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.