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=The Origin And Occurrence Of The Single Umbilical Artery In Normal And Abnormal Human Fetuses=

Alden B. Dawson

Loyola University School of Medicine, Department of Anatomy
NINE TEXT FIGURES

==Introduction==

The single umbilical arteries described in the literature-can be divided into two groups. Group 1 includes all which arise from the abdominal aorta, whether as direct branches or as caudal continuations of the vessel itself; group 2, those which take origin from either the right or left common iliac-hypogastric trunk. Recently two cases of the occurrence of a single umbilical artery in full-term fetuses have come under my notice. These were representative of the two groups just mentioned. In one specimen (Dawson, ’22), a sympodial monster, the single median umbilical artery arose directly from the aorta a short distance below the superior mesenteric artery (ﬁg. 2). In the other, a normally formed fetus, only the left umbilical, appearing as a branch of the hypogastric artery, was present (ﬁg. 1). These two cases, together with a rather extensive survey of the literature, form the basis of this paper.

A single umbilical artery is an almost constant feature of the fetal monstrosity sympodia, and the constancy with which it appears in this class of monster has led many to conclude that the single median umbilical artery is the primary anomaly and that the other concomitant anomalies are subsidiary ‘to it. Johnston (’20) is probably the latest exponent of this theory. Ballantyne (’04), too, after a comprehensive survey of human monstrosities, pointed out that fetuses in which there is only one umbilical artery are generally malformed, and those in which the single artery is mesial in position and arises directly from the aorta are nearly always malformed in one special way, namely, exhibit fusion of the lower limbs or sympodia. He, with many others, believed, furthermore, that the single median artery supplying the cord was vitelline in origin, being the persistent omphalomesenteric artery, and concluded like them that the arterial supply of the placenta was not an allantoic derivative. The latest writer to express this View of the vitelline orgin of the single umbilical artery is Taglicht (’21).

Why there should be normally two umbilical arteries and only a single vein in the fetal cord is not clear. The venous supply of the placenta is primarily bilateral, but the median umbilical Vein of fetal life is the persistent left umbilical of the embryo, the right having atrophied during early embryonic development. Furthermore, in the development of the vascular system of the higher vertebrates there is to be noted a general tendency for primitive bilateral vessels to be transformed secondarily into single, and sometimes median trunks. This is especially true if the vessels supply organs which, like the cord and placenta, are not bilateral.

In many cases it is difficult to determine the manner in which the transformation into a single Vessel is effected. In some vessels it is evident that one member of the pair gained the ascendency and its fellow atrophied consequently. In other cases the two vessels were probably completely fused to form a single. trunk. Apparently, single umbilical arteries may be derived in either way, but the courses and relations of the single blood vessels are by no means identical. Moreover, the manner in which a single umbilical artery may be derived is also greatly complicated by several features of the normal development of these vessels. The primary umbilical arteries which rise ventrally from the abdominal aorta normally migrate from the cervical to the lumbar region. In the latter position (ﬁg. 3) they acquire secondary connections with dorsolateral branches of the aorta, and following the establishment of these dorsal relations the primary or ventral connections. with the aorta atrophy.




Fig. 1 Ventral view of the pelvis of a female fetus, showing the absence of the right umbilical artery. The relations of the‘ right external iliac and the left umbilical arteries have been disturbed to display the smaller vessels distributcd to the pelvic region. For complete description see text.

The substitution of dorsal roots for ventral roots may possibly explain why a single umbilical artery is not more commonly encountered in normal development. The dorsal segmental pairs of vessels are never, in human embryos, converted secondarily into single arteries, while the ventral vitelline series normally undergoes this transformation, and the umbilical or allantoic arteries are regarded as caudal members of the vitelline series. In cases, therefore, in which the dorsal connections are never established or if established fail to persist (and the primary ventral roots are accordingly maintained), it would be expected that the umbilical arteries would exhibit a tendency to duplicate the history of their homologous series, the paired vitelline arteries, and would be accordingly converted into single trunks. These single trunkswould also necessarily arise directly from the abdominal aorta, and not from the common iliac-hypogastric trunk as they do if the normal plan of development is followed. Other cases, in which the single umbilical artery arises from either the right or left hypogastric, admit of another explanation. This will be discussed later.

From the preceding statements it will be evident that there is not, as yet, complete agreement regarding the origin and occurrence of the single umbilical artery in man, and in this regard I wish to present, in the succeeding pages, evidence in support of the following conclusions: 1) that a single umbilical artery, arising directly from the aorta, is not the primary anomaly in sympodial monsters; 2) that the development of such a blood vessel is probably favored by the persistence of the original ventral umbilical roots; 3) that in order to satisfy the facts it is not necessary, except in rare cases (Ballantyne, ’98), to interpret the single umbilical arteries belonging to group 1 as persistent omphalomesenteric arteries, and, 4) that single arteries of group 2 are the result either of the failure of one member of the umbilical pair to develop originally or of the secondary atrophy of the distal as well as the proximal portion of a primary artery on either the right or left side following the establishment of its dorsal connections. The latter of the alternative explanations seems the more probable one, although little direct evidence can be produced to substantiate it.

I wish to acknowledge my indebtedness to Dr. H. D. Senior for many helpful criticisms and suggestions. He is, however, in no way responsible for any of the conclusions drawn in this paper.

==A Single Umbilical Artery in a Normally Developed Fetus==
The subject of this description was a full—term female fetus used for dissection in a course in fetal anatomy. Interest in the condition of the umbilical arteries was aroused on observing a great difference in the size of the right and left common iliac arteries (ﬁg. 1), the left being several times larger than the right. A careful search failed to reveal even a trace of a right umbilical artery. The right hypogastric and the right external iliac arteries, however, were normal in size and position. The right ovarian was abnormal and has already been described (Dawson and Reis, ’22). The right superior vesical artery was also lacking. Four paired lumbar arteries were present, and on the right side an a. lumbalis ima was found.


The arrangement of the arteries from the left hypogastric conformed to what Piersol (’07) has designated fetal type II (p. 810, ﬁg. 725), in which the three large vessels, the superior gluteal, the internal pudendal, and the inferior gluteal arise independently from the main (hypogastric) trunk (McMurrich, ’20, p. 248, ﬁg. 154). The single umbilical artery had practically the same caliber as the abdominal aorta.

==A Single Umbilical Artery in a Sympodial Monster==
{{Online Editor}} - This page terminology is historic and was used to describe abnormal development. This term is no longer used.

The main features of the anatomy of this monster have already
been brieﬂy reported (Dawson, ’22). The umbilical artery was
single and approximately median. It arose from the abdominal
aorta a short distance below the superior mesenteric artery
(ﬁg. 2). Below the point of origin of the umbilical artery the
dorsal aorta was greatly diminished in size and gave off inferiorly
only the lumbar arteries, second, third, and fourth right, and
second and third left. It terminated in a small vessel suggestive
of a middle sacral artery and did not have any further connection
with the arterial supply of the pelvis and lower extremities.

The umbilical artery, on the other hand, was very large, equaling in size the vessel from which it arose. In the upper portion
of the abdominal cavity it occupied a position slightly ventral and lateral (left) to the dorsal aorta and was enclosed in a low
peritoneal fold. More caudally, this fold was materially increased in height and in the pelvic region formed a sickle-shaped
septum which partitioned the rudimentary pelvic cavity into
right and left halves. The umbilical artery which was located
in the free margin of this fold accordingly curved ventrally in
the sacral region and then ascended toward the umbilicus on the
anterior abdominal wall in the midventral line. The artery was
displaced slightly to the left by the descending colon, which was
distended with meconium, as the rectum and anus were absent.
This displacement is somewhat exaggerated in ﬁgure 2 to show
the courses and relations of the dorsal blood vessels.

Shortly after its origin from the aorta, the umbilical artery gave
off an apparently normal inferior mesenteric artery, and in the
sacral region a second and very prominent branch was found.
It arose as a median dorsal trunk at the point of greatest convexity of the umbilical artery as it curved forward and upward
to supply the umbilical cord. This dorsal branch was 1.5 cm.
long and bifurcated in the shallow pelvis, giving rise to two
large lateral vessels Which, after giving off a few small arteries
to supply the pelvis, continued into the ‘fused’ lower limbs.

==A Schematic Outline Of The Various Factors Involved In The Formation Of Variant Umbilical Arteries==

The scheme, outlined below, is based primarily upon the normal ontogenetic plan of the umbilical arteries (Felix, ’10; Hochstetter, ’90; Senior, ’19; Tandler, ’O3), but it is, in parts, supplemented by a study of two dissections I have made and by analyses of the many umbilical variants reported in the literature. The factors are as follows:

1. The failure of one member of the primary pair of umbilical arteries to develop.

2. Variations in the caudal migration of the umbilical arteries from the cervical to the lumbar region: a) arrested migration, the arteries arising from the aorta at a low thoracic or high lumbar level (ﬁg. 4); b) complete or normal migration (ﬁg. 3).




Fig. 2 Ventral view of the abdominal region of a sympodial monster, showing the anomalous arterial supply and the rudimentary urinogenital system. For description see text.


(There may also possibly be cases of normal migration followed by return, thus simulating arrested Inigration.)

3. Variations in the development of dorsal or secondary roots: (1) failure of the dorsal roots to connect with the umbilical arteries (ﬁg. 4), dependent to some extent on 2a; b) normal dorsal root connections established with the primary paired umbilical arteries; 0) unilateral development of the dorsal roots, in cases where both primary arteries are present or where only one member of the primary pair is present.

4. The varying fates of the primary (ventral) and the secondary (dorsal) roots in the condition 3b or 30: a) loss of both primary roots and the persistence of the dorsal root or roots (normal); b) the persistence of both dorsal and ventral roots more or less comptleely; c) loss of the proximal portions (i.e., proximal to the point of origin of the primitive external iliac artery) of the dorsal roots and the persistence of the ventral roots; d) the loss of one dorsal and one ventral root; e) the persistence of two dorsal roots and one ventral root; f) the loss of one dorsal root and the persistence of two ventral roots.

5. The method of transformation of the paired umbilical arteries into a single vessel. (Although in many cases there is no direct evidence to indicate that the single umbilical arteries are derived from primitively paired vessels, still the fact that two dorsolateral connections were made has been accepted as indirect evidence of such a condition, since it hardly seems possible for a single median branch of the aorta to establish these connections.) a) By the loss of one umbilical artery distal to the point of origin of the external iliac artery. (It must be kept in mind, however, that the point of origin of the external iliac artery is not an absolutely ﬁxed one, since this artery may also migrate either eproximally or distally along the common iliac-hypogastric trunk.) b) By the fusion of the two umbilical arteries, inﬂuenced possibly by conditions represented in 2a, 3a, and 4b, 40, or 4f (ﬁg. 5).

6. The varying fates of the lumbar and sacral portions of the abdominal aorta. The lumbar portion, a) persists in condition 3a and 4a, but, b) usually undergoes more or less atrophy caudal to the point of origin of the Ventral umbilical roots in a condition represented by 2a and 5b or 40. The sacral portion is, 0) often missing, especially in sympodial monsters but, d) may persist.



Fig. 3 Diagrammatic representation, ventral view, of the developing abdominal aorta, showing the normal development of the arteries of the lower limbs and umbilical cord. Both dorsal and ventral roots of the umbilical arteries are indicated. The several portions of the arterial system of special interest in this paper are distinguished by hatching and stipple, and this method is adhered to uniformly in all subsequent ﬁgures (4 to 9). r.v., radix ventralis; r.d., radix dorsalis. The other abbreviations do not need explanation. Arrows indicate the direction of blood ﬂow.

Fig. 4 Diagrammatic representation, ventral view, of the developing abdominal aorta, illustrating a condition in which the ventral umbilical arteries have failed to complete caudal migration and to establish secondary connections (dorsal roots) with the aorta.

Fig. 5 Diagram showing abnormal development of the abdominal aorta as seen from the left side. The ventral umbilical arteries have failed to migrate caudally and have fused to forma single median vessel. They have also established dorsal root connections with the aorta. The normal position of the ventral umbilical roots is shown by broken lines.


7. The possibility of a single umbilical artery or any other large single trunk, which arises from the aorta at the lower lumbar level to become terminal in position. The normal middle sacral is rarely terminal.

8. The possibility in cases where the original ventral roots are fused and the dorsal roots atrophy proximally, a) for the distal or persistent (hypogastric) portions of the dorsal roots to be transformed (apparently by fusion) into a single trunk which would accordingly take its origin from the dorsal aspect of the single umbilical artery. This fusion, however, b) may be incomplete or, 0) may not occur at all.


(There may also possibly be cases of normal migration followed
by return, thus simulating arrested Inigration.)

3. Variations in the development of dorsal or secondary roots:
(1) failure of the dorsal roots to connect with the umbilical arteries
(ﬁg. 4), dependent to some extent on 2a; b) normal dorsal root
connections established with the primary paired umbilical
arteries; 0) unilateral development of the dorsal roots, in cases
where both primary arteries are present or where only one
member of the primary pair is present.

4. The varying fates of the primary (ventral) and the secondary
(dorsal) roots in the condition 3b or 30: a) loss of both primary
roots and the persistence of the dorsal root or roots (normal);
b) the persistence of both dorsal and ventral roots more or less
comptleely; c) loss of the proximal portions (i.e., proximal to the
point of origin of the primitive external iliac artery) of the
dorsal roots and the persistence of the ventral roots; d) the loss
of one dorsal and one ventral root; e) the persistence of two
dorsal roots and one ventral root; f) the loss of one dorsal root
and the persistence of two ventral roots.

5. The method of transformation of the paired umbilical
arteries into a single vessel. (Although in many cases there is
no direct evidence to indicate that the single umbilical arteries
are derived from primitively paired vessels, still the fact that
two dorsolateral connections were made has been accepted as
indirect evidence of such a condition, since it hardly seems
possible for a single median branch of the aorta to establish
these connections.) a) By the loss of one umbilical artery distal
to the point of origin of the external iliac artery. (It must be
kept in mind, however, that the point of origin of the external
iliac artery is not an absolutely ﬁxed one, since this artery may
also migrate either eproximally or distally along the common
iliac-hypogastric trunk.) b) By the fusion of the two umbilical
arteries, inﬂuenced possibly by conditions represented in 2a,
3a, and 4b, 40, or 4f (ﬁg. 5).

6. The varying fates of the lumbar and sacral portions of the
abdominal aorta. The lumbar portion, a) persists in condition
3a and 4a, but, b) usually undergoes more or less atrophy caudal to the point of origin of the Ventral umbilical roots in a condition
represented by 2a and 5b or 40. The sacral portion is, 0) often
missing, especially in sympodial monsters but, d) may persist.




Fig. 3 Diagrammatic representation, ventral view, of the developing
abdominal aorta, showing the normal development of the arteries of the lower
limbs and umbilical cord. Both dorsal and ventral roots of the umbilical
arteries are indicated. The several portions of the arterial system of special
interest in this paper are distinguished by hatching and stipple, and this method
is adhered to uniformly in all subsequent ﬁgures (4 to 9). r.v., radix ventralis;
r.d., radix dorsalis. The other abbreviations do not need explanation. Arrows
indicate the direction of blood ﬂow.

Fig. 4 Diagrammatic representation, ventral view, of the developing
abdominal aorta, illustrating a condition in which the ventral umbilical arteries
have failed to complete caudal migration and to establish secondary connections
(dorsal roots) with the aorta.

Fig. 5 Diagram showing abnormal development of the abdominal aorta as
seen from the left side. The ventral umbilical arteries have failed to migrate
caudally and have fused to forma single median vessel. They have also established dorsal root connections with the aorta. The normal position of the
ventral umbilical roots is shown by broken lines.



7. The possibility of a single umbilical artery or any other
large single trunk, which arises from the aorta at the lower lumbar
level to become terminal in position. The normal middle sacral
is rarely terminal.

8. The possibility in cases where the original ventral roots
are fused and the dorsal roots atrophy proximally, a) for the
distal or persistent (hypogastric) portions of the dorsal roots to
be transformed (apparently by fusion) into a single trunk which
would accordingly take its origin from the dorsal aspect of the
single umbilical artery. This fusion, however, b) may be incomplete or, 0) may not occur at all.

==Review of Literature and Discussion==
The review of the literature has been postponed until this time and the somewhat hypothetical explanation of single umbilical arteries interpolated between it and the description of the two dissections in order that the two cases described and the several cases reviewed might be utilized as cumulative evidence in support of the conclusions noted above. The discussion, it is hoped, will also be facilitated by having before us in a schematic form a list of the various factors which may possibly be effective in the formation of variant umbilical arteries. These factors will be referred to by the number and letter under which they are listed. No attempt will be made to review the literature completely. Only cases which are believed to have a direct bearing on the points under consideration have been selected.

A single median umbilical artery in direct continuity with the abdominal aorta has long been regarded as a constant feature of sympodia and its importance has been, I believe, to a large extent over—em};hasized. Johnston (’20) and many earlier writers regarded the single vessel ‘as the primary anomaly. They believed that it was not the persistent member of a pair, but was formed by the ‘fusion’ of the two umbilical arteries, and that it therefore acted both mechanically, by forming an obstruction to caudal development, and physiologically, by resulting in a deﬁciency in the vascular supply to the posterior end of the body.


(The word ‘fusion’ has been rather loosely used in the literature with little or no indication as to whether ‘failure to develop separately’ or ‘secondary union following separate development’ was meant. Unless it is indicated otherwise, as above, by means of quotation marks, the latter meaning is implied when the term is used here.)

If Johnston’s suggestion, that the formation of a single median umbilical artery is the primary anomaly in sympodia and is directly responsible for the defective development of the caudal portion of the body, is correct, it would follow that in all cases of sympodia that there must always be but one artery and it must also be median in position. In reviewing the literature, however, it is obvious that the single umbilical artery in sympodial monsters is not always formed by ‘fusion,’ but is in some cases without question a persistent member of a pair of vessels. As early as 1889 Schwing demonstrated a case of sympus dipus in which “Der Nabelstrang enthalt nur eine Nabelarterie welche aus der linken A. iliaca entspringt” (p. 485). This is apparently an ordinary case of unilateral persistence, with a secondary (dorsal) root, of one member of the umbilical pair. Later Odisio (’92) ﬁgured and described the abdominal arterial supply of a case of sirenomelus, in which it is evident that the single vessel supplying the cord is a persistent left umbilical artery (ﬁg. 7). The arterial arrangement in this monster, however, is not so simple as in the case reported by Schwing, since the original ventral roots of both umbilical arteries have persisted. Duckworth (’O7) has also described a case of low-grade sympus dipus (specimen E) with a single umbilical artery. There is good reason, too, for regarding this single vessel as a persistent left artery which takes its origin from the abdominal aorta by means of the primary or ventral root (ﬁg. 9). A more complete consideration of these cases will be given later.

More recently, Langer (’21) described a case of sympodia in which the left umbilical artery was absent and the right appeared as a branch of the right common iliac-hypogastric trunk.

Besides the four cases of sympodia mentioned above which exhibit unilateral persistence of an umbilical artery, there is a case of sympus dipus described by Gladstone (’06) in which the double arterial supply to the placenta was maintained practically complete. The umbilical artery arose as a single trunkyfrom the abdominal aorta a short distance below the coeliac axis, but soon divided to form a large left and a small right umbilical artery. Neither of these umbilical vessels, however, had any connection with the common iliac—hypogastric trunk.


Single umbilical arteries have also been found associated with other monstrosities than sympodia. Hermann (1822) described two cases of congenital umbilical hernia in which there was a single umbilical artery arising from the aorta. Claudius (’59) reported a case of acephalus in which the umbilical artery appeared as a single branch of the aorta. Strassmann (’95) demonstrated a case of omphalocoele in which a single umbilical artery, arising from the left hypogastric, was present. Weil (’97) described a similar fetal defect with the right umbilical artery absent and the left appearing as a branch of the hypogastric. Emrys-Roberts and Paterson (’06) described a case of ectopia viscerum in which the right umbilical artery appeared as a caudal continuation of the abdominal aorta. The left artery was not present.

The cases reviewed above furnish, I believe, suﬂicient evidence to allow us to discount to a considerable extent the emphasis placed by many of the very frequent association of a single and median umbilical artery with the monstrosity sympodia. The formation of a single median artery by the ‘fusion’ of the original pair can scarcely be regarded as the primary anomaly in sympodia, since occasionally in this type of monster both umbilical arteries may remain almost completely separate, and more fre Fig. 6 Diagram suggesting an interpretation of the abdominal arterial system described by Duckworth (’07) for specimen F. (The labeling in this and all succeeding ﬁgures is the author’s.)

Fig. 7 Diagram suggesting an interpretation of the anomalous abdominal arterial system ﬁgured by Odisio (’92).

Fig. 8 Diagram based on Johnston’s (’20) description and ﬁgure of the arterial supply of a sympodial monster.

Fig. 9 Diagram suggesting an explanation of the anomalous arterial supply ﬁgured by Duckworth (’07) for specimen E.


quently only one member of the pair may persist. Furthermore, other types of fetal defects, as omphalocoele, in which the development of the caudal portion of the body is affected, often exhibit similar variations in the arterial supply of the placenta.

While a median umbilical artery is not invariably associated with sympodia, still it is the most common type of variant single umbilical artery found in this class of monster. The development of the median artery appears to be dependent on the persistence of the original ventral roots, whereby the umbilical arteries maintain the same relation to the abdominal aorta as do the vitelline arteries, and undergo the same changes, i.e., are transformed into single vessels. The umbilical arteries are regarded as caudal precocious members of the vitelline series.

The most simple type of median umbilical artery is represented by a combination of the factors 2a, 3a, and 5b, and is the one most commonly encountered in sympodial monsters (Taglicht, ’21, et al.). The single artery arises from the abdominal aorta at the lower thoracic or upper lumbar level and passes almost directly to the umbilical cord, having no connections with the common iliac-hypogastric trunk (ﬁg. 4). In these cases‘ the primitive umbilical vessels did not complete the normal caudal migration, no secondary dorsal root connections were established, and the paired vessels were transformed into a single vessel in the same manner as the other paired members of the vitelline series. It is possible, however, that in these cases only one member of the primary pair developed originally, but there is indirect evidence, as already noted, that in many cases two umbilical arteries must have been present atian earlier stage of development. Furthermore, in the case described by Gladstone (’O6) the degree of‘ fusion is limited to the short portion adjacent to the aorta. Moorhead (’O5) also reported a case (sympus apus) in which the umbilical artery arose from the aorta as a single trunk and entered the cord as a single trunk, but in the intermediate portion it became double for a short distance.

A single umbilical artery having the course and relations of the type under discussion has been interpreted by many (Taglicht, ’21, et al.) as a persistent omphalomesenteric artery. In rare cases (Ballantyne, ’98) it seems barely possible that the allantoic circulation may be replaced by the vitelline circulation, but, unless there is sufﬁcient evidence of modiﬁcation in the placenta to justify such an interpretation, there appears to be no valid ground for advocating it. There is certainly nothing in the ontogenetic history to preclude the interpretation I have offered.

The relations of the single umbilical arteries, in the previous cases where no‘ secondary dorsal connections were made with the aorta, are relatively simple. On the other hand, in cases where the secondary roots were established, followed by either abnormal loss or persistence of either the primary or secondary roots, the relations of the single artery become more complex and it is often difﬁcult to recognize homologies. An additional complication is introduced by the manner of development of the common and external iliac and hypogastric arteries in relation to the dorsal umbilical root. The second case reported in this paper is of this more obscure type, and, in conjunction with my attempt to interpret this anomaly, I wish to discuss rather fully four somewhat similar cases which represent instructive transitional stages in the transformation of a primarily bilaterally symmetrical arterialsystem into a single median one.

Duckworth (’O7) reported a case of sympus dipus (?), specimen F, in which the abdominal aorta, below the superior mesenteric artery, divided into a large median ventral and a much smaller dorsal vessel (ﬁg. 6). The ventral vessel appeared at ﬁrst sight to be the caudal continuation of the abdominal aorta. The dorsal branch, however, was found to be the true aorta and it retained its original dorsal position, continuing caudally upon the vertebral column to end in a middle sacral artery, after giving off distinct branches to the right and left sides of the pelvis. The large ventral trunk arched forwards over the uterine portion of the cloaca and passed downward in the middle line over the rudiment of the bladder. Immediately above the symphysis pubis it gave off symmetrical branches to each side of the pelvis and then bent upwards to enter the umbilical cord as a single vessel. Each of the symmetrical right and left branches, after giving off a femoral branch at the appropriate point, was ﬁnally traceable to the back of the pelvic cavity and came to an end in the close vicinity of the lateral terminal branches of the reduced dorsal aorta.

The condition of the abdominal arterial system in this case is represented by a combination of the factors 2a, 3b, 4b, 5b, 6d, and 8c. The large ventral vessel was produced by the fusion of the primary umbilical arteries which did not complete their caudal migration and retained their original ventral roots. The secondary or dorsal roots were also established, but they underwent considerable atrophy proximal to the point of origin of the external iliac arteries. They were represented in this portion (normally the common iliac portion) by the lateral branches of the dorsal aorta and the dorsolateral branches from the symmetrical right and left branches of the median ventral umbilical artery. These symmetrical branches are homologous with the hypogastric portions of the dorsal umbilical roots. The ﬂow of blood in the latter vessels consequently must be in a direction opposite to that which it takes in the normal arteries. The lumbar portion of the dorsal aorta is also very much reduced in size, due to the diversion of the blood stream brought about by the retention by the umbilical arteries of their primary high origin.

A case similar in many respects to that described by Duckworth (’07) was ﬁgured by Odisio (’92). A large ventral artery arose from the aorta below the superior mesenteric artery and continued caudally for a considerable distance as a single Vessel (ﬁg. 7). In the region of the pelvis, however, it bifurcated into a small right and a larger left division. The right artery terminated in two relatively large branches; one Went back into the pelvis, the other, the external iliac, supplied the right leg. The larger left artery continued practically undiminished in size to the umbilicus, and gave off along its course a small pelvic branch, which in turn gave oﬁ the left external iliac artery and then passed dorsally and medially into the pelvis to become continuous with a similar artery from the opposite side. A reduced dorsal aorta was present and it terminated shortly after giving off the lumbar arteries.

A combination of the factors 2a, 4b, 5a, and b, 6b and c, and 8d would produce a result quite similar to this case of Odisio’s. The original ventral roots persisted, but failed to migrate-caudally the normal distance, and fused for the greater portion of their course, being separate only in the pelvic region. Distal to its union with the right secondary root the right umbilical artery, however, had completely atrophied. The left persisted and became the single vessel of the umbilical cord. Both dorsal umbilical roots were retained, but their early connections with the dorsal aorta were lost, as the latter vessel terminated a short distance cranial to the level ‘from which its dorsal branches originally arose. Although the portion of the abdominal aorta from which the secondary roots arose disappeared, the proximal ends of the roots have remained in continuity. Apparently most of the blood supplied to the left side of the pelvis and left leg must have followed a circuitous route through the vessel of the right side, which is made up of the unfused portion of the right primary umbilical root and the right secondary or dorsal root, reaching the left leg by way of the common iliac portion of the left dorsal root. It is obvious that the small left hypogastric element, of itself, could not supply the larger vessel going to the leg (ﬁg. 7). _With the exception of the mistake as to the large ventral artery’s being the omphalomesenteric, boh Duckworthe and Odisio offered much the same explanations as given above.

In the second case of single umbilical artery described in this paper (ﬁgs. 2 and 5) the arterial supply of the abdomen did not differ greatly from the two cases already discussed, and represented a condition such as a combination of factors 2a, 3b, 40, 5b, 6b, and 8b would produce. The original ventral roots failed to migrate the normal distance caudally, and the primitive umbilical arteries were fused throughout their entire course. Secondary dorsal connections with the aorta Were established, but they Were subsequently lost proximal to the origin of the external iliac arteries. The portions lost would normally form the common iliac trunks (ﬁg. 5). The distal persisting or hypogastric portions of the dorsal roots were incompletely fused, so that the blood supply of the rudimentary pelvis and ‘fused’ limbs arose as a single vessel from the dorsal surface of the umbilical trunk, and later divided into a right and a left branch (ﬁg. 2). From points near the bifurcation of the single trunk small arteries left the hypogastric portions of the right and left branches and passed to the viscera and walls of the shallow pelvis. The main branches continued as external iliac and femoral arteries to the ‘fused ’ lower appendages.

A somewhat different type of single umbilical artery was described by Johnston ('20). The median umbilical artery in this case did not appear as a branch, but as the caudal continuation of the abdominal aorta (fig. 8). “The common iliac arteries were therefore indistinguishable, but the external iliacs arose by a common trunk from the dorsal aspect of the single median artery and almost at once separated, being normal in the remainder of their course so far as could be traced. Their common trunk gave off a few small branches to the rudimentary pelvis and a single gluteal on each side” (p. 211). The arrangement of the abdominal arterial system in this case could be produced by a combinationiof factors 2b, 3b, 4c, 5b, 6c, 7 and 8a. In contrast with the three cases previously considered, the fused primary umbilical roots have migrated the normal distance caudally. The proximal portions of the secondary roots have atrophied, and along with the fusion of the primary umbilical arteries a fusion of the distal or hypogastric portions of the dorsal roots has also occurred. Because of the loss of the proximal connections of the dorsal roots and the normal lumbar position of the fused primary roots, the lower lumbar and sacral portions of the abdominal aorta have completely disappeared and the single umbilical trunk has assumed secondarily a terminal position.

Another single umbilical artery, having much the same relations as the one described by Johnston (’2(]), was reported in the same year by Lange, the major difference being that the distal persistent or hypogastric portions of the dorsal umbilical roots did not fuse to form a single trunk. The so-called abdominal aorta accordingly underwent a tripartite division into two lateral vessels supplying the pelvis and legs and a large median artery which turned up and entered the umbilical cord.


The division occurred low in the pelvis some distance caudal to the bifurcation of the inferior vena cava. The proximal ends of the lateral branches of the abdominal aorta, according to my interpretation, are each composed of the hypogastric portion of the dorsal umbilical root and the primitive external iliac artery which grew out from the secondary root. The role of the axial or ischiadic artery in the development of the femoral or distal part of these vessels is not taken into account.

In all cases of single median umbilical arteries reviewed there is therefore evidence that the primitive ventral roots have per— sisted, and it seems probable that this persistence has favored the fusion of the originally paired vessels. Occasionally, however, even in cases where both primary roots are retained one member of the umbilical pair may undergo atrophy distally (Odisio, ’92). In a case described by Duckworth (’07), specimen E, to which reference has already been made (p. 331), only the left umbilical artery was present. It arose from the dorsal aorta immediately below the ﬁrst lumbar arteries and passed caudally to the umbilical cord giving rise to a small gonadic artery and a larger vessel which went to the left leg. The interpretation is suggested in ﬁgure 9. The primary umbilical root on the left side persisted and migrated caudally only to a level between the ﬁrst and second lumbar arteries. The left dorsal umbilical root disappeared proximal to the origin of the external iliac artery and the distal persisting or hypogastric portion linked the external iliac with the left umbilical artery. The history of the right side is more obscure. It is entirely possible that only the left umbilical artery made its appearance originally, otherwise we would have to surmise an atrophy of the primary or ventral umbilical root and a persistence of the secondary or dorsal root——a complete reversal of what occurred on the left side. In the absence of any direct evidence, I prefer the latter interpretation.

In other cases where apparently both secondary umbilical roots were established and the primary roots subsequently atrophied, single arteries are produced by the disappearance distally of one member of the umbilical pair ‘(ﬁg. 3), and the persistent artery appears as a branch of the common iliac hypogastric trunk. A somewhat similar condition could also be produced by the failure originally of one member of the umbilical pair to develop. Lateral umbilical arteries of this type have been described in both normal and monstrous fetuses. Schwing (’89) and Langer (’21) reported cases in sympodial monsters. Weil (’97) found this condition associated with congenital omphalocoele. Duckworth (’O7) described a persistent left umbilical artery in an abnormal fetus (specimen A). De Archangelo (’O1) and Mouchotte (’00) found unilateral persistence of the umbilical arteries in normal fetuses, and the case described in this paper (ﬁg. 1) was found in a normally formed female fetus.

In my specimen (ﬁg. 1) a right lumbar ima was present, and on the same side the umbilical artery was absent. Normally the lumbar ima is more often absent than present (Levy, ’O2), and, according to Senior (’19), the chief share in the early formation of the dorsal root of the umbilical artery is taken by a vessel which appears as a branch from the ﬁfth lumbar segmental artery. The early atrophy of the distal portion of. the right umbilical artery, which presumably occurred in this case, and the consequent diversion of the placental stream to the artery of the opposite side may possibly explain why this ﬁfth lumbar segmental artery was not obliterated during the formation of the right common iliac trunk.


==Summary and Conclusions==

The single umbilical arteries described in the literature can be divided into two groups; group 1, including all which arise di rectly from the abdominal aorta; group 2, those which take origin from the common iliac—hypogastric trunk.

Two cases representative respectively of these two groups are described in this paper. The one belonging in group 1 was found in a sympodial monster, the other was present in a normally formed female fetus.

Single median umbilical arteries arising from the abdominal aorta are associated only with sympodia. Occasionally, however, in sympodia the two umbilical arteries remain almost completely separate. In other cases of sympodia the distal portion of one member of the umbilical pair is lost and only one artery is accordingly present in the cord. These exceptions indicate, therefore, that the so-called fusion of the umbilical arteries to form a single median vessel cannot be directly responsible for the monstrous condition.

A list of the several factors which may be concerned in the formation of variant umbilical arteries is given.

The predisposing factor for the formation of single median umbilical arteries, which appear as direct aortic branches, is the persistence of the primary or ventral umbilical roots.

Single umbilical arteries, arising from the abdominal aorta at a high level and passing directly to the umbilicus without any connection with the arterial supply of the lower limbs, have been interpreted by many as persistent omphalomesenteric arteries. These vessels, however, more probably represent fused primary umbilical arteries which did not migrate caudally or become secondarily connected with the aorta at a lower level by means of the so-called dorsal roots. Consequently, such vessels can have no connections with the iliac and hypogastric arteries, which ‘must accordingly develop independently.

Lateral single umbilical arteries which arise from the common iliac-hypogastric trunk have followed the normal plan of development. The absence of an umbilical artery on the opposite side is due either to the atrophy of its distal portion following the establishment of its dorsal connections with the aorta or to the failure of the primary umbilical root to appear originally. In the latter case the dorsolateral vessel leaving the aorta between the fourth and ﬁfth lumbar segments must form the blood supply of half of the pelvis and one leg Without any association with the umbilical arterial supply.


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[[Category:Placenta]][[Category:Cardiovascular]][[Category:Historic Embryology]][[Category:1920's]]