View source for Paper - A model demonstrating the changes in position and peritoneal relations of abdominal viscera during development (1912)

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| [[File:Mark_Hill.jpg|90px|left]] This historic 1910 paper by Bayon describes a model demonstrating the changes in position and peritoneal relations of abdominal viscera during development.

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=A Model Demonstrating The Changes In Position And Peritoneal Relations Of Abdoiniinal Viscera During Development=

Henry Bayon

From the Department of Anatomy, The Tulane University of Louisiana

Three Figures

==Introduction==
Differences in position of the abdominal viscera and in their peritoneal relations at various stages of development occupy the front rank of difficulties which confront the teacher of anatomy. Text-books are lavish in detail, and clearness of description is not lacking in either text or atlas. The fact remains, nevertheless, that but few students obtain a clear idea of the successive changes which occur in the abdominal cavity during growth from the simple arrangement of the gastro-intestinal canal and its common mesentery in the early foetus to the complicated conditions acquired at term.


Huntington meets the difficulty by comparing the dissection of the human abdomen with that of the cat, and a better illustration cannot be found to substantiate the value of comparative anatomy in the study of the development of human organs. Huntington's method consists in directing the student to make comparisons between the abdominal viscera of the cat and those of the human subject. Advantage is taken of the fact that the peritoneal arrangement of the adult cat is much like that of the human foetus in early development. By a series of manipulations of the viscera of the cat, those movements and displacements of the organs, which occur later in the foetus and which result in the permanent fixation of peritoneal relations, may be imitated.


Suggested by Huntington's method, a model is herewith presented which has been found to simplify to our students, the explanation of processes by which the adult conditions in the human are attained. An apology for crudeness of the model should be offered. In its favor is the simplicity of its construction which is suggestive of simplicity rather than complexity in developmental processes. By manipulations of the organs represented, one may easily demonstrate the movements in rotation of the stomach and in torsion of the mesentery upon which the various changes in subsequent peritoneal relations essentially depend. A board about 2 feet long and 7 inches wide (fig. 1) represents the posterior abdominal wall and a piece of muslin covering it represents the foetal parietal peritoneum. To the mid-line of the boiird is attaclunl ti double layer of muslin, the comiuou mesentery. In the upper part of this, the mesogastrium, are enclosed the stomach, pancreas and spleen, and its lower part is made up to represent the mesentry proi)er, which encloses the primitive intestinal loop with some development of intestinal coils in the upper limb of the loop and the caecum and the colon in the lower limb. The stomach, pancreas, spleen and kidneys are represented by cotton cushions and the intestinal canal by a soft cotton rope. The duodeno-colic isthmus is shown with the superior mesenteric vessels passing to the intestine.







Fig. 1. Model representing gastro-intestinal canal before rotation of stomach and intestine.



Fig. 2. Model showing change in relations of viscera attending rotation of stomach; figure shows also first step in twisting of the mesentery at the duodenocolic isthmus.


The formation of the bursa omentahs and foramen of Winslow is illustrated by rotating the stomach from the sagittal to the transverse plane and by folding the mesogastrium (fig. 2). The ventral part of the fold then corresponds to the gastro-splenic omentum, the dorsal part of it to the posterior ligament of the spleen, and incidentally the displacement of the vagi nerves from the sides of the oesophagus to its ventral and dorsal surfaces is demonstrated. Rotation of the stomach is accompanied by rotation of the pancreas and duodenum which latter are thus made to leave their sagittal position for the transverse. The movement of twisting of the mesentery is next performed: the small intestine is made to sweep from right to left below the large intestine, the caecum is carried up from left to right and above the small intestine as in tiguiv 2, and in its travel, the ascending meso-colon is made to pass over the duodenum and pancreas which have rotated with the stomacli and have been made to he in the transverse plane. After this twisting of the mesentery on the duodenocohc isthmus has been understood, it is quite easy to explain how the ascending meso-colon, pressed backwards by the developing convolutions of the small intestine, eventually becomes a parietal layer, and how the pancreas and duodenum, which have been caught behind the ascending meso-colon, lose their embryonic peritoneal covering and appear to have developed in a postperitoneal position (fig. 3). The jejunum is now seen emerging from behind the newly acquired parietal peritoneum and at the duodeno-jejunal angle, the superior and inferior duodeno-jejunal folds and fossae (fig. 3) may be imitated by the twisting of the mesentery.




Fig. 3. Model shows position of abdominal viscera after rotation of stomach and complete twisting of mesentery.




The peritoneal and non-peritoneal areas of the kidneys are made clear and the occasional persistence of the descending mesocolon, in contrast to the more constant disappearance of the ascending meso-colon, is explained by the more extensive travel of the caecum and ascending colon, in comparison with the relatively stationary position of the descending colon.


Finally after the disappearance of the ascending meso-colon has been demonstrated, the new line of attachment of the root of the mesentery proper explains itself.



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