulo-peduncu-
laris. The sulcus medius separates these two ridges. The anterior pallial com-
missure in this section has only fibers connecting the hemispheres.

THE TELENCEPHALON IN CYCLOSTOMES

bony Ng
Seeeliilin s

np
LOH ESTES
tH

B pp.

391

392 J. B. JOHNSTON

Figs. 23-27 Ammoecoetes of Petromyzon dorsatus. Five sections from the
sagittal series from which the model shown in fig. 8 was reconstructed. The
outlines were made with the aid of the Edinger drawing apparatus. The velum
transversum is seen as a distinct fold of the tela in figures 23 to 26, but in figure
27 it joins the eminentia thalami. Figures 25 and 26 show well the course of the
tract which runs up from the medial olfactory nucleus in front of the foramen
interventriculare. This bundle may contain a tractus olfacto-corticalis and pos-
sibly also the fornix column. The fibers of the commissural bundles beginning
with the most rostral successively turn up into the primordium hippocampi (fig.
24). The fibers which go laterally into the hemispheres are not readily seen in
these sagittal sections because they are cut across. These sections show conclu-
sively that the commissure is largely related to the primordium hippocampi.

THE TELENCEPHALON IN CYCLOSTOMES 393

394 J. B. JOHNSTON

n.h

28 29 I i I AME Ad

Fig. 28 A diagram to show the disposition of the velum transversum. The
outline is taken from figure 7, showing the dorsal aspect of the model of the Lam-
petra brain. The tela chorioidea is drawn as it would appear if the epiphysis and
parapineal body were removed. The velum transversum is drawn as a fold of the
tela.

Fig. 29 Professor Herrick’s figure 73 reprinted for comparison with figures 6
and 9 of this paper. The figure is ‘‘a diagram reconstructed from actual sections *
of the cyclostome brain, Ichthyomyzon concolor.”

THE TELENCEPHALON IN CYCLOSTOMES 395

Fig. 30 Lampetra. Transverse section through the caudal third of the left
primordium hippocampi. Golgi method. Most of the dendrites are longer than
they appear in this figure. The distal ends of the dendrites extend nearly to the
outer surface but are too intricately interlaced to be followed.

396 J. B. JOHNSTON

Fig. 31 Lampetra. Transverse section through the primordium hippocampi
just caudal to the interventricular foramen and the anterior pallial commissure.
The cells in the rostral end of the primordium are of the same type as in the caudal
part (fig. 30).

THE TELENCEPHALON IN CYCLOSTOMES 397

Fig. 32 Acipenser rubicundus. Five cells of the primordium hippocampi for
comparsion with those of Lampetra. Note that the eversion of the forebrain in
this ganoid of 30 cm. is about the same as in the adult Lampetra.

398 J. B. JOHNSTON

Fig. 33 Amia calva, about 15 mm. A parasagittal section near the lateral
border of the forebrain, showing three cells of the primordium hippocampi and a
few fibers of the tractus pallii. Golgi method.

THE TELENCEPHALON IN CYCLOSTOMES 399

Fig. 34 Rana. Transverse section of the dorso-medial angle of the right
hemisphere showing the characteristic cells of the primordium hippocampi. Golgi
method.

400 J. B. JOHNSTON

tr.c-h.+c.p.p.

Fig. 35 Scheme of fiber tracts related to the primordium hippocampi in petro-
myzonts. The secondary olfactory neurones located in the caudal part of the
hemisphere are represented by broken lines.

THE TELENCEPHALON IN CYCLOSTOMES 401

Eee aes primordium
hippocampr

bulb olf ih
f

SS
SS Se

NNN

Fig. 36 Cryptobranchus allegheniensis. Transverse section through the tel-
encephalon behind the cerebral commissures. The remnant of the primordium
hippocampi in the telencephalon medium appears on the left side to the right of
the letters p.h.

Fig. 37 Necturus. Sketch of the right half of the forebrain as seen from the
medial surface. This figure is introduced merely to show the general relations of
the medial zona limitans which extends rostrally from the interventricular foramen
and separates the medial olfactory nucleus and primordium hippocampi. Its
formation has been brought about by the evagination of the region which in the
brain of cyclostomes lies rostral to the foramen. Compare figure 5.

402 J. B. JOHNSTON .

taen for.

com.pal.ant.

Seas

rec.rneur.

Figs. 38 and 39 Two drawings of a clay model made to represent a simplified
selachian forebrain. From Johnston ’11 a. Figure 38 shows the medial surface,
figure 39 the rostral surface. The broken line on these surfaces represents the
medial zona limitans hippocampi. It extends from the neuroporic recess through
the interventricular foramen along the medial wall of the hemisphere. Compare
the figures of sections in the paper referred to. This zona limitans is homologous
with the line of separation of the primordium hippocampi and medial olfactory
nucleus rostral to the foramen in cyclostomes. See figures 3, 5 and 6. In figure
38, s.M. marks the continuity of the sulcus limitans hippocampi with the sulcus
hypothalamicus, very much as in Lampetra and Ichthyomyzon. Compare figure
41.

of Deas
~

a See

4S 8

+ fe}
=|

a 15

eon e

(o}

~ Ss

S
Y BR

The visceral receptive column is shaded by oblique lines,

THE TELENCEPHALON IN CYCLOSTOMES

Fig. 40 Diagram of the relations of functional columns dr

of the Lampetra brain.
the somatic receptive column by vertical lines.

is cross-hatched with oblique lines and it is evident that it is the caudal portion

of the column devoted to olfactory and gustatory functions.

The lower border

of the cross-hatched area in the figure is the sulcus limitans hippocampi, both ros-

tral and caudal to the interventricular foramen.

J. B. JOHNSTON

404

nuc. olf. med.

lenc

tele

isp

gram similar to that of figure 40, drawn on the outline of the brain

ig. 41 Di

Owing to the somatic

Drawn from the bisected brain.

of Squalus acanthias.

receptive area being situated on the lateral surface of the telencephalon, its pro-

The medial sulcus limitans

avy line along the lower border of the primordium.

figure overlaps the olfactory area.

aped flexure of the visceral receptive column, the

tes the U-sh

his figure illustra

at the base of the U, and the position of the

attachment of the olfactory peduncle

The axis of the brain

ends in the recessus praeopticus and the great forebrain flexure involves only the

dorsal columns.

een the two limbs of the U.

somatic receptive area betw

THE NUMERICAL RELATIONS OF THE HISTOLOGICAL
ELEMENTS IN THE RETINA OF NECTURUS
MACULOSUS (RAF.)

SAMUEL C: PALMER

TWELVE FIGURES
CONTENTS

I WiehewlWOMONNG suas odsncgeom our DA ay bitte df oecice tae Arle SRR oes Pao oe 405
MR EMIS DO nie al TEMICW. 5 onc cre ete ehae lc tigs Ae oh oaetnly De be Oe LE ee ee 407
ACPBEVG GIN as creas a fils ok yn Red Pesca dare Aik, ceaps fan eke nee 407
BS BO) ag CHET Ve ree oop 5 ee hele dans Stee a ta Oa pane Oe a 411
IRS VWiaterializancdietechmrgueiscs.cccs ast) o> cic bococento sclera e cesta opts ae 412
JN, IIE NAOT gee Sen, Dei on Rg ek eso ee ORME gh rey ear A LU Nd A VK 412
ES Peaie CLM Sere Aria ske tis ene bin al cae ae AUS oe eee 413
IW 2 OLOSVeS AGEN KON IRS co na Goat Oe eae een Sr A RE SE se ee A ds FON ae 417
JANES IMIR DIRS COSI CUS ame ie ERE re eR ETO oie PEON Sk Oe Ca ab ee anes 417
Dee Retin ewlayens eid stew thepeats see Oee aee teee e e e ee 417
In > Cross-sections' of the Optic nerve. 4.068 ete aon 2a ee eee 419
a MUnIGEAtODSes ces oe. oie ae 8S RE aI SAS DES Le eee 420
oe Visita Cell Sie. hos ate Mg, ashlee parle gee tt oie Orie Aiea SEN al oe 420
be Outermuclear layer sco v5) teh ate «eyes Sees ew chorea: 423
ce: Ganglionievlayers 20.55 jie oA nS anne ee te eng tek eee 424
di Millers: fibers 3 2h 61s AT age i ats hee te ed 425
é: Linmer- nuclear layer s)2 ty. cs eee rad oe tet Geese ok: 427
£- OptiG NEF Ve TIDELS . jcaieniac0 kee mae eee ee bre eae eee eke me 429
WEMIDTSCUSSIONG stu creeee ln sehen Ane ea OE oct ee the eee 431
Wile eonretical: CONSID EEA TIONS! Os.4 <4.c1/0 4.15 cree a ee ee sete ee ba eee 436
WN OSOTITEIOL) gy 2) ns | ce ned ere Be A lh 5 Mess ie at oe a 0 Se 438
“CIPULS eho a ese | ce eR RIE Re DR er od Se ake Ne | Mme is 2 439

I. INTRODUCTION

Although the vertebrate eye has long attracted the attention
of investigators and has been the subject of numerous researches,
few attempts to enumerate the histological elements of the retina
and of the optic nerve have been made. The exceedingly deli-
cate nature of the retina has always been a serious difficulty
in the way of its histological study, but with the introduction

405

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5
OCTOBER, 1912

406 £ SAMUEL C. PALMER

of Golgi’s bichromate method and of Ehrlich’s methylene-blue
method for staining nervous tissues, this difficulty has been,
at least partially, overcome, and as a result great advance has
been made in our knowledge of the visual apparatus. We owe
much, also, to the use of osmic acid, which has been so success-
fully employed, not only in the study of the finer structure of
nerve cells and their processes, but also in the enumeration of
nervous elements. In the optic nerve this has not always been
satisfactorily carried out, because the fibers of this nerve are
very small and difficult to stain. The usual treatment has been
to blacken the medullary sheaths with osmie acid, which, however,
leaves the axis-cylinders unstained.

Many theories have been elaborated to explain the structure
and functions of the retinal elements, but where the numerical
relations of these units have been concerned investigators have,
for the most part, confined their enumerations to regions of
special interest, leaving untouched the broader aspect of the
entire retina and optic nerve. It has seemed to me, therefore,
that a complete enumeration of the histological elements of the
retina and of the optic nerve, which have to do directly with the
transmission of visual impulses, would be a desirable addition
to our knowledge of the eye; and I have, therefore, undertaken
to complete such an investigation on one of the lower vertebrates.

There is great similarity in the structure of the retina in all
classes of vertebrates. From the standpoint of the neurone
theory, the visual apparatus in these animals consists of three
distinct layers of neurones. These neurones bear so constant
a relation to one another that a definite terminology has become
associated with them. The first neurones to receive the visual
impulses are the visual cells, which include the rod-and-cone
layer, a majority of the nuclei in the outer nuclear layer, and
processes terminating in the outer reticular layer. The second
set of neurones is represented by the nuclei of the inner nuclear
layer exclusive of Miiller’s fibers and are of two distinct forms,
viz., amacrine cells and bipolar cells. Processes from the latter
form synapses with similar processes arising from the visual and
from the ganglion cells. The third set of neurones consists of

HISTOLOGICAL ELEMENTS RETINA NECTURUS 407

the ganglion cells, which are described by Ramén y Cajal (94)
as sending free branching processes into the inner reticular layer,
and axis-cylinders to the central organ through the optic stalk.

My problem is concerned with enumerations of the rods, cones,
and double-cones, and the nuclei associated with them, of the
nuclei of the inner nuclear layer, and the ganglion layer, of the
Miiller’s fibers, and the fibers of the optic nerve.

All my investigations have been made in the Zoélogical Labor-
atory of Harvard University under the personal supervision of
Prof. G. H. Parker, to whom I am greatly indebted for advice
and valuable criticism.

Il. HISTORICAL REVIEW
A. Retina

Although the literature on the retina and optic nerve in ver-
tebrates is extensive, it is surprising that so little has been done
on the numerical relations of the retinal elements. For the most
part, those who have investigated the retina in this respect have
limited their statements to the fovea and to comparisons between
the number of visual and ganglion cells in central and peripheral
regions. An epitome of the morphology and physiology of the
retina has been published by Greeff (00), but it is not satisfactory
for numerical relations of the elements because of the lack of suffi-
cient data.

Much of what has been written concerning the number of
retinal elements in mammals relates to the human retina. One
of the earliest to consider the question was Krause (’76), who
estimated the number of rods in the human retina to be 130,000,-
000 and of cones to be 7,000,000. Salzer (80) also worked on
the human retina and estimated the number of cones to lie be-
tween 3,000,000 and 3,600,000, but gave no estimate of the num-
ber of rods or of other retinal elements. Foster (’91) and many
other physiologists have apparently accepted the estimates of
Salzer. In regard to the distribution of the rods and cones Foster
writes ‘“‘Over the retina (including the ora) the rods are much
more numerous than the cones, there being two or three rods

408 SAMUEL C. PALMER

in the line joining two cones,” and ‘‘ Toward the extreme periph-
ery of the retina the cones become more numerous and close
to the ora are alone present.”’ Hesse (’00) gives the total number
of visual cells in the human retina as 50,000,000. Stohr (06)
believed that the rods were more numerous than the cones and
that the latter occurred at regular intervals, so that three or four
rods lay between adjacent cones. Pitter (02) has given a great
deal of attention to enumerations of the histological elements
in the retina and in the optic nerve of marine mammals. The
total number of elements in the different layers of the retina
was found to be enormous (table 1). Estimates of the number
of rods ranged from 227,000,000 in the adult Phoca vitulina to
800,000,000 in Macrorhinus leoninus and Balaenoptera physalus.
As no mention was made of cones, except in the case of Hyper-
' oodon rostratus, where they were said to be wanting, the retinas
were presumably pure rod retinas. The nuclei in the outer nu-
clear layer were said to be from six to thirteen times as numerous

TABLE 1
Estimated numbers of retinal elements and optic nerve fibers in certain species of
marine mammals (after Pitter, ’02)

|
|

2 1 c NUMBER OF NUCLEI PER | NUMBER OF OPTIC | , 2
z al & a = SQUARE MILLIMETER IN NERVE FIBERS g a
SPECIES 6 5 a S S - ok wp
eee & < Pp = QA
ers = s is Outer Inner orl . oa <
gag | yaw | nuclear nuclear earn Total HHO
5Sae <A & | layer layer mil <7 &
z si 5 e meter | Pe
Macrorhinus | |
leoninus.......| 90,000 , 800,000,000 1,250,000} 110,000 | 103 767,000 |1:1050
Phoca barbata ..| 120,000 | 363,000,000 1,367,000, 119,000 68 | 174,000 |1:2086
Phoca vitulina.. | 110,000 | 227,000,000 | 1,512,500/ 78,000] 74 147,000 /1:1544

Odobaenus |
6,000,000 | 722,000) 82,000 62 | 111,000

rosmarus......| 110,000") 25 1:23800
Otaria jubata....| 250,000 | 475,000,000 | 2,000,000 181,000 74 | 140,000 |1:2000
Balaenoptera |

physalus...... - 62,000 | 800,000,000} 550,000, 62,000 | 13 | 157,000 /1:5095
Phocaena com- | | |

munis........ - 200,000 | 175,000,000 | 1,350,000, 184,000 | 29} 36,100 /1:4850
Delphinapterus | |

leucas.... | 150,000 | 735,000,000 794,000 98,000 | 28 | 137,000 |1:5560

Hyperoodon
rostratus.. 111,000 | 557,000,000 918,000, 90,000 |

—
~

77,000 1:7200

HISTOLOGICAL ELEMENTS RETINA NECTURUS 409

as the rods, which would make the enormous total for the outer
nuclear layer in Phoca barbata more than 4,000,000,000 nuclei.
In all the species mentioned in table 1, the number of nuclei in
the inner nuclear layer approached more closely that of the rods,
being slightly less in most cases. Equally important is the com-
paratively small number of optic nerve fibers associated with
this enormous number of retinal cells. Pitter estimated that
in Balaenoptera physalus there were only 13 optic nerve fibers
per square millimeter, giving a total of 157,000 for the entire
nerve. In this case there would be about 5000 visual cells to
a single optic nerve fiber. Considerable difference was found
between the number of elements in embryonic and adult retinas.
As a rule the nuclei were more abundant in the former.

Investigation into the numerical relations of the retinal cells
in other mammals, though meagre and fragmentary, indicate a
condition similar to that in man. Chiarini (’06) expressed in a
general statement concerning the visual cells of the dog, the un-
satisfactory condition in which we find this problem in mammals,
when he said, ‘‘ The cones are less numerous than the rods.”

Franz (’09) has given a definite enumeration of the numerical
relations of the retinal elements for the central and peripheral
regions of the retina in birds. The nuclei were found in eight
species to be more numerous at the center than at the periphery.
In the fundus of the retina of Motacilla alba there were on a
line 0.1 mm. in length 266 nuclei in the inner nuclear layer, 60
in the outer nuclear layer, and 50 in the ganglionic layer; but
over the same distance at the periphery there were only 40 nuclei
in the inner, 20 in the outer, and 4 in the ganglionic layer. To
find the total number in one square millimeter, Franz multiplied
these numbers by 10 and squared the product. On this basis
the fundus was stated to have in Motacilla 250,000 ganglion
_ cells and 360,000 rods and cones, in Bubo 36,000 ganglion cells
and 78,400 rods and cones to a square millimeter.

I have been unable to find any enumerations of the retinal
elements of reptiles. It is important to note, however, that the
so-called rods are said to be wanting in some species. Thus
Ramon y Cajal (’94) says, ‘“‘In die Retina der Eidechse die Stib-

410 SAMUEL C. PALMER

chen fehlen.’”’ The number of elements involved is probably
greater in eyes of equal size in reptiles than in amphibians,
because of the larger size of the elements in the latter.

Detailed enumerations of retinal elements in amphibians have
not been made, so far as I can learn, but Howard (’08) estimated
that the rods, cones, and double-cones in the retinas of Necturus
based on estimates in the fundus, were in the relation 4:1 :1
respectively; but he made no mention of his method of obtaining
this result. The outer nuclear layer is said by him to consist
of a single layer of nuclei in the fundus and a double layer at
the periphery, each rod and each cone is described as having a
nucleus and each double-cone, two nuclei. Schultze (’67) believed
that there was only one nucleus to each double-cone.

Franz (’05) has found the number of nuclei per square milli-
meter in the outer nuclear and ganglionic layers in the number
of selachians. The nuclei, in most cases, were found to be more
numerous about the center than at the periphery. In Acanthias
blainvilli the number of nuclei in the outer nuclear layer near
the center of the retina was 24,000 per square millimeter and in
the ganglionic layer in the same region 1200; in Galeus galeus
near the center there were 75,000 nuclei to a square millimeter
in the outer nuclear layer and 1500 in the ganglionic layer. In
the deep-sea selachians there was a great increase in the number
of nuclei in the outer nuclear layer and a decrease in the gan-
glionic layer. Thus, in the fundus over an area of one square
millimeter there were in the retina of Chimaera monstrosa 100,000
nuclei in the outer nuclear layer and only 600 in the same area
in the ganglionic layer.

Enumerations of the visual elements in the eyes of inverte-
brates have been made in some cases. Parker (’90) placed the
number of facets in an adult lobster’s eye at 138,500 and (’95)
the number of ommatidia in the eye of an adult crayfish (Astacus)
at 2500. Hesse (’00) estimated that there were between 2100 .
and 2400 rods in the eye of Pecten jacobaeus. Among cephalo-
pods, the retina of Loligo was said to contain 162,000 rods per
square millimeter and of Scaeurgus only 26,000, with other species
ranging between the two.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 411

B. Optic nerve

Estimates of the number of optic nerve fibers, have been con-
fined chiefly to the optic nerve of man. Kuhnt (’75) found 200
fibers in the diameter of the optic nerve of a new-born child,
and 220 to 240 in that of a man forty years old, giving totals of
approximately 31,400 and 40,000 respectively for the entire cross-
sections. Krause (’76) put the number at 1,000,000 at least,
but later (80) reduced it to 400,000 including both large and
small fibers, and an equal number of very small fibers. Salzer
(’80) also worked on the optic nerve of man and from three nerves
obtained an average of 437,745 fibers.

The only important contribution, to which I have had access,
relating to the number of optic nerve fibers in amphibians is a
short paper by Lauber (’02), who counted 450 fibers in a cross-
section of the optic nerve of Cryptobranchus japonicus.

Among invertebrates Parker (’95) determined that seven
fibers were connected with each ommatidium in the crayfish eye.
This gave a total of 8085 retinal fibers in the case of a young
crayfish and 16,625 in an old one. Proximal to the fourth optic
ganglion these totals were reduced to 2021 fibers in the former
and 4156 in the latter.

It is a generally credited theory that the majority of the optic
nerve fibers originate in the retina and pass centripetally along
the optic stalk to the brain, and that a smaller number arise in
the brain and pass centrifugally to the retina. This view has
the support of such investigators as His (’90), Ramén y Cajal
(91) and Robinson (96). On the other hand Balfour (’81)
did not hold this view, believing rather that the fibers of the
optic nerve were derived from a differentiation of the epithelial
cells of which the nerve was at first formed.

The axis-cylinders of the optic nerve in a majority of verte-
brates are small and medullated. In some amphibians, viz.,
urodeles, the optic nerve was described by Osborn (’88) as ‘greatly
reduced,’ and in some examples of Necturus there was stated to
exist, in the adult condition a persistent lumen which opened into
the T-like expansion of the third ventricle of the brain. Kings-

412 SAMUEL C. PALMER

bury (’95), likewise, describes the optic nerve of Necturus as
hollow for a portion of its length and states that its fibers are
entirely amyelinic. This latter condition is said by Edinger
(92) to be the case in the young of certain other amphibians.

After a careful survey of all the literature at hand bearing on
the numerical relations of the histological elements of the optic
nerve and retina, I have failed to find for any vertebrate a con-
sistent enumeration of these elements which has been carried
out in such a way as to give reasonably safe grounds for compar-
isons. I have, therefore, undertaken this task in reference to
Necturus.

Ill. MATERIAL AND TECHNIQUE

‘ A. Material

It has long been known that the retinal elements in amphib-
ians are very large as compared with those in other vertebrates.
Howard (’08) gives the dimensions of the outer and inner segments
of the rods in several species of amphibians as follows: In the
outer segment the length varied from 244 in Triton to 76 in
Bufo, and the width from 6y in the frog to 12u in both Triton
and Salamandra. The outer segments of the rods in Necturus
are said to be 36 to 40u long and 124 wide. Measurements
made by myself on the diameter of the cones of Necturus just
distal to the ellipsoids averaged 4.8u, and through the ellipsoids, -
where visual cells first come in contact with neighboring visual
cells, they averaged 10u. The diameters of the rods through
the ellipsoids was slightly larger than that of the cones. Slonaker
(97) states that ‘‘“Amphibia have not only long rods, but the
thickest found in vertebrates.’”? In speaking of the cones, he
says, they have the ‘greatest diameter in mammals.’’ Table
2 shows the relative sizes in micra of the rods and cones in rep-
resentatives from all classes of vertebrates. The length of the
elements is non-essential for my purpose, but the diameter is
of especial significance because it is one of the most important
factors in determining the number of elements which can occupy
a given space, when they are crowded together as are the visual
cells in the vertebrate retina. From the measurements quoted

HISTOLOGICAL ELEMENTS RETINA NECTURUS 413

it will be seen at once that, because of the large diameter of the
visual cells, the number of these elements in a given area will
be fewer in the amphibia than in any other class of vertebrates.
The two conditions, viz., large diameter and fewer elements,
unite to make the amphibian retina especially favorable for a
study of the numerical relations of the constituent parts. With
this point in mind I have selected for my investigation the adult
form of Necturus maculosus (Raf.), the common ‘mud-puppy’
of the fresh water streams and lakes of eastern Canada and of
middle and southern United States (Cope, ’89). The specimens
were secured by the Zodlogical Department from Venice, Ohio.

TABLE 2

Comparative sizes of the outer segments of rods and cones in representatives of the
different classes of vertebrates (after Miiller ’56)

DIMENSIONS IN MICRA OF THE OUTER SEGMENTS OF THE
SPECIES EXAMINED Rods = eal ee Gace: oe Rom
(pie Me Mies |) lasses Oo Tee
INTE ee eee Gee 1.5—1.8 | 40.0 —60.0 | 4.0 — 6.0 32.0 — 36.0
125 (430) (a ee 2nOl—3.10) |) 2030.— 2870 Ol —1on0) 25.0 — 30.0
Chameleon...... é 1.0—1.3 60.0 — 80.0
RO Gene aol 6.0 —7.0 | 40.0 — 60.0 5.0 20.0 — 28.0
IRerchewn asa. of. 2.6 40.0 — 50.0 8.0 — 12.0
|

Upon their arrival at the laboratory they were transferred at
once to a fresh-water cement aquarium in a dimly lighted part
of the basement of the Museum of Comparative Zoédlogy, where
they were easily kept in a healthy condition.

B. Technique

I have found that the technique usually employed for the
retina does not give satisfactory results when applied to the optic
nerve; for this reason I have been obliged to make separate prepa-
rations for the two structures.

In order to secure material for a reliable enumeration of the
retinal elements, a fixation fluid was necessary which would not
wrinkle the retina, and at the same time could be followed by

414 SAMUEL C. PALMER

successful double staining, to which I shall refer later, whereby
small fragments of rods could be distinguished from bits of cones.
The large size of all the retinal cells in Necturus has been a great
aid in the identification, and in the accuracy of the counts, of
the separate elements of the retina. The most successful re-
sults were obtained by fixation in Kleinenberg’s picro-sulphuric
mixture. My method was as follows: Live animals were placed
in a bowl of tapwater in which a few small crystals of chloretone
had been dissolved as a means of preventing the discharge
of slime (Cole, ’02). Chloroform was then added gradually
until the animals were thoroughly anesthetized. The eyes were
quickly removed and placed in picro-sulphuric acid, care being
taken to free them from as much superfluous tissue as could be
done quickly. To keep the orientation, a piece of skin was left
attached to the dorsal side of the eyeball, differences in shape
of the pieces serving to distinguish right and left eyes. I found
the pieces of skin useful also in orientating the eyes in paraffin.
The best results were obtained by immersing the unopened eye-
balls in the picro-sulphuric mixture for four or five hours. ‘They
were then rinsed in distilled water a few minutes and dehydrated
by passing them gradually through 35 per cent, 50 per cent, 90
per cent, and 100 per cent alcohol over a period of two days.
When the eye was sufficiently hardened (90 per cent alcohol),
the front face was cut away with a sharp razor, and the lens
removed. Early in my work I found that the heat of a paraffin
bath, extending over a time sufficient to insure saturation with
paraffin, caused considerable shrinkage of the sclera and wrink-
ling of the retina. I, therefore, followed Biitschli’s chloroform
method of de-aleoholization. Transfer from the chloroform-par-
affin mixture of this method to hard paraffin was completed by
the evaporation of the chloroform over a water bath at about
60°C. and a five minute immersion in hard paraffin melting at
about 56°C.

Sections 8» thick were made in one set of eyes parallel to the
antero-posterior! plane of the eye and passing through the optic

1 The terms ‘anterior,’ ‘posterior,’ ‘dorsal’ and ‘ventral’ as applied to the eye-
ball in this account, are used in the sense of comparative anatomy; i.e.. ‘anterior’

HISTOLOGICAL ELEMENTS RETINA NECTURUS 415

nerve, and in another set parallel to the dorso-ventral plane,
and passing through the optic nerve. Series of sections 6u thick
were made through the entire thickness of the retina tangential
to the surface of the eyeball in the anterior, posterior, dorsal,
and ventral regions and in the fundus. The sections were stained
in Heidenhain’s iron haematoxylin as a base, and in a 70 per
cent alcoholic solution of eosin as a counter stain. Thirty minutes
in the mordant (2 per cent ferric alum) and one hour in the hae-
matoxylin gave very satisfactory results. The excess of stain
was washed out in ferric alum of the same strength as the mor-
dant, and the washing was continued until all traces of the haema-
toxylin had disappeared from the outer segments of the rods
and from the reticular layers. At this stage the nuclei of the
outer and inner nuclear layers and of the ganglionic layer were
clearly defined and light blue in color. The nuclei of Miiller’s
fibers were stained a deep blue to blue-black and contrasted
sharply with the lighter blue of the surrounding nuclei. Control
was kept over the process of destaining by examining the slides
every few seconds under the microscope. Two minutes in the
counter-stain were sufficient to color the outer segments of the
rods bright red. The outer and inner reticular layers appeared
as broad red fibrous bands separating the inner nuclear layer
from the outer nuclear and the ganglionic layers, respectively.
The strands of Miiller’s fibers, which stretched radially outward
from the internal limiting membrane, were stained an intense
red. It is clear that the selective qualities of the stains employed
rested primarily with the haematoxylin, for in the process of
reducing the over-stain of the base the outer segments of the
cones, the nuclei of Miiller’s fibers, and the ellipsoids, retained
their color longer than the other elements, thus indicating their
greater chemical affinity for the basic stain. Although the suc-
cess which attended fixation in picro-sulphurie acid and double
staining with haematoxylin and eosin made other methods super-
fluous, nevertheless some entirely successful preparations were
refers to that part of the eyeball which is nearest the anterior end of the animal
(‘internal’ in human anatomy), ‘dorsal’ to that part which is nearest the dorsal

midline (‘superior’ in human anatomy), etc. The deep part of the eyeball, often
called the posterior part, is here referred to as the ‘fundus.’

416 SAMUEL C. PALMER

made with the use of other reagents. Both the vapor of 2 per cent
osmic acid and vom Rath’s picro-osmo-platinic-chloride-acetic
mixture gave excellent preservation of the retinal elements,
though the outer segments of the rods and cones were over-black-
ened. Good preservation and successful double-staining were
obtained by fixation in either Perenyi’s fluid, Fol’s mixture, or
7 per cent nitric acid, followed as before with haematoxylin and
eosin stains.

I have already called attention to the non-medullated char-
acter of the optic nerve fibers in Necturus, hence the usual fixa-
tion fluids in which osmic acid is used to stain the medullary
sheaths are ineffective for the optic nerve fibers, in this animal.
Vom Rath’s fluid gave excellent preservation of the supporting
and vascular tissues, but was unsatisfactory for the nerve fibers.
Ranson’s (’09) modification of Ramén y Cajal’s silver-nitrate
method for non-medullated nerve fibers was tried without suc-
cess. With another modification of this method, that of Mullenix
(09), I succeeded in staining the fibers, but the definition was
poor. The only method tried which brought out the fibers dis-
tinctly was a modified form of Bielschowsky’s (’03) method. In
order to secure the necessarily rapid fixation of the proximal
portion of the optic nerve, I cut away the tissues surrounding
the skull, which was then split at both anterior and posterior
ends. This permitted the formalin to enter the brain cavity
quickly. The non-medullated fibers when impregnated by this
method appeared in longitudinal section as sharply defined
somewhat undulatory, brownish-black to black lines. In cross-
section (figs. 10, 11, 12) they were irregular black spots or streaks
in a yellowish-brown matrix. Dehydration and de-alcoholiza-
tion were carried out as with the retina. Cross-sections of the
optic nerve 5y thick were made close to the chiasma and as near
as possible to the eyeball.

The results obtained with Bielschowsky’s fluid have justified
its use in this case. There is no doubt in my mind that the irreg-
ular black spots and streaks referred to above are nerve fibers.
I was fortunate in having a longitudinal section of an optic nerve
turn up slightly so that the fibers could be seen to end as small

HISTOLOGICAL ELEMENTS RETINA NECTURUS A417

black spots of different sizes. In a longitudinal section individual
fibers could be traced only a short distance. At the distal end
they spread out in bundles along the inner margin of the retina
and disappeared radiating outward between the nuclei of the
ganglionic layer. I was wholly unable to detect a union between
the ganglion cells and the optic nerve fibers, and I am unable
therefore to state the exact relation of the optic nerve fibers to
the retinal elements.

IV. OBSERVATIONS
A. Measurements

a. Retinal layers. The eyeballs of Necturus lie well forward
on the dorso-lateral aspect of the head, where they appear as
shghtly arched whitish bodies. They are unusually small for
the size of the animal, and are approximately spherical in shape.
The retina, which is closely applied to the sclera, has, therefore,
the shape of a zone of one base whose area is only slightly less
than that of a hemisphere. Since the area of a zone of one base
is equal to the area of a circle whose radius is the chord of the
generating arc, the area of the retina in Necturus is equal tothe
area of a circle whose radius is the shortest distance from the
periphery of the retina to the center of its fundus. To obtain
this center I made a camera drawing ( X 101) of a median section
of the eye, and erected a perpendicular at the middle point of
the chord joining the ends of the retina at the ora. The point
of intersection of the perpendicular and the retina marks the
center required. The chord joining this center to the periphery
is equal to the radius of a circle whose area is that of the zone
of one base, which marks the limits of the retina. In many cases
the center lay directly in the optic nerve, while in nearly all the
remaining eyes, it lay very close to that nerve. By this method
I have calculated the minimum, maximum, and average areas
of zones of one base (which hereafter I shall refer to as zones)
for 14 retinas, the three zones coinciding with the external lim-
iting membrane, the middle part of the inner nuclear layer and
the middle of the ganglionic layer (fig. 1, cd, xz, vw). The results

418 SAMUEL C. PALMER

of my measurements are given in table 3. Hight retinas were
measured in the antero-posterior and six in the dorso-ventral
plane. Variations in the thickness of the retinas (figs. 2 to 4),
measured from visual cells to internal limiting membrane, and
irregularities of the retinas, especially at the periphery, are the
causes of the differences of area in retinas nos. 3 and 8, 5 and 6,
and 10 and 14.

In order to enumerate the retinal elements, it was necessary
to adopt unit areas small enough to avoid the distortion at the
margin of the microscopic field and large enough to include a
great number of elements. Convenient sizes were found in a
circular area of 0.013 sq. mm. for the visual cells and one of 0.0078
sq. mm. for the other elements. The areas of the retina in the
zones at the different levels were duly considered, so that the
number of visual cells and nuclei of the outer nuclear layer was

TABLE 3

Calculated areas of zones corresponding to the area of the retina in Necturus and
passing through (1) the external limiting membrane, (2) the middle of the inner
nuclear layer, and (8) the ganglionic layer

| AREAS OF ZONES IN SQUARE MILLIMETERS AT THE

ESIGN? IN -
VTSARC ENE MNOES PLANES OF SECTIONS | =

D282 | External limiting Middle of inner Middle of the
| | membrane | nuclearlayer | ganglionic layer
1 Antero-posterior. . | 12.5664 | 11.7094 10.9073
2 ‘Antero-posterior. . | 13.4484 | 11.8309 10.3138
3 |Antero-posterior. . | ila beara | 13.5815 | 12.0693
4 \Antero-posterior. . 13.8940 | 12s 2255 10.6535
5 |Antero-posterior. 15.0399 | 13.6455 12.3176
6 ‘Antero-posterior. . | 15.0399 | 13.8940 12.8165
ii Antero-posterior. .| 12.0693 10.9133 | 9.8120
8 Antero-posterior. . 15.1777" || LA OT2T I NS une ne
9 Dorso-ventral..... | 14.6303 12.1947 | 9.9743
10 ‘Dorso-ventral..... | 10.8184} 9.70287 8§.6916F
1] Dorso-ventral....., 12.5664 11.4616 10.4257
12 Dorso-ventral..... 13.2541 11.8005 10.4257
13 ‘Dorso-ventral..... | 13.9602 12.3796 10.9073
14 Dorso-ventral..... 10.9351 9.7569 | 8.6916F

Average areas of zones in square
MMMM CCIE: 126 eee ses 13.4698 12.0834 10.7910

* Maximum areas
+ Minimum areas

HISTOLOGICAL ELEMENTS RETINA NECTURUS 419

based on an area obtained for the zones at the external limiting
membrane; Miiller’s fibers and ganglion cells for the zone through
the ganglion layer; and nuclei for the inner nuclear layer from
the area of the zone passing through the middle of this layer.
The number of unit areas in each zone was found by dividing
the number of square millimeters in the zone by the number of
square millimeters in the unit area. The total number of elements
in a layer obviously equaled the product of the number of areas
into the number of elements per unit area. The methods em-
ployed for the other layers were evidently unsuited for enumer-
ations of the inner nuclear layer, for in this layer we have to do
with solid content rather than surfaces. For this layer I have
resorted to counting the nuclei in a cylinder with a head of 0.0078
sq. mm. and with its long axis placed radially. The length of
the cylinders was determined by the number of microtome sec-
tions necessary to pass completely through the layer, the number
of sections being eight in each of the two cases:counted. The
number of such cylinders was found by dividing the area of the
zone of the inner nuclear layer by the area of the cylinder head.
In all cases where elements touch the boundaries of the unit
areas (figs. 5 to 9) they were rated at one-half their value within
the field.

b. Cross-sections of the optic nerve. The areas of the cross-
sections of the optic nerve varied according to their location
(figs. 10 and 11). In all cases examined the nerve was very much
smaller proximally than distally, in one instance the former
amounting to little more than one-third the latter (table 15).
My method of calculating the cross-sectional areas of the nerves
was modelled after that employed by Parker (’95) on the optic
nerve of Astacus. Camera drawings of all the sections to be
measured were made on paper of uniform thickness and weight;
these were then cut out and weighed. A standard unit 0.0015
sq. mm. of the same magnification was also cut out and weighed.
I could then easily obtain the required areas from the arithmet-
ical formula:

X « Y when T is constant

where X equals the area of the cross-section, Y equals the weight

420 SAMUEL C. PALMER

of the drawing, and 7 equals the thickness of the paper. In
sections near the chiasma allowance was necessarily made for the
lumen of the stalk, which becomes obliterated distally.

B. Enumerations

a. Visual cells. The sections used in enumerating the visual
cells were cut tangentially to the surface of the retina in the five
regions already referred to, passing through the outer segments
of the rods and cones, and through the paraboloids of the double-
cones (fig. 1, ab). The visual cells, therefore, were seen in cross-
section, and because of their structure, larée diameter, and differ-
ential staining qualities they were easily distinguished from one
another. I was unable to detect any plan in the arrangement
of the rods and cones, such as Schwalbe (’87) has depicted, but
noted a marked tendency for five or six elements of a kind to
run in lines, a feature which I think is without real significance.
The association of rods or cones in groups of six or eight. (figs.
6 and 8) was of frequent occurrence. Their usual distribution
may be described as irregularly scattered, and free from contact
along their outer segments with neighboring elements (figs. 5 to 9).
With a magnification of 615 diameters the cross-sections of the
rods were bright red, circular to oval in outline, and with the
characteristic vacuolated structure described by Howard (’08).
They were larger than the cones and somewhat more numerous.
The cones appeared as small round, blue-black, homogeneous
bodies scattered irregularly over the field; the double-cones were
far less numerous and much larger than either the rods or the
cones. As one should expect, the paraboloids were fused along
one side (figs. 5 to 9), giving the appearance of double-elements.
Their structure was reticular and took the stain only slightly. In
addition to the elements already mentioned, there were a few
whose identity could not be established with certainty, due, I
think, to disintegration having set in before they were reached
by the fixative fluids. They constituted only a very small per-
centage of the total number of visual cells.

Studies of the cross-sections of the cells in the five regions
described, showing the close relation between the number of
rods, cones, and double-cones, in the different positions, are

HISTOLOGICAL ELEMENTS RETINA NECTURUS 421

clearly set forth in table 4. I have taken the averages from five
retinas in each ease, right and left eyes being used indiscrimi-
nately. Twenty eyes were used, and in five cases counts from
two different regions of the same eye were made, and in two
cases right and left eyes from the same animal were considered.
Averages per unit field for the right and left eyes respectively
show a slightly greater number of rods and cones, and a smaller
number of double-cones and doubtful elements in the left eye.
These differences are shown in table 5. The maximum and
minimum counts are, however, so close in every case as to lead
me to believe that the number of elements involved in right and
left sides is approximately the same, and I shall therefore make
no discrimination between the two.

TABLE 4

Number of rods, cones, double-cones and uncertain elements in unit areas
of 0.013 sq. mm.

REGIONS OF THE EYEBALL IN WHICH THE UNIT AREAS WERE LOCATED

DESIGNATION |

OF Anterior Posterior Dorsal Ventral Fundus
EYEBALLS

BEC NED WEG

R\C|-Di| Xt | Gael |e |e! le) exe Were ep ex

Tr '46.039.5)12
81 70.5/49.5114 | 0 (56.547.514
16r 35.0/44.5121 | 0

211

221 49.2'41.0)14 | 2

3r | 141.0187 |17 |0
231 | 65.5\28.5| 10 | 6.037.531 |16
4r | | 50.026 |20 | 2
241 166.042.5125 | 0
251 64.0/42.0] 8 | 9.5)
6r 47.5147.014 |0 |59.0137.5119 | 1 |
28r 50.5137.0/12 | 1
3lr | 43.0142.515 | 4 |70.5/43.0| 5
331 45.049.5) 18 | 2.5
38 r 156.0/29.5|12 | 0 | |

401 48.0\54.0/10
56r 43. 5/38. 0\14
57r 155.5141. 5/25
59r 49.5136.5110 | 0.5
601 40.5|28.0| 8 | 3

| |

)42.541.014 | 2 |52.5/46.5) 14 | 4.0

a
i=)

Average } | | | |
of 5 Meee. 48. 2)43.1/17.80.4 |43.6/41 |11.8) 1.959.5/41.9) 11 | 5.2 46.236.215.8) 0.8
retinas ) | |

} |

*R, rods; C, cones; D, double-:ones; X, uncertain elements; r, right eye; /, left eye.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 5

422 SAMUEL C. PALMER

From tables 4 to 7 it will be seen that the rods are generally
more numerous per unit field than the cones and double-cones.
Exceptional cases exist, however, where the cones are found
to be more numerous than the rods (table 4, nos. 16 7, 33 1, 40 1),
and I am convinced after examination of a great number of retinas
that such areas are not infrequent in every one of the five regions.
The actual relative values of rods, cones, and double-cones and
the total average number per unit fields, as well as the total average
number per five unit field, are given in table 6, where the rods
consistently outnumber the cones. In table 7 I have brought
together many data for the visual cells. Between the maximum
and minimum retinas there is a variation of 25.per cent, at least,
in the total number of visual cells.

TABLE 5
Average number of retinal elements per unit area in right and left eyes

i] |
5 | AVERAGE NUMBER OF | MAXIMUM NUMBER OF | MINIMUM NUMBER OF
Pp — —~ — — = os
Ho » oO ~ Eo]
Seidl N= ee | 25 = a no = a So
SIDE EXAMINED Sis i fe 5 | gx = = aa g 2 ae
<5 e ke |} os ke oS & Seat
ie 5 2 rae 5 S $4 Be lie ice $a
<8 Py nz Pie Ml) ices am | = eace) ang | ae
ad ne oo Qn Tr o- Qn ns on Qn
ast ao qe 30 Lom} qo 30 av qo 350
zm ow os on ow oe on own on on
p [on] '@) Q foxy .S) (a) — Oo A
; | |— hates
|
Richness. OLOLS M49 RZ Tose 2alelo 70.5 | 47 25 35 26 5
Left 0.013 | 53 AL. | 12.7 | 70.5 49.5 25 Sine 28 8
TABLE 6

Average numbers of visual cells in the five selected unit areas (see table 4)

AVERAGE NUMBERS OF THE SEVERAL KINDS OF

kinds of elements in five

to
bo

combined unit areas....... 95b.4 |. 204.1 es

8.7 | 540.4

HISTOLOGICAL ELEMENTS RETINA NECTURUS 423

To correlate the number of visual cells with the number of
nuclei in the outer nuclear layer, it was necessary to count each
double-cone as two units, on the assumption that each double-
cone has two nuclei. This view is held by Howard (’08), who
found two nuclei associated with each double-cone in macerated
material. My own observations on sectioned material confirm
this relation. The proportions of rods to cones and to double-
cones approximates 3.5 : 2.8 : 1, respectively, which is a decided
increase in the relative number of cones over that given by
Howard. |

b. Outer nuclear layer. The outer nuclear layer, when exam-
ined in radial sections of the eye (figs. 1 to 4) was seen to consist
of a complete single externa! row of nuclei with here and there
additional nuclei lying directly against its inner side. In cal-
culating the number of nuclei in the ‘external’ sheet of which
the ‘single row’ is the section, I have used the method already
employed for the visual cells. The numbers of nuclei per unit
area in the external sheet are given in table 8. In the fundus
the numbers are slightly less than in the other regions. In order
to include the partial ‘internal’ sheet in my enumerations, I
counted the nuclei in the external and internal rows in median
sections from periphery to periphery in eight retinas. In the

TABLE 7

Total numbers of visual cells in retinas of minimum, maximum, and average sizes.
The enumerations are based on the following average numbers of elements in a unit
field of 0.065 sq. mm. area: rods, 255.4; cones 204.1; double-cones, 72.2; uncertain
elements 8.7; total visual cells, 540.4 (table 6)

Eee
lnzaZa 2
}4q Deg < Z
8 <n ahi TOTAL NUMBER OF
i= z & 5 3 S 2

RELATIVE SIZE |g 3 QP a

OF EYEBALLS |8m 5 < On = = ee z = ee ==
Hd 4 oe} m |
azpad es
agae 8 Qa
|PHQR= ag ; Double- | Uncertain! Visual

Ae }
| SBS a sa] I B Rods Cones cones elements | cells
ls z |
oes | | | - ‘ od
Minimum... .| 10.8184 | 166.437 | 42,508 33,970 12,017 | 1,448 89,943

Maximum....| 15.1777 | 233.503 | 59,637 | 47,658 16,859 | 2,032

126,185

Average of 14
retinas..:..| 13.4698 | 207.228 | 52,926 | 42,295 14,962 | 1,803 111,986

424 SAMUEL C. PALMER

external row there was an average of 422 nuclei, as compared
with 121.1 in the internal row. . Since the nuclei of the two layers
have the same average diameters in the plane tangential to the
surface of the eyeball, the ratio of the number of nuclei in the
external layer to the number in the internal layer is 422 : 121.
The total number of nuclei in each of these layers as well as in
the whole outer nuclear layer is given in table 9. By comparing
tables 7 and 9, the number of nuclei in the outer nuclear layer is
seen to exceed the number of visual cells by about 10 per cent; or, if
directly compared for total numbers of elements, there are 121,000
nuclei in the outer nuclear layer to 111,000 visual cells.

c. Ganglionic layer. The nuclei of the ganglionic layer, which
in radial sections of the eye (figs. 1 to 4), are seen to be a single

TABLE 8

Number of nuclei of the outer nuclear layer per unit area of 0.0078 sq. mm.

I ALL IN WHICH E FIELDS WERE ED
SEAT OE REGIONS OF THE EYEBALL IN WHICH THE F WERE LOCAT

THE EYEBALLS SSS SS = = SS ee
Anterior | Posterior Dorsal Ventral | Fundus

71 | | | 55.5
| |
|

Sl | 54
167 5350) 0) |
21 ip A | |
211 | 59 | |
22,1 60 60 | | |
83 r | | |» 49
23 1 | |. S55 oa
24 r | | | 47
24 | | | 43
25 r 42 | 60 |
25 1 | 56it
26 7 58.5 59
28 r 53 | fame
3lr | | 57
32 r 60.5 | 5
38 r 49 | |
39 1 71.5
40 r 56
40 1 | 62

Averages of 5
retinas Dane 58.9 57.9 bay 7 49.7

*r, right eye; 1, left eye.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 425

layer thick, are larger, more rounded and less closely grouped
than are the nuclei of the other retinal layers. Sections from
the five visual regions (table 10) in five retinas show as before a
slight variation in the average number of nuclei per unit area,
but this I believe is due to accidental conditions and is not at
all consequential. Contrary to the condition found in the outer
nuclear layer, the number of nuclei in the ganglionic layer is
greater in the fundus than elsewhere. In table 11 the average
number of nuclei per area of 0.39 sq. mm. is given as 111.1
and the total number of nuclei in a retina of average size is
about 30,000.

' Thus we see that in passing centripetally through the layers
of the retina there is a gradual decrease in the number of elements
composing each layer, except in the inner nuclear layer, so that
according to the views usually expressed, visual impulses aris-
ing in a number of visual cells are transmitted to the central
organ over a greatly reduced number of elements.

d. Miiller’s fibers. Miiller’s fibers were counted to best advan-
tage in tangential sections through the inner reticular layer close
to the ganglion-cell layer, where they appeared as intensely red
spots in a net-work of small light-red fibers. They occurred in
pairs and triplets as well as singly (figs. 1 to 4). I have assumed
that each fiber represents a cell with a nucleus lying generally
in the inner nuclear layer. Slight variations in the number of

TABLE 9

Total numbers of nuclei of the outer nuclear layer in retinas of minimum, maximum,
and average sizes

Minimum.... | 10.8184 | 0.039 | 277.394] 273.
15.177 2 106,400 30,558 | 136,958

Maximum... .| (a OFO39 Wr asOr lee

Average of 14
retinas.....| 18.4698 | 0.039 | 345.379 | 273.4 94,427 27,097 | 121,524

426 SAMUEL C. PALMER

TABLE 10

Numbers of the nuclei of the ganglionic layer per unit area of 0.0078 sq. mm.

DESIGNATION OF REGIONS OF THE EYEBALL IN WHICH THE FIELDS WERE LOCATED
THE EYEBALLS

Anterior | Posterior | Dorsal | Ventral | Fundus

le
9

7 r* | | | 3
1

16 r | | 25:5
21r 14 16.5
7 eA, | 19

23 16
24r ;
24 1 16.5 S).0)
26 r 18.5 26.5
28 r | 18.5
30 1 5) |
Sally 25 |
il Wy | 20 |
32 r 25 24 |
33 | 20 |

237 I 928 1, eos
|

38 r 18
40 r 25.5
40 1 32.9

Averages of 5
retinas 18.0 24.8 21.6 19.7

*r, right eye; lJ, left eye.
TABLE 11

Total numbers of nuclei of the ganglionic layer in retinas of minimum, maximum,
and average sizes

Bgg48 Lar ay 56 if
C aA | Z,
aoag4 = = ze BB
QORZE <5 Be ome OZ
ee oma) o> <
ea O Z is &
47H, & Ba pe 2 & Bom
RELATIVE SIZE OF atasga Zz | 5 By ae
EYEBALLS Bn A, p< | 6% a SOR
aoa < D2 br
<etan me oe ae) Aa m QA
$4 ae a Cee A
asec nas) oneB | i aux aEe
Parag 5 | 2 ek ashe
se2e8Sa QZAS Felo| ape apa
- ae of Sas | bp > 4S }
iS) D A < a
Minimum........ 8.6916 | 0.039 222.861 | Hilal ak 24,760
Maximum....... 13.0690 0.0389 | 335.102 wlan al 37,280
is oes : : —— le i— ae
Averages of 14 | |

TELINASS ban 10.7910

So ie aes Se: ee —— ——

HISTOLOGICAL ELEMENTS RETINA NECTURUS — 427

fibers per unit area occurred, but not sufficiently great to call
for more than passing notice. In table 12 I have given the aver-
age numbers of fibers per unit area and the average numbers
for five retinas in each of the selected regions. The fibers were
counted in unit areas, in some cases in right and left eyes of the
same animal, and in others in two regions in the same eye; but
I could detect no characteristic differences. In table 13 the
average number of fibers in five unit areas is given as 97.5 and
the total number in the whole retina is between 21,729 and 32,672.

e. Inner nuclear layer. The inner nuclear layer presents in
Necturus a variable condition, which makes it, of all the retinal
layers, the most ‘difficult in which to count the nuclei. It con-

TABLE 12
Number of Miiller’s fibers per unit area of 0.0078 sq. mm.

10 HE EYEBALL IN WHICH THE UNI EA
eNO REGIONS OF T Y H T AREAS WERE LOCATED
EYEBALLS Saal
Anterior | Posterior } Dorsal Ventral
| 5

| Fundus ;
Tr | | | oT
21

21 r gs wees | |
Di | 17 hee ol

28 r | 15

31 1 19

40 r 18 |

Averages of 5

retinas 19.1 20.9 18.0 PALS 18.2

™ right eye; iE left eye.

428 SAMUEL C. PALMER

TABLE 13

Total numbers of Miiller’s fibers in retinas of minimum, maximum, and average sizes

BAe LA Zz 6 ] Nl fe es
2 Gina | as | | OF
2 $ < <
Haz a a ep g @
aoHSE a aS ia o &
BOO 49 Ae 2 aa
i Sigil = eI De | 5 & aE
RELATIVE SIZE OF antgka Bie ele | ZS 3)
EYEBALLS lg St ma Z of47 | a 22
B<dHa 3 Pa A | Ay pm
a7 5H 1 mR | ona yA
HAAS i < Bag | “gx Cie S|
paeras Oop aha tm re]
omar aaH ao Seq | aoe <:p
Zea aOM ND Sib | Sa < Bos
N 3}
iS) n a | < a
Minimum........ 8.6916 0.089 | 222.861 97.5 21,729
Maximum...... 13.0690 OF 039) 9) 2335. 102 97.5 32,672
|
Averages of 14 |
GEUIVAS ae ares 10.7910 0.039 276.723 9125 26,980

sists in its usual form of three layers of nuclei (fig. 1), of which
the middle one has fewer nuclei than either of the other two.
In addition a large part of the nuclei of Miiller’s fibers lie within
it (figs. 1 to 3). The number of layers may be as numerous as
four (fig. 3), or even five, or they may be as few as two (fig. 2);
in one case I found only a single layer in a part of one side of
the retina. Such variation makes any estimate of the number
of cells unsatisfactory. Since the most frequent condition is
the three layered one, I have determined the number of nuclei
in a zone of this kind. Figs.1 to 4 show that there is little differ-
ence in the ‘tangential’ diameters of the nuclei of the outer and
inner nuclear layers. With any increase or decrease in the aver-
age tangential diameter of the nuclei of one of these layers over
that in the other, the number of nuclei in a given belt, such as
I have used in the inner nuclear layer, would be found to vary
and I could not then make the proportion as stated, but if the
average tangential diameters of the nuclei of the two layers is
the same the relations between the two would be constant and my
results would hold true. Since this is the case, the total number
of nuclei in the two layers respectively should be nearly propor-
tional to the number of rows as seen in radial section, and the
area of the zone. If, then, the number of nuclei in the outer
nuclear layer is 121,000 and this number varies as the number
of rows and the area of the zone, it varies as their product, and
the number of nuclei in the typical inner nuclear layer in the ret-

HISTOLOGICAL ELEMENTS RETINA NECTURUS 429

ina of average size should be about 167,000. This is a variation
from the average estimates of two retinas of less than 5 per cent,
which is negligible when we consider that the numbers in mini-
mum and maximum retinas vary nearly 45 per cent of the former.

Since Miiller’s fibers are regarded as merely supporting struc-
tures and not a part of the nervous mechanism of the retina, they
have been excluded from the final count of the nuclei properly
belonging to the inner nuclear layer. The data for the inner
nuclear layer of minimum, maximum, and average sized retinas
are found in table 14. The extreme lower limit for the number
of nuclei in this layer is approximately 97,000.

TABLE 14
Total numbers of nuclei of the inner nuclear layer in retinas of minimum,
maximum, and average sizes
(ole AS C4 a] i=
og46 see | NUMBER OF NUCLEI PER OR
, I = 3 2 | CYLINDER NUMBER OF NUCLEI z fe
-& a n Z
° Boog Dm Pusat aoa
= ‘So ze | ] a
Am < Pe a 1 be Se | = Oo, <
Sa lnzas Boa a za4
m3 Anna | BF Heo. | @g 5
Ba Bm ao? ao — Le © Re Zu<
> oe “a@q 5D sO nN | o oO Bm sl Aa
na B24223) 5:6 g g o janes a] Se 2a
<5 o8 S42) oka s = i AO o| SOQ <Dp
a tage] 2Om Ca | ete 5 |,osan] as | faz
& iS) iS} fon] | fon] < = (e) a
WihtbbeNbied soe hAnooaec 9.7028 | 1243.948 | 121} 142 131 141,228 21,729 162,957
With dbl lonlneoneenooone 14.0721 | 1804.115 121 142 131 203,667 32,672 236,339
Averages of 14 retinas} 12.8034 | 1549.153 121 | 142 131 175,959 26,980 202,937

f. Optic nerve fibers. As I have already said, the optic nerve
was transected in two planes, viz., near its two ends, and the
difference in the cross-sectional areas in these two regions was
clearly established. When the fibers in the two regions were
studied, those in the proximal portion seemed smaller and slightly
more numerous to a unit area than in the distal portion. This
led me to suppose that the total number of fibers was less prox-
imally than distally, and my opinion was borne out by actual
counts in the two regions in two optic nerves. Examination
of other optic nerves indicated that similar numerical relations
of the fibers existed in the two regions and was a characteristic
feature of the optic nerve of Necturus. All counts were made
on cross-sections of the optic nerves. Outline camera drawings
(X 755) were made of cross-sections together with the nuclei

430 SAMUEL C. PALMER

of the supporting tissue, all the largest fibers, and all the prom-
inent markings of the optic nerve carefully sketched. The draw-
ing was then marked off with coérdinating lines and the rest of
the optic nerve fibers were drawn in place and counted. By
practice in counting I was able to make out and record the fibers
in the sections with accuracy and speed.

I have counted the fibers in three of the nerves given in table
15 twice each. The results of the second counts were in each
case so close to the first counts that I did not think it necessary
to continue the process for every nerve; thus, in nerve no. | (fig. 12)
I counted 2001 fibers on the first trial and 2003 on the second;
in nerve no. 2, 1657 fibers on the first count and 1661 on the second;

TABLE 15

Areas of cross-sections of optic nerves and numbers of nerve fibers counted at different
planes of transection

CALCULATED AREA IN SQUARE MILLI-
TOTAL NUMBER OF FIBERS IN
DESIGNATION OF ian rape a ate rid Oar CROSS-SECTIONS
NERVES
Close to eye Close to chiasma Close to eye | Close to chiasma
— = |. —— a ———+
1 0.017 2002
2 0.019 ~ | 1659
3 0.019 0.008 1780 $53
4 0.026 0.009 1858 1071
|
5 0.027 2613 |
| |

and in nerve no. 5, 2616 fibers on the first count and 2611 on the
second. The number of fibers appearing in table 15 for these
optic nerves are averages obtained from the two counts. The
complete results of my enumerations, together with the areas
of the cross-sections of the optic nerve, are given in table 15.
The average area near the eye was 0.0216 sq. mm. and contained
by actual count an average of 1982.4 fibers or about 92,000 per
square millimeter; the average of the cross-sections near the
chiasma was 0.0085 sq. mm. with an average of 962 fibers, or
approximately 113,000 per square millimeter. Although the
proximal portion of the optic nerve is smaller in diameter than
the distal part, it is, on the other hand, seen to be richer in fibers
per unit area.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 431

V. DISCUSSION

My intention in this investigation has been, as far as possible,
to make a consistent enumeration of all the nervous elements
in the retina and optic nerve in a single species of animal, and I
have believed the logical choice of species to be some animal
whose retinal cells are very large and few in number. Such an
animal was naturally sought among the amphibians, and espe-
cially among those species whose eyes and optic nerves have under-
gone reduction in size, probably through diminished functioning
powers, and whose histological elements were well known to be
of unusual size. In Necturus I have found an animal in which
both eyeballs and optic nerves are reduced in size; the retinal
elements are extremely large, if not the largest known; and the
optic nerve fibers are entirely non-medullated.

The nearly spherical shape of the eyeball in Necturus and the
close application of the retina to the sclera have made the meas-
urements of the retina comparatively easy and have led, I believe,
to accurate results. The method employed has been described
on page 417. The individual retinal cells are so large and free
from contact with one another that I have been able to count
and number the individual cells in each unit area. Following
this the application of the unit area to the area of the retina has
been a matter of simple mathematical calculation.

An attempt to estimate the total number of visual cells in the
retina of Necturus by counting the rods, cones, and double-cones
in a median section of the eye extending from periphery to
periphery gave a total of 148,000 visual cells for an average sized
retina. This number exceeds that found by the method finally
adopted by about 31,000 cells or 28 per cent. Since in the latter
method every element per unit area was counted and averages
obtained as already stated, and the number of areas in a given
retina is not subject to variation, I am convinced that the number
of retinal cells in Necturus is close to the number obtained by
this means, and that the method of counting elements in a line
as a basis of enumeration of the visual cells should be rejected
on the ground that it gives too large a number of cells.

432 SAMUEL C. PALMER

Where the retinal cells are very small and numerous the difficul-
ties of obtaining accurate counts are greatly increased. Hess
(05) has demonstrated in the retinas of Eledone and Sepia the
great variation which exists in the number of visual cells in closely
approximated regions in the same retina, and thereby implies
the impossibility of obtaining reliable estimates of the total num-
ber of visual cells in a retina from the number in a given ‘belt.’

It is commonly believed that the retinal cells in vertebrates
are not evenly distributed over the retina. Franz (’05, ’09)
states that the visual cells are more numerous about the fundus
than near the periphery; Howard (’08) calls attention to the double
layer of nuclei near the periphery in the outer nuclear layer in
Necturus; and my own observations on the same species show a
slight variation in the numbers of the different elements in the
different regions. Consequently I believe that estimates based
on counts in a restricted region, as for example, the fundus, or
the periphery, give no fair idea of the number of elements in the
retina as a whole, and my observations show that estimates
based on counts of elements in a line of definite length exaggerate
the number of cells in a given retina. Nor can I accept Piitter’s
(02) method, viz., that of computing from the diameter of a
rod the number of visual cells that may be found in a square
millimeter and in the retina as a whole. Figs. 4 to 9 show that
in Necturus the interstices between the visual cells make up a
large portion of the area of a zone passing through the outer
segment of the visual cells, and these spaces must be considered
in the retinas of all species of vertebrates. Without considera-
tion of these spaces the number of elements obtained would greatly
exceed the actual number present.

In order to avoid, then, what appear to me to be errors of meth-
od, I have taken great care to secure accurate counts per unit
area in a number of regions of the retina in several animals.
The retina of Necturus lends itself to a count of this kind, because
the visual cells, the external sheet of the outer nuclear layer,
Miiller’s fibers, and the ganglion cells are each represented by
a single layer of nuclei.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 433

The fovea, when present in the amphibian retina, is small.
I have not been able to find it in Necturus, and Howard (’08)
makes no mention of such a ‘spot,’ but Hulke (’67) and Chievitz
(91)? have seen it in Triton and Salamandra. The frequent
grouping of 6 to 8 cone cells (figs. 5 to 9) in different parts of the
retina of Necturus may, perhaps, compensate for the absence
of a definite fovea.

Enumerations of nuclei in the outer nuclear layer (tables 8
and 9) bring out several important features. On the ground that
each visual cell has its own nucleus there should be in the outer
nuclear layer a number of nuclei equal to the number of rods
and cones together, unless elements of another kind should be
found in either or both the layers compared. The nuclei of the
outer nuclear layer were found to outnumber the rods and cones
by about 10,000. Undoubtedly a majority of the nuclei in the
internal layer together with all those in the external layer should
be associated with the visual cells; but there is a characteristic
eroup in the internal layer, having their long axes at right angles
to the long axes of the nuclei of the visual cells, which appear to
me to have a different function. They may, perhaps, be hori-
zontal cells, which Ramon y Cajal (’94) states are represented in
amphibians by large and small nuclei at two different levels and
constitute the outermost part of the inner nuclear layer. There
are, too, in the internal layer a small number of Miiller’s-fiber
nuclei (fig. 4) whose identity is clearly established by their heavy
stain and fibers. A fourth kind of nucleus may occasionally
wander into this layer. Fig. 2 shows how the outer limits of
the inner nuclear layer may be thrown out of line and individual
nuclei be protruded far into the outer reticular layer. This
would seem to favor Bernard’s (00) contention that the nuclei
of the retinal layers are constantly migrating outward to aid in
the formation of new elements in the more outwardly lying layers.
I have been able to observe an apparent migration of this kind
only in the case cited.

Conditions in the inner nuclear layer show that it is the most
variable of all the layers in respect to the number of its elements.

2 See Slonaker, 1897.

434 SAMUEL C. PALMER

I have called attention to the three-layer condition of its nuclei
as the most characteristic condition, but two or four layers were
not uncommon. Ramén y Cajal (94) points out that the inner
nuclear layer of amphibians consists of a number of ‘types’ of
both amacrine and bi-polar cells, but I have made no attempt in
this study to distinguish between them, and have considered
the layer merely as a whole. Though the results obtained cannot
be adapted to every retina because of the great individual varia-
tion, I am convinced that they are as accurate as possible for the
three-layered average sized zone.

The ganglion-cell layer presents few features of special note
in connection with the number of its nuclei. It consists uniformly
of a single layer of loosely associated, large nuclei. A consider-
ation of vital importance is the failure of Bielschowsky’s impreg-
nation method to demonstrate a union between the ganglion
cells and the optic nerve fibers. Just what the real significance
of this is, I am unable to say, and, when considered in relation
to the number of optic nerve fibers in proximal and distal parts
of the optic nerve, the interpretation becomes even more difficult.

Enumerations of the cross-sections of the strands of Miller’s
fibers per unit area in the inner reticular layer gave better results
than enumeration of their nuclei per unit area in the inner nuclear
layer, because at the plane of sectioning in the reticular layer
there is no other structure with which they might be confused;
secondly, the fibers stand out clearly in cross-section, and each
fiber may be supposed with reasonable certainty to represent
a complete unit; and, lastly, the chance of missing even a single
fiber in the unit areas, was very small.

The objections to using the nuclei as a means of enumeration
lie in the difficulty of distinguishing the nuclei of Miiller’s fibers
from other nuclei in the layer; and secondly, in the fact that
the nuclei of Miiller’s fibers are not always found within the
limits of inner nuclear layer (fig. 4), in which case it would be
impossible to count with certainty all the cells in a given field.

Enumerations of the optic nerve fibers were more tedious than
difficult. The black ends of the fibers contrasted sharply with

HISTOLOGICAL ELEMENTS RETINA NECTURUS 435

the surrounding tissues. Over-blackened margins and the appar-
ent fusion of occasional fibers did not prove to be insurmountable
difficulties, for by focusing, the separate fibers could usually
be distinguished, so that I believe the number of fibers counted
in a cross section is very close to the actual number present.

In addition to variations in diameter in a given nerve, there
are also individual variations which are considerable. Measure-
ments near the chiasma are fairly uniform, but at the distal end
of the nerve I found a range in area of 62.9 per cent. The number
of fibers here correlates in some degree with the cross-sectional
areas of the nerves. Thus in table 15, nerve no. 2, with a cross-
sectional area of 0.019 sq. mm. has an average of 1659 fibers,
and nerve no. 5, with an area of 0.027 sq. mm., has an average of
2613 fibers.

~The number of fibers in other nerves than the optic nerve of
Necturus have been counted or estimated in some instances.
From Salzer’s (80) calculations there are between 60,000 and
70,000 fibers per square millimeter in the human optic nerve;
Birge (’82) has counted 3550 fibers per square millimeter in the
7th spinal nerve of the frog, and 14,133 in the 10th; Hatai (03)
found a variation in the number of fibers in the spinal nerves
of the white rat according to the position of the plane of transec-
tion, there being more in the proximal than in the distal planes,
which is the reverse of the condition in the optic nerve of Nec-
turus; Donaldson and Bolton (’91) record an average of 11,900
fibers to every square millimeter in the dorsal roots of the spinal
nerves of man; Dunn (’00) has found that the total number of
fibers innervating the hind foot of the frog is between 5000 and
6000; and on page 430 I have shown that in the optic nerve of
Necturus there are about 100,000 fibers per square millimeter.

Thus we see that, although in general the visual apparatus
of Necturus is described as degenerate, and the animal’s habits
have apparently brought about a reduced functional activity
of the visual cells, the optic nerve appears to have more nerve
fibers per unit area than any other nerve so far studied.

436 SAMUEL C. PALMER

V1. THEORETICAL CONSIDERATIONS

Theoretical consideration of the optic functions is not the pri-
mary object of my investigation, and I shall enter into it only so
far as my research indicates exceptional conditions in Necturus.

I have found in the visual cells that rods and cones alike develop
at the extreme margin of the retina, the initial. element being
indifferently a rod or a cone. Since this is so, whatever differ-
ences there may be in the light perceiving potentialities between
central and peripheral regions, they must depend largely on the
degree of the functional development of the visual cells in these
regions. The presence of rods and cones alike over the whole
retina—if the theory that rods are organs for light and shadow
perception and cones for color preception is true—indicates
power to distinguish colored lights as well as light and shadow
at the periphery as well as in the fundus. In this connection
Reese (’06) found that Necturus responded to both red and blue
lights, but since no analysis of the lights for purity of color or
intensity was made, it is not evident to what the reactions were
due. Pearse (’10) has shown that Necturus reacts readily to
ordinary light stimuli through both the eye and the skin. From
these investigations it appears that Necturus is capable of dis-
tinguishing colored as well as white light, but on this point there
is need of further investigation.

I know of no positive evidence that horizontal cells exist in
the retina of Necturus, but I know of no other explanation for
the group of cells referred to on page 423 (figs. 2 and 3, ). The
arrangement of the nuclei in the inner nuclear layer seems to
me to preclude the existence of such cells in that layer. Since
I have already shown that the nuclei of Miiller’s fibers may mi-
grate or be pushed outward in some way from the inner nuclear
layer into the outer nuclear layer, it is possible that a similar
change in position has taken place with the horizontal cells, and
that in time they have become permanent constituents of the
outer nuclear layer. Investigation into the identity of these
cells by Golgi’s, or some other stain equally valuable for nerve
processes, is very desirable.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 437

Because of the great variability of the inner nuclear layer, I
cannot help wondering what the influence of such variation may
be on the sight of the animals. Can animals with five layers
of cells in this region see better than those with two? Or does
the number of cells involved have no’ effect whatever on the
clearness of vision?

Enumerations of the optic nerve fibers in cross-sections of
the optic nerve show that distally there are nearly double the
number of fibers that there are in the proximal portion; a con-
dition which suggests at once a dichotomous division of the axis-
cylinders. Such an interpretation of the increase of the fibers
distally would mean that a majority of the optic nerve fibers in
Necturus have their origin in the brain, which is the reciprocal
_ of the condition found by His (’90), Assheton (’92), and Robinson
(96) in other vertebrates. But Robinson also states that the
optic nerve fibers arise in the retina and are more numerous near
the retina even when the fibers have come to occupy the entire
length of the optic stalk. The implication is that some of the
fibers fail at this stage to reach the central organ.

In my treatment of the optic nerve of Necturus with Bielschow-
sky’s fluid, I have been unable to demonstrate a morphological
connection between the ganglion cells and the optic nerve fibers,
but the fibers seem to pass between the nuclei of the ganglion
cells and enter the inner reticular layer. If the fibers can in any
way be shown to be joined to the ganglion cells, then we should
have in the adult Necturus a condition similar to that found by
Robinson in the embryos of higher vertebrates.

Since a direct union, then, between the optic nerve fibers and
the ganglion cells is not an established fact, the origin of the
fibers is a matter of speculation. Do the fibers originate wholly
in the brain and pass centrifugally to the retina, branching with-
in the optic nerve and ending freely in the retina? Or do they
have their origin chiefly in the retina, in spite of the facts that
staining with Bielschowsky’s fluid fails to show positive connec-
tion between the ganglion cells and the fibers, and that only a
half of them reach their destination in the brain? In consider-
ation of these questions the influence of the degeneracy of the

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5

438 SAMUEL C. PALMER

eye, and the fallibility of the stain must be given due weight.
I am unwilling to make any statement as to the origin of the
optic nerve fibers in Necturus, and await with interest further
investigation of this subject by other methods.

VII. SUMMARY

1. The proportion of rods to cones is about the same in all
regions of the retina. Double-cones are wanting at the extreme
periphery.

2. There is no particular plan of arrangement of the visual
cells.

3. In the retina of average size there are about 110,000 visual
cells, of which 53,000 are rods, 42,000 cones, and 15,000 double-
cones.

4. The total number of visual cells varies with the size of the
retina. In maximum sized retinas the number of visual cells
is about 126,000; in minimum sized retinas, about 90,000.

5. The number of visual cells is less than the number of nuclei
in the outer nuclear layer.

6. The total number of nuclei in the outer nuclear layer in
an average-sized retina is 121,000. The number varies from
137,000 in maximum sized retinas to 97,000 in mimimum sized
retinas.

7. The outer nuclear layer consists of two sheets; an external
complete, and an internal loosely scattered sheet, with 94,000
and 27,000 nuclei, respectively, in the average-sized retinas.

8. The nuclei of the internal sheet’ of the outer nuclear layer
consists of nuclei of the visual cells, of Miiller’s fibers, and possi-
bly of horizontal cells.

9. The inner nuclear layer is the most variable of all the layers
in the number of its elements. In an average sized retina there
are approximately 176,000 nuclei in a layer composed of three
sub-layers. The range in the number of nuclei in maximum and
minimum retinas of this structure is 204,000 to 45,000.

10. The inner nuclear layer may have as many as five sub-
layers or as few as two.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 439

11. Nuclei of Miiller’s fibers lie chiefly in the inner nuclear
layer, but a small number may be found in the outer nuclear layer.
In an average sized retina there are about 26,734 of these nuclei,
the maximum and minimum numbers being 33,000 and 22,000,
respectively.

12. The number of ganglion cells in the smallest retina meas-
ured, was 24,758; in the largest, 37,229; and in an average-sized
retina 30,464.

13. The optic nerve of Necturus varies in diameter with the
plane of transection. Near the chiasma its cross section has
on the average an area of 0.0085 sq. mm., and an average of 962
nerve fibers; near the eyeball the average area of the cross section
is 0.0216 sq. mm., with an average of 1982 nerve fibers.

14. The proportion of histological elements of the retina and
optic nerve are approximately as follows: visual cells 111, nuclei
in the outer nuclear layer 121, nuclei in the inner nuclear layer,
exclusive of Miiller’s fibers, 175, ganglion-cell nuclei 30, Miiller’s
fibers 26, optic nerve fibers distally 2, optic nerve fibers proxi-
mally 1.

BIBLIOGRAPHY

AssHEeton, R. 1892 On the development of the optic nerve of vertebrates, and
the choroidal fissure of embryonic life. Quart. Jour. Micr. Sci., n. s.,
vol. 34, pp. 85-104, pls. 11, 12.

Batrour, F. M. 1881 A treatise on comparative embryology. London, Mac-
Millan and Company, 8°, vol. 2, xi + 655 + xxii pp.

Brernarp, H. M. 1900 Studies in the retina: Rods and cones in the frog and
in some other amphibia. Part 1. Quart. Jour. Micr. Sci., n. s., vol.
43, pp. 23-47, pl. 3.

Bretscnowsky, M. 1903 Die Silberimpriignation der Neurofibrillen. Neurol.
Centralbl., Jahrg. 22, Heft 21, pp. 997-1006, 5 Fig.

Birce, E. A. 1882 Die Zahl der Nervenfasern und der motorischen Ganglien-
zellen im Riickenmark des Frosches. Arch. f. Anat. u..Physiol., Phys-
iol. Abth., Jahrg. 1882, pp. 435-480, Taf. 14, 15.

CuraRINI, P. 1906 Changements morphologique que se produisent dans la rétine

des vertébrés par l’action de la lumiére et de l’obscurité. Part II. La

rétine des reptiles, des oiseaux et des mammiféres. Arch. Ital. de
Biol., tom. 45, fase. 3, pp. 337-352, 8 fig.

Curevitz, J. H. 1891 Ueber das Vorkommen der Area centralis retinae in den
vier héheren Wirbelthierklassen. Arch. f. Anat. u. Physiol., Anat.
Abth., Jahrg. 1891, pp. 311-334, Taf. 18.

440 SAMUEL C. PALMER

Cour, A. H. 1902 The technique of biological projection and anesthesia of ani-
mals. VIII. The anesthesia of animals.. Jour. Applied Micr. and
Labr. Methods, vol. 5, no. 11, pp. 2051-2053.

Corr, E. D. 1889 The Batrachia of North America. Bull. U. S. Nat. Mus.,
no. 34, 525 pp., 81 pl.

Donawpson, H. H. and Botron, J. L. 1891 The size of several cranial nerves
in man as indicated by the areas of their cross-sections. Amer. Jour.
Psychol., vol. 4, no. 2, pp. 224-229.

Dunn, E. H. 1900 The number and size of the nerve fibers innervating the skin
and muscles of the thigh in the frog (Rana virescens brachycephala).
Jour. Comp. Neur., vol. 10, no. 2, pp. 218-242.

Epincer, L. 1892 Untersuchungen iiber die vergleichende Anatomie des
Gehirns. II. Das Zwischenhirn. Erster Thiel:—Das Zwischenhirn
der Selachier und der Amphibien. Abhandl. Senckenberg. Gesellsch.,
Bd. 18, Taf. 1-5, pp. 3-55.

Foster, M. 1891 Text-book of physiology. London, MacMillan and Company,
8°, part 3, xxi + 418 pp.

Franz, V. 1905 Zur Anatomie, Histologie, und funktionellen Gestaltung des
Selachierauges. Jena. Zeit. f. Naturwiss., Bd. 40, Heft 4, pp. 697-
840, Taf. 29, 32 Fig.

Franz, V. 1909 Das Vogelauge. Zool. Jahrb., Abt. f. Anat. u. Ont., Bd. 28,
Heft. 1, pp. 73-294, Taf. 6-10, 122 Fig.

Greerr, R. 1900 Die mikroskopische Anatomie der Netzhaut. Graefe-Saem-
isch, Handbuch der gesamten Augenheilk., Teil 1, Bd. 1, Kap. 5, pp.
(A=2125 Tals 152:

Harar, 8. 1902 Number and size of spinal ganglion cells and dorsal root fibers
in white rats of different ages. Jour. Comp. Neur., vol. 12, no. 2, pp.
107-124.

1903 On the increase in the number of medullated nerve fibers in the
ventral roots of the spinal nerves of the growing white rat. Jour.
Comp. Neur., vol. 13, no. 3, pp. 177-183.

Hess, C. 1905 Beitriige zur Physiologie und Anatomie der Cephalopodenauges.
Arch. f. ges. Physiol., Bd. 109, pp. 393-439, Taf. 5-8.

Hesse, R. 1900 Untersuchungen iiber die Organe der Lichtempfindung bei nie-
deren Thieren. VI. Die Augen einiger Mollusken. Zeit. f. wiss. Zool.,
Bd. 68, pp. 379-477, Taf. 25-32, 1 Fig.

His, W. 1890 Histogenese und Zusammenhang der Nerven-elemente. Arch.
f. Anat. u. Physiol., Anat. Abth., Suppl. Bd., 1890, pp. 95-117.

Howarp, A. D. 1908 The visual cells in vertebrates, chiefly in Necturus macu-

losus. Jour. Morph., vol. 19, no. 3, pp. 561-631, pls. 1-5.

Huuke, J. W. 1867 On the retina of amphibians and reptiles. Jour. Anat.
and Physiol., vol. 1, pp. 94-106.

Kinassury, B. F. 1895 On the brain of Necturus maculosus. Jour. Comp.
Neur., vol. 5, pp. 189-205, pls. 9-11.

Krause, W. 1876 Handbuch der menschlichen Anatomie. Hannover, Bd. 1,
8°, xiii + 581 pp., 302 Fig.

1880 Ueber die Fasern des Sehnerven. Arch. f. Ophthalmol., Bd.
26, Heft 2, pp. 102-108, Taf. 1.

HISTOLOGICAL ELEMENTS RETINA NECTURUS 441

Kuunt, H. 1875 Zur Kenntniss des Sehnerven und der Netzhaut. I. Die
Structur des Sehnerven. Arch. f. Ophthalmol., Bd. 25, Abth. 3, pp.
179-288.

Lauser, H. 1902 Anatomische Untersuchungen des Auges von Cryptobranchus
japonicus. Anat. Hefte, Arbeiten, Bd. 20, pp. 3-17, Taf. 1,2.
Mouttenix, R. C. 1909 The peripheral terminations of the eighth cranial nerve
in vertebrates, especially in fishes. Bull. Mus. Comp. Zodl., vol. 53,

no. 4, pp. 215-250, 6 pls.

Miiuer, H. 1856 Anatomisch-physiologische Untersuchungen iiber die Retina
des Menschen und der Wirbelthiere; Anat. u. Physiol. des Auges, 1856,
pp. 52-134. (Quoted from Slonaker, ’97.)

Ossporn, H. F. 1888 A contribution to the internal structure of the amphibian
brain. Jour. Morph., vol. 2, pp. 51-96.

Parker, G. H. 1890 The histology and development of the eye in the lobster.
Bull. Mus. Comp. Zoél., vol. 20, no. 1, pp. 1-60, pls. 1-4.

1895 The retina and optic ganglia in decapods. especially in Astacus.
Mitth. Zool. Sta. Neapel, Bd. 12, pp. 1-73, Taf. 1-3.

Pearse, A. 8. 1910 The reactions of amphibians to light. Proc. Amer. Acad.
Arts and Sci., vol. 45, no. 6, pp. 161-208.

Purrer, A. 1902 Die Augen der Wassersiiugetiere. Zool. Jahrb., Anat. Abth.,
Bd. 17, pp. 99-402, Taf. 2-4, 41 Abbild.

Ramon y Casa, S. 1891 Sur la fine structure du lobe optique des oiseaux et
sur l’origine réelle des nerfs optiques. Internat. Monatschr. f. Anat. u.
Physiol., Bd. 8, pp. 337-266, pls. 23, 24.

1894 Die Retina der Wirbelthiere. Weisbaden, 8°, vili + 179 pp., 7
Taf., 3 Fig.

Ranson, 8. W. 1909 A preliminary note on the non-medullated nerve fibers in
the spinal nerves. Anat. Rec., vol. 3, no. 5, pp. 291-295, 4 fig.

Reese, A.M. 1906 Observations on the reactions of Cryptobranchus and Nec-
turus to light and heat. Biol. Bull., vol. 11, no. 2, pp. 93-99.
Rosrnson, A. 1896 On the formation and structure of the optic nerve and its
relations to the optic stalk. Jour. Anat. and Physiol., vol. 30, pp. 319-

333, pl. 7.

Sauzer, F. 1880 Ueber die Anzahl der Sehnervernfasern und der Retinazapfen
im Auge des Menschen. Sitzungsb. Akad. Wissensch., Wien, Ma‘ h-
naturwiss. Classe, Bd. 81, Abt. 3, pp. 7-23.

Scuutrze, M. 1867 Ueber Stabchen und Zapfen der Retina. Arch. f. mikr.
Anat., Bd. 3, pp. 215-247, Taf. 13.

ScuwaLBe, G. 1887 Lehrbuch der Anatomie der Sinnesorgane. Erlangen, 8°,
xill + 570 pp., 199 Fig.

SLONAKER, J. R. 1897 A comparative study of the area of acute vision in verte-
brates. Jour. Morph., vol. 13, pp. 445-498.

Stour, P. 1906 Stodhr’s histology, 6th Amer. Ed. (transl. by Lewis), 8°, ix +
434 pp.

EXPLANATION OF FIGURES

The drawings are all from Necturus maculosus (Raf.) All the outlines in figs.
1 to 12 were made with the aid of the camera lucida. The sections of the retina
were stained in Heidenhain’s iron haematoxylin followed by a 70 per cent alco-
holic solution of eosin. Radial sections of the visual cells (figs. 1 to 4) were cut
8u thick, and cross-sections (figs. 5 to 9) 6u thick.

The optic-nerve fibers were stained in Bielschowsky’s fluid in every case, and
all sections were 5y thick.

Fig. 1 Semi-diagrammatic drawing of a radial section of a normal retina of
Necturus; cd, xz, vw designate three zones in which the areas of the retinas were
obtained; ab, mn, xz and vw designate the ‘levels’ in which average counts, per
unit areas, were obtained for the different layers of the retina. X 331.

Fig. 2. Semi-diagrammatic drawing of a radial section of a retina with two
sublayers or ‘sheets’ in the inner nuclear layer. n, horizontal cell. X 331.

Fig. 3 Semi-diagrammatic drawing of a radial section of a retina with four
to five sublayers in the inner nuclear layer. mn, horizontal cell. X 331.

Fig. 4 Semi-diagrammatic drawing of a radial section of a retina with two
nuclei, m, of Miiller’s fibers, in the outer nuclear layer. X 331.

442

hee

oe a

rae DS eed
a BS oN > INS X ?
A : : Aa § >
0 = ‘ Léa CA i. @ SEAN
nee ‘ ye : ? [ge ama C OD) ADY HA
a “ * yer 2, EN
A Sy ke NA ee 6 8 é
A = 4 f fe ) ~ =
Pee. ene 2 PB, On aS
_ / . ~ (~ eS | STEN - }
ay ae, U Ne SS} ‘s) yes) O 7 @ Gs! § 5 é
=A) REE Dy 2 ‘4 “T QS Ce C EN (\
> 3 Gy & GC / \ ; \\ Wey
Ce) saa a Ve “ine 4 Z SOY &
SAS ee Sy OOO ROS Bee es
LOY ae CMG (at a INES) ~ ASPs amar, Sy) @
> ay SS } - Deze AS
Ow OQ EXS AOR 6a OYE
Qe J S hy <p e c¥
Qo ene at, ay Zan GE
5 ies exe =. © Od &
<=, © Se > = SS L
5 ES Ors 6
—/ ae = ~
SAGAN (Ny QD BD
(BGO OSs“
SCE SIN Sy ea
An @OSWO ae
os i Ke) = \ 4
DQ SAY, &) {) @ &
PO een OOn
O Aas Das |
Wyse Se eee | IO ‘
Ke LES ~ CE) & oy Sa!
t Dy ms ran poate \
4 oy :
Lea SY
© a 69?
) I" DA LEN
cy ths & \
TD "a J
Qe canes

Semi-diagrammatic drawings of cross-sections of the visual cells
in five regions of the retina. Fig. 5, anterior; fig 6, posterior; fig. 7, fundus; fig. 8,
dorsal; fig. 9, ventral; r, rod; c, cone; cd, double-cone. X 232.

Fig. 10 Semi-diagrammatie drawing of a cross-section of the optic nerve

(no. 4, table 15) near the eyeball. X 431.
Fig. 11 Semi-diagrammatic drawing of the same optic nerve near the chiasma.

Figs. 5 to 9

o, lumen of the nerve. 431.
Fig. 12 Semi-diagrammatic drawing of a cross-section of nerve (no. 1, table 15)

near the eyeball. » 485.

444

iH 2a”

Wes

/ {
{ O\NIK
4 ih N A)
ae, e

ON THE HISTOLOGY OF THE CRANIAL AUTONOMIC
GANGLIA OF THE SHEEP

F. W. CARPENTER

From the Zoological Laboratory, University of Illinois, under the direction of
Henry B. Ward, No. 19

TEN FIGURES

Both anatomical and experimental methods of investigation
have established the fact that the autonomic nervous system of
vertebrates consists, on its efferent side, of two sets of neurones.
The first of these, the preganglionic neurones, have their cell-
bodies in the central nervous axis, and send their neurites outward
by way of the ventral roots of cerebro-spinal nerves to the auto-
nomic ganglia. In the trunk region these preganglionic fibers
pass from the spinal nerves in the white rami communicantes
to the ganglia of the sympathetic trunks, or to ganglia more
distally placed. In the cranial region, preganglionic fibers leayv-
ing the brain by the third, seventh and ninth nerves end in the
ciliary, sphenopalatine, otic, submaxillary and sublingual ganglia,
which constitute the autonomic ganglia of the head.

The efferent nervous impulses which thus reach outlying gan-
glia of the body are carried onward to peripheral tissues (involun-
tary muscle, glands) by the postganglionic neurones. These are
multipolar nervous elements, the cell-bodies of which lie in the
autonomic ganglia. ‘Their distally directed neurites are in mam-
mals, as a rule, nearly or quite devoid of myelin.

By employing modern methods of neurological technique, such
as those introduced by Golgi, Ehrlich and Cajal, it has been
possible to demonstrate very satisfactorily the nature of the end-
ings of the preganglionic fibers in the autonomic ganglia of the
trunk region. These ganglia, according to the terminology pro-
posed by Langley, belong to the sympathetic and sacral subdivi-

447

448 F. W. CARPENTER

sions of the autonomic system. The histological investigations
of Aronson, Retzius, Dogiel, Huber and others on various verte-
brates have led to the general conception of such endings as peri-
cellular, intracapsular networks of fine fibrils, surrounding and
in contact with the cell-bodies of the postganglionic neurones.
These end nets are not to be confused with the intercellular fibers,
often intertwined and concentrically arranged about the ceil-
bodies of the ganglia, but situated outside the cell capsules. Such
fibers include the long extracapsular dendrites of the sympathetic
cells, their non-medullated neurites, and the collaterals and ter-
minal portions of the preganglionic fibers before the latter pene-
trate the cell capsules to give rise to the subcapsular nets.

Our knowledge regarding the terminations of preganglionic
fibers in the cranial autonomic ganglia is, with the exception of the
ciliary, less complete. In the ciliary ganglion pericellular nets
under the capsules have been observed by a number of investi-
gators. Michel (94) and Kdlliker (’94) were the first to call
attention to their presence following the study of Golgi prepara-
tions of mammalian ganglia. Recently Sala (10) and v. Len-
hossék (’10), working with the Cajal silver nitrate method, have
been able to secure excellent demonstrations of these end nets in
the ciliary ganglia of man. That they are present also in birds
has been shown by v. Lenhossék (710, ’11) and the writer (Car-
penter 711), both of whom found, however, that in this group
another form of termination of the preganglionic fibers occurs in
the ciliary ganglion. This is the ‘‘ calyx” ending and its modifica-
tions. Endings of this type have been seen also in the ciliary
ganglion of reptiles by v. Lenhossék (11a).

The histology of the remaining autonomic ganglia in the head
region has received comparatively little attention from investi-
gators.

Original descriptions of the cellular elements of the sphenopala-
tine ganglion are to be found, as far as I am aware, in three papers
only, and in but one of these are the terminations of preganglionic
fibers mentioned. The observations of Retzius (’80) on teased
preparations of the ganglion taken from the sheep and cat fur-
nished for a long time the only source of information regarding

CRANIAL AUTONOMIC GANGLIA OF SHEEP 449

its minute structure. Retzius found the cells mostly multipolar,
with some bipolar elements in the cat. His method did not per-
mit the study of nerve terminations in the ganglion. In 1894
v. Lenhossék described Golgi preparations of the sphenopalatine
ganglion of the mouse, and gave us the only account of fibrillar
end baskets around the ganglion cells. In the recent paper of
Miller and Dahl (710) a good description is given of the mor-
phology of the cells of this ganglion in the horse, sheep, and man,
but no mention is made of intracapsular end nets. The method
of Bielschowsky was used. In one preparation (human) a peri-
capsular ‘Nervenfasernetz’ was observed by them, from which
terminal fibers appeared to run to the cell-body. This will be
referred to later.

In the otic ganglion the terminations of preganglionic neurones
have not been demonstrated. The literature dealing with the
histology of this ganglion is, in fact, very meager. Retzius (’80)
ascertained from teased preparations that the ganglion contained
multipolar cells in the rabbit, cat, sheep and man. Miller and
Dahl (10) have confirmed this, by means of the Bielschowsky
method, for the horse, sheep and man.

The cells of the closely related submaxillary and sublingual
ganglia have been described as multipolar elements by Retzius
(80), Huber (96) and Miller and Dahl (10). Huber alone saw
pericellular end nets. These were observed in Golgi preparations
of the ganglia from young dogs.

METHODS

The nerve terminations described in this paper were demon-
strated by means of intra-vitam staining with methylene blue.
The sheep’s heads were brought to the laboratory about an hour
after the animals had been killed, and injected through the
carotid arteries with a 1 per cent solution of methylene blue in
distilled water. The blood vessels were washed out before and
after the staining by injections of Ringer’s solution. Both this
and the methylene blue solution were used at approximately body
temperature.

450 F. W. CARPENTER

After the ganglia desired for study had been dissected out, they
were fixed over night in a 10 per cent solution of ammonium
molybdate, then washed in running water, dehydrated in grades
of alcohol, cleared in xylol, and embedded in paraffin. The
sections were cut from 25 to 50 micra in thickness.

For comparison, preparations of the otic ganglion were made
by the silver nitrate method of Ramén y Cajal. These were
of some value in showing the form of the ganglion cells and
their processes, but in them the terminal end nets were not
differentiated.

OBSERVATIONS

In this investigation attention has been directed chiefly to the
endings of the preganglionic fibers on the cell-bodies of the post-
ganglionic neurones. In using methylene blue intra-vitam staining
to demonstrate nerve terminations it has been found that the
treatment of the ganglia in such a manner as to differentiate these
clearly usually leaves the cell-bodies, about which the endings are
arranged, partially or wholly unstained. On the other hand, when
the cell bodies and their processes are deeply colored, the endings
of the preganglionic fibers are almost always invisible. It follows,
therefore, that the majority of my preparations are not suitable
for the study of the morphology of the postganglionic neurones.
There occur, however, here and there in the sections, ganglion
cells sufficiently well stained to warrant giving some account of
their structure.

The postganglionic neurones

In the sphenopalatine, otic and submaxillary ganglia of the sheep
the cells are multipolar in character, with long, slender, sometimes
branching dendrites, which penetrate the cell capsule, and often
run for surprising distances among the intercellular fibers. Such
cells are shown in figures 1, 2 and 3. The boundaries of the cell
capsules are marked by dotted lines, except in figure 2, where
the position of the capsule is indicated by several of its nuclei.

Among the processes given off by the cell-bodies, I have often
found it difficult to distinguish the neurite from the dendrites.

CRANIAL AUTONOMIC GANGLIA OF SHEEP 451

In figure 1 the fiber marked A appears to be the neurite, in this
instance arising from a dendrite. It may be traced through the —
thick section in which it occurs for the distance of nearly one-half
a millimeter from its origin. It joins a bundle of fibers lying
along the surface of the ganglion. Throughout its length, as far
as it can be followed, it remains non-medullated.

Preparations of the otic ganglion stained by the Cajal silver
nitrate method also show that the cells of this ganglion are multi-
polar; and, moreover, that some of them are fenestrated, resem-
bling in this respect certain ciliary ganglion cells of mammals
and birds (Sala, -v. Lenhossék) and certain spinal ganglion cells
of mammals (Cajal).

The ganglion which has proved most refractory in revealing
the character of its cells is the ciliary. Here no cells with long,
slender processes, such as those of the other ganglia, have been
brought to light by methylene blue in the six ganglia examined
by this method. In most cases no processes at all are apparent,
but occasionally a cell showing a single thick, branching, extra-
capsular dendrite (fig. 4) has been observed. Whether such
cells are numerous in the sheep’s ciliary ganglion, or occur sporad-
ically only, I cannot say. It would be unsafe to make the latter
deduction merely because a partial and capricious stain like meth-
ylene blue shows them in comparatively few numbers.

Schwalbe (’79, ’79 a ) described the ciliary ganglion cells of the
sheep, studied by the isolation method, as unipolar. In other
mammals (cat, dog, monkey) they have been shown to be multi-
polar by Sala (’10) and Marinesco, Parhon and Goldstein (’08),
who employed the method of Cajal. In some instances the den-
drites extend beyond the cell capsules, in others they are short and
intracapsular. The latter condition seems to bé the rule in the
ciliary ganglion of man.

It appears, then, that the autonomic cranial ganglia of the
sheep contain cells which are allied in their morphological char-
acters with those of the mammalian sympathetic ganglia. Both
are characterized by long dendrites which penetrate the cell
capsules. In the possession of these extracapsular dendrites,
however, the cranial cells of the sheep differ from the elements of

452 F. W. CARPENTER

corresponding ganglia in human beings. In man,as Sala (’10) and
v. Lenhossék (’10) have shown for the ciliary, and Miller and Dahl
(10) for the remaining autonomic cranial ganglia, as well as the
ciliary, the dendrites are contained within the cell capsules. They
are often bent and branched, and may run parallel with the sur-
face of the cell-body for considerable distances, but they do not,
as in the sheep, break through the capsular wall.

The terminations of preganglionic fibers

In the ciliary, sphenopalatine, otic and submaxillary ganglia
of the sheep the preganglionic fibers terminate in end nets of fine,
varicose fibrils embracing the cell-bodies of the postganglionic
neurones (figs. 5, 6, 7, 8,9, 10). These end nets lie inside the cell
capsules, and are at places in direct contact with the surfaces of
the cell-bodies. We have, therefore, in the cranial autonomic
ganglia essentially the same conditions in respect to synapses that
obtain in the vertebral and prevertebral ganglia of the sympa-
thetic subdivision of the system. Here the presence of subecapsu-
lar end nets has been shown by a number of investigators, notably
by Huber (99), who succeeded in differentiating these termina-
tions with methylene blue in all classes of vertebrates from fishes
to mammals.

When examined in detail under high powers of the microscope,
the pericellular plexuses are seen to arise through the terminal
branching of one or more preganglionic fibers. The largest num-
ber observed was four in the ciliary ganglion (fig. 5). Such fibers
perhaps result from the division of a single preganglionic neurite,
or they may be the terminal portions or collaterals of two or more
distinct neurites. In all cases the fibers are non-medullated near
the end nets, but when the conditions are favorable for following
them, they may be traced, in the opposite direction, into bundles
of fibers with thin medullary sheaths.

The fibrils of which the pericellular plexuses are composed
show many varicosities. These vary in size and are distributed
irregularly along the course of the fibrils. Sometimes they are
terminal in position, i.e., they occur at the tips of short free-ending

CRANIAL AUTONOMIC GANGLIA OF SHEEP 453

branches, as is well shown in figure 6, A. The varicosities and
intermediate portions of. the fibrils are often in direct contact’
with the surface of the cell-body, but they are also found in the
space between the latter and its surrounding capsule.

The pericellular plexuses are veritable networks. Anastomoses
between the fibrils are frequent, and at the nodes varicosities
usually occur. This reticulate condition can be accounted for
consistently with the outgrowth doctrine of the development of
nerve fibers by assuming that the growing preganglionic neurite,
on reaching the postganglionic cell-body, divides tree-like into
a number of terminal fibers. ‘These embrace the cell-body on all |
sides, and, meeting with one another here and there, fuse to form
the continuous network.

Although all the end nets are of essentially the same character
in the autonomic cranial ganglia of the sheep, they vary in com-
plexity. In the same ganglion one may observe such compara-
tively simple endings as are shown in figures 8 and 10, and such
complete and intricate networks as those of figures 6 and 9. In
the drawings only the fibrils and varicosities on the upper sides
of the cell-bodies have been represented. By focussing through
the transparent ganglion cells the continuations of the nets may
usually be seen on the surfaces away from the observer.

In my experience with methylene blue used according to the
injection method the end nets of the sphenopalatine ganglion
have proved the most difficult to stain satisfactorily. Very fre-
quently the varicosities have been colored a deep blue without
affecting the delicate fibrils which connect them. The result
gives to the cell-body enclosed by the net a peculiar, spotted
appearance. Figure 7 represents a pericellular plexus of the
sphenopalatine ganglion in which many of the communicating
fibrils are invisible, although some of the varicosities on their
course have taken the stain.

In the introductory references to the literature dealing with
cranial autonomic ganglia mention was made of the pericapsular
‘Nervenfasernetze’ demonstrated through Bielschowsky stain-
ing by Miiller and Dahl (’10) in a single preparation of the spheno-
palatine ganglion of man. These bundles of mtertwining fibers

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5

454 F. W. CARPENTER

are concentrically arranged about the capsules of the ganglion
cells. From them a few centrally directed offshoots ending in
knobsare traceable through the capsular walls to the surfaces of the
underlying cell-bodies. That these extracapsular, nest-like struc-
tures are not identical with the intracapsular end nets described
above is clear from their position, and the inter-relations of their
fibers, which do not appear to anastomose. They are doubtless
bundles of preganglionic neurites on the way to their subcapsular
terminations, the fibers given off to the cell-bodies being the ter-
minal portions of such neurites. The latter, as has been said,
end in knob-like swellings which are in contact with the ganglion
cells. Such simple end organs may, in the human sphenopalatine
ganglion, put the preganglionic neurites in communication with
the postganglionic neurones. However, the foregoing results
with methylene blue staining in the sheep raise the question if
these knobs are not, in reality, the first varicosities of an intracap-
sular end net, the remainder of which has not been differentiated
by the Bielschowsky technique.

SUMMARY

The sphenopalatine, otic and submaxillary ganglia of the sheep
contain multipolar cells with long, slender, frequently branched
dendrites, which extend for considerable distances beyond the
limits of the cell capsules. They resemble in these particulars the
ordinary type of mammalian sympathetic cells.

In the ciliary ganglion the only cells in which processes were
clearly differentiated by methylene blue possessed each a single,
heavy, branched dendrite.

In all the cranial autonomic ganglia (ciliary, sphenopalatine,
otic, submaxillary) the preganglionic neurites terminate on the
cell-bodies of the postganglionic neurones in subcapsular, peri-
cellular end nets of fine varicose fibrils. These endings are similar
to those of preganglionic fibers in the vertebral and prevertebral
ganglia of the sympathetic system.

CRANIAL AUTONOMIC GANGLIA OF SHEEP 455

BIBLIOGRAPHY

CARPENTER, F. W. 1911 The ciliary ganglion of birds. Folia Neuro-biologica,
Bd. 5, pp. 738-754.

Huser, G. C. 1896 Observations on the innervation of the sublingual and sub-
maxillary glands. Jour. Exper. Med., vol. 1, pp. 281-295.

1899 A contribution on the minute anatomy of the sympathetic ganglia
of the different classes of vertebrates. Jour. Morph., vol. 16, pp. 27-90.

vy. K6uurKer, A. 1894 Ueber die feinere Anatomie und die physiologische Bedeu-
tung des sympathischen Nervensystems. Verhandl. Gesell. Deutsch.
Naturf. u. Aerz., Versam. 66, Theil 1, pp. 97-120.

v. Lennoss@K, M. 1894 Ueber das Ganglion sphenopalatinum und den Bau
der sympathischen Ganglien. Beitrige zur Histologie des Nerven-
systems und der Sinnesorgane. Weisbaden.

. 1910 Ueber das Ganglion ciliare (Vorliufige Mitteilung). Verhandl.
anat. Gesell., Versam. 24. (Anat. Anz., Bd. 37, pp. 137-143.)

1911 Das Ganglion ciliare der Végel. Arch. f. mikros. Anat. u.
Entwick., Bd. 76, pp. 745-769.

191la Das Ciliarganglion der Reptilien. Anat. Anz., Bd. 40, pp.
74-80.

MarINneEsco, G., PARHON ET GOLDSTEIN 1908 Sur la nature du ganglion ciliare.
Compt. rend. soc. biol., Paris, tome 64, pp. 88-89.

MicHEuL, J. 1894 Ueber die feinere Anatomie des Ganglion ciliare. Trans. 8th
Internat. Ophthal. Congr. in Edinburgh, pp. 195-197.

Mituter, L. R., unp Dani, W. 1910 Die Beteiligung des sympathischen Nerven-
systems an der Kopfinnervation. Deutsch. Arch. f. klin. Med., Bd.
99, pp. 48-107.

Retzius, G. 1880 Untersuchungen ueber die Nervenzellen der cerebrospinalen
Ganglien und der iibrigen peripherischen Kopfganglien mit besonderer
Riicksicht. auf die Zellenausliufer. Arch. f. Anat. u. Physiol., anat.
Abt., pp. 369-402.

Sata, G. 1910 Sulla fina struttura del ganglio ciliare. Mem. istit. Lombardo
scien. e let., classe scien. matem. e natur., vol. 21, pp. 133-139.

ScHWALBE,G. 1879 Ueber die morphologische Bedeutung des Ganglion ciliare.
Sitzungsb. Jena. Gesell. f. Med. u. Naturwiss. f. 1878, pp. xe—xciii.

18792 Das Ganglion oculomotorii. Ein Beitrag zur vergleichenden
Anatomie der Kopfnerven. Jena. Zeitschr. f. Naturwiss., Bd. 13,
pp. 173-268.

PLATE 1
EXPLANATION OF FIGURES

The drawings are camera lucida tracings of ganglion cells stained with methylene
blue, and seen under a 2 mm. oil immersion objective. The dotted lines indicate
the positions of the cell capsules.

1 Cell from the submaxillary ganglion. A, neurite (?).

2 Cell from the otic ganglion.

3 Cell from the sphenopalatine ganglion.

4 Cell from the ciliary ganglion.

456

PLATE 1

CRANIAL AUTONOMIC GANGLIA OF SHEEP
F. W. CARPENTER

‘ :
; Yas
* *
x,
& i.
; .
b= 3 >
j |
f 4
>
:
‘
a
;
H \ By
j i A %
t---- 4
\ t
:
\
.
.
j ‘
\ YA
7 ‘ a
i

Ria aree ttt

i
1
\
errr

457

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5

PLATE 2
EXPLANATION OF FIGURES

The drawings show the terminations of preganglionic fibers on the cell-bodies of
postganglionic neurones. All are from methylene blue preparations seen under a
2mm. oil immersion objective. The figures have been drawn to the same scale
with the aid of the camera lucida, which has beep used as far as practicable in
reproducing the details of the end nets. Only the fibrils covering the upper sur-
faces of the cell-bodies have been represented.

5 and6 End vets from the ciliary ganglion. A, terminal varicosities.

7 End net from the sphenopalatine ganglion, incompletely stained. The out
line of the cell capsule is shown with two nuclei.

S8and9 End nets from the otic ganglion.

10 End net from the submaxillary ganglion.

458

PLATE

GANGLIA OF SHEEP

CARPENTER

AUTONOMIC

CRANIAL

Ww.

459

THE CEREBRAL GANGLIA OF THE EMBRYO OF RANA
PIPIENS

F. L. LANDACRE anp MARIE F. McLELLAN
From the Zoological Laboratory of the Ohio State University

ELEVEN FIGURES

CONTENTS
NGO CUT LTO Tp rete se ee eet ae Rosi Ot Sow sean AE ASL OA Apette ieee oe ee ae 461
IMIGSI RIEL oie exc ta BS Cnet SURE ERR EE RTE I PMB nH IRE Pe Maan Lia NE 462
he GRICeMITIO-fACTAMCOMPLOX A. 2 sca.ae 2-2 2c < be eee ee ee ee 462
hewalocsopharyngealzanpuon2. 455 .2.2 <0: <2 ad Sbarro AAG een ate ee 464
Pe emt: UlTS LEN sere MERON EN soy coke Scat aie oA. doo SCN ee ees oe Soe 466
TM OVS GA IIS bree OVA Re a cto xc, eee PR IM RTS CHES ena om nbc eRaus AOE e ee ot 467
MpneRCOTsalelia bara lis exe cctt. cries cla exse isis > one tale aera a a so 468
iewventralelaterallis Neos: ese Qe tcp crates ach paren Seis eee ee I orton ee 470
sreneenenralysomatley kes (KUcUlan)y vance ae ees aoe a ese eee eee 472
Sip osce COMO VIS CORalist ket 202 5..hce Ae oar etn Lyne aes Seems ol Maa ie Moet 473
Branchialis X, or first visceralis X....... roan Set Gc ee SE nh eR ie 475
SUMMIT ALY. Ana tdis CUSSTOM 5 sres ect he ee Ee AT7
POE R CUT CACLLEC 152 a seeps sakes es reeked teraeree SeCAS 481
INTRODUCTION

A description of the cerebral ganglia of the frog embryo is
undertaken as a preliminary to the study of the mode of origin of
these ganglia.

This might seem superfluous in view of Strong’s (’95) excellent
work on the same subject but Strong’s work was pioneer in nature
and since it was published there have appeared a number of excel-
lent papers on the cerebral nerves and ganglia in Amphibia.
particularly those of Coghill (02) and Norris (’08) in addition
to numerous papers on other Ichthyopsida. While most of these
papers confirm in general the analysis established by Strong,
particularly for the composition of the trigemino-facial complex.
there are certain features in the composition of the glossopharyngo-

461

462 LANDACRE AND McLELLAN

vagal complex of ganglia that are not as clear as could be desired
in Strong’s work and do not show the resemblance to the type
of composition of ganglia usually found in the Ichthyopsida.

Since the V and VII complex conforms so closely to the type
for Ichthyopsida, one would naturally expect the [IX and X com-
plex to be equally true to type, because the V and VII is usually
the more highly developed and almost invariably has its ganglionic
components more closely fused than IX + X in any given stage.
An examination of embryos younger than that plotted by Strong
shows the [IX + X ganglionic complex to be really much more
typical and not so highly fused as shown on Strong’s plot, thus
enabling one to make a much more detailed analysis.

MATERIAL

The series of embryos from which two were selected for plotting
consists of eighty-six stages taken from one lot of eggs of Rana
pipiens. The first fifty-three stages were taken at intervals of
two hours beginning six hours after laying. From the fifty-
third stage up to the eighty-fifth the intervals were less regular,
ranging from one and three-quarter hours to nine hours, the
average being less than five hours.

Out of this series number seventy-two, 8 mm. in length (1714
hours old) and number eighty-six were chosen for plotting. Num-
ber eighty-six is 135 hours older than number seventy-two, being
3064 hours old and 10 mm. in length. In addition to this series,
a 25 mm. tadpole of Rana pipiens was studied and also a 35 mm.
series kindly loaned by Professor Herrick. Neither of these last
two were plotted, but they were carefully compared with the 8
mm. and 10 mm. embryos plotted. Stage 35 mm. seems to be
similar in all essential respects to Strong’s plot.

THE TRIGEMINO-FACIAL COMPLEX

In the trigemino-facial complex (fig. 1) one point only needs
to be emphasized, namely, the distinctness of the profundus gan-
glion. This ganglion, which in earlier stages is much more isolated
than in the 8 mm. embryo, though not entirely distinct, occupies

GANGLIA OF RANA 463

the’ dorsal and mesial portion of the ganglion. It extends ven-
trally as a distinct ganglionic mass about two-thirds of the total
dorso-ventral diameter of the combined Gasserian and profundus.
The ramus ophthalmicus (O. V., fig. 1) seems at this time to come
entirely from the profundus portion, though doubtless there are
fibers in this ramus derived from the ventral portion or Gasserian
ganglion also. This nerve evidently contains later, if not at this
time, the representatives of both the ophthalmic V and of the
opththalmicus profundus of the ganoids. The distinctness of this
ganglion confirms the position taken by Wilder (92, p. 172) and
confirmed by Strong (95, p. 173), that the ophthalmicus pro-
fundus nerve has fused with the ramus ophthalmicus V and that
probably in higher types the profundus ganglion is fused with
the Gasserian.

The infra-orbital trunk arises from the ventral border of the
Gasserian ganglion and immediately splits into the r. maxillaris
and the r. mandibularis. Smaller twigs described by Strong
could not be positively identified. The apparent difference
between the point of origin of nerves in this complex in the 8 mm.
tadpole as compared with Strong’s description, is due to the fact
that in the older tadpole the head becomes flat, thus altering the
position of the origin of nerves. |

Aside from the difference noted below, the ganglia and nerves
of the 8 mm. tadpole conform closely to the description of Strong,
whose findings we confirm in every detail except that some of
the more minute branches could not be located in our material.
It should be noted here that Strong’s nomenclature is followed
throughout in this paper.

The most striking feature in the arrangement of the V + VII
complex is the dorso-ventral elongation as compared with similar
stages in Ameiurus (Landacre 710) and Lepidosteus (Landacre
12). This is probably due to the fact that it is crowded between
the eye and the ear so that the long axis of this ganglion as well
as of [IX + X hes at right angles to the long axis of the body.
It will be noticed in figure 1 that the special visceral or gustatory
portion of the geniculate ganglion could not be identified. This
is in marked contrast to Lepidosteus at a similar stage of growth.

464. LANDACRE AND McLELLAN

THE GLOSSOPHARYNGEAL GANGLION

The visceral portion of the IX ganglion is quite distinct from
the X (figs. 1, 2, 3 and 7). It lies ventral to the ear capsule,
its anterior end reaching almost to the anterior border of the ear
capsule. The ganglionic cells disappear posteriorly at the level
of the middle of the capsule and the ganglion here dwindles into
a fibrous root which arches around under and behind the capsule
and at the level of its posterior end ascends to enter the medulla
at the same level as that at which the roots of the X enter it. It
was not possible in either the 8 mm. or the 10 mm. stages to iden-
tify a special visceral, or gustatory portion, in the visceral IX,
although a more careful study of earlier stages leading up to these
might enable one to identify it.

The anterior end of the ganglion at this stage abuts against
the posterior end of the thymus gland which consists of a dense
mass of lymphocytes, oval in shape and lying at the same level
dorso-ventrally as the glossopharyngeal ganglion. In stages ear-
lier than that figured (figs. 3, 7, 7.G.) the ganglion overlaps the
gland to a greater extent, usually lying on the dorsal surface of its
posterior end. These relations are important because of the fact
that in early stages it is difficult to distinguish between the gland
and the ganglion histologically, and further, on account of the
fact that the ramus lingualis of the TX lies on the outer (lateral)
surface and the pharyngeal ramus lies on the inner (mesial) side
of the gland.

At the level of the middle of the ear capsule and at the posterior
border, situated sometimes on the dorsal portion of the root of
the IX sometimes surrounding the root, is a small lateralis gan-
glion which we have designated the lateralis [X ganglion. ‘This
ganglion, so far as we know, has not hitherto been identified as a
distinct lateralis ganglion in the frog. Strong, however (95, p.
144), correctly homologizes the nerve arising from this ganglion
(the supra-temporalis) with a lateral line nerve of the LX in fishes.
This is undoubtedly correct, since the ganglion has a separate
existence from early stages and is only accidentally and quite
variously related to the lateral line ganglia of the X.

GANGLIA OF RANA 465

The exact relation of the various ganglia in the [IX and X as
figured in plots 1 and 2 to the ganglia shown in Strong’s plot
is not always easy to determine.

There can be little doubt, however, that the glossopharyngeal
ganglion is identical with ganglion C' of Strong’s plot which occu-
pies the extreme anterior end of the IX and X complex. It is
hard to conceive of the IX ganglion of our plot being combined
with X so as not to bring the IX into the position occupied by
ganglion C.

The appearance of the IX ganglion in plots 1 and 2 is strikingly
similar to that of Menidia (Herrick ’99), and of Ameiurus (Land-
acre 710) and Lepidosteus (Landacre 712) of approximately the
same stage.

In the 8 mm. stage there is only one nerve arising from the
visceralis IX. This is the ramus lingualis of Strong and runs
forward on the outer surface of the thymus gland. In the 10
mm. stage (fig. 2) there are two rami arising from the anterior
end of the ganglion, the larger one running down and forward on
the outer surface of the thymus gland, the ramus lingualis, and a
smaller, the ramus pharyngeus, which runs down and forward on
the inner surface of the thymus gland. We have been able to
detect no trace of the ramus communicans IX ad VII at this
stage in either the 8 mm. or 10 mm. embryo.

In the 35 mm. larva there are three nerves arising from the
anterior end of the IX ganglion. Two of them, corresponding
to the ramus pharyngeus and the r. lingualis of Strong’s plot,
undoubtedly arise from the cells of the ganglion, since the fibrous
bundles disappear in the ganglion. The third nerve corresponding
to the communicating nerve from IX to VEI apparently does not
arise from the ganglion but runs back on the dorsal surface of the
ganglion without diminishing in size and passes into the X gan-
glionic complex. Its behavior in passing the visceral LX ganglion
furnishes strong evidence that it is probably not visceral but
purely cutaneous as Strong describes it.

Of the two visceral nerves, the ramus lingualis is much the
larger. It arises from the anterior end of the ganglion and pur-
sues a course downward and forward on the outer surface of the

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 5

466 LANDACRE AND McLELLAN

thymus gland. The ramus pharyngeus pursues a similar course
downward and forward on the mesial surface of the thymus gland
and is distributed to the roof of the pharynx. The ramus com-
municans [X ad VII leaves the dorsal surface of the [X ganglion
at its anterior end and pursues a course forward and downward
on the mesial surface of the thymus gland which it leaves finally
and, swinging towards the middle line of the body, joins the hyo-
mandibular VII at the posterior border of the eye capsule.

The root of visceral [X can be followed with ease on both the
8 mm. and 10 mm. larvae back to the point where it becomes
fused with that of visceral X (figs. 1 and 2, R.JX). At this point
there is not sufficient difference between the fibers of various roots
to enable us to follow them through the ganglion with absolute
certainty. The apparent course is indicated in figures 1 and 2
and at the point of emergence from the X ganglion to enter the
brain the arrangement with one exception agrees identically with
the description of Strong. Strong describes five roots entering
the brain from the X, but up to the 10 mm. stage only four can
be found. The fifth of Strong’s nomenclature is a pure motor
root and is probably in our plot combined with the fourth.

THE LATERALIS IX GANGLION

This is a small ganglion situated on the root of the [X nerve
just posterior to and at the level of the middle of the ear capsule
(figs. 1, 2, 5 and 9, L.JX). The position is somewhat variable.
In its early stages it has no connection with the lateralis X gan-
glion. It does, however, in the later stages become fused more or
less with either the dorsal lateralis or the ventral lateralis. Its
relation with the root of IX is constant, always being in contact
with it. It may lie dorsal, ventral, or posterior to this root, but
itsone constant relation iswith the IX. The fact that in itsearlier
stages it is completely detached from X leaves little doubt that,
while it later becomes fused with X, it is really a lateralis [X gan-
glion and does not belong morphologically to X. The enormous
size of the auditory capsule, resulting in crowding the root of the
IX back till it joins the X, and the large size of the lateralis X
ganglion account for its later fusion with these ganglia. This

GANGLIA OF RANA 467

ganglion is heavily pigmented like the lateralis ganglion on VII
and X. As to its relation to the lateralis ganglion of Strong’s
plot, we are uncertain. As we shall show later, Strong has
apparently overlooked one of the lateralis ganglia on X owing
probably to the extent of the fusion of the IX + X complex.
Since the lateralis [X may sometimes combine with the dorsal
lateralis X, which is probably ganglion A of Strong’s plot, and
sometimes with the dorsal border of ventral lateralis X, which
seems to be absent as a distinct ganglion in Strong’s plot, it prob-
ably corresponds to the ventral border of Strong’s ganglion A.
This ganglion is composed, however, as Strong states, of two dis-
tinct ganglionic masses, a general cutaneous, the ‘jugular,’ and
a lateralis X. If it unites permanently with ganglion A, it is
with the dorsal lateralis X.

There is one nerve arising from this ganglion. It is quite
small and pursues in a general way the same course as the auricu-
laris X, being quite separate from it, however, throughout its
whole course. It arises from the ventral and anterior end of the
ganglion and runs forward around the border of the posterior
end of the auditory capsule to reach the epidermis. It is applied
very closely to the capsule and is, of course, displaced backwards
by the later growth of the auditory capsule. This nerve corre-
sponds to the ramus supratemporalis of Strong’s plot. The root
of thisnerve is difficult to follow but seems to enter the brain along
with the lateralis roots of X. From the ganglion it follows a
course dorsally and posteriorly along the dorsal surface of dorsal
lateralis X, where it seems to join the fibers of this ganglion (figs.

1 and 2).
THE VAGUS GANGLIA

The vagal ganglionic complex consists of five more or less
distinct ganglionic masses (figs. 1 and 2). With these is associated
in position, as indicated in the preceding section, the lateralis 1X
ganglion. These five ganglia fall into three well defined groups.
First, the most dorsal and proximal portion consists of two ganglia;
the dorsal lateralis (D.L.X.) and the jugular or general somatic
(Cu.X.). Of these two, the dorsal lateralis is lateral in position
and the jugular is mesial in position. They are of nearly equal

468 LANDACRE AND McLELLAN

length dorso-ventrally, but the jugular extends farthest forward
and the dorsal lateralis farthest posteriorly.

The second group (figs. 1 and 2) consists of two ganglia, the
ventral lateralis (V.L.X.) and the second division of visceral X
(G.V.X?). This second group les directly ventral to the first
group. In this second group the ventral lateralis is lateral and
the visceral ganglion is mesial. These two ganglia are approxi-
mately equal in their dorso-ventral length but antero-posteriorly
the visceral is broader.

The third group (figs. 1 and 2,G.V.X") consists apparently of
two branchial ganglia fused, since two branchial nerves arise
from it, but is treated here as one ganglion. It occupies the same
level dorso-ventrally as the second group, but in general shape is
much like the [X ganglion. Its long axis, unlike the two preceding
groups, is in the anterior posterior plane and at its posterior end
it is fused with the second division of visceral X.

THE DORSAL LATERALIS X

This ganglion (figs. 1, 2, 6, 10 and 11), as mentioned above,
occupies the lateral portion of the proximal division of X. It is
also the most dorsal portion of the ganglionic complex. It is
somewhat elongated dorso-ventrally, not reaching so far forward
as the jugular, but extending considerably posterior to any other
portion of the X. It begins abruptly in a rounded anterior end
and diminishes in size as one reads posteriorly, where the most
dorsal of the rami laterales take their origin at the extreme pos-
terior end of the ganglion. The ventral border of this ganglion
is in contact in the later stages, but not in the earlier stages, with
the dorsal portion of the ventral lateralis X. The resemblance
of this ganglion to the lateralis X ganglion in Ameiurus and Lepi-
dosteus (Landacre ’10 and 712) at similar stages of growth is
striking. The large size of its cells, its position, its clean-cut
boundaries and the extension of its posterior border beyond the
posterior limits of the remaining ganglia mark it at once as the
same ganglion. Its position with reference to the jugular and
visceral X is the same in all three embryos.

GANGLIA OF RANA 469

The relation of this ganglion to the lateralis ganglion of Strong’s
plot is doubtful. Strong figures and describes apparently only
one lateralis ganglion in the X and locates it in ganglion A.
If the dorsal lateralis of our plot corresponds to Strong’s ganglion
A, there seems to be no homologue of our ventral lateralis in
Strong’s plot. Our ventral lateralis ganglion is quite distinct in
both 8 mm. and 10 mm. embryos but in later stages seems to
become more closely fused with the dorsal lateralis X. It is
very difficult to determine the limits between the two ganglia in
a 35 mm. tadpole. In the 35 mm. tadpole, where the general
arrangement of the ganglia and nerves is quite similar to their
arrangement in Strong’s plot, the dorsal lateralis X is still the most
dorsal and posterior portion of the complex.

Dorsal lateralis X in both 8 mm. and 10 mm. embryos gives
rise to one nerve. This nerve arises from the extreme posterior
end of the ganglion and pursues a course directly backwards as
in Lepidosteus, Menidia and Ameiurus. This nerve corresponds
to the most posterior R. lateralis, (1) of Strong’s plot, which curves
round behind the auditory capsule before leaving the ganglion.
It splits into two divisions as Strong indicates. Its mode of ori-
gin and the general position of the ganglion leave no doubt that
it corresponds to the ramus lateralis of Ameiurus and Lepidosteus.
It also corresponds to the ramus lateralis superior and its dorsal
branch in Amblystoma (Coghill ’02), and to the lateralis medialis
et dorsalis of Amphiuma (Norris ’08).

The root of this ganglion (figs. 1 and 2), which enters along with
the root of the ventral lateralis ganglion and of lateralis IX,
is the most anterior of the roots of X as figured in Strong’s plot.

The sympathetic ganglia are discussed here briefly on account
of the proximity of the ganglion sympatheticus cervicale of
Strong’s plot (Strong 795, plate 12, gang. sym.) to the proximal
part of the X complex. According to Gaupp (’96), there is no
sympathetic ganglion in the adult frog occupying a position so
close to the X as indicated in Strong’s plot.

The adult frog has a sympathetic ganglion on the second spinal
nerve, the sensory part of the first spinal nerve of the 10 mm.
embryo being absent in the adult. From this first sympathetic

470 LANDACRE AND McLELLAN

ganglion a sympathetic cord extends forward and enters the X
complex, from which a second sympathetic nerve runs forward to
unite with the trigemino-facial complex. The connection between
the glossopharyngo-vagal ganglion, the so-called jugular of the
adult, and the trigemino-facial is intracranial. In the 10 mm.
embryo there are sympathetic ganglia on both the first and second
spinal nerves in the usual positions. The sympathetic ganglion on
the first spinal nerve is quite small, as is also the sensory ganglion
of this nerve. The sympathetic ganglion on the second spinal
nerve is, on the contrary, quite large. This, as stated above,
is the first sympathetic of the adult. A careful examination of
our whole series of embryos reveals no sympathetic ganglion in
the region of the X. In fact, up to our latest stage and even ina
35 mm. embryo it is not possible to follow the sympathetic nerve
from the second sympathetic into the X as a continuous cord and
we have been unable to follow with certainty the intracranial con-
nection between X + IX and V + VII ganglia.

These facts indicate that the sympathetic ganglion and cords
are in & very immature condition in a 10 mm. embryo and even in
a 35 mm. embryo are difficult to follow in detail.

In a 10 mm. embryo the first spinal ‘ganglion is situated 22
sections posterior to the posterior end of lateralis X and the
second spinal ganglion is 48 sections posterior to this point, so
that the first sympathetic ganglion of a 10 mm. embryo which
becomes the first ganglion sympatheticus cervicale is back of the
posterior end of lateralis X, a distance equal to the total anterior
posterior length of IX + X. The change from this condition
to that figured by Strong, if he has correctly located this ganglion,
can only be accounted for by the shifting backwards of the [IX +
X complex by the enlargement of the auditory vesicle.

THE VENTRAL LATERALIS X

This ganglion (figs. 1, 2, 6, 10, V.L.X.) occupies, as indicated
above, the lateral position in the most distal and ventral division
of the second group of ganglia. It is elongated dorso-ventrally ;
at its dorsal border it is in contact, particularly in later stages,
from 10 mm. on, with the ventral end of dorsal lateralis X and

GANGLIA OF RANA 471

sometimes with lateralis IX. The ventral border of the ganglion
diminishes in size and finally gives rise to a lateral line nerve which
passes out with a visceral nerve of the X.

The mesial border of the ganglion is more or less closely fused
with the lateral surface of visceral X but can always be distin-
guished from it by the larger size of its cells and by the fact that
the cells are always heavily pigmented. The position of this
ganglion in Strong’s plot is difficult to determine. Our series is
not complete from 10 mm. to the 35 mm. embryo. The ganglion
seems to shift its position proximally and join the dorsal lateralis
ganglion, although not completely, since there are lateralis cells
distributed along the dorsal surface of the visceral ganglion in the
35mm. stage. It must be identified for the present, provisionally,
in part, with the ganglion A of Strong and in part with the general
position of his ganglion B! and B?, to which he does not attribute
lateralis cells. The ganglion is not distinct in either Ambly-
stoma or Amphiuma, although Norris (’08) shows in Amphiuma
a rather sharp division between the portion of the ganglion from
which his ramus medialis et dorsalis and that from which his
ramus lateralis ventralis arises. The former probably corre-
sponds to the dorsal lateralis ganglion of our plot and the latter
to the ventral lateralis. One nerve arises from the ganglion. It
springs from the extreme ventral end of the ganglion and corre-
sponds to the ramus lateralis (5) of Strong’s plot. It also corre-
sponds to the ramus inferior (Zi.) of Amblystoma (Coghill ’02)
and to the ramus lateralis ventralis (Lat. V.) of Amphiuma
(Norris ’08).

In the embryo frog, as well as in Amblystoma and Amphiuma,
this nerve passes out of the ganglion in conjunction with visceral
fibers. This is not so evident in Strong’s plot, although his
Ramus visceralis does come out of the ganglionic complex at the
same point but the two trunks are separated up to the ganglionic
mass. The conditions in our embryos are quite similar to the
plots of Coghill and Norris, where the lateralis and the visceralis
trunks pursue a similar course for some distance; at least one of
the visceral rami is closely associated with the lateralis ventralis.
The root of the ventral lateralis X passes dorsally to enter the
brain with the roots of the dorsal lateralis X (figs. 1 and 2).

Are LANDACRE AND McLELLAN

THE GENERAL SOMATIC X (JUGULAR)

The somatic X ganglion (figs. 1, 2, 6, 10, Cu.X.) occupies the
mesial position in the proximal mass, or first division of the X
ganglion. It is in the 8 mm. and 10 mm. embryos entirely out-
side the cavity in which the medulla lies. As the head becomes
broader and the whole X complex assumes a position more hori-
zontal, general somatic X comes to lie ventral to the dorsal later-
alis X and also shifts its position somewhat more proximal so that
in 235mm. embryo its anterior end is intracranial, the remainder
of it lying in the jugular foramen. This shifting of position gives
the ganglion the general position occupied by the jugular ganglion
in some of the fishes, i.e., intracranial. It extends further for-
wards than the dorsal lateralis X, but does not reach farther than
the middle of that ganglion posteriorly. Its ventral border is
usually in contact with visceral X, while its lateral, and later its
dorsal border, are in contact with the mesial surface of dorsal
lateralis X. The cells of this ganglion are smaller than those of
either lateralis X but not so closely packed as those of visceral
X. The ganglion is quite large, much larger than the jugular at
similar stages in Ameiurus or Lepidosteus.

There is little difficulty in locating this ganglion in Strong’s
plot. It represents a portion of his ganglion A. It is quite
distinct in all stages of the embryo up to and including the 10
mim. stage. The most conspicuous nerve arising from this gan-
glion is the ramus auricularis, (2) of Strong’s plot. He figures it as
a pure general cutaneous nerve. It seems to be such in the em-
bryo, but arises from the X ganglion in both Amblystoma and
Amphiuma as a mixed nerve containing both general cutaneous
and lateralis fibers. Its point of origin from the jugular ganglion
is so close to the dorsal lateralis that there may possibly be later-
alis fibers in it. Strong’s interpretation of it as a pure general
somatic nerve seems to hold however for the embryos we have
studied.

The ramus auricularis arises from the anterior border of the
ganglion at about the middle of its dorso-ventral extent and arches
forward and outward to curve around the posterior border of the
auditory capsule. A comparison of figures 1 and 2 will show

GANGLIA. OF RANA 473

that the ramus auricularis X takes its origin from the jugular
ganglion farther posterior in a 10 mm. embryo than in the 8 mm.
stage. A careful examination of twenty series lying between the
8 mm. and the 10 mm. stages shows that in all but one of them the
ramus auricularis arises as in the 8 mm. stage In the 10 mm.
stage this nerve arises posterior to the fibrous bundle connecting
the two ventral ganglia of X to the two dorsal ganglia. This
fibrous bundle passes lateral to the jugular ganglion (figs. 6 and
10) and it, is probable that it is the active factor in determining
these relations, 1.e., it may form anterior or posterior to the point
of exit of the ramus auricularis from the jugular ganglion.

The differences between the fibers of different components is
not sufficiently great to enable one, at this stage, to follow the
general cutaneous fibers into all the nerve trunks figured by
Strong. The size of the ganglion is entirely sufficient to furnish,
in addition to the ramus auricularis, the rather large bundles
running out in two of the branchial rami and the ramus commu-
nicans IX ad VII. In describing this last ramus attention was
called to the fact that, while it enters the anterior end of the glosso-
pharyngeal ganglion, it runs past that ganglion and follows the
root of the IX to enter apparently the jugular. Questions con-
cerning the composition of mixed nerves are not easily settled on
the material of the age used in this paper. Fortunately most
nerves, even when mixed in the adult and in later embryonic
stages, are likely to be pure and arise separately from a distinct
ganglionic mass if the proper stage is studied. This is true of the
ramus auricularis, but is not true of the other rami arising from
the jugular ganglion, so that our findings as far as they go con-
firm those of Strong with respect to the rami arising from this
ganglion.

THE SECOND V#SCERALIS X

This ganglion (figs. 1, 2, 6, 10, G.V.X?) occupies the mesial
portion of the distal division of the vagus complex. On its dorsal
and proximal border it is in contact with the jugular and on its
lateral, and later on its dorsal surface, it is in contact with the
ventral lateralis. On its anterior border it is in contact withthe

474 LANDACRE AND McLELLAN

branchial X (figs. 1 and 2, G.V.X'). Its longest diameter, like
all other members of the vagus complex except the jugular and
branchial, is the dorso-ventral. It projects somewhat further
caudad than the ventral lateralis but not so far as the dorsal
lateralis.

The position of this ganglion in Strong’s plot cannot be deter-
mined with certainty. The portion of the X complex from which
the visceral rami arise is represented as a mesial projection
attached to the main ganglionic mass at the level of the ganglion
B2. It is labelled ‘ramus visceralis 3’ but is described by Strong
as containing ganglion cells. There seems no doubt that the
ramus visceralis (3) of Strong’s plot represents the apex of our
visceral ganglion, but whether the proximal part of our visceral
ganglion is represented by B! or B? of Strong’s plot is uncertain.
It is probably represented by B', since the rami branchiales seem,
on his plot, to come from B?. The comparison on this basis har-
monizes the two plots, since in the earlier stages represented in
our plot the branchial nerves come from the branchial ganglion.
The relations in the 10 mm. embryo plot are quite clear and bar-
ring the reduction in the number of branchial nerves are quite
’ typical.

The visceral nerves arising from this ganglion emerge from
its ventral apex. There are two chief divisions at this stage.
The more ventral arises in conjunction with the ramus lateralis
ventralis (L.X.V., figs. 1 and 2) and the other arises somewhat
more proximally and pursues a course directly posterior. This
last branch is undoubtedly the ramus intestinalis (figs. 1 and 2,
V.X.). As to the composition of the first, the branch arising
with the lateral line ramus, there is less certainty. It probably
is not purely sensory, but contains a large motor ramus, (4) of
Strong’s plot. But there are certainly visceral fibers in it also,
probably supplying the fourth gill.

GANGLIA OF RANA 475
BRANCHIALIS X, OR FIRST VISCERALIS X

This ganglion (figs. 1, 2, 4, 8, G.V.X+) stands in sharp contrast
to the remaining portion of X both in its shape and in its position
in the body. It resembles both in shape and position the glos-
sopharyngeal ganglion. Its long axis is parallel to the long axis
of the body. It lies under the auditory capsule like the [X and
not behind it like the remainder of the X. Its general shape
is that of an elongated S-shaped column of cells, free at its ante-
rior border but attached at its posterior border to visceralis X2.
This attachment occurs at the middle or upper third of the ante-
rior surface of the visceralis X. The anterior end of this ganglion
lies under the posterior end of the auditory vesicle. From its ante-
rior end, where a branchial nerve arises, it gradually increases
in size until it fuses at its posterior end with the visceral X2.

The position of this ganglion in Strong’s plot is represented
apparently by ganglion B®. It is from this ganglion that the
branchial nerves emerge in his plot and Strong’s ganglion C is,
undoubtedly the glossopharyngeal. The only question in doubt
is whether branchial X also corresponds to a part of B’. This
seems improbable since B! is the only ganglion left on Strong’s
plot that could represent the visceral X2. The extent to which
the IX + X complex is elongated by the posterior extension of
the auditory capsule makes it difficult to follow the shifting of
the ganglia, since there is a stage between the time when the
ganglia are distinct, as in our plots, and the time when fibril-
lated paths can be followed, in which it is very difficult to deter-
mine ganglionic boundaries and still more difficult to separate
components among fibers.

An interesting question arises here as to the homology of
the branchial ganglia in the frog with the branchial ganglia of
Menidia, Lepidosteus and Ameiurus. In these types there are
four more or less distinct branchial ganglia in the vagal complex.
In Lepidosteus, which at a similar stage of development most
closely resembles the 8 mm. stage of the frog, only one branchial
nerve, that for the second true gill, arises from the first branchial
X ganglion. The remaining three arise from the ventral border

476 LANDACRE AND McLELLAN

of the general visceral ganglion, each branchial nerve arising from
a ventral prolongation extending downwards towards the appro-
priate gill. The condition shown by Herrick (’99, text-fig. 5)
gives the exact relation of these branchial ganglia in Lepidosteus
and Ameiurus, with the exception that the branchial ganglia are
a little larger and somewhat more detached than in Ameiurus
and Lepidosteus and the general visceral portion seems to be
smaller. In the frog there are only two large branchial nerves
and they both arise from the same ganglion. This ganglion has
the same appearance and morphological relations as Branchia] X!
of Lepidosteus (Landacre 712). The question arises whether the
branchial ganglion of the frog represents the branchial X! of
Lepidosteus, Ameiurus and Menidia or whether it represents
two or more branchial ganglia of these types fused. The question
can be answered definitely only by careful study of the embryo-
logical development of the branchial ganglia and nerves. The
condition in the ganoid (Landacre 712) indicates that branchial -
ganglia other than X! are incorporated with the general visceral
X, since these ganglia are much smaller than in Menidia and much
less distinct. The behavior of the second branchial nerve arising
from this ganglion, as will be shown later, indicates that the gan-
glion that we have called visceralis X? really represents the general
visceral X of Lepidosteus plus one or more branchial ganglia
and that the branchial ganglia of X (figs. 1 and 2, G.V.X') repre-
sents principally branchialis X! of Lepidosteus.

As mentioned above, there are two branchial nerves (figs. 1 and
2, Br.X* and Br.X?) arising from branchialis X. These corre-
spond to the rami branchialis (6) and (7) of Strong’s plot. The
anterior (6 of Strong’s plot) arises from the extreme anterior end
of the ganglion and pursues a course downward and forward to
the gill. The second (7 of Strong’s plot) arises toward the poste-
rior end of the ganglion and runs downward and forward to the
gill. This nerve on entering the ganglion, however, is not lost
entirely among the ganglion cells, as is the first nerve, but pur-
sues a course backward on the under surface of branchial X until
it reaches the anterior border of visceral X. It is, however, in
its course diminished in size and it may be possible that some of

GANGLIA OF RANA 477

its cells ef origin lie in the posterior portion of branchial X. It
is hardly probable that all of them lie in branchial X, so that
until the embryological origin is worked out the problem of the
exact morphology of branchial X! will have to be left as indicated
above, i.e., that a part of the cells from which the second branchial
nerve (6 of Strong’s plot) originates lie in the visceral ganglion and
that the visceral ganglion represents the general visceral ganglion
of such types as Menidia, Lepidosteus and Ameiurus, plus the
representative, one or more, of branchial ganglia of these types.

‘SUMMARY AND DISCUSSION

1. The trigemino-facial complex of the frog in stages earlier
than those studied by Strong corresponds in all essential details
with his analysis except in the greater isolation of the profundus.
This ganglion in earlier stages is much more isolated than in
the earliest plot given in this paper, but even in that it stands out.
rather distinctly, indicating its definite character which is lost
by incorporation with the Gasserian. In other respects we con-
firm Strong’s account of the V + VII ganglia in the frog.

2. The glossopharyngo-vagal complex of ganglia, on the con-
trary, if taken in the 8 mm. and 10 mm. stages, shows a much
greater degree of simplicity and isolation of its various compo-
nents than indicated by Strong and furthermore it is much more
typical as compared with such types as Menidia, Ameiurus and
Lepidosteus.

3. The lateralis components in the glossopharyngo-vagal
complex are represented by three more or less distinct ganglia.
These are, (a) a lateralis [X situated on the root of the [X behind
and at the level of the middle of the auditory vesicle dorso-ven-
trally; (b) two lateralis X ganglia situated on the lateral surface
of the cutaneous and general visceral ganglia respectively. Of
these two ganglia, the dorsal lateralis is proximal and the ventral
lateralis distal. The dorsal lateralis lies lateral to the jugular, or
general cutaneous X, and gives rise to one nerve trunk which
immediately after leaving the ganglion splits, giving rise to the
most posterior ramus of Strong’s plot (dorsalis and medialis of

478 LANDACRE AND McLELLAN

Coghill and Norris). This ganglion resembles closely in form
and position the lateralis X of Ameiurus and Lepidosteus in simi-
lar stages of development. It extends considerably posterior to
any other ganglion and the nerve arises at the posterior atten-
uated extremity as in those types.

(c) The ventral lateralis X is the third of these ganglia. It is
ventral to dorsal lateralis X in young embryos, but later, owing
to the flattening of the head, becomes more lateral in position. It
lies lateral to visceralis X? in young embryos and later assumes
a more dorsal position with reference to visceralis X2 and also ~
becomes more closely fused with the dorsal lateralis X. It gives
rise to one nerve which emerges from the ventral apex of the gan-
glion (the most anterior lateral line ramus (5) of Strong’s plot
and the ramus lateralis ventralis of Coghill and Norris).

The presence of two lateral line ganglia on X suggests at once
a homology with the condition in VII where there are two lateral
line ganglia also. As to the distinctness of this ganglion up to
and beyond the 10 mm. stage there can be no doubt. Nor is it
doubtful that it is a lateral line ganglion. The size of its cells,
their heavy pigmentation. and the isolation of the ganglion settles
both these doubts. As to the homology with ventro-lateral VII,
we are not willing to go farther at present than to gives it a name
signifying its composition and position in the X complex. It
gives rise to the same component as ventro-lateral VII, it occupies
the same relative position, 1.e., lateral to a visceral ganglion and in
the distal portion of the complex as does ventro-lateral VII. Its
nerve also runs out in conjunction with a branchial nerve. If it
should prove to have a similar mode of origin to that ganglion
there would seem to be no objection to homologizing them. No
other fish or amphibian studied so far as we know has a distinct
ventral lateralis ganglion. An examination of the reconstruc-
tions of Coghill (02) and of Norris (08) indicates that probably
the same condition will be found in Urodeles, since the lateral line
cells extend well down ventrally toward the origin of the ramus
lateralis ventralis in both cases.

4. The jugular, or general somatic X, as in other Ichthyopsida
above the Cyclostomes, is the only representative of its type in

GANGLIA OF RANA 479

the [IX + X complex. It is situated mesial to the dorso-lateral
X and is consequently proximal of the visceral X. It is very
large in the tadpole, much larger than in the Lepidosteus and
Ameiurus at the same stage of growth and is much farther away
from the medulla. In the 35 mm. tadpole, however, it migrates
towards the medulla and les partly, though not wholly, in the
jugular foramen.

One nerve arises pure from this ganglion at this stage, the ramus
auricularis; others arise also but run out in conjunction with
other components and could not be accurately traced. So far as
they could be followed their distribution agrees with Strong’s
description.

5. The visceral ganglia of the glossopharyngo-vagal complex
lie in three well defined masses: (a) the glossopharyngeal; (b)
the first or most anterior visceral, and (c) the second or most
posterior visceral.

(a) The glossopharyngeal ganglion occupies a position ventral
to the auditory capsule with its long axis parallel to that of the
body. The root is long and curves around behind the auditory
capsule to enter the medulla along with those of X. It seems to
be a pure visceral ganglion, although a cutaneous ramus, r. com-
municans IX ad VII, passes out from the anterior end of the
ganglion. Its fibers, however, can be traced past the ganglion
and apparently enter jugular X, as described by Strong. It was
not possible in the stages studied to recognize the special visceral
or gustatory portion of this ganglion. ‘Two nerves, the ramus
pharyngeus and the ramus laryngeus, arise from the anterior end
of this ganglion.

(b) The first visceral or branchial ganglion of X resembles
in shape and position the glossopharyngeal. It lies under the
posterior end of the auditory capsule with its long axis parallel
to that of the body. Its posterior end is not, like that of IX,
continued into a fibrous root but joins the cell mass of the second
visceral X near its middle region. Gustatory cells could not be
recognized in this ganglion in the stages studied. Two large
nerves arise from this ganglion, the branchial 6 and 7 of Strong’s
plot.

480 ‘LANDACRE AND McLELLAN

The presence of two branchial nerves arising from this ganglion
would suggest that it represented two branchial ganglia fused.
However, there is some doubt as to whether the fibers of the
second branchial nerve arise in this ganglion or partly in this
ganglion and partly in the second visceral ganglion.

(c) The second visceral X ganglion, unlike the glossopharyn-
geal and the first visceral X, lies with its long axis at right angles
to that of the body. It gives rise to two chief nerve trunks; one,
the ramus intestinalis and a smaller ramus which probably con-
tains branchial fibers. The question as to the exact position of
the branchial ganglia in these two visceral ganglia cannot be
definitely settled without further examination of earlier stages.
A eareful study of a close series of embryos will probably show
definitely the number and position of the epibranchial placodes
and their position in the visceral ganglia, thus determining the
number of branchial ganglia in this complex and their location.

6. The failure to distinguish special visceral or gustatory
ganglia in Rana in the stages studied is not to be interpreted to
mean, of course, that they are absent or cannot be isolated. As
mentioned in the introduction, this paper is preliminary to a
study of the mode of origin of the cerebral ganglia in the frog. As
a matter of fact, epibranchial placodes are present in the stages
earlier than 8 mm. and well defined and seem to behave much as
they do in Ameiurus and Lepidosteus. It is hardly probable
that they will be so distinct or can be followed to so late a stage
as in Lepidosteus, since they are not recognizable in the 8 mm.
stage. Neither is it likely that the frog will furnish such definite
evidence as to the character of placodal ganglia as did Ameiurus,
since all nerves arising from the IX seem to contain both general
visceral and special visceral fibers, whereas in Ameiurus they seem
to contain only special visceral fibers.

7. The results of the present paper emphasize the immense
importance of having access to a large number of stages taken at
close intervals from the same lot of eggs, if one is to reach safe
conclusions in regard to the composition and origin of cerebral
ganglia. All ganglia, particularly those derived from the neural
crest, in their early stages are more or less ill defined; following

GANGLIA OF RANA 481

this stage in Lepidosteus, Ameiurus and the frog there is a stage
when the ganglia are better defined, have clean cut boundaries
and give rise to fibrillated nerves, usually well isolated from each
other; following this stage the ganglia fuse together more or less,
their nerve trunks combine and they must be isolated largely by
the difference in size of their nerve fibers. Evidently the second
stage is the one most favorable for determining the number and
position of ganglionic components and this stage can be found
only when the series is complete and taken at close intervals.

LITERATURE CITED

Coeuitt,G.E. 1902 The cranial nerves of Amblystoma tigrinum. Jour. Comp.
Neur., vol. 12, no. 3.

Gaupp, E. 1896 In A. Ecker’s and R. Wiederscheim’s Anatomie des Frosches.
Braunschweig.

Herrick, C. J. 1894 The cranial nerves of Amblystoma. Jour. Comp. Neur.,
vol. 4. :

1899 The cranial and first spinal nerves of Menidia. Jour. Comp.
Neur., vol. 9, no. 3.

Lanpacre, F. L. 1910 The origin of the cranial ganglia in Ameiurus. Jour.
Comp. Neur., vol. 20.

1912 The epibranchial placodes of Lepidosteus osseus and their rela-
tion to the cerebral ganglion. Jour. Comp. Neur., vol. 22, no. 1.

Norris, H. W. 1908 The cranial nerves of Amphiuma means. Jour. Comp.
Neur., vol. 15, no. 6.

StronGc, Outver 8. 1895 The cranial nerves of Amphibia. Jour. Morph., vol.
10, no. 1.

Wiper, H. H. 1892 Die Nasengend von Menopoma alleghanense und Amphi-
uma tridactylum nebst Bemerkungen iiber die Morphologie des R.
ophthalmicus profundus trigemini. Zool. Jahr., Abth. f. Anat. n.
Ontog., Bd. 5, Heft. 2.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 5

482 LANDACRE AND McLELLAN

ABBREVIATIONS

Aud. V., Auditory vesicle

Aud., Auditory ganglion

Au. X., Ramus auricularis X.

Br. X', First ramus branchialis X.

Br. X?, Second ramus branchialis X.

Bu. VIT., Ramus bucealis VII.

B. V., Blood vessel

Cu. X., Cutaneous or general somatic (jugular) ganglion of X.

D. L. X., Dorsal lateralis ganglion of X.

D. L. VII., Dorso-lateral lateralis ganglion of VIT.

Gass., Gasserian or general somatic ganglion of V.

Gen., Geniculate or visceral ganglion of VII.

G. V. [X., Visceral (Glossopharyngeal) ganglion of IX.

G. V. X', First division of the visceral ganglia of X; possibly equivalent to two
branchial ganglia

G. V. X®, Second division of the visceral ganglia of X.

Hyo. VII., Hyomandibularis VII.

L. IX., Lateralis ganglion of IX.

L. X. V., Ventral ramus of the lateral line nerve of X = R. lateralis (5) of
Strong’s plot. Strong ’95, plate 12

L. X. D., Dorsal ramus of tHe lateral line nerve of X = R. lateralis (1) of
Strong’s plot. Strong ’95, plate 12

Man. V., Ramus mandibularis V.

Maz. V., Ramus maxillarus V.

Mes., Mesencephalon

No., Notochord

O. V., Ramus ophthalmicus V.

O. S. VII., Ramus ophthalmicus superficialis VII. |

Opt., Optie vesicle

Pal. VIT., Ramus palantinus VIT.

Prof., Profundus ganglion

R. V., Root of V.

R. L. [X., Lateral line root of IX.

R. IX., Root of IX.

R. P. 1X., Ramus pharyngeus IX.

k.X.V + C., Visceral + somatic roots of X.

R. L. X., Lateral line root of X + IX.

Fee, LOU Olek

S. 7. X., Ramus supra-temporalis X.

T. G., Thymus gland

V.L. VII., Ventral lateral line ganglion of VII.

V. L. X., Ventral lateral line ganglion of X.

V. X., Ramus visceralis X.

GANGLIA OF RANA 483

a ol a ee ae Se” ee Le ad OS ae a ea
SO) (on 110) 16S, (GOSS SON Sy 70) aon G0! 25, 2007/5 s/n) /

oie i

Gv. xa
Be Xr Be Xe R.L|
V X-- AR -- LXV.

Fig. 1 A flat reconstruction of the V, VII, VIII, [X and X cerebral ganglia in
Rana pipiens, 8 mm. in length. The scale at the top of the figures indicates the
position and number of sections 10u in thickness over which the plot extends.
General somatic ganglia are shown with horizontal lines, lateral line ganglia with
cross hatched lines, and visceral ganglia with vertical lines. Special visceral or
gustatory ganglia are not indicated, as their boundaries could not be determined
in embryos of this age. > 100.

484 LANDACRE AND McLELLAN

=
50 4 YO 35 30 25 Jo /F fo a /

Fig. 2 <A flat reconstruction of the [IX and X cerebral ganglia of Rana pipiens
10 mm. in length; shading asin figurel. The scale at the top of the figure indicates
number and position of sections 10yu in thickness over which the plot extends. The
seale at the bottom of the plate indicates the number of the section and the num-
ber of the figure illustrated in succeeding plates. As in figure 1, the special vis-
ceral or gustatory ganglia are not indicated. 1,.2, 3, 4 are the first four roots
according to Strong’s nomenclature (Strong ’95, plate 12, fig. (a) and page 135).
* 100.

Fig.3 A camera outline through the dorsal portion of the right side of the head
of Rana pipiens, 10 mm. in length. The section passes through the anterior end
of the [X ganglion and the origin of the ramus laryngeus. The position of the sec-
tion on figure 2 is indicated at the bottom of that figure (Sec. 2). The details of
the area blocked out are shown on figure 7. X 50.

GANGLIA OF RANA 485

Fig.4 A camera outline through the dorsal portion of the right side of the head
of Rana pipiens, 10 mm. in length. The section passes through the middle of the
first portion of the visceral X ganglion (G.V.X}1, fig. 2) and the posterior portion of
first branchial nerve (Br. X') of that ganglion. The position of the section is indi-
cated at the bottom of figure 2 (Sec. 26). The details of area blocked out are shown
in figure 8. XX 50.

Fig. 5 A camera outline of the dorsal portion of the right side of the head of
Rana pipiens, 10 mm. in length. The section passes through the lateralis IX
(L.1X.) and the second visceral ganglion of X (G. V. X2). The position of this
section is indicated at bottom of figure 2.(Sec. 31) and the details of the area
blocked out are shown in figure 9. X 50.

Fig.6 <A camera outline through the dorsal portion of the right side of the head
of Rana pipiens, 10 mm. in length. The section passes through the four posterior
masses of the X ganglion. The position of this in figure 2 is indicated at the bot-
tom of that figure (Sec. 36). The details of the area blocked out are given in figure
105 x<eeo0:

486 LANDACRE AND McLELLAN

Fig. 7 Details of area blocked out in figure 3. X 200.

Fig. 8 Details of area blocked out in figure 4. 200.

Fig.9 Details of area blocked out in figure 5. 200.

Fig. 10 Details of area blocked out in figure 6. 200.

Fig. 11 Details of the lateralis X ganglion. The position of this section on
figure 2 is shown at the bottom of that figure (Sec. 39). > 200.

DEGENERATION AND REGENERATION OF NERVE
- FIBERS

S. WALTER RANSON

From the Anatomical Laboratory of the Northwestern University Medical School!

TWENTY-NINE FIGURES

The series of experiments upon which this paper is based
was begun with no idea of taking up the question of the regen-
eration of nerve fibers, but with the much more restricted pur-
pose of studying the degeneration of the non-medullated fibers
of the spinal nerves. After it had been demonstrated that the
spinal nerves contain many more non-medullated than medul-
lated fibers (Ranson 711) it was very desirable that the Wal-
lerian experiment should be repeated to determine the direction
of degeneration in these fibers. Work had not progressed far,
however, before it became evident that observations were being
made that had a bearing on the perplexing question of nerve
regeneration and made it necessary to enlarge the scope of the
investigation while not abandoning its original object.

Since, as has been intimated, we shall be concerned in part
with the degenerative and regenerative phenomena in the non-
medullated fibers, it will be best to indicate at this point the
facts which have been previously ascertained in regard to these
fibers.

When ordinary staining methods are used it is possible to
see in the spinal nerves only those fibers which possess a myelin
sheath, since axons not so covered cannot be differentiated
from the connective tissue of the endoneurium. But when

1 Some of the work, on which this paper is based, was done in the Anatom.
biol. Institut, Berlin, the Anatom. Anstalt, Freiburg i. Br. and the Physiol.
Institut, Freiburg i. Br. To the directors of these institutes I am indebt or

many courtesies.
487

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6
DECEMBER, 1912

488 S. WALTER RANSON

these nerves are stained by a modification of Cajal’s method,
which we have called the pyridine-silver method, very many
fine nerve fibers are seen in the endoneurium between the medul-
lated fibers (Ranson ’11). These are stained black with reduced
silver and are devoid of a myelin sheath, while the medullated
axons are light yellow and are surrounded by a colorless sheath
of myelin. The non-medullated fibers may run singly but are
usually grouped into small bundles. Although no attempt
has been made to determine their exact number, it is easy to
see that they far outnumber those which are medullated. On
tracing these fibers back toward the spinal cord, it is found that,
while a certain number can be seen entering the nerve via the
gray ramus communicans (Chase, unpublished observations),
the vast majority of them enter the nerve by way of the dorsal
root. A study of the spinal ganglion (Ranson 712) has shown
that these fibers are derived from the axons of the small cells
of the ganglion by a T- or Y-shaped branching. Because of
the location of the cells of origin in the spinal ganglion, and
because of the characteristic 7- or Y-shaped branching of the
axons there need be no hesitancy in regarding them as afferent
and not sympathetic in function.

As has been intimated, it was our purpose, when the series
of experiments to be reported in this paper was begun, to cut
first the peripheral nerve and then, in other experiments, the
roots proximal to the spinal ganglion in order to determine the
direction of degeneration of these fibers. The division of the
sciatic nerve of the dog was undertaken to exclude by the direc-
tion of degeneration the possibility that some of the non-
medullated fibers might arise from cells located at the periphery
(a common location of such cells in invertebrates). In another
series of experiments the roots, proximal to the ganglion of the
second cervical nerve of the dog, were cut to determine whether
any non-medullated fibers arose from cells located in the gray
substance of the spinal cord. Since the results of these two
series of experiments were complicated by a variety of regenera-
tive changes in the nerve, ganglion and roots, it has seemed best
to present the two series of experiments in separate papers.

DEGENERATION AND REGENERATION OF NERVE FIBERS 489

And the present paper will be concerned only with the results
of section of the sciatic nerve.

The majority of those who have worked with the problem
of the regeneration of nerves had previously taken a definite
position in the contest over the neurone theory and sought in
their experiments on nerve regeneration to find evidence which
would aid them in maintaining that position. The supporters
of the neurone theory believed that the axons were formed
embryologically as outgrowths from ganglion cells and were
regenerated from the axons of the central stump toward the
periphery. On the other hand, the opponents of the neurone
theory believed in a multiple origin of the axons from the cells
along the course of the embryonic nerves, and described a simi-
lar discontinous origin of the new axons in regenerated nerves
by a differentiation of the protoplasm formed from the old
neurilemma cells. The present writer, having never committed
himself in the matter of the neurone theory, was able to take
an entirely unprejudiced attitude and was led to his present
position as he studied the regenerative phenomena which
appeared, unexpectedly and with great clearness, in the prep-
arations of the divided sciatic nerve.

SURVEY OF THE LITERATURE ON THE REGENERATION OF NERVES

Even before the time of Waller the subject had received some
attention, but it was he who first recognized the true nature
of the degenerative and regenerative processes in nerves. He
stated (52) that that portion of a divided nerve fiber separated
from its trophic center underwent complete degeneration and
that regeneration took place through an outgrowth of new
fibers from the central undegenerated stump. His conclusions
were not at once accepted, however, and even to the present day
the outgrowth of the new axons from those of the central stump
is a matter of debate. It would tax too heavily the reader’s
patience to review the literature from Waller’s time to the present
date, but this is made unnecessary by the excellent reviews of the
early literature, given in the articles of Howell and Huber (’92)
and Stroebe (95). According to the summary given by Howell

490 S. WALTER RANSON

and Huber of the problem as it stood at the time of the writing
of their article, three views were then held: (1) According
to one view, the axons did not degenerate in the peripheral
stump after they had been separated from the central nervous
system, so that, after the two ends of a cut nerve had been
approximated, it was only necessary for a peripheral axon to
fuse with a central axon and for a new myelin sheath to be.devel-
oped about it. (2) The view most generally current at that
time was the view of Waller that the new axons grew out from
the central end. (3) But they state that the best of the papers
which had appeared in the years immediately preceding their
work agreed in stating that the axis cylinder is developed anew
in the peripheral end and is connected secondarily to the cen-
tral end. They add that those who maintained that the new
axis cylinders are sprouted from the old ones of the central end
did not claim to have seen the process, since the closest study
with the staining method then in use showed nothing of the
axis cylinder at the point of transition. In the opinion of the
present writer, it was just this lack of a satisfactory axon stain
and the resulting uncertainty of what was occurring at the
transition zone between the ends of a cut nerve that has made
it possible for the supporters of the theory of the autogenous
regeneration of nerves to maintain their position for so many
years.

With the work of Biingner (91), Howell and Huber (’92),
Stroebe (93) and Huber (’95), the modern work on the regen-
eration of nerves may be said to have begun. Biingner (91)
saw and clearly described the formation of the nucleated pro-
toplasmic bands which have occupied so prominent a place in
the supposed histogenesis of autogenously regenerated nerve
fibers. According to him, the nuclei of the neurilemma, increase
in number and protoplasm accumulates about them. Longi-
tudinal striation appears in the protoplasm of these cells which
then become fused into long multinucleated bands. Within
these bands the centrally placed, longitudinally striated pro-
toplasm becomes differentiated into a new axon, while in the
surrounding protoplasm the myelin sheath is laid down.

DEGENERATION AND REGENERATION OF NERVE FIBERS 491
Howell and Huber (’92) also saw and described these proto-
plasmic bands, and, while they were unable to confirm Biingner’s
observations on the differentiation of axons in them, they re-
garded them as ‘embryonic nerve fibers’ capable of receiving and
conducting impulses. In case of a failure of the two ends of
the nerve to unite, regeneration stopped with the formation of
the protoplasmic bands. In case of union of the two stumps,
the bands of the peripheral stump fused with those of the cen-
tral stump; next myelin sheaths were laid down within the bands
and new axons grew down into them from the central stump.

Stroebe (93), using his now well known stain, was able to
demonstrate the outgrowth of new axons from the central end,
but thought that the myelin sheath was formed as a continua-
tion of the old sheath and accompanied the axon in its forward
growth. He was unable to demonstrate any connection be-
tween these new fibers and the protoplasmic bands seen by
Biungner in the peripheral stump.

Working with Stroebe’s method, Huber (’95) was able to
secure much clearer pictures of the regenerating nerve fibers
than had been seen before, and showed that the axons grew out
from those of the central stump and, in some cases at least, en-
tered the substance of the protoplasmic bands of the peripheral
stump. He was able to see some which ended abruptly in the
protoplasm of the bands, their free ends directed toward the
periphery and occasionally presenting bulbous enlargements.

Ziegler (96) ascribed the origin of the new axons to the neuri-
lemma, cells of the central stump and thought that at the time
of their first appearance they had no connection with the old
axons. Galeotti and Levi (95), Kennedy (’97), and Wieting
(98) thought that the new axons developed in situ in the periph-
eral stump. It is clear, therefore, that even before Bethe began
his work the opinions of those who had worked at the question
from the histological side were about evenly divided. This
shows that the histological methods at their disposal were not
adequate for the solution of the problem.

Since investigators had failed to show conclusively the nature
of the regenerative processes:when the two stumps had been

492 S. WALTER RANSON

allowed to unite, Bethe (’03) decided to follow the example of
Philipeaux and Vulpian (’59) and determine what would occur
in a nerve fully cut off from its central connections. He worked
with the sciatic nerve of young dogs and to prevent the union
of the cut ends he adopted special operative procedures: (1)
In some dogs he grasped the sciatic nerve at the great sacro-
sciatic foramen, tore it out along with the motor roots and
spinal ganglia and cut it off in the middle of the thigh. (2) In
others he cut the sciatic in the middle of the thigh, left the
peripheral stump in place, cut off 3 em. from the central stump
and thrusting it through one muscle, sewed it into another.
At that time he considered the second method as reliable as
the first. In these ways he believed that he had effectually
excluded the possibility of any union between the central and
peripheral stump; and in carefully conducted autopsies he was
unable to find any trace of such connection in those cases which
he considered successful. Also physiological evidence of the
absence of connection between the central and peripheral ends
was obtained at autopsy in the absence of reflex movements
on stimulating the distal stump and the absence of movement
in the muscles innervated by the sciatic nerve on stimulation of
the central stump.

Under these circumstances, which seemed both anatomically
and physiologically to exclude the possibility of any union with
the central nervous system, Bethe obtained evidence of regen-
eration in the peripheral stump. Many medullated fibers were
present. Stimulation of the peripheral stump caused contrac-
tion in the muscles of the leg but no reflex movements. He
also noticed that some time after autogenous regeneration had
occurred a slow degeneration set in which caused, after a time,
the complete disappearance of all regenerated fibers. This
Bethe considers an important point in favor of the autogenous
nature of their regeneration, since, he assumes, fibers which
have formed central connections do not undergo a second degen-
eration. In his somewhat limited study of the development
of these autogenously regenerated fibers he distinguishes five
stages: (1) protoplasmic band formation; (2) differentiation

DEGENERATION AND REGENERATION OF NERVE FIBERS 493

of these bands into axial strands and granular sheaths ‘Achsial-
strangfasern’; (3) appearance of fibrils in the axial strands in
the neighborhood of the nuclei; (4) fusion of these discontin-
uously formed fibrils: into fibrillar bands; (5) discontinuous
formation of a myelin sheath. Bethe maintains that such
transformation can occur only in young animals and even then
only in a limited number of the fibers. Many fibers in young
animals and all in adult animals are incapable of developing
beyond the stage of protoplasmic bands without some stimulus
from the central stump.

So convincing did these experiments of Bethe appear that
they excited the greatest interest and have led to many at-
tempts to secure confirmation of his results. Miimnzer (’02),
Head and Ham (’03) and Mott, Halliburton and Edmunds
(04) presented evidence to show that all new axons in the periph-
eral stump were outgrowths from the old axons of the central
end. But there have appeared two investigations, those of
Langley and Anderson (’04) and Lugaro (’05), which not only
show that Bethe’s conclusions were wrong, but show clearly
the fallacies upon which his erroneous conclusions were based.
The work of Langley and Anderson (’04) was carried out on
kittens and young rabbits. Experiment 5 is typical of their
results. The right sciatic nerve was cut high up in the thigh,
turned down and sewed into the skin above the knee. After
251 days the sciatic was cut above the first point of section
and the femoral nerve was cut near the inguinal ligament. The
peripheral sciatic stump, twelve days after the second operation,
contained no sound medullated fibers but many degenerated
ones. Summing up all their experiments they say:

We find that all the medullated nerve fibers, which reform in the
peripheral end of a nerve, degenerate when the nerves which run to
the tissues near the cut end are cut near the spinal cord; in other words,
in our experiments all medullated fibers in the peripheral ends of the
cut nerves were fibers which had become connected with the central
nervous system. If then, autogenetic regeneration of fibers had oc-
curred, every one of them had become connected with the central end
of some nerve fiber. On the autogenetic theory this seems to us in
the highest degree unlikely.

494 S. WALTER RANSON

It is important not to overlook the possibility of fibers grow-
ing into the distal stump from other nerves in the neighborhood.

Against the physiological tests of the absence of connection
between the two ends of a divided nerve, failure to get reflex
movement on stimulation of the peripheral stump or movement
in the muscles of the leg on stimulation of the central stump,
tests upon which Bethe has always laid the greatest stress, Langley
and Anderson raise the following objections: (1) In some experi-
ments in which anatomical connections could be demonstrated
they were unable to get any reflex response by stimulating the
peripheral stump. (2) It is possible that at a certain stage of
regeneration the conductivity of the junctional portion is too
small to give a reflex effect under the conditions of the experi-
ment. (3) When the regenerated axons come from the femoral
or obturator, as is sometimes the case, stimulation of the cen-
tral end of the sciatic would not affect them.

Lugaro (’05) saw that the operative methods employed by
Bethe, did not exclude the possibility of downgrowth of axons
from fibers still connected with the central nervous system.
In order to remove all possible sources of such contamination,
he resected the lumbo-sacral nerves together with their asso-
ciated spinal ganglia at their exit through the dura mater in
young dogs and cats, and was unable to find any medullated
fibers in the sciatic four months after the operation. In three
young dogs, in which he removed the lumbo-sacral spinal cord
and its associated spinal ganglia he found after three months
the same absence of medullated fibers in the sciatic nerve.

Raimann (’05) cut away that portion of the lumbo-sacral
spinal cord and associated ganglia from which the sciatic nerve
arises; but his positive results, taken in connection with the
negative ones of Lugaro, can only show the great tendency for
fibers to grow into the degenerated sciatic from the obturator
and femoral, which with their associated portion of the spinal
cord remained intact in Raimann’s experiment.

Segale (’03) is of the same opinion as Lugaro and distinguishes
between compensation due to ingrowth from other nerves and

DEGENERATION AND REGENERATION OF NERVE FIBERS 495

regeneration—processes which are associated in the functional
restoration of divided nerves.

We must still mention briefly a few of the less important
contributions on the side of autogenous regeneration. Van
Gehuchten (04) repeated Bethe’s experiments with positive
results, but did not make a microscopic examination of the
intervening scar nor attempt to cause the degeneration of the
new fibers by secondary section of all the nerves going to the
leg. Ballance and Stewart (01), Fleming (’02), Durante (04),
and Modena (’05), have made observation in favor of an autog-
enous regeneration of nerve fibers; but since they present no
new evidence we need not go into their work in detail here.

Bethe (07) has attempted to meet the objections raised by
his opponents, but, as it seems to the present writer, with very
little success. So far as his paper is not a mere repetition of
former experiments it may be divided into three parts: (1) He
considers the facts brought to light by Cajal’s new silver method,
but we can best take up Bethe’s objections to this method in
another part of this paper. (2) He reports experiments to show
that when an axon is divided near its cell of origin no regener-
ation occurs. That his negative results, so far at least as the
spinal ganglion is concerned, are to be explained on the basis
of inadequate histological methods, will be shown in another
paper when the effects of cutting the nerve roots are taken up.
(3) He présents experiments designed to meet the objections
of Langley and Anderson and Lugaro. In spite of the length
already reached by this review it will be necessary for us to
analyze these experiments in some detail.

In reply to Lugaro he presents a case, in which after extirpa-
tion of all the roots belonging to the nerves going to the hind leg,
regeneration was recognizable in the peripheral sciatic stump.
In a young dog he tore out both sciatic nerves, but failed to
bring the spinal ganglia with them in either case. Several
weeks later he opened the canal and removed on the left side the
2to 7 L. and 158. roots. Some months later regeneration could
be demonstrated in the peripheral stump. But there is one

496 S. WALTER RANSON

serious objection to this experiment, since previous to the removal
of the roots and ganglia on the left side he had torn out both
sciatic nerves. Hence there was present in the pelvis the torn
central fragments of the right sciatic nerve. So great was the
regenerative energy of this right sciatic stump that it was found
at autopsy that its fibers had grown out of the right great sacro-
sciatic foramen and established an anatomically demonstrable
connection with the right peripheral stump. Under these cir-
cumstances it is hard to convince oneself that a few regenerated
fibers may not have taken a different course, grown across the
anterior surface of the sacrum out of the left great sacro-sciatic
foramen and down to the left peripheral stump. Bethe’s other
experiments with removal of the roots were negative, a fact
which he can only explain as due to the poor state of the general
health of the dogs upon which so mutilating an operation had
been performed.

To meet the objections of Langley and Anderson he performed
two experiments in which several months after the tearmg out of
the sciatic he tried to cut all possible connections with the spinal
cord and six days after the secondary operation still found
undegenerated medullated fibers in the peripheral stump. But
in one of these cases it is clear that all possible central connec-
tions were not divided. In this case the second operation con-
sisted in cutting the roots associated with the nerves going to
the leg, and as autopsy showed, he failed to cut the 1 S. root.
In the other experiment the secondary operation consisted in
(1) cutting the femoral and obturator near the pelvis, (2) cutting
the 1, 2, and 3 S. nerves at their exit from the intervertebral
canal, and (3) ligature and division of the tissue at the normal
point of exit of the sciatic nerve. Since in the primary opera-
tion the 6th and 7th L. roots and ganglia had been torn out.
with the sciatic, this control seems to have been fairly complete. *
It is plain however that this experiment was very complicated
and gave opportunities for error in the operations and subse-
quent observations. In the opinion of the present writer the
positive results of Bethe in these three cases are to be attributed
to his habit of tearing out the sciatic nerve, producing a lesion

DEGENERATION AND REGENERATION OF NERVE FIBERS 497

of unknown extent at an unknown level and rendering difficult
the accurate application of Langley and Anderson’s test of the
presence of central connections by subsequent division of all
nerves going to the leg. Positive results obtained by compli-
cated and uncertain methods cannot outweigh the negative
results obtained by simpler operative procedures.

More recently Wilson (’09) has repeated some of Bethe’s
work but came to no definite conclusions as to the nature of
the processes involved in the regeneration of nerves.

Space has not permitted a detailed report of all the work that
has been done with the object of studying the changes which
occur in a piece of nerve permanently cut off from the central
nervous system; but enough has been given to show that this
line of experimentation has, as yet, given no satisfactory evi-
dence of the capacity of a stretch of nerve completely separated
from the central nervous system to undergo an autogenous regen-
eration. On the contrary, the more recent experiments of this
sort show that so great is the regenerative capacity of the cen-
tral stump in young animals that it is a matter of the greatest
difficulty to exclude the possibility of axons from the central
having reached the peripheral stump, and it is equally difficult
to exclude the possibility of axons having grown into the periph-
eral stump from other nerves in the vicinity. The only experi-
ments that are entirely satisfactory are those of Lugaro, involv-
ing the removal of the entire lumbo-sacral portion of the spinal
cord and the associated spinal ganglia, and these experiments
were negative.

The reason that so many have attempted to solve the problem
in this way is that no stain was available prior to 1903 which
was capable of unraveling the complicated processes going on
at the point of union of the cut ends of a divided nerve; and
any attempt to determine what was going on in this zone with
the use of any of the usual stains could searcely lead to con-
vineing results. Under these circumstances it was but natural
that an effort should be made to determine what happened
under much simpler conditions in an isolated peripheral stump,
not with the idea that any regeneration occurring here would

498 7 S. WALTER. RANSON

be essentially different from that occurring when the two ends
are in apposition, but with the idea that the process would be
easier to analyze, and that in this way evidence would be obtained
which could be applied in the analysis of the more complex
conditions obtaining in the divided and reunited nerve.

Fortunately we now have in the method of Cajal a technique
giving a sharp stain of the finest branchings of axons and
enabling the investigator to see clearly the complicated changes
going on near the cut surfaces and to correctly understand the
mechanism of nerve regeneration. With the solution of the
problem, which is given by this new method of staining, there
ceases to be any reason for an attempt to secure an isolated
stump for study, since it would be highly improbable that there
would occur in an isolated stump a process which was essentially
different from that which occurs in the peripheral stump when
in connection with the central nervous system.

A number of observers have made use of Cajal’s method for
the study of degenerative and regenerative changes in nerve
fibers. Perroncito (05) and Cajal (08) have obtained brilliant
results. Marinesco (’05, ’06), Poscharissky (07) and Tello (’07)
have also made use of this method. As we proceed with the
discussion of our own results we will point out in what ways
our results differ from those of others who have used this method.

TECHNIQUE

The experiments were made on the sciatic nerve of adult
dogs. With strict aseptic precautions the nerve was exposed
in the upper part of the thigh and cut with a sharp scalpel or
scissors. The ends were in some cases allowed to retract; in
others a stretch of 1 cm. was removed and retraction allowed;
and in still others, without resection of any of the nerve, the
two ends were approximated with sterile silk or catgut sutures.
The dogs were allowed to live for a period of from one to thirty-
five days and at the autopsy a short stretch of the proximal
stump and a longer stretch of the distal stump together with
the intervening scar were removed and subjected to histological
analysis. Since we deal only with the early stages of regenera-

DEGENERATION AND REGENERATION OF NERVE FIBERS 499

tion, and with them only from the histological standpoint, little
if any information would have been secured by electrical stimu-
lation of the stumps. The omission of these physiological tests
of regeneration was the more excusable, since, as has been men-
tioned, the majority of the autopsies were complete before it
was determined to extend the scope of the study from the degen-
erative changes to include the regenerative processes as well.
With two exceptions the wounds healed by primary intention.
In Dog 1m the cutaneous stitches came out on the fourth day,
but this dog was killed on that same day and the deeper parts

of the wound were free from infection. Dog rx became infected
and was discarded. Dog 1 died about twenty-four hours after the
operation probably from late effects of the anaesthetic. The
other dogs remained in excellent health until they were killed.
Table 1 shows what experiments were made.

The tissue was prepared by the pyridine-silver modification
of Cajal’s method, the steps of which are as follows: The nerve
is placed for forty-eight hours in absolute alcohol to which has
been added 1 per cent of strong ammonia. The pieces are then
washed for two minutes in distilled water and transferred to
pyridine for twenty-four hours, after which they are washed
in many changes of distilled water for twenty-four hours. They

500 S. WALTER RANSON

are then placed in the dark for three days at 35°C. in a 2 per
cent aqueous solution of silver nitrate, then rinsed in distilled
water and placed for one or two days in a 4 per cent solution of
pyrogallic acid in 5 per cent formalin. Sections are made in
paraffin and after mounting are ready for examination. This
modification has many advantages over the original Cajal method
when applied to the peripheral nervous system. It is only occa-
sionally that one obtains with the older method a satisfactory
stain of the non-medullated fibers, while when pyridine is used
these fibers stand out with great clearness, not only in their
normal state but also in the early stages of degeneration. The
various regenerative phenomena in these fibers also stand out
with great clearness. Cajal was able with his method to observe
some of these changes in the non-medullated fibers but seems to
have seen relatively few of these fibers showing that his method
was not especially suited for their study. Perroncito (’09), who
used the original method, states that ‘“‘the first phenomenon
which is noticed in the peripheral stump of a divided nerve is
a clearer differentiation of bundles of non-medullated fibers
which run between the medullated fibers.” The old Cajal
method in the hands of the writer has, only rarely, given a clear
differentiation of the non-medullated fibers, and one gathers
from the statements of Perroncito and Cajal that it has only
been in injured nerves that they have seen them clearly, and
even then with less distinctness than that with which they
appear in the pyridine-silver preparations. They consider that
these fibers are of sympathetic origin and fail entirely to appre-
ciate their great number. As a result of the inadequacy of the
old Cajal method many of the most important steps in the degen-
eration and regeneration of these fibers also escaped their atten-
tion. It is evident, however, from their figures and descriptions
that when they use the term ‘non-medullated fibers’ they refer
to the same structures which are designated by that name in
the present paper.

Another objection to the old Cajal method, as applied to the
study of regenerating nerves, is that by this method it is diffi-
cult to get both the old and the new axons to stain in the same

DEGENERATION AND REGENERATION OF NERVE FIBERS 901

preparation, as each requires a different amount of ammonia
in the fixing solution (Cajal ’08). Cajal advises the use of a
mixture of medium strength in order to stain both, but says
that in practice it 1s very difficult to get just the right concen-
tration. All this difficulty is avoided by the use of pyridine,
which causes the old medullated axons to stain yellow and the
old non-medullated axons, as well as all newly formed fibers, a
dark brown or black. The new technique is also much more
certain in its results. With pure chemicals and clean glass-
ware no failures need be anticipated. It also has the advan-
tage of giving a uniform stain throughout a large piece of tissue.

Against the use of the Cajal method in the study of regen-
erating nerves, Bethe (07) has raised the following objections:
(1) The myelin sheaths are not stained. This is of course true
and, since these sheaths are represented only by colorless spaces,
the method is of little or no value in the study of their degen-
eration and regeneration. If, however, we wish to study the
changes in the axons, this very transparency of the myelin
sheaths renders the preparations more serviceable. The very
faint yellow of the connective tissue and the transparency of
the myelin sheath make it possible to use relatively thick prep-
arations (12 to 15u) in which the axons can be followed for
a relatively long distance. (2) It shrinks the axons. This is
also true and is a defect which it has not been possible to over-
come. (3) It is uncertain in its action. Bethe excuses himself
for not having used Cajal’s method by saying that his material
was too valuable to jeopardize by the use of such an uncertain
technique. This objection certainly cannot be applied to the
pyridine-silver method. (4) Only very small pieces of tissue
2 or 3 mm. thick can be used. On the contrary, either with the
old Cajal method or the pyridine-silver modification, the best
results are obtained with larger pieces. It is, of course, essential
that one be able to study large sections in order to secure a
correct idea of what is going on at different levels. The prepa-
rations which form the basis of this paper are, for the most part,
longitudinal serial sections of pieces of nerve from 5 to 8 mm.
thick and from 15 to 20 mm. long. They represent sometimes

502 S. WALTER RANSON

the central or peripheral stump by itself, sometimes the two
united stumps with the intervening scar. These large pieces
of tissue were none too large, as the staining is perfect through-
out. The use of such serial sections makes it possible to trace
with certainty the course of the axons, but has involved the
preparation of several thousand sections, and has precluded the
use of other stains.

The results of this investigation can best be assembled under
the following headings:

Early changes in the distal stump
1. Degeneration of the medullated fibers and formation of nucleated pro-
toplasmic bands
2. Degeneration of the non-medullated fibers and the formation of nucleated
protoplasmic bands
3. Abortive autogenous regeneration in the distal stump
Early changes in the proximal stump
1. Changes in the non-medullated fibers
Early abortive regeneration
Cellulipetal degeneration
Formation of new axons
2. Changes in the medullated fibers
Formation of a zone of reaction
Fibrillar dissociation
Early branching of the axons in the immediate neighborhood of the
lesion
Formation of lateral branches at some distance above the lesion
Formation of fiber bundles and skeins
Mechanism of the regeneration of nerve fibers
1. Proliferation of axons in the central stump
2. Penetration of the new axons through the scar
3. Utilization of the protoplasmic bands as pathways for the new axons in
the distal stump

EARLY CHANGES IN THE DISTAL STUMP

1. Degeneration of the medullated fibers and the formation of
nucleated protoplasmic bands

Leaving out of account, for the moment, the interesting meta-
morphoses of the nerve fibers which occur in the distal stump
in the immediate neighborhood of the cut surface during the
first three days, we confine ourselves in this section to the changes

DEGENERATION AND REGENERATION OF NERVE FIBERS 9503

which occur at a distance of at least 5 mm. from the end of the
stump. At that distance from the cut surface no changes can
be detected in the medullated fibers in Dog x1, killed one day
after the operations The medullated axons still show their
characteristic, smooth contour and uniform light yellow stain
characteristic of them in their normal state. In Dog x11, killed
two days after the operation, many axons have an irregular
surface and are stained more intensely but less uniformly than
normal axons (fig. 1). The same changes are seen in Dog 1,
which died about twenty-four hours after the operation. On
the third day, although these changes are somewhat more
advanced, there is as yet no fragmentation of the axons. This
begins on the fourth day and is shown in figure 2. One of the
fibers, a, is broken up into large granules, staining dark brown
and grouped into clumps of irregular size and shape. ‘These
masses are for the most part still connected with each other.
There is a very marked difference in susceptibility of the axons
to degenerative changes. Many of the fibers at this stage are
normal in appearance or are in the stage described as character-
istic for the second day. Such a fiber, showing only very slight
alterations, is seen in figure 2, b.

Changes in the myelin sheaths cannot be clearly seen in these
specimens. Howell and Huber (’92) found the first evidences
of segmentation of the myelin sheath on the fourth day. It
is therefore plain that granular degeneration of the axons is well
advanced before the segmentation of the myelin sheath begins.
This agrees with the observations of Bethe (’03).

After eight days the first 3 mm. of the distal stump are almost
completely degenerated; the degeneration becomes less and less
marked during the next 2 mm.; and at a distance of 5 mm.
from the cut surface we have a condition which is characteristic
for the remainder of the distal stretch included in the section
(an additional 5 mm.). It is probable that this stage of degen-
eration would be found throughout all the rest of the distal
portion of the nerve. It is also probable that those who have
described the degeneration as progressing from the point of
injury downward along the nerve have been misled by this rapid

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6

504 S. WALTER RANSON

degeneration in the first few millimeters of the stump. All
measurements of this sort, referred to in this paper, were made
on longitudinal sections with the aid of the microscope and
mechanical stage. ’

At a distance of 5 mm. from the cut surface eight days after
the operation, the axons of the medullated fibers are broken
up into small irregular clumps of dark brown granules (fig. 3, a).
The myelin sheaths are divided into elliptical segments, separated
and surrounded by the now abundant protoplasm of the neu-
rilemma cells, and containing the granular remains of the axons.
In the preparations of this stage the nuclei are not differen-
tiated, although it is known from the observations of others
that at this time the nuclei of the neurilemma are rapidly in-
creasing in numbers. There are a few medullated fibers whose
axons are not fragmented, but are stained very intensely, have
a fairly uniform contour and an intact myelin sheath. Cajal
(08) has called attention to these resistant fibers. Since there
are all gradations between the most susceptible and the most
resistant, there seems to be involved not a distinction in the
kind of fiber, but in the functional state, nutritive condition,
and vitality of the fiber at the moment of the lesion.

Fourteen days after the operation there are no longer any
unfrzgmented medullated fibers, although some are in the early
stages of degeneration. In most of the fibers the protoplasm
has increased in quantity and the myelin is divided into drop-
lets, while the remains of the axons are less in evidence. Nine-
teen days after the operation the protoplasmic bands of Biingner
have made their appearance (fig. 4). The small quantity of
protoplasm surrounding the nuclei in the normal fiber has in-
creased and surrounded the fragments of myelin. And as the
remains of the axon and myelin have been absorbed, this proto-
plasm has come to fill the old neurilemma sheath. In the mean-
time the nuclei have increased in number. Asa result, we have
a continuous band of protoplasm containing many nuclei (fig.
4, a), and occasional droplets of myelin (b). Scattered through
the remains of the myelin are fine, darkly staining granules
representing the remains of the axon. The protoplasm some-

DEGENERATION AND REGENERATION OF NERVE FIBERS 505

times appears distinctly striated, as is shown in the drawing
at one end of the band. Such a longitudinal striation has lead
Bingner, Bethe, and others to suppose that they had before
them the beginnings of a new axon. Even Marinesco (’05)
using Cajal’s method was at first led into this error; but later,
perhaps with better preparations, he changed his view and
adopted the conception of the outgrowth of the axon from the
central stump. There are absolutely no transition stages between
such striations and the new axons, which, when they first appear
in the peripheral stump, are sharply defined from all surrounding
structures (fig. 28). Even at this stage, nineteen days after
the operation, these protoplasmic bands are capable of serving
as paths for the developing axons. A considerable number of
fine black fibers can be seen in the proximal part of this distal
stump. They le in the protoplasmic bands and run around
the droplets of myelin. These new axons can be followed by
a study of the serial sections back to the scar through which
they have traveled from the central stump.

In Dog x, in which 1 cm. of the nerve was excised, a careful
study of serial sections fails to show any axons which have
pierced the intervening scar and entered the distalstump. In
these preparations, therefore, we are able to study the proto-
plasmic bands without any complication from ingrowing axons.
The length of time from operation to autopsy in this experi-
ment was twenty-five days. Most of the detritus from the
axons and myelin sheaths has been absorbed, but one sees scat-
tered through the field a few good sized droplets. The proto-
plasmic bands have assumed a fairly uniform contour and stain
a light yellow. Fine black granules are scattered through the
protoplasm. These are sometimes arranged in parallel rows,
giving a striated appearance. In none of these fibers is there
any indication of the beginning of an axon. This is significant
when taken in connection with the preceding case in which the
two stumps were united, and in which, although the time between
operation and autopsy was six days shorter, new axons could
be seen in many of the protoplasmic bands in the neighborhood
of the sear.

506 S. WALTER RANSON

In the dog which was killed thirty-four days after the removal
of 1 em. of the sciatic nerve, the distal stump showed proto-
plasmic bands like those already described except that the drop-
lets of myelin were smaller and scarcer. A few showed new
axons within them; but these axons could be followed for long
distances, were sharply differentiated from the protoplasm of
the band and were connected with fibers in the sear. No tran-
sition stages could be seen which might be interpreted as the
development of axons in situ. More will be said about the
relation of the new axons to the protoplasmic bands in the last
section of this paper.

2. Degeneration of the non-medullated fibers and formation of
nucleated protoplasmic bands

So far as we are aware no one has described the degeneration
of the non-medullated fibers of the spinal nerves. Tuckett
(96) presents experiments showing that the sympathetic axons
lose their affinity for methylene blue on the second day after
separation from their cells of origin. Cajal and others who have
used the silver method as he directs have apparently been able
to see these fibers in the spinal nerves only when they were
undergoing regenerative or degenerative changes and possessed
an. increased affinity for the silver. Cajal states that he has
followed the degeneration of the non-medullated fibers during
the first eight days, but his observations clearly refer only to
the immediate vicinity of the lesion where the fibers have under-
gone an abortive regeneration. He states that the centrally
directed end bulbs (which we will describe in another place)
and the non-medullated fibers which carry them, stain well
until the third day, after which they gradually fade out and
are no longer visible after the sixth or seventh day. ‘These
statements are correct only when they are made to apply to
the distal stump within 1 mm. of the cut surface.

At a distance of 5 mm. from the cut surface one day after
the operation (Dog x1), many of the non-medullated fibers are
no longer uniformly stained but are distinctly granular. At
the end of the second day (Dog x11), the fibers become broken

DEGENERATION AND REGENERATION OF NERVE FIBERS 507

up into segments of varying length. Short, light segments
alternate with longer, very much darker segments (fig. 5). The
dark segments are granular, a detail which has been omitted in
the drawing. For control we have the normal nerve from Dog
x1, carried through the same solutions at the same time as the
divided nerves of Dogs xt and x1r. As these changes are not
seen in the normal nerve, we may be sure we are not dealing
with artifacts. Three days after the operation, the darker
segments, still granular in appearance, stain less intensely than
in the specimen taken a day earlier. A considerable number of
smooth, black, uniformly stained, non-medullated fibers can be
seen—but these are not so much in evidence as at a later date
when the other fibers have undergone more complete degen-
eration. Again in this experiment we have the normal nerve
carried through the same solutions at the same time as the
divided nerve, to serve as a control, and show that the described
changes are not artifacts due to an irregular deposit of silver.

Two dogs were killed four days after the operation. Both
showed only a little advance over the specimen taken on the
third day; but many of the fibers are already taking a light
yellow stain with little differentiation into lighter and darker
segments.

After eight days many of the non-medullated fibers are no
longer visible, others appear as light yellow bands along which
an occasional nucleus can be seen.

It is at this stage when the other fibers are very lightly stained
or have disappeared that the resistant undegenerated fibers
are most evident. ‘These are more numerous and persist longer
than the resistant medullated fibers. Since the majority of
the non-medullated fibers degenerate very early and since there
are few fibers which show an intermediate degree of resistance,
it is possible that we are dealing here with two different kinds
of fibers. Those which degenerate early in the first week may
be afferent spinal fibers; while those which degenerate in the
second and third weeks may be of sympathetic origin. This
supposition is the more probable because the susceptible fibers
represent about the same proportion, which on other grounds

508 S. WALTER RANSON

we would assign to the class of afferent spinal non-medullated
fibers, while the resistant fibers correspond in number to the fibers
of sympathetic origin. Cajal (08) in one place called attention
to the slow degeneration of the non-medullated fibers, over-
looking entirely the much larger number which degenerate very
early, while in another place in the same monograph he states
that all the non-medullated fibers have disappeared by the sixth
or seventh day.

In Dog v, fourteen days after the operation, the non-medul-
lated fibers are represented by narrow yellow bands stippled
with dark brown fine granules. The nuclei are not differen-
tiated in this preparation. A considerable number of resistant
non-medullated fibers still retain their intense black uniform
stain but they present for the most part an irregular contour
(fig. 6). Some of these fibers seem to. be present after nineteen
days, but in this specimen new axons have grown in from the
central stump and might be confused with persistent axons.
The peripheral stump of the specimen taken twenty-five days
after the operation is not contaminated with new axons from
the central stump and here it can be seen that all the old axons
have degenerated.

In Dog vy, nineteen days after the operation, the degenerated
non-medullated fibers are more clearly visible than on the eighth
and fourteenth day, and the nuclei upon them are well differ-
entiated. The fibers are fine yellow bands with many nuclei.
Surrounding many of the nuclei there are considerable accumu-
lations of protoplasm. A short section of three such fibers is
represented in figure 7. The fibers are not interrupted as the
drawing would indicate, but can be followed for considerable
distances even in relatively thin sections. The fibers andthe
protoplasm about the nuclei still contain dark brown granules.
After twenty-five days these fibers present the same picture
as in the preceding specimen. They are clearly differentiated
and the nuclei are sharply stained. These fibers are grouped
in bundles and lie between the protoplasmic bands formed by
the medullated fibers, from which they can be distinguished
by their small size and by the absence of myelin droplets.

DEGENERATION AND REGENERATION OF NERVE FIBERS 599

In the preceding paragraphs we have recorded the changes
as they can be observed from day to day in the degenerating
non-medullated fibers. These observations may be summarized
and interpreted as follows. The axons of the majority of the
non-medullated fibers begin to degenerate within twenty-four
hours after they have been separated from their cells of origin.
They first become granular and after two or three days become
broken up into segments of lighter and darker staining. The
darker stained segments represent the fragmented axon, the
hghter segments represent accumulations of unstainable sub-
stance probably of fluid character. It is not easy to determine
whether the active process is a vacuole formation with exten-
sion in the long axis of the fiber causing separation of the frag-
ments of the axon, or whether a retraction of the fragments
leaves the empty spaces within the neurilemma to be filled with
exudate. On the fourth day the dark segments have begun to
disintegrate and by the eighth day the dark segments have
disappeared, the remains of the degenerated axon are distributed
as brown granules through the probably fluid contents of the
neurilemma sheath. During the next stage, eight to fourteen
days after the operation, the fibers are not very clearly seen.
But by the nineteenth day the nuclei of the neurilemma have
increased greatly in number and the fibers again become clearly
visible, since with the increase in the number of nuclei the pro-
toplasm has also increased and filled in the old neurilemma
sheath. We have, therefore, as the terminal stage of the degen-
eration of the non-medullated fibers nucleated protoplasmic bands
which differ from the similar bands formed from the medullated
fibers only in size and in the absence of myelin droplets.

In this connection certain observations of Perroncito (’09)
are cf great interest. He noticed that in the neighborhood
of the bundles of non-medullated fibers spindle shaped cells
appeared on the third and fourth days and that these became
more numerous on the seventh and eighth days and lay in con-
nection with bundles of connective tissue fibers. He failed
to recognize the formation of the protoplasmic bands from the
medullated fibers and stated that at last ‘“‘in place of the nerve

510 S. WALTER RANSON

there remains a connective tissue strand consisting of connective
tissue fibers and very long spindle cells.’”’ These cells, accord-
ing to him, arise from the spindle shaped connective tissue
cells which appear between the nerve fibers shortly after division
of the nerve. He adds:

But before we assume that these are true connective tissue cells,
we must seriously consider one objection. We know that between
the medullated nerve fibers there were bundles of non-medullated
fibers. Could not these spindle cells represent cells associated with

the non-medullated fibers and be homologous to the cells of Schwann’s
sheath? This objection has, however, many weak points.

It is clear that Perroncito is here describing the same phe-
nomena which we have interpreted as the formation of proto-
plasmic bands from the non-medullated fibers. His drawings
show, however, that his preparations clearly differentiated little
more than the nuclei in question. The pyridine-silver prepa-
rations, on the other hand, clearly differentiate, not only the
degenerating non-medullated fibers, but also the protoplasmic
bands derived from them.

While a few non-medullated fibers, probably of sympathetic
origin, may persist for two or three weeks, all non-medullated
fibers in the peripheral stump undergo degeneration before the
end of the fourth week. This shows that the direction of Wal-
lerian degeneration is the same for the non-medullated as for
the medullated fibers, and excludes the possibility that any of
them might arise from cells located at the periphery, unless
one cares to. consider the very remote possibility that the slowly
degenerating non-medullated axons undergo a cellulipetal degen-
eration toward peripherally located sympathetic ganglion cells.

3. Abortive autogenous regeneration in the distal stump

It will be remembered that all the descriptions and drawings
in the two preceding divisions of this paper refer to the distal
stump at a distance of at least 5 mm. from the cut surface. It
was necessary to choose a point at some distance from the cut
surface, because changes occur in the immediate neighborhood
of the lesion which are essentially different from those seen in

DEGENERATION AND REGENERATION OF NERVE FIBERS 511

the remainder of the peripheral stretch. These changes have
been described by Perroncito (’05), Poscharissky (’07), and
Cajal (08), with whose observations our own are in full accord.

These changes begin very early. One day after operation
they are already well adanced in both the medullated and non-
medullated fibers. In the millimeter nearest the cut surface
the non-medullated fibers possess lateral branches, and the
fibers as well as their branches end in bulbs (figs. 8 and 9). The
mode of formation of these branches is the same as the mode
of formation of the similar branches seen in the immediate
neighborhood of the lesion in the proximal stump; but, since
the successive stages are more clearly seen there, we will describe
their formation when describing the central stump. The side
branches are usually as large as the parent stem. The end
bulbs are very characteristic, differing markedly from those
seen on the ends of fibers taking part in the ultimate regener-
ative changes. These bulbs have a darkly staining core with
a neurofibrillar network, and a peripheral lightly staining zone,
which is often of considerable thickness and shows no visible
neurofibrils. These side branches are so numerous and _ their
end bulbs so large that they separate widely the original fibers
of a bundle. The last 0.5 mm. of the stump assumes a charac-
teristic appearance under low magnification due to the replace-
ment of the parallel bundles by a network, the individual fibers
of which are separated by large end bulbs. It seems probable
that the outer lightly staining zone of these end bulbs represents
ap. excessive accumulation of interfibrillar substanee.

The growth of lateral branches and the formation of end
bulbs does not progress much, if any, after the first day, but
remains stationary during the second, third and fourth days.
We have unfortunately no intermediate stages between the
fourth and eighth days, and during this time the products of
this abortive regeneration have almost entirely disappeared.
There are to be seen after eight days shadowy outlines of the
bulbs and a somewhat more definite indication of the branched
fibers. A few of the fibers and end bulbs are still clearly stained.
After fourteen days there are still a few scattered fibers show-

a? S. WALTER RANSON

ing end bulbs and one small fasciculus at the periphery of the
nerve in which many well stained side branches and bulbs are
seen. These resistant elements correspond to the central ends
of the resistant non-medullated fibers, which, it will be remem-
bered, retained their staining reaction for a period of two or
three weeks. All of these resistant fibers with the branches
and bulbs at their central ends have entirely disappeared before
the twenty-fifth day and no traces of them are to be found in
the preparation taken on that day.

Changes of the same nature occur in the medullated fibers.
In the immediate vicinity of the lesion (0.5 mm.) many of the
medullated axons present a zone of reaction, which separates .
the, as yet, normally staining distal stretch, from a very short
disintegrated piece of the axon at the cut surface. This zone
of reaction becomes more marked on the second and third days.
There is almost no limit to the variety of appearances which the
reaction zone may assume; but the fiber illustrated in figure 10
may be taken as showing the principal factors involved. The
myelin sheath in this part of the fiber is already broken up and
appears as granular detritus filling the old sheath. Imbedded
in this mass we have the axon and its products. The central
and peripheral ends of the fiber are marked ¢ and p, respec-
tively. The proximal part of the axon has completely degen-
erated; fragments of it can be seen at a. At 6, the axon shows
a sharply defined club-shaped enlargement which represents
the end of the living part of the axon. Following the axon in
a peripheral direction, one sees at the distal end of the enlarge-
ment a distinct neurofibrillar reticulum. Below this the axon
contracts, expands, contracts again and goes over into a second
wider meshed fibrillar reticulum. From both of these reticula
fine black fibrils, d, are given off which run by themselves in
the degenerated myelin. These isolated fibrillar branches are
also seen on the central side of the club-shaped enlargement.
The reaction in the medullated axons therefore consists of (1)
the formation of a distinct line of separation between a short
dead segment and the remaining distal stretch of the fiber,
which is still living, (2) the appearance near this line of separa-

DEGENERATION AND REGENERATION OF NERVE FIBERS 513

tion of a distinct neurofibrillar reticulum, and (3) the formation
of fine fibrils which leave this reticulum and run independently
through the degenerated myelin.

The manner of formation of at least some of these inde-
pendent fibrils is shown in figure 11. In the peripheral part
of the drawing (p) there is a well-marked neurofibrillar reticu-
lum from one side of which there arises a lateral branch ending
in a bulb showing a distinct reticulum. On the central side
this fiber presents two branches ¢ and c’. It is probable that.
c’ represents a pre-existing collateral and not a new formed
branch. Most of the fibrils arising from the central end of
the reticulum pass into this branch.

Many, perhaps a majority, of the medullated axons, never
show any of these changes but undergo an uncomplicated degen-
eration throughout their entire extent. Those fibers which
show no reaction near the lesion represent, in all probability,
the more susceptible fibers, which are well advanced in degen-
eration throughout their entire extent by the fourth day. The
more resistant the fiber, the more marked is the reaction near
the lesion and the more tardy is the fragmentation of the re-
mainder of the distal stretch. By the eighth day most of the
products of this reaction have disappeared and by the fourteenth
day there are no longer any traces of them.

The changes which have been described in the medullated
and non-medullated axons of the distal stump are without sig-
nificance for the ultimate regeneration of the nerve, since all
the products of this reaction suffer complete degeneration and
disappear. In themselves, however, these changes are of the
highest interest. They show that that portion of a fiber which
is separated from its trophic center does not die at once. It
continues to live for two or three days and possesses sufficient
vitality to cause a rearrangement of its fibrils into a complicated
reticulum and to give rise to lateral branches. The presence
in reacting medullated fibers of fine fibers budding off from the
side of a reticulum as shown in figure 11, and the fact that some
of these fine fibers pierce the neurilemma and run out into the
endoneurium can only be interpreted as true branching, although

514 S. WALTER RANSON

it is probable that others of the independent fibrils within the
old sheath have gained their independence by the degeneration
of the fibrils which surrounded them. In the case of the non-
medullated fibers the lateral branches with their end bulbs
constitute the chief evidence of the reaction. One might assume
that the appearance of the neurofibrillar reticulum was only
a peculiar manifestation of degeneration. But the formation
of new branches can only be interpreted as regenerative in char-
acter and accepted as evidence that the axons live in the distal
stump for some time after being severed from their trophic
centers. Cajal (’08) places the same interpretation on these
phenomena.

Harrison (’08) found that, after cutting the nerves of the
tail of the larvae of Rana sylvatica, the two cut ends of many
nerve fibers had united by a protoplasmic bridge within one
or two days. In these fibers the degeneration of the peripheral
part of the axon was immediately arrested. These observa-
tions find support in the evidence just presented to show that
a portion of an axon severed from its trophic center continues
to live for two or three days.

While Cajal (08) and others, who have used his method in
the study of the regeneration of nerves, saw and described the
changes in the non-medullated fibers of the distal stump, just
as they have been described here, they leave the impression
that only a few scattering fibers are involved. They seem,
also, to have overlooked the fact that exactly similar changes
occur in the non-medullated fibers of the proximal stump.

HARLY CHANGES IN THE PROXIMAL STUMP
1. Changes in the non-medullated fibers

The changes in the non-medullated fibers may be divided into
three stages: (a) early abortive regeneration; (b) cellulipetal
degeneration; (c) the formation of new axons. .

a. Early abortive regeneration. By early abortive regeneration
in the non-medullated fibers of the proximal stump we mean to
designate a reaction exactly analogous to the abortive regen-

DEGENERATION AND REGENERATION OF NERVE FIBERS. 515

eration of these fibers in the distal stump. In the last 0.8 mm.
of the proximal stump one sees at the end of twenty-four hours
the formation of lateral branches on the non-medullated fibers.
The stages in the formation of these branches are illustrated in
figure 12. The earliest stage is seen at d, and consists in the
development on one side of the fiber of a spherical mass several
times thicker than the fiber and staining only a trifle less intensely
than the fiber itself. These masses seem to possess the power of
ameboid movement and work their way out of the fiber bundle in
which they orignated, pulling on the fiber and forming a V-shaped
bend in it. Three stages of this are seen at d, c and e. As
the mass moves farther it comes to be connected with the V-
shaped bend in the old fiber by a single limb which is formed
behind the mass as it moves forward. Thus the V becomes
transformed into a Y (fig. 12, 6). As the lateral branch is formed
it often happens that the distal limb of the V degenerates. The
distal limb of the V in ¢ can be followed only a short distance
when it goes over into a finely granular thread (not shown in
the drawing) and disappears. The fiber and bulb seen at a
are to be accounted for in this way. The bulb appears as if on
the end of a fiber which has turned at right angles and left the
bundle.

The composition of the bulbs on the ends of the lateral branches
varies. At first (fig. 12, c, d, e) the neurofibrillar content is
fine and uniformly distributed, giving to the bulb a stain almost
as dark as that of the fiber. At this stage the fibrillar plexus
can only rarely be seen. As growth continues the interfibrillar
substance increases greatly in quantity and out of proportion
to the increase in fibrillar substance. This may, in rare cases,
lead to the formation of a wide meshed neurofibrillar reticulum
(fig. 12, 6) or more often to the accumulation of a large mass
of lightly staining substance about a central fibrillar core. This
central core is about the size of the original bud from the side
of the fiber.

It should be noted that the bulb shown at 6 is an exceptional
one in the clearness with which the fibrillar reticulum is stained
and in the fact that it gives off secondary branches. There

516 S. WALTER RANSON

were two of these secondary branches, each ending in a little
ring. More than one lateral branch may be given off from a
single non-medullated fiber. On one fiber two such buds in
the early stages of formation were separated by not more than
twice their own diameter from each other.

These early branches do not appear to develop much after
the first day and on the second day are already overshadowed
by the transformations of the axons of the medullated fibers.
On the third day, coincident with the beginning of a cellulipetal
degeneration in the fibers from which they arose, these branches
and end bulbs become indistinct in outline and begin to lose
their affinity for the stain. And after four days one can dis-
tinguish only indistinet shadowy outlines of the bulbs and fibers
(fig. 18, c). These products of the early regenerative activity
of the non-medullated axons in the proximal stump are there-
fore abortive and very rapidly undergo degneration. It is an
interesting fact that their development in the proximal stump
did not progress as far as that of the similar structures in the
distal stump and underwent degeneration earlier. This early
abortive regeneration is an expression of the local vitality of the
cut fiber just as is that of the peripheral stump. The reason
for the final degeneration of these products is to be found in
the fact that a cellulipetal degeneration occurs in the fibers
from which they arose, thus cutting them off from their con-
nection with the cell body. :

b. Cellulipetal degeneration. Coincident with the beginning
of the degeneration of the products of the non-medullated fibers
near the cut surface, changes are noticed in the fibers them-
selves. These changes, first noticed on the third day, are well -
advanced on the fourth and extend up the fibers as far as they
are included in the section. On the eighth day the alterations
in these fibers at various distances from the cut surface (meas-
ured with the aid of a mechanical stage) are as follows: In the
last 0.5 mm. there are only a few shadowy outlines of the non-
medullated fibers; at 3 mm. from the cut surface the fibers can
be clearly seen but are in the late stages of degeneration similar
to those in the distal stump, on the same day and at the same

DEGENERATION AND REGENERATION OF NERVE FIBERS 517

distance from the cut surface. From this point to a point at
a distance of 10 mm. from the lesion the intensity of the degen-
eration decreases until at 10 mm. there are exhibited changes
similar to those seen at the end of the second day in the distal
stump. There are here the same breaking up of the fibers
into light and dark segments and the same granular staining
as has already been described in the distal stump. In the proxi-
mal stump, however, there is the important difference that the
intensity of the process decreases rapidly in a central direction;
and although our section, only a little more than 1 em. in length,
does not permit us to say at just what point the degeneration
ceases, there can be little doubt that it does not extend more
than 2 cm. up the nerve. We are dealing here with a celluli-
petal or retrograde degeneration.

A. slow, ascending, cellulipetal, or retrograde degeneration
has been noted in the medullated fibers in cases of long stand-
ing amputation (Ranson ’06). It is questionable whether such
a degeneration occurs in any of the medullated fibers within
the time covered by this series of experiments; no clear evidence
of its occurrence could be found after thirty-four or thirty-five
days. Its occurrence in the non-medullated fibers is of special
interest since it indicates a greater susceptibility of the neu-
rones, of which they form a part, to lesions of the peripheral
nerve. On cutting the dorsal ramus of the second cervical
nerve in the white rat, near the ganglion, Ranson (’06) noted
that 52 per cent of the cells in the associated ganglion under-
went complete degeneration. It was later shown (Ranson ’09)
that the cells which disappeared were the small cells, which we
now know to be associated with the non-medullated fibers;
while very few, if any, of the large cells, which are associated
with the medullated fibers, disappeared.

While in those experiments the cut was made very close to
the ganglion, in the present series of experiments the sciatic
was divided at a relatively great distance from the ganglion.
And, following the law that the intensity of the reaction in
the cell depends upon the proximity of the lesion in the axon
to the cell-body, the division of the non-medullated fibers

518 S. WALTER RANSON

in the sciatic involved only a limited cellulipetal degeneration.
While, of course, the usual axonal reaction must have occurred
in the small cells, these did not degenerate. The spinal ganglia
associated with the injured sciatic nerve in Dogs vir and vItt,
killed thirty-four days after the operation, and Dogs rx and x,
killed twenty-five days after the operation, were prepared by
the pyridine-silver method. In these ganglia the small cells
and their associated non-medullated fibers were apparently
as numerous as in normal ganglia, although, since no counts
were made, it would be impossible to be sure that none had
degenerated. The non-medullated fibers in the ganglia and
adjacent portion of the nerves stained in a perfectly normal
manner, showing that they were not involved at that level in
a cellulipetal degeneration. Another piece of evidence, show-
ing that the cellulipetal degeneration in the neighborhood of
the lesion did not involve the degeneration of the entire neurone,
is found in the subsequent regeneration of these fibers.

c. Formation of new axons. On the fourteenth day the ma-
jority of the non-medullated fibers in the proximal stump are
still m the late stages of degeneration. They appear as light
yellow, delicate bands, closely resembling the early stages of
proteplasmie band formation, in the distal stump. There are
present, however, on the fourteenth day, many sharply stained
black fibers in the bundles of light yellow ones. One bundle,
in which the regenerative changes have gone particularly far,
is seen in figure 13. In a bundle of sharply staining fibers one
sees five end bulbs, three directed toward the periphery, p,
and two towards the center, c. From this time on there is a
constantly increasing number of sharply staining black fibers
in these bundles. On the nineteenth and twenty-fifth days
there are numerous end bulbs and an increasing number of
fine black fibers. After thirty-four days the bundles of non-
medullated fibers in the last centimeter of the proximal stump
are larger and more compact than in the normal nerve; and
these bundles can be traced, in longitudinal sections, out of
the cut end of the nerve into the sear. <A cross section of the
stump taken a short distance above the cut at this time shows
a great increase in the number of these fibers (fig. 26).

DEGENERATION AND REGENERATION OF NERVE FIBERS 519

The interpretation which is to be placed on these okserva-
tions is as follows: The non-medullated fibers degenerate a
short distance (about 2 em.) in a central direction and the
degenerated portions undergo the changes looking toward the
formation of protoplasmic bands. But before these are fully
formed the cellulipetal degeneration has been arrested and
regeneration begins. The fibers above the point where the
degeneration ceases begin to grow downward and on their ends
bulbed extremities can be seen. The great increase in the
number of these fibers in the proximal stump near the lesion
indicates that there also are formed lateral branches, although
on account of the compactness of the bundles it has not been
possible to observe the branching directly. Cajal describes
and figures the branching of non-medullated fibers in the proxi-
mal stump, but it seems probable that he was dealing, not with
the original non-medullated fibers but with new axons, which
had branched off from the medullated fibers (fig. 22). The
new non-medullated axons follow the old fiber bundles as path-
ways and at the cut end of the nerve they finally reach the scar,
into which they run.

2. Early changes in the medullated axons of the proximal stump

a. Formation of a zone of reaction. In the immediate neigh-
borhood of the lesion one sees changes in some medullated axons
that greatly resemble those seen at an early stage in the distal
stump. Figure 14 represents a typical fiber of this sort at the
end of the first day. At d one sees the axon staining like the
normal axon a light yellow; but it is beginning to increase in
diameter. As we follow it from the central (c) toward the
peripheral end (p) it increases in size and assumes a darker
stain. At the same time, indications of a neurofibrillar reticu-
lum make their appearance. At 6 the axon is several times
its normal thickness, filling and distending the neurilemma.
It shows at this point, and for a short distance ‘above, a dense
deeply staining reticulum. This corresponds to the club-like
zone of reaction seen in figure 10, except that the neurofibrillar
reticulum is more pronounced. At a the disintegrated remains

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6

520 S. WALTER RANSON

of the axon can be seen and this degenerated stretch extends
to the cut surface 0.2 mm. distant. As can be seen, there is
not a, very sharp border between the degenerated portion of
the axon and the zone of reaction. Isolated portions of the
reticulum extend into a lightly stained intermediate zone. At
a, the neurilemma can be seen; at 6, it is stretched over the
swollen axon and is not differentiated, while at c, both the neu-
rilemma and myelin sheath can be seen in the preparation but
were not indicated in the drawing. More rarely one sees two
dense fibrillar reticula, separated by a zone of light staining
through which run a few connecting fibrils.

b. Fibrillar dissociation. In many axons there occurs a sepa-
ration of the neurofibrils due to accumulation of an excess of
interfibrillar substance, and at the same time the individual
fibrils become much more sharply stained. This process occurs
alike in fibers which have formed a zone of reaction and in those
which have not. Figure 15 represents a short stretch of an
axon 0.5 mm. from the cut surface two days after the lesion.
On following this axon toward the cut surface it is seen to go
over into a narrow band of fibrils which connect it with a zone
of reaction near the lesion. Between the part of the axon,
which was drawn, and the zone of reaction there is a stretch of
about 0.2 mm. in which most of the axon is fragmented and
only a narrow band of fibrils connects the two. The accumula-
tion of interfibrillar substance seems to be more abundant on
one side of the axon where large spaces are present between the
fibrils. There does not seem to be any new formation of fibrils
and only such rearrangement as would naturally take place ~
in case of an oedematous swelling of the axon. It will be noticed
that the network is most dense at the periphery of the axon.
When this process is carried to its full extent, as one sometimes
sees it on the second, third and fourth days, the axon becomes
converted into a fine meshed network forming a hollow cylinder.
The myelin sheath having disintegrated, this net-like cylinder
lies immediately beneath the neurilemma. ‘These appearances
would, of course, be best understood on the hypothesis that
the fibrils of the normal axon are not isolated but are united

DEGENERATION AND REGENERATION OF NERVE FIBERS 521

with each other to form a network, the meshes of which are
drawn out in a longitudinal direction.

c. Early branching of axons in the immediate neighborhood of
the lesion. The fibers which give rise to these branches undergo
no degeneration at the point of division nor do they form at
their cut extremity a darkly staining zone of reaction. We
are dealing here with fibers which either possessed a greater
vitality or were less severely traumatized in the cutting of the
nerve. There seem to be two chief modes by which the branches
arise from these fibers:

1. Some of these fibers begin to grow distally very soon after
the lesion and by the end of the first day have grown out of
their sheaths into the exudate. Here they immediately break
up into a great number of fine branches. Figure 16 represents
two such fibers one day after the operation. At c and c’ they
are leaving their sheaths and growing into the exudate. A
large fusiform lateral branch is given off from one of the fibers.
This large lateral branch, as well as the two main fibers, show
the neurofibrils very clearly—these fibrils are however more
nearly parallel in their arrangement and not so closely set as
in the zone of reaction shown in figure 14, 6, and on the whole
give the ends of the fibers a much more normal appearance.
At many points these axons give off fine fibrillar branches which
end in small cylindrical or spherical expansions. In the sur-
rounding exudate there are numerous isolated rings which repre-
sent cross sections of the expanded ends of other fibers. This
is a very characteristic ending for the fine branches of the medul-
lated axons at this stage—an elongated club-shaped end bulb
whose fibrillar substance is located at the periphery, in cross
section appearing as rings and in longitudinal section as hollow
clubs.

2. Instead of arising from the ends of axons, extremely fine
side branches may arise from the surface of the axon within
its sheath. Axons giving rise to branches of this sort show no
degenerated stretch near the lesion nor any dark zone of reac-
tion. They show however a certain amount of fibrillar disso-
ciation in that the axons are swollen and the fibrils are much

nae S. WALTER RANSON

more sharply differentiated than in normal axons. Some of
these fibrils detach themselves from the axon at its surface
to form fine branches, which run in various directions on the
surface of the axon and after a short course end in small bulbs
(fig. 17). Some of these branches, which arise near the cut
surface find their way out into the exudate, but most of them
continue to grow within the old sheath. In the absence of the
myelin sheath, which is entirely disintegrated in these last few
tenths of a millimeter of the proximal stump, these branches
reach the neurilemma and immediately underneath this they
continue to grow in a circular or spiral direction, interlacing
with one another. In this way there develops by the third or
fourth day, just beneath the neurilemma, a hollow cylinder
formed by fine interlacing fibers, within which the old axon can
be seen (fig. 18, a, b). Many of these fine fibers can be seen
ending in little rings. While the majority of them remain
within the old neurilemma sheath, a few, leaving it at the cut
surface, run into the exudate and a few others, piercing the
sheath, run into the eudoneurium.

‘In figure 19 the axon is seen giving off some relatively coarse
branches, some of which have arranged themselves in a tubular
sheath. The axon and part of the sheath are cut away in one
place, where they run out of the section.

In some of the medullated axons the fibrillar dissociation
represented in figure 15 and the branching illustrated in figure
17 seem to be associated in the production of a tubular network.
Sometimes the central axon can be seen to break up into this
network and be reformed from it again at a lower level.

The formation of a zone of reaction, the fibrillar dissociation,
and the formation of the early collateral branches within the
old neurilemma sheath, together with the tubular networks
which have just been described, constitute the early changes
in the medullated axons which were first seen by Perroncito
and which Cajal has called Perroncito-phenomena. On _ the
eighth, fourteenth and nineteenth days all of these structures
become less and less evident, and their place is taken by paral-
lel coursing fibers, of which there are a large number within

DEGENERATION AND REGENERATION OF NERVE FIBERS 523

the remains of one old neurilemma sheath. The steps in this
substitution are not clearly presented in the preparations stud-
ied. But it seems probable that some of the fibers of the net-
work atrophy and that others assume a more parallel course.
It is certain that many branches arise from the axons at a slightly
higher level and, growing down within the neurilemma sheaths,
help to take the place of the disappearing network. It is obvi-
ous that these plexuses, as such, take no part in the final regen-
eration, although individual fibers, derived from them, may do
so. Nineteen days after the operation none of the old net-
works are to be seen; but instead, only parallel coursing fibers,
branching fibers and twining fibers held together in bundles
by the old neurilemma sheaths. All of these earliest phenomena
are confined to the last few tenths of a millimeter of the proxi-
mal stump.

d. Formation of lateral branches at some distance above the
lesion. On the eighth day, when the tubular arrangement just
described has begun to disappear, one sees that the medullated
fibers are giving off lateral branches at a higher level. These
are of good size and can be seen coming off as high as 5 mm.
above the cut. These side branches become more and more
abundant in each of the three succeeding stages, fourteen, nine-
teen, and twenty-five days after the operation. On the nine-
teenth day, they can be seen in large numbers (fig. 20) chiefly
in the terminal 5 mm. of the nerve. They end in bulbs and
usually run within the old sheath, predominantly in a peripheral
direction, but some run spirally, and others centrally, in the
old sheath, and still others pierce the sheath and run in the
endoneurium. In figure 21 one sees a bundle of fibers formed
in this way within an old sheath. The old axon is thicker,
lighter and more centrally placed than its branches which are
accompanying it toward the periphery. Two of these branches
are seen to end in bulbs directed peripherally. Two fine fibers
leave the sheath and run in the endoneurium. One branches
a second time in the connective tissue and the resultant fibers
run out of the section. The other turns peripherally parallel
to and just outside the old sheath and ends in a large end bulb.

524 S. WALTER RANSON

After thirty-four days all the medullated fibers in the last
5 mm. of the proximal stump are transformed into bundles of
fibers in this way. In Dog vu, in which the nerve was sutured
and in which therefore the chemiotactic influence of the distal
stump was brought into full action on the growing fibers of the
proximal stump, most of the newly formed axons grow directly
downward into the scar. As is shown in figure 23, the fiber
bundles are composed of more or less parallel fibers. In Dog
vil, however, where a piece of nerve was resected and the influ-
ence of the distal stump therefore was less potent in controlling
the course of the growth of fibers in the central stump, there
are more recurrent fibers. Some fibers instead of passing directly
down the old sheath grow in a spiral direction beneath the old
neurilemma, producing tangled skeins like that illustrated in
figure 24, b. The medullated fiber (a) has been transformed
into a bundle of parallel fibers. These structures are seen in
cross section in figure 25. In all these bundles and skeins, bulbs
on the ends of individual fibers are seen and form a prominent
part of the picture. These two bundles in figure 24 lie side
by side in the preparation and a small group of fibers can be
seen leaving Bundle a and running into Bundle b. While therg-
fore on the whole such a bundle represents the branches of one
old axon, branches may grow from one bundle into another or
from a bundle into the endoneurium. Both recurrent fibers
and tangled skeins are also seen in smaller numbers in Dog
vit where union of the cut ends favored the action of the chemio-
tactic influences from the distal stump on the growing axons.

Fibers with bulbous extremities are very numerous in these ~
bundles and skeins. These end bulbs form a prominent part
of the picture in all the preparations where regenerating axons
are seen. Cajal has correctly interpreted them as analogous
to the enlarged extremities seen by many observers on the ends
of developing nerve fibers and hence ay may be regarded as
the growing tips of the axons.

Cajal believes that the tangled skeins arise from the tubular
networks which appear shortly after the lesion. This, how-
, ever, does not seem to be the case. They arise from the lateral

DEGENERATION AND REGENERATION OF NERVE FIBERS 525

branches given off from the axons at a later date and at a higher
level. When these branches instead of growing in a peripheral
direction, coil spirally beneath the neurilemma or turn back-
ward in a central direction, they produce the tangled skeins.
These skeins are seen in the process of formation on the twenty-
fifth day at a time when all of the tubular networks have dis-
appeared and are often seen farther up the nerve than the level
at which the tubular networks appeared. The fact that they
are more abundant, when the union of the cut ends is prevented,
is readily explained by the less potent attraction exerted on
the growing branches by the distal stump, but would not be
explained by Cajal’s hypothesis.

Cajal is of the opinion that the normal mode of regeneration
of the medullated axons consists of the three following stages:
(1) degeneration of a short stretch of the axon near the cut sur-
face; (2) the formation of a bulb on the axon above this stretch;:
and (3) growth of the axon out of the sheath into the scar where
branching occurs. This sequence of events occurred in few,
if any, of the fibers in our sections. In our preparations the
essential factor in the regeneration of the medullated axons of:
the proximal stump was the formation of lateral branches at a;
distance of 1 to 5 mm. above the cut surface and within the old:
sheaths, within which they grew peripherally until they reached.
the scar. The fact that Cajal worked chiefly with young dogs
and rabbits, while this work has been done on adult dogs is
sufficient to explain this difference in the results.

The recent statements of Dominici (’11) that no new axons:
can be observed growing out of the proximal stump during the
first month are not supported by an account of detailed obser-
vations, and his negative results are clearly due to an inade-
quate technique.

MECHANISM OF THE REGENERATION OF NERVE FIBERS

We havé been concerned in the preceding sections of this
paper with a variety of changes occurring in the proximal and
distal stumps, many of which, so far as we can see, take no

526 S. WALTER RANSON

part in the ultimate regeneration of the nerve fibers. It is our
purpose in this section to trace the steps in the formation of
the regenerated axons, restating briefly those observations
already mentioned which are of significance in the final process
and linking them together in a coherent whole.

1. Proliferation of axons in the central stump

On the first day after the lesion some of the axons grow out
into the exudate and break up into many branches (fig. 16).
Others on the first day give off fine branches from their surface
within the sheath in the immediate neighborhood of the lesion
(fig. 17), some of which find their way into the exudate. Thus,
from the end of the first day on, fine nerve fibers, which are
demonstrably branches of the medullated axons of the proximal
stump, are present in the developing scar. The chief contri-
bution to the new axons, which enter the scar from the cut end
of the proximal stump, comes from the branching of the old axons
at a somewhat later date (fig. 20). These side branches from
the medullated axons are given off chiefly in the last 5 mm. of
the proximal stretch; and, while a few are formed as early as
the eighth day, they are constantly increasing in number to
the thirty-fourth day. Running for the most part within the
sheath of the old axon from which they arose, they arrange
themselves into fascicles of parallel threads (fig. 24, a) when
their course toward the periphery is direct, and into tangled
skeins (fig. 24, b) when for any reason they fail to grow directly
toward the periphery. Some idea of the enormous number of
such branches can be obtained from a study of cross sections
of the proximal stump just above the lesion (fig. 25). Thus
within the space formerly occupied by one fiber there may be
fifty or even more. These bundles of fine fibers, derived as
branches from the old medullated axons, run compactly until
they leave the old sheath and plunge into the scar. Here they
scatter out in every direction. Some of these fibers never reach
the scar but turn backward in the proximal stump. Where-
ever it is possible to see these fibers ending within the thickness
of a section they are tipped with a bulb.

DEGENERATION AND REGENERATION OF NERVE FIBERS 527

In the case of the non-medullated axons, which after an abor-
tive regeneration undergo a cellulipetal degeneration for some-
thing more than one centimeter up the proximal stump, true
regeneration begins about the fourteenth day. There occurs
a downgrowth of new axons from above the point where the
degeneration ceased. ‘These new axons, on the growing ends
of which small bulbs can be seen, grow toward the cut surface
in the degenerated bundles. These new axons continue to
increase in number until by the thirty-fourth day the bundles
of non-medullated fibers in the last part of the proximal stump
are larger and more compact than in a normal nerve. Although,
because of the smallness of these fibers and the compactness
with which they are grouped, it is not possible to demonstrate
the occurrence of lateral branches on these fibers, there can
be no doubt but that they have increased greatly in number.
This is evident in the longitudinal sections, but even more so
in transverse sections taken a short distance above the lesion
(fig. 26, a). Here one sees large bundles of non-medullated
fibers so closely grouped as to resemble a sympathetic nerve.
Compare this drawing with figure 25 taken at a lower level and
showing the multiplication of the branches of the medullated
fibers. It will be seen that the medullated fibers in the neigh-
borhood of the non-medullated bundles in figure 26 have not
yet begun to give off branches. Hence the large increase in
the non-medullated fibers cannot be due to the side branches
of the medullated fibers growing into the bundles of non-medul-
lated fibers. These bundles can be traced to the end of the
central: stump, where they go over into the scar intermingling
with the branches of the medullated fibers from which they can
no longer be distinguished.

This enormous increase in the number of fibers in the termi-
nal part of the proximal stump is one of the most striking obser-
vations that have been made on these preparations—and it seems
to the writer one of the most significant for the interpretation
of the nature of the regenerative process. It fits logically into
the scheme of the outgrowth theory. As we shall see, a great
number of fibers fail to find their way through the sear to the

528 * $$. WALTER RANSON

more favorable pathway formed by the distal stump, and the
large number of branches increases the probability that at least
one branch will reach that pathway and develop into a fune-
tional fiber. This multiplication of branches is, then, a means
for compensating the loss of fibers in the scar. That more
than one branch of a fiber of the central stump may make such
connections and develop into a functional fiber is shown by
the physiological experiments of Osborne and Kilvington (’08),
who showed that when the peripheral stumps of the tibial and
peroneal nerves were united with the central stump of the tibial
nerve, and regeneration had taken place, it was possible by
stimulating the peripheral end of the peroneal to obtain con-
tractions in the muscles supplied by the tibial. These contrac-
tions could still be obtained after the tibial nerve had been
divided above the point of the previous union, thus showing
that some motor fibers in the central stump of the tibial had
sent at least one branch into each nerve.

It seems probable, however, that at best only a few of the
many branches of a central axon make connections with the
distal stump and that the rest atrophy and disappear.

2. Penetration of the scar and loss of fibers

It is in the tracing of these new-formed fibers through the
scar and into the distal stump that the study of the serial sec-
tions, in their serial order, was found of most advantage, since
in them it was possible to demonstrate very convincingly the
origin and course of these fibers.

As has been stated, the first nerve fibers make-their appear-
ance in the exudate on the first day. These are the fine non-
medullated branches of the medullated fibers (fig. 16). No
nerve fibers at any time grow out into the exudate or scar from
the distal stump. After the first day little progress in the out-
growth of fibers is made for several days. A few fibers can be
seen in the immediate neighborhood of the central stump on
the second, third and fourth days, but in number and length
they are not much in advance of those seen on the first day.
This temporary arrest of the outgrowth of fibers is probably

———

DEGENERATION AND REGENERATION OF NERVE FIBERS 529

associated with the violent reaction going on in the neurone at
that time—the so-called ‘axonal reaction.’

Unfortunately the eight-day specimen was divided into proxi-
mal and distal stumps by a cut through the scar near the cen-,
tral end before the tissue was prepared by the pyridine-silver
method; and, as a result, the stain of the central portion of the
scar is not good. On the fourteenth day, however, the scar
is beautifully stained and fibers can be seen in large numbers
leaving the central stump, plunging into the scar, and running
through it in every direction. The same is true of the nine-
teen-day specimen. Here many fibers are seen working their
way centrally in the thickened perineurium of the central stump
in which they form a plexus connected with the plexus in the
scar. These represent a portion of the aberrant branches that
never find their way into the distal stump. Where fibers are
seen to come to an end within the thickness of a section, they
are tipped with a small bulb. -On the twenty-fifth day (Dog
x, in which union of the stumps was prevented by excision of
1 cm. of the nerve) the mass of scar tissue covering the end of
the proximal stump is penetrated in every direction by these
fine nerve fibers; from this mass covering the end of the central
stump, they can be followed in gradually decreasing numbers
upward in the thickened perineurium for 4 mm. and distal-
ward in the scar for a distance of 18 mm. As one goes distally
in the scar the number of fibers gradually decreases. No fibers
reach the distal stump, and no fibers grow into the scar from
the distal stump.

Figure 27 is drawn from the scar in the immediate neighbor-
hood of the central stump of the specimen just described. It
will be noticed that the fibers are arranged in bundles. The
explanation of the formation of these bundles is the stereotro-
pism demonstrated by W. H. and M. R. Lewis (’12) in growing
fibers. When the growing tip of one fiber comes in contact
with another fiber, it follows this second fiber just as, in the
experiments of the authors just mentioned, growing fibers run
along the under surface of the cover glass. It will be further
noted that the bundles, while crossing each other in a more or

530 S. WALTER RANSON

less irregular manner, run, for the most part, in a general direc-
tion from center (c) to periphery (p). This predominant direc-
tion is due to the chemiotactic influence exerted upon the grow-
ing fibers by the distal stump. There are in the field three
branching fibers (a). Notice that in each case the centrally
directed limb of the Y is the thickest fiber, while the two periph-
erally directed limbs are thinner, and represent the branches.
Had these fibers arisen in situ, the branching fibers would in
themselves be difficult to account for; but the fact that the
central limb of the Y is almost always the largest of the three
would be even harder to explain. There are no end bulbs repre-
sented in the drawing, and in fact there are few in this region.
This is the oldest portion of the nerve plexus in the scar and the
fibers are already of great length and few can be seen having
a true termination within the thickness of a section. As one
approaches the distal extremity of this plexus, 9 to 13 mm.
from the central stump, these end bulbs become relatively much
more numerous, since we are dealing here with the growing
ends of the fibers. Often in the place of an end bulb one sees
the end of a fiber breaking up into a large number of fine branches.
It is an interesting fact that the farther distally in the scar the
plexus goes the more parallel its fibers become, and the more
directly they run toward the distal stump. This is explained
by the fact that the earliest fibers penetrate the scar at a time
when the distal stump has not undergone the alteration neces-
sary for the exercise of the chemiotactic influence and their
direction is very irregular. These early fibers by stereotropism
govern the direction of the bundles. On the other hand, the
early fibers in the distal portion of the plexus are from the first
under the chemiotactic influence of the distal stump which is
stronger because of the proximity of the distal stump.

Dog vu, killed thirty-four days after the operation, serves
as a good illustration of a scar when the two ends of the nerve
have been sutured. The suturing was not well done and a gap
of some size between the two stumps was filled with scar tissue.
Into this scar the fibers from the central stump can be followed.
The fiber plexus in the scar is very much like that in Dog x.

DEGENERATION AND REGENERATION OF NERVE FIBERS 531

But in this case the plexus, composed in its distal part of fairly
parallel fibers, is directly connected with the distal stump into
which the bundles run in great numbers.

While of course it is not possible to follow individual fibers
out of the central stump through the scar and into the distal
stump, yet by a study of serial sections of different stages, it
is possible to convince oneself that all the nerve fibers in the
scar are outgrowths of central axons.

3. The utilization of the protoplasmic bands as pathways for the
new axons in the distal stump

We have already described in the distal stump the multipli-
cation of the nuclei of the neurilemma, the increase of the pro-
toplasm which surrounds them, and the formation from these of
nucleated protoplasmic bands. These bands are formed as the
final stages in the degeneration of both medullated and non-medul-
lated fibers. In none of the specimens was it possible to see any
indications of the development of axonsin situ. Occasionally one
sees in them a pseudo-striation due to longitudinal rows of gran-
ules, but there are no transition stages between these and the
sharply stained, regenerated axons. Negative results of this
sort, obtained from preparations which sharply differentiate
the finest branch of an axon, are in themselves of great signifi-
cance. But even more important is the evidence of the direct
growth into these protoplasmic bands of the fine nerve fibers
of the scar.

In Dog v, killed fourteen days after the operation, and Dog
vi, killed nineteen days after the operation, in both of which
the cut ends of the nerve were united by sutures, nerve fibers
had entered the distal stump from the scar. In the nineteen-
day specimen they can be seen to run into the protoplasmic
bands; but in the fourteen-day specimen these bands are not
sufficiently well developed to permit one to say whether the
new axons have entered these developing bands or not. In
Dog x, killed twenty-five days after excision of 1 cm. of the
nerve, the band fibers are well developed and clearly differ-
entiated, but there is no trace of a new axon in the sear covering

So S. WALTER RANSON

the end of the distal stump, nor in the protoplasmic bands.
Their absence in this case, twenty-five days after the operation,
although well developed protoplasmic bands are present, and
their presence in other specimens, fourteen and nineteen days
after the operation when the protoplasmic bands are only in-
completely formed, speaks strongly against their development
in situ in these bands. Moreover, in both the fourteen- and
nineteen-day specimens, nerve fibers from the central stump
had reached the distal stump through the scar.

Probably the most instructive preparations, however, are
those from Dog vu, killed thirty-four days after the removal
of 1 em. of the sciatic nerve. A study of serial sections shows
that the scar covering the distal stump is devoid of nerve fibers
except in one very limited area—here there are a few fibers.
All of the protoplasmic bands in this specimen are devoid of
new axons except a few in that part of the distal stump over-
laid by the innervated portion of the scar. Here a few of the
bands can be seen containing sharply staining axons. Figure
28 shows five bands in this location, down one of which a new
axon is growing. The axon can be seen to end in an enlarge- ,
ment directed distally. The presence of a few of these sharply
staining axons in protoplasmic bands adjoining the only part
of the sear which contains nerve fibers, while all the rest of the
bands are empty, is a strong point in favor of their growth into
the distal stump from central fibers. The presence of end bulbs
like the one seen on the fiber in figure 28 is evidence in the same
direction.

Cajal lays stress on the occurrence of branching in the axons
in the protoplasmic bands. Such branching has been observed
occasionally in these preparations, but its value as an evidence
of the down-growth of the axons seems to the present writer
not to be very great.

In Dog vit, killed thirty-four days after section of the sciatic
with primary suture, great numbers of fibers from the scar run
into the distal stump. Several axons often run down one pro-
toplasmie band. Figure 29 represents a cross section of this
distal stump. At a is seen a large protoplasmic band (formed

DEGENERATION AND REGENERATION OF NERVE FIBERS 533

from a medullated fiber) containing five new axons, and at b
a bundle of fine protoplasmic bands (formed from non-medul-
lated fibers), in several of which new axons have appeared.
All new axons lie in protoplasmic bands, never between them.
It has been supposed by others that the axons may run between
the bands as well as within them. This appears to be the case
in longitudinal sections; but in cross sections one always sees
the light yellow protoplasm of a band surrounding every axon.
About some of these axons a faint halo of myelin is deposited
by the thirty-fourth day.

No cases were studied in which sufficient time had elapsed for
the complete regeneration of the nerve. We expect to make
other experiments on young dogs with a view to determining
the structure of a fully regenerated nerve and especially the
relative proportion of medullated and non-medullated axons

which it contains.
SUMMARY

1. The idea, first clearly stated by Biingner, that the new
axons arise in the protoplasmic bands through a fusion of longi-
tudinal striations which have developed in situ, has been shown
by the application of the Cajal stain to be without foundation.
The axons, when they first make their appearance in the distal
stump, are fully developed and clearly differentiated from the
surrounding protoplasm. They do not appear as discontinuous
fragments, but as long fibers, which, when traced peripherally,
may either run out of the section or end within a protoplasmic
band with a terminal bulb, and when traced centrally either
run out of the section or into a plexus of axons in the scar. In
these findings all recent investigations agree. Perroncito (’05),
Marinesco (’06), Poscharissky (’07), and Cajal (08), who have
used the Cajal stain, Pupura (’01) with Golgi stain, and Krassin
(06) with methylene blue, have all reached the same conclu-
sion. Their results are in full accord with those of the present
investigation. Even Bethe (’07) is silent on the question of
the histogenesis of the regenerated axons in the distal stump,
since in his last article he makes no attempt to defend his for-
mer views on this subject.

534 S. WALTER RANSON

2. The attempts to obtain regeneration in a peripheral stump
permanently separated from the spinal cord and spinal ganglia
have led to negative results. So great is the regenerative energy
of the central stump in young animals that the new axons to
which it gives rise may bridge very great gaps to reach the dis-
tal stump; and new axons may grow into that stump from other
nerves. Bethe’s elaborate precautions to prevent such union
have clearly not been adequate, as is shown by the experiments
of Langley and Anderson (’04) and Lugaro (’05). Nothing
short of the complete removal of the entire lumbo-sacral spinal
cord with the associated spinal ganglia can be regarded as effec-
tually preventing such reunion and these experiments have
been negative. Since, however, such experiments are open
to the objection that the high grade of marasmus caused by
such an operation could in itself be sufficient to account for
negative results, no very valuable evidence is likely to be fur-
nished by this line of experimentation. Since we now have,
in the Cajal method, a technique which enables us to see clearly
how regeneration occurs when the two ends of the nerve are
allowed to unite, there ceases to be any reason for attempting
to secure an isolated stump. It is highly improbable that there
would occur in such an isolated stump a process essentially dif-
ferent from that which occurs when the two ends are allowed
to unite.

3. It can be shown by the Cajal stain that the axons of both
medullated and non-medullated fibers in the central stump
give rise to a large number of branches which make their way
through the scar and enter the protoplasmic bands, which they
utilize as pathways toward the periphery. Perroncito, Mari-
nesco and Cajal have reached these same conclusions on facts
similar to those presented in the preceding sections of this paper.
Poscharissky, whose observations agree with those of the others,
hesitates to draw any conclusions. The facts upon which the
conclusions just mentioned are based have already been sum-
marized under the heading “The mechanism of the regener-
ation of nerves.”

DEGENERATION AND REGENERATION OF NERVE FIBERS 9535

4. The axons of the peripheral stump do not die at once after
the division of the nerve, but live for two or three days at least,
and undergo changes in the neighborhood of the lesion which
must be regarded as an abortive regeneration. After a few
days all the newly formed structures degenerate and disappear.
This abortive regeneration has no significance for the ultimate
regeneration of the nerve and is of interest only because of the
light it throws on the life processes within the neurone: These
phenomena, first seen by Perroncito, have been fully confirmed,
not only in the present investigation, but also by Poscharissky,
Marinesco and Cajal.

5. Alterations in the axons of the proximal stump can be
noticed within twenty-four hours after the lesion. They con-
sist of the formation of fine branches, and the rearrangement
of the neurofibrils of the old axons to form the most compli-
eated networks. These changes are limited to the immediate
neighborhood of the cut surface and are too varied to summar-
ize in detail. These were also first seen by Perroncito and con-
firmed by the others who have used the Cajal technique.

6. The new observations presented in this paper concern
almost exclusively the non-medullated fibers which are now
known to outnumber the medullated fibers in the spinal nerves.
These observations have been summarized in the section on
“The mechanism of the regeneration of nerves.”

BIBLIOGRAPHY

BaLuance, C. A., AND STEWART, P. 1901 Cited after Cajal.

Betue, A. 1908 Allgemeine Anatomie und Physiologie des Nervensystems.
Leipzig.

x 1907 Neue Versuche iiber die Regeneration der Nervenfasern. Archiv

f. d. Gesam. Physiol., Bd. 116, p. 385. ¥

BUnener, O. v. 1891 Ueber die Degenerations- und Regenerationsvorginge
am Nerven nach Verletzungen. Betr. z. path. Anat. u. z. allg. Path.,
Bas 10)-p.. 320

“Casat, RaM6n y. 1908 Nervenregeneration. J. A. Barth. Leipzig.
~ Dominici, M. 1911 Experimenteller Beitrag zum Studium der Regeneration

der peripheren Nerven. Berl. Klin. Wochensch., Bd. 48, p. 1937.

> Durante, G. 1904 A propos de la théorie du neurone. Rev. Neurol., vol.

12, p. 573.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, NO. 6

536 S. WALTER RANSON

Fiemine, R. A. 1902 Cited after Cajal.

FrossMAN, J. 1898 Ueber die Ursachen, welche die Wachsthumsrichtung der
peripheren Nervenfasern bei der Regeneration bestimmen. Beitr.
z. path. Anat. u. z. allg. Path., Bd. 24, p. 56.

GaLEoTtTi, G., AND Levi, G. 1895 Ueber die Neubildung der nervésen Ele-
mente in dem wiederzeugten Muskelgewebe. Beitr. z. path. Anat.
u. Z. allg. Path.,: Bd. 17, p: 369:

Harrison, R. G. 1908 Regeneration of peripheral nerves. Anat. Rec., vol.
1, p. 209.

Heap, H., anp Ham, C.S. 1903 The process that takes place in a completely
isolated sensory nerve. Jour. of Phys., Lond., vol. 29, p. v1.

Howe; W. H., anp Huser, G. C. 1892 A physiological, histological and
clinical study of the degeneration and regeneration in peripheral nerve
fibers after severance of their connection with the nerve centers. Jour.
of Phys., Lond., vol. 18, p. 335.

Huser, G. C. 1895 A study of the operative treatment for loss of nerve sub-
stance in peripheral nerves. Jour. Morph., vol. 11, p. 629.

KENNEDY 1897 Cited after Bethe, 1903.

Krassin, P. 1906 Zur Frage der Regeneration der peripheren Nerven. Anat.
Anz., Bd. 28, p. 449.

Lanauey, J. N., Aanp ANDERSON, H. K. 1904 On antogenetic regeneration in
the nerves of the limbs. Jour. of Phys., Lond., vol. 31, p. 418.

Lewis, W. H., anp Lewis, M. R. 1912. The cultivation of sympathetic nerves
from the intestine of chick embryos in saline solutions. Anat. Rece.,
VOles Os spite ;

Luaaro, E. 1905 Zur Frage der antogenen Regeneration der Nervenfasern.
Neurol. Centralb., Bd. 24, p. 11438.

Marrinesco, G. 1905 Recheres sur la régénérescence antogéne. Rev. Neur.,
vol; 18, p: 1125;
1906 Etudes sur le méchanisme de la régénérescence des fibres ner-
veuses der nerfs périphériques. J. f. Psy. u. Neur., vol. 7, p. 140.

Marinesco, G., AND Minza, J. 1910 Nouvelles recherches sur 1|’influence
qu’exerce l’ablation du corps thyroide sur la dégénérescence et la
régénérescence des nerfs. Compt. Rend. Soc. de Biol. Paris, vol.
48, p. 188.

Mopena, G. 1905 Die Degeneration und Regeneration des peripheren Nerven
nach Lésion desselben. Arbeiten a. d. Neurol. Inst. Wien. Univ.,
Bd., 12, p. 243. ‘

Mort, F. W., Hatitisurton, W. D. anp Epmunps, A. 1904 Regeneration of
nerves. Jour. of Phys., Lond., vol. 31, p. vu.

Minzer, E. 1902 Giebt es eine autogenetische Regeneration der Nerven-
fasern? Neurol. Centralbl., Bd. 21, p. 1090.

OsBorNeE, W. A., AND Kitvinatron B. 1908 Axon bifurcation in regenerated.
nerves. Jour. of Phys. Lond., vol. 38, p. 268.

Prerronciro, A. 1905 Cited after Cajal.
1908 Zur Frage der Nervenregeneration. Beitr. z. path. Anat. u. z.
allg. Path., Bd. 44, p. 574.

DEGENERATION AND REGENERATION OF NERVE FIBERS 537

~Prerroncito, A. 1909 Uber die Zellen beim Degenerationsvorgang der Nerven.
Folia Neuro-biol., Bd. 3, p. 185.

Poscuarissky, J. 1907 Uber die histologischen Vorgiinge an den peripher-
ischen Nerven nach Kontinuititstrennung. Beitr. z. path. Anat. u. z.
allg. Path., Bd. 41, p. 52.

Purpura 1901 Cited after Cajal.

Ramann 1905 Discussion of paper by Marqulies. Neurol. Centralbl., Bd. 24,
p. 1015.

~ Ranson, 8. W. 1906 Retrograde degeneration in the spinal nerves. Jour.
Comp. Neur., vol. 16, p. 265.
1909 Alterations in the spinal ganglion cells following neurotomy.
Jour. Comp. Neur., vol. 19, p. 125.
1911 Non-medullated nerve fibers in the spinal nerves. Am. Jour.
Anat., vol. 12, p. 67.
1912 The structure of the spinal ganglia and of the spinal nerves.
Jour. Comp. Neur., vol. 22, p. 159.

SEGALE 1903 Cited after Cajal.

~STrRoEBE, H. 1893 Experimentelle Untersuchungen iiber Degeneration und
Regeneration peripherer Nerven nach Verletzungen. Beitr. z. path.
Anat. u.z. alles Path: Bdl 13; p. 160.
1895 Die allgemeine Histologie der degenerativen und regenerativen
Processe im centralen und peripheren Nervensystem nach den neues-
ten Forschungen. Centralbl. f. allg. Path. u. path. Anat., Bd. 6, p.
849.

TeL1io, F. Cited after Cajal.

‘Tucxett, J. L. 1896 On the structure and degeneration of non-medullated
nerve fibers. J. of Phys. Camb., vol. 19, p. 267.

Van GEHUCHTEN, A. 1904 Cited after Cajal.

Water, A. 1852 Cited after Cajal.

WietTine, J. 1898 Zur Frage der Regeneration der peripherischen Nerven.
Beitr. z. path. Anat. u. z. allg. Path., Bd. 23, p. 42.

Witson, J. G. 1909 The present position of the theory of autoregeneration of
nerves. Anat. Rec., vol. 3, p. 27.

* ZIEGLER, P. 1896 Untersuchungen iiber die Regeneration des Achsencylinders

durchtrennter peripherer Nerven. Arch. f. Klin. Chirurgie, Bd. 51,

p. 796.

PLATE 1

EXPLANATION OF FIGURES

The drawings were made from pyridine-silver preparations of the degener-
ating and regenerating sciatic nerve of the adult dog.

1 Ocu. 3, Obj. 2 mm. Degenerating medullated axon in the distal stump
on the second day.

2 Ocu. 3, Obj. 2mm. Two medullated fibers from the distal stump on the
fourth day. Degeneration has progressed much farther in a, than in b. The
neurilemma can be seen bounding the unstained myelin sheath.

3 Ocu. 3, Obj. 2mm. Medullated fiber from the distal stump on the eighth
day; a, fragmented axon surrounded by an elliptical segment of myelin.

4 Ocu. 3, Obj. 2mm. Early protoplasmic band formed from a medullated
fiber. From the distal stump on the nineteenth day; a, nucleus; b, droplet of
myelin containing fragments of axon.

5 Ocu. 3, Obj.2mm. A bundle of degenerating non-medullated fibers from
the distal stump on the second day.

6 Ocu. 3, Obj. 2mm. Undegenerated non-medullated fiber from the distal
stump on the fourteenth day.

7 Ocu. 3, Obj. 2mm. Three protoplasmic bands formed from non-medul-
lated fibers. From the distal stump on the nineteenth day.

8 Ocu. 3, Obj. 2mm. Non-medullated fiber from the neighborhood of the
cut surface of the distal stump, showing new formed lateral branch with end-
bulb. End of first day; c, toward the center; p, toward. the periphery.

9 Ocu. 3, Obj. 2 mm. Non-medullated fiber from the neighborhood of the
cut surface of the distal stump, showing branching and two end-bulbs.. End
of first day; c, toward the center; p, toward the periphery.

10 Ocu. 3, Obj. 7. Medullated fiber from the neighborhood of the cut sur-
face of the distal stump on the third day; a, disintegrated portion of the axon;
b, club-shaped extremity of the living part of the axon; d, isolated neurofibril;
c, toward the center; p, toward the periphery.

11 Ocu. 3, Obj. 2mm. Medullated fiber from the neighborhood of the cut
surface of the distal stump on the third day, showing fibrillar reticulum, iso-
lated fibrils, and one fibrillar side branch with bulb; c, c’, toward the center; p,
toward the periphery.

12 Ocu. 3, Obj. 2 mm. Formation of side branches and end-bulbs on the
non-medullated fibers near the cut surface of the proximal stump at the end of

the first day.

538

PLATE 1

DEGENERATION AND REGENERATION OF NERVE FIBERS

S. WALTER RANSON

Dy ere <

539

PLATE 2
EXPLANATION OF FIGURES

13 Ocu. 3, Obj. 7. Bundle of regenerating non-medullated fibers in the
proximal stump, on the fourteenth day; c, toward the center; p, toward the
periphery.

14 Ocu. 3, Obj. 2 mm. Medullated fiber from the neighborhood of the cut
surface of the proximal stump at the end of the first day; a, degenerated portion
of the fiber; b, zone of reaction with neuro-fibrillar reticulum; d, only slightly
altered portion of the axon; c, toward the center; p, toward the periphery.

15 Ocu. 3, Obj. 2mm. Fibrillar dissociation in a medullated axon in the
neighborhood of the cut surface of the proximal stump on the second day.

16 Ocu. 3, Obj. 2mm. Two medullated axons, which have grown out from
the cut surface of the proximal stump and given off fine branches in the exudate;
c, c’, toward the center; p, p’, toward the periphery.

17 Ocu. 4, Obj. 2mm. Medullated axon from the neighborhood of the cut
surface of the proximal stump at the end of the first day. Many fine branches
arise from its surface and end in small bulbs.

18 Ocu. 4, Obj. 2mm. From the neighborhood of the cut surface of the
proximal stump on the fourth day; a, obliquely cut medullated fiber with a tubular
plexus of fine branches beneath the neurilemma; 6, another tubular plexus
derived from a medullated axon; c, row of degenerating non-medullated fibers
and their end-bulbs.

19 Ocu. 3, Obj. 7. Plexus derived from a medullated axon. From near
the cut surface of the proximal stump on the second day.

540

DEGENERATION AND REGENERATION OF NERVE FIBERS PLATE 2
S. WALTER RANSON

PLATE 3
EXPLANATION OF FIGURES

2) Ocu. 3, Obj. 7. Branching of a medullated axon. From a point several
millimeters above the cut surface of the proximal stump on the nineteenth day;
a, point in old axon from which arises an extremely short branch which at once
divides into two; c, toward the center; p, toward the periphery.

21 Ocu. 3, Obj. 7. Branches of a medullated axon of the proximal stump
several millimeters above the cut surface on the twenty-fifth day; c, toward the
center; p, toward the periphery.

22) Ocu. 3, Obj. 7. A branch on the side of a non-medullated fiber which
might itself however be a branch of a medullated axon. From the proximal
stump on the fourteenth day.

23° Ocu. 38, Obj. 7. Bundles of new axons in the proximal stump on the thirty-
fourth day.

24 Ocu. 38, Obj. 7. A bundle and a tangled skein of new axons from the
central stump on the thirty-fourth day; c, toward the center; p, toward the
periphery.

25. Ocu. 3. Obj. 7. A cross section of three bundles and one tangled skein
of new axons. From the central stump thirty-four days after the operation.

PLATE 3

DEGENERATION AND REGENERATION OF NERVE FIBERS

8S. WALTER RANSON

ar)
uw

PLATE 4
EXPLANATION OF FIGURES

26 Ocu. 3, Obj. 2mm. From a cross section of the proximal stump on the
thirty-fourth day showing the increase in the number of non-medullated fibers ;
a, bundle of non-medullated fibers; 6, medullated fiber.

27 Ocu. 3, Obj. 2 mm. Bundles of new axons in the scar on the twenty-fifth
day; a branching fibers; c, toward the center; p, toward the periphery.

28 Ocu. 3, Obj. 7. Five protoplasmic bands, down one of which a new axon
is growing. From the distal stump thirty-four days after the operation; c,
{toward the center; p, toward the periphery.

29 Ocu.3,Obj.2.mm. Cross section of the distal stump on the thirty-fourth
day; a, protoplasmic band from a medullated fiber containing five new axons;
h, bundles of protoplasmic bands from non-medullated fibers some of which con-
tain new axons; c, droplet of meylin in a protoplasmic band.

PLATE 4

DEGENERATION AND REGENERATION OF NERVE FIBERS

8S. WALTER RANSON

545

THE CESSATION OF MITOSIS IN THE CENTRAL
NERVOUS SYSTEM OF THE ALBINO RAT

EZRA ALLEN

From the Philadelphia School of Pedagogy and The Wistar Institute of Anatomy and
Biology

TWENTY-TWO FIGURES
: INTRODUCTION

While different observers have recorded the fact that mitosis
continues in the central nervous system after birth in mammals
which are relatively immature when born, the exact period of
its cessation In any one such animal does not seem to have been
determined. The purpose of this paper is to record results of
studies which I have been pursuing, with many interruptions,
for three years, in the effort to discover how long cell division
may continue after birth in the central nervous system of the
albino rat.

The literature on this phase of vertebrate growth is not exten-
sive. Buchholtz (90) records mitoses in all parts of the central
nervous system of new-born dogs and rabbits and those a few
days old. Sclavunes (’99) states that in new-born dogs, cats
and white mice dividing cells are to be found in the wall of the
central canal of the cord, in its white substance, in the sub-
stantia gelatinosa, in the anterior gray horns, at the point of
entrance of the dorsal and ventral nerve roots, ‘among the cells -
of the spinal ganglia,” in the dorsal and ventral septa of the
cord, in the dura, and “‘abundantly”’ in the arachnoid and under
the pia. Hamilton (’01) found mitoses in the cerebrum and spinal
cord of the albino rat in animals four days old. Addison (11),
in his study of the Purkinje cells of the same animal, notes mitoses
regularly occurring in the cerebellar cortex at twenty-one days,
and in one individual at twenty-two days after birth.

547

548 EZRA ALLEN

MATERIAL AND TECHNIQUE

I am indebted to The Wistar Institute of Anatomy and Biology
for the albino rats used in the study and for the use of its labora-
tory equipment. I am indebted to Dr. Stotsenbtirg, of the Insti-
tute, for a supply of rats as needed and for courteous attention;
to Dr. H. D. King for a method of imbedding and staining; to
Dr. S. Hatai for valuable suggestions. To Dr. H. H. Donaldson
I am especially indebted for constant aid and criticism.

My method of work was in general as follows. Healthy rats
of the following ages were used: 1, 4, 6, 7, 12, 15, 18, 20, 30, 52, 70,
about 120 days old, and one about two years old. In all, some
twenty-five different animals were studied. Record was made of
the weight, body-length and sex. After chloroforming the animal,
the brain and cord were quickly removed, fixed in Carnoy’s fluid
and imbedded, the younger specimens in paraffin the older in
eelloidin and paraffin. Frontal sections were then cut at 8 micra
and stained with either iron-alum-haematoxylin or thionin, fol-
lowed by eosin or erythrosin. Thionin was found to differentiate
the mitotic figures with sufficient clearness for this:study. By
using the mechanical stage, the sections were thoroughly explored
with a magnification sufficient to detect mitoses. Only those
cells which showed mitotic figures clearly were enumerated; the
earlier stages of prophase, being more difficult to identify, were
not considered. The Zeiss 4 mm. objective and No. 4 eye-
piece usually sufficed; in doubtful cases the 2 mm. oil immersion
objective and eye-pieces higher than No. 4 were employed.

Two methods of record were used. With the younger material,
diagrams representing the sections studied were outlined and on
these the approximate location of the dividing cells was indicated,
the number / being employed for the cells in section No. 1, the
number 2 for those in section No. 2, etc. (figs. 1 to 4). When
the examination of a series was complete, this method showed
graphically the distribution of the dividing cells in that portion’
of tissue both in cross section and longitudinally. The other
method, usually employed for the older material, was to tally the
cells as discovered opposite the number of the section, regional
location being indicated by columns if desired.

MITOSIS IN CENTRAL NERVOUS SYSTEM 549

All the figures are from frontal sections of the cord and brain of the albino rat.

Figs. 1 to 4 Diagrammatic drawings of frontal sections through the cervical
cord and at three different levels of the cerebrum of a one-day-old rat. Each
figure shows the position of a dividing cell in the section of the series corresponding
to that number. The dotted lines outline gray matter. The ventral portion of
the tissue appears at the bottom.

Fig. 1 Distribution of the dividing cells in ten consecutive sections of the cer-
vical cord at the level of its greatest area. 75.

As to the portions of the central nervous system studied. At
first examination was made at various levels throughout the length
of the cord, cerebellum and cerebrum to determine whether mito-
sis was limited to a particular locality. Then, in order to deter-
mine numerical relationships, attention was focussed upon cer-
tain definite levels. For the spinal cord, the sections showing
greatest area in the cervical, thoracic and lumbar levels; for the
cerebellum, sections passing through the region showing greatest
area, and for the cerebrum sections passing through the optic
chiasma were chosen. In each instance frontal sections were
used. The number of sections thus studied varied a little—
in the cord at least ten and frequently more: in the brain at
least five and frequently more.

'
G
‘
‘
'
{
1
\
\
i
\
‘
‘
4

MITOSIS IN CENTRAL NERVOUS SYSTEM ool

Fig. 2 Distribution of the dividing cells in five consecutive sections cut through
the frontal lobe of the cerebrum dorsal to the olfactory lobe. 25.

Fig.3 Distribution of the dividing cells in five consecutive sections cut through
the optic chiasma. X 25.

Fig. 4 Distribution of dividing cells in five consecutive sections cut through
the mid-brain and the occipital lobes of the cerebrum posterior to the lateral
ventricles. < 25.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 22, No. 6

B52 EZRA ALLEN

As a basis for determining the comparative rate of cell divi-
sion the number of mitoses per cubic millimeter was obtained.
With the aid of the camera lucida or projection apparatus, draw-
ings were made of the first and last sections of a series. These
drawings were then measured by the planimeter and the mean
area taken. Since the sections were of a fixed thickness (8 micra)
the volume of the tissue in question was readily calculated. The
number of dividing cells in the series of sections had already been
determined, so that the necessary data for finding the number of
dividing cells per cubic millimeter of tissue were at hand.

STATEMENT OF RESULTS
The distribution of mitoses

A brief statement will first be made under this head to be fol-
lowed by more detailed explanation. The results of this study
show that at birth mitoses are occurring in each division of the
central nervous system, at all levels of the cord, cerebellum and
cerebrum. An examination of figures 1 to 4 will make it evident
that the general distribution, however, is unequal. Table 2
(p. 557) indicates at different ages the relative mitotic activity
per cubic millimeter at the three principal levels of the cord and
at one level of the cerebellum and cerebrum respectively. Figures
2 to 4 show the relative longitudinal distribution at three levels
in the cerebrum, as well as the fact that in this organ the region
of greatest activity is in the walls of the lateral ventricles. In
the cerebellum dividing cells are most abundant in the cortex.
Table 2 shows the relative rate of mitosis at different levels for
the ages from one day to twenty-five days after birth. This
table shows also that cell division stops earliest in the cord, a
little later in the cerebellum and still later in the cerebrum.
With these data in mind we may pass to the details.

1. The distribution as it appears in frontal section will be better
appreciated by a preliminary consideration of the embryonic
differentiations of tissue as they appear in the central nervous
system. The original epiblastic layer forming the wall of the
neural tube is early converted into a protoplasmic framework

MITOSIS IN CENTRAL NERVOUS SYSTEM 553

(myelospongium) which has a columnar and radial disposition
and shows three layers: (a) the innermost or germinal zone;
(b) a middle nuclear or mantle zone crowded with daughter cells
which have migrated from the actively mitotic germinal layer;
and (c) an outer nuclear-free reticular or boundary zone. (His
89 and ’04; Hardesty ’04; Bryce ’08). The seat of mitotic
activity is confined at first to the germinal zone but later spreads
to the mantle layer (Hamilton ’01; Hardesty ’04). Activity
continues in these two layers with increasing age, but becomes
more rapid in the latter (the middle nuclear or mantle). Hamil-
ton (’01), writing of the spinal cord of the albino rat, states: “As

TABLE 1

Giving the percentage of ependymal mitoses in the spinal*cord of the albino rat from
one day to fifteen days old, based upon the number of mitoses in ten sections from
the cervical, thoracic and lumbar levels respectively, excepting that in the fifteen-
day rat twenty sections at each level were used.

AGE | TOTAL NUMBER OF MITOSES EPENDYMAL MITOSES mrtg ee,
days I ie 7 yer
1 | 47 4 8.5
4 96 0 0.0
115 6 oe
2 22 2 9.0
15 4 1 25.0
Morals... 284 13 | 4.5

The percentage of 13 to 284 is 4.5, the percentage of the ependymal mitoses to
the total number of mitoses during the period from 1 day to 15 days.

development proceeds, there is a relative increase of extra-ven-
tricular mitoses, so that by the end of the first day after birth
they are greatly in the majority.”” My preparations from the
one-day cord of the same animal confirm this observation. At
this age the mitoses are distributed in the ependyma, in the white
and gray regions, in the fiber tracts, in the nerve roots, in the
enveloping membranes and among the spinal ganglion cells.
With advancing age the distribution appears as shown in table 1,
the data for which were obtained by adding together the number
of mitoses found in ten sections taken from the cervical, thoracic

554 EZRA ALLEN

and lumbar regions of the cord respectively, with one exception,
viz., that twenty sections instead of ten were used from each
region as a basis for the figures for the fifteen-day specimen.

Hamilton (’01), from observations on twenty-five consecutive
sections from the lumbar cord of one new-born rat, concludes
that the greatest number of mitoses is in the anterior gray column.
This relationship apparently does not persist during the later
stages of mitotic activity, as shown by my sections. Further-
more the animals which I have studied show great individual
variation at the same age. In addition, the same animal varies
greatly in its number of mitoses in series of sections taken at only
short distances apart in the same approximate level.

The ependyma of the cerebellum shows very few mitoses in the
one-day-old animal. © In the cortex they are abundant; there are
few in the intermediate tissue. This condition prevails through-
out the length of the organ. By the age of twelve days cell
division is confined to the cortical area and does not reappear in
other portions.

The cerebrum shows a distribution the reverse of that found
in the other two divisions. While at birth it is diffuse, the great-
est amount of activity is seen in the germinal and mantle layers
about the lateral ventricles (fig. 3). The activity external to
these layers grows less until at the age of twelve days there is
scarcely any cell division elsewhere. Furthermore, the activity
about the lateral ventricles is not equally distributed. It is least
on the ental lateral surface and the ventral portion of the ectal
wall; greatest along the roof and dorsal portion of the ectal lateral
wall, where the mantle layer is widest (fig. 7). This distribution is
to be seen in the animal one day old at whatever level of the ven-
tricle we may section. In the older animals the region of activity
becomes limited to the small portion of the ectal lateral wall lying
a little ventrad from the point of union of this wall and the roof.
(See further discussion of this zone under the topic Structural
Correlations).

2. A comparison of sections from the same rat taken at differ-
ent levels shows that the rate of mitosis is not equal throughout
the length of the central nervous system. The cord is the region

MITOSIS IN CENTRAL NERVOUS SYSTEM 955

of the least and the cerebellum the seat of the greatest activity,
while the cerebrum in that portion where cell division is most
rapid exhibits an activity somewhat greater than that of the cord.
Table 2 (p. 557) contains figures illustrating these different rates.
In addition, mitotic activity is unequal at different levels of the
cord and cerebrum. Table 2 brings out this relativity for the
cord. The rate of cell division is seen to be lowest in the thoracic
and highest on the whole in the cervical portion. In the latter
it rises on the sixth day to a rate equal to the most rapid exhibited
by the cerebrum (on the fourth day), and more than twice as
rapid as that of the cerebrum at six days. From a comparison
of numbers of dividing cells at the three levels of the cerebrum,
it is found that the greatest number is in the region of sections
which pass through the optic chiasma.

This unequal longitudinal distribution is still further illustrated
in a small way within the limits of each level, as shown by the
markedly greater number of mitoses to be found in two or more
consecutive sections of a series, this greater number standing out
prominently from the relatively smaller number in the sections
immediately preceding and following. Three illustrations fol-
low, chosen from many which show the same relationship. The
figures representing the number of mitotic cells in each section of
_ the series run as follows: (1) from the cerebrum—4, 5, 7, 9, 11, 16,
14, 21, 3, 9, 3, 9, 3, 4; and (2) from the cervical cord 4, 0, 2,
3, 5, 8, 1, 4, 2. The numbers italicized in each series mark
this grouping of mitotic activity, which may be termed a ‘locus’
of activity. Similar loci.appear in the cerebellum. (3) A bril-
liant illustration presented itself in the cerebrum of a twenty-
five-day specimen, an age when the mantle layer is not so crowded
with nuclei as it is in younger material. This illustration will
also show the tendency of cells to form groups and to retain a
group identity. In this instance three well-marked groups of
closely-packed, densely-staining nuclei were found, each well
differentiated from the surrounding nuclei, and each showing
mitoses. (See mn'~mn? in fig. 10; enlarged view of one group is
to be seen in fig. 21). These groups extended through three con-
secutive sections of 8 micra. I have not endeavored to ascertain

556 EZRA ALLEN

whether such loci are constant in their appearance at fixed points
of the system or vary with different individuals. The large num-
ber of such loci found within small portions of the tissue at all
ages and in each individual examined shows the necessity of using
a considerable number of consecutive sections if one desires to
make wide application of figures obtained from any one level.

3. Mitosis continues for different periods after birth in the
different levels. It ceases first in the cord. Very few dividing
cells are to be found in the fifteen-day cord at any level, as shown
in table 1 (p. 553). No dividing cells were found in two eighteen-
day-old specimens, although sections widely distributed in the
different levels respectively were examined. No mitoses were
found in the cords of older animals. The eighteen-day period
may then be regarded as the time when mitosis has ceased in
this portion of the system, having ceased between this and the
fifteen-day period.

In the cerebellum it continues until some time between the
twenty-second and twenty-fifth day, while in the cerebrum it
continues still longer—to a slight degree in material about 120
days old, further discussion of which is taken up under the topics
which follow.

4. Table 2 shows the distribution of dividing cells per cubic
millimeter at three levels in the spinal cord and at one in the cere-
bellum and cerebrum respectively. The data for these figures
come from consecutive frontal sections at the different levels as
fully described in the introduction (p. 552). Each number in
the table is not an average from several different rats but is taken
from the records of one individual. For a given age, the numbers
italicized are from the same animal. It will be noticed that the
figures for the cerebellum in each of the animals of the first three
ages are not from the same, animals as those which furnished the
figures for the other levels. This substitution is due to certain
technical difficulties which presented themselves, such as failure
to get good sections or to obtain true frontal sections in the
desired locality. These three cerebella are the only ones of these
ages upon which estimations were figured; others might have
furnished slightly different figures.

MITOSIS IN CENTRAL NERVOUS SYSTEM , 557

TABLE 2

Showing the number of mitoses per cubic millimeter of nerve tissue in the central
nervous system at certain levels. The figures are taken from calculations of the
volume of tissue and the number of mitoses in ten consecutive sections at each level of
the cord, five in the largest portion of the cerebellum and five in the cerebrum in the
region of the optic chiasma (see p. 652). The numbers italicized are from the same in-
dividual of that age. Theletters (a), (b) and (c) refer to different rats of the same age.

| CORD

CEREBELLUM | CEREBRUM

AGE es aT = 7 =
Cervical Thoracic Lumbar
days
1 208 || 115 259 1597 | 430
4 Lo ater gre ao) CT | Ditiple |. eeey,
6 | 46 | 236 | 320 (7-day)4848 | 193
12 46 15 eae | 839 | BT,
20 00 =| OOn | 00 | (a) 00! (a) 18
20 | 00 | 00 OOM =) NEY RG NG) 27
20 | OO. | 00 00 Cf (c) 520 |
25 | 00 | 00 | 00 00 a7

The differences of quantitative distribution which appear from
this table if one reads the figures from left to right (accord-
ing to the same age) have been noted on page 555. If one reads
the columns downwards, it appears that the rate of cell division
increases after birth (a confirmation of Hamilton ’01) until the
sixth day in the cord and the seventh in the cerebellum, but in the
cerebrum only until the fourth day; after these respective dates
the rate decreases rapidly. Cell division has ceased in the cord
at the twentieth day, in the cerebellum at the twenty-fifth day,
but in the cerebruin is still continuing at this last age at the same
rate as for the twentieth day in specimen 6.

Since these figures are taken from so limited a number of
animals of each age, and from a length of only 80 micra in the
cord and 40 micra in the brain at each level, they are to be inter-
preted as representing the general movement of mitotic activity,
not as furnishing the basis for an accurate curve which will show
the rate of mitosis after birth. More data must be gathered
before such a curve can be constructed. However, the wide
difference at each age between the rate in the cerebellum and the
other levels indicates that we are safe in concluding that this
organ presents the greatest degree of activity. There is good

558 js EZRA ALLEN

reason for this condition since at birth the cerebellum is devel-
oped to only a slight degree, and its growth thereafter is very
rapid during its first twenty-five days of life.

Hamilton (’01) found that the rate of cell division is less at
birth than before birth. Unfortunately her paper does not give
the embryonic age at which the rate is highest. Otherwise we
might fix approximately the two periods in the life history of the
albino rat when this factor of growth is most important in the
cord and cerebrum. Since the figures given by her are not in
terms of number per cubic millimeter, we have not the data
needed for an exact comparison of the two phases of growth.

STRUCTURAL CORRELATIONS
1. Correlations in the spinal cord

If we compare sections of the cervical cord from one-day and
twenty-day rats respectively, we see several morphological differ-
ences (figs. 5 and 6). (1) In the first place, the wall about the
central canal of the one-day animal shows germinal cells in mito-
sis, and shows also that its myelospongium at each end lacks
nuclei. Neither of these phenomena appears in the older material.
In addition, the form of the canal in the older differs from that
of the younger in that it approaches more nearly the strongly
elongated oval assumed in the adult cord. (2) The number of
cells in the immediate vicinity of the canal of the twenty-day
animal is less than in the one-day old. (8) There is greater
degree of maturity in all the cells of the older as indicated by
their size and cytoplasmic development. And (4) the number
of migrating cells is much less in the older than in the younger ani-
mal, although the region of greatest migrating activity remains
the same in both ages—the region just ventral to the canal.

In most vertebrates the germinal and mantle layers about the
canal have been completed some time before birth. One known
exception is the chick. Merk (’86) figures the cord of a chick
of seven days and five hours old which shows a nuclear-free
space in the germinal zone at each end of the canal, a condition
found in the albino rat at six days.

cerebrum of albino rats of different ages. They show the ventral side downward
on the page. The letters indicate the same structures throughout: ventr, ventral;
ect, ectal; ent, ental; r, roof; V.iii, third ventricle.
Fig.5 One-day rat, cervical cord. X S84.
Fig. 6 Twenty-day rat, cervical cord. 84.
559

560 EZRA ALLEN

The germinal layer is completed progressively in the different
levels of the cord in the albino rat. The completion is earliest
in the thoracic region, where it is fully formed by the twenty-
day period. It matures next in the lumbar region, where the
wall is closed in nearly every section of the twenty-five-day and
in every section of the thirty-day-old animals. In the cervical
region, finally, a few sections at the last-named age still show
a nuclear-free myelospongium at the ventral portion. The
dorsal end is closed at all levels in the interval between the six-
day and twelve-day periods.

2. Correlations in the cerebellum

The most interesting feature here is the external granule
layer. Mitosis continues in this layer after it has ceased in all
other parts of this organ. It ceases when the inward migration
of the nuclei has taken place, a movement which is usually com-
pleted between the twentieth and twenty-fifth day (Addison
11). I found that in one specimen examined the migration had
been completed at twenty days. Addison (11) found in one of
his preparations dividing cells in this layer at twenty-two days.
Examination of two twenty-five-day specimens prepared by me
revealed no mitoses; neither was any trace of the external gran-
ule layer present.

3. Correlations in the cerebrum

The well developed and persistent mantle zone lying along the
ectal wall of the lateral ventricles is of particular interest, for in
it occur the dividing cells found in the oldest specimens which
show mitoses, and this layer, unlike the external granule layer of
the cerebellum, never entirely disappears in animals up to two
years of age, the oldest which I have examined (fig. 9). The
one-day and twenty-five-day specimens both show dividing cells
at every level along the entire length of the ventricles. In each
case they are most abundant at the level of the optic chiasma.
The mantle zone, while in general following the outline of the
ventricular wall, is not of the same thickness throughout in any

NERVOUS SYSTEM 561

MITOSIS IN CENTRAL

oy} JO UOTJIPUOD OYA MOYS 0) BUUSeIYO OIYdO YSnoIyy UOTZOS

[®

§ puv J sainsy Ul sv ‘UINIgs1e0 IROA-OM], 6 “SIT
12 X ‘2 eansy ul sv ‘umaqaio0 AVp-xIQ g ‘Sly
IZ X ‘|B AepNoIQUOA

quot (otoydsturoy ouo) funaqodieo “yra ABp-ouQ, 2 “BLT

Kee)

ALLEN

EZRA

562

ou0O

‘VS X

‘OT OANSY Ut sv ‘uMaAqesio0 TOA-OMT, TT “SIT

(ecg *d 008) S][OO OATPOR JO TNO] OF AOJorI pW pUT ,WUE ‘UW S19}JO] OUT, “FS X “o[Bos Josey v uo
JUOA ]t

opPFURI OY} MOYS OF OTOL

21018

[ oy} Jo uorazod

[esiop “Winaqolod Avp dAY-AQUOMT, OT “Sy

> WA

MITOSIS IN CENTRAL NERVOUS SYSTEM 563

frontal section (figs. 7to 11). It is widest at the point where the ~
ectal lateral wall and the roof meet, and wider all along the ectal
lateral wall than along the ental wall. In the one-day animal the
layer extends all around the ventricle, but, beginning at the ven-
tral portion, it is gradually reduced in extent until at twenty-
five days old it consists of a single layer on the ental lateral wall;
on the roof it is in almost the same condition, while on the dorsal
portion of the ectal lateral wall and extending well outward at
the point it is still several cells in thickness (fig. 10). Reduction
is nearly complete along the ental lateral wall at the six-day period
(fig. 8). In the twenty-five-day specimens cell division is occur-
ring only in the portion of the ectal lateral wall and roof be-
tween mn! and mn} in figure 10. In this region a total of eight
dividing cells was found in a seventy-day animal in five frontal
sections at the level of the optic chiasma, these being along the
ectal lateral wall, with none on the roof.

The mantle layer persists in this limited region along the ectal
lateral wall in the two-year animal, as shown in figures 9 and 11.
The active portion of this layer continues in advanced age to
occupy the region a few cells in width external to the germinal
layer, as shown by figures 21 and 22. There is evidently some
connection between this layer and the “‘Uebergangsschichten”
of His (’04) shown in his section of the human foetal cerebrum
of four months.

NATURE OF THE DIVIDING CELLS

The tissues ultimately found in the nervous system are the
neurones, the neuroglia and the connective tissue. In addition
we find occasional leucocytes and a relatively greater number of
lymphocytes. Hardesty (04) from his study of the developing
neuroglia of the pig, concludes that, ‘‘With the present tech-
nique there is nothing to show that all the products of the mitoses
(germinal cells) in the ependymal layer are not indifferent ele-
ments from the first—capable of developing into either neurones
or neuroglia.” The neuroglia tissue has a double source of origin,
arising from both the ectoblast and mesoblast. Hatai (’02) con-

Figs. 12 to 22. Camera lucida drawings of portions of tissue in cord and cere-
brum chosen to show dividing cells. All the drawings were made with the Zeiss
2mm. oil immersion lens and No. 6 eye-piece, tube length 176 mm. The drawings
have been uniformly reduced to make the magnification as printed equal 800 diam-
eters. The letters indicate the same structures throughout: mli, membrana
limitans interna; g, dividing cell in germinal layer; mn, dividing cell in mantle
(middle nuclear) layer; ep, ependymal cells; dt, cells in differentiated tissue; leu,
leucocytes; ca, cell of capillary wall.

Fig. 12 Four-day rat, cervical cord; dividing cell in germinal layer. > 800.

Fig. 13 Six-day thoracic cord; large dividing cell in posterior horn. This cell
is one of two dividing cells very near each other, each of which showed its chomo-
somes in three consecutive sections of 8 micraeach. > 800.

Fig. 14 Twelve-day thoracic cord; small dividing cell in posterior horn. 800.

Fig. 15 Twelve-day thoracic cord; mesodermal dividing cell of capillary found
in postero-lateral tract; same section as figure 14. 800.

Fig. 16 Six-day cerebrum, cortex; leucocyte within a cross section of capillary
and a dividing cell. It is difficult to determine whether the granular mass about
the nucleus of the leucocyte is its cytoplasm or other material. > 800.

564

Figures 17 to 22 are from the cerebrum of rats of different ages, showing por-
tions of the zones bordering the ectal lateral wall of the lateral ventricle at about
the locality marked mn? in figure 10, with the exception of figure 19, which is from
the cortex.

Figs. 17 and 18 One-day cerebrum; small portions of germinal layer separated
from each other by only a few cells. > 800.

Fig. 19 One-day cerebrum; small portion of the cortical region of the same
section as figures 17 and 18. > 800.

Fig. 20 Six-day cerebrum; adjacent portions of germinal and mantle layers.
x 800.

Fig. 21 Twenty-five-day cerebrum; two dividing cells in mantle layer, the
lower at the edge of a group of cells (mn? in fig. 10). (See p. 555.) X 800.

Fig. 22 120-day cerebrum; germinal and mantle layers and two cells showing
cytoplasm in the first layer of differentiated tissue. At this age the ependymal
cells are clearly differentiated; they began to appear in the twenty-five-day
material, as shown in figure 21. The reduction in the number of cells in the two
inner layers is to be noticed. > 800.

565

566 EZRA ALLEN

firms the observations of Fragnito and Capobianco with regard
to the mesoblastic source:

From these observations the conclusion is drawn that the neuroglia
nuclei in the white rat as well as in the mouse represent two distinctly
characterized types: namely, nuclei the structure of which resembles
very closely that of the nerve cells, and the nuclei the structure of which
resembles very closely that of endothelial cells which form the capillary
wall. These two types of nuclei have been derived from the ectoblast
and mesoblast respectively. The latter type has probably two sources
of origin; that is, they are partly derived from mesoblastic cells immigrat-
ing from the meninges (Capobianco and Fragnito), and partly from
proliferating endothelial cells of the walls of the capillaries, these cells
having separated from the capillary wall and migrated into the surround-
ing tissue, where they constitute one type of the neuroglia elements.

Hamilton (01) differentiates two types of dividing cells in the
cerebrum and spinal cord, the one, large with cytoplasm well
developed and the chromosomes more scattered, the other small
without cytoplasm and with the chromosomes solidly bunched.
The former, she thinks, develop into nerve cells and the latter
into neuroglia. Hardesty (04) is of the opinion that the neuroglia
cells cannot be differentiated from the inward-migrating white
fibrous corpuscles. My observations lead me to agree with
Hardesty, and so far as my methods of staining reveal any differ-
entiations there seems to be no way of determining whether the
small dividing cells are to become neurones, neuroglia cells or
white fibrous corpuscles, since the small neurones which show
processes very plainly are no larger than some of the dividing
cells (figs. 14 and 16).

My preparations indicate that division in the two sizes of
mitotic cells does not continue to the same period in the cord and
cerebrum. In the cord, the large cells are found dividing in
various regions up to the sixth day (fig. 13). While twelve-day
specimens still show some mitoses in the germinal zone, the divid-
ing cells of the extra-ependymal regions possess the characteris-
tics of the smaller type. In the cerebrum the chromatic mass in
the dividing cell measures up to 7.5 x 8 micra in the younger
material, while in 70-day and 120-day material, a list of measure-
ments runs as follows, the tissue from the two animals having

MITOSIS IN CENTRAL NERVOUS SYSTEM 567

been prepared in the same manner: 70-day—5 x 4, 5.5 x 5, 6x4,
6 x 3 micra; 120 day—6 x 4,4x 5,4x4micra. None were found
measuring more than 6 x 4 micra.

The dividing cells which I have enumerated in this study are
believed not to be leucocytes or lymphocytes for the following
reasons: the size of the nuclei in leucocytes found in blood vessels
in my preparations is from. 3.2 x 3.2 micra to 3.8 x 3.8 micra,
while the chromatin material in the nerve nuclei measures from
4 x 4.2 in anaphase to 7.5 x 8 micra in prophase and metaphase.
Moreover, after the dividing cells have disappeared from all other
areas they are still to be found in the limited zone along the lat-
eral ventricles of the cerebrum which has already been described.
They are to be found also in the neighborhood of capillaries but
this association is not constant.

The differentiation from lymphocytes is easier. These are
found scattered through the tissue; they are smaller than the
leucocytes and are readily recognized by the characteristic nuclei,
their chromatin being gathered into one, two or more well sepa-
rated, densely stained spherical masses, the outlines of which are
always smooth and regular, lying in a clear nuclear matrix
bounded by a limiting membrane of uniform thickness.

CONCLUSIONS

1. Mitosis ceases in the central nervous system of the albino
rat as follows: (a) No mitoses are found in the cord at any level
after the eighteenth day. This is somewhat previous to the
complete cellular differentiation of the wall of the central canal,
a stage accomplished in the thoracic region by the twentieth day
after birth, in the lumbar region by the thirtieth day after birth,
while at this last-named age the cervical level shows in occasional
sections a portion of the wall still incomplete. (b) In the cerebel-
lum mitosis ceases when the migration of the cells in the external
granule layer is complete, a condition reached between the twen-
tieth and twenty-fifth day after birth. (c) In the cerebrum mitosis
continues with a considerable degree of activity to the twentieth

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL, 22, NO. 6

D668 EZRA ALLEN

day after birth, after which it is found to a slight degree in the
mantle layer along the ectal lateral wall of the lateral ventricles,
this layer persisting at least to the age of two years. The lat-
est observation of dividing cells in this locality was in 120-day
material.

2. The rate of mitosis increases for a time after birth, reaching
its high point at about the seventh day for the cord and cere-
bellum and about the fourth day for the cerebrum.

BIBLIOGRAPHY

Bryce, T. H. 1908 Quain, Elements of Anatomy; vol. 1.

Bucuuoitz, A. 1890 Ueber das Vorkommen von Karyokinesen in Zellen des
Centralnervensystems von neugeborenen und jungen Hunden u. Ka-
ninchen. Neur. centralblatt, Bd. 9, pp. 140-142.

Hamittron, Atice 1901 The division of differentiated cells in the central ner-
vous system of the white rat. Jour. Comp. Neur., vol. 11, pp. 297-320.

Harpvesty, I. 1904 The development and nature of the neuroglia. Am. Jour.
Anat., vol. 3, pp. 229-268.

Harat, S. 1902 On the origin of neuroglia tissue from the mesoblast. Jour.
Comp. Neur., vol. 12, pp. 291-296.

His, W. 1886 Zur Geschichte des menschlichen Riickenmarks u. d. Nerven-
wurzeln. Des XIII Bandes d. Abhandl. d. math.-phys. Klasse d.
kénigl. Sachsischen Gesellschaft d. Wissenschaften No. VI.

~ 1889 Die Neuroblasten und deren Entstehung im embryonalen Mark.
Arch. fiir Anat. u. Entwick.
* 1904 Die Entwickelung d. menschlichen Gehirns wihrend d. ersten
Monate. Leipzig.
Merk, L. 1886 Die Mitesen im Centralnervensystem. Denkschr. d. math.
naturw.Klasse d. kaiserl. Akad. Wiss., Bd. 53, Wien.

. Sctavunos, G. 1899 Ueber Keimzellen in d. weissen Substanz d. Riicken-
marks von iilteren Embryonen und Neugeborenen. Anat. Anzeiger,
Bd. 16, pp. 467-473.

SUBJECT AND AUTHOR INDEX

7 oa , sex, weight and relationship upon the
number of medullated nerve fibers and on
the size of the largest fibers in the ventral

root of the second cervical nerve of the albino

rat. The influence of 131
ALLEN, Ezra. The cessation of mitosis in the
central nervoussystem of thealbinorat. 547

ARPENTER, F. W. On the histology of the
cranial autonomic ganglia of the sheep. 447

Cauda equinas or the sciatic nerves. Experimen-
tal studies of paralyses in dogs after mechani-
eal lesions in their spinal cords, with a note
on ‘fusion’ attempted in the 99

Centers in teleosts. The olfactory tracts and 177

Cerebral ganglia. The epibranchial placodes of
Lepidosteus osseus and their relation to the 1

nerve of the albino rat. The influence of
age, sex, weight and relationship upon the
number of medullated nerve fibers and on the
size of the largest fibers in the ventral root of
the second 131

Cranial capacity. A comparison of the European
Norway and albino rats (Mus norvegicus and
Mus norvegicus albinus) with those of North
America with respect to the weight of the cen-

tral nervous system and to 71
Cyclostomes. The telencephalon in 341
EGENERATION and regeneration of nerve
fibers 487

Dogs after mechanical lesions in their spinal cords,
with a note on ‘fusion’ attempted in the cauda
equinas or the sciatic nerves. Experimental
studies of paralyses in 99

Donautpson, Henry H. A comparison of the
European Norway and albino rats (Mus nor-
vegicus and Mus norvegicus albinus) with
those of North America with respect to the
weight of the central nervous system and to
cranial capacity. 71

Dunn, ExizaBpetH Hopxrns. The influence of
age, sex, weight and relationship upon the
number of medullated nerve fibers and on the
size of the largest fibers in the ventral root of
the second cervical nerve of the albino rat. 131

EISS, Henry O. Experimental studies of
paralyses in dogs after mechanical lesions in
their spinal cords, with a note on ‘fusion’

attempted in the cauda equinas or the sciatic

nerves.

‘Fusion’ attempted in the cauda equinas or the
sciatic nerves. Experimental studies of paral-
yses in dogs after mechanical lesions in their

spinal cords, with a note on 99
ANGLIA and of the spinal nerves. The
structure of the spinal 159

of the embryo of Rana pipiens. The cere-
bral 461
of the sheep. On the histology of the cra-
nial autonomic 447
OHNSTON, J.B. The telencephalon in cyclo-
stomes. 341

ANDACRE, F. L. The epibranchial placodes
of Lepidosteus osseus and their relation to
the cerebral ganglia. i}

and McLEeLian, Marie. The cerebral gan-

glia of the embryo of Rana pipiens. 461

Lepidosteus osseus and their relation to the cere-

bral ganglia. The epibranchial placodes of 1

ih eee Manrige, Lanpacre, F. L. and.
The cerebral ganglia of the embryo of Rana

pipiens 461
Mitosis in the central nervous system of the albino
rat. The cessation of 547

ECTURUS maculosus (Raf.). The numeri-
eal relations of the histological elements in

the retina of 405
Nerve fibers and on the size of the largest fibers in
the ventral root of the second cervical nerve

of the albino rat. The influence of age, sex,
weight and relationship upon the number of

medullated 131
fibers. Degeneration and regeneration of oF
4

Nerves. Experimental studies of paralyses in
dogs after mechanical lesions in their spinal
cords, with a note on ‘fusion’ attempted in the
cauda equinas or the sciatic 99

The structure of the spinal ganglia and of

the spinal 159

Nervous system and to cranial capacity. A com-
parison of the European Norway and albino
rats (Mus norvegicus and Mus norvegicus
albinus) with those of North America with

respect to the weight of the central 71
——-system of the albino rat. The cessation of
mitosis in the central 547

LFACTORY tracts and centers in teleosts.
O The 177

ARALYSES in dogs after mechanical lesions
P in their spinal cords, with a note on ‘fusion’
attempted in the cauda equinas or the sciatic
nerves. Experimental studies of 99
PaLMER, SAMUEL C. The numerical relations of
the histological elements in the retina of Nec-
turus maculosus (Raf.). 405
Pipiens. The cerebral ganglia of the embryo of
Rana 461
Placodes of Lepidosteus osseus and their relation
to the cerebral ganglia. The epibranchial 1

Re pipiens. The cerebral ganglia of the
embryo of 461

Rawson, S. Wactrer. Degeneration and regener-
ation of nerve fibers. 487
The structure of the spinal ganglia and of
the spinal nerves. 159
Rats (Mus norvegicus and Mus norvegicus albinus)
with those of North America with respect to
the weight of the central nervous system and
to cranial capacity. A comparison of the

European Norway and albino 71
Rat. The cessation of mitosisin the central nery-
ous system of the albino 547

569

570

———The influence of age, sex, weight and rela-
tionship upon the number of medullated nerve
fibers and on the size of the largest fibers in
the ventral root of the second cervical nerve

of the albino 131
Regeneration of nerve fibers. Degeneration and
487

Retina of Necturus maculosus (Raf.). The nu-
merical relations of the histological elements
in the 405

EX, weight and relationship upon the num-
ber of medullated nerve fibers and on the size
of the largest fibers in the ventral root of the

second cervical nerve of the albino rat. The

influence of age, 131
Sheep. On the histology of the cranial autonomic
ganglia of the 447
SHELDON, RatpH Epwarp. The olfactory tracts
and centers in teleosts. 177

Spinal cords, with a note on ‘fusion’ attempted in
the cauda equinas or the sciatic nerves. Ex-

INDEX

perimental studies of paralyses in dogs after
mechanical lesions in their 99

ELENCEPHALON in cyclostomes. The 341
Teleosts. The olfactory tracts and centers
in 177

ENTRAL root of the second cervical nerve of
the albino rat. The influence of age, sex,
weight and relationship upon the number

of medullated nerve fibers and on the size of

the largest fibers in the 131

EIGHT and relationship upon the number
of medullated nerve fibers and on the size
of the largest fibers in the ventral root of

the second cervical nerve of the albino rat.
The influence of age, sex, 131
of the central nervous system and to cranial
capacity. A comparison of the European
Norway and albino rats (Mus norvegicus
and Mus norvegicus albinus) with those of
North America with respect to the 71

2
¥ Z,

//f 0

=S>=co
—=——
——-,

rade
ye by
2 3;
soa
2.
a

>. >
a3

a x
eal ae
ee!
pare SS

Blt):
raat
Sea wits
5] ates) ;

Panag afi
Peet a

ee ae ee eh
Pat fe et

el
Pee

os)
12 RRR el ele initia be
SIR 918 G)® ta ie ele ie 1
” * }

* > = 4 : ‘*- Oe Z i 12 @%
deahitelahitessctetetatenateteseadivivteteie misererelsastatetsieees

Ai in id To's
7 Yi ae
* Me 21 F e945

Got Oos
BB.
es ee
~*
>
.
.

#434 , sta! CAL AL aL LD MILE OTE Seta sn 14 ha! tele le titseyss*

Jesters
Haas
* La
+ +3
i 49
elelatels latataleietetalels!
aalylatale Talalelelele
ialisl 94
0 brie ete lel
Ris le ie koe %
,.

74" ’
e719 otele LPL AL Be
139 hota 3 seats

BPG HISD

aaatelasateiitie
ay
ieitats ne

Tinie. *
7 ve a oF J bf ® ‘oe f' iq 4 1616? 8 16 . obey b 4)

Wi) aa alae ates #iye late

Miguel aaa
inti
SNE
, oF

)
3 os
.. oP
Ra

Telalelyel

143474 Tale lels le)
aie 8
we
. uni ; ee
4 iy

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Journal of comparative neurology"

See other formats