Paper - The development of the spiral coil in the large intestine of the pig

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Lineback PE. The development of the spiral coil in the large intestine of the pig. (1916) Amer. J Anat. 20: 483-504.

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This historic 1916 paper by Lineback describes the development of the large intestine of the pig.

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The Development of the Spiral Coil in the Large Intestine of the Pig

Paul E. Lineback

Harvard Medical School, Boston, Mass.

Twenty-Three Figures (1916)


The student of human anatomy who happens to examine the viscera of the adult hog will be greatly impressed by the spiral arrangement of the ascending colon. For the colon in the pig, after arising from the caecum which is almost entirely on the left of the mid-ventral line, passes at once to the left, and then swings around the abdominal cavity in voluminous coils. The small intestines are mostly hidden behind it, though they appear in the right iliac fossa, and altogether the colon is the principal object seen when the abdominal cavity is opened.

To describe the course of the pig's colon in detail is a difficult undertaking, which John Hunter skillfully attempted in the following passage {Essays and Observations, 1861) :

It makes five spiral turns like a screw, coming nearer the center; at the end of which it is bent back upon itself, passing between the former turns as far as the first: but in this retrograde course it gets nearer the center of the screw, so that it is entirely hid at last, then makes a quick turn upward, adhering to itself and to the left kidney, as high as the first spiral turn; from thence it passes across and close to the spine, and before the mesentery, adhering to the lower surface of the pancreas, and, as it were, encloses the fore-part of the root of the mesentery; it then passes down the right side before the duodenum, gets behind the bladder, and forms the rectum.

Hunter's description was cited by Owen who notes that "the spiral turns of the colon, above described, form one of the characteristics of the Artiodactyle order." To a certain extent this is true, but the cow and sheep, and doubtless other forms, present considerable modifications of the arrangement found in the pig. These are all more or less adequately described in the text-books of veterinary anatomy. The spiral coil in the pig is clearly figured by Sisson, as seen both dissected and in situ, and he adds a diagram of its course.

The musculature of the pig's colon is also peculiar, in that it possesses two taeniae instead of three throughout most of its course, and it was while studying the development of these taeniae that my attention was diverted to the coil itself by Dr. F. T. Lewis. At his suggestion the following account of its embryological history has been prepared, and it is a pleasure to record my indebtedness to him for cooperating throughout this work. Such an extraordinary and conspicuous formation has not escaped previous study, but the existing descriptions are so meager that they should certainly be supplemented by further investigation. This was Martin's opinion when in 1889 he pubUshed the first of his papers containing most of the information now available.

In the Schweizer-Archiv fur Thierheilkunde Martin presents a series of diagrammatic figures showing the probable evolution of the spiral colon in the sheep, including hypothetical drawings of some stages which he had not actually observed. They are accompanied by a brief description, containing references to corresponding stages in the cow, but Uttle is said regarding the pig. In 1891 Martin supphed a new set of diagrams of the development in the sheep, and a fuller description. In brief, he considers that the colon, which previously has been quite straight, forms a loop, the apex of which soon becomes bent like a hook. The loop continues to elongate spirally, as one of its limbs grows slower than the other, and thus we have the beginning of the spiral coil."

In the same year ('91) Bonnet pubhshed modifications of Martin's earlier diagrams which are clearer, but apparently more arbitrary. He records the formation of a primitive loop of the colon" in embryos of the horse. This, he observed, has become somewhat S-shaped in a specimen measuring 10 cm., but it never makes more than one revolution. In the pig. Bonnet finds that a corresponding loop "winds itself spirally around an imaginary axis and forms the colon-labyrinth, later shaped like a bee-hive, consisting of 3^ concentric outer and 3^ excentric inner convolutions."

In 1901 MacCallum described the development of the pig's intestine, intending to show that its coils are measurably constant. In a 32-mm. embryo, he states that the large intestine, in the region where it turns to form the rectum" is thrown into 'irregular twists.' The complexity of this rectal group of coils is said to increase in later stages, but its further evolution is not described in detail. However, it is clear that MacCallum failed to find a primitive loop, produced from an otherwise straight colon, which elongated and grew into a helicoid spiral, as described by Martin and Bonnet; and in the following study it will be shown that the course of development is more complicated than these authors have represented.

Beginning with an embryo of 12 mm., it will be found, upon dissection, that the intestine has formed its primary loop extending into the umbilical cord, and that torsion has not yet occurred. The intestine at this stage may therefore be compared with that of human embryos of 7-10 mm. In both forms, the large intestine occupies the greater portion of the posterior hmb of the loop, beginning at the small bulbus coli, which marks the future caecum (fig. 1). The apex of the loop in the pig is more persistently attached to the vitelline duct than in man, and this duct has been cut across in figures 1 to 4. Moreover the length of the primary loop in the pig is greater than in human embryos. In the pig the distance from the base of the loop to its point of attachment to the yolk-stalk is between 1 and i of the length of the entire embryo. (For example, in figure 1 it is J, and in the reconstruction of a 12-mm. pig by Lewis it is I). In human embryos possessing a primary unrotated loop, as reconstructed by His, Elze, and Lewis, the length of the loop is between 7 and 1^ of that of the whole embryo. It is not improbable that the distinctly longer and more slender loop in the pig provides for the more extensive intestinal convolutions, characteristic of the pig in the stages immediately following.

In pig embryos of 24 mm. the torsion of the primary loop has begun, so that the large intestine passes across the left side of the duodenum and becomes the anterior limb of the loop (fig. 2). It extends from the freely-projecting caecum in a remarkably straight course, free from all convolutions, to the rightangled bend where it descends to the rectum. The other hmb of the loop, which forms the small intestine, has become three times as long as the colic limb and is thrown into many convolutions, arranged in linear series. Together they form a striking and characteristic figure quite unlike anything seen in human development. By referring to Mall's reconstructions of the intestines of two 24-mm. human embryos (1897, Tafeln 21 u. 22) or to Johnson's more comparable drawing of a 22.8-mm. specimen (Lewis, '12, p. 321) the differences will be apparent.

According to Mall ('97) the convolutions of the human small intestine are quite constant, and there are six w^hich are primary. With many secondary subdivisions, he found that these could be identified in the adult. Following Mall, MacCallum studied the development of the coils in the pig and likewise found that in "embryos of the same size the coils are constant in their arrangement and definite in their position." But this conclusion ought not to be accepted without further investigations. In MacCallum's figures .of embryos of 23 and 25 mm., there is a well-marked stretch of small intestine toward the apex of the loop, which is quite free from coils. No such interval is shown in figure 2, and having found it but once in many embryos dissected, I must regard it as exceptional. The four primary groups of MacCallum are not apparent in my specimens, and the individual coils in figure 2 cannot be homologized with those in MacCallum's reconstructions.

The torsion of the primary intestinal loop is carried much further in the pig than in man. The human intestine rotates through an arc of approximately 180°, so that the original posterior limb becomes anterior and vice versa. That is, it accomplishes such a rotation as is nearly completed in figure 2 and stops at that point. But the pig's intestine goes further, performing a complete revolution, as shown in figures 3 and 4.

After this rotation of 360°, the Hiiib of tlie loop which was originally posterior has again become posterior (as seen by comparing figs. 1 and 4), but the anterior limb now crosses it twice. As duodenum, it passes down on the right side of the colic or posterior hmb, then bends to the left beneath the colon, and finally passes upward crossing the colon a second time, but now on its left side. Figure 3 is an interesting intermediate stage in this process. The first rotation, of 180°, has been completed, even to the apex of the primary loop (which is not the case in figure 2), and the second rotation of 180^ has occurred in the proximal part of the loop, but not distally. The rotation extends from the proximal portion of the loop outward, and the process has been completed in the distal part of the loop in figure 4.

Martin observed a similarly complete rotation in tlie sheep and described it as follows:

The more the small intestine forms coils, the more it crowds the recurrent colic limb dorsally and at the same time to the right and caudally, until it is surrounded b}^ a ring of coils of small intestines; and the half axial rotation about the mesentery in a 56-day embryo is transformed into a complete rotation. Thereby the relation of duodenum to the large intestine becomes changed. Earlier only' a simple crossing took place, but now there is an encircling.

In the pig, MacCallum described the rotation in connection with the various groups of coils which he recognized. Thus he states that 'Group D,' which includes those coils of the small intestine which are nearest the caecum, "has rotated posteriorly, dorsally, and to the right It thus moves past Group C and carries the caecum with it, so that the beginning of the large intestine lies dorsally and posterior to Group D." Correspondingly a group of coils of the large intestine (Group E) is said to "rotate through three-quarters of a circle." Although it is apparent that the rotation was observed, its description is unnecessarily involved, since it is based on groups of coils of questionable distinctness, rather than on the limbs of the primary looi?.

The formation of coils in the large intestine begins in pig embryos of about 30 mm. At 35 mm. (fig. 4), they are well developed and are gathered in a knot between the caecum and the splenic flexure. This flexure it should be noted, is the only one which is found in the pig, so that the pig's ascending colon corresponds with both the ascending and transverse colons of human anatomy. A sinuous condition, preceding the formation of distinct coils, is seen in the 30-mm. embryo, figure 3. Similarly MacCallum found coils of the colon in pigs of 30 and 32 mm., and at 40 mm. he states that they 'form a conspicuous mass.'

The transformation of the mass of coils into the well-arranged spiral of the adult may be followed in special dissections, and from a large number of such preparations ten have been chosen for illustration (figs. 5 to- 14). The final condition is shown in figure 14, representing the colon from an adult, and this is preceded by a figure of the spiral foiu' weeks after birth (fig. 13). The other drawings are from embryos ranging from 50-120 mm. Throughout the series, the small intestines have been cut away near the colic valve, but in figures 5 to 11 a short piece of the ascending portion of the duodenum has been retained for orientation. Around this the colon makes a characteristic bend, and then, at the splenic flexure, it becomes the descending colon, which is free from coils or kinks even in the adult. In all the dissections the rectum has been cut away, and the entire mesentery has been removed. The coils of the colon have separp.ted from one another, but only so far as necessary to show the course of the tube. This necessitates a slight displacement of some of the flexures, but none has been omitted or radically altered.

In order to understand the stages in embryonic development included in this series, it is necessary to have in mind certain features of the condition to be finally attained, which are presented in figures 15 to 19. The apical portion of the coil in the adult (fig. 14), and likewise in the more advanced embryos, presents the curious pattern shown in figure 15 (from an embryo of 200 mm.). The observer will be uncertain whether the point a or the point b is the actual apex. If a is selected, the adhesions of the mesentery and of the adjacent coils may be torn apart so that the spiral may be unwound as shown in figure 16. It would then consist of two parallel limbs, which, in this specimen, make 3| revolutions. If b is taken as the apex, the coil may be unwound as shown in figure 17. Beginning at the valve of the colon as before, there are now only three revolutions. It is evident, however, that the unwinding shown in figure 16 is natural, and that the other is an 'artificial' dissection, for the adhesions yield more readily in the former and there is less tearing of the mesentery. Moreover, at the base of the spiral, the proximal and distal limbs of the coil early become adherent to one another and to the body-wall, establishing a fixed point. The basal hmbs retain this position in figure 16, but have been separated in figure 17, so that, the former is clearly the correct picture, and the true apex is at a.

Additional revolutions may take place without changing the apical pattern. If half a turn is added to the coil shown in figures 15 and 16, the bend a will be carried up between y and z toward b, and the conditions shown in figures 18 and 19 will result. In figure 19 the bend ap, which before unwinding the coil appears to correspond with b in figure 15, is clearly the true apex.

The number of revolutions actually produced varies, and small fractions, generally neglected, appear quite as often as whole or half turns. Hunter, in the passage cited, speaks of 'five spiral turns,' evidently referring to the five tiers shown in figure 14. In this specimen, however, beginning at the valve of the colon, there are but four revolutions, and this appears to be the normal number. Bonnet's statement that there are 3^ can be applied to this specimen only by regarding b as the apex instead of a.

The length of the spiral portion of the colon in the young adult (fig. 14) is 2.6 meters. The distance from the cohc valve to the apex is 1.4 meters, or 53 per cent of the total length. Thus the apex is finally located just beyond the middle of that part of the colon which forms the spiral.

In the following description the terms proximal or outer limb will be applied to the part of the colon leading from the caecum to the apex, and distal or irmer limb to the part from the apex to the splenic flexure. The inner hmb in the adult is of much smaller diameter than the outer, except toward the apex; and its revolutions, which closely accompany those of the outer limb, are hidden within the dome-shaped mass. Having in mind these relations and the descriptions of previous writers that a primary loop, with its apex at the middle point, simply winds up to produce the adult form, the conditions in the embryo may be carefully examined.

At 50 mm. (fig. 5), as in' the adult, the colon may be divided into two nearly equal parts. The proxitmal half (in fig. 5 and in the following drawings) has been heavily stippled to contrast with the distal half. Beginning at the caecum, which at this stage points ventrally, the colon passes toward the dorsal bodywall, near which it makes a rather sharp turn and doubles back upon itself. After running ventrally it redoubles by a sharp turn and goes dorsally. This folding continues back and forth throughout the proximal half. Distally the colon consists of several short coils, irregularly arranged, w^hich become adherent to the body-wall near the duodenum. Except at this fixed point, the colon at this stage is freely movable.

The most notable feature of the followdng stage (fig. 6, from an embryo of 55 mm.) is the elongation of the first loop in the proximal half of the colon. The proximal or outer half of this first loop is now clearly a portion of the basal convolution of the permanent spiral. In figures 7 and 8 (from embryos of 64 and 75 mm. respectively) the first coil has further elongated, accomplishing, in figure 8, one half of a revolution. In connection with this development, the caecum has shifted toward the left of the bod}'- where it becomes permanently located, and the entire colon has become twisted upon itself, duplicating the torsion of the primary intestinal loop of earher stages. In other words, the part of the colon toward the caecum has come to cross the left side of the distal part of the colon, just as, in the 24-mm. stage (fig. 2), the large intestine crosses the left side of the small intestine. In fact the arrangement shown in figure 8 might well suggest to a student of human embryology a large intestine surrounding coils of small intestine. Where the crossing takes place, the proximal and distal portions of the colon become adherent to one another and thus the basal ends of the ascending and descending portions of the future spiral become fixed. It is therefore from this basal portion outward that the future spiral is to be established, clearly necessitating a rearrangement of the irregular coils existing in the 70 mm. stage.

From the stages which have now been considered, it is evident that the method of development in the sheep described by Martin and accepted by Bonnet is not applicable to the pig. The colon does not present a simple primary loop, but shows many convolutions. It is true that among these the first or basal loop has a definite bend or apex as seen in figures 5 to 8, but this, unlike the apex in Martin's primary loop, does not become the apex of the spiral in the adult. If it did so, the proximal tenth of the colon in the 50-mm. pig must produce the proximal half of the adult spiral, and the distal nine-tenths would produce only the distal half; but there is no evidence of such unequal growth. It is therefore reasonable to suppose that the proximal half in the embryo, which has been heavily stippled, will produce a correspojiding proportion in the adult. Accordingly the future apex may be approximately located at the transition between the dark and hght stippling, at a point' which in these stages has not been definitely established.

The continued advance of the spiral arrangement of the outer coil is clearly shown in figures 9 and 10 (embryos of 90 and 95 mm. respectively). No further torsion of the colon than that already recorded has taken place, but the winding up of the outer basal coil has advanced from | a revolution in figure 8, through 1 revolution in figure 9, to 2 complete revolutions in figure 10. The way in which the bends of earher stages are obliterated in this process is suggested in figure 9, where several are evidently about to be taken up in a well-rounded curve. The first of these, at a, has nearly disappeared. It occurs at a point 2% of the distance from the ileo-colic junction to the place where the colon comes into relation with the duodenum. In figure 8 the apex of the bend a is at I, of this distance, and accordingly the flexures labelled a in the two figures may be regarded as homologous. But in figure 9, a no longer marks the apex. The bend which it designates has been incorporated in the outer coil, together with the reversed bend h, and a new apex appears at c (which may fairly be compared with c in figure 8). Beyond this point, in figure 9, the proximal half of the colon still pursues a zig-zag course as in earlier stages, but it swings back and fourth through shorter arcs, and the transfer of the apex from c to ^ is alrejidy suggested. To accomplish this, the flexures d, e, and / are destined to pass through the condition at present exhibited by a and h. In the 95-mm. embryo (fig. 10) this has taken place, and slight irregularities in the outer coil are all that remain of the former to-and-fro oscillations.

The outer or ascending spiral develops in advance' of the inner, descending spiral, as may be seen in the figures already examined. The coils in the distal half of the colon are quite disorganized in figures 5 to 8. Beginning in figure 9 (at g) and more extensively in figure 10, the apical portion of the ascending coil is accompanied by a descending coil, and thus the final relation between the outer and inner coils is beginning to appear. An apex is thus estabhshed which will not advance further by taking up flexures in its path, but chiefly through elongation, which it shares with the rest of the colon, and by becoming more tightly wound about its axis. However, it will be shown that a slight advance of the apex along the inner or descending limb is yet to occur, at the time when the characteristic apical pattern is produced.

The final stages are shown in figures 11 to 14. In the embrj^o of 110 mm. (fig. 11) three revolutions have been completed, and except for the loosely wound apex, the spiral appears finished. ^ The flexure a is destined to turn to the right and upward into the concavity of the flexure c, and thus it will form the apical pat ^ The counting of the revolutions in the figures will be facilitated by placing a straight edge from the ileo-colic junction to the apex tern already discussed. At the same time the apex will advance from a to 6. This has happened in the 120-mm. embryo (fig. 12), and accordingly 3| revolutions are there present. The same is true of the coil from a pig four weeks after birth (fig. 13). Gradually the spiral becomes more compact and its coils more adherent to one another, and at the same time the portions of the inner coil which are visible on the exterior become buried. These changes are clearly shown in the figures. In the adult (fig. 14) the apex of the coil has rotated so that instead of pointing downward, it is directed toward the left, and thus four revolutions are completed. Less of the inner coil is exposed than at birth, and only half a turn can now be observed at the apex. With these relatively slight changes in the constitution of the coil, its general appearance has been transformed through the development of the sacculations, which at birth are scarcely indicated.

The principal morphological feature of the developing coil which the figures fail to suggest, is its increase in size and much greater increase in length. This can be shown by measurements; and at the same time the position of the apex can be more accurately located. The following table, therefore, includes the total length of the spiral part of the colon (from the cohc valve to the contact with the duodenum), and also the distance from the colic valve to the apex of the coil. The apex in the earlier stages is temporary, and in the 95-mm. specimen (fig. 9) it must be chosen somewhat arbitrarily. When the distance from the colic valve to the apex of the coil has reached 50 per cent of the length of the entire spiral, the permanent apex has presumably become estabhshed. Accordingly, in the table, the distance to the apex is followed by the percentage, which it represents, of the spiral part of the colon. Measurements of the small coils are made with some difficulty, so that the results are only approximately correct; but even with these limitations, the measurements are found instructive.

Stage of development

Spiral part of colon

From colic ■

valve to the apex

50 mm.





, 10 per cent

55 mm.





, 12 per cent

64 mm.





, 10 per cent

75 mm.





, 15 per cent

90 mm.





, 25 per cent

95 mm.





, 38 per cent

110 mm. 2





, 50 per cent

120 mm.





, 56 per cent

4 weeks





, 50 per cent

6 weeks





, 51 per cent

young adult





, 53 per cent

Average of two specimens.

The way in which the coil develops suggests the possibihty of several sorts of anomaUes, some of which were observed in a series of one hundred adults and one hundred embryos examined for this purpose. Five of the adults had coils with an additional half- turn, just as the embryo of 180 mm. shown in figure 18 has half a turn more than is usual at that stage (cf. fig. 16). No adult showed less than four revolutions, and none showed reversals or other malformations of the spiral. Among the embryos, anomalies were more abundant. Figure 21 represents the colon of an embryo of 55 mm. which is placed beside a normal one (fig. 20) for comparison. In the anomaly the basal coil has begun to rotate dorsally and to the right, in the reverse direction. Three other specimens of coils reversed from the base were found among the one hundred examined. A second type of anomaly was observed in an embryo of 108 mm. (fig. 23, likewise placed beside a normal specimen, fig. 22). Here the spiral began to wind in the normal direction, but evidently encountered a sharp flexure which could not be taken up, so that a reversal occurs at the point x. Presumably at a stage corresponding with that shown in figure 8, such a bend as is there labelled a persisted, and the advancing apex took the direction of the flexure b. Accordingly, beyond the point x in figure 22 the coil is reversed. The inner coil has adapted itself to the outer throughout, and in its concealed portion it reverses its course opposite x. Another very similar anomaly was found in an embryo of 95 mm., in which the inner coil likewise reversed so as to accompany the outer in its abnormal course. Since six cases of partial or complete reversal were found in one hundred embryos and none among one hundred adults, the question arises whether the condition may be ultimately corrected, or whether like a volvulus, it may lead to fatal results. But the number of specimens examined is perhaps too small to be significant in this respect.


In a series of drawings which largely explain themselves, an attempt has been made to present the development of the colon in the pig in greater detail than heretofore.

The torsion of the primary intestinal loop, which in man stops at 180*^, proceeds to a complete revolution in the pig; in this it corresponds with the development in the sheep as described by Martin.

But the spiral coil in the pig does not begin as a single loop of the colon which simply winds up, as in the sheep, according to Martin and Bonnet. On the contrary it arises as a knot of kinks and coils. The first of these forms the basal portion of the outer limb of the permanent spiral.

Within the limits of the colon there then appears a rotation or torsion, so that the proximal part crosses the distal part, and the basal coil encircles the other convolutions in the way that the human colon encircles the small intestine.

The basal coil advances by taking up secondary flexures in its path until it makes two revolutions. By that time the apex of the coil is about midway in the course of the spiral part of the colon, and further growth of the spiral is chiefly by the coiling of the apex. In estabhshing the characteristic apical pattern, however, the apex advances half a turn further along the inner or descending limb of the coil.

In case the basal loop is turned in the wrong direction, or if having started normally it encounters bends which do not yield, complete or partial reversals of the spiral occur, six cases of which Y\'ere found in embryos.

Literature Cited

Bonnet, R. 1891 Gruridriss der Entwickelungsgeschichte der Haussaugethiere. 272 pp. P. Parey. Berlin.

Elze, C. 1907 Beschreibung eines menschlichen Embryo von zirka 7 mm. grosster Lange. Anal. Hefte, Abth. I, Bd. 35, pp. 409-492.

His, W. 1885 Anatomie menschlicher Embryonen. III. (Eingeweiderohr, pp. 12-25). F. Vogel, Leipzig.

Hunter, J. 1861 Essays and observations on natural history (etc.). Posthumous papers, edited by R. Owen., vol. 2, (pp. 120-121 cited.) Van Voorst, London.

Lewis, F. T. 1903 The gross anatomy of a r2-mm. pig. Am. JoUr. Anat., vol. 2, pp. 211-225.

1912 The earlj^ development of the entodermal tract. Human Embryology, ed. by F. Keibel and F. P. Mall, vol. 2, pp. 295-334. Lippincott, Philadelphia.

MacCallum, J. B. 1901 Development of the pig's intestine. Johns Hopkins Hosp. Bull., vol. 12, pp. 102-108.

Mall, F. P. 1897 Ueber die Entwickelung des menschlichen Darmes. Arch, f. Anat. u. Entw., Jahrg. 1897, Suppl.-Bd., pp. 403-434.

Martin, P. 1889 Die Entwickelung des Wiederkauermagens und -Darmes. Schweizer-Arch. f. Thierheilkunde, Bd. 31, pp. 173-214. 1891 Die Entwicklung des Wiederkauermagens und -Darmes. Festschr. f. Nageli u. Kolliker, pp. 59-80.

Owen, R. 1868 On the anatotoy of vertebrates, vol. 3 (p. 474 cited). Longmans, London.

SissoN, S. 1914 The anatomy of the domestic animals. 2d. edition, (pp. 483488 cited). Saunders, Philadelphia.


All the figures represent dissections of the intestines of the pig.

Figs. 1-4 The stomach and *he small and large intestines seen from the left side. X 14 diam. Figure 1, embryo of 12 mm.; figure 2, 24 mm.; figure 3, 30 mm.; figure 4, 35 mm. b.c, bulbus coli.

Figs 5-7 The coils of the colon, slightly displaced so that their course „,ayb 'followed, seen obliquely in left-ventral view. Figure 5, embryo of 50 mm -figure 6, 55 mm.; figure 7, 60 mm. tall X 14 diam. Cae., caecum, Col. asc, TendTng colon; Col. desc, descending colon; Duo., duodenum; 11, deum.

Figs. 8-10 Same dissection and view as figures 5-7. Fig. 8, 75 mm. ; figure 9, 90 mm.; figure 10, 95 mm.: all X 10 diam.

Figs. 11-12 Late stages in the development of the spiral coil of the colon. Figure 11, embryo of 110 mm.; figure 12, 120 mm.: both X 7 diam.

Figure 13, from a pig 4 weeks after birth; natural size. Figure 14, from a young adult; ^ natural size.

Figs. 15-19 Sketches showing the arrangement of the spiral and its apex. Figure 15, the apical pattern, and figures 16 and 17, two methods of unwinding the coil, from an embryo of 200 mm. Figure 18, the spiral and figure 19, its apex, from an embryo of 180 mm. ; the spiral here presents half a revolution more than that shown in figures 15 to 17. The letters mark points referred to in the text.

Figs. 20-23 Anomalies of the spiral. Figure 21, abnormal coil from an embryo of 55 mm., placed beside a normal specimen (fig. 20) for comparison: X 14 diam. Figure 23, an abnormal coil from an embrjj^o of 120 mm., placed beside a normal coil (fig. 22) from an embryo of 100 mm. : X 7 diam.

Cite this page: Hill, M.A. (2020, July 10) Embryology Paper - The development of the spiral coil in the large intestine of the pig. Retrieved from

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