Paper - Studies of the intestine and peritoneum in the human foetus - part 5
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Reid DG. Studies of the Intestine and Peritoneum in the Human Foetus: Part V. (1913) J Anat Physiol. 47(3): 268-281. PMID 17232957
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Studies Of The Intestine And Peritoneum In The Human Foetus
By Douglas G. Reid, M.B., Ch.B. Edin., B.A. Trin. Coll. Camb.,
Demonstrator of Anatomy in the University of Cambridge.
Part V. The Convolutions of the Small Intestine (Mesenteric Plications)
For this study two foetuses, 25 and 37 mm. long, and twenty foetuses, ranging from 12 to 22 cm. in vertex-coccygeal length, were specially examined. The small intestine was carefully drawn in sitn. It was then removed piecemeal, being simply steadied with forceps as this was being done. Thus practically no displacements occurred. The mesentery was not cut. A thin rim of intestine was preserved.
In a former paper I have described the line of the root of the mesentery, and have indicated that this presents an upwardly directed portion upon the fourth stage of the duodenum, and a portion whose direction, at one time transverse, becomes more oblique during, or even before, the descent of the caecum, the result of traction upon, the mesentery by the genito- mesenteric fold. Thus the angle between the two parts opens up. A line which passes downwards through the right end of the third portion of the duodenum to the right deep abdominal ring (the line of the unmodiﬁed subduodenal portion of the genito-mesenteric fold), and a line which passes through the junction of the third and fourth parts of the duodenum and the left deep abdominal ring, will serve to map the portion of the abdomen, below the duodeno-jejunal ﬂexure, into a central and right and left lateral regions.
The liver rested upon and concealed a portion of the small intestine. On viewing the small bowel from the front, and before any part of the liver had been removed, I noted that the superﬁcial parts of the intestine in the central region sometimes have as a whole a vertical direction (see ﬁg. 1). This was well marked in Nos. XVII., IX., and XX. On examining these foetuses (see ﬁgs. 3, 4:, 5) after the small intestine had been removed it is seen that the loops in the central region lie vertically and are simple. This was especially the case in No. XVII.—13 cm. long. Here ﬁfteen simple loops, parts of which are deeply placed, are present. They are all of practically equal size. Their long axes are parallel to one another and at right angles to the line of the root of the mesentery. Studies of the Intestine and Peritoneum in the Human Foetus 269
Two classes of cases may be recognised according to the arrangement of the “superﬁcial” (anterior) parts of the small intestine in the central region as a Whole. The ﬁrst class is characterised by vertically directed pieces of bowel, and may be termed the primitive. The second is characterised by loss of parallelism, general irregularity, or preponderance of horizontal parts, and may be termed the secondary. The foetus 37 mm. long (see ﬁg. 18, A) may already be put in the secondary class. P0siti0n.——There are no intrapelvic coils. In the 25 mm. embryo the intestinal loop lies in the umbilical cord (coelom). In the 37 mm. foetus the caecum lies in the middle line in the upper part of the umbilical oriﬁce; and in this oriﬁce are also vertically disposed terminal parts of the ileum (parts numbered (11) and (12) in ﬁg. 18, A). These parts are therefore still in a somewhat more anterior plane than the rest of the intestine.
Fig. 1. Foetus 19 cm. long. The ﬁgures in this ﬁgure and in ﬁg. 2 show the parts of small intestine and mesentery which correspond to one another. (In this foetus the left root fossa was relatively a. deep one (4 mm.), and a piece of small intestine could easily be introduced into it.)
Fig. 2. The same foetus as that from which ﬁg. 1 was drawn. The ﬁgures in this ﬁgure and in ﬁg. 1 indicate the parts of the mesentery and small intestine which correspond.
“Embryos of 40 mm. long either have the intestine in the cord or in the peritoneal cavity ” (Mall). F0rm.—Two forms, primitive and secondary, of small intestine may be recognised depending on the presence of any small loops upon the longer loops. No. XVII. (ﬁg. 3) is a primitive form.
Fig. 3. Foetus No. XVII., 13 cm. long. The 1i11e of the root of the mesentery is indicated by the interrupted line. In this and in the succeeding diagrams the originally left lamina of the mesentery is indicated by the stippling.
Fig. 4. Foetus No. IX.
No large loops of pelvic colon are present in this specimen. The secondary forms are variable.
Dz"recti0n. — In the left lateral area the loops have a horizontal direction, tending to become vertical in the lower part of this region (see, e.g., ﬁg. 7).
Fig. 6. Foetus No. II.
Speaking generally, they are placed at right angles to a line drawn parallel to the root of the mesentery upon the fourth portion of the duodenum. The upper horizontal loops are concealed chieﬂy by the transverse colon and mesocolon and liver and to some extent by the stomach; sometimes, in addition, the lower of these are covered by parts of vertical loops of small intestine. The originally right lamina of the mesentery of the ﬁrst loop is anterior (see, e.g., ﬁgs. 3, 4) in twelve foetuses (60 per cent. of cases).
Fig. 8. Foetus No. XVIII. The retro-duodenal fossa is indicated by the non-stippled I area. It lies behind the fourth portion of the duodenum.
The course taken by the bowel immediately succeeding the duodeno- jejunal ﬂexure is most variable. Almost any direction may be taken except directly upwards or backwards. In many cases, but not all (see ﬁg. 1), the horizontal parts of the loops in the left lateral region could be recognised before the intestines had been removed (i.e. “ superﬁcially ”), and formed quite a characteristic feature of the left lateral region.
Fig. 10. Foetus No. XII. The pelvic colon is indicated by an interrupted line.
In the central region the coils of small intestine are usually placed vertically, at right angles to the line of the corresponding portion of the root of the mesentery. The central area may be invaded by loops whose necks are placed either in the left or (as in No. II. see ﬁg. 6) in the right lateral region.
Fig. 11. Foetus No. X.
Fig. 12. Foetus No. III.
In No. II. there are two large horizontal loops which are directed by the liver and colon into the central area, the lower encroaching upon the left lateral area.
In the right lateral region the loops are usually vertical and at right angles to the line of the corresponding root of the mesentery. In a foetus 6 cm. long the loops of intestine in the left lateral area also present a horizontal direction, the loops to the right of this being vertically disposed.
Fig. 13. Foetus No. VIII. The thick interrupted line indicates the pelvic colon. The arrows indicate the direction of the movement referred to.
Fig. 14. Foetus No. VIII. The bend referred to has been undone. The arrows» indicate the direction in which the movement had occurred.
In a foetus 37 mm. long these directions have also already been acquired to some extent, although it is the superﬁcial parts of the small intestine in the left lateral area that present the horizontal disposition (see fig. 18, A), and the horizontal direction is not so apparent when the direction of the intestinal border of the mesentery is studied as a Whole (see ﬁg. 18, B).
Fig. 15. Foetus No. XV.
Fig. 16. Foetus No. I.
I shall now describe a special variation in the form of the small intestine. This variation, which is present in Nos. XI., XII, XIV-, and XVIII. (see ﬁgs. 7, 8, 9, 10), is associated With the M-Shaped form of pelvic colon, or with the compressed omega form. Little or no room exists between the limbs of these forms of pelvic colon. A large loop of small intestine lies in the right part of the abdominal cavity. Upon it are a number of small loops. Its mesentery is moulded over the right loop of the M—shaped pelvic colon in XI. and XVIII., and over the compressed omega in XII. and XIV. Its right limb lies partly in front of the caecum, and is related to the genito-mesenteric fold.
The arrangement of the “superﬁcial” parts of the loops of small intestine in Nos. XII. and XIV. Was characteristic. Immediately over the middle line were vertical folds of intestine, and on either side of these tiers of horizontally placed folds. The horizontal parts on the left were parts of the horizontal loops of the left lateral area of the abdomen; and those on the right Were smaller loops lying upon the large colic loop of small bowel. In No. X. (see ﬁg. 11), where there is an M—shaped form of pelvic colon, this type of arrangement is not present; but the caecum is placed relatively higher than in the foetuses with this arrangement. If the M—shaped or compressed omega forms of pelvic colon are relatively small, they may then not be associated with any special arrangement of the coils. There is no form especially characteristic of the primitive omega, because of the size of the space between the limbs of this form of colon. The modiﬁcations produced here were of the nature of bends. This is Well seen in Nos. III. and VIII. (see ﬁgs. 12, 13, 14) in relation to the curved right limb of the omega. Bent loops are also shown in relation to the liver (see, 6.5)., ﬁgs. 3, 5, 11)., In VIII. an extensive bending has taken place.
Fig. 17. Foetus No. VII.
Fig. 17. Foetus 37 mm. long, 6. The interrupted lines in A indicate the position of the lower border of the liver and of the umbilical oriﬁce. The upper border of the oriﬁce lies opposite the lower border of the liver (cf. ﬁg. 1). In B the interrupted line indicates the course of the duodenum. The parts of intestine and mesentery which correspond are indicated by ﬁgures. The stomach and ﬁrst part of the colon (passing backwards from the umbilicus) lie in a. more horizontal plane than the ﬁgures appear to indicate. Normally the testes and descending colon are in contact with, and completely concealed in front by, small intestine. But the posterior abdominal wall l1as been straightened by traction exerted upon it through the hook, and they are thus rendered visible.
The upper extremity (opposite B in ﬁg. 13) of a loop had apparently at one time occupied a position (indicated by A in ﬁgs. 13 and 14) in the neighbourhood of the caecum, and has been displaced by the right limb of the pelvic colon. It had moved through half a circle downwards along the right limb of the omega, then upwards (in front of a central loop of small intestine), so that it comes now to lie between the limbs of the primitive pelvic colon and in front of another loop (see ﬁg. 13). Unusual distension of the small intestine with meconium rounds off the dihedral angles formed by the plications of the mesentery along the vertices of which lie blood—vessels (see ﬁg. 15).
Is there evidence of a constant tendency towards the acquisition of an arrangement such as described by Mall ?1 I examined the small intestine of a 25 mm. foetus, and found that the drawing which I had made of the small intestines was exactly similar, except as regards the relative length of some of the loops, to that given by Mall for an embryo 24 mm. long.
The bends and the direction of the intestine, as well as the foldings of the mesentery, are exactly similar in my foetus to what is ﬁgured by Mall (plate ii. ﬁg. 6).
There appears, then, to be primarily no haphazard arrangement. But already in a foetus (obtained from Dr Yolland of Bromley) 37 mm. long I cannot recognise the primitive loops which Mall has described. At ﬁrst (see ﬁg. 18, A) it seemed that the part numbered (1) was Mall’s second loop. But careful examination showed that it was only a small part of a relatively large loop 2 (see ﬁg. 18, B), and, moreover, its mesentery was turned in the “ wrong ” direction. (The bowel immediately succeeding the duodeno—j ejunal ﬂexure—Which lay in its adult position—went markedly forwards.) Where, then, are the six primitive loops that Mall has described?
The arrangement of the small intestine in a foetus 6 e111. long I found was similar, and as complex as in the older foetuses. It shows no closer resemblance to the arrangement described by Mall than do the majority of the older foetuses.
In the larger foetuses (from 12 to 22 cm. long) which I have examined up to the present, the modiﬁcations which have taken place quite obscure in most cases the six loops of small intestine which Mall describes, if they ever existed, although in some cases (see, e.g., ﬁg. 1) an approach towards the arrangement which he ﬁgures, a11d which is sometimes found in’ the adult, may be seen.
Zlfec/cel’s D/ivertIiculum.—-This is present in two out of twenty—one foetuses (96 per cent.) specially examined for it; but since January 1907 I have met With it only in three foetuses and in two adults. It is not present in either the 25 or the 37 mm. foetuses.
It projects from the more caudally situated portion of the ileum (opposite + in ﬁg. 3). It is cylindrical in form, with no smaller pouches upon it; and is 6 mm. long in No. XVII. (13 cm. long) and about 10 mm. long in No. XIX. (20 cm. long). Its diameter is equal to that of the bowel into which it opens, but is somewhat constricted at its base in No. XIX.
- 1 “Development of the Human Intestine and its Position in the Adult,” by Franklin P. Mall, The Johns Hopkins Hospital Bulletin, Nos. 90—91, September—October 1898.
- 2 It will be seen that it is essential to determine the arrangement of the Whole mesentery. To my mind certain of Mall’s ﬁgures do not adequately show this. For this reason I cannot accept all that he asserts regarding the arrangement of the small intestine in these specimens.
It arises from the anterior wall of the intestine, and takes a rectilinear course towards the umbilicus in No. XVII. and towards the anterior abdominal wall in No. XIX.
Its extremity is free.
In No. XVII. a branch of the superior mesenteric artery crosses the front of the ileum and lies upon the process along the line of a slight fold of peritoneum.
While none of my specimens showed any features inconsistent with the generally received theory of its origin from the vitelline duct, there is no satisfactory explanation of the origin of the comparable duodenal pouches, an example of which I have described in the Journal of Anatomy and Physiology, vol. xlii. p. 194.
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