Paper - Breech fused twin monster (1934)

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Siddiqi MA. Breech fused twin monster. (1934) J Anat. 68: 118-123. PMID 17104508

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This historic 1934 paper by Siddiqi describes the human abnormal development of conjoined twinning. Note the term "monster " is a historic term, no longer used to describe abnormal development.

Modern Notes: twinning

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Breech Fused twin Monster

Online Editor - Note the term "monster" is a historic term, no longer used to describe abnormal development.

By Pror. M. A. H. Siddiqi, M.S., F.R.C.S. (Ene.)

Department of Anatomy, University of Lucknow, India

The specimen to which the following description applies has been in the College Museum for some long time. No details regarding its birth or its history are available.

Fig. 1. Anterior view. Fig. 2. Posterior view.

External Features

The accompanying two photographs represent the anterior and posterior surfaces of the twin monster. The posterior surface presented a single genital tubercle encircled by a pair of genital folds or swellings midway between the buttocks of the two foetuses. Beyond the junctional area, the parts were normal in every respect and were characteristic of a seven months’ foetus. The Breech Fused Twin Monster 119

front view shows that the ventral abdominal walls of the two foetuses were continuous; a single median navel marked the junction of the two.

Dissection of the abdomen revealed that in each foetus the abdominal oesophagus and stomach were normal. The ventral mesogastrium and its derivatives were also normal. Of the folds derived from the dorsal mesogastrium the gastro phrenic and gastro splenic ligaments were normal, but the greater omentum retained its early foetal character in that it was attached directly to the posterior abdominal wall without the intervention of a transverse colon. Its attachment to the posterior abdominal wall coincided with that of a normal transverse mesocolon. The pancreas was present between its two layers near the root.

The omental bursa was normal with the exception of its lower posterior boundary due to lack of fusion between a transverse mesocolon and the dorsal mesogastrium.

The first and second parts of the duodenum were normal but the third part was poorly developed. The third part turned sharply forwards at the duodenojejunal flexure. The duodenum was not crossed by the root of the mesentery proper.

In each foetus the loops of the small intestine, 37 cm. in length, were attached by a mesentery to the posterior abdominal wall. The terminal loops opened into and became continuous at right angles with a common colon.

The large intestine was a common wide thin-walled tube, 15 cm. in length, running directly backwards across the middle of the common peritoneal cavity. It was slung in the middle line by two mesocolons which became continuous on either side with the corresponding mesenteries proper of the two foetuses (fig. 4). No demarcation between the various parts of the colon was possible and there was no trace of an appendix. The lowest part or common rectum was apparently sandwiched between two urinary bladder sacs.

The colic tube was attached on either side by a mesocolon continuous with the two mesenteries proper. The attachment of this continuous enterocolic mesentery on the posterior abdominal wall is V-shaped, the apex of the V corresponding to the enterocolic junction.

Fig. 3 shows the attachment of the mesenteries to the posterior abdominal wall and the relation of structures present in the actual specimen.

The cavity of the rectum, as shown in fig. 8, opened by a comparatively small circular aperture into a common bladder cavity.

The kidneys and ureters of both foetuses were normal in size and position.

Like the distal limb of the gut the analage of the bladders and external genitalia had also undergone fusion. As shown in figs. 3, 5 and 6, there was a common bladder transversely situated at the junction of the two foetuses. After opening the peritoneal cavity, as in fig. 8, the central part was hidden from view by the orientation of the terminal part of the colon on its anterior surface. The lateral parts were visible as hard pyramidal sacs with urachal prolongations to the navel. After dissecting the rectum from the anterior Gastro phrenic surface of the bladder the aperture of communication between the two cavities was well demonstrated as in fig. 6, and the fused nature of the bladder was revealed. On opening the bladder from its anterior aspect a transversely folded ridge was seen partially dividing the cavity into two parts, each part having ureteral openings and an internal urinary meatus leading into a urethral canal (fig. 7).

Fig. 3. Structures of the post abdominal wall Fig. 5. Recto vesical junction. of the twin monster after removal of digestive system (diagrammatic).

Fig. 6. Anterior surface of bladder.

Fig. 9. Breech twin apposition (diagrammatic). Stage IT.

The urethral canals traversed a mass of cavernous tissue and converged as they passed into the common genital tubercle (fig. 5).

Two undescended testicles with their corresponding ductus deferentia were present in each foetus. Each ductus deferens, after crossing the hypogastric artery and the ureter, passed between the rectum and bladder, and further dissection proved that it ultimately became confluent with the bladder wall (fig. 6).


The foregoing description may be explained by reference to the usual development of the digestive tube from the primitive U-loop. The proximal limb with its mesentery has given rise to the small intestine, and the distal limb with its mesentery to the large intestine which in this case has fused with that of the opposite side, resulting in a common colic tube with the corresponding mesenteries on either side attached to it. Such a fusion of the entire distal limb of the U-loop must have taken place by a breech approximation of the two equally aged embryos when the gut was in the U-loop state and before any herniation took place, i.e. before the 5th week of development. Such a complete and uniform fusion could not have been possible either in the umbilical sac or in the peritoneal cavity after reduction had taken place.

Figs. 8 and 9 have been diagrammatically drawn to show the possibility of such an occurrence. The distal limbs of the two loops which would otherwise have given rise to the terminal ileum and to the whole of the colon have fused into a single colic tube which, with the persistent original mesenteric attachments of the two distal loops on either side, have given rise toa median septum.

The part of the ventral body wall caudal to the body stalk also fused, resulting in a common peritoneal cavity and a common umbilical cord.


  1. Certain peculiarities in a breech fused twin monster are described.
  2. A common anterior abdominal wall, navel, genital tubercle and peritoneal cavity are present.
  3. There is a single common colon with which the small intestines of both foetuses are continuous.
  4. The anal canal is absent. The distal end of the common colon opens by an orifice into a common bladder cavity.
  5. There is a common urinary bladder presenting a transverse ridge showing its double origin.
  6. There are two urethral canals which converge and pass into a common genital tubercle.
  7. The ductus deferens terminates on the bladder wall. Its continuity with a urethral canal is not traceable.
  8. An embryological explanation of the above peculiarities is given.

Cite this page: Hill, M.A. (2021, June 12) Embryology Paper - Breech fused twin monster (1934). Retrieved from

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