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BIOLOGY

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Inn- re/inn ft 'I j'mm Cailiard's Medical

Journal, _ hy >,,, m

• in tli, /,rnj,

MBTH <'tBccum»s IN THK EMBBYO: PLAO

FFLE THE Ax.UX" IlESPIKAT

BKPIRATIOX ix THK XEW-BOBX : THE CHANGE is MECHAXICS wmcn THB

YI58 TO THE AlB-CHAUBEB IX THE EGO.
\I Di THE TISSUES Or THE WoMB.*

Br W. H. TKII'I.riT. .V I

M

seen that respiration and circulation most be treated together, since
i a connected movement for pumping the commerce in and through the
organism for elaborating structure and evolving force, and ***** the whole •
founded in the power of producing rhythmical changes in pressure, the fluids
flowing from high to low pressure in conformity with organic law ; that the
••stines and bloodTeasds are necessarily allied in respiration in order
to make importation and transportation a connected movement between the
ceD-timod and environment, which the scheme calk for. In other words, that
xstptM? action in respiration compel* the commerce in the Teaauh, while the
action in the heart, arteries and venous system circulates it through the organ
the action being unified throughout by means of the nerroas com-
binatians in the medulla oblongata, in which the respiratory, raso-motor
dontary motor centres, are correlated, the one calling for the other, as has
folly set forth in the preceding pages, and that the vital phenomena,
:nical and physiological, appertaining to respiration, circulation absorp-
tion, etc., are readily explained and accounted for, giving absolute proof of
the correctness of the premises, as before remarked. We now follow this
matter a little farther, and take op

CI BrrLATIOX IX THE EXBBTO,

a subject which, it most be admitted, is at present veiled in deep obscurity.
This is nevertheless susceptible of ftrjJhmmtitw^ The embryo is an aquatic

•""" * — — y "•"*• *-'~ri — I ' *~ r-"— "— — •"**-* "~- — T ruiinnaij if tii

Body : or. tfte Xeehaoic* in Scepintjoo. airrtrttM Absorption. Etc.,- ehapun zrt Md rrii.

r

:. : /.:"•:••/: :

•• • « ; •; ...

animal, since it leads a subaquatic existence, being placed under water (Fig.
1) and deeply buried in the maternal tissues, which would account for the
peculiarities that obtain in its circulation approximating it to the stages in de-
velopment represented in fishes and amphibia.

FIG. 1. — GRAVID HUMAN UTERUS AND CONTENTS, showing the relations of the cord, placenta,
membranes, etc., about tbe end of the seventh month. 1, decidua vera ; 2, decidua reflexa ;
3, chorion; 4, amnion. (After Dalton.)

The physical conditions under which the embryo is evolved determine
the special vascular arrangements for effecting circulation, while the trans-
formations which accompany this provide for the radical physical changes
which are ushered in at the end of the term, when it becomes an air-
breather, the fundamental circumstance underlying it all being an adjustment
ivith pressure, and the power of effecting rapid rhythmical changes in pressure, or
of producing the universal pumping actions going on in the body. For ex-
ample, we have seen that the rhythmical expansions and contractions pervad-
ing the body in the air-breather, and known as respiration, compel oxygen and
aliment in the circulatory apparatus for evolving force and producing growth ; so,
in like manner, a similar necessity exists in the embryo for compelling the nutri-
tive and force-producing elements in its circulation for producing growth and
evolving force, which is principally expended in elaborating its structures.
But since the embryo feeds in the uterine sinuses from which the com-
merce is obtained, and into which the waste products are returned, this calls
for the differentiation of the special organ known as the placenta, and which
answers to the more highly differentiated lungs and intestinal canal which are to
substitute it at the end of the intra-uterine term as the relative adjustments with
the larger environment, lower pressure, and higher order and amount of work
which this involves.* The placental souffle, then, which is distinctly heard
through the maternal structures is the analogue of respiration in the air-
breather, the relative ratio of the movements to the pulsations in the foetal heart

•For further particulars, see Part II. of this work, "On the Relation of Gravitation to
Development," to be issued shortly.

being also the same, or as 1 to I of tin- latter, whilst the villi are the analogues
of tilt* villi is tin- intestinal canal, tho ono 1n'ing submerged in the sinuses, the
other in the juices in the intestine. Since the pumping action in respiration is
absolutely es-ential for compelling the comineive in tin' vessels, it follows that
this circumstance shmilil l)o represented in the t>mbryo,\i8 the maternal blood
(loos not enter the embryo, the latter feeding out of lEe sinuses simply by
menus of the villi in the pkoenta/and tliis pumping action spoken of ; for here,
as elsewhere in the Ixxly. there are no means for increasing circulation but by
rlii/tliiiu'rtil I'/HHt'ifx in fi-is.-iii-t'. The result must then be the action in the
plaeeiita simulating respiration. The relative frequency of this movement to
the action taking place in the f<etal heart is as 1 to 4, or the same as in respira-
tion.

Tli i is. in the case of the placeutal souffle it is 30 to 35, and in the foetal heart
tho pulsations are from 120 to 140 per minute ; while, in the case of the air-
breather, the pumping action in the trunk or respiration is from 16 to 20, and
in the heart from fiO to 80 per minute. Again, tliis action in the placenta
servos not only to pump the tluids in and out of the sinuses, but at the same time
it also aspirates tho venous blood in the embryo for effecting oxygenation in it
the same as obtains in the lungs : the heart and vessels assisting in the one as
well as in the other, since it all forms a connected movement. We now see that by
reason of the great increase in pressure that obtains in the embryo, the action
in the organs for changing pressure is materially assisted, since the fluids flow
more readily in consequence. And here comes in the benefit of the
amniotic fluid, which not only increases pressure in proportion, but at the same
time it serves to transmit the force in the placenta and uterine walls to the
emlirvo for compelling corresponding changes in pressure upon the blood in con-
nection with the special functions.

As illustrating this fact, .we see that when the placenta expands for aspirating
the tluids in the uterine sinuses, the organ advances into the uterine cavity, it
swells out and occupies more room, and, by thus encroaching upon the embryonic
area, it produces corresponding increase in pressure upon the liquor amnii and
omliryo, with low pressure in itself, which fulfils the conditions for increasing cir-
culation from the embryo to the placenta, at the same time, that it should aspi-
rate the fluid in the uterine sinuses. It could not do otherwise in the
very nature of things. During contraction in the placenta, the opposite
conditions should obtain, since this would determine high pressure in the latter
with low pressure in the embryo, the blood in consequence flowing through the
umbilical vein with augmented speed, and for the reason that contraction
should induce the volume of the placenta, which would inevitably reduce
pressure in the embryo in proportion, the blood flowing from one into the
other in conformity with organic law. To this, again, must be added the
action in the heart for aspirating the blood in the placenta. The media
in which the animal lives obviates the necessity for the extensive arrange-
ments for reducing pressure in the chest, which obtain in the lighter media
of the atmosphere, the heart, together with the force in the placenta and
umbilical vein, being sufficient for the purpose.

A subaquatic existence calls for but slight reduction in pressure in
order to compel movement ; accordingly, we have the blood rushing in and
out of the heart as a result of the rhythmical expansions and contractions in this
organ ; while for increasing this action, the vessels are combined in the
mechanics by means of the vaso-motor apparatus, and which, undoubtedly, con-
nects with the action in the placenta. The right ventricle is thicker and stronger
than the left, as adjustment for this mechanics, since the diastoles should
aspirate the blood in the two cavse, while the two systoles would produce high
pressure in the arterial system for increasing circulation in the capillaries.

'By means of this combined action in the placenta, heart and vessels, a rapid
circulation is readily effected under the high pressure that obtains in intra-
uterine life ; but anything which should interfere with this mechanics by
reducing pressure, e.g., escape of the amniotic fluid, would promptly destroy
life. How, otherwise, account for this circumstance, since the vascular connec-
tions are uninjured? Moreover, the lividity of the skin, which occurs in these
cases, proves conclusively the existence of venous stasis in the systemic capil-
laries, and insufficiency of the heart's action to carry on circulation in the
absence of the normal pressure upon the embryo. The same circumstance
occurs to the air-breather when carried to too great an altitude, nothwithstand-
ing the extensive arrangements for changing pressure in the chest, which exist
in the latter. This circumstance may be especially noticed in balloonists, and
also in persons ascending mountain ranges, respiration and circulation
becoming more and more embarrassed as the journey is proceeded with,
and venous stasis more and more conspicuous, till the limit of endurance
is reached or life itself is terminated, as occurred in the celebrated case at
Paris, in which the voyage was made by two balloonists, one losing his life, the
other being unconscious when the balloon descended.

THE ACTION IN MEDUSA CONTRASTED WITH THE ACTION IN THE PLACENTA.

The action in medusce feeding in the juices in the sea, piimping them in and
out of the internal compartments by means of rhythmical expansions and con-
tractions for changing pressiire upon them, may be taken to illustrate the
mechanical action in the placenta, which feeds in the juices of the womb,
pumping them in and out itself from the maternal sinuses. Thus the peduncles
(Fig. 2, a, a, a) answer to the tufts while the mantle represents the body of the
placenta. But to make the analogy complete, a tubing should project from the
convex surface of the latter to represent the umbilical vein and arteries, and
which, for obvious reasons, are not present. The analogy is more striking,
however, than would appear on the surface, since from the periphery of the
stomach a system of radiating canals extends to the edge of the mantle, dividing,
subdividing and anastomosing to form a continuous and complicated capillary
plexus around the free margin of the mantle, inclusive of the colored lobes, to
form the respiratory apparatus. This may be taken to represent the circulation
on the distal side of the placenta, and though, for obvious reasons, the force is
increased in the embryo, still the mechanical principle is the same for both cir-
calations.

In tin- mantle, as \\vll as in the placenta, nnstri|>t-d miiM-l. ^ are present for
hflMMillg tin- .•iiiT.i.'v nf tin- rhythmical expansions ami c. mil-actions. But
muscles arc nut essential in this action, a notable example nf which is
bnythed in tin- In-art itsi-lf, which expands ami cniitracts rt'gularlv and rhvth-
micallv liefon- a nniscl.- or m-r\.- is ili-\ -loped in tin- protoplasmic and un-
diH'en-ntiated \vallsip. -J'.l'.li, also in capillaries ami in earlv animal forms.

It is interesting to note tin- fact in ttris connection i which has already been
comim-nt^l upon in tin- higher stages of ili-vdnpnicnt i. that <-r,ri/ ///<»(•.•;/<«•«/ of
the animal, l.v rxtrinHni,' nr retract in.i; tin- mantle ami tin- Imincln-il ]K3dtlLcle8,
must ./'// increase circiilatimi ami n-spiration in roiTespnnilence. It could

not In- ntherwi>e. Niiim-r..n- -tminita in tin- rounded extremities of the peduncles
(a, a, "i atl'onl fi-ci- in^i-i-ss mid ogress to the tlimls in the central canals (b,c).

Fin. 2.— MF.DI-SA (Rhtinntoma cuvieri). A, a, a, eight peduncles; 6, c, internal canals leading
up to the stomach; <l, stomach; e, e. <?, e, aurmountinj; ovarial sacs (four); /, k. lateral respi-
ratory canals; h, h, respiratory lobes on free margin of mantle (colored); I, I, thin membranous
l> trillions separating the caviiy of stomach from the ovarial sacs; i, i, external opening to
ovarial sacs; m, oesophageal passage. (After Grant)

The capillary loops at the sides of the peduncles (/, k), which function as ab-
sorb-in; and respiratory vessels, may be taken as the simile of the capillary
hxips in the tufts of the placenta.

This brief description will serve to explain the mechanical principle in the
placenta, and it now remains to be seen how this action is assisted by the action
takin j place in the womb itself ; or how the maternal and foatal circulations are
made to connect for effecting mutual interchange, the former supplying the
nutritive and force-producing elements for the growth and elaboration of
tissue, the latter yielding up the waste products to be borne back through the
maternal channels to the environment from which everything is derived, and
into w!iich, in due time, everything is returned in the form of waste
and tin il dissolution.

MODE OF CONNECTING THE MATEENAL WITH THE FCETAL CIRCULATION.

The circulation of maternal blood in the uterine and placental sinuses is the
same in principle as that for circulating air in the lungs, namely, by rhyth-
mical changes in pressure in the sinuses, which is produced by the action taking
place in the womb itself ; taking the placental sinuses to represent the alveoli,
and the uterine the tracheal system, the blood flowing in and out of this system
of canals by^reflux action for renewal, just as the pulinonic air flows in and out
of the tracheal system for renewal, only that in the former the fluid passes into
the venous system of the mother and is returned by the arterial, both terminat-
ing by capillary openings in the canals, while the placental souffle answers to
the respiratory murmur.

We have already spoken of the role which the placenta plays in this respect,
and it now remains to take up the very important one which the uterus itself

FIG. 3. — LONGITUDINAL SECTION OF A LATELY GRAVID WOMB, showing the canal system.
Taken from a case of post partem bffimorihage (partly diagrammatic). 1, peritonieum ; 2,
uterine canals (sinuses); 3, openings to canals on the mucous surface corresponding with
openings to placental sinuses; g, Fallopian tube; /, ligament toTtrtCTyr-r, round ligament.

(fir-tv^^l

performs for completing this deeply-interesting mechanics, which it would be
difficult to overestimate, underlying, as it does, embryonic life.
First, with regard to the uterine sinuses, we may mention that this canal

a which is channeled in the walls of the gravid \\,m\l) does not consist of
veins or arteries enlarged for the purpose, but, on the contrary, that the proper
substances of the womb itself (muscles and connect he tissue i compose the actual
walls, which are lined by a tleliente uieinbnine answering to the lining mem-
brane of the vessels. The difference is very material, since the vessels are
enabled to expand ami contract themselves for increasing circulation, while in
the ca>'' of the sinuses, the walls of the womb would have to expand and contract
in order to HIKW«- circulation in them, mid that this is the case will appear more
obvious as we proceed, the mechanics undoubtedly calling for such a condition.

When a longitudinal section is made of a gravid womb at full term, this canal
^v-teni is seen to traverse its substance in various directions from near the central
IM nt ions, but trending to the internal or mucous surface where they connect with
the placenta (Fig. 3 — '2, 3). They never penetrate to the external surface to
form continuous tubes with the arteries or veins; but on the contrary, both
these systems of vessels connect with this system of canals by means of capil-
Itirit ••*, the arterial emptying and the venous discharging from these common
mains. Hence this blood is mixed as a matter of necessity.

The next important point is the method this system of canals exhibits in con-
necting with the placenta! sinuses, which is done by projecting the lining mem-
brane in/') l/i'' t>>(lixtan<-e of the placenta (Fig. 4, c, c, c, c). This spreads out at once

FIG. 4. — VKIUII u. SI:CTHI\ OK I'I.ACF.NTA, showing arrangement of maternal ami f<rtul vessels.
A, n, chorion; l>, >>, ileciilua; 0, < . . . . , urillres of uterine sinuse.j. (After Dalton.)

to form the large cavitary spaces in which the highly ramified placental tufta
are suspended and submerged in blood.

The walls of these large cavities in which the lining membrane of
the uterine sinu>es is merged answers to the outer surface of these highly-rami-
fied tufts which tit into this as the fingers in a glove, the vascular loops being
contained inside of them (Fig. 5, a, a). It is easy to perceive that this out-
side wall and the wall of the capillary itself in// rr< n<- lx>tween the. maternal and
foetal blood, and that interchange would have to be effected through these two.

8

membranes ; hence, to be very active it would call for considerable force for
producing this.

FIG. 5.— EXTREMITY OF FCETAL TUFT, from human placenta at term, in its recent condition.
A, a, capillary bloodvessels. Magnified 135 diameters. (After Dalton.)

During attachment, when the sinuses are filled with the maternal blood they
are greatly larger than after detachment, when the blood is forced out, and the
tufts are compressed against each other in the maternal passages, reducing
the placenta fully one-half its size. At the time of birth, the necks of the
uterine sinuses, where they join the placenta, are readily torn through (Fig. 4,
o, c, c, c), and, peeling off easily with the decidua, the organ is expelled, unless,
forsooth, abnormal nutritive changes in the parts have made the union more
intimate.

The problem in the mechanics concerns the manner by which the blood is
speeded in and out thesf sinuses commensurate with the increasing wants of the
growing embryo, and how this in turn is connected with the arterial and venous
systems of the mother for compelling correspondence in them, the whole forming
& connected movement — a movement within a movement, so to speak.

We have seen that change of pressure is the law of the animal circulation., ;md
it now remains to make rigid application of this principle in mechanics to
the special phenomena, .anatomical and physiological, appertaining to this inter-
esting region, in order to make them also intelligible, which otherwise are utterly
inexplicable.

It follows, that for increasing circulation in the placenta we must provide
for rhythmical changes in pressure, since no other force applies for producing
it, and we must connect the action in the womb (which expands and contracts
regularly and rhythmically) with the action in the placenta, so that when the
latter [expands for producing low pressure, the former contracts for producing
the opposite, and vice versa.

In this manner an active circulation in and out the placental sinuses could be
readily produced.

The following facts may be given in support of this opinion :

1. The womb must expand and contract regularly and rythmically in order to

increase circulation in tin' sinuses. since tliis is essential for changing piw-.ure
upon tin- l)l<HHl, while the va^t numlier of muscles and nerves in tln> walls of the
womb are the provision for more energetic action than is possible to the
placenta, which is composed almost entirely of vascular loops.

'2. The womli .-.ii IT* HI in/* -the emliryo. and its a<-tion would therefore be more
etl'ective for producing the changes in pressure upon it, which is also in imilnlii •/.
<•(' ir/nit t'iki'x /ilni-i in /In- uiitiiinn of the grow ing chick, it beJBgZOOked to mid
fro in the egg b\ the slow rhythmical expansions and contractions taking place
iu the amnion i|i. -I'.I'.M. and by alternating this ai-tion with the one taking place
in the placenta, it is readilv jH'rceived how a rapid circulation could be main
tained in the maternal and placental sinuses for compelling correspondence
lietwecn this and the energetic circulation in the emliryo, since it all forms a
connected whole. This would also be in conformity with the principle
in the circulation, the blood flowing from high to low pressure. As
the placenta i-.i-fiiimlx for reducing pressure within itself, and for increasing
pressure in the emlir\o. *///, <///«///. ..W// and /»iri JMWXH with this action the entire
muscular walls of the womb <;<ntr<i<t for increasing pressure in the maternal
sinuses for eomi>elliiig this blood in the placenta, at the same time by increasing
pressure upon the embryo it should determine a more rapid movement
from the latter to the placenta ; the one involving the other. But when the
placenta contracts for increasing pressure (thereby compelling the blood out
of itself in two directions, or toward the embryo and the maternal sinuses),
the uterine walls expand for reducing pressure in the embryo and the uterine
Minist s, thus greatly expediting the placental efflux; and, taking it all in all,
there can lie very little doubt but that the force which is represented in the
muHled murmur of the placental souffle is mainly the product of the muscular
uterine walls, though l>oth undoubtedly contribute to it.

'.'<. This action in the uterus and placenta would account for the very curious
and suggestive n/i/ii/n//// in that portion of the canals connecting the uterine
with the placental sinuses, being upon a line almost paraUeJ with the transverse
axis of the uterus and placenta, which is precisely what is called for by the
special mechanics, in order to effect the lateral or to-ond-fro movements, the
vessels simply elongating and contracting with these, as the case may be, with-
out interfering with the calibre of the tubes. Were the vessels straight, it
would be utterly impossible to operate this mechanics, since the lateral move-
ments should obliterate the vessels by closing the calibre. It could not be
otherwise, in the very nature of things. In the accompanying diagrams (Figs.
3, 4), the vessels are represented as nearly perpendicular, but this is done
simply for better definition.

I. lint the strongest proof, perhaps, of this higher function of the womb is
furnished in the \asmlar and nervous connections subsisting lietween it and
the maternal organism. And as all this relates to circulation for building up
and elaborating the embryo, obviously the mechanics for increasing circulation
in the womb commensurate with that in the embryo should extend to the vessels
of supply or the feeders, as also the discharging vessels, or the arteries and
\eins. It must be shown how this new movement, this new life set going

10

within the other, twines its arms around the maternal vessels and feeds itself in
the measure of its necessities, by means of this pumping action in the womb and
placenta which represents respiration. The spermatic and uterine arteries are
the feeders (Fig. 6, <s, «), while the accompanying veins are the discharging

FIG. 6.— Showing the ARTERIES AND VEINS TO THE WOMB, fi, spermulic artery and veins
(ovarian); u, uterine artery and vein; 1, vessels passing between the muscular fibres: 2, peri-
toneum; g, Fallopian tube;/, ligament of ovary; r, round ligament: /', inferior ligament or
duplicating of peritonaeum corresponding with Douglas's Cttl de eac; r. vagina.

vessels. To this must be added the uterine lymphatics, which arc very large in
the impregnated womb. They terminate in the pelvic and lumbar glands. The
spermatic arteries and veins have similar origin and termination, as in the
male, while the uterine artery is a branch of the internal iliac, with the venous
return through a vein of the same name. The deeply suggestive fact to
note in this connection is that the dense plexuses of nerves to the fundus and
sides of the womb converge in the nervous ganglia about these vascular trunks,
or the spermatic and hypogastric ganglia (Fig. 7, e, ir, r). It will be seen that
the nerves to the fundus (v, x) converge in, or radiate from, the spermatic gan-
glion (ic), which surrounds the spermatic artery and vein (e) (which corresponds
with the attachment of the placenta), while those in the neck and sides from the
hypogastric ganglion (r) are brought in direct relation with this ganglion by
means ot intercommunicating nerves (/) for unifying the action throughout.
Tims, nervous force to the womb is literally lanked upon the bloodvessels,

3

KliJ. 7 <;\\..i.i\ \\n NI.KW.S in inn liiimn lm:i s AT THfc Kxt> OK TI1K NINTH MONTH.
.1. tin' fnndus and bod) o( Ilu- uterus, having Hie peritonaeum diss<cted off from left side; b,
the vagina covered willi nerves proceeding Irom the inferior bonier of the left livpoi::i.-liii
ganglion: e, rectum: </. left ovarimn ami Kallopian tube; e, trunk of left spermatic vein and
artery eurroanded by tin- left spermatic ganglion; /, aorta divided above the oripin of the
right speimatic artery: ;/, venacava: h, trunk of right spermatic vein: i, ri^'lit ureter: k. Hie
I HO copl- 'if the ^reat .-ivinputhetii- pussin^ down along the front of aorta: /. trunk of inferior
•I'titenc artery with the nervous plexus connecting with the right and left cords of Hie
ijiallietk-; //,. 1 1n' two cords of the i;reat sympathetic at '.he lioint of bifurciition into tin-
riu'lit and left hypo^aslric nerves; n. r\f\\\ hypoi;:iftric nerve with its artery injected, procetd-
ini; to neck of uterue to terminate in the ri^'lit h\pn<;astnr gati.nlion; <>, left bypoaMlta nerve
B left hjpou'astric ^iingliii, and ^ivin^ oil branch'- to the left gub-peritoneul
^an^lia : ,i. hxmorrfaolda] nerves and arterj : •/. sacral nerves entering the whole outer surface
of the hjpoga-trir gunglion: r, left hypogiistric ganglion with the arteries injected; »•. nervi-
of i '. nerves with an injected arlen proceinling from the upper part of left hypn-

L':i-tric ganglion along the body of the uterus, and terminating in the left spermatic ganglion:
'i. continuation of these nerves and the brunches which they L'ive off In the snb-peritoneal
plexuses: /-. >oine nen es passing upward beneath the sub-peritoneal plexuses; and an
nici.-ing fiee|\ with them; "•. left :-pcriu:itic irangliou. in which the nervea and artery from the
hyiiog.istric ganglion, and the branches of the lefi sub peritoneal plexuses terminate, and from
which the nerves of the fiindus uteri are supplied: .r, left sub-|ieriton«'al plexuses covering the
Ixxh of the uteru>: //. left sub-peritoneal ganglion, with numerous brandies of nerves exten. I
ing between it and left li\ nerve and ^arglia: ^, left common iliac artery cut across

and turned aside to expose left hypogastric nerve and ganglion. (After Dr. R. Lee.)

12

and if this means anything it means that circulation shall be in correspondence
with the physiological requirements, or supply equal to demand, the cardinal
circumstance being the </i-»t/1/i and elaboration <>f the embryo, which is the object
and purpose of the organ, the others being simply incidental.

It conies to this, namely, that the nervous force for expanding and contracting
the uterine sinuses should expand and contract the uterine bloodvessels at one
and f/ie n<une time, thereby causing afflux and efflux of blood through them for
compelling correspondence throughout which the scheme calls for. Furthermore,
this wou'd accord with the action in the vessels in respiration, as indicated
by the undulations in arterial tension. But would not this mechanics inter-
fere with the due circulation of blood in the placental sinuses'? Certainly
not, and for the following reasons : 1. Efflux of blood through the veins
is by means of capillary vessels, which tend to retard escape, while the flow of
blood in and out the placenta] sinuses takes place through large canals (Fig.
5, c,c, c, r). But in addition to this, the expansion in the placenta, which occurs
during systole of the womb, should also determine the blood in this direction.

2. During diastole in the womb and its sinuses, for aspirating the placental
sinuses, the hic/h j»-i'xsuri- in the arterial system causes this blood to flow into
the uterine sinuses as rapidly as the blood coming from the placenta ; at the
same time, the valves in the veins of the uterus obviate reflux from the venous
a- if stem. When the womb contracts for compelling the blood in the placenta
and venous system, the pressure in the arterial inhibits reflux in this direction.
Thus the mechanics for increasing circulation in the uterine and placental
sinuses is complete in every respect, nor does it require extensive expansion and
contraction in the womb in order to effect increased circulation through the
sinuses, but a moderate and limited amount, sufficient only for producing
rhythmical changes in pressure upon Hie blood, as must appear obvious : some-
thing similar to what takes place in the spongiic, which have muscles (Norway)
for producing a more rapid circulation in and out this canal system.

Tltis expansion of the irouJ) and arterial feeders would explain the sudden and
enormous escape of arterial blood in post partem haemorrhage, for the placenta
being no longer attached, the flow of blood through the uterine sinuses must
necessarily be purely arterial. In other words, when contraction ceases and
the movement of expansion sets in, the flood-gates are thrown open to the
arterial system.

In reference to the nervous centre for this pumping action in the womb,
which answers to respiration in the foetus. There can be very little doubt
but that the spinal-cord functions as the common reflex centre of nervous force
for producing the rhythmical expansions and contractions in the gravid womb
simulating respiration. The following are the reasons for this allegation : 1.
The very intimate connection subsisting between the womb and spinal cord by
means of the hypogastric ganglia and sacral plexus with the intercommunicating
nerves. 2. The fact that the lumbar portion of the spinal cord undergoes en-
largement during gestation (Mathews Duncan). 3. The fact that reflex action in
the womb is readily produced by applications to the skin surface, a circumstance
well known and practised by the profession. All these facts fall readily

i::

into line when viewed from this standpoint, and. no scientific reason existing in
the eontrarv. we may conclude tin- fact MS logically pio\en. Indeed, the gist of
tin- question is not win-tin i 'tin TI 'is a retlex centre in tlir spinal cc.nl fur the

womb. Imt whether this centre produces tin- rhythmical expansion* and oontno-

tions in that organ :is alleged. A full and sulVicicnt answer to this is fnmislicil
.11 the fact nf tlif total absorption of tin relative phenomena, :matomic;il and
physiological, w hieh otherw U,- are utterly inexjilicalile, underneath all which
:s the organic law on which animal life itself is constructed, railing for
rhythmical changes in pressure in the contents of the gravid womli and in the
uterine sinuses for increasing circul at ion. Nor is it reasonable that the enor-
nions nunil>er of muscles and nerves in the woml) are for compelling Otti the
cmiteiits at the end of the term simply. Imt, on the contrary, that they jH-rform
an active and essential part in the work of construction whirh ]>rci-edc8 expul-
sion, lieyond a shadow of a doiilit. they arc not idle in all this while.
:ally when supreme necessity would h:ive it otherwise; Oil the contrary,

they an- n* /'<•/•'- /•«/ for carrying on circulation, while at

the end of the term they are available for insisting in expelling the embryo,
hence pe, form an active ;••./< from the beginning to 'the end of their existence,
as is e\er the c;i.se with tin- miiM-les and nerves.

( )nc oth'-r circumstance in tliis connection, namely, the very l<n-ln<»ui course
of the arteries in the womb i Fig. C> i, which undoubtedly is adjustment with
this action, |K'rinittiiif; the rhythmical ex]iansions and contractions to take place
without involving any strain to the vessels. The veins, it will be perceived, taki >
a straight (Miu-sc, wliile the arteries are serpentine or ln>nt njvm themselves.
HUB is tine to the fact that the veins are more extensile, and possess greater
IMI-.VCI-S of elon^atiiiL,' and shortening than the arteries, the yellow elastic coat of
the latter tending to limit their actions. It will IK? remembered that this cir-
ciini.-t nice has forcible illustration in th" splenic artery and vein, the former
being almost twice- the length of the latter, to allow for expansion in the stomach
when fixxl is taken, otherwise this would involve prodigious strain to the vessels,
with great re luction of the calibre. But the same remark will apply to the ves-
sels of all the hollow viscera. Thus everything is in correspondence. Of course,
the arc of movement in the womb and placenta is necessarily more limited than
in the lungs, in 'which considerable space is required for sucking in the air
simultaneously with the venous blood, but which would not apply for the foetal
circulation, as the oxygen is furnished by art.-ri.'il blood at "/»• «ml the samr lini'
with the nutritive and force-producing elenvnts, which the scheme calls for in
order to generate force, since it is by a combination of the two that force is
evolved. The inclusion of the intestines with respiration by means of the
I meumogostric nerves has its explanation in this circumstance, as has been
fully set forth in the preceding pages. Differentiation in the organs
cannot, for obvious reasons, work any change in the fundamental principle
underlying the mechanics for increasing circulation, which is by rhythmical
changes in pressure involving a pumping action for compelling the commerce in
the bloodvessels and expelling waste products, while the speed of the currents
thus produced is determined by the rapidity and energy of the rhythmical ex-

14

pausions and contractions pervading the organs, inclusive of the heart ami
vessels, since it all forms a connected movement for increasing circulation be-
tween the cell brood and environment, from which everything is obtained and
into which the waste products are returned, the two going on simultaneously.

With the expiration of the intra-uterine term, expansion of the maternal
passages sets in for reducing resistance to the egress of the embryo,
and the womb and abdomen contracting simultaneously for increasing pressure
in the womb, the contents are compelled out in the environment. Here, as
elsewhere, the Jaw of pressure applies for compelling n/nri'/ncnf in flic con-
tents of the, Iwlloiv viscera for which xj>fri<t/ adjustments obtain in the organs and
organism, the underlying principle being rhythmical i-lnn/ifs hi jircsNim:

The atmosphere being invisible, it is difficult to realize the important relations
this sustains to the mechanics, nevertheless, the fact is incontrovertible, that
from centre to circumference, and from surface to surface of the body it is
corner-stone and foundation to all t/te mechanics conccnii-i/ in circulation.

It is passing strange the matter should have escaped attention so long,
espacially in this age, when thnujh.f is reaching do.vn into the organic basis of
life. Indeed, one needs to go there if he would unravel the tangled skein
in animal structure and function, since the definite arrangements that obtain in
the organs with every stage in development show unmistakably a common
relation to fundamental forces in nature underlying it all, notably pressure run/
gravitation. The animal body is not outside and independent of the organic laws,
but, on the contrary, is in entire conformity with them, while the arrangements
which obtain in the structures represent the relative adjustments for special
work.

KESPIEATION IN THE NEW-BORN : THE CHANGE IN MECHANICS WHICH THIS INVOLVES.

The first thing in the new-born is to start respiration for compelling
in the commerce in the environment in place of the uterine sinuses, and
the action in the placenta for which this is the substitute, the oxygen passing
in by way of the kings and the aliment through the intestinal canals. But this
requires fresh adjustments in the mechanics of circulation to bring it in cor-
respondence with this circumstance, notably, circulation of the blood in the
lungs, and the attaching of the intestinal apparatus to this movement by
means of the nerves connecting in the medulla oblongata, a matter which has
already been fully considered in the preceding pages. The first thing, there-
fore, is to start respiration, when it will bo in order to consider how tin
mechanics in circulation swings into this pendulum movement for compelling
correspondence throughout, with the blood ever flowing from high to low
pressure in conformity with the organic law underlying the organism itself.
One end of the nervous system, so to speak, is .t/iread out in the skin
surface, the other through the organism, while the medulla oblongata functions
as the common centre to it all ; any impression, therefore, made upon the skin
surface is promptly reflected to the medulla oblongata, thence over all the
structures for producing the reflex actions connected with respiration and
circulation, The irritations attendant upon parturition from friction agains*-

15

tlir maternal structure^ .-in- calculated to produce these reflex actions;
l>ut tlir contact nf tin- sentient surface \vitl> the stiiiuilus in tho atmosphere itself
woiiM also excite it. And if tin- child should lie injured by tin' rude experii-ne.-s
incident il to |>.-irtiiritii>n. a yet more powerful means fur exciting tin- reflex
actions connected with respiration is furnished by the su.ldeii application of
cold t i the surface, as in sprinkling cold water upon it, or a sudden, shurp
slap with the open hand may lie substituted instead, as is commonly practised.
List, lnit not least, c.irlionie arid, ;LS it accumulates in .the blood, acts UK
a special stimulus to respiration. It cries out hi pain, and, presto! the
liemal mechanics is changed. The low pressure which is produced in the
aheoli by expansion of the lung's during inspiration compels xiiiinllnin-onn afflux
of air and blood in the alveoli ; while the high pressure which is produced l>v
tin- subsequent c-int ruction during e\]iinition causes *////«//</»<.,»> efflux in
these tluids. which (low from high to low pressure in conformity with organic
law the one (lowing out liy retlux action through the route of ingress, the
oilier p.-is.,iiu into 'he left chambers of the heart and arterial system on its way
to the cell-liroo 1. as has already been described in the air-breather. This
•I'.aiidonment of the old route for the new is readily explained, since it is in
sti ict accordance with physical law, l>eing in the direction of least resistance.

For example, we /<•<//« the mechanics with high pressure in the arterial sys-
since this extends through tho ductus arteriosus to the semilunar valves of
the pulmonary artery, the floor of support to the arterial column. Hence, when
the alveoli expand during inspiration for sucking in air through the trachea,
the high pressure- in the pulmonary artery and ductus arteriosus compels this
blood to flow straight on to the low-pressure areas in the alveoli rimulianeaualy
\\ith the alflux of air, or in the direction of least resistance, in place of forcing
its way in the arterial system against high pressure, which would be contrary to
law. And the ductus arteriosus, though still filled with blood, as in the case of
an artery, beyond the ligature to where a collateral branch is given off, shrinks
an 1 contracts till it becomes a solid, impervious cord.

For closing the foramen ovale the following mechanics apply: After birth
the inpour of blood in the left auricle by way of the pulmonary veins is as
rapid as it is in the right auricle through the venae cavse, and pressure is at
equilibrium in the two auricles, which at once suspends all tendency in the
lil ood to pass from one side into the other during auricular diastole ; whilst
during the auricular systole and the high pressure this produces hi the auricles
causes this blood to flow into the expanding ventricles, where low pressure
invites it, the same applying for either auricle. But gravitation also
should compel it in this direction, since the ventricles are under the auricles.
Thus a dual force applies (suction and gravitation) for compelling this blood in
the ventricles during the auricular systole, and the foramen ovalu, being thus
abandoned, is closed and obliterated by membranous formation.

But in uitra-uterine life the matter is different ; here the whole blood is

• The intimate connection galisiuinu' iwtw.f i in.- r ••>:>! r. ,ui'l the glcin an Tun- ia of

• •.!-> 'li'inninlratiiMi in tin1 tulult liy tin1 sann- IIH- i;is. Kur fxample, every impact of mid walrr
• tin* akin i>r."'l !.••'•- <|i i~ n<> lir iuspinilinu or ex[> union ill tlie luiigi ; not deep, however,
l>ul very energeiir.

1(5

poured into the right auricle, that from the upper cava passing at once in the
right ventricle, while that in the lower cava (which includes the blood from the
umbilical vein) passes through the right into the left auricle, with which it
directly communicates, guided by the Eustachian valve, but also pushed over
and deflected in this direction by the weight of the descending current from
the upper cava ; but if the head be downward then by its own weight the blood
would gravitate in this direction, the influx of blood from the upper cava also
compelling it. And 'with the absence of blood as a counter-force in the left
auricle this blood is necessarily compelled in the latter, thence in the left ven-
tricle and aorta, while that in the right ventricle passes in the arterial system
at the aortic arch by way of the pulmonary artery and ductus arteriosus. After
birth, however, the pumping action in the lungs reverses all this in manner as
above described. The pulmonary artery in the embryo, in place of dis-
charging through the lungs, left auricle and ventricle, empties its blood at
once into the aorta as it passes under the arch, and which is also in the direction
of least resistance, since it is impossible for this blood to thread its way
through the capillary meshes of the unexpanded alveoli. This circumstance has
forcible illustration, even in the air-breather, and when the alveoli are filled
with residual air, by simply inhibiting inspiration by closing the mouth and
nose so as to prevent expansion in the lungs, the blood, in consequence, rapidly
accumulating in the right side of the heart and venous system. Tn the space
of a minute there is lividity of the lips and whole cutaneous surface from
venous stasis in the systemic capillaries. If longer than this, an appalling
venous suffusion pervades the surface ; in the face most, for this is the most vas-
cular portion, with the large venous trunks in close proximity to the heart.
Even the eyes are forced outward, becoming prominent from distension of the
iutra-orbital veins caused by obstruction in the cavernous and lateral sinuses.
But the instant the obstruction is removed and the lungs are permitted to
expand the dammed-up blood surges through the alveoli, and all runs on as be-
fore. In other words, the heart and vessels are unable to carry on circulation
in the absence of the pumping action in the lungs, for which afflux and efflux
of air is essential. But all this has been sufficiently explained.

INCUBATION. CIRCULATION IN THE EGG.

Why should there be an air-chamber to the egg (Figs. 8 and 9) ? We
are now prepared to furnish a scientific explanation to this physiological problem,
otherwise inexplicable, viz., the contents of the egg for developing the chick is
enclosed by a firm unyielding wall of living marble, and since the animal circu-
lation is dependent upon rapid rhythmical changes in pressure, it follows that
provision should be made within the shell for effecting this, otherwise the action
in the heart and vessels could not take place. This air-chamber (g), together
with the important relations it sustains to circulation and elaboration in the
growing chick, organilogically, therefore, must be regarded as one of the most
essential and important elements in egg-structure, the underlying principle to all
the nutritive changes which are ushered in under the action of external temper-

17

iituri'. The Hccomiunvin^ illustration i FiU'. Hi will serve to impress the
mutter.

Tin- discipline in tin- nutrithe processes requin-s the blood to be brought
from tlie vitellus and a • rated in the allantois. thence to be dispatched through
the Imdy territories. Accordingly tun great venous trunks (omplialo-meseraic
veins i, one in each fold of the aplanahnopfetm, embnofng the vitellus, are the

KI<;. s. MuiiRAM OK l-ntti.'- Koa. A, yelk; '. vitel!im> membrane; c, chnlaziferous membrane;
d, albumen; e. f. miililli* anil internal shell memiirane.-i : y, uir chamber; A, calcareous shell.
(Aft«r Dalton.)

first evolved, while at the terminal ends or confluence the heart is formed by the
blending of the walls of these venous trunks.

According to His. the heart is developed by the coalescence of a layer of the
splauchnopleure with a similar layer from the somatopleure, the hollow cavity
formed by the union bein^ in free communication with the adjacent omphalo-

FIC. !). — Eoo or FOWL is I 'HOC BSD
circulation, terminal sinus, etc.

[)KVKt.opjiEXT, showing area vasculo.ia. with vitelllne

meseraic veins. According to Foster and Balfour " the upper end of the heart
is developed out of the mesoblast of the splanchnopieure," but " increases in
length step by step at the expense of the continually coalescing ouiphalo-

18

meseraic veins." Thus the fact is undeniable, that the heart is developed
in the venous system in connection with the vitettus. The rhythmical ex-
pansions and contractions in this organ (the punctum saliens of early authors)
serve to pump the vitelline fluids in the bulbus arteriosus and the two aortse
which are developing at the other end of the heart. But for this air-ciishion
within the egg (Figs. 8 and 9, g), neither these rhythmical expansions in
the heart nor the changes in pressure for compelling circulation in the vitelline
fluids could take place, since the unyielding shell would inhibit these actions, as
must appear obvious.

Respiration is provided for in the following manner : The aUantois (a diverticu-
lum of the intestinal canal) is pushed out around the amnion which contains the
embryo, and expanding its vast capillary net-work of vessels (whose footstalks
spring from the two iliac arteries, as do the umbilical arteries in the mammalian
embryo) against the shell-membrane or chorion becomes the respiratory organ of
the chick, by means of which the venous blood is constantly arterialized, the oxygen
passing in and the carbonic acid passing out through the pores in the shell by
the action of the polar forces. But " at the time the heart first begins to beat,
the capillary system of the vascular and pellucid areas is not yet completed,
and the fluid which is at first driven by the heart contains, according to most

observers, very few corpuscles The course of the blood then,

during the latter half of the second day, may be described as follows : The
blood brought by the omphalo-meseraic veins falls into the twisted cavity of
the heart, and is driven thence through the bulbus arteriosus and aortic
arches into the aortic trunk. From the aorta by far the greater part of the
blood flows into the omphalo-meseraic arteries, only a small amount passing on
into the caudal terminations. From the capillary net-work of the vascular and
pellucid area into which the omphalo-meseraic arteries discharge their contents,
part of the blood is gathered tip at once into the lateral or direct trunks of the
omphalo-meseraic veins. Part, however, goes into the middle region of each
lateral half of the sinus terminalis, and there divides on each side into two
streams. One stream, and that the larger one, flows in a forward direc-
tion until it reaches the point opposite the head, thence it returns by the
veins spoken of above, straight to the omphalo-meseraic trunks. The other
stream flows backward, and becomes lost at the point opposite the tail."*

The following from the same authors is deeply suggestive: "Soon after its
formation the heart begins to beat, at first slow and rare pulsations, beginning
at the venous and passing on to the arterial end. It is of some interest to note
that its functional activity commences long before the cells of which it is com-
posed shoiv any distinct differentiation into muscular or nervous elements." It
would be difficult to overestimate this circumstance, since it establishes beyond
peradventure the power in the higher as in lower animals to effect rhythmical
expansions and contractions in the soft tissues in the absence of any muscle or
nerve for producing them. But at present the significance of these rhythmical
expansions and contractions taking place in the heart concerns us most, since
the manifest purpose is to increase circulation ; and as this can only be done by

* Fos'.er and Balfour's •' Embryology."

1'.'

pumping the blood of the omphalo'iMSwaio veins, it follows that both expan-
sion and contraction is necessary for accomplishing this, the one for aspirating
this fluid, tin- other for pn>|>ellini; it. This would explain why the action should
In-ill a <il this r/(//(i////c hi urt. ( )f course, as the area of circiilntioii increases it
would c.-Jl for corresjKMidmg increase of force for effecting it. Accordingly, prea-
"I for facilitating circulation at the same time that additional force
i> placed ii]x)ii it ; notablv, the former is produced \>\ tin1 ainniotic fluid and the
latter by the action in the ainnion.

Tin' aiuiiion closes around the embryo of the chick on the fourth day,
and on the fifth tluid U^'ins to collect in the sac, and by the seventh the
embryo is submerged in a considerable quantity of water. "By the seventh
day very obvious movements U'gin to api>ear in the amnion itself : slow vermic-
ular contractions creep rhythmically over it. The amnion, in fact, begins to
pulsate slowly and rhythmically, and by its pulsations the embryo is rocked to
and fro in the egg. This pulsation is due, probably, to the contraction of
involuntary muscular fibres, which seem to be present in the attenuated
jHirtion of the mesoblast, forming part of the ainniotic fold" (Foster and

K-llfoUM.

The physiological significance of this accumulation of amniotic fluid, and the
rhythmical contractions and expansions in the amnion, may not be doubted for
a single moment, since the former would increase pressure, while the latter
should produce the necessary changes in pressure in the embryo for compelling
respiration and circulation to be in correspondence with the nutritive and func-
tionid processes in the growing chick, both of which are constantly extending
their limits and requiring more and more force for effecting them. These
slow pulsations in the amuion of the chick answer to the placental and
uterine souffle in gestation, the principle being precisely the same. How other-
wise explain this circumstance ? But, as has already been remarked, a II pulsa-
tion* relate to changes in pressure, and these pulsations in the amnion, together
with the amniotic fluid, relate to changes in pressure in the embryo for increas-
ing circulation of the juices.

The explanation of the mechanics is sufficiently easy ; notably, there are two
cardinal points from which to regard it — one in the allantois, the other in the
embryo. First, commencing with the movement of expansion in the allantois.
The increase in pressure which this produces in the embryo through the am-
niotic fluid should cause the venous blood to flow with increased energy towards
the allantois, the point of low pressure within the egg (the heart and vascular
>\ stem, of course, assisting in this); the contraction or condensation of the
amnion. by relieving pressure in the allantois, enables this to expand part passu
with contraction in the amnion for aspirating the venous blood, at the same
time that it aspirates the air through the outer membrane and pores of the shell.
When the movement is reversed by expansion of the amnion, the reduction in
pressure which this effects in the embryo, together with the simultaneous in-
crease of pressure it produces in the allantois by forcibly compressing this
against the shell wall, causes the aerated blood in the latter to flow with aug-
mented speed into the heart of the embryo, as also through the tissues of the

20

1 'liter; since thet blood vascular system woiild be less embarrassed and be more
free to act in cousequei:ce.

. |But the allantois itself also participates in this action, the fluid it contains
enabling it to effect such rhythmical compression of the capillary plexuses

TIG. 10. — DIAGRAM OF YOUNG EMBRYO AND ITS VESSELS, showing circulation of umbilical
vesicles, and also that of allantois, beginning to be formed. (After Ualtou.)

(Fig. 10). The following forcible illustration (Fig. 11) by the distinguished
biologistjat Jena will serve to impress the matter. At this early stage in develop-
ment (third week in gestation), it will be seen that pressure is increased at the
•cardinal points, namely, vitellus (a), the body of the embryo (c), and allantois

FIG. 11.— HUMAN EMBRYO IN THE THIRD WEEK. A, large globular yelk-sack; f>, allantois;
c, amnion ; d, tufted cborion. There are yet limbs. (After llueckel.)

(b). As the embryo and allantois are elaborated out of the material in the
vitellus, this would explain the greater accumulation of fluid in this locality for
compelling circulation toward those two points, whilst the rhythmical contrac-
tions of the yelk sac should greatly expedite it. For increasing circulation

•Jl

between tin- cnibrvo :uul aliantois (c, /'i, commensurate pressure is prcxluced by
iici-iiinuliitiiHi of fluid in these two jitiints or jioles of tin- circulation. This, to-
gether witli tin1 action in tin- mtmihranes themselves, and the heart and vessels,
is siillicient forcaiTvine; on circulation in the iaitiul stages of embryonic evolu-
tiou ; lnit witli tin- incr. "\\tli comes increasing difficulty for effecting it;

hence the pumping :ictii>n whicli is set up in the placenta and womb, together
with tin' accumulation of iimiiiotic lluid for transmitting these actions upon the
embryo, a.- described above. Tlnis, even tiling is in correspondence — the
liquor iimuii, the inoreaoBg growth of tin- placenta .-mil the number of muscles
and nerves in the walls of the womb — and so continues till the close of preg-
nancy. In other \vonls, it all forms a coniu-ctc d whole in the mechanics of the
i-mhryoiiie circulation.

In tlic case of the bird, the jillantois answei-s to the placenta, since it pumps
in both o\\L,'en and nutriment ; only that the pumping action in the abdomen
(the soft hinder parts of the bird) for pumping air and blood through the
alveoli, is set up in the hitter days of incubation, when rapid atrophic changes
soon obliterate the umbilical vessels, and, breaking the now attenuated and
fragile sht 11-wall witli its b«ak, it finally makes its escape, leaving the allantois
and atrophied membranes behind.

MODE OF GRAFUMi Till. o\l\l l\ THE TISSUES OF THE WOMB.

In jiHiiiiiH'iliii tho ovum is not discharged from the maternal passages, but i«
retained in the expanded oviducts at the point ol juncture, which answers to-

FIG. 12.— A VERTICU Sn Tins FROM THE FIG. 13.— Same tubules, greatly magnified.

UTERINE Mi'cors MEMBKAXK, showing the (After Dalton.)

numbers and position of the tubules.
A, free surface ; 6, attached surface.

(After Dalton.)

the womb, where growth and elaboration are effected through the vascular con-
nections established between it and the maternal circulation. Briefly, the mode
of closing this is as follows : The uterine mucous membrane is virtually but a
dense mass of single, straight follicles, arranged perpendicularly to the free sur-
face (Figs. 12, 13), and with the closed end resting against the muscular

22

walls of the womb. At intervals, fine bloodvessels course up between them,
and, reaching the mucous surface, surround the tubules with a capillary network.
But when fecundation is effected vascular turgessence at once sets in, producing
rapid growth and development of the membrane — of the follicles especially ;
and, coming in contact with this highly vascular and tumified surface as it leaves
the Fallopian tube, the ovum is rapidly incorporated with it, by means of the
•shaggy villosities which are thrown out from the outer surface (Fig. 14, «..),

FIG. 14.— OVUM OF THE RABBIT, from a Graaflan follicle J6 of an inch in diameter. A, epithe-
lium of the ovum; 6, zona pellucicla, with radiating striations (vitelline membrane);
c, germinal vesicle; rf, germinal spot; e, vitellus. (After Waldeyer.)

FIG. 15.— IMPREGNATED UTERI'S, showing connection between villosities of chorion and decidual
membranes. (After Dalton.)

which grow into the expanded orifices of the tubules, and function as temporary
villi for pumping the abundant albuminous secretions of the glands in the in-
terior of the ovum. Of course, they contain all the elements of tissue struc-
ture. With the ingrowing of the shaggy tufts of the chorion in the follicles,
the mucous membrane expands around the ovum for bringing the follicles in
contact with every portion of the chorion till the whole is completely enclosed,
forming what is known as decidua reflexa, while that portion of the membrane
•with which it first came in contact, in immediate relation with the muscular
walls, constitutes decidiia, vera, the part that enters the structure of the
placenta which is subsequently formed. At this time the villosities of the
chorion project into the uterine follicles in every direction (Fig. 15), but as
growth proceeds, aiirl more and more nutriment is needed in the embryo, the
villi in relation with decidua vera become vascular, while those in relation
with decidua reflexa are atrophied, in consequence of which this portion of the
•chorion becomes bald. Finally, the transformations which occur in the placenta

'

* •

convert the tubules int.. pl.-iccnUl sinuses, and tli.' villi of the chorion into vaa-
culiir loops, •Demanded and embraced liy the lining membrane of the HiiiUKOM,
like the finders of a glove i I'i^. 16), aa before remarked; hut since the osipil-

l.irv lm>ps ore projected ill the villi, the natural inferenee is that the Walls of tllO

latUT coalesce with tin' walls of the sinuses to form this intervening mem-
brane. In this manner the embryonic and maternal structures are inseparably
Mended.

! 1 . I-,. <KI M FROM TIIK MOLE. A, nucleus; 6. cell body; c, thickened corpuscle traversed by
pores. (After Leydig.)

FIG. ir. TIIK UIMVX K.Ki FROM THE OVARY OK TIIK FKMAI.E: MUCH ENLARGED. The entire
egg is a simple, globular cell. The greater part of the spherical egg-cell is formed by the
egg-yelk, or the granular cell-sulwtance (protoplasm), which is composed of innumerable
delicate yelk granules, with a little intervening substance. The germ-vesicle, answering to
tlif .Til kernel (nucleus) lies in the upper part of the yelk. It contains a dark nucleolns or
••ii-spoi. Thi-^lolmlur 11111*4 of yelk is surnmn<lr<l l,y u thirk transparent egg-memlirane
'«"'« 'I'liix i- penctraU'd by the pore-canals, in the form of very

numerous hair-like lines, which run rapidly towards the centre of the globe; through these
the thread-shaped, moving sperm cells pass, in the process of impregnation, into the egg-yelk.

'Hie common relation which animal life sustains to the organic laws has

forcible illustration in the very ova, the structure being fundamentally the same

If. and 17). The absence of a shell wall permits expansion in the

chorion /,-iri ;>assu with the growth of the embryo, while the womb expands in

concert with this action in the chorion and embryo.

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to $1.00 per volume after the sixth day. Books not in
demand may be renewed if application is made before
expiration of loan period.

SEP 16 1930

NOV 2 4 1939
&

60m-7,'29

jrtg

399398

UNIVERSITY OF CALIFORNIA LIBRARY