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II. On the origin of the pulmonary arteries in mammals

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11. ON THE ORIGIN O F THE PUTXONARP ARTERIES
I N MAUMALS.
JOIIN LEWIS BIIEMER.
I l a r u u l d Nctlicul School.
In 1902 I publishcd a p a p a on this subject,' a rcsiiini! of which
is here given. The pulrnonary arteries i n man, rabbit, cat,, :uid dog,
appear as symmetrical vessels, one rising from each fifth, or piilmonary arch. With the growth of the truncus pulmonplis, and its
torsion about the bulbus aortq the two pulmonary arches are wound,
as it were, around the bulbus, and their malls thus brought into
contact are absorbed, so that the truncus pulmonalis grows longer at
their expense, the point of bifurcation moving continually farther
from the heart. The left arch, being the outside one in this rolling --p
proces3, receives the most pull, beconies the strnighkr and therefore tho
larger vessel, and is shortened more rapiay. As a rcsult, the point of
bifurcation of tlic truiicus pulmonalis reaches the left piiliiionary
artery while the right piillnonary artery is still s e a arising froin the
right arch some distance dorsal to this point. (See diagram, page
338). The portion of the right pulmonary arch between the origin
of thc pulmonary artery and the dorsal aorta becomes obliterated, the
anterior portion of the arch remains continiioiis with the artery,
and we then have the condition described by Rathke,-the
two pulinonnry arteries apparently arising together from the left piilmonary
arch. It should be noted, however, that the right pulmonary artery
of thc fetus includes, beside the homolognc of thc left pulmonary
artery, the proximal portion of the right pulmonary arch.
In the pig, although the pulmonary arteries first appear, as iisual,
as symmetrical offshoots, one from each pulmonary arch; and although
the fetal condition is practically the same, the intermctliatc steps
Am. Jour. Annt., Vol. I, No. 2, p. 135, 1902.
(334)
Pulmonary hrteries in Mammals.
335
are different. The two arteries, while their points of origin are
still far apart, bend toward each other lower down, and soon
anastomose to form a long vcssrl, connected at its upper end with
both the right and the left pulmonary archFs, and forking at its lower
end to send a branch, to either lung. Soon the upper, or proximal,
part of the right pulmonary artery becomes obliterated, leaving the
common stem in communication with the left arch only, thus forcing
the blood to hot11 Inngs to pass throiigh the Icft pidiiiontiyy arch.
Since 1002 I hare been able, through 11(w acquisitions to thcx
IIarvarcl Embryological Collwtion, to tracc the drv-dopmrnt of the
pulmonary arteries in other mairimals,-opossiim, sheep, and gniiwa~ tPA.
.
Rt,€?A.
Lt.p.'a.
/Y
FIG.l.-Guiiiea-pig, 7.7 niiu. (11. IC. C., Series 151'2, sections 10-233.)Dorsril
view. P . A., pulmonary arches, left and right; p. a., pnlmonary artery ; T . P.,
triincus pulmonolis. x 125 diam.
pig, a d to malie a few observations on the cow and deer. In the
opossum and sheep the picture is essentially the same as in man, rabbit, cat, and dog, though in the sliccp thc two pulmonary arteries arc
Lronght to the bifurcation a t almost the same time, so that very little
of the right arch plays a permanent rGle i n the right pulmonary
artery. I n the guinea-pig, on the other hand, the development of
these arteries follows very closc.ly that described in the pig, but with
oxit: important difference. I n both animals the arteries originate as
symmetrically placed vessels from the right and left pulmonary
arches, iii both they bend toward each other and anastomose, niitl i n
both the upper end of onc pulmonary artcry, from the arch to the anas-
336
John T,e&
Eremer.
toniosis, becomes obliterated, leaving the anastomosis and the lower
ends of both arteries connected with o d y one arch. I n tho pig the
left arch remains in communication with the cotnbincd pulmonary
arteries, in the guinea-pig the right; in the pig the entire right piilnionary arch from the bifurcation of the truncns puhnonalis ~ C C I I K I ~ S
x
FIQ. 2 . 4 u i n e a - p i g . 8.0
125 diani.
inin.
(11. E. 0. series 1513, sections 277-315.)
Fro. 3.--C:uirrea-pig, 8.2 UIUI. ( H . E. C. series 770, sections 230-256.)
r. p . a.. ronjoined pulmonary artericis. The lower portion of the pulmonary
arteries not shown. x 126 diam.
obliterated, in the guinea-pig the antcrior part of the arch, as f a r as
tlie origin of the right pulmonary artery, lwoines incorporated i n
the adult pulmonary artery, and only the posterior part is lost.
Minor differences of development occur in the two animals, ap, may
be seen by comparing the accompanying drawings with the figures
of pig enibryos in the former paper. The piiltnonary arteries in the
giinea-pig are seen to forin a meshwork of capillaries and to preserve
Pulmonary Arteries in Mammals.
337
their irregular course even after the upper part of the left artery has
bt-collie obliteratcd. From the beautiful injection of the blood vessels of eiiibryos made by Dr. 11. 11. Evans of the Johns Hopkins
Medical School, it is probable that in all embryos the pulmonary
arteries, in common with all other small arteries, arise at first by a
capillarj network, and that only later the main channels become
1;irpr and free from the surrounding capillaries. Remnants of this
capillary origin of the pulmonary arteries are not infrequently seen
in einbryos, as for instance the short resscl froin the right arch in
Figure 2, loop formations near the pulmonary arch, side twigs from
the arteries, even ( i n one instance in a sheep embryo of 10.0 mm.,
H. E. C. series 1340, sections 398-490) an artery which is double
tlironghont iriost of its course, making a very long loop. I n the
gnix1c.a-pig this earl) conditioii lasts longer tliaii in the pig or the
other mammals studied,-the pulmonary arteries are later in straight(wing out aiid becoming distinct channrJls.
Another minor difference lies in the fact that, although in both pig
and guinea-pig the two pulmonary arches are w-ound about the bulbus
aortae as described above, in the guinea-pig thcre seems to be no
fiision (or at least a niucli delayed fiision) bttwecn the two, so that
the truiicus pulmonalis is not lengthened, as in other mammals, at
the expense of the two arches; tlip two arches inerely lie one below
the other, side by side. This is shown i n Figure 3, in which the left
arch is seen to overlap the right for a considerable distance; if fusion
had taken place, as in the pig, the pulmonary artery would already
seem to spring from the bifurcation instead of distinctly from the
right arch as i n the drawing.
I n 100.1, two years after my first article, Sakurai published a
paper in which he dcscribes the growth of the pulmonary arteries in
the deer.' The original starting point is the same, two symmetrical
biids, one from each pulmonary arch ; but the left pulmonary artery,
according to this author, moves toward the bifiircation of the trunciis
pulmonalis, and then continues farther to the right until i t arises
distinctly from the right arch, near to the origin of the right artery.
zAtiat. Anzeiger, Band X S V , No. 14, 11. Xl, 1W.
John Lewis Bremer.
338
Diagram II a
I ~ I A Q R A ~I.-Shows
I
the original symmetry of the pulinonary arteries, and,
in the second figure, the result of the torsion about the bulbus aorta?. A,
truiicns pulnionnlis, itt the point of the original bifurration ; B , point on left
pulmonary arch where the left pulmonary artery rises; C, same for right
side.
DIAGRAM
11.-(a) In the pig ; shows the original syniiiietry, the pulnionary
arches less wide spreading, tlie arteries nearer together. In the serond figure,
tlie anastomosis o i the nrtrries, arid in tlic third figiire, tlie result of torsion.
( h ) Saiiie for tlie gninea-pig.
Pulmonary .\rtrries in 3Iainmals.
339
I feel obliged to doubt, not tlie figures in Sakurai's paper, but the
interpretation of them. Certainly in tlic deer3 in this laboratory
I find nothing that would lead one to suspect that the deer differed
from inan, rabbit, sheep, cat, or dog in thc development of its pulmonary arteries. I n embryos up to 0.8 mm. in length the picture
is the usual one, tlw two pulmonary arteries approaching each other
as the bifurcatiou of the truncus puhuonalis is brought farther
dorsal; :and in an eiribryo of 18.6 mm. (H. E. C., series 1230),
whose general characteristics show it to be younger than the oldest
figured by Sakurai, the left pulmonary artery is seen arising from
a short stmi common to it, and the right pulmonary artery. The 1'0sterior part of thc right pulmonary arch no longer exists. The arteries are well established, with thick walls, so that any migration would
sceni impossible. A short coninion stem for tlie two pulmonary
artc~iusin th(>fe.tus is not, iiiicommon, niid I should prefer to intcr~ial
of this commoii
prct Sakiirai's last figure as an ~ i ~ i ~ slengthening
stein rather than a s a niigratioii of the left artery along the right
arch, especially as tlic landmark, tlic posterior part of the right pnlnionary arch, is lacking.
I f we accept this interpretation of Sakurai's,figures, the different
methods of the derelopmcrit of the pulmonary arteries so f a r reported
fall into two main groups, one of which may bc subdivided. (1) I n
man, cat, dog, rabbit, sheep, cow, deer ( ?), and opossum the devclopment may be described by Diagram I. ( 2 ) I n the pig and guineapig the development differs from that of thc other mammals mentioned, and may be shown roughly in Diagram 11, (a) representing
the pig, (b) the guinea-pig.
I n this curious grouping of the animals studied, generic lines
seem to have no influence. I n my former paper it was suggested
that the large size of the auricles in the pig embryo caused the cro\vding together of the pulmonary arteries and their consequent anastomosis, and I again offer this explanation. Tn tlie guinea-pig also
tlie auricles are very large at the time ivheii tlie piilmonary arteries
'Cerriis canrcolzrs. The luhoratorr is indebted to Professor Franz Keibel
for the eubrsos.
,740
;Toliii Lrwis Werner.
arc growing, but there seems to be no crowding of the tissue Burrounding the trachea from the sides. The mechanism seems to bc
slightly more complicated. The large auricles and largc sinus venosus
separate the trachea posteriorly from the bulbus aortae and the
triinciis piilmonalis anteriorly more, it seems to me, than is usual in
animals without the large auricles. The aortic arches are straightened out more, the figure they present with the bulbus or trunciis
bccomes inore like a Y than like a tuning fork, and hence tlie piilm n a r y arteries, starting out a t right angles to the piilmonary
arches, point toward each other instead of backward, as in other
animals. This purely mechanical result of large aiiricles seems to me
to account for thc difference of devclopnic-nt between the pig and the
guinea-pig and all other mammals studicd. The cause of the larger
aiiricles I do not know; nor can I cxplain why, after the anastomosis, the left artery i n one case, and the right in the other, should
remain permanently.
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