Paper - Omphalopagous twins in the human subject

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Gemmill JF. and Stewart J. Omphalopagous twins in the human subject. (1916) J Anat Physiol. 50: 316-323.

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This historic 1916 paper described the abnormal development of conjoined twinning. Thoraco-omphalopagus is the most common types of conjoined twins (28% of cases).

Historic Embryology - Twinning 
1915 Twin embryos 17-19 somites | 1916 Conjoined Twins | 1922 Monozygotic origin identical twins | 1927 Separate amnions | 1942 Twin chorion | 1955 Twins and multiple birth
Carnegie Embryos: 8505a 8505b 7170a 7545 9009a and b 9123 5542B 5935A 5621A

Modern Notes: Twinning

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Omphalopagous Twins in the Human Subject

By Dr James F. Gemmill And Mr James Stewart.


Ventral union, limited (as far as the parietes are concerned) to the umbilical region, can occur in human twins, and accordingly the type 0mphalopagus should receive a place in the classification of Mammalian Double Monstrosities, its position being intermediate between Xiphopagus and Lecomopagus or Ischiopagus.

Description of Specimen

The specimen consists of full-time female twins united face to face in the umbilical region by an isthmus which expands mesially to form a sac of considerable size. In each twin the epidermis of the body wall extends over the neck of the isthmus and over a small portion of the sac, but not more than a quarter of the total surface of the sac has natural skin over it, the remainder being covered by a thin, pinkish, semi-transparent membrane. Both subjects are in rather an emaciated condition and one of them has well-marked talipes varus on the left side. There is no anal aperture in either case, but the twin with the club-foot shows an anal depression. The labia are well developed, and on separating them a distinct opening is seen in each case. This has proved to be the external opening of the urogenital canal.


Length from top of head to coccyx, 28 to 30 cm. Full length when stretched out, 62 to 63 cm. Circumference of common sac, 276 cm. Circumference of neck of isthmus in club-foot twin, 18 cm.; in other twin, 8 cm.

Only one umbilical cord is present, its place of origin being the middle of the common sac, on the side away, from the club-foot. A cut edge of membranous tissue running transversely round the sac is probably a remnant of the fused amnia. The twins had a common placenta and a short common umbilical cord.

They survived for several days. A third child, born shortly after them, had separate membranes and placenta, was healthy and well developed, and is still alive. The clinical aspect of the case has been described elsewhere (Lancet, London,’April 1, 1916) by Dr Robert Jardine, in whose wards at the Glasgow Maternity Hospital the birth occurred, and through whose courtesy and that of Professor T. H. Bryce the specimen was handed to us for examination.

Peritoneal Cavities and Mesenteries

The peritoneal cavities of the twins communicate freely in the central mass, which consists chiefly of coils of intestine. The dorsal mesentery is retained throughout, except that the commencement of the duodenum is bound down to the posterior abdominal wall near the middle line. The great omentum is absent, but in both twins there is a wide epiploic foramen leading into a peritoneal recess lying behind the stomach and clothing about half of its posterior aspect.

GemmillStewart1916 fig01.jpg

Fig. 1. Outline drawing of specimen, showing the general character of the union.

Alimentary Canal

In both twins the small intestines proceed in coils through the stalk into the central mass, where they unite 2'5 cm. from the ileo-caecal junction. The common canal opens into a large caecum which shows two vermiform appendices, each appendix being placed slightly to the left of the mesentery coming from the twin to which it belongs. The caecum and colon are very greatly distended with faecal material. The large intestine is 23 cm. long, its lumen admitting the passage of two fingers.

It is contained within the central mass, but towards its termination it sends a short horn into the pelvis of the twin without the club-foot, the horn being continued as a solid fibrous band in the direction of the anal depression previously noted as being present in this twin.

Vascular System

No branches of the superior mesenteric arteries proceed to the caecum or the colon, which are entirely supplied by the inferior mesenteric arteries. These vessels pass through the connecting stalk into the central mass, where, after branching repeatedly, they are distributed each to its own side of the intestine. A superior haemorrhoidal branch is absent. Three of the hypogastric or allantoic arteries are of large size and enter the umbilical cord, while the remaining one, namely, the right hypogastric artery of the_ twin without the club-foot, is a small vessel which becomes lost on the abdominal wall of this twin in the region of the isthmus neck. Two umbilical veins are found in the root of the cord, one coming from each twin.

GemmillStewart1916 fig02.jpg

Fig. 2. Common caecum and fused portion‘ of intestine opened up. The appendix of the twin without the club-foot is on the left of the figure, while the opening into the appendix of the club-foot twin is shown in the floor of the cavity.

Urogenital System

In both twins all the Mullerian duct derivatives are doubled, the Fallopian and uterine tubes in each being widely separated from one another, the latter opening into vaginae dilated with fluid. The vaginae open in turn into the urogenital canal, and the contained fluid was found to have plentiful urinary salts in solution.

GemmillStewart1916 fig03.jpg

Fig. 3. Diagrammatic representation of a dissection of the urogenital system of the twins, looked at from above. The cavities of the vagina: and bladders have been opened up so as to exhibit the floor of each with the various openings leading therefrom. A, on side of twin with club-foot. B, on side of twin without club-foot.

In the central mass, below the insertion of the umbilical cord, is a large principal bladder with two necks, one passing downwards into the pelvis of each twin and continued into a corresponding urogenital canal. This bladder receives the two ureters of the club-foot twin, but only the left ureter of the second twin. The last-named twin has its right ureter opening into a small accessory bladder in the right hypogastric region. This bladder is surmounted by a small urachus, and opens through a short narrow passage into the body of the principal ‘bladder. It will be remembered that the right hypogastric artery of the same twin was small

GemmillStewart1916 fig04.jpg

Fig. 4. Diagram of urogenital system of twin without the club-foot, showing the various openings into the b adders and urogenital sinus. In the case of the club-foot twin the arrangement is similar, except that no accessory bladder is present, both ureters opening into the principal bladder.

and did not pass into the neck of the isthmus. The urachus and small hypogastric artery, just referred to, hint at a second but altogether rudimentary umbilical complex on the side of the isthmus opposite to that on which the functional umbilical cord is placed. The two necks of the principal bladder lead each into a urogenital passage which, after receiving

the openings of a pair of vaginae, comes to the surface between the labia majora.


The specimen belongs to the “Siamese Twin ” group of monsters, in which there is anterior and posterior doubling (Anakatadédymus, Forster (5)), the union being on the whole a face-to-face or ventral one. In this case the union is exactly face to face, except for the fact that the umbilical cord is single and comes off from one side of the central mass.

With the doubtful exception referred to below, our specimen appears to be unique among mammalian monstrosities, since no example of “ Siamese Twins” has so far been described in which the union is confined to the umbilical region, leaving the skeletal structures of both sternum and pelvis entirely unconnected with one another. Thus in Saint-Hilaire’s classification (7, pt. iii. p. 67) the group of monsters which might be expected to include the specimen described in this paper, contains the following types: I sch7§opagé, Xiphopagi, Stcrnopagi, Ectopagi (43.6. with lateral union along whole of thorax), Heonipagi (73.3. with lateral union along whole of thorax and neck). Similarly in SchWalbe’s (8, p. 113) classification, the group into which our specimen should fall is subdivided as follows: P7°osopoth07°a,copagns, Thocr-acopagus, Sternopagns, Xiphopagns, I lcoamlphopagns, I leothoracopagns, C'cphalo-v}leo-thoracopagns. There is a similar blank in the classificatory systems of other authors, c.g. Forster (5), Ahlfeld (1), Stewart (9), Tarufli (10), and Ballantyne (3). Cleland’s sub-type, Union confined to the neighbourhood of at common umbilicus, contains but is wider than Omphalopagus, since it includes also the xiphopagous Siamese Twins (4, p. 134).

The term Omphalopagus was introduced by Geoffrey Saint-Hilaire (7,: pt. iii. p. 107) to describe a double monster chick in which there was superficial union in the umbilical region by the anterior portion of the vitellus. He adds that a double human foetus figured by Aldrovandi (2) is the only other example of this kind of monstrosity he could find described. Aldrovandi’s figure shows twins united by a narrow isthmus at the umbilicus ; one of them having only a single hind-limb, a right limb to judge by the figure. The description (2, p. 634) is as follows: “ Pariter in Page Vallis superioris Arni Tertanio nuncupato, anno salutis humanae post millesimum, et trecentesimum decimo sexto monstrum natum est referens duos Gemellos umbilico copulatos, quorum alter duo crura, alter vero unum tantummodo habebat ut in Icone I ostenditur.” Doubt has been thrown by Taruffi on the correctness of Aldrovandi’s figure, on the ground that the monstrosity had been previously figured by Licosthenes not ad natwram but from a somewhat more detailed description than that given by Aldrovandi. Taruffi believes the specimen was really an example of Diccphalns tripus tctrabrachins (10, pt. ii. p. 574).

The omphalopagous type of monstrosity finds its best illustration among the osseous fishes. In the trout and salmon, for instance, union of symmetrical twins by the yolk-sac only is by no means uncommon (Gemmill, 6), and in rare cases survival for a time may occur. As Geoffroy Saint-Hilaire (7, pt. iii. p. 107) pointed out, omphalopagous union can readily occur where- ever the egg is large and the yolk-sac is not cast off but taken into the body.

It need hardly be said that the twins are unioval in origin. Probably the germinal areas from which they developed were situated opposite to one another on the wall of the blastocyst. There may have been only one entodermic sac, but more probably there were two such sacs which became confluent posteriorly on their ventral aspects. The fused portion of intestine in our specimen corresponds with the tract normally developed behind the origin of the omphalo-mesenteric duct. from the apex of the primitive umbilical loop of intestine. , The great hernia into the central sac recalls in exaggerated form the exomphalic condition of portions of the alimentary canal, which is characteristic of the earlier stages of human development.

We may note that instances of simple bifurcation of the umbilical cord (71.9. funicular union) may occur in the case of-homologous twins (Ahlfeld, 1, p. 17). In our specimen the cord and placenta were unfortunately not available for microscopical examination, so that we cannot say whether a yolk-sac and vitelline duct were present. It would appear, however (Ahlfeld, 1, p. 17), that homologous twins sometimes possess completely separate yolk-sacs.


  • Acc. Bl. . . Accessory bladder.
  • R. Umb. Cd. . Rudimentary umbilical
  • Acc. Umb. Cd. Accessory umbilical cord. cord.
  • Am. . . . . Amnion.
  • Rt. H3/p. Ar. .. Right hypogastric artery.
  • A0. . . . . Dorsal aorta.
  • Rt. Ur. . . . Right ureter.
  • Cl. Ft. . . . Club—foot.
  • Rt. Ut. . . . Right uterus.
  • Col. . . . . Fused colon.
  • Rt. Vag. . . Right vagina.
  • Fal. Tb. . . Fallopian tube.
  • CSt. . . . . Connecting stalk.
  • Il. . . . . Ileum.
  • U. G. S. . . Urogenital sinus.
  • II. C’. V. . . Ileo-colic valve.
  • Umb. Cd. . . Umbilical cord.
  • Lt. Hyp. Art. . Left hypogastric artery.
  • Umb. V. . . Umbilical vein.
  • Lt. Ur. . . . Left ureter.
  • Un. Int. . . Fused part of intestine.
  • Lt. Ut. . ,. . Left uterus.
  • Ur. . . . Ureter.
  • Lt. Vag. . . Left vagina.
  • Urach. . . . Urachus.
  • Op. Bl. . . . Opening of bladder into
  • Op. . . Opening from uterus into urogenital sinus.
  • Os Ut. . . . Os uteri.
  • Vag. vagina.
  • Ver. App. . . Vermiform appendix.
  • Pr. Bl. . . . Principal bladder.


1. AHLFELD, Die Missbildungen des Menschen, Leipzig, 1880.

2. ALDROVANDI, Monstrorum Historia, Bologna, 1642.

3. BALLANTYNE, J. W., Antenatal Pathology and Hygiene, “ The Embryo,” Edinburgh, 1904.

4. CLELAND, J ., Memoirs and Memoranda of Anatomy, London, 1889, p. 134.

5. FORSTER, AUGUST, Die Missbildungen des Menschen, Jena, 1861, p. 34.

6. GEMMILL, JAMES F., The Teratology of Fishes, Glasgow, 1912.

7. SAINT-HILAIBE, GEOFFROY, Histoire des Anomalies, Paris, 1836.

8. SCHWALBE, ERNST, Morphologie der Missbildungen, Jena, 1906.

9. STEWART, C., Catalogue of Teratological Specimens in Museum of Royal College of Surgeons, London, 1893.

10. TARUFFI, CESARE, Storia della Teratologia, Bologna, 1881.

Cite this page: Hill, M.A. (2024, June 23) Embryology Paper - Omphalopagous twins in the human subject. Retrieved from

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