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Gift of

Dr. 0. S. Strong

Digitized by tlie Internet Arcliive

in 2010 with funding from

Open Knowledge Commons (for the Medical Heritage Library project)

http://www.archive.org/details/physiologypractiOOwild

"I have been in the hnbit of advisiug my students to dissect the CAT as a convenient prelitpiaavv [to
practical Human Auatoniy."— yo^d*^/! Leidy.

"It seems to me that the first dissections should be made on CATS and doj^s until a good technique has
been acquired, so that the supply of human cadavers, which is always insufficient, can be fully utilized to
the best advantage."— y. 6". Billings.

"There is so close a solidarity between ourselves and the animal world that our inaccessible inward
parts may be supplemented by theirs. A SHEEP'S heart or lungs or eve must not be confounded with
those of man ; but so far as the comprehension of the elementary facts of the physiology of circulation and
of respiration and of vision goes, the one furnishes the needed anatomical data as well as the other." —
Huxley.

Physiology Practicums

KXPI.ICIT DTRECTIONS FOR EXAMINING

PORTIONS OF THE CAT, AND THE HEART, EYE,
AND BRAIN OF THE SHEEP

AS AN AID IN THE

STUDY OF ELEMENTARY PHYSIOLOGY

SECOND EDITION, REVISED
WITH THIRTY KIGTJRKS

BURT G. WILDER, B.S., M.D.,

Professor of Physiology, Vertebrate Zoology, and Neurology in Cornell University ; formerly
Professor of Physiology in the Medical School of Maine and the University of
Michigan ; President ( 1 885) of the American Neurological Asso-
ciation and of the Biological Section of the Amer.
Association Adv. Science, etc.

PUBLISHED BV THE AUTHOR

PRE.SSES OK THE ITHACA JOURNAL

I«95

COPYRIGHT, 1893, 1895, BY BURT G. WILDER. ALL RIGHTS RESERVED.

Price, |i.oo, post-paid. Address the author, Ithaca, N. Y.
/ji Preparation : How to Prepare Specimens for Physiology Practicums.

By the author : Dissection of the Sheep's Brain : being part IV of Physiology Practicums,

with Plates XVIII-XXV and an Appendix on the Removal and

Preservation of the Brain. Price 40 cts., post-paid.

By the author and S. H. Gage : Anatomical Technology as Applied to the Domestic Cat :

an Introduction to Human, Veterinary, and Comparative Anatomy. Third,

from the second revised, edition. Pp. 600, 120 figs, 4 lithograph

plates. A. S Barnes & Co., New York, 1892. I4.50.

By Simon Henry Gage, Professor of Anatomy, Histology and Embryology in Cornell

University : The Microscope and Microscopical Methods. Fifth edition, rewritten,

greatly enlarged, and illustrated by 103 figures in the text. Price |i. 50

post-paid. Comstock Publishing Co., Ithaca, N. Y., U. S. A.

PREFACE TO THE FIRST EDITION.

About ten years ago, in the effort to enable the members of the gen-
eral class in Plnsiology at Cornell University (150-180 in number) to
study for themselves intelligently certain parts of the cat and sheep as an
aid to the comprehension of the functions and relations of the correspond-
ing human organs, I put alcoholic specimens before them and wrote on
the blackboard brief directions which were orally amplified and illustra-
ted. A few years later these directions were written upon cloth sheets
that were suspended before the class. They were amplified and printed
in the fall of 1S89 and issued in their present form in 1892.

The separation of the sheets and plates has obvious inconveniences
but upon the whole the practical advantages are greater.

From the first the assistants and students have cordially cooperated
toward increasing accurac)' and explicitness.

It is to be hoped that ere long as much as is here included may be
required for admission to this and other universities, so that the instruc-
tion therein may commence upon a foundation both higher and more
substantial than at present.

Ithaca^ N. F. , December 26, i8gj.

PREFACE TO THE SECOND EDITION.

The text has been revised and largely rewritten. An effort has been
made to correct the errors and omissions detected during the three years'
use of the work at Cornell University and elsewhere. For helpful sug-
gestions I am particularlv indebted to my assistants, Dr. P. A. Fish and
Dr. B. B. Stroud.

The changes in the illustrations comprise new figures of the cat's
skeleton, and of the sheep's heart and brain. Two outlines have been in-
troduced into the text.

The order has been modified so as to bring the examination of the
head and neck just before that of the eye and brain. The eleven practi-
cums are combined so as to form four Parts, each dealing with a natural
group of subjects.

A teaching experience of twenty-seven years leads me to believe that
explicitness should be a main feature of directions for beginners. To
credit them with unlikely knowledge, jtidgment and skill, or with inspir-
ation that will serve in place of those attributes, may compliment them
and simplify the task of the writer. But there result perplexities, the
formation of faulty methods, and the waste of time and material.

When, however, there has once been established a sound basis of
fact and manipulation, the student may safely and profitably venture upon
unfamiliar ground. He may either apply the directions to different
forms, or re-examine the same forms in different ways. For example, the
brain of the cat, dog, monkey or man may compared with that of the
sheep, and the sheep's brain may be explored in ways other than that
presented in the following pages.

September 20, i8g^.

CONTENTS.

PRACTICUM. SUBJECT. PAGES. PLATES'. .

fH t The Cat : Its Form, Skeleton, Skin-Muscles, and Axillary

^ >-< / Vessels and Nerves 5-8 I-IV

Ph I^. Dissection of the Cat's Arm 9-16 I, II, IV, V,

I

fH Iljl. Thoracic Viscera of the Cat 17-23 VI-VIII

^S liV. The Abdomen of the Cat 23-28 VIII-XI

Oh W. The Heart of the Sheep 29-36 XII-XIV

Si-; ■^I. The Head and Neck of the Cat 37-48 XV-XVII

<t: Vfl. The Eye of the Sheep 47-52 XVII-XX

VIII. The Brain of the Sheep : its Ectal Features and Segmen-
tal Constitution 49-53 XVIII-XXII

fi _ IX. The Mesal Aspect of the Sheep's Brain ; Endymal Con-

^ > tinuity and Ccelian Circumscription 54-62 XXIII-XXV

P^'~' X. Dissection of the Sheep's Brain . 6367

XI. Dissection of the Brain continued ; Study of its Transec-
tions 68-74 XVIII-XXV

LIST OF PLATES.

Plate I.

II.

III.

IV.

V.

VI.

VII.

Vljl.

IX.

X.

xt;:

XIII.
XIlV.

XV.
X'tl.

xyiii.

XVIII.
XIX.
XX.

XXIII.
XXIV.
XXV.

The Skeleton of the Cat. From Straus-Durckheim's "Anatomic du Chat."

The Ectal Muscles of the Cat, seen from the Left Side.

Ventral Aspect of the Cat's Thorax.

Right Axillary Region of the Cat after division of the Pectoral Muscles.

Right Arm of Cat, partly dissected.

Thorax of the Cat, opened from the Right Side to show the Lungs.

The Cat's Thorax, after removal of the Right Lung.

Diaphragm of the Cat, its Cephalic or Thoracic Aspect.

Abdominal Viscera of the Cat, from the Left Side.

Abdominal Viscera of the Cat, after removal of the Small Intestine.

Pelvic Viscera of the Female Cat.

Ventral and Dorsal Aspects of the Sheep's Heart. Two figures.

Heart of the Sheep, the Right Auricle opened.

Heart of the Sheep, the Left Side opened.

The Salivary Glands of the Cat. From "Anatomical Technology."

Head and Neck of the Cat, from tlie Left Side, partly dissected.

Mesal Aspect of the Right Half of the Cat's Head. From "Anatomical Technol-
ogy" and "Reference Handbook of the Medical Sciences."

Braiu of the Sheep, the Cerebrum sliced to near the level of the Callosum.

Ventral Aspect of the Sheep's Brain, the Eyes attached.

Ventral Aspect of the Sheep's Brain after the removal of the Hypophysis and
Parts of the Cerebrum and Cerebellum.

Left Side of the Sheep's Brain after removal of most of the Cerebrum and Cere-
bellum.

Dorsal Aspect of the Sheep's Brain after removal of parts of the Cerebrum and
Cerebellum.

Mesal Aspect of the Right Half of the Sheep's Brain.

Sheep's Brain, the Paracoeles (Lateral Ventricles) exposed.

Transection of the Sheep's Brain at the level of the Medicommissure ; Part of
the same enlarged. Two figures.

FIGURES IN THE TEXT.

Fig. I, p. 6, Left Side of the Cat.

Fig. 2, p. 19. Right Side of the Cat's Thorax, showing Lines of Incision.

figure is wrongly numbered 6.
Fig. 3, p. 69. Dissection of the Left Olfactory Bulb of the Sheep.

On p. ig this

PHYSIOLOGY PRACTICUMS.

PART IV. THE BRAIN.

PRACnCUM VIII. THE GENERAL FEATURES AND SEGMENTAL
CONSTITUTION OF THE BRAIN.

PI,ATES REOUIRED : XVIII-XXIII.

Suggestion . — The comparative unt'ainiliarity of most students with the parts of the
brain and with their names renders it particularly desirable that the directions should be
read and the plates examined in advance of the practictirn.

Caution. — The specimens should not be allowed to dry. Dip them occasionally in
alcohol or formalin, or hold them over a dish of it and squeeze some upon them from a
pledget of absorbent cotton.

§ I. General Topography of the Sheep' s Brain. — Determine the
regions and aspects as follows :

a. As a whole the brain is obviously symmetric, i. e.^ composed of
right and left halves approximately identical, notwithstanding artificial
differences due to injury during removal from the skull or to distortion
during hardening.

b. The two ends differ, in that one presents a single, mesal or azy-
gous projection, the remnant uf the myel (spinal cord), while at the other
there is a mesal notch between the two OLFACTORY BULBS ; the latter, of
course, is the cephalic end, and the former the caudal.

c. Of the two remaining aspects, the more regularly convex is dorsal.^
while the ventral \s irregular and presents several elevations and depres-
sions.

§ 2. Close the eyes, handle the brain, hold it in various positions,
and test the prompt recognition of the several regions by the touch.

§ 3. Great Divisions. — By a transverse depression the caudal fourth is
demarcated from the cephalic three-fourths. The former consists mostly
of the CEREBELLUM, the latter mostly of the cerebrum Note that the
cerebrum presents a mesal furrow^ while the cerebellum is highest at the
meson ; also that the cerebral surface is cut up into tracts, g^•res or GYRI,
by sinuous furrows, fissures, while the cerebellum presents several series
of jiarallel narrow ridges, FOLIUMS, and alternate short furrows, rimulas.
a. The human cerebellum presents a furrow between two lateral masses, but with
most mammals the form is more nearly as in the sheep.

§4. Make an outline drawing of the left side of the entire brain,
natural size, indicating the following features :

a. The irregular ventral outline, which at present serves merely as
a base-line for the rest and need not be accurately represented.

b. The convex dorsal outline,- with its abrupt cephalic and caudal
declivities, and the oblique furrow between the cerebrum and the cere-
bellum.

go Practieum VIII. The Sheep's Brain. . ^

c. The caudal projection of the myeh

d. The slight, cephalic e,\teiisioii of the left olfactor}' bulb.

e. The numerous subdivisions of the cerebrum and cerebelhim -need
not be indicated, but the following should be :

f. The line separating the foliated cerebellum proper from the
OBLONGATA constitu'ing the ventral portion of that region. '.

g. Two or three lines approximately parallel with the main outline
of the cerebellum, demarcating the mesal and one or two lateral series of
foliums.

h. On the cerebral region, a line beginning at the root of the olfac-
tory bulb and extending dorso-caudad to the middle of the length of the
cerebrum, then caudad and slightly ventrad. The convoluted mass dor-
sad of this line is the cerebrum proper, pallium or mantle ; the ventral
portion, although sometimes corrugated in parts, is not stricth' convol-
uted, and — from its direct continuity with the olfactory bulb — is called

the OLFACTORY TRACT.

§5. Make an outline, uatural size, of the base or ventral aspect of
the brain. PL XIX may be employed for comparison, and for ascertain-
ing the names of parts, but the drawing should represent the specimen.
The following order will be found most available :

a. Represent the meson by a straight line the length of the brain,
but light enough to permit portions to be erased later; then the lateral
outlines of the whole and tlie boundary between the cerebral and cere-
bellar regions.

b. All the parts and lines already noted from the lateral aspect, the
olfactory bulbs and tracts and their lateral bonndaries ; the lines between
the cerebelhnn and the oblongata.

c. Tlie PONS, a bridge-like mass whose elevated cephalic margin
corresponds with the boundary between the cerebral and cerebellar
regions and which, laterad, is evidently continuous with the cerebellum.

d. The mesal furrow upon the cephalic part of the cerebrum is in-
terrupted abruptly by an x-shaped elevation, the chiasma. On PI. XIX
is seen that the cephalic diverging arms of the x are continued laterad to
the eyeballs ; they are the optic nerves. The caudal arms, less distinct
in the actual specimen, are the OPTic tracts.

e. Between the chiasma and the pons should be a mesal, sub-splier-
ical mass, the HYPOPHYSIS, as shown in PI. XIX, connected with the
base of the brain proper at three or four points ; the most important of
these attachments is at the middle of the cephalic border.

In the actual brain any one of the following conditions may exist :
I. The hypophysis may be cut, torn by the saw, or flattened by
pressure. 2. The mesal pedicle above mentioned may present an artifi-
cial orifice through which preservative was injected into the cavities of
the brain. 3. The entire hvpophysis may be cut or torn off, leaving a
mesal orifice, the lura, as in PI. XX.

/ In the interval at either side of the hypophysis is the CRUS, a
column-like mass, overlapped laterad by the margin of the olfactory
tract, and caudad emerging from entad of the pons.

§ 6. The Arachnoid. — The outlines of the parts just mentioned are
somewhat vague. If the brain be supported on the fingers of both hands,
and the thumbs be placed on the widest and most prominent part of the
olfactorv tracts (corresponding, on PI. XIX, to the letters / 0 rji/ on one
side and on the other to the area laterad of the numbers 4 and (5), and the
parts be pressed alternately laterad and me.sad, there will be recognized a

Practieum VIII. The Pia, Vessels, and Nerves. SI

slieet of membrane which is alternately tense and wrinkled. This mem-
brane is the ARACHNOID.

§7. The Subarachnoid Space. — At the (real) left of the hypophysis,
with the forceps tear the arachnoid ; there will be disclosed an interval
between it and the apparent surface of the brain ; the subarachnoid
SPACE. Note similar conditions in the following localities : {a) In the
triangnlar interval between the crns, the pons, cerebellum, and cerebrum ;
{b) in the deeper interval between the cerebrum and cerebellum when
the latter is tilted caudad ; (r) between the two halves of the cerebrum ;
[d) between the dorsum of the m\el and the overhanging cerebellum ; {e)
between the margins of the olfactory bulbs and the adjacent cerebral sur-
face ; (/) along the lines of the principal fissures and rimulas.

Upon the intervening areas the arachnoid may be recognized as con-
stituting the surface, but as adhering closeh' to what is subjacent.

g8. The Pia. — After the removal of the arachnoid from tlie crus at
the left of the hypophysis there will be disclosed BLOOD-VESSELS and a
fibrous, delicate sheet of tissue, the pia, which adheres quite closely to
the brain substance. To facilitate this examination the hypophysis may
now be pulled off. The pia will be seen to follow closely all the contours,
and to dip to the bottom of the mesal cleft caudad of the elevation,
TUBER, wiiich supported the hypophysis.

a. In the first edition this was called torus. Tuber is to be preferred
as a simple reduction of the name commonly emploved, tuber cinereum.

§9. The Blood-vessels of the Pia. — The decided resistance to the
removal of the pia at this point is due to the considerable number of ves-
sels which leave it and enter the substance of the brain. With a lens mav
be recognized the holes (vascular foramina) transmitting these vessels,
whence the names given to the triangular area, posTCRIBRUm and "pos-
terior perforated space." With less ease, all surfaces denuded of the
pia may be seen to be finely punctate, as if by pin pricks, and the ental
surface of the pia to present a woolly aspect called tomentum, from the
large number of broken vessels ; see Handbook, VIII, Fig. 4687, and § 11.

§ 10. The Cranial Nerves. — Upon the lateral part of the pons is a
fibrotis cord resembling the optic nerve ; it is the rojot of the trigemin-
us (trifacial or fifth), the sensitive nerve of the teeth and skin of the
face, etc. If pushed from side to side it will be seen to really emerge
from the brain just caudad of the pons or perhaps through its caudal mar-
gin ; in man it emerges nearer its cephalic margin.

a. The other cranial nerves are smaller and apt to be detached with the pia, but
traces of them may be seen at either side of the oblongata. One, the oculo-motor, springs
from the crus near the mesal cleft ; on PI. XX a short piece of it is shown on one side (the
real left, apparent right) ; on the other the slit left by its extraction is marked j. Another
cranial nerve, the troclilearis. is represented on PI. XXII, 4.

Note. — If there is but one brain available, follow the directions in ^ 11 upon it ; if two,
upon the second follow the directions in (! 12. Adjoining students may agree which they
will respectively follow.

§ II. Alba and Cinerea. — With the large scalpel, dipped in alcohol,
slice off the dorsal half of the cerebellum, avoiding injury to the cere-
brum. The cut surface will present two colors, the ental parts lighter,
the ectal darker. The former is the alba, composed of fibers only ; the
latter the ciNEREA, consisting of fibers and cells. If the alba does not
extend across the meson renioxe a thin slice until it does. Make a dia-
grammatic drawing, indicating the general outline and the tree-like
branching of the alba toward the peripher\'.

B2 Practicum VIII. The Alba and Cinerea. '

§ 12. Slice oflf the caudal third of the cerebellum, avoidino- injury
to the oblongata, then the cephalic third, avoiding injury to the subjacent-
parts.

§13. The Cerebral Alba and Cinerea. — Slice off the dorsal fourth.
of the cerebrum. Not more than the dorsal fourth should be removed at
the first section. The largest available scalpel should be selected, the
blade dipped in alcohol, and the cut made with a slow and steady sawhig
movement. The plane of section should be nearly parallel with the long
axis of the cerebrum and if either end is farther ventrad than the other
let it be the cephalic.

b. . On either cut surface note the relations of the alba and cinerea ;
here, as also in the cerebellum, these are sometimes called more specifi-
eally medulla and cortex. The cortex forms a continuous ectal layer
as in PL XVIII, following the fissures.

a. The detached areas of cinerea represent portions of the cortex
at the bottoms of fissures that open on the dorsum.

b. At the ends of the mesal (intercerebral) fissure, note the arach-
noid crossing from one hemicrebrum to the other ; near the caudal end is
an orifice corresponding to i in PL XXIII.

c. Divaricate the two halves of the removed piece and note that the
mesal surfaces are covered by the pia which also dips into the fissures.

§ 14. Exposing the Callosiim. — On Plates XVIII and XXIII note
the location and extent of the callosum, the great cerebral commissure.
Note also on PL XVIII the directions of the several oblique surfaces b
and c which are approximately at 45° with the surface a.

§ 15. Apply the scalpel across the middle of the length of the left
olfactory bulb and slice oif the cephalic end of it and of the left cerebrum.
If the piece comes off freely or adheres only by the pia, then transect the
other at the same level and angle. But if it hangs to the opposite side by
any nervous substance, the cephalic end or genu of the callosum, the
right cerebrum and bulb must be cut a liltle farther cephalad so as to
clear the genu entirely. Remove the caudal ends at a similar angle, so as
to present the surfaces <:, and expo.se the splenium.

§ 16. The narrow surfaces d^ at either side of the meson, must be
cut with extreme care. From PL XXV, especially from the enlarge-
ment of part of it, it will be seen that at the bottom of the mesal inter-
cerebral FISSURE is a slight lateral extension at either side, the cal-
LOSAL FISSURE. In making the cuts the object should be to remove the
apposed mesal portions of the two cerebrums just to the level of the cal-
losum and as far laterad as the callosal fissures extend so as to expose the
free dorsal surface of the callosum in its entire width. The convexity of
the tracer may be used to advantage in lifting from the callosum the
overhanging edges, and these may be more safely trimmed afterward.

a. The oblique narrow surfaces e and/need no special directions ;
but even when tliey are cut, in order to see between the cephalic ends of
the cerebrums it will be necessary to divaricate these slightly and to
remove the arachnoid and pia, perhaps even a slice of the cortex at either
side.

? 17. Labeling the Bi'ain.—V pon a bit of paper as long as the greatest width of the
cerebrum and about half as wide, write zvii/t pencil or India iniz (common writing ink is
washed out by alcohol) your name, the number of the practicum section (thus Pr. II) and
the number of the window (thus, W. VII). With a small pin at either end attach it across
the brain about in the position of the word cerebrum in PI. XVIII.

Practicum VIII. The Encephalic Segments. 53

S i8. Study of the Eiiceplialic Segments. — Refer to tlie leclure in
wliich the segmental constimtion of the brain is presented as a funda-
mental conception of the organ.

S 19. So far as possible each student should make enlarged drawings
of the following preparations. They should be kept wet as directed in
the initial Caution.

§ 20. Frog'' s Brain^ entire^ exposed by removing parts of the head on
either side. — The dark disk at the side of the head is the tympanodisk
{7)iembrnna tympani), which in this animal is at the level of the rest of
the skin since there is no ectal ear ; Pract. VI, § 29.

a. Recall what was said in the lecture as to the e.Kceptional mesal
fusion of the olfactory bulbs in the tailless Amphibia (frogs and toads).

b. The real conaritim is attached to the cranium and was removed
therewith ; the dark mesal mass that might be taken for it is a plexus.
The caudal region of this brain is obscured by the metatela ; see § 21.

§21. Second Frog^ s Brain., Lacking the Metatela. — Only the caudal
half of this need be drawn, showing the sides and floor of the large tri-
angular cavity, metacgelE (corresponding to the greater part of what is
commonh- called the "fourth ventricle") and the narrow cerebellum
which was hidden in the other specimen by a cephalic protrusion of the
metatela.

§22. Dissected Sheep's Brains^ such as are Represented in Plates
XX-XXII. — -The descriptions of these figures should be studied carefully
in advance. The drawings should be twice the natural diameter of the
specimens and should represent them rather than mere copies of the cor-
responding figures.

§23. After the outlines of the dorsal aspect (PI. XXII) are made
satisfactorily the surfaces may be distinguished as follows :

a. The cut or artifical surfaces may be left blank, or the oblique
ones shaded slightly.

b. The natural surfaces that were covered by pia may be colored
red.

c. The other natural surfaces are covered by the endyma, which
lines the cavities and may be colored yellow, £•. ^.,'the caudatum, its
CAPUT and cauda, and the habena just at the side of the mesal diaccELE.

d. A sharp red line may be employed to indicate the cut edge of a
pial or ectal surface, e. g.., at the left of the cerebrum.

e. A yellow line may represent the cut edge of an endymal or ental
surface, e. o-. , along the lateral margin of the caudatum.

f. Where the pia and endymal have been in contact and have been
cut or torn away leaving a sharp or ragged edge of membrane, a ripa, e.
g. , there should be parallel red and yellow lines.

g. The cerebral and cerebellar cortex may be indicated by a slight
shading or b\- a more appropriate gray color.

PRACTICUM IX. THE MESAL ASPECT OF THE SHEEP'S BRAIN.

PLATES REQUIRED, XXIII, XXV.

S I Inevitable Imperfection of the Specimens. — -An absolutely perfect
condition of both mesal aspects of a medisected brain could only result
from the combination of tlie following conditions :

A. The brain was normal.

B. It was hardened with neither deflection of the long axis nor tilt-
ing of the cerebellum to one side.

C. It was divided accurately upon the meson throughout its entire
length and height.

a. Reference to Plates XXIII, XXIV, XXV, will show that the
chances are against the passage of the knife exactly between the apposed
surfaces without cutting either, and against the cutting of azygous parts
precisely at the meson. For example, in PI. XXV, near the center, is a
dorso-ventra) dark area representing a narrow cavity, the pseudoccELE,
bounded at either side by a thin lamina, the hemiseptum. The actual
parts are onlv one-fourth the dimensions in the lower figure. If, instead
of bisecting the pseudocoele the knife should pass a very slight distance
to the right or left of the meson, then, at that point, in place of two nat-
ural surfaces would be two cut surfaces ; and if it should pass still farther
laterad, it would open the cavity at the other side of the hemiseptum so
that one-half of the brain would present a surface and the other a cavity;
this would be confusing enough, yet it is only one of many possible and
even probable conditions.

b. Indeed the happy combination indicated in ? i has not occurred in the writer's
experience. He has found that practically the best plan has been to cut a trifle laterad of
the meson, preferably to the left, then to shave ofi" from the right half the parts of the
left that adheres to it ; in other words, one-half of the brain is sacrificed to the other.

c. Even with this method the result is uncertain ; the specimens submitted to the
class at this practicum have been selected from several hundred. They must be studied in
turn by all the members of the class ; hence they should be handled with great care. In
lifting place the fingers and thumb upon the ventral and dorsal surfaces respectively ;
make no pressure upon the mesal parts ; keep them, andindeed the entire specimen, con-
stantty wet with alcohot.

% 2. The good meson may be either right or left, preferably the
former for readier comparison with the wall-maps of the sheep, cat,
human and chimpanzee brains and with the figures. But in addition
there are a right and a left half-brain, with poor mesons. Even if they
are not really mates, i. e., halves of the same brain, they will serve cer-
tain purposes in this practicum, and may be handled more freely, but still
with care.

§3. Appose the mesons of the two half-brains, and review the
base or ventral aspect in comparison with Plates XIX and XX. The
HYPOPHYSIS has been removed ; in the midst of the TUBER, the slight
elevation to which it was attached, is a mesal orifice, the lura, resulting
from cutting or tearing off the stem of the hypophysis.

The lura leads dorsad into a shallow depression in the mesal surface,
(PI. XXIII, diacoele), indistinct in one, perhaps both, of the poor half-
brains, but more or less distinct in the good preparation. Trace this
depres.sion dorsad and then caudad, and note that in the region of the

Praetieum IX. The Encephalic Segments. SS

GEMiNA, the MESENCEPHAL, its depth, /. e.^ its lateral diameter, is some-
what greater, while its dorso-veiitral diameter is less ; it is thus a furrow,
and of course with its opposite constitutes a sub-cylindrical tube, the
MESOCCELE, often called the aqueduct. .Its relation to the gemina ma)- be
seen also in the transection of this region, corresponding with the line
D-D across PI. XXIII.

§4. The detailed stud}- of the encephalic meson may conveniently
follow this order :

a. Recognizing the larger masses.

b. Recognizing the six segments.

c. Determining the continuity of the mesal cavities.

d. Determining the complete circumscription of the cavities.

e. Discriminating between the several kinds of surfaces and cut
edges.

f. Drawing the specimen in hand.

g. Comparing the parts visible at the meson with the same as seen
in transections ; to be done at Pract. XI.

h. Comparing the mesal aspect of the sheep's brain with that of man
and other animals.

§ 5. Promment Pai-ts. — At Pract. VIII were seen the cerebrum,

CEREBELLUM, OLFACTORY BULB, PONS, CHIASMA and HYPOPHYSIS ; also,

upon removal of the dorsal part of the cerebrum, the mesal part of the
CALLOSUM.

§6. The Segments. — a. The entire cerebellum, pons and preoblon-
gata (cephalic part of the oblongata) constitute the epencephal.

b. The rest of the oblongata, postoblongata, is the metencephal.

c. The MESENCEPHAL includes the crura, postgeminum and pregem-
inum.

d. The DIENCEPHAL is represented by the Inpophysis and adjacent
parts, the conarium and adjacent parts, and the medicommissure connect-
ing two considerable masses, the thalami, seen in PI. XXII.

e. The cerebrum constitutes the prosencephal.

f. The Rhiiiencephal comprises the olfactory bulbs and their crura ;
also parts of the olfactory tracts, of the precommissure and of the aula
which are commonly regarded as constituents of the cerebrum.

g. The segmental constitution of the brain is discussed in the lectures on the develop-
ment of the organ : See Anat. Teclinology, p. 405 and Handbooli, -VIII, p. 114 and IX, p.
loi, for admissions of the modification of the writer's views upon the subject.

§7. The Mesal Cavities. — These are indicated on PI. XXIII by the
darkly shaded area ; their forms are more fully exhibited in Handbook
Fig. 4703.

a. The cavity of the myel is a slight, cylindrical canal, the myrl-
OCCELE (not named in PI. XXIII).

b. The METACCELE is slightly higher and (as will be seen later) con-
siderably wider.

c. The EPiCCELE has a marked dorsal extension into the cerebellum.

d. The MESOCCELE is tubular but curved and somewhat irregular.

e. The diaccele, surrounding the medicommissure, is irregular,
narrow, but extensive in the other directions.

f. In this view of the brain the prosoccele is represented only by
the AULA, a small space cephalad of the medicommissure, at the dorsal
end of the slight, curved furrow named aulix. But if the preparation be
held obliquely there will be seen a narrow passage, the porta, leading
latero-cephalad into the paraccele (lateral ventricle) of tliat side ; this
will be exposed at the next praclicnm.

56 Praetieum IX. The Coelian Parietes. \

g. Small as is the aula a part of it constitutes the mesal division of
the Rhmoccele, the larger portions being hidden within the olfactory
bulbs.

§8. Ccelian Parietes. — The walls of the brain cavities, ventral, lat-
eral, and dorsal, are comparable with floors, sides and 7'oofs.

a. Beginning with the mesoccele the crura constitute a substantial
floor. At the meson the roof is of moderate thickness, but at either side
the geminal lobes are massive.

§9. The preoblongata is reinforced by the pons. Part of the epiccele
is a dorso-ventral extension into the massive cerebellum. But if the cer-
ebellum be tilted slightly laterad (more freely is the extra half-brain), its
cephalic part will be seen to overhang a thin lamina, the lingula, which
is the true roof of the cephalic part of the epiccele, and which is contin-
uous with the VALVULA, a similar thin portion of the mesoccelian roof.

§ 10. The floor of the metacoele is obvioiis. Its roof is even thinner
than the lingula. If the cerebellum of the extra half-brain be tilted
latero-cephalad there will appear a membranous sheet, continuous
caudad with the roof of the myelocoele, and cephalad attached to
the cerebellum at some point on the caudal wall of the dorsal extension
of the epiccele. This metateLA consists of the pia. which follows the
ectal contour of the parts, i;nited with the endyma that lines the cav-
ities.

§11. The diacoelian floor is variously constituted. The tuber, to
which the hypophysis is attached, is thin ; but caudad is the prominent
albicans, and cephalad the chiasma ; dorsad of the chiasma is another
thin portion, the terma {lamina tertninalis). The terma is so thin that
even when it has escaped injurv in the medisection of the brain it may
not be readily recognized unless three points are borne in mind : i. Its
direction is dorso-caudad ; 2. It starts from the dorsal surface of the
chiasma rather nearer its cephalic margin than is represented in PI.
XXIII ; 3. Dorsally it is continuous with a distinctly oval thickening, the
PRECOMMissuRE, opposite the middle of the medicommissure.

§ 12. The diacoelian roof is irregular in direction and varions in com-
position, and will be most easily traced from the end next the mesence-
phal. The conarium has already been recognized (§6) between the pre-
geminumand the splenium, the caudal end of the callosum. By gently
moving its caudal end, its ventro-cephalic angle will be found to be con-
tinuous with the mesoccelian roof b}' a curved and corrugated lamina, the
POSTCOMMissuRE. Just dorsad of this is a short triangular recess in the
substance of the conarium. If the parts are examined closely, especially
with a lens, the opposite boundary of this recess will be recognized as a
subcyliudrical lamina, the supracommissure. Just dorsad of this will
be seen a membrane, the diatela, represented in PI. XXIII by a white
line. Really the ventral ental surface of the diatela presents a series of
ridges constituting a fringe, the diaplexus. Traced caudad the diatela
will be found to form a sort of pouch on the dorsal side of the conarium ;
it appears to be attached near its tip, as shown in PI. XXIII, but ma\'
commonly be detached nearly or quite to the supracommissure. Traced
cephalad the diatela will be found loosely attached to the parts dorsad of
it until, at a point dorsad of the middle of the medicommissure, it is no
longer separable easily.

§13. The Lateral Boundary of the Dorsal part of the Diac^sle. —
Excepting, perhaps, the metacoele the cavities so far inspected present not

Practieum IX. Coelian Circumscription. S7

only floors and roofs but definite and continuous sides. But the middle
portion of the dorsal part of the diaccele seems, at first sight, to extend
laterad indefinitely upon the dorsum of the thalamus, and if the student
is already aware that each cerebrum contains a cavity, the paraccele
(lateral ventricle), he may well infer that here is a direct communication
therewith.

Since this idea is rank morphologic heresy, the parts should be
examined very carefully.

§ 14. Hold the less perfect extra half-brain in the left hand ; press
the left thumb firmly against the mesal surface of the mesocoelian floor
(PI. XXIII crura) ; place the tip of the scalpel handle (or similar smooth,
dull instrument about i cm. wide) ventrad of the middle of the diatela,
and press it against the parts dorsad of it ; increase the pressure very cau-
tiously until it can be seen that, at the distance of 2-3 mm. from the
meson, the diatela unites with the dorsum of the thalamus and the diaccele
is there limited ; compare Plates XXII and XXV.

a. But when this line of attachment is traced cephalad it will be
found to cease dorsad of the cephalic slope of the medicommissure. From
this point cephalo-ventrad nearly to the level of the precommissure there
is evidently a passage extending laterad ; thi.'^ is the PORTA, (foramen of
Monro) and the cavity into which it leads is the paraccELE (lateral ven-
tricle) to be examined later. The mesal cavity between the two ]3ortas is
the AULA, the small mesal division of the prosocoele, the general cavit}'
of the prosencephal ; see Handbook Fig. 4703. The roof of the aula is
not the diatela but the mesal part of the fornix, /cw. in PI. XXIII, to be
examined later.

§ 15. The Crista. — ^Just dorsad of the precommissure is a slight
rounded elevation, the crista. If the plane of section has coincided
with the meson it will appear as in PI. XXIII ; but it has passed sinistrad
of the meson, with a right half it may remain entire.

§ 16. The Habena. — Just cephalad of the conarium is a low ridge,
widest and most distinct caudad, but becoming both narrowt-r and fainter
it extends dorsad, cephalad and laterad along the dorsal slope of the
thalamus ; this is the habena. If the supracommissure is examined
with the lens it will be seen to be a transverse band connecting across the
meson the dorsal parts of the caudal ends of the two habenas.

§ 17. Coeliaii Circumscription and Endymal Continuity. — From the
examination just concluded it ina)- be seen that the mesal series of cavi-
ties is circumscribed by continuous parietes, floors, end, roof and sides,
covered by the lining endyma ; also that this circumscription would still
be maintained even were most of the eerebrtim and cerebellum removed.

§18. The Surfaces that Appear upon the Mesal Aspect. — The two
kinds are natural^ and artificinl ox cut The roof of the mesocoele furn-
ishes an example of each. The shaded area represents the mesal slope of
a lateral .convexity, the right half of the pregeminum. The unshaded
area just dorsad of the mesocoeie represents the depressed roof between
the lateral masses, which was divided by the medisection. All the other
unshaded areas represent cut surfaces; e. g., cerebellum, medicommis-
sure, hypophysis, etc. Certain jiarts that are distinctly fibrous are indi-
cated by dots, e. g., the callosum, pons, chiasnia.

The divisions of the cerebellum ifoHums) are not shown, and neither here nor else,
where has the cinerea (gray nervous substance) been distinguished from the alba, except-
ing that the fibrous parts indicated by dots are of course alba (white nervous substance)-
The color difference between the alba and cinerea does not appear distinctly upon alco-

58 PracLicum IX. Endymal Continuity.

holic specimens ; the distinction of the two kinds of substance may be observed to better
advantage upon brains hardened in formalin or in potassium dichromate, to be exam-
ined at Pr. XI.

§ 19. With one exception (to be considered presently) the nat.ural or
uncut surfaces are of two kinds : endymal^ enlal or entocoelian, and pia/,
ectal or ectocoelian.

a. The first includes all the true encephalic cavities whose circuni-
scription has been traced already (S8j. The lining membrane is smooth
and in certain lights sliining. The difference between the endymal sur-
face and a cut surface may be seen b)- comparing the mediconimissure
with the slighth' depressed area surrounding it.

b. The triangular, shaded area just ventrad of the cephalic three-
fifths of the callosum represents the hemiseptum, the lateral wall of the
narrow mesal cavity, pseudocoele (fifth ventricle). This cavity has no nor-
mal communication with the true encephalic cavities, and is cut off from
the ectal, pial surfaces by the pia which extends from the rostrum, the
tip of the callosum, to the crista ; so far as the writer is aware no mem-
brane of any kind has been recognized upon the surface.

c. All ihe other natural surfaces are covered by pia. For its char-
acter and relations see Pract. VIII, §8 If time permits it may be traced
over all tiie parts, in close contact with them.

§20. The Cut Edges of Metnbranes. — The cut edge of the endyma
is indicated on PI. XXIII by the continuous black line at the ental margin
of all the divided parietes. So much of the endyma, however, as consti-
tutes the ental layer of the diatela is represented by the corresponding
halt of the light line. The pial edge corresponds, for the most part, to
the ectal margin of all the divided parietes. In the metatela it and the
endyma are practically one. On the lingula, valvula and terma it is not
easily separable without tearing those attenuated parts. Opposite the
middle of the medicommissure, instead of following the line of the im-
mediate roof of the cavity, it is deflected to the tip of the callosum, the
rostrum, passes over the genu, along the dorsal side of the callosum,
dipping into the callosal fissure. It then passes about the splenium to the
ventral side of the fornix [fern.) continuing as far cephalad as the point
where the diatela cea.ses to be attached, the dorsal end of the porta (§ 14,
a). Here it turns upon itself, and becomes united with the endyma to
form tlie diatela.

§ 21. The Velum. — From the foregoing it will be seen that between
the diaccele and the ventral surface of the fornix and splenium there are
two layers of pia, continuous cephalad but diverging caudad. One be-
longs to the diencephal, the other to the overhanging cerebrum ; the two
layers of pia, with the vessels between them, are commonly called the
VELUM, but it must not be forgotten that the closer junction of the ven-
tral laver with the endyma constitutes the diatela. The relations will be
clearer when PI. XXV is studied.

§ 22. Drawirtg the Mesal Aspect. — The specimen in hand is to be
drawn, enlarged two diameters. PI. XXIII and the foregoing text maybe
used for reference and comparison, but the figure is not to be copied. The
following method will be found convenient :

a. Support the specimen in a small dish or upon a bed of cotton,
(or cloth, or Japanese napkin) so that the meson is nearly at an angle of
45° with the table and thus nearly at a right angle with the line of vision.
L,et the length of the callosum be nearly horizontal.

/;. Keep the specimen wet with alcohol. If by inadvertence it act-

Practieum IX. Drawing the Meson. 59

ually becomes dry, call the assistant's attention to it, and immerse in
water for a few moments.

c. Make four light horizontal and parallel lines twice the length of
the brain, coinciding respectively with the dorsal convexity of the cere-
brum, the ventral convexity of the pons, the dorsal margin of the cal-
losum and the ventral margin of the medicommissure. At right angles
to these make three perpendicular lines coinciding respectively with the
cephalic convexity of the cerebrum, the caudal convexity of the cerebel-
lum and the caudal margin of the medicommissure. The intermediate
line will be very nearly in the middle of the length of the brain. By
measuring with the dividers double the distance of any point from the
places of intersection considerable accuracy may be attained.

§ 23. The cavities should be outlined first and fully their natural
dimensions, twice enlarged ; that is, since these spaces at most are rather
slight, while the encompassing masses are considerable, the latter may
be diminished with less risk of obscurity in the drawing.

a. The callosum and medicommissure should be outlined first ;
although often nearly circular, as in PI. XXIII, the latter is by no means
always so, being sometimes oval or elliptical.

b. Next the floor of the mesal cavities ; if as is commonly the case,
the hypophysis has been removed, it may be omitted or copied from the
figure.

c. Then the roof of the mesoccele ; the ental line should be sharp
and clear to represent the endyma, the ectal line of the cut surface not
quite so heavy, but distinct, to represent the pia. The convex outline of
the geminums should be light, and the intervening pial surface indicated
later by light shading. If the three kinds of sui faces — cut, pial and en-
dymal — are not at first easily discriminated, hold the specimen so that the
light strikes successively at diff^erent angles.

d. Next the thin lamina, valvnla and lingula, roofing in the com-
municating portions of the mesoccele and epicoele. Observe the caution
given in § 9 and get these parts from the less perfect specimen ; their
precise thickness may not be worth taking time to ascertain, but the two
lines representing the pial and endymal coats of the lingula should be
about as near together as they can be and yet be distinguishable.

e. The myeloccele (central canal of the myel) is seldom visible for
any distance in medisected brains unless special pains have been taken to
expose it ; if the section has passed to the side opposite that to which the
specimen belongs, the continuation of the metacoele with the myeloccele
may sometimes be seen as a funnel-shaped orifice by looking obliquely
latero-caudad at the extremity of the metaccele ; the presumed continua-
tion may then be represented by two parallel, interrupted lines.

f. The membranous metatela (§ 10) is shown in PL XXIII as a sin-
gle line representing the union of the endyma with the pia which is
reflected from the dorsum of the myel upon the ventral surface of the
overhanging cerebellum ; the place of reflection is located in the figure at
the angle between the ventral surface of the cerebellum and the dorsal
extension of the epiccele ; but in some — perhaps most — specimens the
membranous lamina may be traced for some distance dorsad of this angle ;
there may not be time to ascertain the condition in the specimen, but an}-
doubt may be recorded.

g. The dorsal extension of the epicoele should be given its full
width or even more.

§ 24. The mass of the cerebellum may now be outlined. Unless
there is plenty of time a single line, as in PI. XXIII mav suffice. But if

60 Praetieum IX. Drawing the Meson.

there is opportunity for elaboration later, there may be introduced some
of the foliums between which the pia dips in folds ; the first outline
might then represent the arachnoid which, as seen in Pract. VIII, passes
over the rimulas, bridges the interval between the cerebellum and the
cerebrum not far dorsad of the pregeminum, and passes from the caudal
convexity to the myel.

a. If preferred, as in PI. XXIII, the cerebellum may be represented
as if tilted caudad enough to exhibit more clearly the interval between it
and the cerebrum, but as this would involve shifting the oblongata also,
the same end may be attained by diminishing the width of the cerebel-
lum somewhat, or by reducing the length of the cerebrum ; the exacti-
tude of these dimensions is not essential for the purpose of the present
examination.

§ 25. The cut surfaces of the conarium, postcommissure and supra-
commissure may be outlined next ; the conarium may be made a trifle
smaller than it should be in case, later, room is lacking between it and
the overhanging callosum to show clearly the diatela as resulting from
the junction of the diacoelian endyma and the ventral layer of the velum,
and also tlie dorsal layer of pia which adheres to the callosum and fornix
(§20).

a. Besides the fringe-like diaplexus referred to in § 12 there may
appear the whole or part of the mesal vela?' vein (PL XXV) which passes
between the two layers of the velum and opens into a blood-sinus, the
depression caused by which is indicated in PI. XXIII by the shaded tract,
/, just caudad of the splenium. It may be better not to try to show this
vein.

§ 26. The heavy line representing the endyma should be continued
from the dorsal end of the porta (at about the letters yrw.) with slight
undulations to represent tlie crista and precommissure, to the chiasma
and so back to the tuber.

§27. The ectal or pial outline of the parts just named present no
serious difficulties, but care must be taken to discriminate between the
mesal cut surface of the chiasma and the retreating pial surface of the
optic nerve. The terma must be represented, like the lingula, by two
barely separated lines, diverging dorsad at the precommissure. At or near
the crista the pia makes a sharp turn cephalad to the rostrum and extends
dorsad of the callosum, while the outline of the fornicommissure extends
in the opposite direction.

§28. The fibrous constitution of parts like the callosum and pons
may be indicated by dots. In some, even alcoholic, preparations, the cut
surface of the cerebellum may present traces of the color diflTerence be-
tween the alba, radiating from near the epiccele as larger and smaller
branches and fringes, and the cinerea constituting a rather thin cortex at
the periphery of the foliums ; if so the cinerea may be shaded lightly.

§ 29. The mass of the hemicerebrum, which might naturally have
been drawn first, is to be last done, together with the olfactory bulb. The
fissures may be shown as lines, preferably red, to indicate the folds of
vascular pia that dip into them. Strictly, the callosal fissure also should
be so represented, but if so, just ventrad of it the ctit edge of the pia cross-
ing the meson should appear as a narrow black line.

§30. The Arachnoid. — Since, as seen in Pract. VIII, §§6, 7, the
arachnoid bridgfes the intercerebral fissure, leaving the mesal surface of

Praetieum IX. Comparison with Man. 61

either cerebrum near its dorsal margin, its cut edge should be shown as a
delicate line along the curvature ; it may be seen more distinctly if the
specimen be placed in alcohol or water deep enough to just cover the
meson. The writer has not yet traced completely the arachnoid line
upon a medisected brain.

§ 31. Shading. — When the outlines are satisfactory then the natural
surfaces, both pial and endymal, may be lightly shaded, the recesses and
intervals more heavily, approximately as in PI. XXIII. All the cut
edges of pia and endyma sliould be shown as distinct lines.

§32. Continuity of Membrane Lines. — The continuity of the en-
dyma has been mentioned in § 17 ; the same is true of the pia ; i. e.,
starting from any point, the pia may be traced caudad to the cut end of
the mvel ; then cephalad, and dorsad or ventrad as the case may be, and
again caudad to the other margin of the myel.

§33. Coloring. — This endymal and pial continuity may be more
readily recognized upon the drawing if the cut edges of the endyma are
represented by yellow lines and those of the pia by red. The fissures
also, as containing folds of the vascular pia, may be made red ; if so,
the extent of the callosal fissure may be indicated by a thickening of the
red line corresponding therewith. The metatela and diatela will require
red and yellow lines in contact.

§ 34. Comparison of the Mesal Aspect of the Sheep'' s Brain with that
of Man. — For this purpose there should be actual specimens, prepared in
the same way as the sheep half-brains ; but the difficulties presented by
the sheep brain are far greater with the human ; indeed the writer has
never seen an even approxiinately perfect preparation. The best speci-
mens in the museum are reprsented in Handbook figures 4684, 47 11 and

4718 ; copies of the first and third are supplied to the class ; see also the
wall-map enlargement of the first.

§ 35. The student should note for himself, as concisely as possible,
the more obvious differences in proportion, relative position, form, etc.,
beginning with those of a more general character. The fissures need not
be considered.

The following differences might escape notice from the imperfections
of the figures, but the\' merit attention as relating to known or presumed
peculiarities of the human brain, shared in some cases, perhaps, by those
of the apes :

a. The interruption of the metatela, constituting the metapore ;
this is considered in the description of the figure ; see Handbook Fig.

4719 and Vol. IX, Fig. 422.

b. The presence, on the dorsal side of the lingula (§ 9 ) of three or
four ridges, indicated in the figure by the serrated outline ; see Handbook
Fig. 4719 and Vol. IX, Fig. 422.

c. The smallness of the medicommisstire in man ; most of it is cov-
ered by the word diencephal ; see Figs. 47 11 and 4718.

d. The extension of the rostrum of the callosum so as to be contin-
uous with the terma just dorsad of the precommissure, thus completely
circumscribing the pseudocoele by nervous tissue ; this is clear in Figs.
47 1 1 and 4718, but in Fig. 4684 the extension, copula., is obscured by
names.

e. The olfactory bulb and cms are hidden by the depth of shading,
but their smallness mav be seen in Figs. 4718 and 4689.

f In man there are two albicantia, as seen in Figs. 4689, 4712 and

62 Praetieum IX. Comparison with Man.

4738. Hence a medisection passes between, and the retreating convexity
of the right one should appear as shading, as in Fig. 471 1.

g. ' Between the dorsal portions of the two hemicerebrums projects a
fold of dura, the/a/,r. Fig. 47 11. This carries before it the arachnoid and
hence the cut edges of the latter follow the ental margin of the falx in-
stead of lying near the dorsal margin ; it is faintly indicated in Fig. 4684
by the interrupted line J.

PRACTICUM X : DISSECTION OF THE SHEEP'S BRAIN.

PLATES REQUIRED : XVIII-XXV.

§ I. At the best the time available at two ordinary practicums is
altogether inadequate for the demonstration and comprehension of the
macroscopic structure of the brain. All the exercises should be re-
peated wheu opportunity offers. Upon the transections many hours may
be profitably spent.

§2. For reference during this practicum and the next there should
be a good mesal aspect, as in PI. XXIII, and preparations such as are
shown in Plates XX-XXII and XXIV.

a. If two brains are available one may be dissected as directed below and the other
transected at the levels indicated by the dorso-ventral lines A — G upon PI. XXIII, and
elsewhere if desired.

b. If two students are working together and have each a brain, one may be used for
the transections ; of the second brain the left paracoele may be exposed by one and the
right by the other ; the non-dissector should watch and cooperate.

c. With modifications that need not be specified the following directions apply to
either half of a medisected brain.

d. Wherever the tracer is mentioned iu this practicum the syringotome would be
preferable ; Anat. Technology, Fig, 15 ; Ref Handbook, VIII, Fig. 4880.

§3. The Cerebellum. — From this may have been removed already
either the dorsal portion or the cephalic and caudal convexities, or all
three (Pract. VIII, §§ 11,12). On the lateral aspect, overhanging the pons
note several series of foliums. With the tracer push them dorsad. They
will easily break away from a stem of alba which is continuous ventrad
with the pons and extends dorso-caudad into the central alba of the cere-
bellum. This stem is the MEDIPEDUNCLE, designated in PI. XXI
by 7, but the number is very indistinct.

§4. The Metatela. — Depress the postoblongata and push the caudal
part of the cerebellum dorso-cephalad. If this is done cautiously and the
brain has been well prepared, there will be seen the metatela, the mem-
branous roof or the metacoele, Pract. IX, § 10, § 23 y^ But often it
adheres to the cerebellum so as to be torn more or less.

§ 5. The Lingula and Valvula. — These are to be exposed by tilting
the cephalic part of the cerebellum caudad, Pract. IX, §9, and 23, d ;
they too may be torn in the process ; but if now the cerebellum be cut off
almost at the level of the oblongata the entire metepieoele (fourth ventri-
cle) will be exposed, and by blowing from its caudal portion the lingula
and valvula may be demonstrated satisfactorily. There may also be seen
the apex of the metacoele where it narrows to become continuous with the
myelocoele ; also the lateral extensions of the cavity referred to in § 7, a.

§6. The Other Peduncles. — The prominent ridges at either side of
the valvula are the prepeduncles, connecting the cerebellum with the
geminums. The postpeduncles, extending ventrad and caudad to the
oblongata, are not distinct in the sheep ; see Handbook Fig. 4721.
The GEMINUMS have been seen in Pract. VIII, PI. XXII. Sometimes on
one or both sides there remains the slender trochlearis nerve (PI.
XXII) meeting its opposite in tiie valvula.

§7. The Flocculus. — Of the short series of foliums mentioned in
§3 the two farthest ventrad constitute 'On.^t flocculus. To isolate it, the
tiers farther dorsad must be torn away as directed in § 3. If it is pushed
caudad it will be seen to have a slender stalk of its own connected with
the caudal margin of the medipeduncle.

a. For details respecting the flocculus and the cerebellum see Dr.
B. B. Stroud's paper in the /ottr. of Comp. Neurology for June, 1895.

64 Praetieum X. The Paraeoelian Floor.

b. Just caudad of the flocculus and peduncle is a tufted plexus which covers. (and prob-
ably closes) a lateral extension of the epicoele The relation and significance of these parts
are still under investigation ; meantime consult Handbook Fig. 4702 and Vol. IX, p. 5i6.-~
If, as held by some, these lateral recesses open into a subarachnoid space, the general
statement in Pract. IX, § 17, must be qualified accordingly.

§8. Opening the Left Pai'acoele (lateral ventricle). — This is most
safely accomplished in its cephalic portion, the precoknu, where there is
but one mass that may be unintentionally injured by cutting too deeply.

a. If the cerebrum has not been sliced off as directed in Pract. VIII,
§§ 13-16, PI. XVIII, it should be now.

b. Be/ore 7naking any of the incisions here directed the scalpel should
be dipped in alcohol.

c. Note the location of the cephalic end, genu, of the CALLObUM,
Plates XVIII and XXIII, and bear in mind (i) that the cavity to be
opened is nearly at its level ; (2) that it is nearer the mesal than the lat-
eral margin of the hemicerebrum ; (3) that the near proximity of the cav-
ity may be recognized by the appearance of a dark area 2-3 mm. in diam-
eter about one-third of the way from the meson to the lateral border. This
dark area is not due to a difference in the color of the mass, but only to
the existence of the cavity.

d. From the cephalic slope of the left hemicerebrum (PI. XVIII b)
cut a triangular slice, the thicker end including a part of the surface a,
the thinner approaching the olfactory bulb, but not quite reaching it.
If this does not open the cavity, or expose the dark area mentioned in
(<:), remove a second but thinner slice, and, others if necessary till the
precornu is opened.

e. From Fig. 3, p. 69, and the dotted lines in PI. XXIV, note that the
precornu is continuous with the cavity of the olfactory bulb, but defer the
demonstration for the present ; Pract. XI, §8.

f Remove the "corner" between the surface a of PI. XVIII and
the new surface b so as to expose the cavity a little farther caudad. In-
troduce tlie tracer cautiously a few millimeters only and note that there
is a shallow cavity bounded by a roof and floor.

g. Carefully avoiding cutting the floor, remove successive thin slices
farther and farther caudad till the floor of the exposed cavity presents the
appearance shown in PI. XXIV. It may be neces.sary to remove a
wedge-shaped slice from the caudal end, c, and to use the scissors care-
fully at the mesal side of the cavity.

h. Since the cephalic part of the cavity extends not only laterad but
also ventrad there is a natural temptation to open the ventral extension
near the meson ; for the present this should be avoided.

§ 9. The Paraplexus. — In the middle of the floor of the paraccele is
a vascular fringe, perhaps lying flat as in PI. XXIV, perhaps in a more
compact roll. This is a fold of pia, with blood-vessels, all covered by
endyma, and constituting the paraplexus. How it gets into the para-
ccele is discussed in the lectures ; later in this praetieum (§ 21) its relation
to the velum will be shown. For convenience, at this stage, on the left
side so much of the paraplexus as can be seen should be trimmed closely
to its line of attachment, but not pulled upon.

§ 10. The Paraeoelian Floor. — The removal of the paraplexus ex-
poses the more substantial constituents of the floor, as seen in PI. XXIV.
Cephalad is the pear-shaped caudatum, the convexity of which really
looks quite as much mesad as dorsad. Farthest caudad is the hippocamp
{hippocampus major). Between it and the paraplexus is a less distinct
elevation, the fimbria.

Practicum X. The Medicor'nu. 65

a. The Cella. — The largest portion of the paraccele corresponds to what has been
called the CELLA {cellamedia) ; see Handbook Figs. 4703, 4740, 4746, Vol. IX, fig. 61, and
the preparations and photographs. In man there are three extensions of the cella : ceph-
alic, PRECORNU, ventral, MKDICORNU, and candal, POSTCORNU ; the last is wanting
in the sheep as in most other mammals. As to the human paratela,^ see 4 21, y.

S II. The Medicornu. — At tlie caudal end of the paraccele there is
evidently the beginning of a ventral extension, the medicornu. Intro-
duce the tracer for a few mm., on the left side, and remove a slice of the
caudal end of the hemicerebrum ; by constantly "feeling one's way"
and removing thin, wedge-shaped slices, it will be po.'^sible to follow this
horn-shaped extension of the paraccele ventrad, laterad, cephalad, and at
last even slightly mesad to the extremity of the elevation on the ventral
aspect of the brain which overlaps the optic tract and is numbered ./ in
PI. XIX.

a. The complete exposure of the medicornu will involve cutting
away a considerable part of the caudal and lateral portions of the hemi-
cerebrnm, as indicated in PI. XXIV. The convexity of the tracer mav
be used in pushing up the overhanging edges of the parietes so that they
may be more easily cut away with tlie scalpel or in some cases the scis-
sors. Toward the ventral end, the tip of tlie medicornu, especial care
must be taken not to pull or push upon the parts lest they break at some
of the thinner places.

b It will be found that the iiippocamp is not regularly convex as in-
dicated by PI. XXIV, but flattened slightly in places, and terminates as
a blunt point at the tip of the cornu.

c. Tlie fimbria maintains a nearly uniform width and surface.

d. The paraplexus continues to near the tip, and should be trimmed
closely, as directed in §9, but ivithoiit pulling ttpoji it.

e. The caudatum, as already seen (§ 10), tapers caudad ; there seems
to be some difference among the brains as to the extent of its cauda
along the medicornu. In the sheep the writer has not as yet recognized
the tenia of the human brain ; HavdbookVW\ 145.

f. Note that in potassium dichromate specimens, the fimbria and
hippocamp are light (alba) while the caudatum is dark (cinerea).

§ 12. Make a drawing of the dissection at this stage from the lateral
and ventral aspects. In combination with PI. XXIV they will illustrate
the notable changes in the direction or the cavity ; it extends success-
ively caudad, laterad, ventrad, cephalad and mesad.

§ 13. Tra7isecting the Right Medicornu. — In accomplishing this
there is to be removed a mass representing approximately the ventro-
latero-caudal eighth of the right cerebrum ; on PI. XIX the piece is
bounded as follows : Laterad and caudad by the general outline ; mesad by
the S-shaped mesal border of the olfactory tract, along the numbers j, /
and (5/ cephalad by an imaginary line drawn latero-dorsad from the chiasma.
The two incisions required to dislodge this piece are to be made as fol-
lows :

a. Hold the brain with the myel away from you and the ventrum
uppermost. With the scalpel point, from the depressed area just laterad
of the cliasma (PI. XIX, j), cut laterad and very slightly cephalad across
the olfactory tract and into the pallium for about the same distance, stop-
ping at the greatest lateral convexity of the cerebrum.

b. Turn the brain so that the right side is uppermost. Dip the scal-
pel in alcohol. Begin at the caudal margin of the cerebrum opposite the
flocculus. Push the point in for at least 2 cm. (nearly an inch) and cut
with a sawing movement to the lateral end of the first incision.

66 Practicum X. The Hippoeamp and Fimbria.

c. If the caudal end of the part ventrad of the incision be gently
elevated it may be detached ; the operation should be performed slowly
and the scissors used promptly for dividing any vessels that ma}- resist the'
separation ; all pulling should be avoided.

d. The detached piece is to be wet with alcohol, and handled with
great care, for reasons that will appear presently.

§ 14. From the undulating surface exposed by its removal remove
the tough and adherent pia, beginning at the margin of the pons, and
note that at the cephalic margin of the optic tract it ceases by an irreg-
ular edge, evidently torn. Compare the denuded parts with PI. XX I
where, however, everything is reversed, since it represents the left side.-

§ 15. Examine the concave mesal surface of the detached piece,
handling it as little as possible and note that its natural surfaces are also
covered by pia ; defer the removal of the pia till the cut surface has been
examined.

§ 16. On either cut surface (more conveniently on that of the de-
tached piece) the following features may be observed and a drawing made
if time permits.

a. Not far from the middle of the length, but nearer the mesal than
the lateral surface, a crescentic slit, its convexity directed laterad ; from
comparison with the leftside this can be nothing else than the transected

MEDICORNU.

b. The lateral wall of the cavity is consituted by the general mass
of the ALBA, but the convex mass at its mesal side is mostly cinerea, with
a cephalic edge of alba. Comparison with the floor of the left medicornu
.shows that these are respectively the hippocamp and the fimbria.

c. The cortex at the lateral side of the section may be traced caudad
over the end of the hemicerebrnm to the mesal side, with the usual undu-
lations at the fissures. For a short distance on the mesal side near the
caudal end it is thin, but thickens suddenly at the hippocamp.

d. Opposite the cephalic portion of the cut end of the hippocamp
is a slit which may be traced to the ventral end of the piece ; this is the
HIPPOCAMPAL FISSURE, probably the most constant of all the mammalian
fissures and one of the earliest to appear in development.

e. The alba forming the central part of the general section is thin
in the caudal part of the roof of the cornu, thickens somewhat just cau-
dad of the cornu, on the ental surface of the hippocamp becomes so thin
as to be hardly recognizable, but constitutes the whole of the fimbria.

§ 17 It appears then that the hippocamp and fimbria are simply
specialized parts of the paraccelian parietes, but with inverse proportions
of the two constituents ; the former consists mostly of cinerea, being thus
properly a cortical part ; the latter consists wholly of alba, being thus a
medullary part ; Pract. VIII, § 13.

§ 18. 77/1? Rima. — As has doubtless been observed already, along the
cephalic margin of the fimbria is a crevice between it and the surface
that broke away when the piece was detached. This is the rima (part of
the "great transverse fissure").

§ 19 Under favorable conditions, if the piece is manipulated so as to
put the mesal surface slightly on the stretch, the following points may be
observed :

a. The rima will be widened especially near the cut end.

b. At the other (ventral) end it ceases a few mm. from the extremity,
although a rupture easily occurs so as to extend the natural crevige.

Practicuni X. The Rima. 67

c. At one or more points in its course there are membranous adhe-
sions of the margins of tlie rima.

d. These adhesions are more apt to persist in brains hardened with
alcohol, especially if the cavities have been filled with the preservative.

e. Within the medicornu is a membranous, vascular lamina, the
PARAPLEXUS, already seen on the left side (§ 9). It commonly rests closely
against one of the walls, but may be separated therefrom with tiie
tracer or a stream of air. One edge is free ; the other readies the rima
and is there connected with its margins.

§ 20. If now the pia be removed from the mesal surface of the piece,
beginning at the caudal margin, it will be found to dip into the hippo-
campal fissure as a fold, and then to continue over the fimbria to the rima
where it connected with the paraplexus. At the rima or just cephalad of
it, however, it was torn when it was removed ; otherwise it would be
found to be reflected caudad upon the optic tract, etc.

a. The piece may now be bent so as to open the rima widely and
expose the cornu and plexus. The latter will be found to cease at about
5 mm. from the extremity of the piece. A careful examination, espec-
ially of an alcoholic preparation, would show that the rima also ceases
there, and that its apparent extension is also due to the rupture of the
thin wall.

§ 21. The relation of these parts and their interpretation from embry-
ology and comparative anatomy are considered more fully in Analoniical
Technology, § 13 12, and in the Handbook VII pp. 1 18 and 144. Here it can
only be stated tliat, notwithstanding the ease with which the margins of
the rima may be separated in preserved specimens, the dissection ot fresh
brain and tlie study of sections of liardened ones leave no doubt respect-
ing the following points :

a. Between the overlapping parts of the cerebrum and the genicu-
lums, etc., are two layers of pia, one belonging to the diencephal, the
other to the prosencephal.

b. These two, with the vessels between them, constitute the velum.

c. Were there no rima, the continuity of the two apposed layers of
the velum would be along the cephalic margin of the optic tract, at the
boundary between the two segments.

d. The interruption of the continuity of the wall of the paracoele,
from the dorsal end of the porta to near the tip of the medicornu, consti-
tuting the rima, permits the entrance of the margin of the velum into
the paraccele as a paraplexus.

e. The paraplexus carries before it the lining endynia, which there-
fore, although extended over the plexris, connects the two margins of the
rima, and thus maintains endymal continuity and coelian circumscription ;
Pract. IX, § 17.

f. In the human adult the rima is i — 2 cm. wide at the middle of
its length, tapering at the ends. The interval is closed, however, by the
apposed endyma and pia, constituting the paratela. Through this thin*
translucent strip appears the subjacent thalamus, to which it sometimes
adheres ; this has given rise to the statement current in works on Descrip-
tive Anatomy that the thalamus enters into the composition of the floor of
the "lateral ventricle." A similar condition exists in apes. But in the
human fetus, up to four months at least, the rima is narrow as in the
sheep and most other mammals. See the figures referred to in § 10 a, also
Fig. 4749, and the writer's paper, "The relation of the thalamus to the
paraccele," Jour, of Nerv. and Mental Disease, '^\\\\\ 1889.

PRACTICUM XI: DISSECTION OF THE SHEEP'S BRAIN CONTINUED";,
STUDY OF TRANSECTIONS.

§ I. Exposing the Right Paracoele. — This may be done (see Pr. X,
§8) with some confidence at the cephalic and caudal ends, using the
left as a guide, since presumably the parts are at the same level on the
two sides.

§ 2. Removing the Callosiim. — Between the two paracoeles and
slightly overhanging their mesal parts is the mesal portion of the callos-
um. The overhanging thin portions are to be trimmed off carefully with
scissors,

§ 3. The Septum. — But when the intermediate portion of the callosum
is removed it will be found that the two paracoeles are separated at the
meson by a thin partition which is very easily torn. This is the SEPTUM
{septum liicidiim of Human Anatomy).

§4. The Pseudoccele. — By reference to Plates XXII, XXIII and
XXIV and to Pract. IX, § 19 it will be seen that this partition be-
tween the two paracoeles is really double ; each half, hemiseptum, repre-
sents part of the mesal wall of the corresponding paracoele. Their dor-
sal portions are often so thin and so closely apposed as to be separated
with difficulty ; in PI. XXIV they and the intervening slit-like pseudo-
code are too thick.

§5. The Genu and Spleniiim. — At the cephalic end the callosum
turns ventrad, as seen in PL XXIII ; it also extends laterad and cephalad,
the right and left halves diverging at about a right angle. The conditions
are nearly the same at the caudal end, the splenium.

§ 6. On the left side, from the region between the cephalic slope and
the medicornu (corresponding nearly on PI. XXIV with the unshaded
area between lines 5 and g) remove a slice 2-3 mm. thick. Note :

a. The undulations of the cortex, corresponding with the insula
(island of Riel) of the human brain, less covered in the sheep.

b. The gray mass of caudatum, constituting thus an entocinerea.

c. The intermediate alba into which more or less of the entocinerea
intrudes in streaks, giving the appearance which has caused the name
STRIATUM to be applied to this tliickened portion of the parietes.

d. If time permits make a drawing of this section.

§7. Demonstration of the Porta. — Remove part of the caudatum as
follows : On PI. XXIV draw two pencil lines from a point corresponding
with the bottom of the fissure 8 respectively to the mesal end of lines 5
and 9. Cut along the two lines holding the scalpel so that it is at about
45° with the cut dorsal surface. On pushing out the piece thus separated
and trimming off the free cephalic end of the paraplexus there will be
found an orifice 2-3 mm. long and about i mm. wide, oblique in direction
and admitting the tracer or probe meso-ventro-caudad. This is the porta
(foramen of Monro) of the left side, the sole communication between the
left paracoele and the aula, the mesal division of the prosccoele, and thus
indirectly the other mesal cavities ; see Handbook Figs. 4710, 4729, 4739-
4745, and Pract. IX, § 14^'.

Praeticum XI. The Rhinoeoele. 69

§8. Demonsiratiiig the Continiiily of the Paraccele with the Rhino-
eoele.— This continuity is shown from the dorsal side in Fig. 3 and from
the ventral in preparation No. 2653. It may be exposed from the left
side as follows :

a. From the left side cut oflF successive slices, being guided by the
dotted line / in PL XXIV and by the line of the paracoele. The result-
ant surface will be concave, and look laterad and also slightly dorsad. If
the cuts are made cautiously the precornu may be traced tlirough the
olfactory crus as a very narrow passage, expanding considerably in the
bulb. Compare Handbook Fig. 4729 and Ajiatomical Technology., PL IV,
Fig. 16. Tliis stage should be drawn from the left side if time permits.

olf. strait
medulla (alba)
cortex (cinera)
precornu

Fig. 3.
EXPOSED

LEFT OLFACTORY BULB OF THE SHEEP,
X 2. From a preparation by Dr. P. A. Fish.

THE RHINOCCELE

The object is to show the continuity of the paracoele with the cavity of the olfactory
bulb through the narrow strait. Compare Plates XVIII and XXI L See Pract. IX, | 6,
for fuller consideration of the relations of these cavities.

§9. The Precomniissure.—Ow PL XXIII note the location of the
mesal section of the commissure just ventrad of the porta. Draw an im-
aginary line on that figure, or on a real meson, beginning at the depres-
sion (postcribrum) just caudad of the albicans, passing between the chi-
asma and the precominissure, then ventrad to the genu and so to the
cephalic convexity of tlie cerebrum.

a. From the specimen cut away so much as may be estimated to lie
ventrad of this line, being guided by the location of the porta, the level
of which should not be reached by the first incision by at least 2 mm.

b. On the right may be recognized the alternate streaks of alba and
cinerea constituting the striatum which has been divided on the left by a
sagittal section (§ 6, c).

c. From the region just ventrad of the porta very cautiously remove
thin slices, until, just cephalad of the mesal cavity (cephalic part of dia-
coele), there appears a well defined tract of alba about i mm. in diameter,
crossing the meson and curving cephalad so as to form a crescent. This
is the PRECOMMissuRE (anterior commissure). The cephalic arms might
be traced to the olfactory bulbs, of which they constitute a commissure,
as seen in preparation No. 2653 ; a pair of caudal arms is less easily
traced into the corresponding hemicerebrums.

§10. The Aula and Portas. — Dip both the specimen and the scal-
pel in alcohol ; note the location of the porta as exposed on the left side ;
apply the edgealongthe oblique sinistro-cephalic margin of the cerebrum

70 Practieum XI. The Aula.

a.s left by the previous dissection, and at one sweep remove so much as
lies ventrad of the middle of the porta.

a. If both portas have been thus transected they will be found tp be
narrow passages converging caudo-mesad to a small mesal cavity, the
AULA.

§ II. The cut area cephalad of the transverse passage thus consti-
tuted is nearly square, its four sides forming angles of about 45° with the
meson, but the two cephalic sides are prolonged as the nearly parallel
borders of a thin mesal extension, tlie septum between the two paracoeles,
commonly called septum huiduvi.

a. If the tracer (better the syringotome) be applied accurately at the
middle of the total area and gently pushed cephalad upon the meson, the
tip of the left index being at the time applied just dorsad of the cut end
of the mass, it will be found tiiat the apparently continuous surface may,
in its cephalic portion, be separated at the meson into a right and left
portion, each tapering into the corresponding half of the thin projection
just mentioned.

b. Each of these thin lateral parts is a hemiseptum ; the mesal
space between them is the pseudoccELE ("fifth ventricle") PI. XXIII,
Pract. IX, § 19, b, and Plates XXIV and XXV.

The thicker lateral portions are the fornicolumns (pillars of the
fornix) united at the meson ; see § 31.

c. The masses just caudad of the portas are the thalami, joined
across the meson by the large medicommissure, which, unlike the pre-
commissure, consists of cinerea. The cut surfaces exposed present, be-
sides some smaller tracts, extensive areas of alba diverging from the pons
cephalad in the crura, and laterad of the thalami as the "internal cap-
sule" and radiating in the substance of the cerebrum.

§ 12. Remove the remnant of the right striatum along the cephalic
margin of the fimbria, and transect the left hippocamp, etc.^ at the same
level as the right ; the brain is now nearly symmetric.

§ 13. Trim off so much of the caudal end of each hemicerebrum as
lies caudad of the medicornu, that is, so much as in PI. XXIV projects
beyond the furrow marked 10 ; this will include also the splenium, the
caudal end of the callosum. While cutting, a finger should be kept upon
the middle of the mass to steady it.

a. There will now be exposed the large pregeminum, already seen
in PL XXII, and at the meson, upon its cephalic margin, a soft, ragged
mass. This might well be mistaken for the conarium, but it is really the
membranous sack upon the conarium itself, indicated inadequately in PI.
XXIII, and mentioned in Pract. IX, § 12, e. The tip of the sack has per-
haps been opened in cutting off the splenium ; it should be cut off cleanly
with the scissors to expose its considerable cavity and the plexuses that
cover its ental surface. The examination of the conarium itself may be
deferred for the present.

§14. The Fornix. — The curved, cap-like mass now visible cephalad
of the pregeminum and conarium is composed of the following parts :
The two fimbrias at the margins ; the two hippocamps nearer the meson ;
at the meson, the remnant of the septum ; and, concealed thereby, the
conjunction of the two pairs of parts. Now although the hippocamp and

Praetieum XI. The Fornix. 71

fimbria of either side are primarily mere constituents of the floor of the
paracoele of that side, yet since the fimbria is, in one sense, disconnected
from the parietes at the opposite side of therima, and since the hippo-
camps are united at the meson, therefore it is often convenient to deal
with this secondary combination of parts under the single name, fornix ;
see Handbook, VllI, pp. 13S-139.

§ 15. Removal of the Fornix. — In the preparation from which PI. XXII
was drawn, the fornix was pushed off hastily, carrying with it the mem-
branous roof of the diaccEle. This may be avoided as follows :

a. At either side lift the cut end of the fimbria and hippocamp
enough to disclose vessels and bands passing between them and the sub-
jacent parts ; divide these with the scissors and repeat on the other side
till the meson is approached ; here special pains must be taken, and it
may be necessary with the forceps to pull the conarial sack from the
recess between the mesal ends of the gyres bordering the hippocamp
fissure.

b. When the lateral and caudal parts of the fornix are free the whole
may be gently pushed dorsad and diconnected ; dip it in alcohol.

§ 16. The Conarial Sack. — Push this away from the conarium a little
and place the tip of the thumb on the apex of th-e conarium so as to
steady it ; the sack may then be pushed and pulled from the dorsal
(properly cephalic) aspect of the conarium.

§ 17. The Velum. — The pia covering the diencephal and mesence-
phal and the apposed ventral surface of the fornix constitutes the velum.
Its latero-cephalic borders are the paraplexuses ; one of these has been
trimmed off" but the dorsal part of the right should remain ; Pract. X,
§21.

§18. The Velar Vein. — This was mentioned in Pract. IX, §25, a.
It may now be seen just cephalad of the conarium, formed by the junc-
tion of a pair from opposite sides. The corresponding velar arteries are
not easy to recognize unless the arteries have been injected.

§ 19. The Diaiela. — At the meson and for 2-3 mm. at either side the
velum covers the diacoele ; it is here more vascular,- and thicker from the
fusion with it of the endyma, and from the formation of the diaplexu.ses ;
this mesal strip is the diatela, seen in transection in PI. XXV.

§ 20. The cephalic end of the diatela presents a deep notch, corre-
sponding to a triangular area (the delta) on the ventral surface of the
fornix which here constitutes the roof of the aula ; see Anatomical Tech-
nology, § 12 17, and PI. IV, Fig. 14.

§ 21. The Habena. — Introduce at the notch just indicated the point
of the narrower blade of the scissors and medisect the diatela to the hole
made by cutting off the sack (§30). Reflect the halves in opposite direc-
tion. At the sides of the diacoele will be seen the habenas already
studied from the mesal aspect in Pract. IX, § 16. If the dissection has
been done carefully, just laterad of the habena will be recognized the line
of reflection of the endyma upon the diatela constituting the lateral
boundary of the diacoele. If upon either side the diatela and velum be
torn off", along that line will be left a membranous ridge, the ripa, the
.ragged edge of the combined pia and endym. This ripa may be traced

72 Practicum XI. The Study of Transections.

to the dorsal end of the porta, and thence latero-caudad along the rima.

§22. The Medicommissure. — This has been cnt from the ventral
aspect in § ii, c, and is shown in Plates XXIII and XXV. Its presence,
size and circular outline ma^^ be recognized now by divaricating the
thalami slightly and letting the light strike between them. In the sheep
as in most mammals it is much larger than in man.

§ 23. The Study of Transections. — To each four members of the
section will be supplied a set of transections of one brain, to be handled
with great care. But if preferred, as suggested in Pract. X, § 2, «, certain
of their own specimens may be transected, and then examined more

freely.

§ 24. The following general propositions, suggestions, and directions
as to the study of transections of the brain apply for the most part to
other organs, to entire animals and in some respects to microscopic sec-
tions as well.

§25. The two cut surfaces resulting from a transection at a given
level are identical in form and composition.

a. After the section is made one or both of the surfaces may be
trimmed or sliced off, or imprinted or otherwise modified from its origi-
nal condition, but this does not affect the correctness of the general
proposition.

§26. Wiien a transected region contains a cavity both cut surfaces
will present interruptions of equal area and form.

§ 27. If the transected cavity continues of uniform shape, size and
direction in both directions then photographs or shaded drawings of the
two surfaces will be identical in that respect also.

a. But if the cavitv changes in size, shape or direction, then cor-
responding differences will appear in the photograph or in an accurate
shaded drawing.

§28. Absolute transections of a perfectly symmetric mass, e.g.., a
regular, homogeneous cylinder, will produce symmetric cut surfaces ; i. e..,
the right and left will be identical in form and composition although
reversed in direction.

a. But, firstly, even were the two halves of a brain absolutely ident-
ical, originally, some asymmetry always results from the manipulations
and agencies to which it is subjected.

b. Secondly, it is probable that no absolutely exact transection of a
large and complex brain like that of the sheep is ever made.

§ 29. The student must be prepared for recognizable and sometimes
marked differences between the right and left sides of the section.

a. An absolutely symmetric drawing of a transection justifies the
inference that one side has been simply copied from the other.

§30. In drawing transections of the brain, and indeed of most or-
gans or organisms, there commonly arises a practical difficulty due to the
great difference in the size of parts. A drawing of moderate size may leave
the smaller features obscure, while an enlargement of the whole such as
to exhibit these features clearly may waste space and time.

§ 31. The difficulty may be met in either of three ways :

Practicum XI. The Study of Transections. 73

1. The whole may be shown of moderate size and the more complex
areas enlarged sufficiently as separate drawings. This is the common
method with maps and is employed on PL XXV.

2. The whole may be enlarged, but time may be saved by not in-
cluding certain features where the omission would occasion no misappre-
hension. For example, on PI. XXIII the subdivisions of the cerebellum
are omitted, the omission being stated in the description. On PI. XXV
a part or all of the ciuerea might have been indicated merely by a line
corresponding with its ental inargin.

3. With transections, unless it be desired to exhibit differences be-
tween the two sides, natural or caused by the obliquity of the section, a
portion of one side may be omitted altogether, as in Fig. 122 of Anatom-
ical Technology.

Whichever method is adopted it is well to remember that drawings
are seldom on too large a scale.

§ 32. While it is desirable to maintain the natural proportions of the
several parts and cavities, the cavities may be somewhat reduced, if neces-
sary, in order to afford space for the distinct representation of outlines.

a. For instance, the cavities of the diacoele and the paracoele may
be encroached upon for the sake of indicating distinctly the membranes
and plexuses.

b. On the other hand, where the parts are superposed, as the cere-
bellum upon the geminum and the cerebrum on the cerebellum, it is per-
missible to increase the distance between them so as to represent the out-
lines, meninges, etc.

§ 33. Keeping in mind what was said in § 26, an admirable test of the
student's powers of observation, interpretation and delineation will be
afforded by his drawing the two cut surfaces made by a given transection
at two different times and then comparing ; still more severe will be the
test if these surfaces, or one of them, be so drawn by two individuals.

§ 34. The general level of a transection may be determined by unit-
ing the section with its neighbors.

§ 35. The exact level may require the detailed comparison of the
principal or most easily identified features (cavities or masses) with the
meson (PI. XXIII) and with the dissections (Plates XX-XXIV).

§ 36. It will be easier for the beginner to take first the mesencephalic
transection (D) both because a single segment only is included and be-
cause the cavities and walls are comparatively simple. Next sections G
and F, then C and B, and lastly E (PI. XXV).

§37. Section C presents special difficulties of two kinds.

a. The cerebellar outline is very irregular on account of the numer-
ous foliums and the intervening rimulas. These need be represented on
one side only.

b. — The cavity is a horse-shoe-shaped slit, concave dorsad, and nearlv
filled by a projecting mesal lobe of the cerebellum. But really between
this lobe and the oblongata there is a delicate lamina, the lingula (PI.
XXIII). The space ventrad of the lingula is the epicoele, a part of the
true brain cavity ; the space dorsad is seen in PI. XXIII.

§38. With section B the conditions are similar. Between the post-

74 Praelicum XI. Defibrillation.

oblongata and the overhanging cerebellum intervenes the membranotis
metatela, the roof of the nietaccEle, and this may adhere so closely to the
cerebellum as to be at first ignored.

§ 39. With section F the main difficulty is due to the thinness of the
dorsal part of the septum and the narrowness of the pseudocoele betweeij
the two halves.

§40. Defibrillatio7t. — The fibrous structure of certain regions may
be roughly demonstrated upon a half-brain as follows :

a. Grasp the chiasma and pull latero-dorso-caudad. The optic
TKACT may be separated from the subjacent parts and traced, gradually
widening, over the lateral aspect of thepregeniculum and perhaps to the
pregeminum.

b. Grasp the cerebelltim and pull laterad and then ventrad ; the
MEDIPEDUNCLE will be seen to be cnntinuous with the pons.

c. Grasp the olfactory htilb and pull ventro-caudad so as to tear off

the OLFACTORY TRACT.

d. Divide the posioblongaia by a sagittal section. Pull the lateral
and mesal portions apart slowly and steadil}'. The separation will con-
tinue into the cerebrum and the fibrous structure will be particularly
obvious in theCRUS.

PHYSIOLOGY: PRACTICUM VIII: PLATE XVIII.

THE RRAIN OF THE SHEEP, THE CEREBRUM SLICED TO NEAR THE LEVEL
OF THE CALLOSUM ; X 1.5.

- olfactory bulb inclosing rhinoccele

'--genu (of callosum)
--cortex (cinerea)
medulla (alba)

— Sylvian fissure
— callosum

- F^ — spleniuni I of callosum)

C — r^^:s:^f'^^'~f vermis imcsal lobe)

lateral lobe

poitoblongata
myel (spinal cord)

The following points are illustrated :

A. The general proportions of the two great masses, CEREBRUM and CEREBEL-
LUM.

B. The constitution of the cerebellum bv a mesal lobe (VERMIS) and a pair of LAT-
ERAL LOBES.

C. The junction of the two halves of the cerebrum by a thick sheet of fibers, the
CALLOSUM ; its rounded cephalic and caudal margins are the GENU and SPLENIUM,
respectively ; PI. XXIII.

D. The relative positions of the two kinds of substances in the larger part of the
cerebrum ; the ALBA (white substance) is central ; the CINEREA (gray substance), is per-
ipheral, constituting the CORTEX.

E. The relation of the corte.N; to the FISSURES.

F. The passage of the ARACHNOID membrane across the mouths of the fis.sures, as
at I and 4, while the PIA dips to the bottom as a fold.

G. The existence of a cavity (RHINOCCELE or olfactorv ventricle) in the OLFAC-
TORY BULB ; see PI. XXIV and p. 69, Fig. 3.

Defects.— Th.^ cerebellar divisions (FOLIUMS) are not shown in detail. In the dark
interval (6) between the cerebellum and cerebrum should appear the cut ends of vessels
one of which is shown in PI. XXIV. There is no indication of the thin layer of cinerea on
the dorsum of the callosum ; PI. XXV.

PHYSIOLOGY : PRACTICUM VIII : PLATE XIX.

VENTRAL ASPECT OF THE SHEEP'S BRAIN WITH THE EYES AT-
TACHED; X 1.3.

From the specimens commonly examined the brain here represented differs as follows :
a. The EYES have been retained with OPTIC NERVES, b. The HYPOPHYSIS is
retained. c. Besides the TRIGEMINUS NERVES (marked 5), on the actnal brains
there are more or less distinct signs of the roots of the other cranial nerves.

The numbers indicate parts as follows : i, a small portion of the PALLIUM or fissured
region of the CERREBUM, projecting mesad of the OLFACTORY BULB. 2, the OL-
FACTORY CRUS, connecting the OLFACTORY TRACT with the BULB. 3, a slightly
depressed area just cephalad of the OPTIC TRACT. 4, a part which distinctly projects
over the tract. 5, The root of the TRIGEMINUS, the great sensory nerve of the face. 6,
a slight ridge, not always distinct, crossing the CRUS. 7, the TRAPEZIUM, concealed in
the human brain, by the caudal margin of the broad PONS. 8, the PYRAMID, less dis-
tinct than in man and not exhibiting a DECUSSATION.

Some details are more fully shown in PI. XX.

PHYSIOLOGY: PRACTICUM VIK: PLATE XX.

BASE OF SHEEP'S BRAIN AFTER THE REMOVAL OF THE HYPOPHYSIS
AND PARTS OF THE CEREBRUM AND CEREBELLUM ; enlarged.

olfactory bulb

INSULA
olfactory fissure

PREGENICULUM

POSTGENICULUM

CRUS

CEREBELLUM

The cephalic and caudal regions are nearly the same as in PI. XIX, but the following
differences should be noted : a. The absence of the frontal "parts of the cerebrum be-
tween and laterad of the OLFACTORY BULBS, b. The indication of the MESAL (i)
and LATERAL (2) ROOTS of the bulb. c. Between the two the irregular triangular area,
PRECRIBRUM ("anterior perforated space") presenting orifices for the transmission of
vessels, d. The removal of the HYPOPHYSIS ; this exposes a slight elevation, TUBER,
and an orifice, lura, leading into the diacoele. e. The CRURA and OPTIC TRACTS
are more fully seen. f. The PONS presents more distinctly the mesal emargination of
its caudal margin.

I, Mesal root of olfactory bulb. 2, lateral root. 3, cut surface of olfactory tract and
pallium. 4, depression caused by the extraction of the right oculo-motor nerve. 5, Cau-
dal emargination of the pons. 6, Ventral mesal sulcus of the oblongata. The unnamed
shaded line across the cms just cephalad of the oculo-motor nerve was intended to repre-
sent the cimbia.

PHYSIOLOGY : PRACTICUM VIII ; PLATE XXI.

LFFT SIDE OF THE SHEEP'S BRAIN AFTER THE REMOVAL OF MOST OF
THE CEREBRUM AND CEREBELLUM ; X i-

Cfinarium

o^-^

^■cN^ thalamuij i _,^ ,

i?

4' ^ pons postobloiigJta

The CEREBELLUM is left of its natural height, but the cephalic and caudal convexi-
ties are sliced away so as to expose the parts which are overhung b}' them. In a compan-
ion preparation the dorsal portion of the cerebellum has also been removed, with the
cephalic and caudal convexities, but the lateral "overhangs" are retained.

The CEREBRUM has been cut down to the level of the THALAMI ; the caudal por-
tion cut away along the oblique line of its projection over the part marked 5 ; the lateral
portion so as to expose the part marked 3 ; also the cephalic projection which, as seen in
Plates XIX and XXV, overhangs the OLFACTORY BULBS.

The short lines on the surface of the olfactory bulb represent the OLFACTORY
NERVES. The cut end of the left OPTIC NERVE is dotted to indicate its fibrous structure.

I, OLFACTORY CRUS ; compare with PI. XX. 2, a part of the PALLIUM which has
not been cut. 3, OLFACTORY TRACT. 4, (indistinct), CHIASMA. 5, PREGENICU-
LUM (external or anterior geniculate body), distinct in man but here little more than a
lateral portion of the thalamus. 6, TUBER (c;«frf?;w/), the slight convexity to which
the HYPOPHYSIS is attached ; in PI. XX it is the area just caudad of the chiasma. 7,
the MEDIPEDUXCLE, continuing the PONS to the lateral mass of the cerebellum. 6,
the TRAPEZIUM ; compare with PI. XX.

Excepting the unshaded areas, representing cut surfaces, all the parts seen in this fig-
ure were covered by PIA.

At the dorsal end of the cerebellum are seen a few FOLIA, its leaflet-like divisions ;
these are not shown in anj' other plate.

Besides facilitating the recognition of certain important parts this figure well illus-
trates the srgmetital constitution of the brain, which is obscured in the entire organ by the
preponderance of the cerebrum and cerebellum. There is a series of more or less distinct
masses demarcated by constrictions of greater or less depth. Admitting that there is still
some doubt as to number and limits of the segments the following assignments may be ac-
cepted provisionally :

Olfactory bulbs and crura, \ RHINENCEPHAL.

Cerebrum ] PROSENCEPHAL (fore brain).

Thalami, conarium, hypophysis, \ niENCEPHAL (inter-brain),
chiasma, and geniculums, J ■

Geminums and crura |- MESENCEPHAL (mid-brain).

Cerebellum, pons and preoblongata, ]- EPENCEPHAL (hind-brain).

Postoblongata 1 METENCEPHAL (after-brain).

PHYSIOLOGY: PRACTICUM VIII : PLATE XXII.

DORSUM OF SHEEP'S BRAIN AFTER THE REMOVAL OF PARTS OF THE
CEREBRUM AND CEREBELLUM.

Litercerebral fissun

SJ'lv

olfactory biilbl

, / I 7 j RHINENCEPHAL

olfactory cms I

1 1

caput of caudatum j

Iprosence-

msula I PHAL

V '\ \ ^ - Cauda of caudatum J

;^Y!\T" — 7 habeua 1

rTTW medicommissure

, n'^^n/vI thalamu.s .^DIENCEPHAL

V '^LD^ preg-emculum

*^ ' postgeniculuni

ff^^ couarium '

pregemiuum 1

'-MESENCEPHAI,
postgemiuura )

,^£^ pons I

X'-l flocculus l-EPENCEPHAL

— cerebelluui

postoblongata j- METENCEPHAL

Compare with PI. XVIII. From the cerebellum have been cut the dorsal part
and also the caudal. On the cut dorsal surface are seen the central alba and the periph-
eral cinerea, but the outline of the latter is diagrammatic onl)'. At the sides are the tiers
of foliums constituting theflocculus.

From the cephalic end of the cerebrum have been cut the parts projecting over the
olfactory crura, but part of the cephalic slope marked b in PI. XVIII is here marked 1.
With the dorsal portion were removed the entire callosum and the fornix excepting the
cephalic vertical part. This and the mesal walls of the paraccEle are really cut at a lower
level than the larger cut surface on the left. On the rigiit the insula has been exposed by
pushing up and breaking off the overhanging parts. The ectal surfaces, covered by pia,
are indicated by irregular lines representing the blood-vessels.

The ental surfaces, covered by endyma, are those of the caudatums in the paracoeles,
the habenas, medicommissureand conarial pouch ; and the floor of the aula and purtas.

The irregular line laterad of the habena and extending around the endj'mal area on
the conarium represents a ripa (shore-line). It consists ol the cut or torn edges of the pia
from the dorsum of the thalamus and of the endyma from the habena which united to form
a membranous roof of the diacoele, the DIATELA, which has been removed.

Similarly the pial, dorsal surface of the thalamus is demarcated from the endymal sur-
face of the caudatum by a ripa which meets the other at the porta.

The CONARIUM, although a constituent of the DIENCKPHAL, is tilted caudad so as
to rest upon the PREGEMINUM, and the niesal part of its exposed surface is likewise
covered by end}'ma.

I, cephalic slope. 2, mesal wall of PARACCELE ; at a higher level this would be one
of the HEMISEPTUMS. 3, horizontal cut surface of cerebrum. 4, the mesal, vertical
portion of the paracoele. 5, indicates the location of the ripa between the thalamus and
caudatum, but it is overhung by the latter so as not to appear in this view. 6, extension
of the diacoele upon the conarium. 7, mesal furrow of the pregemiuum.

PHYSIOLOGY: PRACTICUM IX: PLATE XXIII.
MESAL ASPECT OF RIGHT HALF OF SHEEP'S BRAIN ; X 2.

f — ■ spkiii il iissure

^ f .Iwttli

'"■^ luUiji

, , , C^ ^.^ °-'^ "J^

This figure is semi-schematic, certain details being omitted for the sake of clearness,
e. g., the divisonsof the CEREBELLUM, the VESSELS, and the MEMBRANES, ARACH-
NOID and PIA. The pia, however, is represented by the line between the ROSTRUM and
the CRISTA.

The tuber is the Tuber cinereum, called torus in the former edition.

The objects of the figure are : To show most of the MESAL PARTS; to illustrate
ENDYMAL CONTINUITY and its concomitant, CCELIAN CIRCUMSCRIPTION ; to in-
dicate the PLANES OF TRANSECTION which are most instructive, A—G. Compare
Plates XX, XXII, XXIV XXV. For fuller description see Practicum IX.

PHYSIOLOGY: PRACTICUM X: PLATE XXIV.
SHEEP'S BRAIN, THE PARACCELES (lateral ventricles) EXPOSED ; X 2.

This figure represents a stage of dissection intermediate between Plates XVIII and XXII.
By the removal of successive slices the PARACCELES have been opened ; the left has then
been more completely exposed by oblique sections, and the PARAPLEXUS trimmed off
so as to expose the wide FIMBRIA and the furrow between it and the HIPPOCAMP. The
plane of section did not coincide exactly with the CALLOSUM ; the caudal three-fifths of
this is represented by the transverse lines ; also the cephalic end, the GENU ; but an in-
termediate portion is wholly removed, exposing the narrow PSEUDOCCELE ("fifth ven-
tricle") and its thin lateral walls, HEMISEPTUMS. The HEMISEPTUM is here shown
to be only a porion of the general mesal wall of the paracoele. The Pseudoccele (PI.
25) has no connection with the true cavities of the brain. The only communications of
the paracoeles are through the PORTAS with the mesal AULA (PI. XXII).

The two FIMBRIAS and HIPPOCAMPS connected by a mesal part (PI. XXV) consti-
tute the FORNIX.

The HIPPOCAMP is sometimes called hippocainpus major.

I, INTERCEREBRAL FISSURE. 2, CALLOSAL FISSURE. 3, VESSEL. 4, inter-
rupted lines indicating the continuation of the paracoele into the RHINOCCELE. 5,
PRECORNU. 6, CAPUT of the CAUDATUM. 7, SYLVIAN FISSURE crossed by
ARACHNOID. 8, VESSEL at bottom of fissure. 9, CAUDA of CAUDATUM. 10, part
of caudal wall of paracoele.

PHYSIOLOGY : PRACTCUM IX : PLATE XXV.
A. TRANSECTION OF SHEEP'S BRAIN ; ■ 1.5.

irachnoid
ntercerebral fis

HABENA

MEDICOMMISSURE

diaccele

optic tract
olfactory tract

The plane of section approximales E in PI, XXIII. The HYPOPHYSIS has been re-
moved and the DIACCELE is open ventrad at the LURA (PI. XX). The OPTIC TRACT is
cut obliquely ; its fibrous structure is roughly indicated bv lines. The masses connected
by the MEDICOMMISSURE are the THALAMI. The CALLOSUM is indicated by lines.
The INTERCEREBRAL FISSURE is bridged by the ARACHNOID ; in man the 'falx de-
scends into the fissure for a greater or less distance carrying the arachnoid before it. The
fissure here named rhinal is named olfaciory in PL XIX.

B. ENLARGEMENT OF THE CENTRAL REGION OF A,

intercerebra] f.
pia

— cortex

callosal fissure
callosal cinerea

ENDYMA
-- paracoele
J_ PSEUDOCCELE
»__ HEMISEPTUM

foruicom missure

VELUM
■=- velar vein
- — RIPA

DIATELA
-^^ DIAPLEXUS
diaccele

raediconimissure

This wasdesigned to eshibit more clearly the relations of the CAVITIES to the MEM-
BRANES and PLEXUSES, but some points are obscured by the shading.

The mesal DIACCELE and the lateral PARACCELES are lined by smooth ENDYMA,
represented bj' a heavy line. In the diacoele the endyma may be traced dorsad upon the
mesal surface of the THALAMUS and over the dorso-mesal ridge representing the HAB-
ENA, as far as the point called RIPA, (see PI. XXII, left side.) Here it is reflected mesad
upon the ventral surface of the VELUM

The velum consists of the PIA covering the ventral surface of the FORNIX and the
dorsal surface of the thalami. together with CONNECTIVE TISSUE and VESSELS (of
■which only one is shown). Near the meson there hangs into the diacoele at each side a
plexus (DIAPLEXUS) covered by the endyma.

At the interval (RIMA) between the margin of the fornix and the caudatum (i) the
velum extends into the paraccele as the PARAPLEXUS, covered, however, by the endyma
which is reflected off at 3 and the point opposite.

A thin layer of the cortex extends across the callosuni.

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