Paper - Development of the human intestine and its position in the adult (1898)
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Development of the Human Intestine and its Position in the Adult
By Franklin P. Mall.
Professor of Anatomy, Johns Hopkins University.
- This paper has appeared in German in the Festschrift fur Professor Wilhelm His zum 22. October, 1897, Archiv fur Anatomie, Supplement-Band, 1897.
Our knowledge of the early development of the human intestine is very complete, and at first thought it seems impossible to contribute anything new to it ; yet, when we consider the topographical anatomy of the adult intestine, we are struck by the fact that there is dispute regarding the position of its various parts, and nothing is known about the development of its convolutions.
The aim in this study has been to follow the successive stages of the development of the human intestine, loop by loop, from the simplest form in the embryo to the adult. As a result, it has been found that the various loops of the adult intestine, as well as their position, are already marked in embryos of five weeks, and that the position of the convolutions in the adult is as definite as the convolutions of the brain.
The present study is closely associated with one recently published upon the development of the human coelom, and the embryos here described were also published in part at that time.f In that paper the shifting of the viscera was emphasized in connection with the development of the coelom, while in this paper only the convolutions of the intestine are considered.
- Mall, Journal of Morphology, vols. 12 and 14.
The set of specimens in my possession is fairly complete, as all the important stages are represented. It is self-evident that a subject like this can be studied only by resorting to models, as a simple comparison of sections gives no opportunity to study the loops. A number of important stages were selected aud modeled according to the method of Born. A list of these embryos is given in the accompanying table :
Table op Embryos Modeled. Lengtb in mm.
From Whom Obtained.
Ellis, Elkton, Md.
C. O. Miller, Baltimore.
W. S. Miller, Madisou, Wis.
C. O. Miller, Baltimore.
Douglas, Nashville, Tenn.
Ellis, Elkton, Md.
Wilson, Worcester, Mass.
These models were then compared with one another, in order to follow the growth of the loops from stage to stage, using as guides the outline of the intestines in the sections and the blood-vessels, as well as the dissections of other embryos and those of the adult.
The loops which appeared to be homologous in the various models were next painted with the successive colors of the spectrum, beginning with the duodenum, and ending with the csecum. In this way, loops whose position were at first obscure, were finally found to have meaning. It is noteworthy that the successive stages in the development fit into one another accurately, showing that the first loops in the embryo are destined to form certain loops in the adult, and that this primary folding is in no way a haphazard process.
Early Formation of the Alimentary Canal
The observations, upon the human embryo, of the first formation of the alimentary canal from the entoderm have now been extended to the very earliest stages.* In Graf Spec's embryo v. H. the entoderm lines the wh ^le of the umbilical vesicle, and is in no way incorporated within the body of the future embryo. In fact, its plane is curved away from the entoderm, and is just the reverse of its direction in a later
The next older stage is found in Graf Spec's embryo Gle, in which there is shown the beginning of the fore-gut. These two stages, given by Graf Spee, are the important ones to make our knowledge of the develojiment of the alimentary canal complete, and from them we can easily follow thi'ough the successive stages until the adult form is reached.
After Graf Spee's embryo Gle, we have next to observe the constriction of the umbilical vesicle from the entoderm. The beginning of this constriction is already well marked in Kollmann'sf embryo Bulle, my embyro No. XII, J and His's§ embryos SR and Lg. Unfortunately, we have no data regarding the extent of the alimentary canal in Kollmanu's embryo Bulle, nor His's embryo SR. My embryo XII, however, is of about the same stage as the other two, and it has been cut into sections which are about perfect. The history of this embryo, as well as its coelom, have been described by me recently, so I need not repeat them at this time.
Embryo No. XII
Carnegie Embryo No. 12 (2.1 mm. Long).
The Figures 1 and 2, on Plate I, give the external form of the embryo, as well as the extent of the alimentary canal, which was taken from a reconstruction. The entoderm is already divided into fore-gut, mid-gut, and hind-gut. The fore-gut marks the pharynx, from which there are four diverticula on the dorsal side ( Br', Br"), one on the ventral side (T), and two near the mouth ( M and S ). These diverticula mark the first two branchial pouches, thyroid gland, mouth and Seessel's pocket respectively. At the junction of the pharynx and the umbilical vesicle there is a large diverticulum of the entoderm into the septum transversum, L, the beginning of the liver.
The hind-gut is a sharply defined cavity lodged in the tail of the embryo, communicating on the one hand with the allantois. All, and on the other with the neural tube by means of the neurenteric canal, N. C.
The attachment of the umbilical vesicle to the body indi
Graf Spee, His's Archiv, 1889 and 1896. tKollmann, His's Archiv, 1889 and 1891. t Mall, Journal of Morphology, vol. 12, 1897, p. 417. 'i His, Anatomie mensch. Embryonen, 1885.
cates the extent of the mid-gut from which the future intestine is to arise. The coelom is already beginning to be incorporated into the body to form the body cavity, and in the region of the liver and the omphalo-mesenteric vein the peritoneal cavities of the two sides of the embryo communicate freely, showing that at this early stage there is no complete ventral mesentery as has been described. This communication, marked 0, gradually approaches the communication above the allantois, 0', and ultimately cuts off the umbilical vesicle altogether. A stage just before the umbilical vesicle
Fig. a. — Reconstruction of Embryo No. II. Enlarged 17 times. V and X, fifth and tenth cranial nerves; 1, 2, 3 and 4, cast of the branchial pocliets ; 1 and 8, first and eighth cervical nerves ; 12, twelfth dorsal nerve; A, auricle; V, ventricle; L, lung; S, stomach; P, pancreas; WD, Wolffian duct; K, kidney; M, mesentery; ST, septum transversum; O, openings which communicate with the peritoneal cavity on the opposite side.
is completely separated from the embryo is represented in Fig. A, taken from embryo No. II.* By comparing Figs. 1 and A it will readily be seen that the spaces marked and 0' in the two embryos are the same.
The intestinal canal of embryo II is given in Fig. 3. The drawing was made from the right side and gives the irregularity of the tube more accurately than my previous figures have done. The part between the liver duct and the cjecum, of course, marks the extent of the small intestine, and the part behind this, the large intestine. At this early stage, therefore, the cajcum is distinctly outlined. Attached to the small intestine there is this marked umbilical stem, but the vesicle no longer communicates with the intestinal canal. From the
Mall, Jour, of Morph., vol. 6; and vol. 12, p. 429.
umbilical stem there haugs down an extensive papilliform process which, from its appearance in section as well as its presence in younger embryos, shows that it is nothing more than an island of vessels and villi from the umbilical vesicle. These seem always to be incorporated within the body at this point and degenerate later on.
Thus far it is very easy to follow the formation of the intestine, when the embryos already described by His are also taken into consideration. My embryos, Nos. XII and II, are from the end of the second and fourth weeks respectively, so it takes about two weeks for the intestine to become outlined after the entoderm is incorporated within the body of the embryo. The intermediate stages have all been described by His in his great monograph. In his Atlas the external form of embryos intermediate to XII and II is given, and in the text the alimentary canal of embryos Lg, BB, Lr and R is again pictured in woodcuts. They all show the gradual constriction of the stem of the umbilical vesicle to form the intestinal tube between it and the liver.
As the umbilical vesicle is being separated from the intestine, all of the viscera are moving from the anterior end of the embryo towards its tail. This is also the case with the diaphragm and the origin of the cceliac axis and the superior mesenteric arteries from the aorta.* A comparison of figures A and 1 shows that the whole stem of the umbilical vesicle in embryo XII must have moved toward the tail through the space of at least ten body segments to have gained the position it holds in embryo II.
At the same time that the intestine is bending towards the ventral median line the loop is also beginning to turn upon itself, so that the aboral end moves towards the left side, and the oral end to the right of the body. This process is already beginning in embryo II, Fig. 3, but rapidly becomes more marked, as is beautifully shown by the His embryos and their models made by Ziegler. By this process the loop is separated into right and left halves, the left half to form the large intestine, and the right half, the small intestine. In a short time, however, as the loof) grows longer and longer, not all of the left half is occupied by the large intestine, as the cascum is now no longer in the middle of the loop.
EXTENSION OF THE LOOP INTO THE CORD.
As the loop of intestine enlarges it extends immediately into the umbilical cord, as was first shown by Meckelf for the human embryo. To what extent this is common to the mammals is not known, but my experience is that it is frequently found in other mammals, and from the examination of many pigs' embryos I can state that in them a portion of the intestine always extends into the cord.
Figures 4, 5 and B are from embryo IX, a specimen about five weeks old. The intestine extends into the cord as a single loop, with the plane of its mesentery horizontal to the long axis of the body. In general its arrangement is much like that
of His's embryos Si, Sch*, KOf and 11M|. It is noticed in the figures that the large intestine lies altogether within the sagittal plane of the body, a position it retains until the intestine is returned to the peritoneal cavity proper. The right half of the loop has a number of small bends in it, which are of great importance in the further development of the intestine. I have marked them with the numbers 1, 2, 3, 4, 5 and 6 in order to follow them with greater ease in the drawings of older embryos.
•Mali, Jour, of Morph., vol. 12, pp. 441 and 442. t Meckel, Meckel's Archiv, 1817.
Fio. B. Reconstruction of Embryo No. IX. Eulars^ed 20 'times.
ST, septum transversum; L, liver; S, stomach; C, caecum; W, Wolffian body; K, kidney; 1 to 13, dorsal f^anglia; O, omphalo-meseuteric artery; SC, suprarenal capsule; X, communication between pleural and peritoneal cavities.
In the middle of the mesentery of the loop and in the median line lie the omphalo-mesenteric vein and artery. At the point where these vessels cross the intestine. Fig. 4, u, we have a landmark which is of use in comparing the intestine of this embryo with that of older embryos. The point of communication between the umbilical vesicle and the intestine also represents the position of the persistent Meckel's diverti
His, A. m. E., Ill, p. 19. fHis, Abhandl. d. sach. Gesch., XIV, Taf. II, Fig. 3.
JHis, ibid.XV, p. 677.
culum. If the adult intestine is about six meters long, and if the distance from the cjecum and Meckel's diverticulum is about one meter, then the length of the intestine between the omphalo-mesenteric vessels and the caecum is about one-sixth of the whole intestine. In both embryos IX and X, as well as in His's embryos Si and Sch, the extreme bend of the intestine (Fig. 4, u) marks one-sixth the distance from the crecum to the duodenum.
The blood-vessels to this whole loop within the umbilical cord arise from the omphalo-mesenteric or the future superior mesenteric artery. AVhen this is compared with the arterial supply in the adult intestine it is again found to correspond. In this early stage the omphalo-mesenteric artery supplies the same portions of the intestine that the superior mesenteric artery does in the adult. Not only by the form of the large intestine, but also by its blood supply can we divide it into two portions, that jwrtion which is at right angles to the body, supplied by the superior mesenteric artery, and that parallel with the body and supplied by the inferior mesenteric artery.
The relation of the intestine and liver to the body of the embryo is given in Fig. B.
Fig. C. — Reconstruction of Embryo No. X. Enlarged 8 times. 1 to 13, dorsal ganglia; SC, suprarenal capsule; W, Wolfflan body; K, kidney; L, liver; S, stomach; C, ciecum.
BEGINNING OF THE CONVOLUTIONS. A stage somewhat older than the one just described is given in Figures 6, 7 and C. In comparing Figures B and C it is seen that the liver has descended decidedly ; it has moved
away from the head to the extent of at least three segments. While in embryo IX the septum trausversum is opposite the eighth dorsal nerve, and the lower edge of the liver opposite the first lumbar nerve, in embryo X the septum is opposite the eleventh dorsal, and the lower edge of the liver opposite the second sacral nerve. In other words, the septum has descended three segments and the lower edge of the liver six segments. Not only has the liver descended through its absolute growth, but the whole organ has descended ajso. This movement has had a marked effect upon the form of the large intestine, and the direction of the intestine in general, as the figures will readily show.
While this movement is taking place the convolutions are also becoming more and more distinct. Every loop as outlined in embryo IX is more marked in embryo X. In general, the twisting has become more pronounced as the caecum is approached. The loops 1, 2 and 3 are only slightly more bent in X than in IX, while the loops 4, 5 and 6 have become much more sharply defined. In general, the length of the loops has doubled itself while the diameter of the intestine increased but one-third.
Pjo d. — Reconstruction of Embryo No. VI. Enlarged 8 times. S, stomach; SC, suprarenal capsule; C, ca'cum ; K, kidney; W, Wolffian body.
The next embryo (VI) I have modeled is only slightly larger than No. X. I give the same views for this embryo as I gave for Nos. IX and X. Fig. D compared with Fig. C gives the general relation of the intestine to the body. The large intestine has not changed its position much ; it has elongated, but has uot increased its diameter. There is now added to the cisecum a marked vermiform appendix. The stomach has descended more than before, the great omentum forming a sac and extending well over the large intestine.
A comparisou of Figs. 6 and 7 with Figs. 8 and 9 shows the growth of the small intestine. The duodenum is still bulged at its stomach end and only the lower portion of it is as small as the rest of the intestine. This enlarged duodenum is so decided that, at first sight, one might think it belongs to the stomach, but since the liver and pancreatic ducts open into it in all the specimens, there is no doubt but that it belongs to the intestine. Of course there is the possibility of these ducts shifting, but this seems to me very improbable.
The second portion of the intestine, 2, is now curved towards the dorsal side of the embryo, and, as in embryo X, this is also the case with its mesenteric attachment. We are all familiar with this portion of the intestine in section, as it has this hooked mesentery showing that the intestine has bent backward. The next portion, 3, is bent upon itself to such an extent that it rolls around on the dorsal side of the omphalomesenteric artery, to project to the left side of the clump, as shown in Fig. 8. It also has the hooked mesentery in section, as the mesentery is very much bent upon itself.
It has been customary for embryologists in discussing sections of the intestine with me to call this portion of the intestine the duodenum, on account of its position, as well as for its very characteristic mesentery. At first I was strongly inclined towards this view, but more mature consideration of models convinced me that both the loops 3 and 3 are finally transferred to the left side of the body to form the upper part of the jejunum.
The fourth portion of the intestine. Fig. 8, 4, has its beginning in the earlier embry.j on the left side of the mesentery as shown in Fig. 6. It is readily seen by the comparison of the two figures that the loop 4, in Fig. 8, is only an exaggeration of the same in Fig. 6. While this loop begins on the left side it ends on the right. In all the figures the extreme bend of the loop 4 is marked a, and a comparison of the figures will readily show that this is always the homologous loop.
Following the loop 4 there is the loop 5, which is altogether on the right side in embryo X, Fig. 6, and about equally distributed on both sides in embryo VI. In both Figs. 6 and 8 the end of the loop 5, b, approaches the loop 3, and this relation is also present in Fig. 10. In the figures this point is marked b, and the similarity of this loop in them is very apparent. Loops b and 3 are just touching in Fig. 6, while in Fig. 8, through the elaboration of loop 4 and its gliding to the right side of the mesentery, the loop 5 has been brought nearly in contact with loop 3. At any rate the relations of loops 5 and 6 to the umbilical vein in both figures show that the numbering of the two loops is not far amiss.
The loop b in Figs. 4, 6, 8 and 10 holds the same relation to the ca3cum and umbilical vessels in all four embryos. This point seems to be the fixed point for the loop on the right side of the mesentery as the point marked a is for the left. Between b and the ctecum the intestine is thinner and the loops are smaller than in the upper part of the intestine. |
For this reason as well as for the fact that there is no sharp landmark other than the umbilical vessels between loop b and the cascum, I have classed this whole region as one group and marked it with the single number 6.
The convolutions in embryo XLV, Figs. 10 and 11, are only an exaggeration of those of embryo VI. The loops 1, 2 and 3 are much the same as before. The loop 1 is again defined by the extent of the head of the pancreas. The loops 2 and 3 together are now S-shaped instead of a simple curve as in embryo VI. My interpretation of this is that the loop 3 is held in place by the opening of the umbilical cord, as at this point the intestine leaves the body, while the loop 2 is beginning to rotate to the left side of the body with the rest of the intestine. The loop 4 on the right side has enlarged, however, and has pushed its way in between the loops 3 and 5. On the left side the loop 4 has made for itself another twist, so it now appears as several loops. The loop 5 is much as it was before, only it has increased its length somewhat. It is easy to see the loop 6 of embryo VI converted into that of embryo XLV by imagining x in Fig. 9 to be drawn over to the opposite side to form x in Fig. 10. In so doing x' and x" remain back to form the loops marked the same in Fig. 11. In addition to this the loop y in Fig. 9 has become bent over to the left side to form y in Fig. 11.
All these twists and curves in the small intestines of the four embryos just descril)ed can be followed fairly well in the figures, and the reader may think that there is considerable imagination required to do this. Any one, however, who may study the models in which the corresponding loops have been marked as in the figures will not doubt regarding the accuracy of this description. It is a most remarkable fact that four specimens should correspond as well as they do here. Were the whole affair more or less haphazard no comparisou whatever could have been made.
Rotation of the Small Intestine
A comparison of embryos II, IX, X, VI, His's Pr and KO, shows that the change in position of the intestine and its future twisting is due to the descent of the abdominal viscera, accompanied by the relatively rapid growth of the small intestine. The following table gives the measurements of the intestines in these embryos as well as the level of the stomach
ind the caecum. The measurements of the intestine of embryos Pr* and KOf have been taken from the illustrations given by His and are only approximations. The position of the stomach here given is its lowest measurements including the omental bag.
Table giving tue Position and Length of the Small Intestine.
Length of Intestine.
Number of Embryo- Position of Stomach.
II 1 Dorsal
3 Lumbar 5 Lumbar 1 Sacral
Position of Csecum. Small. Large.
(• Dorsal 1.7 mm. 1.5 mm.
10 " 3. 1.5
13 '< 4. ;i
5 Lumbar 9. 3.7
3 Sacral I'J. 7.
1 Sacral ' 34. 8.
His, Atlas, Theil III, Taf. 1, Fig. 4. fHis, Abhandl. d. K. S. Ges. d. Wiss., U
Bel. XIV, No. 7.
A study of this table by comparing it with the illustrations shows that the intestine is gradually elongating and at the same time being pushed towards the pelvis by the large liver and other organs descending upon it. In No. II the intestinal canal is still a comparatively straight tube, but in Pr and KO it is already well bent, is much larger than in No. TI and is pushed into the cord. In No. IX it is located in the cord. From No. II to No. IX the small intestine has increased its length five times and the large intestine over two times, and the space which they should occupy within the body has remained the same. Under these conditions the intestine must escape if it has a chance, and the coelomic space within this cord naturally receives it. This movement of the intestine is due to mechanical causes and, were the ccelom of the cord not there to receive it, the intestine no doubt would make room for itself within the body. I do not think that the umbilical ducts had anything to do with it any more than to keep the opening in the cord open, for, before the intestine begins to enter the cord, its connection with the duct is severed.
After the intestine has entered the cord. No. IX, Fig. B, the small intestine grows rapidly, as the table and Figs. C and D show. Embryos IX, X and VI are all about the same size, but no doubt VI is considerably older than IX ; the organs are all firmer and more developed, and the small intestine has increased its length considerably more than the large intestine. The organs have all been pressed down to the pelvis as far as they will go, as Fig. D. shows. In so doing the large intestine makes a sharp bend in the neighborhood of the fourth lumbar segment, in all of the embryos given in the above table. This bend, therefore, may be looked upon as a fixed point toward which the viscera descend, but beyond which they do not go. Of course after the intestine is in the cord the loops may descend lower, but within the body this is a very fixed point.
After the intestine is within the cord its further elongation and its mesenteric attachment causes it to be thrown into coils, as shown in the plates. The large intestine lies, however, in the sagittal plane of the body, partly within the body and partly within the cord. It does not grow as rapidly as the small intestine ; and, as the small intestine is folded into coils, the whole begins to rotate around an axis which is identical with that of the large intestine. By this process the small intestine is gradually turned from the right to the left side of the body, and in so doing is rolled under the superior mesenteric artery. This takes place while the large intestine has an antero-posterior direction and before there is any transverse colon. This latter is the result of a kinking which is to follow, and is in no way formed by a shoving of the large intestine over the small, as given in the Hertwig diagrams.
Return of the Intestine to the Peritoneal Cavity
Although it is comparatively easy to understand how the intestine leaves the peritoneal cavity to enter the cord, it is extremely difficult to see how and why it returns. When the intestine enters the cord the communication of coelom with the body cavity is very free and the intestine is small, but when the intestine returns to the body cavity the intestine is large, while the opening is small. Fig. D.
In embryo No. II, and in younger embryos, the belly stalk is very large and contains within it no muscles nor permanent blood-vessels of the abdominal walls of the future individual. It is not until the muscles wander, carrying with them their nerves and to a certain extent their blood-vessels, that the belly wall is finally completed.* In embryo No. VI, for instance, the rectus abdominis is about half-way around from the dorsal to the ventral median line, thus leaving a large area between the two recti, which is little more than a membrane. It seems that, until the abdominal walls are fairly completed, the intestine remains within the cord, and, at the last moment before the two recti come together in the middle line, the intestine returns to the peritoneal cavity.
In very young pigs' embryos, when the mammary ridge is still over the muscle plates, I have found that the segmental arteries form an anastomosis with one another throughout the extent of this ridge. This artery goes through a series of muscles which have just been split off from the muscle plates. As the embryos grow, the mammary ridge wanders towards the ventral median linef and carries with it this anastomosis of segmental arteries and the portion of muscle plates which are destined to form respectively the internal mammary, deep epigastric arteries and the rectus abdominis muscles. The nerve connections of the various segments of the rectus are formed as the muscle is splitting off from the muscle plates, and in this way the origin of the different parts of the rectus is indicated, as already shown by Nussbaum. What I have here described for the pig can also be verified for the human embryo, and this will make it plain how the lateral body walls are formed from the belly stalk.
But the closing off also takes place from above downwards. In an early stage, while the septum transversum is still in the neck, the umbilical vesicle also extends upwards. The heart is first closed off by the beginning of the membrana reuniens, and the ventral wall is completed by the amnion moving over the embryo from left to right.J Then the umbilical vesicle is pinched off from above downwards, corresponding with the descent of the liver and other viscera. In embryo II the stalk extends from opposite the third dorsal vertebra to opposite the second sacral, while in embryo IX it extends from opposite the second lumbar segment to opposite the fourth sacral. In other words, the oral end of the stalk has receded eleven segments, and its aboral end two segments ; or the whole stalk is moving away from the head, and its attachment to the body is rapidly becoming smaller and smaller. Later the growth of the abdominal walls is greater between the cord and the pelvis, as shown by the sections made by Merke].§
At one time I thought of the possibility of the expansion of the coelom of the cord and its incorporation with the abdominal cavity, and this was also carefully investigated. Were this
See also Nussbaum, Verhandl. d. anat. Ges., 1894, '95 and '96. to. Schultze, Anat. Anz., Bd. 7 ; and Verhandl. d. phys. med. Ges. Wurzburg, Bd. 26. t Mall, Journal of Morphology, vol. XII. i Merkel, Abhandl. d. k. Ges. d. Wiss. in Gottiugen, Bd. 40.
the case it would be necessary to find stages in which the rectus abdominis had wandered up into the stalk to incorporate it and to enclose the intestine within it. No such stage has ever been found, while on the contrary the recti nearly close the communication between the stalk and peritoneal cavities, before the intestine slides back into the body.
The return of the intestine into the body must take place very rapidly, for I have never seen a specimen in which it is in the process of returning. Embryos 40 mm. long either have the intestine in the cord or in the peritoneal cavity, and, if it is in the latter, the communication between the cord and peritoneal cavity is open and surrounded by a thin membrane, showing that it also is being closed. This membrane now closes the whole opening, and later the recti muscles wander into it to complete the abdominal walls.
Since I was unable to find the desired stage in the human embryo, I examined a number of pigs' embryos, hoping in this way to find stages in which the intestine is returning to the peritoneal cavity.
In a pig's embryo 12 mm. long a single loop of intestine extends into the extra-embryonic cojlom, beyond the cord and on the right side of the body. It is still in communication with the umbilical vesicle, which, in turn, is attached to the ventral body wall over the heart. As the loops of the intestine increase in number in older embryos, they make room for themselves below the liver and in front of the Wolffian body, for, unlike the human embryo, there is considerable space in this region. In general the greater number of loops remain within the body cavity of the embryo, and the loops within the cord are not numerous. The increase of loops within the body cavity and their rotation seem to draw upon the loops within the cord, so that when the embryo has reached 35 mm. in length, the loops have all returned to the body cavity.
No doubt, in the human embryo some similar mechanism is present in the return of the loops to the peritoneal cavity, but, as the critical stage has not yet presented itself, this question must be left open for future observation.
Position of Loops After the Intestine has Returned to the Peritoneal Cavity
Although it is extremely difficult to understand how the intestine returns to the peritoneal cavity, it is not difficult to recognize the various loops after their return. Unfortunately I have not been able to study carefully a good stage between embryos XLV and XXXIV, as the various specimens of this stage at my disposal were not perfect, or if so, the series of sections were broken. It was not until a number of good specimens had been spoiled for this present purpose that I found that, by removing the ventral abdominal walls, good series could be obtained. If this is not done, the intestine is very liable to be imbedded poorly, and as a result the sections are not perfect. Dissected specimens, on the other hand, cannot be relied upon, for, when once handled, it is impossible to replace the intestines to their original position with certainty, unless they have been modeled as soon as the abdominal walls were removed. Of course dissection is an extremely good method of control, but for a comparison of the loops I think that no method will improve the model. Then it was found that all the loops represented in No. XLV are again recognizable in XXXIV, and on this account it is believed that an intermediate stage is unnecessary, unless that stage is one in which the intestine is in process of returning from the cord to the peritoneal cavity.
A comparison of Figs. 10 and 13 shows that the loops of XLV are again represented in XXXIV. The marked change is that the mesentery of the large intestine has increased greatly. The loops of the upper part of the intestine have rolled completely to the left of the superior mesenteric artery, and the loops which were formerly within the cord have now been transferred in Mo to the right side of the body. While this has been taking place the stomach has been enlarging also, and by the tilting of the intestine the pyloric portion of the stomach, d, has come nearer the cscum, about to the point marked d' in Fig. 10.
This shifting of the loops, half to the right and half to the left side, as well as the sliding down of the stomach towards the Cfficum, has finally locked the duodenum (loop 1) around the root of the mesentery, as shown in Figs. 13 and 13. As the loops come out on the left side. Fig. 13, we have the beginning of the second group of loops (3) of the intestine. The deeper layer of these loops, not shown in the figures, is a single curve lying immediately in front of the mesocolon. The loops 3 together can easily be imagined as arising from the same as in Fig. 10 by a simple bending of the portion on the dorsal side of the large intestine towards the ventral median line. The loop 3 which lay formerly on the right side of the body is now altogether on the left side. In the illustration, with the exception of its ending in loop 4, it cannot be recognized as the loop 3 of Figs. 10 and 11. In the models, however, the loop 3 forms a distinct cluster situated between the loops 2 and 4, and therefore, by exclusion, it must represent the loop 3 of embryo XLV.
The similarity of the loop 4 in embryos XLV and XXXIV is very striking. Its beginning, the arrangement of convolutions and their position are much the same in both embryos, if the change in position of the intestine in the older embryo is taken into consideration. The next cluster I have marked 5, and the remaining portion 6. The loops 6 are again smaller, and their diameter is less than those of the upper part of the intestine.
In this embryo we can see pretty well the adult form of the intestine, only that the mesentery is transverse to the body rather than diagonally downward toward the right side. In this embryo we also see the relation of the intestine to the mesentery better than in the adult. At this time the mesentery is relatively simple, as but few secondary adhesions have taken place. Unraveling this stage into the one represented by embryo XLV, we can fully understand the relation of the mesentery to the abdominal viscera. These two stages represent beautifully the arrangement of the intestine in the dog and monkey respectively.
The following table gives the length of the various loops of intestine in the embryos described. The measurement was taken along the distal border of the intestine and therefore is considerably longer than along the mesenteric border. But this is a border easily measured, and the length of the hardened iutestiue is considerably less than where it is taken out fresh and stretched. The table shows that the lower end of the intestine grows more rapidly than the upper end until the intestine is returned to the peritoneal cavity, when the upper end of the intestine grows more rapidly. ^
IN Millimeters of
THE DIFFERENT Pt
THE DIFFERENT EmBRTOS
No. of Enil>ryo.
Intee- Small tine. Iniestine. I
It is not difficult to follow the development of the intestine from embryo XXXIV to the adult, by simple dissection ; but, in order to be more certain of the relation of the deeper layers of the intestine of an older embryo, I had the intestine of a four months' foetus modeled. In this, however, the mesentery was not included, as the loops only were desired. The intestine was removed from the body in toto, and carefully imbedded in paraffin, after which it was cut into sections 100 /a thick. These were drawn upon wax plates, at a scale of ten, thus making each plate one millimeter thick. The intestine outlines were then cut out, and the remaining frame-work of wax plates was carefully piled, and the cavities cast with plaster of Paris. After the plaster had set, the wax was melted in hot water, leaving the plaster cast of the intestines enlarged ten times.
Figs. 14 and 15 are drawings of this model, and they show about what would be expected in a stage more advanced than embryo XXXIV. The large intestine has become more extensive, the transverse colon having become bent forward, and the descending colon having a very marked S in it before it passes over to the rectum. The intestines, as a whole, are shifted more to the left side of the body, so that the colon encircles the intestine rather than simply marks its border. The lower part of the small intestine is filled with a great quantity of meconium at this stage, showing that vermicular action must take place at this early time, as all this substance has been propelled downward to the cfficum. This same condition I have noticed in other embryos of the same stage.
The loops have shifted somewhat over one another, but one could not unwittingly separate the model so that it would not fall into its respective groups. This separation is given in Fig. 15.
It is evident that the loops are now shifting and adjusting themselves to the space they have to occupy. The loops 2 and 3 are still recognizable, while the loop 4 has been pushed back of them and extends over about as great an area as loop 6. The loop 5 lies about in the middle line, is more to the left than in the younger specimens, and is destined, ultimately, to
lie in the left iliac fossa. The loop 6 will descend into the pelvis when the pelvis becomes large enough to hold it, making room for the green, which is shifted to the right side and to the umbilical region. All this will be accomplished with the descent of the caecum to form the ascending colon, thus bringing about the re-arrangement of the position of the loops by a rotation of the lower end of the intestine toward the pelvis.
Position of the Intestine After Birth and in the Adult
It is relatively easy to follow the intestines in an older fcetus or in a new-born child after they have been hardened in formalin or other substances which keep the intestines sufficiently in place while they are being handled. I have examined the intestines by this method in a number of new-born children, and have found them much the same as in fcetus XXXIV and XLVIII. The intestine passes over and back along its mesenteric attachment from left to right, while in foetus XXXIV and XLVIII, the direction of the mesentery of the intestine is at right angles to the axis of the body, in the new-born this attachment is from the left hypochondriac region diagonally downward towards the right iliac fossa, with a curve somewhat towards the right fossa. This makes its course a curved line, which is also curved spirally around the body. While above it is left and deep, below it is right and superficial. The intestine now is attached along this line, crossing and recrossing it, over and back again from duodenum to csecum. In so doing, the convolutions above lie to the left of the mesentery, and are piled upon one another, making the planes of their circles at right angles to the body, while below and to the right they lie in front of the mesentery, and the planes of the convolutions are jjerpendicular to the body.
For the adult I have examined the intestines of about 50 cadavers, in which 41 were not diseased nor adherent in any way. Of them, one-half were negroes. The intestines were all coagulated in position, the cadaver being on its back, with about 1.5 to 2 kilos of pure carbolic acid. It was injected in 33 per cent, solution to preserve the subjects for dissection. After the abdominal cavity was opened the position of the intestines was either sketched or photographed and then the intestines removed, loop by loop, making a tracing of their course at the same time. In this way the general course of the intestine was followed. In removing the loops it was found that in nearly all specimens they came out as distinct groups, as for instance the group on the right side of the body was usually one loop crossing the middle line but twice; once to communicate with the loops above, and once with those below. To follow the intestine in this way the method was amply sufficient, but free-hand modeling or corrosion gives a much more satisfactory result. The models of three specimens which I have made in this way have proved to be of great value in gaining a clear idea of the position of the intestines. A large number of diagrams, sketches, photographs, and models were compared with one another till I was finally able to convert them into a common scheme, by which I have been in the habit of demonstrating the course of the intestines to students, and then immediately verifying it on the cadaver. In doing this, it is necessary to be prepaied for the variations, and these again can be classified.
Work of Henke, Sernoff and Weinberg
It was generally believed that the intestines within the abdominal cavity had no definite position until a few years ago, when Ilenke* demonstrated that this was not the case. A glance at the various standard test-books on anatomy shows that there is a tendency among them to locate the main groups of the small intestine in fairly definite portions of the abdominal cavity. Gegenbaurt gives an illustration copied from Luschka in which the jejunum and ileum are located respectively in the upper and lower portions of the abdomen. In the text he expressly states that the jejunum is located in the upper portion of the abdominal cavity and extends down to the left iliac fossa. The ileum, however, is located in the lower portion of the abdominal cavity and in the pelvis, and extends over to the right iliac fossa. HoffmannJ gives an excellent illustration of the coils of the small intestine, locating the jejunum mainly in the umbilical and left iliac regions, with the ileum within the pelvis and lower abdominal regions. Similar descriptions are given by Testnt§ and by Q,uain,|| with the exception that they are more cautious about locating definite loops. Quain states, "the jejunum lies above and to the left side of the ileum, but the coils are so irregular that the position of any individual loop offers but little clue to the part of the intestine it belongs," while Testut states that tlie position of the intestine changes, due to the muscular contraction, and so on.
The first decided step in advance to locate the position of the intestine was made by Henke when he studied carefully the spaces in which the intestine may lie. He found that the abdominal cavity may be divided into four compartments, the greater of which lies within the concavity of the diaphragm and is filled with the organs which are more or less firmly fixed with ligaments. The other three compartments are separated from one another by the ridge formed by the two psoas muscles and by the vertebral column. This makes a right and left compartment and a lower compartment which extends into the pelvis. Into these three compartments the intestine must accommodate itself, and Ilenke thinks it has a fairly definite position. He is cautious enough, however, to state that under certain conditions the loops may shift from one space to another, but what the regularity of the position is, or what the rule of the shifting, is difficult to determine from Henke's paper. His illustrations, however, are very good, but, according to my experience, do not represent the normal type of the intestine. Of course, we could not expect them to do so, for the number of cadavers he studied carefully appears to have been but three.
Henke's method of study was to make sketches of loops of intestine and then to remove them, sketching again the loop
•Henke, His's Archiv, 1891.
tGegenbaur, Anatomie, 1890, Bd. 2, S. .59.
^ Hoffmann-Rauber, Anatomie, 188G, Bd. 1, S. 557.
<> Testut, Anatomie, 1894, t. 3, p. 505.
II Quain, Anatomy, 189«, vol. 3, pt. 4, p. 103.
below. By combining the drawings he finally outlined the course of the intestine from the duodenum to the ca3cum. Of course, he examined a great number of intestines in fresh cadavers, but it is difficult to trace the course of the intestine in them, as the slightest disturbance will make one's result uncertain. While, therefore, he gives very little certainty regarding the course of the intestine, he states definitely that the course of the loops on the left side is horizontal to the body, while on the right side it is perpendicular.
A few years later Sernoff* studied a few cadavers more carefully and with more accurate methods than Henke, but did not verify Henke's result. Sernoff injected the cadaver with a large quantity of chromic acid, and in this way the intestine and mesentery were hardened in position. Then, alter opening the abdominal cavity, a cast was made of the intestine, and finally the surface loops were stained with fuchsiu. In this way the surface loops were marked after disturbing the intestine for purpose of exploration and measurement. Next the intestine was removed, showing the form and position of the mesentery which was left within the body. I'he method throughout is accurate, but the number of specimens is not numerous enough for any generalization of the position of the loops. Only two records of intestines in normal position are given, and although Sernoff believes that these are diametrically opposed to each other in position, I think it is not difficult to see that there is a great similarity in them. The fact that a higher loop may be on the right of a lower one in one case and the reverse in another does not necessarily overthrow a general scheme. Also, it is not of much significance regarding the general course of the intestine that in specimens 2 and 3 (he does not picture No. 2) the direction of the convolution is not horizontal above and to the left and perpendicular below and to the right.
Recently Weinberg! has studied a number of specimens in new-born infants very carefully. He gives good illustrations and descriptions of ten specimens which were studied with the method employed by Sernoff. In general, Weinberg's specimens are all after the same plan, showing that the intestine goes over and back, antero-posteriorly, beginning at the upper left side and ending in the lower right side. In seven specimens out of the ten the large upj)er segment of the jejunum lay in the left upper part of the abdominal cavity. In three specimens, only a short portion of the jejunum lay in the left hypochondriac fossa and the rest came up in contact with the ventral abdominal wall. The direction of the loop ill this region was mainly transverse to the body, and, in general, the extent of them was about two-fifths of the length of the small intestine. Following these loops there is a group of irregular convolutions which lie in the left iliac fossa, and include the middle fifth of the intestine. Then the intestine crosses the left psoas muscle, and the remaining two-tifihs of the small intestine lie between this and the right psoas, as well as ou the right side of the abdominal cavity. The direction of the convolutions of this portion is mainly perpendicular. The extent of the intestine which comes in contact
Sernoff, Internat. Monatsch. f. Anat. u. Phys., 1894. t Weinberg, Internat. Monatsch. f. Anat. u. Phys., 1896.
JOHNS HOPKINS HOSPITAL BULLETIN.
with the anterior abdominal wall is about one-third of its whole length, which corresponds with the measurements given by Sernoff for the adult.
In general, Weinberg's results confirm Henke's and give for my purpose the important intermediate stage between the foetus and the adult. I have also examined the intestine of a number of new-born babies after they had been hardened in situ in formalin or in carbolic acid and can confirm the work of Weinberg.
In describing the direction of the loops of the intestine in the various portions of the abdominal cavity it is not well to state the direction of the external loop to the body cavity, for this loop may be only the connecting link between two more important loops above and below. The main loops must be isolated whether they are superficial or deep, and the plane of the circle which they describe makes the general direction of the loop. If the intestine makes a continuous spiral, then the direction of any one of the loops is about parallel with the circles the loops describe ; but if the spiral reverses itself, then the connecting loop is at right angles with the plane of the circles. If this is not considered, it may be that the suj)erficial loops are perpendicular, while the main loops are transverse to the body axis.
POSITION OF THE INTESTINE IN FORTY-ONE CADAVERS.
The cadavers had all been carried in the sujiine position for at least two kilometers over the rough cobblestones of Baltimore before they were delivered at the laboratory, and this shaking may account for the regularity of the arrangement of the intestine. They were then injected with about 1.5 to 2 kilograms of carbolic acid crystals in the form of a 33 per cent, solution into the femoral artery. This coagulates completely the abdominal and thoracic viscera. After that the bodies were frozen and some of them were not studied until two years later, while most of them were opened at about the end of a year. The older bodies are preferable, as the surplus water has evaporated and the tissues are fairly dry and somewhat hard.
In all of these specimens the general direction of the intestine was diagonally across the abdomen from the left hypochondriac space towards the right iliac fossa, usually diverging once or sometimes twice towards the right side of the abdomen and always towards its end, into the cavity of the pelvis.
The general form and position of the mesentery is well shown in Fig. 17, as well as in Figs. 5 and 8 by Sernoff. These figures show the large curves made by the mesentery to attach itself to the loops, first on one side of the root of the mesentery and then on the other. I have tried to follow rather the greater groups of couvolutions, for it is hopeless to attempt to number every individual loop. .
In 31 of the specimens the arrangement of the loops was after the same plan ; therefore I shall consider this the normal, and the arrangements of the intestine in the other specimens as variations of this plan. In these specimens the jeji;num first arranged itself into two distinct groups of loops situated well up in the left hypochondriac region. Each group made more than a complete circle, and both of them
came in contact with the anterior abdominal walls. They are marked 2 and 3 respectively in Fig. 16, the loop 2 being the one which communicates with the duodenum. After this the intestine passes through the umbilical region to the right side of the body. This loop is marked 4 in the figure. Then the intestine recrosses the median line to make a few convolutions in the left iliac fossa (5), after which it fills the pelvis and lower abdominal cavities between the psoas muscles (6). The course of the intestine which has been pictured in Fig. 16 is given in Fig. 18.
When now this arrangement of the intestine is compared with that of foetuses XXXIV and XLVIII, as well as with Weinberg's specimens, it is fairly easy to see the gradual transformation of XXXIV into the adult type. Fig. 12 still shows the intestine about equally distributed on both sides of the body, with the caecum still very high. In Fig. 14 there is already a marked descent of the cfficum towards the future pelvis. In comparing these two figures it is to be observed that Fig. 12 is a ventral view and Fig. 14 a view from above. The outlines of the stomachs in the two figures will show from what point the models have been drawn.
When we pass from these two specimens to the figures of Weinberg, we see a similarity between them and most of his figures, but in a number of them the intestines have begun to shift more and more. In general there is a tendency for the irregular lines of mesentery to bend towards the left iliac fossa, for, with the descent of the csecum, the whole mesentery is rotating towards the left side. Weinberg's Fig. 18 shows this well. Hand in hand with this movement one or more loops move towards the right side of the body, as his Figures 11 and 19 show. As yet there is no marked pelvic cavity to take the lower end of the ileum, and as soon as the pelvis is large enough to hold it, we can easily imagine the intestine pictured by Weinberg in Figs. 5, 9, 11, 16, 17, 18 and 19 to be converted into my Fig. E by a simple descent of the ileum into the pelvic cavity. The other few specimens may be considered as variations.
In a shifting of this sort it is probable that the middle loops of the intestine would be transferred to the right side, while the upper half would remain on the left side, and the lower half in the pelvis and lower abdominal regions. According to Sernoff's three measurements, on an average 41 per cent, of the length of the intestine is on the left side, 41 per cent, in the pelvic cavity and about 18 per cent, on the right side. In embryos IX, X, VI and XLV the loops 2, 3 and 4 together are shorter than the loops 5 and 6, while in XXXIV and XLVIII, these first three groups are somewhat greater in length than the lower two. In the younger embryos it was the ileum which grows more rapidly, while in the older embryos the jejunum is beginning to overtake the ileum. So from these measurements, as well as from the indication in Figs. 12 and 14, it is the loop 4 which is destined to cross the middle line and to take its position on the right side of the body.
Heuke showed that it is not difficult to separate the intestine into two great groups, the dividing line of which is the left psoas muscle. This, usually, is also the limit between the loops 4 aud 5, as shown in Fig. 16. The diagrammatic
JOHNS HOPKINS HOSPITAL BULLETIN.
Fig. E shows this still better between loops 4 and 5. When the loops 5 are within the pelvis this separation made by the psoas is still more marked. Also in those specimens iu which the position of the intestine is as iu Fig. E, the loop 4 can be lifted towards the left side, making a beantiful demonstration of the attachment of this loop. A glance at Fig. 17, as well as at Sernoff's Figs. 5 and 8, will easily explain why this should be so.
Fig. E. — Scheme of the intestine. The arrows indicate the Tariations. The variations a and bb were most frequent ; the variation e least frequent.
VARIATIONrf IN THE POSITION OF THE INTESTINE.
One of the most common variations I have found is one in which there were no intestines on the right side of the peritoneal cavity. The loop 4 had been transferred to the left side of the body, as indicated in Fig. E by the arrow a. Otherwise the intestine had its usual position. It is this loop which is so easily isolated and, probably on this account, it is readily displaced by an enlarged caecum or ascending colon. It may possibly be that this loop can be shaken to the left side, and this could easily be tested by experiment. In one of these specimens the sigmoid flexure of the colon filled the right side of the abdominal cavity.
The second variation, as w^ell as the first, occurred six times. It is marked by the arrows bb in Fig. E. The loop 4 was again displaced to the left side, and the loops 2 and 3 were displaced to the right side. In other words, the very upper part of the jejunum formed the loop on the right side of the body.
The third variation occurred five times. In these specimens the intestine had its normal position, with the exception that an additional loop arose out of the pelvis and filled a portion of the right side of the body, as indicated by the arrow c. Sernoff's specimen, pictured in Figs. 3, 4 and 5, is to be included with this group.
The next variation occurred two times. It is indicated by
the arrows d in Fig. E. The large loop 4 was again drawn to the left side, and the space it formerly occupied was filled by two loops, one from the upper part of the jejunum, and the other from the lower part of the ileum.
The last variation occurred once. It is marked by the arrows e. The loop 4 was displaced and its place taken by a large loop which arose from the ileum within the pelvis. Henke's specimen B seems to belong to this group, if I can judge by his illustrations.
The variations given above all fit within the common scheme and can easily be explained. In all of my specimens I found but one extreme variation, and in this the intestine crossed the middle line at the beginning of the jejunum and then filled the right fossa. From here it descended immediately into the pelvis and filled it and the lower abdominal cavity completely. Then it left the pelvic cavity and filled the left fossa, extending up to the beginning of the duodenum. When it hud reached this point it took a fairly direct course along the descending colon over the floor of the pelvis, and passed directly to the cascum. Henke* has also described a variation practically identical with this. WeiubergI has also described one similar to this, only that the jejunum descends immediately to the pelvis and then gradually rises to the left side, and finally over to the right side. What kind of a mechanism can bring about this extreme variation is not possible to state.
It could be asiBerted that these few instances of marked variations indicate the normal, but in my specimens it is one in forty-two; in Weinberg's, one in ten; and in Henke's specimens it is not stated how many cadavers were examined carefully.
SHIFTING OF THE INTESTINE.
Henke has stated that the loops of the intestine may shift from one of the abdominal fossas to the other, and, no doubt, this is true. We are familiar with the fact that a distension of any of the pelvic viscera pushes all of the loops of intestine out of the pelvis,J and emptying it again allows the loop to descend to the floor of the pelvis. So likewise a distension of the colon or a certain number of loops of small intestines will displace a certain member of loops from their natural position. Since, however, the intestine was located after one plan in 41 cadavers, I do not think it probable that ordinary shaking will displace any number of loops. Pure mechanical disturbances, as by returning the intestines after operation, will also be overcome by the intestines shifting about to their normal position, guided by the attachment of the mesentery, its length and the space within the abdomen. To give this last question a thorough test I made a number of experiments upon dogs. In these animals the intestine is closely rolled up in a very regular fashion below the stomach, and the whole is carefully tucked in by the very large omentum. Upon opening an animal, one is struck with the neatness and accuracy of the
»Henke, His's Archiv, 1891, p. 101, Taf. IV, Fig. 12. \ Weinberg, Internat. Monatsch. f . Anat. u. Phys., 1896. I Among others, Garson, His's Archiv, 1878.
JOHNS HOPKINS HOSPITAL BULLETIN.
adjustment of the omentum, and it is easily disturbed by handling. When, however, the intestine and omentum are withdrawn through an abdominal wound, they are disturbed to such an extent that it is impossible to return them to the abdominal cavity as they were found, with the omentum covering them. After the intestines have been pushed into the abdominal cavity in a haphazard way and the animal sewed up, using all antiseptic precautions, the loops as well as the omentum readjust themselves as they were before, provided no marked inflammation takes place. So in the dog, the intestine and omentum seek their normal position after they have been disturbed.
Fia. 1. — Profile view of Embryo No. XII. Enlarged 38 times. The body wall over the heart has been cut out. Am, amnion ; UV, umbilical vesicle; OV, optic vesicle ; AV., auditory vesicle; Oa, third occipital muscle plate ; Cb, eigthth cervical muscle plate ; H, heart; P, pericardial cavity ; VOM, omphalo-mesenteric vein ; MR, membrana reuniens ; D, D', openings which connect the peritoneal cavities of the two sides with each other.
Fig. 2. — Same as Fig. 1, but half of the model has been removed to show the extent of the ectoderm and entoderm. Br', Br", first and second branchial pouches; M, mouth ; S, Seessel's pocket ; T, thyroid ; L, liver ; NC, neurenteric canal.
Fig. 3. — Intestine of Embryo II, viewed from the right side. Enlarged 34 times. C, caecum; M, mesentery ; y, remnant of yolk sac.
Figs. 4 and 5. — Intestine and liver of Embryo IX. Enlarged 25 times. C, ciecum ; OMA, omphalo-mesenteric artery ; HV, hepatic vein ; UV, umbilical vein ; PV, portal vein ; FW, foramen of Winslow ; GB, gall bladder.
Figs. 6 and 7. — Intestine and liver of Embryo X. Enlarged 12i times. U, position of umbilical vessels ; C, caecum ; FW, foramen of Winslow.
Figs. 8 and 9.— Intestine and liver of Embryo VI. Enlarged 12i times.
Figs. 10 and 11. — Intestine and stomach of Embryo No. XLV. Enlarged 16 times.
Figs. 12 and 13.— Intestine of Embryo No. XXXIV. Enlarged 4 times. Viewed from the ventral side. In Fig. 13 certain loops have been lifted off to show the deeper loops.
Figs. 14 and 15.— Intestine of Embryo No. XLVIII. Enlarged 2* times. The view is from the ventral and cephalic side of the model. The mesentery was not included in the model. Fig. 15 is a dissected model to show the deeper loops. The lower part of the intestine is enormously distended with cell debris, etc., showing that vermicular action is present at this early stage.
Fig. 16. — Usual position of the intestine in the abdominal cavity. Although this is an actual specimen, it represents the condition in twenty-one out of forty-one cadavers. The numbers in the figure mark the parts which are homologous with the loops correspondingly numbered in the other figures.
Fig. 17. — Usual position of the mesentery.
Fig. 18.— Course of the intestine. This figure is taken from a model made from the same cadaver from which Figs. 16 and 17 were drawn.
To summarize the results of this investigation in a few words : The active principle of the suprarenal capsule has been isolated iu the form of a powder of a light gray to brownish color, whose percentage composition is expressed by the formula CnHuNO*. A primary amine and a methylindol are easily split off from its molecule by treatment with powdered alkalies.
Should molecular weight determinations prove that the above formula correctly expresses the molecular weight of the new base, it will be seen that its molecule can contain only one substituted benzene ring in addition to the nitrogenous complex of atoms from which the skatol is derived. Oxidation and substitution experiments are, however, still necessary before more definite statements can be made as to the constitution of this compound.
In its native state, as found in the suprarenal capsule, this substance differs by one chejjiical reaction only from its state as described in this paper. Chemically considered, the difference in composition between its native state and as here described must be very slight. And yet this difference which is just marked enough to give a greater stability to the substance is also great enough, apparently, to deprive it of its power to raise the blood-pressure, for, jn the physiological experiments, thus far made, small quantities of the new base were found to be inactive in this respect.
I wish to express my thanks to my assistant. Dr. Walter Jones, for the valuable assistance rendered in making the analyses recorded in this paper.
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