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THE JOHNS HOPKINS HOSPITAL REPORTS MONOGRAPHS. NEW SERIES No. V
THE ORIGIN AND DEVELOPMENT OF THE LYMPHATIC SYSTEM
BY
FLORENCE R. SABIN
(From the Anatomical Laboratory of The Johns Hopkins University, Baltimore)
BALTIMORE
THE JOHNS HOPKINS PRESS
1913
[Copyright, 1913, by Th« Johns Hopkins Pret»l
#^2^~
/TL>
CONTENTS.
PAGE
I. Introduction
1. Morphology of the vascular system, the angioblast . . 1
2. Morphology of the lymphatic system 4
II. Historical -I
1. Vasa serosa 4
2. Lymphatics with open mouths 4
3. Discovery of endothelium 0
III. Embryology 7
1 . Introduction 7
2. Lymphatics as dilated tissue spaces s
3. Analysis of Budge's work s
4. Statement of the three arguments lor the origin of lymphat- ics from the veins 10
A. Growth of lymphatic capillaries by sprouting 10
B. Lymphatic and non-lymphatic zones 18
C. Direct budding of the lymphatic vessels from the veins 21
IV. Primary lymphatic system in different forms -24
1. Primary lymphatic sacs in the pig 24
A. General summary of the sacs 24
B. Origin of the jugular sacs 25
C. Origin of the renal sacs 35
a. The retroperitoneal sac 35
b. The iliac sacs :;>;
c. The cisterna chyli 36
D. The thoracic duct 40
2. Primary lymphatic sacs in human embryos 45
3. Primary lymphatic sacs in rabbit embryos 17
4. Primary lymphatic sacs in cat embryos 48
5. Primary lymphatic system in birds, posterior lymph heart and jugular lymph sac 50
6. Primary lymphatic system in amphibia, anterior and poster- ior lymph hearts 55
V. Peripheral lymphatic system 59
1. In the pig 5!)
A. Prom the jugular sacs 50
B. From the renal sacs 63
2. In other forms 65
VI. Origin and development of lymphatic glands and their relation
to primary lymph sacs 05
S
II COS rENTS.
PAG]
VII. Comparative morphology of primary lymph sacs, lymph hearts,
lymph glands and amphibian lymph aaca 7u
VIII. Various other tln-nrles in regard to the origin and development
of the lymphatic system 72
1. Mayer-Lewifl Anlagen 72
2. Kxtra intimal and perineural spaces and fenestration 75
Growth of lymphatics by the addition of tissue spares 77
IX. Conclusions B2
x. Literature B8
THE ORIGIN AND DEVELOPMENT OF THE LYMPHATIC
SYSTEM.1
By FLORENCE R. SABIN.
(From the Anatomical Laboratory of the Johns Hopkins University,
Baltimore.)
I. INTRODUCTION. 1. Morphology of the Vascular System, the Axgioblast.
Until the past few years our knowledge of the morphology of the lymphatic system was in a very unsatisfactory state. Our con- ceptions of such main questions as the origin of the first lymphatics, the time of their appearance, the relations of the lymph hearts and sacs of the amphibia to the lymph glands and duets of higher forms, the relation of the lymphatics to serous cavities and to the various forms of tissue spaces, and the development of the lym- phatic vessels within an organ have heen so vaguely understood that the opinions of no two investigators approached agreement.
A clear conception of any system must be based on an under- standing of its fundamental morphology, as, for example, the morphology of the arterial system was placed upon a satisfactory basis by The discovery and comparison of the aortic arches in dif- ferent animals. An example more closely in touch with our knowl- edge of the lymphatic system is the study of the fundamental morphology of the blood vascular system. Our knowledge of this is in the process of being built up. but a foundation has been laid for the clear understanding of the vascular system in a series of discoveries. The first and most fundamental of these is that the blood vessels arise as blood islands in the extraembryonal mem- branes. The earlier embryologists on the other hand believed that the first vessels were spaces without walls, which the pressure of the circulating blood hollowed out. The best description of the
1 Aided by a grant from the Baltimore Association for the Promotion of University Education of Women and by the Carnegie Institution of Washington.
• rn i /.'. Sabin.
lood islands and th< of the meaning of this
Hid in two works of Bis, " Untersuchung
ueber die erete Anlage des Wirbeltierleibes " in L868 I »p. 95-103)
and in " Lecithoblast and Angioblast" in L900 (pp. 868-295). The
. of blood islands, however, dates back to the work of
Wolff (154) and Pandei (101), who introduced the name, and
perhaps do on< : in i mbryologj has a more extensive litera-
tun I tainly a most iniciv>iinur iu-cnint of the development of
vascular problem can be followed through the of von
I' • rost and Leber! | 108), Remak | L24-125), Reichert
(121-123), Koelliker (67-71) and Thoma (148). The second
it advance was the dis lil 1 \i ssels I iui are
lined b) endothelium (Hoyer 18), which followed soon after the corresponding discovery in lymphatics by von Recklinghausen, 'i third • involves the proof t! ow bj
sprouting of their em a, I'm . ■ ■ - i and I. (108), Eis
(47), Rouget (126) and Arnold (5); the fourth that the main vessels of the body wall, including the posterior pari of the aorta (Evans 33-35), even the anterior part of the aorta and lateral hear! anlagen, arise as a capillary plexus or as solid angioblast cords (Bremer 15), which invade the body from the extraembryonal mem- branes. Finally a complete conception of the developmenl of I vascular system is based on thi that the blood vessels of the
extraembryonal membranes invade the body wall (His II). and that within the body wall th< lillaries of endothelium gradu-
ally invade or spread over I bod o I al there are definite vascu- lai and niin-\a.Miihir layers and zones. His i 17) discovered the fad that bloi i Is grow into the central nervous ; but the theory
of vascular and non-vasculai which is essential to an v md-
ing of the develop al of the vascular system we owe to Mall (80-81 I.
li iia- been worked out by his pupils, notably Evans (33-i 5). Its meaning can be grasped by studying figs. 4, 5 and 6 in connection with fig. 437 (Evans 35), which all show I skin dorsal to the
centra] nervous s] • a non-vascular zone, which for a long
time is nol reached by the blood vessels in the centrifugal growth, of discoveries, notwithstanding the gaps and uncer- tainties in our knowledge of the early stages which were well brought out by Minol (98, pp. 183-485) and by Evans (35, pp. 551-
.i in 1911, uncertainties in part since removed l>\ the work of
Tin Origin and Development of the Lymphatic System.
Bremer (15), offers a consistent as well as a constructive theory of the vascular system which goes far to modify the force of the following words of Koelliker quoted by Riickert and Mollier (128, p. L019) : " Ueber die erste Bildung der Gefasse und des Blutes herrschen wohl ebenso viele Ansichten, als Forscher sich ueber diesen Gegenstand ausgesprochen haben, was auf jeden Fall be- weist, dass derselbe zu den schwierigsten gehort." The theory thus outlined is that the fundamental morphology of the vascular system is based on the specificity of the endothelium, or in the words of His (47, p. 325), on the fact " Zu den am friihesten sich sondernden Gewebsanlagen gehort der Gefasskeiin oder Angioblast. Seine Sonderung erfolgt sehr scharf, und sein Wachsthum geht nach durchaus eigenthtimlichen Gesetzen vor sich." It includes the discovery of Mall (83-87) that endothelium may produce reticu- lum, a process which he has shown takes place both in the liver and in the heart; but maintains that there is an early differentia- tion of two tissues, namely, endothelium and mesenchyme, so that the angioblasts once formed give rise to all the vascular endothelium of the body.
The opposing theories in the varying forms of the origin of blood vessels from tissue spaces, their growth by the addition of tissue -I Hires or by the addition of connective tissue cells, and the differ- entiation of endothelium from mesenchyme over extensive areas within the body wall find their most recent evidence in the works of Riickert (127), Riickert and Mollier (128), Halm (40), Bon- net (14) and Maximow, 1909 (90, p. 511). These views, however, must be traced through the earlier works of Gotte (37) and Reich-
ert (121-123). The evidence for the continued origin of bl 1
vessels from the mesenchyme is for the most part from the inter- pretation of appearances in sections. Hahn's work, however, in connection with the difficult point of the origin of the heart and aorta is experimental. He removed the vascular membranes on one side of early chick embryos and obtained a heart anlage and aorta on both sides. He thought that he could entirely exclude a growth from one side to the other as well as remnants of the mem- branes on the same side and concluded that both heart and aorta arise in situ from the mesenchyme and not from the endoderm of the yolk sac not from an ingrowth from the extraembryonal mem- branes.
■i .'.'. : ibin.
Morpiioi ; Lymphai 5 : \l.
I' u d m the following pages that the lymphal iblem
i- closely connected with, or rather is a fundamental part of, the
thai the study of the « thro* on the
or. to put it more strongly, that the same kind of
rohlems. The fundamental morpb the
lymphatic system has, howi en put on a i v sal
asculai ring
rst lymphatics bud ofE from the veins. Moreover, lympha n at a comparatively late stage, long after the forma-
tion of ' ! islands has
[I. HISTORICAL.
1. V iSA S] ROSA.
I mil the primary origin of anj system is known our co it a essarily hazy and vague and this is oowhere better illus- trated than in i tion with the lympha em. The views of eenth century may well be summed up in the hypothetical sa " of Boerhave (13), Sailer (41) and others, which were tiny channels too small to allow corpuscles to pass, supposed to connect arte] ins and lymphatics at their tips. The conception which underlies vasa serosa may be traced hack to the experiments of NTuck (100), who injected air into the arteries and found it r< g in the lymphatics, as may be represented in the diagram Vasa >sa meant the idea that the arteries finally branched into vessels too tiny to carry the corpuscles, but the term likewise repri a whole ague conceptions, such as Bichat"s (r>i ahsorbents and ex- iants, which soughl to make definite - ■ idea of the nature of
lymphatics.
2. Ly M I'll \ti< - with ( )i'i;\ Moi I us.
In the latter half of the eighteenth century the conception o
was modified through the work of William Hunter (50)
: Munro, who believed that lymphatics began with open mouths.
The views of these English observers, at shown bj Cru (23),
involved the idea that the mouths of the lymphatics opened directly
'face of the body, into the cavity of the intestine and the
air - well as into I issues. T ie theory
ed with disi I ie lym] lusive
Th( Origin and Development of the Lymphatic System. 5
organs of absorption for the body, and the physiological theories of filtration.
Fig. l. — Diagram to show the " vast serosa " of Boerhave, Haller and others. The veins are striped, the lymphatics are dotted, and the " vasa serosa " which connect them are cross-hatched. The connective tissue is indicated by lines.
The doctrine, or as His (44) terms it, "the dogma of lymphatics with open mouths/' was first combated by ft definite counter theory by Schwann (139), following his discovery of the cell in the animal body. The theory of Schwann and notably of Virchow (150) was that in place of vasa serosa and hypothetical connections which did not exist hollow connective tissue cells spanned the gaps between blood vessels and lymphatics, fig. 2.
Fig. 2. — Diagram to show the theory of Schwann and of Virchow that, the blood vessels are connected with lymphatics by hollow connective tissue cells. The veins are striped, the lymphatics dotted and the hypothetical lymph vessels are cross-hatched. The nuclei denote the fad thai cells have been discovered.
/' ■ • /.'. Sabin.
1 - ■ ■ ■ ; o Endoi in in m.
In contrast to these hypothetical relationships of lymphatics, the work of von Recklinghausen (119) gave the first definite theor} which was actually based on the interpretation of direct observations of I lymphatic capillary. Through the use of silver nitrate solutions re- duced in direct sunlight, he discovered that the lymphati d by a definite cell layer of endothelium. This is clearly one of the most important discoveries in histology. Von Recklinghausen interpreted the silver pictures to d at the finest lymphatic capillaries were lined by an epithelium, but that these capillaries communicated bj wide openings with Saftcanale or lymph radicles, which formed the real ro< the lymphatics. Subsequently he described rm ■ it <■ openings lata in the serosa of the diaphragm < 120).
Fig. ?,. — Diagram to show von Recklinghausen's theory of the relation of lymphatics to tissue spares. All of the tissue spaces are cross-hatched to indi' lOthetical lymphatics.
The von Recklinghausen figures seemed to offer a perfectly to" Qstration of the relations of open lymphatics, especially in
view of the fact that thi 0f anatomists already b
i» o atics. But it is of gnat interest to follow the writu
Hi- at this pen',,,]. His (in. who was just publishing in favoi open lymphatics, and saw von Recklinghausen's paper as his own v. ng to press, at fii jnized in von Recklinghausen's des riptions
rmation own views. On careful studying of the silver
pictures, however. Hi- | i.o saw that the discovery of endothelium was step whii . insl ad of proving that lymphatics are open and
The Origin and Development of the Lymphatic System. )
withoui definite limits, tended rather to throw the balance of proof in the opposite direction: that the discovery of endothelium gave the con- ception of lymphatic capillaries not as indefinite spaces without walls. hut as limited by a definite membrane. 'I'd quote his words (45, pp. 457-458), •" Wenn ich nach den eben gemachten Auseinandersetzungen der einen Aufstelhmg v. Recklinghausen's, namlich derjenigen vom Vorkommen eines Epithels in den feineren Lymphgefassen des Diaphragma vollkommen heistiinnic, so bin ich durchans anderer Ansicht als jeiier Antor hinsichtlich der Saftcanalchen und ihrer Bezie- liung zu den Lymphgefassen; furs erste namlich Leugne ich das VTor- kommen von Saftcanalchen in dem Sinn von v. Recklinghausen, und zweitens halte ich die Verbindung der von ihm als Saftcanalchen gedeuteten Theile mit den Lymphgefassen nur fur eine scheinbare," and later in his interpretation of the silver picture he says: "Je dtinner und blasser die supervasculare Schicht ist. um so leichter wird es den Anschein haben, als oh die hellen Figuren der intervascularen Bindegewebskorper unmittelbar in die Lymphgefasse selbst einmiinde- ten, um so eher wird man uebersehen, dass in AVirklichkeit der Zusam- menhang jener Figuren nicht mit den Gefassen, sondern mit den Gefassen ueberlagerten verzweigten Korpern sjattfindet." Further he adds that if the openings pictured by von Recklinghausen exist, there would be no reason why any injection of a finely divided mass should not fill practically all of the Saftcanalchen or tissue spaces as ex- pressed in fig. 3, and this is obviously not the ease. Thus after a care- ful study and interpretation of the silver reaction on the lymphatic vessels, on the albuminous fluid of the interspaces, and on the cell bodies of the connective tissue corpuscles, His was led to believe that the significance of the von Recklinghausen discovery was that lym- phatics are lined throughout by an endothelium rather than that the silver method demonstrates open lymphatics.
111. EMBRYOLOGY.
1. Introduction.
It is. 1 think, clear that the problem in this state could only he attacked successfully by embryology with the purpose of establishing the fundamental morphology of the system. The importance of this is best expressed by His (44, p. 223), "Von den mancherlei offenen Frasren, die seii mehr denn ".'(Hi Jahren in den anatomischen Schriften
- bin.
- l. npbs] stem discutirt zu werden pfl fin so unmittelbares physio) i
i - n Lymphgefasse in den K Mag
man sich ueber die Bildung i I mphe and ueber
wirksamen Kjafte eine Theorie machen, nan
wil . lert diese als ganz unerlassliche Grund praezisere
-; • Ifin .1 hen Verhalten der ersten Wurzeln i
■mm ci: \ tellung wirklich aus der Beobachtung
entsprossen, sei sie our hypothetisch an aen." It is without
question thai a com 3ion of the relations of the lymphatic capil-
lar on an understanding of the fundamental morphol
Of ! 111.
■.'. I.\ \l I'M \TK - A.S I * 1 1 v II. I> TlSSl I Sp k
T ■ relation of the lymphatics to tissue spaces Eormulal -1 by von Ri ckli eni irely in agreement with the eai
gal - al conditions recorded liy !'• - (l<!). It was the
practically universally I idea up to L900 that lymphatics ai
by the dilatation of ! bj the fluid thai exuded fr
the blood vessels; that this dilatation of tto periphery, i that 1 he vi reins and
join Thus I le growth of the lymphatic vessels was thoug
rom the periphery to the center. This view was well stated in 1894 by Gulland i:'.'-1). who found the lymphatics first in I - bcu- taneous tissue and then along the- extremities in fo human,
bovine and rabbit, between 3 and I cm. long, and thought that tfo vessels subsequently joined the veins. Ei thought thai the Eorce of fluid in the tissues formed the lymp , so that the] arose by an
entirely different method from his conception of the origin of blood i. 167).
3. I'm i h . i 's Work.
An account of the newer work on the oi mphatic
stem must begin with Budge i 11 22). Budge was led to a study of the lymphatic system in birds through uoticii I variati
sterior lym rts in the adult (21). The posterior lymph
hearts had beei in birds by Panizza (103), A. F. J. Mayer
(quoted by Stannins) and Stannius ( 1 12). Budge had already begun
The Origin and Development of the Lymphatic System. 9
to study lymphatics in the adult liver (17) and in bone (18) by mi of injection, and in 1880 (19) he described studies of a system of canals whirl) he could injed in mesoderm of three-day chick embryos. These injections, which can be easily repeated, giving the exact pat- terns of Budge, were really made into the extraembryonic coeloni. as has been shown by Mall (81) and myself ( 129), and have nothing to do with the lymphatics. They are not, as Budge himself noted, lined by endothelium: indeed Budge himself was most cautious in Ids inter- pretation, for he says (19, p. 325), "Mit Absicht habe ich den Aus- druck Lymphgefassystem fur das eben beschriebene Canalsystem vermieden. weil mir hierfiir noch nicht Ajnhaltspunkte genug gewon- nen zu sein scheinen. Und doch liegt der Gedanke hieran nahe." In 1881 Budge (20) announced the important discovery that there was a plexus of lymphatic vessels accompanying the allantoic arteries of chicks easily injected from the sixteenth to the eighteenth day of incu- bation, and that these injections ran to the thoracic duet. The next year ('21) in a fuller paper he described that these allantoic lymph- atics not only entered the thoracic duct but drained into the posterior lymph heart, which played a great role in relation to the allantois. He injected the lymph heart through the allantoic vessels by the tenth day. and noted that the posterior lymph heaft was preceded, as seen in the living chick (8 to 12 days), by veins, and that subsequently the lymph heart appeared, which could be distinguished by the fact that it pulsated with a different rhythm from the blood vessels. After Budge's death his work was brought together by Hi- ( 22 ) and formu- lated somewhat in this manner: There are two lymphatic systems, a transitory ami a permanent system, the first consisting of spaces in the extraembryonal membranes analogous to the coeloni and found only in early stages. The second, consisting of the true endothelial-lined vessels which accompany blood vessels — which Budge so successfully injected. The thoracic duct he thought arose from the first -\ stem and was the only permanent part of the first system. Thus Budge's work, which was a reaching out into a dark field and had genuine important discoveries, was in line with the prevailing theory that lymphatics are related to tissue spaces, and introduced a misleading conception that lymphatics form after the same manner as the coeloni and indeed in pari as an extension of the ccelom as far as the primativ system and thorai ic duei are eon erned.
1" ■ n, . /.'. Sabin.
rHE Arguments fob the Venous Origin of the Lymph mi System.
I shall now take up the proof of the theory thai the lymphatic i- derived from the veno ■ m. and will subsequently
analyze the <>p|»>»in;: theory, which, in its most recenl from, lymphal addition of tissue spaces (Kampmeier 66 and
essentia] elements in the establishing of the venous origin of the lymphatics have been (1) the proof that lymphatic capillai
x by the sprouting of their endothelial wall and not by the addition or hollowing out of connective tissui This argumenj iwn
the method of growth by sprouting. (2) The proof that lym- phatics gradually invade the body from 1 1 periphery, establishing point of lymphatic and non-lymphatic zones. This means that the main ducts grow as capillaries by the same method as the per- ipheral capillaries. This argument is known as the one of lymphatic and non-lymphatic zones. (3) Thai the original lymphatic ducts
bud off din om the veins. This is known as tit igin of the
kin; v budding.
Thus the study involves three elements: The nature of the lym- phatic capillary, the nature of the lymphatic ducts, and the nature of the first lymphatics or the lymph sacs. Bach one of these three lines of proof involves the stud} of endothelium; the first lymphatics are buds ■ adothelial lining of the veins; these endothelial buds invade body down to the ultimate capillaries by the cell division of their i ndothelial wall.
A. GROWTH in LYMPHATIC CAPILLARIES I'.Y SPROl KNG.
A study of the method of growth of lymphatic capillaries is neces- sarily ass ted with the study of the method of growth of bl I
Ear back as the time <>t" Schwann (Ki'M. who first Baw the capillaries in the living tadpole's tail and who vaguelj dis- tinguished those which carried blood from those which had no cor- puscles, there is a clear recognition that the two forms of capillaries grow by the same method. This method Schwann thought to be by the addition of hollow connective tissue cells.
in growth by Bprouting was introduced quite recently by His, but the first description of the process dates back to the year 1844, to
The Origin and Development of the Lymphatic System. 11
the work of Platner (106) and of Prevost and Leberl ( L08). Platner described the growth of capillaries as seen in the living tadpole's tail. He analyzes Schwann's idea of the addition of cells as necessarily merely an inference from the appearance of the vessels in one stage, for when actually seen growing new cells are never added on. He says that rather each new vessel is a process of a preceding one and describes these processes as long, thin Auslaufer, which form loops and soon show a double contour. He says that the tiny processes never contain nuclei and are not cells, so that the interpretation of Schwann of the addition of cells could not possibly hold. Platner says that the same process of growth in the living tadpole had been observed by Prevost and Lebert. Indeed, in the same year (108) they published a series of four papers, in which they describe the growth of capillaries, not only in Batrachians, but more in detail in connec- tion with the Wood islands in the chick. They definitely use the term centrifugal growth and describe the process in the following graphic terms (p. 239): " Les vaisseaux poussent des saillies laterales par decollement partiel des lamelles du feuillet vaseulaire, saillies plus on moins arrondies ou pointues, allongees, formant des espece< d'eperons qui souvent iinissent par se rencontyer, provenant de deux cotes different*, et etablissent ainsi des vaisseaux de communication." They thought that the processes or " spurs " were for the most part hollow from the start and state that the larger vessels grew by the same method as the smaller.
In 1846 Koelliker published two papers (67 and 6S), in one of which he announced the discovery of lymphatic capillaries in the tadpole's tail (67). He described the characteristic differences as seen in the living form between the two types of capillaries, the irregulari- ties and more numerous processes of the lymphatics as well as their connection with the superior and inferior caudal lymph trunks. In the other paper he gives a most valuable analysis of the views of the early embryologies, Wolff, von Baer, Eeichert and others on the prob- lem of the growth of vessels. He takes up the various views of growth (p. 118) which were then being discussed, namely, growth (1) by the addition of unbranched cells, or (2) by branched or stellate cells, or (3) by spaces hollowed out by the force of the heart heat, or ( I ) from spaces produced by fluids in the tissues as well as (5) by the then new work of Platner, Prevost and Lebert, showing centrifugal
12 /,'. Sa
that the vascular and lymphatic capillaries ■. by the addition of branched or star-shaped cells.
later, 1850, Remak (125) rediscovered the lymph in the tadpole's tail by watching the living embryo, and, without knowing of the preceding work, he hurriedly published an even more grapl ription of the form and growth of lymphatics than I
Subsequently, after seeing Koelliker's work, he added a (p. 182 183) to emphasi e the fad that if the growth be wai in the living form star-shaped cells are oever added — neither to the
blood capillaries, : to the lymphatic capillaries, oor, he adds, to the
growing nerves. Many years later, 1886, Koelliker (71, p. 34), in an article mainly on nerves, corrected his view" of the growth of the lymphatics by the addition of connective cells in favor of i rovi !h by sprouting. The years from L863 to L861 represent a greal advance in our con- ceptions of the lympl stem. The historical article of lli~ (lit on the lymphatic system must form the basis of any work w bi< b with the development of the problem. In 1865 Strieker (143) pub- a paper in which he expresses a doubl in regard to Koelliker's of lymphatics in the tadpole's tail, on account of the fact that
ed bl I capillaries bad also the blind sprouts, lie. however,
submitted the bl I capillaries to an experimental study of greal
lie stimulated them with the vapor of ammonia and gives the following description of his results:
Ich sah ein Gefassstiick. welches seinem Baue nach unzweifelhaft zu den
D gezahll werden musste, sich im Laufe von fiinfzehn Minuten
zweimal bis nahe zum V"erschwinden des Lumens verengern und bis ziira
Bn iienrlnrchmesser eines Blutkorperchens wieder erweitern. Icli sah
varicose Gefasse sich so veranderen, dass der Baueh an Stelle des Halses zu
kam. mul umgekehrt. Mil den Formver&nderungen ging gewohnlich
• ine andere VerSnderung Hand In Hand. So wurde beispielweise eine
eingeschniirte Kapillargefassstrecke so blass, wurden deren Conturen so
undeutlicb, (lass ich sie kaum niehr von der Umgebung unterscheiden
konnte, wahrend nach bis zwanzig Mil as Gefass wieder in seiner
urspriinglithen Iieutlichkeit zu si hen war.
- lie discovered the contractility of endothelium. He found that
ricitj was a still better stimulant for observing this contractility.
lie discusses bis ndpoint of determining the nature
of the capillary wall, especially ii ction with the silver prepara-
of Aeby, A.uei i I th (quoted from Strieker 143),
The Origin and Development of the Lymphatic System. 13
which has already given the suggestion of a lining of flattened cells for blood capillaries. Strieker saw clearly that the wall of the capil- lary was of living protoplasm, hut was confused in regard to whether the blood stream was inter- or intra-cellular. He was perplexed also in regard to the existence of cells or not, since he was dealing with the growing- tip, which we now know to be a syncytium. This idea occurred to Strieker, as is plain in these words, " I 'ass bei dem Aufbau von Kapillargefassen ueberhaupt Zellen mit einander verschmelzen, und dass solche Verschmelzungsspuren spater einma] durch Silber- niederschlage kenntlieh werden konnen, lasst sich ferner auch nicht leugnen." Strieker also noted the sprouts of blood vessels as indi- cating their method of growth.
1 have already taken up the fact that von Eecklinghausen's work- on the endothelium of lymphatic vessels, studied by means of the silver nitrate method, settled the question of the cellular nature of the lining of lymphatics, especially in connection with the analysis of the work by His, who had regarded lymphatics as vessels without walls (44, p. 229), and saw by a thorough study of preparations made by the silver method that lymphatics were lined throughout by endo- thelium.
In 1867 L anger (75), as a conclusion to a series of studies on the lymphatic system in amphibia, published a study of the lymphatics in the tadpole's tail. He was able to make complete injections of the blood vessels and the lymphatics and gives a most interesting analysis of specimens as observed in alcohol from the standpoint of weighing the evidence on the method of growth. He describes the uninfected capillary as often appearing to have a single contour, while the injected one had the complete wall. He could not find in the alcoholic speci- men the tiny processes previously described in the living form. He noted, however, the larger sprouts, the loops and blind processes, and says that the nuclei are definitely within the contour of the wall of the capillary, so that he makes the distinction between the vessel and the surrounding tissue. He concludes that the various forms of the processes must indicate the process of centrifugal growth for the lym- phatic capillary as well as for the blood capillary.
Again in 1873 the growth of the lymphatics and Mood vessels bj the method <d' sprouting was observed in the tadpole's tail and very clearly described by Rouget. By the use of curare he was able to beep the larva still. He also emphasizes the great number id' tiny filaments
1 1 /.'. Sabin.
the lymphatics and the fact thai they aever join with the con-
- Tin - rvation of the growth of capillaries by sprouting
iver and over again where there was the chance oi - ■ ■ ! u ur the 3s in ag form or of obtaining injected specimens,
and yet during all these years the observations were Dot generally ted, since as the fundamental morphology of the Lymphat : was unknown, tin- significance of the observations c-< m 1«1 not be understood.
It is. however, oot true that everj who studied the living
- .Hi described the process of the sprouting of the endothelial wall of hi.- - .Mill of lymphatics a- showing the method of
growth. Indeed at leas! 31 rve*rs have doubted whether iliere
tun different kinds of capillaries in the tadpole's tail. I have already noted that Strieker doubted the presi dee "f lymphatic capil- laries in the tadpole's tail.
Wysotzky (155), whose work, since it is published in Russian, 1 quote from Mayer (89), thought that the capillaries without blood merely young blood capillaries. S _ ■■■:■■ Via er (89), in an interesting and valuable paper, " I die Bh gefasse im Schwanze der Batrachierlarven," gives first
an excellent analysis of the literature on the subject of the capillaries in the tadpole's tail. Be brings out the fact that it was the presence of an occasional red corpuscle in the "lymphatic" which was the stumbling block in accepting the presence of lymphatic capillaries. !|. then records an observation which in reality cleared up the entire difficulty in regard to the "empty capillaries." \- E. Et. Clark (26) - shown. Mayer, however, failed to see the bearing of his own servations. Slayer used curare and the electric current to anaes- thetize the larva and then covered the tail with a cover slip. When he ked the water out from under the cover slip he noted that the iod would gradually stop flowing or even go in the reverse direction in the blood capillaries and that the vessel would collapse, so that
ked like ,1 solid cord. Thus he also observed the contraction of endothelium. Furthermore, he noted that the "other empty vessels" (namely, lymphatics), contracted more frequently than the blood capillaries. When, however, he studied these other empty vessels lie thought that thi onal cells in them flowed now toward tin center,
now toward, the periphery, and he ended with the somewhat vag
The Origin and Development of the Lymphatic System. lo
and erroneous conclusion thai the empty vessels', though they might have some of the functions of the lymphatics of the adult, could not properly be grouped with them. We now know that the two sort- of empty vessels are (1) the collapsed blood vessels which Mayer himself observed and (2) the true lymphatics (E. If. Clark, 26).
The work of Mayer, however, has another point of great interest lo us beside the important observation of the contractility of endo- thelium, namely, what we call Mayer-Lewis anlagen. Mayer noted the long strands of cells (endothelium) which often -pan the gap between two capillaries; indeed, he figures them, some that look entirely solid and some that have, here and there, a patent lumen. In reality both blood capillaries and lypmhatic capillaries have thesi strands and sprouts, and it is one of the must remarkable qualities of the two forms of endothelium that no sprout from a lymphatic capillary ever joins a blood capillary and vice versa. However, Mayer's mistaken idea that these strands of cells connected with two different kinds of capillaries, namely, the vessels which arc always empty, in other words, the lymphatics and the blood capillaries, aided in his confusion of the lymphatics with the blood vessels. Besides these strands of endothelium he saw small hollow vessels, having the same lining as the capillaries, which he thought to be entirely isolated. These he interpreted as follows ( p. 236 ) :
Unseren Erfahrungen nach sind nun die beschriebenen Bilder nur gewisse Stadien der Ausschaltung von Bestandtbeilen des Blutgefassystems aus der
normalen Circulation Bei genauerem Studium der letzteren For-
mationen ergibt sicli, dass die Wandungen derartiger mit freien Spitzen in das Gewebe hineinragenden, und ausserhalb jeder Kommunieation mit Geiassrobren stehenden Fragmente beziiglieh des Aufbaues ihrer Wand entweder niehr den Typus der blutleeren oder demjenigen der bluthaltigen Rohrehen sich nabern.
Most of (he apparently isolated anlagen seen in sections are due to the collapsing of the vessels which connect them with the rest of the capillaries through the contractility of the endothelium which Strieker and Mayer observed. In sections they may occur in great numbers through the contraction of the endothelium due to the fixing agent. The possibility of entirely isolated vessels and the meaning of the apparently isolated vessels are fully discussed later in connec- tion with the theory of the growth of lymphatic capillaries by the addition of Mayer-Lewis anlagen in section AIM.
/,'. - abin.
I thai the periphera] capillaries grow entirely
then it is a perfectly logical h
lymphal . from the veins, from to periphery,
r than from the periphery to the veins. This h - was
Ranvier (113), based on the evidence of the m( i ■ i »>d of
growth "f the lymphatic capillaries within the peripheral pl<
r i 110-118), in a Beries of Btudies between the years L895 and
injection aphatics in a varii ty o For
example, he injected the exceedingly abundant plexus in I otery
foetal pig 10 cm. long, as well as in the ral and rabbit. Ee also
the lymphatics in the amphibia. Thes im an
of the form of the develi • - looking like collarettes in the. walls of lymphatic ducts, the
with blunt terminal kn which
■ g are often found in tl is well be
ts, either ending free or as bridging a gap in the aetwork to another vessel. From all of these forms of growing lymphatics Elan- saw that the growth nf lymphatics was from eenteT hew, and even though he thought that the lymphatics did not begin in a mammalian embryo until it v.. I L0 cm. long, a stage al which the embryology of thi i may be called completi . aevertl went
■ !\i'i-. for he deduced the -!- that the lymphatics grow from the veins. He likened growth to the growth of a gland (113). In mj own work 1 was led to the same view by tracing the lymphatics in and younger
embryos hack to the veins, and the next section will include thi .:■ oce which 1 regard as essential to establish the hjTpothesis of Ranvier as the correel theory of the origin of the lymphatic system. Tl count of the evidence for growth b is, however, not yet
complete. As far as the evidena e obtained by the observation
of injected specimens, it was especially well described and figured by MacCailum (79). He added the observation of watching thi jection in »scope and showed that extravasations are due
cplosive rupture of the lymphatic wall, [njected specimens of developing lymphatic capillaries are now well known; excellent fig given by Bartels ( I d 10,
p. 43). They show a large number of sprouts, I" ley are taken
from the skin of a iryo 6.5 cm. long. 'I xacl
lary, superficial, Bne-meshi d pli jus iwing
The Origin and Development of th I n phatic System. 17
from the deeper coarse-meshed or subcutaneous plexus, and, sine* secondary plexus is growing actively, it shows many sprouts.
The proof of growth by sprouting from injection? is always an interpretation of appearances, and though it is a logical inference, one must turn to the observation- of the living forr onclusive
proof. This has been given by E. R. Clark (25-26), who lias again restudied the classical object, the tadpole's tail. The introduction of chloreton anaesthesia is one of the factors that have made this study possible, since the same specimen can he kept alive for weeks, notwith- standing repeated doses. Dr. Clark's devise of an upright chamber, so arranged that the tadpole can be kept upright without the pressure of the cover slip, and the finding of larva of the form Hyla picker- ingii in the spring of 1910, a form which has few pigment cells, have all combined to make his studies so valuable and convincing. He has described not only the complete history of a lymphatic capillary. watched through periods of weeks, hut has followed every connective tissue cell in the neighborhood (30) through several generations. Dr. Clark has shown that the wall of the lymphatic capillary is in ceaseless activity. In the living form the wall is in part hyaline, in part granu- lar. The nuclei are surrounded and obscured by granular protoplasm. so that they are clearly seen only when dividing. The wall is of irregular thickness, often extremely delicate, and from the sides and tips are sent out numerous tiny processes, some hyaline and - granular, which may be well described a- amoeboid. A few of these persist and grow into permanent lymphatics. Most of them are with- drawn. These tiny sprouts, indicating the functional activity of the vessel, do not disappear in alcoholic specimens (26, p. 403). They are at first without nuclei, hut nuclei wander into them from parent stem ; indeed, two nuclei may pass each other as they advance or recede. This proves that the growing amoeboid wall of the lym- phatic capillary is a syncytium and explains the failure to obtain the silver markings at the growing tip. The silver markings indicate the more stable lymphatic capillary.
E. E. Clark's most recent observations (30) show that increased activity of the lymphatic wall in the sending out of many of the tiny processes is a sign of growth, so that an area can thus be selected watch the processes of the formation of new vess
As far as the relation to the surrounding connective cells is con-
ed. the growing, and, we might also say, the functioning', amoeboid
up- avoid the cell bodies and processes of the mesenchyme cells.
L8 /.'. Sabin.
Thus there can be [uestion in regard to the method of growth
of the peripheral capillaries. Bi th blood and lymphatic capillaries iv the activity of the protoplasm of their walls. The endo- thelium at the growing tip ia a syncytium, the processes advance and ede; they are tiny, hair-like vessels, and they receive tlicir nuclei 'ii the parent stem. There are differences in the appearance of the two t\ capillaries probably associated with the pn and
nee of the circulating blood and the difference of function. The lymphatics have very many more tiny sprouts, only a few of which are permanent; that is, their wall is much more amoeboid and the much more irregular. Thus on positive evidence, oamely, the of the process ui the Living Eorm, whjch is the best evi- dence known to anatomical science, we are justified in the conclusion that capillaries grow by sprouting.
I'.. \.\ VI'll \ I lo \\|. \ii\-U M I'll A I 1. ZOK
second argument in Eavor of the venous origin and the centrif- ugal growth of Lymphatics by their own endothelium is that it
3hown that lymphatic vessels gradually invade the body from certain limited -. Thus if injections of vessels are made from th
in larger and larger embryos an evi asing /"tie of
lymphatic capillaries can be demonstrated. Moreover, for each stage the zone of vessels is constant.
I iegan my work with the study of the development of lymphatic
nds in the embryo pig and to obtain injections of them introduced. oeedle into the foot pads. By taking younger embryos a sta was soon readied when no injections of the foot pad- ever entered lymphatics, but al I one could still injed - in the
skin over the body. This was the beginning of the proof that lym- phatics bud oil' from the vein- and grow peripheralward instead of the 3abin l'."-1 ).
In an embryo pig 5 cm. long (Sabin L30, fig. 5) a simple p lymphatic capillaries has al st i atirely covered the body. I say capil- laries advisedly, adopting Ranvier's (US, p. 74) criterion of val for lye ducts in contrasl to then- absence in I The body i- first invaded by lymphatic capillaries, and the primary plexus shown in fig. :. (Sabin L30), which is the anlage of the d< subcutaneous plexus, was injected by a single puncture of the nee, lie.
Tlic Origin and Development of the Lymphatic System. 19
Subsequently this plexus develops valves, but at this stage the entire lymphatic system can theoretically be injected from any one vessel, because there are no valves, or, in other words, because it is entirely a capillary system. Nearly the same stage is shown for a human embryo in figs. 505 and 506 (Sabin 134). This was a remarkable spec- imen, in which air rilled the lymphatics, and it lias the additional in- terest of showing the beginning of valves in the vessels of the skin, namely, those of an occipital duct and in the axillary and inguinal ducts.
If earlier stages of embryo pigs are taken the cutaneous vessels, as shown by injecting them, gradually recede, as seen in bus. 1 to 4 (Sabin 130), to two points, one in the neck and one in the groin. The earliest lymphatics reach the skin in the neck of an embryo pig about 18 mm. long. All injections of the lymphatics of the skin of the anterior part of the body between the stages of 2 and 5 cm. long can be seen to run into two symmetrical sacs in the neck closi to the jugular vein. These anterior lymph sacs, which have now been identi- fied in a very great number of forms, can be found in pig embryo- in earlier stages than the first cutaneous lymphatics. In my first paper I traced them back to the stage of 14 mm., when they are small empty sacs, close against the anterior cardinal vein. *In reality they lieu in in the pig of 10 to 11 mm. and their method of origin will be discussed in the next section.
The argument of lymphatic and non-lymphatic zones thus consists in the fact that the first lymphatics are sacs close to the veins, and from this stage onward lymphatics can be injected in wider and wider zones until they cover the entire surface of the body.
It is necessary to prove that each zone represents the limit of the growth of the lymphatics for a given stage. To prove an injection is complete for any stage such as one shown in fig. 6 (Sabin 135), it is e - ntial to have abundant material and to show by injection that the lymphatic tips always rupture along a given line when the pressure is increased. The shape of the lymphatic vessels at the line of growth will vary according as the vessels are progressing rapidly or not; for example, the rounded ends of fig. 2 (Sabin 129) are from an area where lymphatics grow slowly, while the margins of fig. 6 ( Sabin 1 •'!.", ) , with numerous pointed sprouts, are from a rapidly growing zone. Fur- thermore, sections of the skin in the lymphatic and non-lymphatic zones show a sharp contrast in the presence or absence of the large lymphatic
en* /.'. 8abin.
_.•■ (Sabin 130), which are easy to identify. The method
-. however, inadequate t" define the Limits of growth,
the large vessels, for the tiny lymphatic Bproute can only
found in sections when the plane of cutting is favorable.
This pi d of the lymphatics in the Bkin has been confirmed
by Polinski (107) in bovine embryos. The patterns which he Bhows
make a most interi rison with those of pig, cat and human
embryos. In the bird the same progression of zones is shown to 6ome
hi in the injections of Mierzejewski (96).
Beside the definite zones the lymphatics grow into definite layers. !,' aviei (118) ooted thai the superficial lymphal ics are deeper than the blood vi --• -. They follow the vessels into the skin and each plexus - deeper than the corresponding blood vascular plexus (Sabin 130). The development of the lymphatics into the intestine, as worked out by Beuer i 13), illustrates the point of the definite layers into which the lymphatics grow particularly well. The lymphatics for the intestine
iw from the retroperitoneal Bac, which arises from the renal veins (Baetjer, 8). The vessels form a rich plexus in the mesentery and from this plexus a series of vessels grow into the intestinal wall and penetrate to the submucosa. II< re they form at first a of units
shown by Heuer in fig. I" (43), which has been copied as fig. 508 ( Sabin 134 ). These primary vessels soon form the submucosal plexus of ducts, from which the mucosal capillary plexus and lacteals develop on the one hand and the serosal vessels on the other.
This fact, thai the body is invaded by lymphatics, bas an especial interest, because il was the clue which enabled us to trace back the lymphatic ducts to their beginnings and show that they arise from the veins and grow toward the periphery. It is, further- more, the key h\ which the developmenl of the lymphatic system within each organ may be traced to the ultimate capillaries. [1 is considered again in relation to the development of lymph sacs, for re it can l>c taken up in connection with its exact relations to vaseular and non-vascular zones. Both the blood vascular and the lymphatic systems invade the body by the growth of their capillaries. I systi 'M has it- definite zones and layers which can be followed in orderly progression. Tee invasion of the body by the blood capillaries
• i plete than by the lymphatic capillaries; Eor example, the
lymphatic capillaries do nol grow into the centra] nervous system, nor into the int< rspaces between musi le fibers.
The Origin and Development of the Lymphatic System. 2!
C. DIRECT BUDDING OF THE LYMPHATICS FROM THE VKIN-.
As has been stated, il was the study of the decreasing zones of lym- phatic capillaries which led to the discovery that the first lymphatics are sacs close to the veins. In mammalian forms the first lymphatics are the anterior lymph sacs which bud off from the anterior cardinal veins. These jugular lymph sacs were noted by Saxer (138) in 1896 in his extensive study on lymph glands, but he did not recognize their significance. They can readily be made out in sections of pig embryos 14-20 mm. long, or in sections of any mammalian embryo of the corresponding stages. The fact that they are the first lymphatics in mammals and that they lie close to the vein, separated only by the double endothelial wall, led me to the conclusion that the lymphatics budded directly off from the veins and it is gratifying to find that this reasoning has been justified by further investigation (Sabin 129, E. E. & E. L. Clark 29 and Hoyer 40a).
To follow the development of our knowledge in historical sequence the next step was taken by F. T. Lewis (76) in a series of excellent reconstructions of the anterior lymph sacs m rabhit embryos, the best figures we have had up to the present time of the form of the early sac. Lewis carried the study still further back and showed that the definite sac was preceded by a blood-filled capillary plexus. This blond- filled plexus has proved to lie a very important observation. From the presence of blood Lewis made the logical inference, with the evidence at his command, that these vessels were blood capillaries and that hence lymphatics were I rans formed blood capillaries. The observation of the blood-filled vessels has been confirmed by Huntington and McClure (54) on the cat and by myself in human and pig embryos (132-138) and we have all accepted the theory of transformed capil- laries until new evidence has now shown us the correct explanation of the presence of the blood.
This new evidence has been furnished by the work of E. R. and E. L. Clark (27-29). E. L. Clark began with the study of the allan- toic lymphatic vessels in chick embryos. From the allantoic vessels she was led back to the posterior lymph hearts and the lymphatics of the body wall. The injections of Mierzejewski (96) show that the primary line of growth for the lymphatic vessels in the skin of the chick is along the thoraco-epigastric vein (96, figs. 1 to 4). E. L. Clark noted that in early stages the lymphatic vessels along this line
i: ■'•in.
■ .1 with blood and thai the blood in them was stagnant, in rapidly circulating venous blood. I in- lymphatics invade the -kin in the chick while they are in the i once an advantag . \'<\ means of fine cannul is E. L I was able :■> inject individual vessels of this blood-
in the living chick and watch the ink flow to the pul- aph heart and then* - veins. These blood-filled vessels
usual characteristics <>t' lymphatic capillaries, in that they • r and more irregular than blood capillaries, hut the essential in E. h. Clark'.- work is that by using a form in which the lym- i! in the living embryos she discovered a criterion for recognizing lymphatics, namely, th< tanl blood in
contrasi t" tin- circulating bl
With this importanl criterion she lias followed back the origin of
rior lymph In art-. Since Sala ( L31 ) it has been known that
in the chick the posterior lymph hearts develop opposite t
bram irst five < (137,p.269). Sala described
ginning during the sixth day by a hollowing out of
the mesem iut by watching the living i nbryo
during the fifth day 1-'.. \\. an. I I-'.. Ij. Clark hav skin
al veins i- a comparatively □ □ so that brilliant direct illumination enables them to see in I
of tiny blood-filled buds close to the main coccygeal \<;ii ami Thi ilood in ightly different color
from the circulating blood. They proved thai are always in
connection with the parent vein, for a direct injection of them always into the vein, hut no injection i leripheral blood capil-
laries ever til they bud nil' from the veins ami are filled
with blood fri the parent vein. It is of course evi-
dent that tiii- process cam en in the body wall of the chick with
■ with which every cell division can he followed in the tadpole's tail ; neverthi agnant blood a proved b} u
tion I al lv till the developing vessels, so that it i- an adequate
criterion oj of their development.
By selecting a chick which shows the-e primary lymphat ami
Qg it under observation under high power in a warm chamber
E. R. ami E. I.. Clark i •-"•| i have been able to se hi l-filled
lymphatic buds join with each other to Eorm a deep circumscribed lymphatii of the pi lymph heart. It is clear
The Origin and Development of the Lymphatic System. ".'■'<
from Sala's description that it was this plexus which he described as the beginning of the lymphatics. While the deep lymphatic capil- lary plexus is being transformed into a lymph sac and pulsating lymph heart, lymphatic vessels are already growing toward the skin, where they gradually extend. They grow first along the lateral line to anastomose with the jugular lymphatics. There is a continuous peripheral growth of the hymphatics from the time of the first buds on, and the entire blood-filled stage takes hut a few hours. Neverthe- less, it is long enough to enable one to watch the buds form a plexus; the plexus becomes a sac and lymph heart, and the lymphatics from it spread out in the skin. Injections prove that in every stage of their development, from the primary buds onward, the lymphatics conned with the parent veins; thus there is no separation from the vein and subsequent rejoining, as all of the recent workers. Lewis, Huntington and McClure and myself, have thought from the difficulty of finding the connections with the veins in serial sect ion-.
The posterior lymph heart in the chick is especially advantageous for study, since it is in the first place sufficiently superficial to be seen in the living embryo, and in the second place it is covered by a non-vascular zone. In mammalian embryos no qaudal lymph hearts develop. It is very interesting to note in injected embryo pigs that the corresponding area in the skin at the root of the tail, instead of being a non-vascular zone, is an area of especially wide blood capil- laries. This area, seen in fig. Mi; (Evans 35), is constant, and. as
it almost always retains a little 1)1 1, can be injected when a partial
injection of the veins of the lower part of the body is desired.
The work of the ('larks adds the final proof of the theory that the lymphatics hud oil' from the veins. Moreover their method is so simple that anyone may convince himself of the essential results by a few hours observations. Their injections have corrected two errors,
namely, the idea that the lymphatics are transformed hi I capillaries
and that they temporarily separate from the veins.
Thus 1 regard as proved the three points which have been stated as essentia] in establishing the origin of the lymphatics from the veins. Stated in reverse order they are: First, the lymphatic system begins as a series <>i endothelial buds which sprout out directly from the veins as a new type of vessels, namely, lymphatics. These buds unite to form plexuses which develop into sacs. These sacs may become lymph hearts. Second, from these lymph sacs or hearts lymphatic 2
/.'. Sabin.
ually invade the boch in orderly sequence in definite
and characterise z « and layers. The growth is always in the
illary bed, that is, all lymphatics develop as capillaries, and the - to develop become the first lymph trunks or ducts. Third, ethod of growth throughout is bj the sprouting of the proto- plasm and the nuclear division of the endothelial of the capillary wall, ultimate capillaries are distinguished bj the absence of valves, hi n word, • a continuous growth and invasion of the 1 >< >< 1 \ 1 . \
lymphatic capillaries from the primary sprouts which bud off from tin veins to the ultimate peripheral lymphatic capillarii -.
IV. PRIMARY [A'MPHATK SYSTEM IX^ DIFFERENT
FORMS.
I. I'im M vi:y \.\ \iril \ I [< SACS IX THE PlG. A. GEN EG \l. SI M MAR'S 01 nil - \< 5.
I - . begin ' e section on the special anatomy of the lymph sacs by .-I detailed description of the origin of the lymphatics in the | since thai is the best known form. I can now describe the origin of all ol the lymphatic sacs in the pig and give the relation of the main ducts i" all of imitive sacs. On the basis of our knowledge of
lymphatic system in this form I shall give whal is known of the lymphatic - in other mammals, in birds, reptiles and amphibia,
and shall then be in a position i inpare the primary lymph sacs in
mammals with tin- amphibian lymph hearts and sacs.
In the pig the lymphatics bud off from the veins in two places, from the anterior cardinal veins and from the veins of the Wolffian body. There are two sets of paired sacs, the jugular and the iliac; and two unpaired sacs, the retroperitoneal and the cisterna chyli. In the most
neral terms the jugular sacs drain the anterior half of the body; the iliac sacs drain the posterior half of the body, while the retroperi- toneal or prae-aortic sac drains the viscera. The cisterna chyli with
the thoracii innects the jugular and renal lymphatics. Ini
•ific terms the jugular lymphatics bud off from the anterior cardi- nal veins, form large sacs in the neck, from which lymphatics grow to the head and nek. the foreleg and thorax, and to the heart and lungs. From the left sac arises the jugular stem of the thoracic duct. All the rest of the lymphatic sacs hud off from the vena cava, where il is ;, part of the median mesonephritic vein, from the median
The Origin and Development of Ihe Lymphatic System. 25
phritic vein and the veins in the dorso-medial edge of the Wolffian bodies. The lymphatics which grow from the ventral surface of the mesonephritic veins make the large retroperitoneal or prse-aortic sac; those which grow along the dorso-medial edge of the Wolffian bodies, lateral to the aorta, form the iliac sacs, and those which grow dorsal tn the aorta make the cisterna chyli and thoracic duel. The thoracic duet is formed in small part from a dud from the lefl jugular sac; in larger part from a plexus which surrounds the aorta from the cisterna chyli. The retroperitoneal sac drains the diaphragm and the abdominal viscera, except the permanent kidney; the iliac sacs drain the permanent kidney, the abdominal walls, the hindlegs, tail and em- bryonic membranes.
B. THE .11(11 I. Alt SACS.
As has already been stated in part 111, the spreading of the primary superficial lymphatic capillaries in the skin of the embryo pig takes place while the embryo is growing from 20 to 50 mm. long. The first lymphatic buds are found when the embryo is aboui 1 1 mm. long (fig. 6); the sac is well formed at is mm. (fig. ]). and reaches its maximum size in an embryo 30 mm. lone (»fig. 8). It remains as a large sac until the embryo measures -"it) mm., when it begins to be transformed in pan into lymph glands (fig. 16).
An understanding of the development of the jugular sac depends on a knowledge of the veins of the region. Indeed. 1 was not able to inject the early stages until 1 had so mastered the pattern of the blood vessels that a little bl 1 in any of them enabled me to repro- duce the whole picture and so avoid the blood vessels.
The study of the form of the earlv anterior cardinal vein is shown for the chick by Evans (34) in his figs. 1 to '■'>. These figures show that the primitive deep dorsal segmental branches drain the ventro- lateral surface of the spinal cord. They bring out the gradual curve of the anterior cardinal vein and the more marked bend of the pos- terior cardinal vein, where the two join the duct of Cuvier. This stage is shown for the chick in cross section by Evans (35) in his fig. 437 B, as well as in ( Evans 34) his fig. 4.
In fig. 4 is given an injection of the blood vessels in an embryo pig "t mm. long, a stage just before the lymphatics begin. The curve of the dorsal border of the cardinal veins toward tin duct of Cuvier is
/ ■:-. in ■ /,'. ^
I as mi. ii :, k. Dor as it is oi E this
-.1111. < 111!.!
\ sing from the cardinal veins there i- a -nit- of seven ental bi extending in the nervous Eystem between the
le primitive posterior cerebral vein (Mall 143), which arches
A ■
-
Fio. i. Injected specimen to show the anterior cardinal vein and its
branches in an embryo pin which measured 7 mm. in Its greatest diameter.
Magnified aboui 28 times. This is a stage before the lymphatic vessels
begun. A = aorta arches; D. C. = duel of Cuvier; V. c. p. = vena
ci rebralis posterior; V. 5 = fifth segmental vein.
downward over the medulla and cord and the cerebral end of the arm bud. The firsl two of these branches drain the medulla, and hence there are ii\'' spina] or segmental branches proper. Each of these branches has n corresponding artery which lies slightly caudalward and nearer the midline. Only the lower four segmental arteries are injected in this specimen. The relative position of artery and vein
Thr Oviijin and Development of the Lymphatic System. 21
shows in fig. I-m (Evans 35). Each of the five spinal veins drains ,1 plexus of w i 1 1 1 ■ capillaries, which marks the presence of the develop- ing spina] ganglia.
It is. however, the superficial veins which arc of more interest from the standpoint of the lymphatic system. Along the dorso-lateral bor- der of the cardinal veins there is a series of intersegmental sprouts, varying from one to four or five in each interspace. These sprouts drain a superficial capillary plexus which is developing in a groove in the neck which is a continuation of the groove dorsal to the Wolffian ridge. The arteries fur this superficial capillary plexus come from the deep segmental arteries (Evans 35, fig. 137). The connections of the plexus with the cardinal vein are most abundant near the poste- rior cerebral vein. This superficial capillary plexus of the body wad has a most interesting development. For the area between the limb buds it has been worked out by Dr. Helen W. Smith (111), whose figures are copied by Evans (35). This superficial plexus in the tail region shows a constant zone of widened capillaries (35, fig. t61 i corresponding to the position of the posterior lymph hearts in birds. For the neck region it is necessary to know this plexus in order to locate the jugular lymphatics, and therefore its development will be followed in further stages.
The ventral branches of the anterior cardinal vein are represented at this stage by one large pericardinal vein, which receives branches from the gill arch region. The common stem for the branchial and pericardial vessels connects with the anterior cardinal vein, but it drains directly into the duet of Cuvier (see Grosser and F. T. Lewis as quoted by Evans 35, p. 660) on the right side of this embryo, while on the left side of the same specimen it opens into the anterior cardinal vein.
The earliest lymphatic buds have been found in embryo pigs measuring from Ki to 11 nun. lone-. All of my measurements mean the greatesl length and are made on the fresh specimen. The stage of the first lymphatics is shown in two figures, fig. 5, a total mount of an embryo injected with India ink through the umbilical artery in a specimen 11 mm. long, and fig. 6, a cross section 250 /i thick. through the lymphatic area in an embryo measuring 11 mm. The blood vessels were injected with India ink, and the lymphatics are Idled with blood.
/ • /.'. Sabin.
.
km
Fig. .">. — Injected specimen of the anterior cardinal \<'in and its branches in an embryo pig measuring 11. mm. in its greatest diameter. Magnified about 33 times. This Is the stage at which the lymphatic vessels begin to develop. The vessels were injected with India ink through the umbilical artery. D. C. = duct of Cuvier; V. c p. vena cerebralis posterior; F. a. v. = primitive vena ulnaris; V. 5 Hftn segmental vein.
The Origin and Development of the Lymphatic System. 29
The blood vessels show a great development. The five spinal seg- mental veins are clear, draining the large plexuses around each spinal ganglion; the ganglia are now farther ventralward than in the pre- ceding stage. The superficial capillary plexus shows the mosl marked changes. There is a continuous sheet of superficial capillaries in the
L s
A cv
Fig. 6. — Section through the third segmental vein in an injected embryo pig which measured 11 mm. in its greatest diameter. The section, which is 250 |U thick, shows the relation of the jugular lymphatic sprouts or buds to an anterior cardinal vein. Magnified about 40 times. The blood vessels were injected with India ink through the umbilical artery. The lymphatic sprouts. L. s., have a natural injection of blood; these lymphatic sprouts lie in a non-blood-vascular zone dorso-lateral to the anterior cardinal vein. A. c. v. = vena cardinalis anterior; g — groove.
neck, anastomising with the branchial vessels, with the pericardia] vessels and with the abundant capillary plexus of the arm hud. Opposite the medulla the connections of this superficial plexus with the anterior cardinal vein are very numerous, while opposite the heart a lew veins connect ii either directly with the anterior cardinal vein or more frequently with the main segmental branches. It is this
/.'. Sabin.
the third, fourth ami fifth segmental veins, thai is the lymphatic a
• ■ the lymphatic area definitely it is neeessan to noti details "t' the superficial veins more carefully. The superficial plexus ateral groove is finer meshed and of smaller capillaries than • -•. The groove is an important land mark and it shows best in
i, fig. 'i. From the plexus in the groove a -I i of wide
lillaries i< growing dorsalward external to the myotomes, ami loops from this sheel connect with 'lie deep plexus around the spinal cord. The -kill over the entire dorsal surface of the cord i- an entirely non- ular area at tl . From the ventral border of the super-
ficial plexus in the groove a sheet of wider and more opi Q-meshed capil- laries covers the surface of the embryo over the anterior cardinal I i - rfaci contour of this, the lymphatic area, is a swelling i in fig. 6, which 1 shall call the jugular lymphatic ridge. T • blood capillaries of this area are very superficial ami drain into the cardinal vein in four ways: ( 1 ) Through the plexus in the groove ami it- dorso-latera] superficial veins: ( ".' ) in .-mall pari through direct branches t" the lateral surface of the cardinal vein; (.'!) through branches of the ventro-lateral surface of the anterior cardinal vein which drain the pericardium ( lie.. •">): ami (I) through anastomoses with the capillaries (fig. 5 > of the primitive ulnar vein. The primi- tive ulnar vein has developed from the diffuse capillary arm bud plexus of the preceding stage. It enters the lateral surface of the sterior cardinal vein directly opposite the fifth segmental branch. Thus a part of the blood <>i' the branchial region and of the pericar- dium drains through the superficial plexus over the lymphatic ridge rimitive ulnar vein, [n a little older embryos, namely, those 12 mm. long, a ■' vein has developed from the arm bud plexus
jusl alward to the primitive ulnar, which now receives the hi 1
'ii the plexus of the lymphatic ridge. The complete description of this superficial plexus involves a study of the origin of the external jugular vein which I do no! wish to go into until I can illustrate it adequately. I bring up the point here because A. II. (lark (24) has -hewn thai occasionally a lymph trunk in the neck in older pigs opens directly into the externa] jugular vein near its point of union with the internal jugular vein. It is therefore of importance to note that the capillary plexus in the arm bud, from which this pan of the internal jugular vein comes, i- presenl in the embryo when the lymphatic- an
,AW~
mvt Of I
The Origin and Developme.nl of the Lymphatic System. 31
budding out, though the interna] jugular vein as a whole is formed considerably later.
For the present the interest in the superficial blood capillary plexus is that ii covers the lymphatic ridge. It will be seen in fig. 6 that tin lymphatic ridge includes a non-vascular area. Tin- non-vascular area is bounded bv the anterior cardinal vein and its dorsal branches, the plexus of the groove, the wide-meshed superficial plexus and the ventro-latera] branches of the anterior cardinal vein. An occasional direct lateral branch of the cardinal vein cuts through the otherwise non-vascular area. Within this area arc seen the blood-filled lymphatic buds. They lie in the angle between the anterior cardinal vein and its dorso-lateral branches and connect with both. They arc opposite the third, fourth and fifth dorsal segmental veins, and extend a distanci of L5 nun. from the primitive ulnar along the anterior cardinal vein. The tiny lymphatic buds arc already sending sprouts away from the parent vein.
The presence of stagnant blood, winch has proved so valuable a criterion in the living embryo, must be used guardedly in studying sections, unless there is a complete vascular injection. In the lym- phatic area I have noted in the fresh embryo that the blood capillary plexus of the groove is often empty, while the superficial plexus over the lymphatic area and over the pericardium tend to retain sonic blood. The blood vessels of an area where lymphatics arc budding must be thoroughly known before one can be sure of the lymphatic buds. The early lymphatic buds are packed with blood to an extent not common for the veins, which perhaps shows best in figs. 490 and l!M (Sabin l-'M). for the jugular lymphatic buds in a human embryo.
I have not yet succeeded in injecting the first jugular lymphatic buds in the pig as B. \j. Clark- has done for the early stages of the posterior lymph heart of the chick. In the embryo 1".' nun. long they can be seen in the fresh embryo, and sections >\\n\\ that they have formed a plexus along the margin of the anterior cardinal vein. To see the lymphatic buds at 12 nun. the embryo should be placed in warm Locke's solution while the heart is still beating, and it should be viewed tinder the high powers of the binocular microscope with the direct sunlight focused upim it. The lymphatic area is wider in the dorso- ventral direction than in lie. <i, hut its dorsal boundary is clearh marked b\ the surface groove. If the superficial blood capillary plexus is empty tin1 lymphatics can then he seen looking like a cluster
/.'. Sabin.
"i 'lull red grapes against the cardinal vein; in the older specimens • ■I the IhiiI- are markedly larger than others, while ai 1 I mm. -i of them in;i ki -~ n definite sac with large sprouts p dorsalward. At this stage, namely, 11 nun., the sac can be in-
•
5 i
-As-
Pro. 7. Injection of the left Jugular lymph sac in an embryo pis which measured 18 mm. in its greatest diameter. The specimen was fixed in in per cent formol and cleared by the Spalteholz method. Magnified about 30 times. The glass canula which shows piercing the upper border of the arm bud shows the point of injection. A. c. - anterior curvature of the lymph sac; A. s. = apex of the lymph sac; 1. = glass canula used for injection; S. s. = stalk of the lympb sac: V. j. i. = vena jugular interna.
by direel puncture. The preceding or plexus stage is shown bj E. !.. Clark for the corresponding sac in the chick in fig. L5. The beginning -.n i- shown for the human embryo in lLr. I!M (Sabin 134).
It is not easj to gel perfect injections by direel puncture, but by the timi the embryo is Ifi nun. the dorsal sprouts from the sac arc
'I'lii' Origin and Development oj the Lymphatic System.
Fig. 8. — Injection of the right jugular lymph sac in foetal pig measuring 3.5 cm. Magnified about 10 times. After A. H. Clark ( 24 I : this specimen was shown as fig. :'. in 130; it has since been cleared by the Spalteholz method so that it shows the relation of the superficial lymph vessels to the jugular sac. It shows a complete injection of the suprascapular and oc- cipital plexuses, but an incomplete injection of the superficial cervical plexus. S. s. = the stalk of the sac showing faintly through the shoulder; V. 1. f. = vena linguofacialis.
I . - ■''ill.
sufficiently that the sac can be injected indirectly throu«
11. The process by which a lymphatic plexus becomes a sac has been called confluence or cavernization by Ranvier (117-118). He says iliai when two lymph vessels lie in contact the endothelial wall between
11 disappears (possibh ii i- retracted) and thus large sacs develop. It i- exceedingly interesting that this pi es no! take place when
lymphatic endothelium rests on venous endothelium, as is the ca "I the jugular lymph sac.
The si interesting in the formation of the jugular sac is
.mi 111 fig. ', from an embryo 18 nun. long. To injecl the sac al this stage ii i- again important to note the plan of the blood capillai
In fie. ii it will I"' noted that there is a tiny 1.1 1 capillary which cuts
across the lymphatic area from the superficial plexus to the deeper veins and divides the lymphatic area into two parts, a ventral jugular part and a dorsal part. By the time the embryo is from 16-20 nun.
ig the path of \h\- slender vessel is occupied by a considerable plexus
.1 1 vessels and i.\ nerves as well. The sprouts from the main
jugular sac (fig. '. i have grown up into the dorsal lymphatic area and
there developed into an abundant plexus. It i- this plexus which can
• injected, as is shown by the glass tube which pierces the arm bud.
'I'h iginal sa< is shown just lateral to the shadow of the internal
jugular vein. This is difficult to inject by direct puncture, because the blood capillary plexus over it has become double and is excessively abundant. Moreover the sac is now just mesial to the developing externa] jugular vein and li.- very close to it. 'The blood capillary plexus of the groove shown in fig. 6 is now deeper in. and the entire area of the groove so dense a vascular area that no canula can enter the
■
zone without filling the hlnml capillaries lint juM ventral tn the groove in the dorsal lymphatic area almost every puncture will fill the lymphatics, provided it avoids the superficial blood capillaries. This dorsal lymphatic area is destined to be the posterior triangle of the iie.k: even in this earlj stage it looks translucent and continues to do «... for it is always uncovered by muscle, lying between the trapezius and the sternocleidomastoid muscles (fig. 11 i.
A description of the form of the sac in fig. 1 will make the basis
i the des< ription of the peripheral lymphatics of the head, neck and
thorax worked out by A. II. (lark (24) and given in section V. Phi
primitive sac is the portion above the arm hud and lateral to the
The Origin and Development of the Lymphatic System. 35
interna] jugular vein. This becomes the internal jugular trunk; the cerebral end of this portion is an abundant lymphatic plexus, the anlage of a single gland in the pig (A. 11. Clark) which drains the pharynx. In the dorsal lymphatic zone the rest of the sac is a com- plete arch from which develop the lymphatics of the shoulder, head. neck, face, arm and thorax. The dorsal areli of the sac becomes by far its largest portion, as will be readily seen in fig. 8, from an emhryo 3.5 cm. long. This is the same specimen shown as fig. 3 (Sabin 130). It has since been cleared by the Spalteholz method, so that it shows the sac as well as the superficial lymphatics.
The transition stages between fig. 7 and fig. 8 are very easy to inject and can be readily imagined. The further development of the sac, especially with reference to the lymphatics along the external jugular vein, is brought out in the sections on the peripheral lymphatics and glands.
('. THE RENAL SACS.
The study of the rest of the lymph sacs in the pig may well begin with the interesting and valuable work of Silvester (140). Silvester lias shown that in the monkey all of the lumbar and mesenteric lym- phatic ducts drain not by the thoracic duct into the jugular veins, but directly into the renal veins or the surface of the inferior vena cava near the renal veins. This he shows in a number of figures from bcaul i ful injections.
A. RETROPERITONEAL SAC.
It had previously been discovered by Lewis {](',) in a study of rabbit embryos that a lymphatic sac develops just ventral to the median mesonephritic vein. Baetjer (8) proved that this, the retroperitoneal or prse-aortic sac, arises from the ventral surface of the large vein which connects the two Wolffian bodies in emhryo pigs measuring from 17 to 23 mm. long. Baetjer's fig. •">, from an emhryo 1!» mm. long, shows the blood-tilled lymphatic buds which have been slightly injected from the veins. These buds rapidly form a large sac which lies in the root of the mesentery and is the place of origin for all of the mesen- teric lymphatics (Heuer, 43); those that grow to the stomach and intestine, the liver, the capsule of the Wolffian bodies and the repro- ductive glands. The blood-filled lymphatic buds can be seen in the fresh embryo pig 11* to "in mm. long, if the intestine is pushed to the ?,
.. v ibin.
side and the veins are emptied of blood by injecting them with salt solution.
The retroperitoneal - the largest of all the lymphatic sacs
in the pig. As shown in Sevier's fig. 3 (43) it spreads oul lehind
rectum and covers the entire area in the rooi of the mesentery • II the two Wolffian bodies. It spreads over the ventral bui of the Wolffia ■- as far as the edge of the reproductive glands.
It was from injecting this sac thai Eeuer was able to study the devel- opmenl of the lymphatics of the intestine.
This Bac would give an excellenl opportunity to study the proa - cavernization. Injections of it with silver citrate give beautiful 3, showing the endothelial-covered trabecular that cross its lumen. Total preparations of the silvered sac remind one of the tri uli' iii the wall of the cavity of the la-art. These trabecule, which are tl the process of transferring the sacs into lymph
glands, slmw especially well in sagittal sections of pig embryos 20-25 inn), long.
2. Iliac Sao — Cisterns Chtli.
I tan now bring Borne evidence to Bhow that the iliac lymphatics
which drain the legs, tail ami abdominal wall, and the cistcrna chyli which forms the lower part of the thoracic duct, arise togi ther as buds from veins of the Wolffian bodies. A complete account of this process nerd- ii more extensive illustration of the hlood vessels of the region than I i .in give at this time. In the pig the lymphatics which hud I/it' from the veins of the Wolffian body ami grow forward dorsal to the aorta to form the cistcrna chyli ami caudalward along the edge of the Wolffian body to form the iliac lymphatics, do nut begin until the i mbryo is 22 mm. Inn-. | found that they arise from the niesone- phritic veins because a direel puncture of the blood-filled buds entered the main vein- and not the blood capillaries. In a litter of pigs which measured '.'•'! mm. I washed out the blood vessels with Locke's solution, am] then opened the specimens ami pushed one of the Wolffian bi over toward the midline, a plexus of blood-filled lymphatics was then readily seen dorsal to the aorta. I succeeded in puncturing some of the hii i sels of the plexus forming the cisterna chyli in three ■a the ink run from the lymphatics into the mesone- phritic vein-. In all of these injections the cisterna chyli i- ohscured travasations at the point f( injection, hut they all show the
The Origin and Development of the Lymphatic System. 31
iliac lymphatics. For the present I shall describe the renal lymphatics from sections which can be done in the blood-packed stage.
The description of the iliac lymphatics, however, needs an outline of the blood vessels of the region. If the veins of the prevertebral space between the level of the median vein connecting the Wolffian bodies and the root of the tail be injected it will prove that they
Fig. 9. — Section through the hilus of the Wolffian bodies to show the place of origin of the iliac lymphatic vessels and the abdominal part of the thoracic duct in an embryo pig 23 mm. long. (Specimen 23b.) Magnified 50 times. A. = aorta; G. s. s. c. = gl. suprarenalis s. corticalis; L. v. = lymph vessels filled with blood; M. v. — vena mesonephritica; R. s. = retro- peritoneal lymph sac, a part of which is filled with blood, a part empty; W. b. = edge of the Wolffian body.
are enormously abundant. In the embryo measuring 20 mm. the segmental veins draining the cord and the body wall make an extensive network, which drains in part into the median vein of the Wolffian body and thence directly to the vena cava, while farther caudalward this same plexus drains directly into the large surface
/.'. Sabin.
veins of the Wolffian body. Opposite the lower p the Wolffian
plexus i- direetl) continued into the iliac veins. < injected embryos at i: is stage, namely, 20 mm., Bhow that ill" entire area lateral to the aorta and between the two Wolffian bodies is practically filled with ;i plexus rmental veins. By the
time the embryo is 22 or !'■'< mm. long, however, there is a small non- vascular area along the dorsal-medial edge oi thi Wolffian bodies, and into this small area the iliac lymphatics bud. The earliest specimen in which I have found these blood-filled buds measures 22 nun.; the
i ini.n is of interesl because it shows clearly that the buds lie against the veins of the Wolffian body itself as well as the median mesone- phritic vein. The place of origin of the cisterna chyli and iliac lym- phatics can be best seen in fig. 9, which is a cross section of an embryo measuring •-'.'! nun. through the median mesonephritic vein. Just lateral to the aorta are the masses of the sympathetic nervous system through which run- the great plexus of the segmental veins, and the cortex of the adrenal bodies. Ventral to the aorta is the mesonephritic vein, and the retroperitoneal sac, Borne of the buds of which are full of blood and some now partly empty. In the dorso-medial edge of the two Wolffian bodies is the plexus of blood-packed lymphatic buds which arches acros midline, and. as shown in fig. 10, which is farther
• bralward, forms a definite blood-filled cisterna chyli in the midline.
My various series of cross sections of pigs of about the same meas- urement are interesting, because they show the progression of the buds. In a specimen (23a) the iliac lymphatics extend only as far as the 1 1 i 1 n in of tlie permanent kidney which lies dorsal to the lower pole of the Wolffian bodies. The iliac buds lie throughout their course in the same relative position to the Wolffian bodies and the aorta as is shown in fig. 9. In this specimen (23a) the iliac lymphatic plexus i- spreading over the capsule of the permanent kidney, showing that it receives lymphatics while they are in the blood-filled stage. In later stages I have injected lymphatics from the iliac sac around the pelvis of the kidney. It is thus clear why the lymphatics of I kidney drain into the iliac lymph glands, while those of the repro- ductive glands which develop ventral to the Wolffian body drain into the prae-aortic glands. In a series 23b from the same litter as 23a iliac plexus is complete, extending from the mesonephritic vein to a dilated sac opposite the bifurcation of the aorta. It was this swollen end of the iliac lymphatics that I identified in embryos 25 nun. long
The Origin and Development of the Lymphatic System. 39
and called the posterior sac in 190] (Salmi 129). The space for the iliac chain in the pig is small, much smaller than in human embryos, and the iliac vessels in the pig are therefore very inconspicuous in cross sections, except in the blood-filled stage. They can be round, however, when one knows that they lie between the segmental veins and the dorso-medial edge of the Wolffian bodies or kidneys. Sagittal seetions are, however, brilliant for the iliac lymphatics and eisterna chyli in
\0
"%r * ■ -:pKJ^i
Sv.
w.b.:
i
JkSLi £.c.
\^0mS&&? i . ^ ■■■■•■'■ ■ gssc
^to y5 ■ ■ • ■ v ■ ■ ■-■".■/ .; ■ .r, / \V',iS- ?:'-■/?/ i-JM.v.
M.v.1.
!•-■'- •/.
Fig. 10. — Section through a plexus of vessels filled with blood which marks the beginning of the eisterna chyli in an embryo pig 23 mm. long. (Specimen 23b.) Magnified 40 times. The lymphatics are filled with blood, the blood vessels are empty. A. — aorta; C. c. = eisterna chyli; G. s. s. c. = Gl. suprarenalis s. corticalis; G. s. s. m. = Gl. suprarenalis s. medullaris; M. v. = vena mesonephritica; S. v. = segmental vein; W. b. = edge of the Wolffian body.
the blood-filled stage. In a sagittal series of a specimen 23 mm. one can see the entire iliac chain in a single section, from the mesone- phritic vein to the blood-filled sac just caudal to the Wolffian body. From this caudal swelling, from which a large group of iliac glands develops in the pig. three sets of vessels grow out: (1) a plexus which completely surrounds the umbilical arteries, (2) the femoral vessels, and (3) the ileo-inguinal vessels.
10
/,'. Sabin.
I I. I in I HOB U IC DUCT in THE PIG.
The thoracic duel is easy to inj.it after it is <'u*<' fully formed, but in the early - dingly difficult. In later Btages it inn be
injected indirectly either from the retroperitoneal sac or from the iliac- sac. Mon over it lies in the edge of the wall of the aorta, which guides or a direct injection. In the lower thoracic region it forms such an abundan! plexus around the aorta that if the m
w ^
Fig. 11. — Section through the 7th cervical vertebra of an embryo pig measuring 19 mm. Magnified 45 times. The blood vessels have been injected with India ink through the umbilical arteries. This is the stage just pre- ceding the development of the thoracic duct. B. v. p. = plexus of blood vessels ventral to the vertebra; E. = esophagus: J. 1. s. = jugular lymph Bac; N. b. = nervus sympathetica ; T. = trachea; V. j. i. = vena jugularis interna.
avoids the azygos vein it is almost certain to enter Lymphatics. Pensa's i L05) series of injections in different forms, as well as fig. i (Heuer t.3), show thai n ostanl characteristic of the lower thoracic part
of the duct i" be a complete plexus around the aorta, while the upper thoracic portion consists of one or two ducts.
The thoracic duct forms from two places: (1) a duel which grows downward from the left jugular 3ac, and (2) a plexus which buds out from the mesonephritic veins and completely surrounds the aorta.
The Origin and Development of the Lymphatic System. 41
Before the thoracic and renal segments have met, however, it is mosl difficult to inject them.
The early jugular trunk I have never injected directly and only once indirectly from the jugular sac. It will be readily seen that ink injected into the jugular sac usually takes the line of least resistance, the physiological path into the veins. Once in an embryo 23 mm.
.■•■■■'.■■■- 1
Fig. 12. — Section through the point of origin of the jugular part of the thoracic duct in an embryo pig 23 mm. long. (Specimen 23a.) Magnified 40 times. The left jugular lymph sac and the beginning thoracic duct emptying into it were injected in the specimens; in the drawing the veins are arbitrarily shown as injected and the lymphatics as empty. The thick- ness of the endothelial lining of the lymphatics has been exaggerated. A. = aorta; D. t. = ductus thoracicus; E. = esophagus; N. s. = nervous sym- patheticus; N. v. = nervus vagus; J. 1. s. = jugular lymph sac; V. j. i. = vena jugularis interna.
long I filled the sac, and on pressing the head forward the ink shot into the thoracic duct. The pressure obviously could Dot be regulated. In 1911 I reported this specimen (23a) at the meeting of the Ameri- can Association of Anatomists in connection with an unfinished study of the thoracic duct. Dr. McClure requested the specimen for Mr. Kampmcier. who was also studying the thoracic duct in the pig at
I'- net /.'. Sdbin.
the time, and he has published, with my permission, a valuable recon- struction <>f in;. ten in the Anatomical Record for L912 (Kamp- meier 66 ).
I • thoracic duel needs to be considered in relation to the reins region. I g. 11 is a section through the seventh cervical verte- bra of an embryo pig 19 mm. long, which i> before the thoracic duct i complete vascular injection. Ii n ill be seen that there is a vascular zone ventral to the vertebra, and from this zone veins surround the sympathetic nerves and enter the dorso-medial border of the internal jugular vein. The esophagus has a plexus of blood vessels in the submucosa, but dorsal to the esophagus is a non- vascular zone of loose connective tissue. The jugular stem of the thoracic duct grows into this non-vascular area dorsal to the esopha- - i- Bhown in fig. 12 from 23a. In this tracing; of the section the veins are arbitrarily made black and the lymphatics are shown empty, though in the section the left lymphatic sac and its ducts w< injected. The thoracic duct lies in the margin of the vascular zone. \- Kampmeier's reconstruction of this specimen show-, there is a considerable plexus of lymphatics dorsal to the esophagus nea; their
place of origin from the jugular sac. This plexus c sets with the
left jugular sac in three places. From the injected plexus a short
duct follow- the left cardinal vein and I think grows to the heart
and lungs. A longer vessel crosses to the right side and i- the jugular men! of the thoracic duct. This crossing of the duct behind the aorta I have frequently, though not always, noted in older stages.
The right lymphatic duct curve- ventralward and -row- t • > the heart and lungs. 1 1- course is shown in Ii;:. 13 for an embryo 25 mm. long. The asymmetry of the thoracic duct is confined to the jugular portion and corresponds with the asymmetry of the aorta. It is interesting to note that Sala I 137, Taf. 1 I. Fig. 16) and Pensa I 104, Taf. 15, Fig. Vi picture a symmetrica] thoracic duct m the bird.
The position of the cisterna chyli has already been shown in figures 9 and in. The cisterna chyli and lower part of tlie thoracic duct arise in common with the iliac sacs from the mesonephritic veins on either side, a- -hown in fig. '.'. These lymphatic buds from the two ■ dorsal to the aorta and grow both cerebralward and. caudal- ward along the dorsal wall of the aorta. This makes an abundant plexus of blood-filled lymphatics along the ionise of the abdominal aorta. Anj sections of pig embryos of this stage will show that the
The Origin and Development of the Lymphatic Syst
em.
43
veins around the aorta arc very abundant, so thai the non-vascular space is small. .Inst opposite the adrenal anlage, however, there is a
transition zone which is less vascular. It marks the end of the azygos veins. Below this level the segmental veins drain through the Wolffian bodies, and here the lymphatics form a wider plexus, winch becomes the cisterna ehyli, fig. 10. As in the adult there is a gradual tran-
Va..._
1
£>
m& \
-D.t.
s
i
L
-Nl.v.
Fig. 13. — Section through the upper thoracic region of an embryo pig measuring 25 mm. in which the blood vessels are injected, to show the vessels of the right lymphatic duct approaching the heart. Magnified 40 times. The injection of the blood vessels was made through the umbilical artery. A. = aorta; D. C. — duct of Cuvier; D. t. = ductus thoracicus; E. = esophagus; L. = lymph vessels to the heart from the right lymphatic duct; N. v. = nervus vagus; P. = pericardium ; T. = trachea; V. a. = vena azygos.
sition between the cisterna ehyli and the rest of the aortic plexus, both the part which extends caudalward and the part which extends cerebralward. Figure 10 shows the cisterna ehyli while it is still a plexus and not a sat-. The series shows that in many places this dorsal plexus of lymphatics is sending sprouts around to the ventral pre- aortic sac. All of the abdominal sacs, the retroperitoneal, ventral to the aorta, the two lateral iliac sacs and the dorsal plexus connect with
H • /'. Sabin.
In following th iralward from the level of fig. 9
ii i- clear that the blood-filled lymphatics not only arch across the midline dorsal to the aorta, but tbej follow the border of the Wolffian be lateral to tl i. Above the adrenal bodies the Wolffian
bodies approach very close to the aorta, and some of the lymphatic buds curve around the ventral surface of the aorta. Thus in a sp men 23 nun. long there is a plexus of blood-filled lymphatics surround- ing Lhe aorta and extending into the lower thorax as Ear as I :>ral
• ■ of the Wolffian bodies. At the cerebral end oi the Wolffian bodies there are large veins which curve ventral to the aorta and conned the veins of lhe capsule of the Wolffian bodies. Some of the lymphatics are n< ar i dian veins.
i Finding of the renal lymphatics in the blood-packed Btage makes it quite certain that the thoracic duel arises in two places: First, the jugular stem, which can lie injected from the left jugular sac ami develops long after the jugular sacs arc entirely empty of blood; and.
■ndlv. the renal plexus, which surrounds the aorta and forms a defi- nite cisterna chyli.
These two observations, namely, ( l ) the presence of hlood in one
pail ami its absence in the other, and ('.') the fact that injections prove a connection of the jugular -tern with the jugular sac. ami of the abdominal plexus with the mesonephritic veins, make it quite cer- tain that the two portions of the thoracic duct are distinct Erom each other in embryo pig- measuring' 23 mm., and hence that the thoracic dint begins in two places. Practically the entire question at issue between those of us who think that the lymphatics grow by their own endothelial wall and those who do not centers around the question of how the thoracic duct develops, or, t.1 put it more specifically, how these two lymphatic anlagen become connected. The discussion centers around my specimen 23a, which Kampmeier studied and which be - a- hi- mosl conclusive evidence of the theory of the growth of lymphatics by the addition of tissue spaces. On the other hand, it is my theory that the thoracic duct grows from these two anlagen Erom the same method by which other lymphatic capillaries
can be Been to grow in a living spei i n, namely, by the sprouting of
their endothelial wall. It is time that 1 have nut yet sufficiently mastered the difficulties of injecting the renal lymphatics to demon- strate the progression of the thoracic duct and indeed it may not pn.\e possible to gel as conclusive proof of the origin of the deep lym-
The Origin and Development of the Lymphatic System. 45
phatic sacs as of the more superficial ones; yet the inference that they arise in the same manner is in harmony with our modern knowl- edge of morphology. I wish to postpone a discussion of Kampmeier's evidence until I have described the thoracic duct in a human embryo, and discussed the development of the theories opposed to my own — of which Kampmeier's work is a part (See. VIII).
2. Primary Lymphatic System in Human Embryos.
On this description of the lymphatic system in one mammalian Form I shall base an account of what is known of the primary system in other forms. All of the primary lymphatic saes have been found in the human embryo. The jugular sac is the earliest to appear. It has been found as a few blood-packed buds in two embryos measuring 8 and 9 mm. (Mall collection, No. 397 and No. 163, Sabin 134.) They are on the lateral surface of the anterior cardinal vein near the duct of Cuvier and were described as veins (Sabin 133, 131), since at that time the blood-filled buds were thought to be blood capillaries. The blood-packed buds extend along the lateral surface of the anterior car- dinal vein and very early develop sprouts that project dorsalward. These are plain in an embryo measuring 11 mm. (Mall collection. Mo. 353, figs. 7 and 8, Sabin 133, and figs. 490 and 491, Sabin 134.) The figures of this specimen, together with the reconstruction of Lewis (Harvard collection No. 1000, measuring 16 mm.; Xo. 189, measuring 11.5 mm.; and No. 1332, measuring 16 mm., figs. 1-3, Lewis 78), show that the jugular lymphatics in the human embryo not only bud from the anterior cardinal veins, but from the posterior cardinal vein, and the common stem or plexus which forms the origin of the primitive ulnar and thoracoepigastric veins. A largo extension of the jugular sac along the primitive ulnar vein is characteristic of human embryos (fig. 12, Sabin 133, or fig. 493, Sabin 134, and figs. *.; and 3 after Lewis 78).
In a human embryo 10.5 mm. long I have found a small sac only partly filled with blood (figs. 3-6, Sabin 133, and figs. ISS. tsii. Sabin 134). This specimen has also a beginning thoracic duet. These two facts show that there is considerable variation in the rate of growth of the lymphatic system of different specimens.
The study of human embryos has also brought out the fait that the openings of lymphatics into the veins can only lie made out when
16 /.'. Sabin.
tion happens t" be cut in the right plane foi each valve. For the jugular sac frontal sections are the h -. 192, 194, Sabin 134).
A ik'u . iii the Mall collection, No. 160, measuring '.'1
in connection with the renal lymphatics. A care- ful ruction of this specimen with abundant illustrations would In' of value, but for the present 1 ran give only a description. I in- jected the embryo with India ink into the umbilical artery while the heart was >iill beating. The vascular injection i< almost perfect. The embryo was then put directly into bichloride-acetic and the fixation ccellent.
In marked contrast in the embryo pig of about the same length. Wolffian bodies are disappearing, being pushed caudalward by the iving permanent kidneys. The cerebral pole of the Wolffian bodies
• far to the side opposite the median mesonephritic Vein which, as Baetjer (8, fig. '. i shows, connects tli<' Wolffian h<>die< opposite their lii I ii i n in embryo pigs measuring 20 nun. This median vein in the human embryo (No. 160) passes over the ventral surface of the adrenal bodies and -till receives the veins of the cerebral pole of the Wolffian bodies. Ii also ; a plexus of veins from the permanenl kidneys.
It i- markedly asymmetrical mi account of the development of the vena cava on the right side.
B lod-filled lymphatic buds completely surround this mesonephritic vein in the midline, making the anlage of the retroperitoneal or prae-aortic sa< ; some of those that come from the dorsal surface of the \ein have pushed between the ma>se> of the sympathetic ganglia ami reached "the dorsal surface of the aorta. In some sections, the retro- peritoneal buds are partly emptied id' their blood. The area at the root <<( the mesentery opposite the median mesonephritic vein i- small in the human embryo as compared with the corresponding area in I pig and the retroperitoneal sac is correspondingly small.
The iliac sacs and the beginning thoracic dint are also present. Uong the dorso-medial wall of the kidney in the angle between the mental veins and the plexus of renal veins are two long iliac sacs. 'I'h.', are evidently farther advanced than the retroperitoneal sac, for they are nearly empty. The one on the left side measures I 8 mm. ami extend- t < » the bifurcation of the aorta. On the right side the empty Bac i- considerably Bhorter, hut it- lower part i- replaced by blood-filled buds along the inferior vena cava.
The Origin and Development of the Lymphatic System. 47
In tracing the lymphatics cerebralward, from the level of the hilus of the kidney, there is a small lymphatic capillary plexus in the place of the cisterna chyli and the two lateral sacs become a plexus of small ducts which can be traced the entire length of the permanent kidneys and then along the dorso-lateraJ. surface of the aorta, jus! ventral to the azygos veins. This small plexus of ducts is nearly empty on the left side, but full of blood on the righl side. The two plexuses can be followed almost to the level of the bifurcation of the trachea. Some blood in the plexus on the left side just before the vessels end makes it possible that the renal part of the thoracic duct does not yet connect with the jugular part of the duct.
This particular specimen is interesting in regard to certain /.ones of dilated tissue spaces which arc conspicuous along the aorta. There are some of these large spaces near the bifurcation of the aorta, in the root of the mesentery near the retroperitoneal sac, and along the ventral surface of the aorta, especially opposite the mesentery of the stomach and opposite the bifurcation of the trachea. I have studied them with care to see if they have any definite relation to the develop- ing lymphatics and am sure that they have not. Sometimes they are near the lymphatics and sometimes not. Those in the thorax are no! adjacent to the lymphatic plexus. They can be distinguished from the endothelial-lined lymphatics, but if one were convinced that lym- phatics came from tissue spaces one might imagine transition pictures between the tissue spaces and the ducts. Tins is particularly true when the endothelium of a lymphatic vessel sags away from the surrounding tissue, a picture familiar to histologists in sections showing lymphatics in adult tissues. The further discussion of the thoracic duct is in part VIII.
All of the primary lymphatic system is present in a human embryo measuring 30 mm. ( Mall collection No. 86, lig. 12, Sabin 133, copied as tig. 493, Strieker 144). This stage represents the maximum size of the jugular sac. The dorsal arch is huge and its line of separation from the jugular part is indicated by the perforation for the cervical nerves and blood vessels. The very small mesenteric sac and larger iliac sacs are distinct as well as the complete thoracic duct.
.'!. Primary Lymphatic System in Rabbit Embryos.
In 1906 F. T. Lewis (7(!) published a valuable paper on the lym- phatic- system in rabbit embryos. Besides excellent reconstruction of
I on n< ■ B. Saot'n.
primar) lympha tern in rabbits, the i at and the pig, this papei
has three important points: First, the discovery thai the early lym-
- are filled with blood, which has proved to be of Buch value,
a that it> ; i- understood. Second, the discovery of the
retroperitoneal sac which he described as lying adjacent to the mesen-
ic veins. Be also showed the iliac sacs and cisterns chyli; all of which we now know tunic from the renal veins (Sabin L36). Third, he ooted that lymphatic ducts when they are reconstructed from - tions appear a- a row of beads. Since these rows of beads occurred
mg ili.' veins in his reconstructions ami since he could nut find the connections of the early sacs with th< veins lie was led to suggest that lymphatics might arise from multiple anlagen splil off from the veins
mg their course. The apparently i~"laic<l endothelial-lined vessels found in serial sections we 'all Meyer-Lewis anlagen. 'They arc dis- ■i \ I I 1 .
The jugular sac in rabbits has an early extension along the primitive ulnar \< in like thai of the human embryo. The dorsal portion of the sac, I'"!- the posterior triangle of the neck, arises Erom a large stalk from the primary jugular portion between the level of the ith ami 5th cervical iici
I. Pbimabt Lymphatic System i\ ihe Cat.
The primary lymphatic system in the cat will be described from the
extensive work of Euntington ami McClure (51-58 ami 91-94), one
instruction of Lewis (76) and a few injections of my own. The
work of Euntington and McClure has been mainly on the development
of the jugular lymph sacs and the thoracic duct in the cat and their
servations are for the most pari broughl together in two extensive papers (54 ami 58). Their work is difficult to analyze ami cannot be done entirely accurately without seeing their sections. They have relied mi the appearances of sections ami the appearances of wax modi from them 1" differentiate lymphatics, ami since these are nut ade- quate criteria it is impossible to he BUre that all the structures shown
lymphatics are lymphatics; in fact, one can he certain that some "i'
them are n.it. Their theories in regard to il rigin ami development
of the lymphatic system ari' discussed in sec. VIII. In the article (.Mi on the jugular lymph sac of the eat figs. 8 to vM may he disre-
fled a- evidence, since thej are diagrams. Figure 22, which they
The Origin and Development of the Lymphatic System. 49
group under "Early Venous Stages," is, I think, a reconstruction of the cardinal veins before the lymphatics begin (and is therefore to be compared with Evans' (34) fig. 3, and with my fig. 4 in this paper). In their fig. 22 the fourth segmental vessel is shown ami described (page 226) as " formed by the confluence of two extended para-neural channels." This is intended to indicate the beginning of the lym- phatics, but since their fig. 43 from an embryo 10 mm. long shows undoubted lymphatics in the blood-packed stage, I think it is prac- tically certain that the specimen measuring 5 mm. does not show lym- phatics. It is not necessary to prove that veins do not open into the tissue spaces around nerves.
The description of the stages between 5 and 10 mm. is bound up with the discussion of "fenestration." In reconstructing the veins Huntington and McClure have noted the pattern of the developing veins, which is especially well shown in fig. -i, in connection with the pericardial veins. In this specimen the pericardial veins drain into a loop which connects the anterior cardinal vein with the duct of Cuvier. The formation of this loop is a part of the process by which the peri- cardial veins shift from the duct of Cuvier to the anterior cardinal vein. Numerous small loops are seen along the anterior cardinal veins in figs. 4 and 5. They are characteristic of the veins. They suggested to Huntington and McClure a vague conception of a rela- tion to the lymphatics which they expressed as follows (p. 204 in 54) : " In a subsequent stage confluence of these ' fenestra? ' results in the more or less complete separation of the primary vein into two parallel secondary channels, which appears to be a uniform principle in the development of parallel venous trunks. Or, as in the case of the jugu- lar lymph sac, further extension of the same process may result in separating from the main venous channels elements which unite to form a closed sac entirely distinct from the vein from which it arose. The term ' fenestration ' means, therefore, in the sense in which it is em- ployed in this paper, one of the last stages in the definite crystalli- zation of the venous system out of an indefinite antecedent plexiform condition, and the determination of an important element in lymphatic organization, closely associated witli the embryonic venous system." The lymphatics which they thought formed by this process they termed "' veno-lymphatics." Both terms "fenestration" and " veno-lymphat- ics " should drop out; there are no veno-lymphatics, for the lymphatics bud directly from the veins as lymphatics, and fenestration is a term
/,'. Sabin.
that • better than the actual process of growth by Bprout-
\\ which the veins are formed.
spires of the models from embryos measuring ', mm., for example fig. •'!•'>. represeni lymphatics in the early plexus stage;
I Wo not, however, find any mention of the presence oi U I. Figure
the beginning of the enlarging of the plexus into sa< -. From their later si -. it; to 65, bul much better from Lewis, fig. 6
. cm In' made "in the especial characteristics of the jugular i . are i l ) thai tin- jugular Bac in the cal arises from the posterior cardinal vein as well as from the anterior cardinal rein. This point i< well shown in Euntington and McClure figures. i •.' ) The cerebral end of tin- rentral or jugular portion of the Bac is rery large. This is th< part that drains the larynx. (3) The internal ar trunk is small. (I) The dorsal apes of the. sac which lies in the posterior triangle of the neck is large. (See Lewis' fig. 6.) It is connected with the cerebral end by a slender vessel. In injections of the sac in embryos between 30 and 60 mm. long ii Looks very much sac in ;i bovine embryo as shown by Polinsld ( 101 ) in his fig. "t. It lies nearer the arm than the corresponding portion of toe sac in the i>i'_r. (5) There is a large extension though possibly a dis- tinct sac (Lewis, fig. 6) along the primitive ulnar and thoracoepi- gastric veins. This sac is very conspicuous in older stages, extending into the axilla and receiving large trunks from the thoracic wall, makes the jugular lymphatic sac in the cat more like the human than the |iiur I sec. V |.
seg ntal divisions of the sac a- indicated by colors in the
Euntington and McClure figures air arbitrary and nut as valuable as the divisions 1 have jusl ljimh. which correspond to the function ■ if '!n' differenl glands which develop from tin' sac.
Lewi-' figure also Bhows a verj interesting view of the retroperito- neal ami ilia. as a continuous plexus, whirl: again emphasizes the fact that the n-nal sacs anastomose with each other.
'.. 1'i:im\i;v Lymphatic System in Birds, Posterior Lymph
Beart lnd .Ii i;ii.\i; \a \i rn S u .
The history of our knowledge of the lymphatic system in birds is mosl interesting. Tin- early discoveries >>\' the posterior Lymph hearts by Panizza, A. F. .1. Mayer, ami Stannius, a- well as the work of
The Origin and Development of the Lymphatic System. 51
Budge on the relation of the heart to the allantoic vessels, have already been given. From that time on there was no advance until the work of Sala (137), who studied the development of the posterior lymph hearts and thoracic duct. He described the posterior lymph hearts as arising in relation to the lateral branches of the first live coccygeal veins, during the seventh day of incubation. We now know that the posterior lymph hearts bud from the veins during the 5th day (E. R. and E. L. Clark, 29), so that Sala was describing the trans- formation of the plexus into the sac. He noted the connections with the veins but described the sac as arising from excavations in the mesenchyme. His work, published a short time before my paper on the origin of the lymphatic system from the veins (Sabin 129), was an advance over the preceding work, for it placed the first lymphatics near the veins instead of in the periphery. Sala figured the thoracic duct in the bird as a symmetrical structure (Taf. 14, Fig. 16), and this is also shown in Pensa (104, Taf. 15, Fig. 3). Sala described the early stages of the thoracic duct as being solid cords of cells. This observation, which has been confirmed by Mierzewski (96), makes it necessary to restudy the thoracic duct in the chick, which is now pos- sible through the great improvement in our metfiods of injection.
The most recent work on the lymphatic system in birds has been done by Mierzewski (96), Jolly (50), Miller (97) and E. E. and E. L. Clark (27-20).
I have already brought out the fundamental importance of the Clarks' work, showing that the lymphatics bud off from the veins in a non-vascular zone, and show a continuous growth to the periphery. Mierzewski had shown that the early lymphatics grow along the lateral line of the embryo, as shown in his fig. 3. It was these lymphatics which grow to connect the posterior lymph heart with the jugular lymph sac that E. L. Clark observed in their blood-filled stage and which led her to watch the process of budding in the living embryo.
The process may best be described in a quotation from p. 254 (20) :
The first evidence of lymphatics in the tail region of living chicks is the appearance of a number of separate knobs, filled with stagnant blood, a little darker in color than the circulating blood, just lateral to several of the most anterior of the dorsal intersegmental coccygeal veins. The connections with the veins cannot be seen, since the knobs lie between them and the ob- server, but ink injected into the knobs can be seen to pass directly into (he main intersegmental veins. Between the separate knobs no anastomoses can be seen, nor can any be discovered by injection.
4
:. Sabin.
i (in about fifty-five minutes), similar ones
thi-m which have i'n. > ions with them, thus forming
ter. The new om-s are lot ati i parti; <m either side of the first
ami partly BuperficiaJ to them. Their Injection now show- • tiny
•a hat like bunches of grapes, connected, as wer<
. with ilii-saiiir ii ■ Dtal % .in.-. an- still separate
from one another.
14. — Afti r Miller. Diagram from an reconstruction of the veins and of tii. cervical and upper thoracic regions of a chick embryo 13.5
mm. Ion;-', after 5 'lavs and 10 hours of incubation: ri.uht side. 1. Pra?-
cardinal vein. 2. Post-cardinal vein. 3. Duct of Cuvier. i. Intersegmental 5. Lateral group of vascular Islands and veno-lymphatlc
vessels. 9. Spinal (cervical) nerves. 9a Brachial plexus. Aft< r Miller,
Amer. Jour of Anat, 1912, Vol. 12, Bg, 12.
The Origin and Development of the Lymphatic System. 53
C.L.D.
Fig. 15. — After E. L. Clark. Lateral view of the jugular lymphatic plexus of the right side of a chick embryo 14 mm. long after an incubation of 5 •lays and 20 hours. The measurement was the greatest length and was taken after fixation. With a very fine canula (the lumen of the point being about 15 /i in diameter) diluted India ink was injected under a binocular microscope into one of the superficial lymphatic capillaries in the skin between the fore and hindlegs. From here the ink filled the deep jugular lymphatic plexus, and from there a few granules entered the vein through five connections (C). The drawing was made with the help of a camera lucida with a Zeiss binocular microscope (oculars No. 4, objective A3). Magnified 67 times. A. = vessel which connected the superficial lymphatic capillaries with the jugular lymph plexus and which was injected; A. C. = vena cardinalis anterior; P. C. = vena cardinalis posterior; D. C. = duct of Cuvier; C. = communications between the jugular lymphatic plexus and the veins: T. D. = deep lymphatic vessel; T. E. V. = vena thoraco-epi- gastrica: C. L. D. = cervical lymph vessel. After E. L. Clark's fly. I, Anal. Record, 1012, Vol. 6, p. 268.
."> I ... - ibin.
There Is a rapid »n of these blood-filled structures, and soon, in
u an hour ami a half after their lirst appearance, connections between
bborlng clusters maj a Injection a1 this Btage with India ink
iws an anastomizing plexus, connected, as before, with the Intersegmental
reins. Injection with silver nitrate shows distinct endothelial markings
in the walls of the plexus.
During this plexus formation there is a steady extension toward the sur- fai '.and by the time anastomoses have formed betv shoring (-lusters
sprouts havi grown to the surface and Btarted to extend In the region superficial to the plexus and also ventralwards. It now bt possible
jtudy with more minuteness the changes which are going on. since these sprouts are quite superficial and arc developing in a plane parallel with the surface. Observation and successive records of these sprouts in the living chick reveal a rapid extension ventrally ami also anteriorly, ac- companied by a pit xua formation. Two or three sprouts are seen to lead and soon numerous connections develop hit ween them. Various iwrtions of the Irregular plexus thus formed enlarge and become more densely packed with blood which continues to back up from the vein. Then new sprouts grow out in advance and the same process of extension accompanied by plexus formation is repeated. If a single sprout is selected and frequent careful drawings are made the changes are seen to be rapid and striking. The
rout becomes wider and longer. Branches appear, and they in turn in- crease in width and length. From a branch a connection forms with the original sprout, thus forming a loop. New branches and connections are formed, making a plexus. Branches from neighboring loops or plexuses meet one another and anastomose. The several parts of the plexus are rpiite irregular in size. Most of the lymphatic vessels are several times as wide as a blood capillary, while some of the connections are as small as, or even smaller, than a blood capillary. Throughout the blood in these new- forming lymphatics is markedly darker in color than the circulating blood.
This work thus corrects the idea that lymphatics arc transformed blood capillaries. They bud oui from the veins as Lymphatics ami gradually invade the body as a new type of vessels.
Miller's work (97) mi the anterior lymph sac is chiefly valua in giving an excellenl chance to contrast the method of reconstruction with the method "f injection in an ana where an injection can be obtained. Figure I I is cop m Miller's fig. <;. and li.ir. 1"> i> from
an injection hy E. I.. Clark's (27, fig. 2 ) of the plexus in the same
The |"'int- of the apparently isolated islands of lymphatics ami the separation of the sac from the veins show by .Miller are errors which are cleared up by 1-'.. I-. Clark*- work. The jugular lymphatic plexus i- connected with the vein in a number of places and is a con- tinuous endothelial-lined plexus of lymphatics.
The Origin and Development of the Lymphatic System. 55
The jugular lymph plexus develops into a small sae (M tiler's fig. 6 I which becomes a single jugular gland. This small, fusiform gland has been studied by a number of observers and has been worked out in all its relations by Jolly (59) in his interesting paper on the lymph glands in buds.
Miller (97, page t89) quotes Mierzewski as having seen rhythmical contractions of the jugular lymph sacs. A reference to Mierzewski's paper, however, will show that he consistently .-peaks of posterior lymph heart and jugular lymph plexus and his reference to pulsation (page 479) is a confirmation of Sala's observations in the posterior lymph hearts. Miller notes the absence of muscle ami the point should be emphasized, because the jugular lymph sac in birds becomes not a lymph heart, hut a lymph gland.
The iliac lymphatics in birds are very well brought out by .lolly (59) in his article on lymph glands. He does not consider their origin, but his fig. 15 shows their distribution extremely well, and his fig. 11, pi. XI, gives the exact histological picture of a lymph sac with connective tissue bridges for a bird on the 18th day of incubation. This is the method by which the primary sacs become lymph glands, as is shown in section VI.
6. Primary Lymphatic System ix Amphibia, Anterior and Posterior Lymph Hearts.
It is not possible at this time to give a complete account of the development of the lymphatic system of the amphibia and feptilia, but enough evidence is at hand to show that the lymphatics are derived from the veins. The remarkable subcutaneous lymph sacs in the frog have always attracted interest and stimulated a curiosity to unravel their development as was brought out by Langer (75) in 1868. Some recent experiments of Abel (1) which combine anatomical and pharma- cological methods add to this interest.
Meltzer (95) had published experiments to show that a smaller dose of a drug produced convulsions when injected into a cardiectomized frog than into a normal one. He concluded that the drug traveled through the tissue spaces.
Abel found that a dye, acid fuchsin, when injected into the lymph sacs of a normal frog was distributed widely over the body by the blood vessels. In a cardiectomized frog a small dose injected into the
mi,- iv no 1\ mphatics, onlv
iwly; "ii the other hand, a small amount of the fluid injected into a lymph sac traveled rapidly, but in clu the lymph ing to their anatomical conecti
\\": ed the lymph heart in the cardiectomized fi
it was pumped, not through : r\ to tl sels, but
through th the nervi rplained
lal] dose. If the lymph tied
It I ■ anterior lymph hearts of the ampl
bud off from i bra] veil (B , or in a more primil
ental veins which arc going ertebrals i Ivnower 74). They d( vi lop earlii
sterior hearts and have been found in I!, palustris, R. sylvatica and R. virescens measuring about 6.5 mm., and in R. temporaria and Bu measuring about 1.5 pun. Eoyer noted the prese
blood in the early - if In, ili anterior and posterior hearts.
ECnower brings out the fad in coi ion with the anterior hei that they lie "ii t' om which they derive the stria
muscle of their wall. ] I think, a very important point. The
particular myoto ne Knower has shown may vary.
The : i of the anterior lymph hearts can be readily seen in
the dorsal surface of the tadpole, iehind the pr - ind thus
they can
Prom the anterior lymph heart develop two symmetrical ves
of which m ard toward the head, the "the r backward toward
tail. The posterior duct as described by i1 livides into two
running to the tip of the tail dorsal to the myoton other pas ag icl along the ventral margins of the myotoi
form the ventral caudal trunk. It is the brai
dal trunks which ha studied so much in the living specimen.
There is also a lateral branch which runs caudalward from the an- terior lymph hi i the lateral surface of the myotomes half way between the dorsal and ventral branches. This lateral trunk quently i - n ith thi • ior l\ mph heart. Wieliky (153), Jossifov (G2-65), and Favaro (36)
terior lymph heart arose from the dilation oi udal lymph
trunks which grow from the anterior lymph heart-, and Jourdain (61) di a rapid destruction oi i on-
Tin Origin and Development of the Lymphatic System. 51
nective tissue. Knower and Hojrer, however, have found that they bud oil' from the posterior vertebral veins considerably later than the anterior lymph hearts, and they have been well worked out by Baranski (9). Baranski shows that they arise by several buds from the endothelium of the posterior vertebral vein and its branches. His fig. 1 shows particularly well the heaping up of the endothelium so that it looks like a solid mass at the point of origin. Practically nothing is known of the origin of the deep lymphatics in amphibia.
It lias thus been shown that the lymph hearts of amphibia arise as buds or sacs from the endothelial wall of segmental veins. They lie on the myotomes, from which thev derive the striated muscle of their wall.
The subcutaneous lymph sacs of the anura are secondary structures. Tins was found out by Ranvier (116) in 1896, and also by Knower and Hover. They are derived from duets which grow from the lymph hearts. They have been comparatively little studied. Hover (49) found that the large sac on the ventral surface of the head (sacc. submaxillaiis) developed from a branch of a duet from the anterior lymph heart, and that the lateral sacs are derived from the lateral lymph trunks.
This point has been just shown in conncctftn with the sacs of the extremities by Frl. Goldfinger (38), who has injected the primary ducts and then the increasingly denser lymphatic plexus up to the final lymph sacs. This process of cavernization could be studied here by silver nitrate injections.
Since the above was written Hoyer (49a) has published an article in which he gives a general review of the origin of the lymphatic system in vertebrates, and Hoyer and Udziela have given the first comprehensive description of the lymphatic system in a urodele (49b). In a salamander larva the lymphatic system opens into the veins first through symmetrica] axillary lymph sacs or sinuses, and secondly through a series of subcutaneous lymph hearts which pump the lymph into the vena lateralis (Meyer 88a and Marcus 87a).
There are six longitudinal lymph trunks, four superficial and two deep (Hoyer 49b, Taf. XII, Figs. 1. 2 and 5). (1) The median, dor- sal, longitudinal lymph trunk, which extends from the point of the tail to the middle of the he, id ; (2) a medial, ventral caudal trunk, which branches around the cloaca and opens into the inguinal sinus as is shown in fig. 2 (49b); ('■'< and 1) symmetrical lateral trunks, which
Sabin.
i.il to the myotomes and open in pan into tl aenta]
I \ n i j > 1 1 hearts and in pari into the axillary Binus, and ( • "> and 6) the
bral lymph trunks. The Bubvertebral lymph trunks are
- with many an rhich extend from the tip of
the tail to a point opposite the Btomach, where they unite to form a
rna chyli. From the cisterna chyli four vessels run forward to
ciliary plexu6, the paired thoracic duel and the two paravertebral
lymph truii
The axillary lymph sacs open by three or four branches into the cardinal veins and receive the following vessels: (1) The lateral superficial lymph trunks; (2) the paravertebral vessels; (3) the thor- duct; (4 - of the cranial part of the stomach and esopha-
a vessel which run- in the groove between the pericardia] and pen: . -: (6) a vessel which comes from 4;he base of the
skull: (7) superficial vessels fron ide of the head, and (8) the
lymph i the fori legs.
B des thi axillary sac there are two other sacs or sinuses, one of which lies dorsal to the aorta at the base of the heart, namely, the sinus lyinphatieus cordis ( Hoyer 19b, fig. 5), and is in the course of tin- jug- ular lymph trunks and the other of which make- the paired sinus of the inguinal region.
The segmental lymph hearts receive three groups of vessels: (1) branches from the Bubv< lymph vessels (which agrees with
Marcus 87a, in Gymnophioncni : (2) dor.-al and Neu- tral segmental branches, and (:S) the longitudinal lymph trunk. They open into the vena lateralis. The segmental lymph heart- and nus lymphaticus cordis have striated muscle in their walls. It is clear that a knowledge of the origin of this system would be of great value. ;i- Hoyer says: " Ers1 wenn die beriihrten noch zwi haften Punkte durch weitere Untersuchungen vervollstandigt -em werden, w i id eine gewisse Grundlage zu vergleichenden Betrachtungen Lymphgefassystems der niederen Wirbeltiere geschafiEen -em" I I !'h. p. 555).
imsen (145) and Huntington i'<'.) have worked on the de- velopment of the lymphatic system in reptiles. Strom-en shows that the posterior lymph hearts develop in relation to the coccygeal veins. He describes the process mbination of veins and dilated spaces
similar to Sala's decription for the corresponding hearts in birds. Thi- method of formation has now been disproved by the observation
The Origin and Development of the Lymphatic System. 59
of the process in the living chick. He notes thai the striated muscle of the heart comes from the myotomes. Huntington (57) states that in the reptiles there are jugular lymph sacs like those of mammals. The lymph vessels of reptiles he describes as arising from tissue spaces.
V. PERIPHERAL LYMPHATIC SYSTEM.
1. In the Pig.
A. i - 1 :< > \r Til i: .i dgtjlak i.vm rn sacs.
I shall again base the description of the peripheral lymphatics on the vessels in the pig, since more of the main trunks have been worked out in that form than in any other. The description is taken from the work of A. II. Clark CM). "I' Heuer ( 13) and myself.
The development of the jugular sac in the pig has already been given in section 1 \'. A study of the distribution of the lymphatic vessels from thi' jugular sac mu«1 he based mi the form of the jugular sac as seen in li.u's. ] and 8. In fig. 1 there is a. primary sac between the internal and external jugular veins and a complete arch of lymphatic capillaries extending into the dorsal lymphatic area. This entire plexus becomes transformed into the sac, so'that, as shown in Bg. 8, the sac consists of a stein along the internal jugular vein ami a com- plete dorsal arch. Through following the fate of this sac A. II. Clark divides it into three parts, the sac stalk: the anterior curvature along tin' internal jugular vein ; and the apex, in the posterior triangle of the
heck.
The sac -talk becomes the deep jugular lymphatic trunk. It is usually uiie large vessel, hut may give oil' lymphatics which run direct I \ in the pharynx. The anterior curvature becomes a lymph gland and it sends vessels to the pharynx and Eustachian tube and to the nose.
The apex of the sac. as is seen in fig. 8, becomes the largest part of the jugular sac. This part lies in the posterior triangle of the neck ami develops in the pig into one gland, the largest in the neck (Clark 24). This corresponds to the group of -'lands in the pos- terior triangle of the neck particularly well shown in Bartels (I'M fig. ;!() from new horn child.
The tact thai the jugular lymph sac in the pig develops into two lymph glands ami the deep jugular lymphatic trunk is well brought
'.'. - |6lH.
""t :• pig o 5 cm. long. The - - • iowm in the depth
and the swollen anterior curvature (deep jugular gland) and apex (gland of the posterior triangle) stand out through the relativelj small lined mil: ve«
16. -Injection of the jugular lympb sac. the superficial cervical plexus, and the superficial lymphatic vessels in the neck of a total pig 5.5 cm. long. After a II. Clark (24). The specimen was fixed in forma- lin l" per cent formol and made transparent by the Spalteholz method. Magnified , times. The figure is to bi compared with fig. 5 In the \m< r Journ. "i Anat.. L904, Vol. 3, p. 118, which shows a complete injection of thi superficial lymphatics of the same stage. A. s. = apex of the lymph a< whicb forme the lymph i:Ian<l of the posterior irianule of the neck; A. c. = interior curvature of the lymph sac, which forms the deep jugulo-pharyngeal lympb gland; C. p. superficial cervical lymphatic plexus; s. g.= lympho- dular Bubmaxillaris; S. s. = stalk of the jugular lympb sac.
I''1' the apes of the sac superficial lymphatic vessels grow both
from the dorsal and fr the ventral border. Those from the dorsal
and caudal border make a large plexus of superficial lymphatics which,
The Origin and Development of the Lymphatic System, iil
as shown in fig. 8, grow (1) over the scapular region and (2) over the occipital region. The lymphatics from the ventral border of the apes arc most interesting and complex. They grow ventrahvard as shown in figs. 8, 16 and LI ami form a very extensive plexus along the course of the external jugular vein, lateral to the sternocleidomastoid muscle. This is the superficial cervical plexus and it becomes a large group of superficial lymphatic glands in the adult pig (Clark 24).
The cervical plexus not only connects with the apex of the sac. but, as is shown faintly in fig. 1(1. its caudal end has a group of vessels that connects with vessels that follow the external jugular vein. In a mesial sagittal section of injected pigs 5 to 6 cm. long il is plain that a very abundant plexus of Imyphatics from the root of the sac stalk completely surrounds the external jugular vein, and this external jugular plexus has numerous connections with the cervical plexus at its caudal end. The plexus around the external jugular vein empties mainly into the sac stalk, hut a single vessel may join the external jugular vein. It must be said in general that the cervical plexus develops from the jugular sac in two places: (1) from the apex of the sac over the sternocleidomastoid muscle, and (■.' ) from the sac stalk along the external jugular vein.
From the cervical plexus there are seven sets of lymphatic capillaries (fig. 16). From the cerebral end of the cervical plexus vessels grow (1) behind the ear, and into a new facial plexus from which vessels grow (2) between the eye and the ear, and (3) over the face. From the ventral border of the cervical plexus there is (I) a set of sub- maxillary lymphatics which supplies the lower jaw and tongue and (5) superficial lymphatics for the skin of the neck. From the caudal end of the cervical plexus grow (6) the superficial lymphatics of the arm, and (7) the superficial lymphatics of the thorax.
Thus to sum up the superficial lymphatics for the jugular sacs: from the sac stalk and anterior curvature arise the pharyngeal, Eustachian and nasal vessels, from the apex of the sac arise the suprascapular anil occipital lymphatics, while from the cervical plexus arise the pos- terior auricular, temporal, facial, submaxillary, anterior cervical and the superficial lymphatics of the arm and thorax. These groups of lymphatics begin as distinct plexuses of vessels which arise from the sac or from the secondary cervical plexus which in turn comes from the sac. In fig. 8 is shown particularly well how distinct the groups may be at the start. Subsequently all of the groups anastomose and this is an important point.
/ /.'. Sabin.
In - ' will be seen, for example, thai the large vessels of the
suprascapular region drain into the apex of the sac, but - of them
small connections with the cervical plexus. In fig. IG these connections are so much more abundant that thev exceed in qui
Fig.
pleXlls
Ij mph
i urns.
Of 111"
lymph
lii ial
.\i the
S g.
17.- Injection of the jugular lymph sac and the cervical lymphatic of a foetal pig 7.5 cm. long to show the relation of the developing
inds i" the jugular sac After A. II. ('lark (24). Magnified 5 -. Fixed in 10 per cenl formol and cleared by the Spalteholz method.
iex of the sac, which is now a lymph gland In the posterior triangle
neck; the anterior curvature of the sac, which is now a deep jugular
gland, Ilea behind the sternocleidomastoid muscle. C. p. = super
en leal lymphal Ic plexus, which will become a .uronp of lymph glands.
i erebral end of the cervical plexus a developing facial l> mph gland;
lympho-glandula submaxillaris.
.1 pass i" the sa< itself. This poinl of the anastomoses i the 'Illicit It groups of vessels is well shown in fig. 5 (Sabin 130), where practically all of the superficial lymphatics in the embryo pig 5.
The Origin and Development of the Lymphatic System. 63
long have been injected from one puncture. This is a complete injec- tion, which it is clear thai fig. 16 is not. In fig. 5 (Sabin L30) for example the lymphatics between the eye ami ear are terminal ducts.
Good examples nf the anastomose- of different groups of lymphatics are shown in fig. l(j in the vessel which connects the submaxillary ami the facial plexus; moreover the thoracic, cervical ami brachial plexuses are continuous.
In the embryo pig from 5 to 5.5 em. long there are no valves in the ducts. It is also the stage of the simple primary plexus of lymphatic-. In fig. 1G a secondary plexus of liner lymphatics is growing more superficially and. by the time the embryo is from 6 to 7 cm. long there is a deep plexus with valves and a finer-meshed superficial plexus.
The relation of the jugular lymph sacs to lymph glands is shown in fig. 17. Here it is clear that the sac stalk and anterior curvature lie beneath the sternocleidomastoid muscle and that the apex nf the sac lies in the posterior triangle of the neck. That the cervical plexus is now a lymph gland is clear, and there is a facial and submaxillary gland also. The cervical plexus becomes a group of glands.
The account of the peripheral lymphatics from the jugular sacs is not complete without mention of the lymphatics of the heart and lungs. These lymphatics have not yet been worked orft, but it can be said that there are two sets of lymphatics for the lungs, the deep and the super- ficial or pleural. The deep lymphatics develop from the jugular sacs ; they follow the trachea and are present in a pig measuring v'.'i mm. and a human embryo measuring 20 mm. I have not injected them anil when reconstructed they show the Mayer-Lewis anlagen ; that is, in reconstruction they split into a chain of beads. The pleural lymphatics I have injected from the retroperitoneal sac, through the diaphragm to the caudal surface of the lung. Injections of the thoracic duct as, for example, fig. 7 (Nuck 100), also shows vessels from the thoracic duct to the lung. Therefore the lung seems to have a double supply of lym- phatics, part from the jugular sac and part from the renal sacs by way of the diaphragm and by way of the thoracic duct.
R. THE PERIPHERAL LYMPHATICS FROM THE RENAL SACS.
The retroperitoneal sacs give rise to the lymphatics of the abdominal viscera except the kidney-. The sac as it lies in the mot of tin mesen- tery has been figured by lienor (4-'?>). It spreads over the ventral
■ /.'. Sabin.
\, - and suppll capsule aa well
inds. Prom the sac v< row to the Btomi
tttire intestine, including il • q. The lymphatics of
troperitoneal sac. The de- the lymphatics of the diaphragm, liver, the
•i.i! and pan< • ; yel been worked out.
II. ■ d the lymphatics of the intestine from
ritoneal ultimate lacteals. While the embryo
to 4 tin. long a very abundanl plexus "I' capilla - out in nil rv. The lymphl ach the wall of the
in:- . the time the embryo i> 1 cm. long. They first enter the
mill form then a primary plexus. Eeuer's 9 and
in -li.iw that tlie early vessels in the submucosa have a segmental air t. which i-. however, nearly hist as the complete plexus
The plexus of the mucosa, and of the S( rosa are1 both second- ary, 'i - develop from lucosal plexus and are present in a pig measui ti. T ie mesenteric vessels and mucosal plexus i ralves.
iliac lymph I the th fa ii d ct: The lymphatics which
arise from the veins on nm a very
simple pattern. Starting from the veins at the hilns of the I Wolffian bo v grow caudalward along the edge of the WolJ
to make the ilia sacs, bralward along the dorsal sur-
aorta to form the cisterna chyli. The lymphatics doi to the aorta grow in two directions: (1) caudalward to form a chain of prevertebral lymph nodes and (2) cerebralward b duct.
The iliac lymphatic ire two long symmetrical sacs extern
from the bilus of the Wolffian bodies to the level of the bifurcation of tl a. In an embryo 23 mm. long they drain into the mesone-
phritic time theembryo is •.'■"> to 21 nun. long this
ection is lost and the two iliac sacs converge into the median cisterna chyli dorsal to the aorta.
The caudal end of the iliac lyn - in the pig is a sac of con-
erable size, from which thn of lymphatics can be injected:
ilio-lumbar, the femoral and a plexus which surround the umbil- ical i ilio-lumbar superficial lymphatics are very con- mown in figs. I and 5 (Sabin L30). This is in mai otrasl to the human embryo, where they form part of the inguinal group.
The 'hit/in and Development of the Lymphatic System. 65
2. Peripheral Lymphatics in Other Forms.
The pattern of the superficial lymphatics in the human embryo is shown in the two figs., 505 and 506 (Sabin 134). This was a re- markable specimen of an embryo 5.5 cm. long which had been kept in formalin some time. On transferring it to freshly made up alcohol, air filled the entire superficial lymphatic system. It shows the primary superficial lymphatic plexus. Valves in a few duets, namely, the occipital, the thoracic and the inguinal, indicate the oldest vessels. The differences between the superficial pattern in the human and in the pig are mainly the fact that in the human embryo the thoracic lym- phatics ;ire much more prominent, draining into the axilla, while in the pig they drain into the superficial cervical plexus, and all the posterior lymphatics drain into the inguinal region in the human embryo. In the human embryo the deep lymphatics for the arm grow from an extension id' the jugular sac along the primitive ulnar veins, and the deep lymphatics for the legs grow from the iliac sac along the femoral veins. This shows in fig. 193 (Sabin 134).
Rabbit ami eat embryos arc like the human in having a marked development of the jugular sac along the primitive ulnar vein (Lewis 76). In this respect they differ from the pig where the axillary lym- phatics are smaller. In lie'. 7 is shown a deep vessel from the jugular sac. which is, I think, the axillary duet in the pig. In the rabbit and the i at the axillary sac may possibly arise independently of the jugular sac, and in the rabbit a conspicuous chain of peripheral vessels grows along the thoracoepigastric vein (fig. 8, Lewis 76). Injections id' cat embryos show that the axillary lymphatic trunk is very large.
The superficial pattern of the lymphatics in bovine embryos, as shown by Polinski (107), is much like thai of the pig.
In the chick the primary lymphatic vessels in the skin connect the posterior lymph heart with the jugular lymph sac along the lateral line in the course of the thoracoepigastric vein Mierzewski (96) and E. L. Clark (27 and 29).
VI. ORIGIN" AND DEVELOPMENT OF LYMPHATIC GLANDS AND THEIR RELATION TO PRIMARY LYMPH SACS.
It is easy to prove that the lymphatic sacs in mammals and (la jugular lymph sac in birds become in part lymph glands. I shall define primary lymph gland- as those which are derived from the primary lymph sacs.
/ • net /.'. Sabin.
jugular lymph sac in the pig it is clear in Sg. 16 that i lymph glands develop: ill the deep jugular lymph node which - the pharynx an •• code in the p triangli
bich drains the -kin of the anterior part of the body. A. II.
I has shown that these two glands are single glands in the adult pig and that tl me the largesl of all the cervical ads. In tlic human embryo these two glands are represented by ads, the glands of the posterior triangle and the di jugular glands. In the human embryo also the group of deep axillary glands comes from an extension of the jugular sac along the primitive ulnar vein and hence they are primary lymph glands. Thus the pri- mary nodes for the anterior pari of the bodj are i 1 i deep jugular nod< -. the nodes of the posterior tria I) the axillary nodes. The ation of the primary lymph gland, both to the various structures of tlif neck and to the stalk of the jugular sac, that is, to the jugular lymph trunk-, is shown especially well in fig. K from pig 7.5 cm. long. The anterior curvature and the sac stalk lit1 behind, that medial to the sternocleidomastoid muscle. Of the primary nodes in the neck the deep jugular nodes drain a restricted area, nam<fly, I pharynx and nose; the axillary lymph nodes drain the arm. and the larg of the posterior triangle drains all the rest of the head, fa neck and thorax, either directly or through the superficial cervical cus. The nodes of the superficial cervical plexus are secondary to the primary lymph sac nodes. It has been brought out that these ups of lymphatics do not remain distinct as thej arise, Imt all be- e connected with each other through anasl ses of the lymph
From the retroperitoneal sac develop the retroperitoneal lymph nod< -. From the iliac sacs in the pig there is a (ham of small nodes lateral to the aorta and a large group of glands on either side oppoe the bifurcation of the aorta. These are primary iliac nod,'-. Itorsal to ! ta is a chain of nodes from the lower end of the cistema
chyli to the bifurcation of the aorta. Thus the renal lymphatics give ri.-e to three groups of primary lymphatic glands: (1) prae-aortic or retroperitoneal, (2) symmetrical iliac nodes lateral to the aorta, and i :: i prae-vertebral nodes dorsal to the aorta.
'I ' • idary lymphatic nodes develop along the lymphatic vessels.
The most extensive group of secondary nodes in the enihryo pig is the one which comes from the superficial cervical plexus along the external
The Origin and Development of tin' Lymphatic System. 6'
jugular vein. In fig. 17 this plexus is shown as one large lymph gland. From the cerebral end of the plexus vessels are forming a gland al the point where the lymphatics divide to form the facial and the temporal lymphatics. The cervical plexus in the adult pig becomes a group of at least a dozen small lymph glands. In both figs. 17 and 18 there is a developing submaxillary lymph gland along the course of the facial branch of the linguo-facial vein (fig. 8). The small fa< ial node and the submaxillary node are tertiary nodes compared with the jugular lymph sac. They show how lymph glands develop at points where lymph ducts radiate out on their development. The primary, secondary and tertiary nodes are constant in the pig.
The mesenteric glands are secondary for the retroperitoneal sac. The secondary glands from the iliac sac are very simple, for there are only two of them: (1) The ileo-inguinal gland, which is very charac- teristic of the pig and which remains as a single gland. Its position is readily made out in fig. 4 (Sabin 130), for the superficial lymphatics of the posterior body wall radiate to it. Like the superficial cervical glands it is superficial. (2) The inguinal glands in the pig become a large group of superficial glands, the position of which can be made out in fig. 5 (Sabin 130). The lymph ducts from the inguinal lymph glands develop to the leg, the ventral abdomiiral wall and the external genital organs. The efferent vessels of the inguinal group of glands and ileo-inguinal gland converge to the large group of primary iliac glands opposite the bifurcation of the aorta.
The histological development of lymph glands is now well under- stood. The work of Saxer (138) on developing lymph glands considers primarily the development of lymphocytes which I shall not attempt to discuss in this paper, confining the work to the development of the gland as a whole. From the time of Breschet (16) it has been known that lymph glands begin as a plexus of lymphatic ducts. Their de- velopment can be followed through the work of Ranvier (117), Bartels (10). Gulland (39), Kling (72), Jolly (59), Lewis (77), and Sabin (131).
The primary lymph glands, which, with the exception of the post- aortic, develop out of sacs, begin by a bridging of the sac by bands of connective tissue covered by endothelium. In the case of the retroperi- toneal sac these bands are never absent (figs. 498 and 409, Sabin 13 1 ). For the jugular lymph sac they show well in human embryo 30 mm. long in fig. 495 (Sabin 134). That these bridges are entirely covered
■■■'■- /,'. Sabin.
dothelium is best broughl out by total mounts of silver nitrate in-
or the retroperitoneal Bac in the pig. When the prima are thus completely bridged by these bands
are practically a dense plexus of lymphatic capillaries and are therefore in the firsl praenl of lymph glands. A.I
this - connective tissue Bepta are undifferentiated and contain
only in. sen< bj me and blood capillai
We arc now in a position to consider the question of which
lymph nodes in the embryo. This point has been discussed by Lewis (77) and Sabin (131 and L34). Ii depends on the criterion
[f th criterion is recognizing the formation of a pies lymphatic capillaries with undifferentiated connective tissue bi
e anlagen of a gland, then it is clear that the primary lymph glands, that i-. those that come from the lymph sacs, are the
rlands to begin for each region of the body. Thus the jugular- subcli 3ac in tin' human embryo i- . ■ ed at 30 mm.
and is therefore a plexus of lymphatics, the anlage of a lymph gland. A.t tl i we are agi re are do lymphocytes (Kling (72),
Lewis ind Sabin i 13] | i. If. on t! ther hand, the crrl
pment of the first lymphocytes in the body, we must say that this point lias not been reii e all the primary
embryo have been determined. Saxer | L38, !'■ :;<1) notes that lymph nodes arc lK-ginning in the neck, the terior mediastinum, the retroperitoneal outside of both
and along the Wolffian bodies in bovine embryos 4.5 cm. long, «i«<l in shi the same length describes in wander-
in the same areas. Kling (72) has no specimens of human embryo between 3] mm., where, he says, then- are no lymphocytes in -i!lar\ glands, ami ]n ni.. when lymphocytes .ire present in many glands. Lewi- (',;) finds lymp in human embryos 42 mm.
I'1' finds that they occur practically simultaneously in the glands around the internal jugular vein (primary lymph m and certain " isolated subcutaneous lymph -land-.'" of which he figun - one or two along the linguo-facial vein and its branches. The relation "I' tl • [ids to lymphatic vessels will he readily made out by a
-nel fig. 16. Figure 8 shows the ducts from the th" linguo-facial vein at a Btage even younger than Lewis's isolated glands, namely, a pig measuring •"..•"> cm. Moreover the be- ginning cervical plexus from which these submaxillary vessels come
The Origin and Development of the Lymphatic System. 69
shows plainly in fig. 7 from an embryo much smaller, namely, i ne measuring 18 mm., and they are readily injected in embryos 30 mm. long, fig. 2 (Sabin 130). Thus it is almost certain that the ducts for Lewis's early facial glands in human embryos were present, but could not be found, in sections. It is probable that the lymphocytes begin in human embryos which measure about 40 mm. and they probably develop almost simultaneously in the primary and in the secondary glands.
The plexus stage of developing lymph glands has been shown by reconstruction by Kling (72) and Lewis (77), and by injection in fig. 10 (Sabin 131).
The whole question of the structure of a lymph gland may be summed up in a word by a quotation from Ranvier (p. 1038 in 117) : •* Un ganglion lymphatique est un angiome caverneux lymphatique qui a etc d'abord angiome simple." The development of a gland involves, however, two processes: (1) the formation of lymph sinuses out of lymph plexuses, and ( 2 ) the formation of lymph cords and lymph folli- cles in the trabecular. A comparison of Jolly's (59) plates from lymph glands in birds, Kling's (72) figures of human lymph glands, and my own (131) from the developing glands in the pig. will show that the relative proportion of these two parts varies exceedingly in differ- enl glands.
The formation of lymph sinuses can be best understood by beginning with Jolly's figures. He shows that in the birds, instead of the mam- malian sinus, there is a diffuse plexus of lymphatic vessels with lym- phocytes in the septa between the vessels. He also brings out the Eai t that very large vessels may pass directly through the gland. Thus it is clear that the sinus of birds is a simpler structure than that of mammals. On this account the complete covering of endothelium is very plain in Jolly's figures. Out of a plexus of capillaries such as Jolly shows, the mamalian lymph sinus is formed, as can be seen in fig. 15 (Sabin 131 ), by an increase in the density of the lymphatic plexus until the septa are reduced to a framework of reticulum covered by endothelium. In this figure all the stages of the formation of a sinus can he seen in a single section. In the lower part of the specimen every lymphatic vessel is plain with its complete lining of endothelium, while in the upper part the septa arc in places already reduced to a line. This stage is from an embryo pig 24.5 cm. long, which is the
R - ''in.
studying the formation of the sinuses. The question of • opraent of reticulum hae been taken up by Mall (84).
rd to the formation of the lymph cords and follicles, the funda- mental point is the question of the origin of the Lymphocytes themselves. This I shall not undertake to discuss. The lymphocytes may
or diffusely in all of the trabeculse of the developing node and thi6 simplest form of a gland. This form is Bhown by Jolly (59) in his plate IX. fig. ;;. for the lumbar glands in birds, by Kling (72), plate X.WII. fig. 11. for the axilla r\ glands in human embryos ami in fig. 9 (Sabin I'M) from the primary jugular lymph glands in the pig. It will be noted thai all of these figures are from primary lymph glands. The definite follicle- may develop in the center or in the periphery of a node, and there is every possible variation in
proportion of the diffuse cords and the definite follicles. Thi are two processes in the development of the follicle: (1) an increase in the number of lymphoi orming a definite clump, and (2)
formation of a tuft of blood capillaries. Both the cords and the follicle- form along the blood vessels, the follicles coming at the cap- illary bed.
A- I have said, the earlj glands which come from the primary sacs pass through the form of diifuse distribution of Ihe lymphocytes. Follicles which develop later, however, ma\ heuin at once a- clumps of lymphocytes, making very definite follicles Burrounded by a lym- phatic plexus. A number of such tiny follicles are to he seen in li.Lr. L6 - 131), which is the developing group of inguinal lymph
glands in a pig 2 1.5 cm. long.
Lymph glands may he either simple, consisting of one follicle with a peripheral sinus, or compound, with many follicles ami cords, and both peripheral and centra] sinuses.
The subject of haemolymph glands ha- been taken up by Belly in the Ergebnisse fur Anatomie ami Entwickelungsgeschichte for 1902.
VII. COMPARATIVE MORPHOLOGY OF THE PRIMARY LAM I'll SACS, LYMPH HEARTS, AMPHIBIAN LYMPH SACS Wl> LYMPH GLANDS.
We are now in a position to consider the comparative morphology of lymph sacs ami lymph hearts. 1 -hall not attempt to analyze the work of Pavaro (36a) and of Allen (2-4) on lymphatic- m fishes,
The Origin and Development of the Lymphatic System. ', l
both of whom state that vessels may function now as veins and now as phaties, hut beginning with the amphibia, it is certain that Lym- phatics bud off from the veins in certain definite areas and form plexuses which are transformed into sacs. The essential structure of these sacs is the endothelial lining. A primary lymph sac is there- fore one which buds off from the endothelium of a vein.
In the amphibia, probably in the reptilia, and in the case of the posterior lymph sacs in birds, the primary sacs bud off from segmental veins and rest on the myotomes. They derive striated muscle from the myotome-, which has been shown at least in the ease of the anterior lymph hearts in amphibia (Knower 74), and the posterior lymph hearts in reptiles (Stromsen 1-15) and pulsate rhythmically, in a word, they become lymph hearts.
The lymphatic sac- for the anterior part of the body in birds and all of the lymphatics in mammals do not come from the vertebral and coccygeal veins, but from the anterior cardinal veins in the neck, and the renal veins in the abdomen. These sacs do not lie on the myotonies, they do not receive striated muscle, but rather are transformed into lymph glands. Thus the bird represents a transition stage having a posterior lymph heart and a jugular lymph gland. I shall keep, therefore, the term anterior and posterior lympfi hearts, and use the terms jugular and renal lymph sacs. The embryological classification is :
fl. Lymph hearts.
a. Anterior, amphibia.
b. Posterior, amphibia, reptilia and birds. Primarv
Lymph J 2- Lymljh sacs (Stands).
a. Jugular- — birds and mammals.
(Retroperitoneal. Iliac. Cisterna chyli.
The subcutaneous and deep lymph sacs of the amphibia are not primary, but secondary. They are transformed lymphatic duets. Thus the amphibia have primary lymph sacs which become lymph hearts, lymph duets which become secondary sacs, and lymphatic capil- laries. Mammals have primary lymph sacs which become primary lymph glands, lymphatic duets which develop valves and along which secondary glands are formed, and thirdly, lymphatic capillaries without. valves. 5
Sacs.
; •.' . j ■'■■in.
VIII. \ Al.'lul - OTHER THEORIES l\ REGARD TO THE ORIGIN AM» DEVELOPMENT OF THE LYMPHATIC S"S STEM.
1. M LYER-LEWIS Am m,i \. In the precedii a given a consistent accounl of how
the lymphatii off from the vein- and gradually in
The places where the lymphatics bud off vary in different
j; ia the amphibia and reptiles, and in the case of the post
lymph hearts in birds the primary lymph sacs lie in the myotomes and
striated muscle and become lymph hearts. In the higher forms
interior lymphatics come from the anterior cardinal vein and it*
branches, the caudal lymphatics '1" not develop (mammals) and the
Fin. 18. — Diagram to show the theory of Ranvier and myself that the lymphatics arise Crom the veins. The veins are striped, the lympl dotted.
rior lymphal e from tie ?ena cava and renal vein-. From
of origu Li ed all the lymphatics i body
down to the ultimate capillaries.
! without opposition. 1 1 I it was mad< irst theory of the origin of the lymphatics
that they anise in the periphery as dilated tissue spaces and towards the cent* i and (39). This was questioned by Sala (137), showing that the first lymphatics in birds were against the
-. and by my proving in L902 that the jugular lyi - are
the first lymphatics in mammals and that they bud m the
anterior cardinal veins. Thus I substituted for the tl ries shown in
The Origin and Development of the Lymphatic System. 73
figs. 1. 2 and 3 the simple hypothesis of Eanvier, shown in fig. 18. This indicates that lymphatics bud off as lymphatics from the veins and have the same relation to tissue spaces as have blood capillaries.
The most difficult obstacle in regard to this theory is what we call Mayer-Lewis anlagen. Mayer (89) noted in the tadpole's tail certain isolated vessels which he thought were evidences of the degeneration of blood vessels.
Eanvier (11 1. p. 578) in studying the plexus of lymphatics of the great omentum in a new-born cat noted that a great many of the vessels terminated in cul de sacs. Sonic were attached by extremely slender threads, so that they looked as if they were becoming iso- lated by the atrophy of the intermediate part. Since in the adult cat there are no lymphatics in the omentum. Eanvier interpreted this as a method n\' degeneration of lymphatic vessels.
The study of the method of degeneration of blood and lymphatic capillaries is an important one. It is obvious that there must be a destruction of capillaries, since a single vessel or a few vessels come from a plexus of capillaries. In Clark's observations (25, p. 191) the usual method of degeneration is by retraction of the processes, but he has also observed (26, p. 410) together with Mayer and Eanvier, that an occasional segment of a blood capillary or lymph capillary may become detached and be left to atrophy. This is in accord with some of the findings of pathology. We must, therefore, conclude that detached, degenerating vessels do occur, though they do not represent the usual method of degeneration.
F. T. Lewis (76) found that in reconstructions lymphatics looked like chains of beads, and to explain this phenomena he suggested that lymphatics might grow by small detached portions of blood vessels. These hypothetical lymphatic anlagen we call Lewis anlagen.
It is clear in watching lymphatics grow, that they never pick up isolated vessels, but grow by the increase in the protoplasm of their own wall ; yet it is clear also that reconstructions of uninfected lym- phatics appear like rows of beads.
To study this point it was necessary to submit the method of recon- struction to comparative tests with the method of injection and when possible with the method of growth in the living form. This has been done three times (Clark, E. E. 26; Clark. E. L. 27, and Sabin 135).
The best opportunity for studying this point is the tadpole's tail, where, in the living specimen, or in the tail fixed in alcohol, the entire
/ /.'. S ibin.
lymphatic Bystem cai a and drawn. Thia was done by Clark.
The specimen was then mi in serial sections and both blood capillaries and lymphati reconstructed. Two reconstructions were made,
one with the 1 nun. Zeiss objective, and the other with a 2 mm. Zeiss
oil immersion lens. Both reconstructions Bhow that neither I>1 1
capill r lymphatic capillaries can be reconstructed completely,
ibtained with an oil immersion lens, 10th powers show
capillaries in the form of rows of beads (figs. •">. u' and '•. Clark 26, copied as 6gs. 513 and 51 1. Sabin L34 i.
This te6t of Clark's is the best possible test, because it is a recon- struction of exactly the Bame specimen from which the original draw- ing was made. This point cannot be made in testing the method of in- jection and that of reconstruction. For this tesl I (135) used, however, symmetrical plexuses in the same embryo. An embryo pig ".'7 mm. was chosen in which there was an almost complete injeetidn of the occip- ital superficial lymphatics. Many of the sprouts on the margin had ruptured. The injected plexus could of course be reconstructed, while a istruction of the empty lymphatics on the opposite side showed the entire plexus split up into isolated vessels i figs. 6, ] and 8, Sabin 135 i. On the injected side there was just one lymphatic vessel which did not recei jection mass, and there was an extravasation just at its
This is readily explained by the fact that vessels are often con- nected by very slender strands to the main plexus, as, for exampli ,
near the point of injection in li,ur. 1*. and a rupture might readily ii- in such an area before the end of the vessel was reached.
test of the two methods has now been made a third time by Mrs. E. K. Clark (27) in her injection of the jugular lymphatic rresponding to the one which Miller (97) has reconstructed. The two results are shown in figs. 1 I and 1">.
A i omparison of the injected jugular sac in a pig 18 nun., shown in : . with reconstructions of the corresponding stages in the cat (figs. 60 to 62, Huntington 55), also brings out the same point that, wherever the injection iucih.nl can be applied, it demonstrates more continuous lymphatics in an area than can be reconstructed, even as isolated vessels.
Undoubtedly an occasional hi 1 capillary or lymphatic capillary
may from the main plexus and atrophy, but the apparentlj
isolated vessels found in Berial sections along the course of grow- ing lymphatics conned in life. Lymphatics do not grow h
Tin- Origin and Development of the Lymphatic System. 75
tached blood vessels, and hence the hypothetical Mayer-Lewis anlagen do not exist, that is to say, they are nol anlagen of Lymphatics, but arc parts of a continuous vessel. It is clear that reconstructions of growing lymphatics are valuable, even though they show the lym- phatics as rows of beads, provided only the true lymphatics are in- cluded; that is to say. the endothelial-lined vessels. For example, Lewis (76, figs. 7 and 8) shows that the early lymphatics in the rabbit grow along the thoracoepigastric vein.
2. ExTRA-IXTIMAL AND PERINEURAL Sl'ACI'.S AXD FENESTRATION.
Huntington and McClure (51) began their work on the lymphatic system in 1907 with a study of the jugular lymphatics in the cat. They thought that lymphatics began as clefts between the intima, the vein and the surrounding mesenchyme, so that for a time the wall of a lymphatic was half venous endothelium and ball' mesen- chyme. These spaces they called " extra-intimal " lymphatics. As far as the jugular lymphatic sacs were concerned they subsequently abandoned this idea, accepting the theory that the jugular sacs are derived from the veins (Huntington and McClure .">4), but they have since revived the extra-intimal theory in connection with the thoracic duct (Huntington 58).
Their work on the jugular sacs has been given in section IV. In genera] they accept the theory of the venous origin of the jugular sacs, but they confuse the picture (1) by the inclusion of some peri- neural spaces (fig. 22, Huntington and McClure r>4) and (2) by the idea of fenestration.
The perineural spaces are an interesting phenomenon. I con- sidered them in my first paper in 1902. Along the entire central nervous system and following the peripheral nerves are dilated tissue spaces. Within the spinal canal these spaces are the anlage of the spaces of the pia-arachnoid. Along the nerves we call them perineural spaces. All sections of embryonic tissue show them. They arc of undoubted significance for the physiology of the growing nerves, but rhey never bear any relation to the lymphatics. Injections of them outline the nerves and never enter lymphatic vessels — occasionally they can be injected from the pia-arachnoid, but usually the dense tissue between the vertebrae prevents this.
The question of fenestration was considered in section IV. Paral- lel veins are formed by the -ami' process of sprouting of endothelium
Flort i ■ ■ /.'. Sabin.
by which iill otl are formed, and the term ation,
giving ll --n-.il of the splitting of the wall of a vein
. does 1 1 ■ > i describe the actual process and is misleading, ow know thai the jugular sacs bud directly from the anterior cardinal ympliatics and grow by the sprouting of their endo-
thelium.
\- 'ia- been said, Huntington and McClure believe thai the jugular
lymphatics come fr the veins, bul thai thej remain only as a means
immunication between the veins and the lymphatic ducts. The lymphatic ducts they mink develop in a variety of ways.
entire o of the thod of growth of the lymphatic
system is now concentrated on a study of the methods of growth of the thoracic duct, li is probable thai the thoracic duel arises in two - : thai it i- formed in mammals by an asymmetrical down- growth from the left jugular sac and by a plexus which arises sym- metrically from the renal veins and grows along the course of the aorta.
second portion arises later than the first and is in the U l-filled
I mm.) when the jugular stalk is empty. These two an] grow as do .ill other lymphatics and join by the same proi i -- ;■ which any lymphatic plexus is formed.
opposing views are broughl out in two papers, oni by Hunting- ton (58) and one by Kampmeier (66). Huntington describes a compli- cated method of origin of the thoracic duct, including (1) a jugular stalk . (2) extra-intima] spaces, and (3) general tissue spaces. Kamp- meier, on the other hand, gives a clear and excellent presentation of
the il ry of the origin of lymphatics by the addition of tissue spaces.
1 will begin with the work of Huntington (58). His memoir on the peripheral lymphatics has excellent photograpl - tions, so thai
ii is i-ii.-v to see what he is considering as lymphatics. For example, l to 9 are tissu< -. l«> to 12 are extra-intimal spi
13 to 19 are probably lymphatics. Figure 25 shows the iliac d 76. Numerous examples of extra-intimal spaces ar< shown i 147. Perhaps the besl figure of an extra-intimal space »o. L11A. Figun - i - 15? are h mphatii -. The theory of the origin of lymphatics from extra-intimal sp has been especially described in an article by Huntington in 1910 (55). In a diagram on page 109 be gives bis idea thai a space which forms around a degenerating vein eventually includes the entire vein, which then disappears so that the lymphatic is lefl with a wall of nch\ me.
Thr Origin and Development of the Lymphatic System. I".
There are numerous points which rule out the theory of the origin of the lymphatics by extra-intimal space?. (1) These spaces can be varied at will by changing the fixation. In my experience they arc much more common with lymphatics than with veins. We have sec- tions of adult human tonsils, in which all surrounding lymphatics have extra-intimal spaces. In the human embryo, 460, the large jugular segment of the thoracic duct has one area where the endo- thelium has sagged from the surrounding tissue. There is, I think, no question hut that the extra-intimal spaces are artefacts. This is made the more certain by the fact that they do not occur in the living tadpole's tail, but are found along the veins after fixation.
(?) In connection with the presentation of the extra-intimal spaces, Huntington gives no proof whatever that the structures he figures are degenerating veins. Most of the extra-intimal spaces he shows are along the line of the pulmonary and cardiac lymphatics arising from the jugular sacs. I think it probable from their size and position that the structures he is dealing with are shrunken lymphatics and not veins. The pulmonary and cardiac lymphatics (fig. 13) will, when reconstructed, give the same appearance id' iso- lated lymphatic vessels as all other lymphatic trunks.
(3) The third point against the theory that lymphatics grow by extra-intimal spaces is this: the growing lymphatic tip always keeps as far as possible from the blood capillaries, just as in the adult the ultimate lymphatic capillaries are as far as possible from the blood capillaries; as, for example, in the relation of the central lacteals and peripheral blood capillaries in the villus. The point of the avoid- ance of the blood capillaries and of the mesenchyme cells as well by the growing lymphatic tip has been well described by Clark (26). Moreover, in certain tadpoles the lymphatics grow out ahead of the blood capillaries where no blood capillaries have ever been. Therefore, lymphatics do not grow by extra-intimal spaces, for extra-intimal -pace- are artefacts; there is no evidence that lymphatics follow degenerating veins and on the other hand the growing lymphatic tip, far from following the blood capillaries, avoids them as much as possible.
3. Growth ok Lymphatics i:y the Addition of Tissue Spaces.
With these various structures as anlagen of lymphatic capillaries,
Huntington ami McClure have included certain of the tissue spaces
lying along the course of the lymphatics. This theory Huntington
/. - l&ttt.
brought oul lly in a study of the lymphatic system in rept
\ •• r a confused account of the origin of tin- anterior lym hearts he describes the development of the peripheral lymph vessels out of tissi - He says that whereas in mammals the greater
Dumber of the lymphatic vessels come fr extra-intimal spaces (57,
p. :'~r! ) in reptiles, on the other hand, the lymphatics come from
- w lllhil: 11 tO the Mill-.
theory that in the pathway of developing lymphatic < — La certain tissue spaces enlarge ami are added onto the growing tips been worked mil by two pupils of McClure, Kampmeier (66a) an.! Stromsen (146a), both of whom published their work in 1912. Kampmeier's first article (66) is a preliminary report of the second 6a i. II*' has worked on the development of the thoracic duct in the pig and bases most of his conclusions on a reconstruction of a speci- men of mine. Kampmeier thinks that the thoracic duct develops in an anterior-posterior direction bj the addition of certain connective i -lie spaces which enlarge in the pathway of a developing vessel. This is a return to the dew of the earlier embryologists, except that >. believed that the growth was from the periphery toward lie center. To a certain extent Kampmeier still holds to the theory of lym- phatics from extra-intimal spaces; that i-. he believes that a part of thoracic duct follow- veins that are degenerating. A vein which lies in the pathway of a developing lymphatic vessel he call- a " veno- lymphatic." This is a different use of the term from that of Hunting- ton and McClure, who used the term to mean a vein which was trans- formed into a lymphatic vessi I. This latter use of the term can well giveD up. since veins do not become lymphatics. The replacing of degenerating veins Kampmeier doe- not regard as a fundamental process in the development of lymphatics, since they may or may not follow -mh \ein-. Hi thinks that in the development of the thoracic duct about half the duct .ohm- from extra-intimal spaces (66a, p. 134). It i- interesting to note in connection with the degeneration of \ein> in Kampmeier's work that he -peak- of the plexus of veins medial to the oervous sympatheticus, fig. 11 (or fig. II in 66a), as veno-lymphatics ; that i-. a- veins which disappear a- the thoracic duct form-, and yet this same plexus of veins can he readily injected
in embryo pigs '.'". to oil mm. long in which the thoracic dl
mII formed. It is true that the blood vessels may not -how in uninfected specimens, just as the plexus of blood capillaries around
The Origin and Development of the Lymphatic System. <9
the air cells of an adult lung cannot be reconstructed from sections of uninfected specimens. The degeneration of blood vessels can only be followed by mean- of complete injections of different stages.
Kampmeier finds another example of lymph vessels which grow by the extra-intimal replacement of veins in the region where the thoracic duct empties into the jugular sac In his fig. 8 from an embryo 20 mm. long he shows vessels in which their is a considerable sagging of the endothelium from the surrounding tissue, making the so-called extra-intimal spaces. Kampmeier".- embryo measuring 20 mm. is about the same stage as mine, measuring 23 mm., since mine was measured before fixation, and hence his figure can be com- pared with fig. 1".'. in which a lymphatic injection make- n easy to separate veins from lymphatics. As Eoyer says (49b. p. 536 ) : " Den Verlauf der Lymphgefasse nur an nicht injizierten Serienschnitten zu verfolgen, ist eine muhevolle und zeitraubende Arbeit, deren Ergeb- ni>se, wie wir mis selbst iiberzeugt haben, hochstens nur fiir grossere Lymphstamme, deren Lage man kennt, als sicher zu bezeichnen sind. 1st der Verlauf von Gefassen und deren Verastelung noch unbekannt, so lassen sich auf Grund von Serienschnitten nur Vermutungen iiber Verlauf und A^erastelung derselben austellen. Erst wenn man iiber Gefasse und ihre Aeste mit [njektionsmasse gefiillt vor sich sieht, erhalt man einen guten Einblick in die Verteilung derselben. deren Verfolgung selbst an nicht injizierten Serienschnitten dann keine wesentlichen Schwierigkeiten mehr bietet." Although it is not pos- sible to be entirely sure in regard to Kampmeier's sections, yet it is at least probable that he is dealing in large part with lymphatics and not with veins at all. The sagging id' the endothelium from the surrounding tissue L have found more often with lymphatics than with veins, and yet in (issue- lived in Zenker's fluid, which Kamp- i'h ter uses exclusively; it may occur in any of the veins ami even in the aorta. Kampmeier says, with reference to this group of vessels (fig. s ami fig. ".'!» in 66a, p. Hid), that they are mesenchymal, peri- vascular spaces into which the jugular sac opens freely; that is, he thinks that the jugular sac in an embryo 20 mm. long opens freely into the tissue space-. This point is easy to disprove, for in contrast to the early stages of the thoracic duct the jugular sac in this stage is easy to inject. II tin- were true then every injection id' the sac m this stage would show extravasations. This is. however, not so. In fig. '. is an injection of the sac in an embryo 18 nun. long and 1 can
■ ■ ■ /,'. Sabin.
_ .t certainty on the basis of many injections that the jugular sac has .1 complete endothelial wall and is a closed vese
I - ■ us 1 ear thai Kampmeier has uol de nstrated that this upper
l>;in of the thoracic duct replaces degenerating reins.
• 1 point, however, in Kampmeier's work is 1 1« » t that some
nf tlie lymphatics replace degenerating reins, but that they develop
out of tissue spaces. As the chief proof of this theon he uses .1
onstruction of an injected specimen of mine. Notwithstanding the
I that this injection is the only one which has yet been made in ;i
mammal in this early stage, Kampmeier does not hesitate to call it
I as ejected indirectly through the jugular lymph sac, from which the injection mass ran into the thoracic duct. At a cer- tain point in the injection there is an extravasation (Kampmeier, fig. 13, line 15), and in exactly the same position in. the next section large endothelial-lined empty space. 1: 1- therefore merely an arbitrary decision whether the emptj vessel was actually connected with the injected pari or not, thai is to Bay, there 1- as much evidence for the one vie^ a- for the other. No one who has had experience with tin- injection method would be sure thai the first injection in a new region was a complete one. The spaces which Kampmeier has shown as lymphatics in my specimen arc lined by endothelium; that is, they are the spaces with which Lewis (76) has made us familiar; they arc imt the mesenchyme spaces which Kampmeier and Strom- sen regard as the anlage of lymphatics.
Stromsen (146a) has injected the prevertebral lymphatics in turtles ;iinl finds that in advance of the injected zone there arc enlarged tissue spaces which he thinks arc going t<> become lymphatics. Kamp- meier says that it 1- easy to select tissue spaces which are -nine to become lymphatics for, "histologically, all incipient lymphatic an- lagen, whether thej are spaces independenl in position or spaces fol- lowing, transforming and expanding the discarded pathways nf redundant \> uous channels, are decidedlj different from cither an active vein or a mature lymphatic "' ( Kampmeier 66a, p. 130). Strom- sen (1 16, p. 354) adds to this ability to select tissue spaces which are going to become lymphatics tin- further point, that such enlarged tis- .-11. c only in the pathwaj <<\' developing lymphatics. These
two points can he easily disproved by anyone who has access to serial
embryos. Km- example, why were nol the enlarged tissue spaces in Kampmeier elected as lymphatics? <nn>i| examples
The Origin and Development of the Lymphatic System.
81
of such spaces are the constantly occurring spaces in the parietal pleura on either side of the vertebra. They arc always present in the stages in which the thoracic duct is developing; they are adjacent to
the vascular zone just internal to the ribs and they never have any relation to lymphatics. A definite, constant group of such spaces is also to 1h found in the subcutaneous tissue of the mid-dorsal line of certain stages ami they never become lymphatics. The pia-arachnoid and perineural spaces likewise never become lymphatics. In fact, large as well as small groups of such spaces are a constant occurrence in sections of embryos; sometimes near lymphatics and sometimes far
Fig. 19. — Diagram to show some of the various structures which Hunt- ington and McClure have described as lymphatics, a. = true lymphatic capillaries; b. = Mayer-Lewis anlagen, also true lymphatic capillaries; c. = extra-intimal hypothetical lymphatic capillaries; d. = tissue spaces. The perineural spaces are not shown. The veins are striped, lymphatic capillaries dotted, and hypothetical lymphatic capillaries are cross-hatched.
from them. The selection of certain tissue spaces as destined to become lymphatics is an arbitrary selection and brings us hack' to the confused standpoint of the earlier embryologists ; a standpoint which would indeed justify the view of Bartels that the question of the relation of the lymphatics to the tissue spaces is " cine philosophische, keine anatomische Frage."
The difficulty of finding out the method of growth by observing sections is best illustrated by following the different theories of their growth in the pages of Huntington and Met lure. Some of these methods arc shown in the diagram, fig, 19. This development of the
B. - tWn.
n ho have not follow* d the sul efully. However, dow thai the origin and method of
ivth of tin' lymphatic system has been cleared up, bo that the funda- mental morphology is understood, the controversy has had this great value, tlint it has brought up for analysis and discussion every con- ceivable method of growth. Lymphatics do nol arise as dilated per- ipheral tissue - ifter the manner of the ccelom as the earlier embryologis ght; they do not grow by the addition of holloa con-
ssue cells, as Schwann and Virchow thoughl ; they do n as perineural spaci s, uor bj ition of a vein, aor by extra-intimal
fts, nor by the pi re addition of connective tise ces, nor
by the addition of detached blood vi --■ Is, but they bud from the vi and grow by the sprouting of their endothelial wall.
IX. CONCLUSIONS.
most important result of this study on the morphology of the lymphatic system is the emphasis it throws on the importance of endothelium as a tissue. The angioblast is one of the earlj to ■ entiated ; ii is nol an inert lining Eor vessels, but an activi ly
iwing functioning tissue. In its place of growth it is a syncytium of actively amoeboid protoplasm. Mollier (99) has shown that in the spleen it may be reticular; Mall (86 and 87) has shown that it may give rise to reticulum. Undoubtedly the further development «{ our knowledge of endothelium depends on the development of the new experimental anatomy.
lymphatic endothelium buds off from the veins. It is always a little different in appearance from the endothelium of the veins, and the lymphatic capillary is different in size and form from the blood capillaries. The growing lymphatic tip has the remarkable character- istic that it avmd- the blood capillaries, while it i- attracted by other lymphatic capillar]
Endothelium i- the essential tissue of the lymphatic system. In the lower • es lymph hearts are formed by the addition of striated
muscle t<> primary lymph sacs. In the higher forms lymph glands formed by the development of lymphocytes around the ducts. This take- place not only in the wall of the primary lymph sacs, along plexuses of 3, so that there are primary and secondary
lymph glan
The Origin and Development of the Lymphatic System. S3
The fundamental morphology of the lymphatic system has been es- tablished, but there remain many gaps in our knowledge of the system as a whole. The deep lymphatics in amphibia and reptilia are almost unknown; in fact a complete account of the Lymphatic system- in both of these groups would be of great value. In birds the origin of the iliae lymphatics and the growth of the thoracic duct would he most interesting. In mammals the gaps in our knowledge are especially in regard to the development of the lymphatic system within many of the organs; for example, the heart and lungs, the liver, spleen, kidneys and reproductive organs. A study of the embryology of the lymphatic system makes it more certain that the central nervous system has no lymphatics. The lymphatics invade the body, hut not completely; the nervous system is a permanent non-lymphatic area.
It is now possible to define the lymphatics. Lymphatic capillaries are tubes of endothelium; they are derived from the endothelium of the veins, and they have the same relation to tissue spaces as have blood capillaries.
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