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العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Grosser O. Lewis FT. and McMurrich JP. The Development of the Digestive Tract and of the Organs of Respiration. (1912) chapter 17, vol. 2, in Keibel F. and Mall FP. Manual of Human Embryology II. (1912) J. B. Lippincott Company, Philadelphia.

XVII. The Development of the Digestive Tract and of the Organs of Respiration: Introduction | Early Entodermal Tract | Mouth and Its Organs | Oesophagus | Stomach | Small Intestine | Large Intestine | Literature | Liver | Pancreas | Pharynx and its Derivatives | Respiratory Apparatus | Figures | Literature
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Intestine Development

The Development of the Small Intestine

Frederick Thomas Lewis
Frederick Thomas Lewis (1875-1951)

By Frederick T. Lewis


The early stages in the histogenesis of the small intestine are like those of the stomach, which have already been described. The further differentiation of the epithelial tube proceeds as follows :

Vacuoles in the Duodenal Epithelium

In embryos of 6.5 and 7 mm. the duodenum usually presents a well-defined round lumen, bounded by a 2-3 layered epithelium. In slightly older embryos the epithelium proliferates, and vacuoles are formed within it, especially on the dorsal and right sides of the tube. Later the proliferating epithelium bridges and subdivides the original lumen, as seen in the section of a 10 mm. embryo, Fig. 279, A. Of the three cavities found in this section, the upper one is a vacuole, and the two lower ones are parts of the original lumen. In this embryo there is still a continuous passage from the stomach to the jejunum. The outer surface of the epithelial tube is generally smooth, but occasionally at this stage — niore frequently in somewhat older embryos — the masses of cells surrounding the vacuoles produce local bulgings of the basement membrane. At 22.8 mm. (Fig. 279, B) the outpocketings are so numerous that the epithelium appears folded, and mesenchyma has begun to extend inward between the pockets or folds. In sections the vacuoles cannot be distinguished from the main lumen. A model of the duodenum of this embryo, made by F. P. Johnson, shows that the passage from the stomach to the jejunum is completely blocked by epithelial septa (Fig. 280). At 30 mm. (Fig. 279, C) the vacuoles begin to become confluent so that a central lumen is re-established. The projections between the vacuoles remain as the foundations of villi.


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Fig. 279. — Cross sections of the duodenal epithelium. X 130 diam. A, at 10 mm. (Harvard Collection, Series 1000). B, at 22.8 mm. (Harvard Collection, Series 871). C, at 30 mm. (Harvard Collection, Series 913).


Tandler (1900) was the first to recognize that the duodenal lumen, in embryos from " 30 to 60 days," is normally "more or less completely " obliterated. In an 8.5 mm. specimen he recorded a complete obliteration between the outlets of the duct of the dorsal pancreas and the common bile-duet. At 14.5 mm., when the proliferation is at its maximum, he found that the bile and pancreatic ducts emptied into closed cavities, and that below them the duodenal epithelium formed a solid cord of cells. Forssner (1907) likewise found that, in places, the lumen was completely obliterated in embryos of 11.7, 14, and 22.7 mm. ; and at 30.5 mm he described transverse septa dividing the lumen into compartments. Other embryos, of 18.5, 21, and 31 mm. respectively, showed no epithelial vacuoles or occlusions. Schridde (1908) failed to find a solid stage.


Tandler considered that the cause of the occlusion was the resistance exerted upon the expanding epithelium by the surrounding mesenchyma. He found that the diameter of the mesodermal tube of the duodenum increased very slowly in embryos from 7 to 15 mm., whereas from 15 to 20 mm. the increase is rapid. Forssner has confirmed this observation, and thinks it " not improbable that purely mechanical factors play a part in producing occlusions." Both Tandler and Forssner have compared the vacuolization in the duodenum with* that in the oesophagus.


Vacuoles {Diverticula) in the Jejunum and Ileum

The lower portion of the small intestine never presents a subdivided lumen such as is found in the duodenum, but its epithelium contains scattered vacuoles, which develop in a very characteristic manner. These vacuoles occur chiefly along the portion of the intestine found within the umbilical cord, and they are situated along the convex surface of the intestinal coils, opposite the mesenteric attachment.

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Fig. 280. — Model of the duodenum of a 22.8 mm. embryo (Harvard Collection, Series 871), seen in longitudinal section. X 120 diam. (After F. P. Johnson.) In an embryo of 14.5 mm. there are three of these structures, all of which are near the bend of the primary loop of intestine. In a 16 mm. specimen seven were counted, and at 22.8 mm. thirty-two were present.


The intestinal vacuoles are first indicated by a concentric arrangement of the basal nuclei, and in this stage they have been described as "buds" or " pearls.' 1 In the centre of such a bud a small cavity can often be detected (Fig. 281, A). In later stages the cavity communicates with the intestinal lumen, and the bud forms a knob-like basal projection (Fig. 281, B). These projections often have a somewhat constricted neck, and the overhanging portion may become asymmetrical, extending aborally along the intestine. Thus Fig. 281, C, is an aboral section of the diverticulum shown in B. Four of the thirty-two diverticula in the 22.8 mm. embryo project aborally. One diverticulum, longer than any of the others, extends laterally so that its tip penetrates the dense mesenchyma of the muscularis (Fig. 281, D). Usually they are in close relation with the epithelial layer, and they cause no disturbance in the course of the circular muscle fibres. In older embryos (Fig. 281, E and F) the folded appearance of the epithelium renders the detection of the diverticula more difficult. It is probable that, by the enlargement of their necks, some of them are incorporated in the general epithelial layer. Others, however, retain their identity. One of these was found and modelled by F. P. Johnson in an embryo of 134 mm., — a stage when the villi are well developed and the intestinal glands are being formed (Fig. 282). Some of the glands open into the base of the diverticulum. Around it the mesenchyma is dense and suggests the formation of lymphoid tissue. This is apparently the oldest embryo in which such a structure has been found, and they are not known to occur after birth.

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Fig. 281. — Cross sections of the epithelial tube of the intestine, showing the development of diverticula . X 130 diam. A-D, from an embryo of 22.8 mm. (Harvard Collection, Series 871). E and F, from an embryo of 30 mm. (Harvard Collection, Series 913).


The intestinal diverticula were described independently by Keibel (1905) and Lewis and Thyng (1908). Keibel noted and figured the two stages in their development (buds and diverticula) and recorded their presence in several mammals, including man. Lewis and Thyng described similar structures, but included with them certain more compact buds which occur chiefly on the dorsal wall of the intestine in the lower duodenal region. These were found frequently in the pig. In an 18.1 mm. human ernbryo there are two buds of this sort situated on the dorsal wall of the intestine as it turns forward to enter the umbilical cord. Lewis and Thyng compared the diverticula with somewhat similar structures found along various epithelial tubes, such as the mammalian bile-ducts and the large intestine in amphibia. They appear to be localized centres of cell proliferation, which either arise in the outer layers of the intestine or are due to the outward displacement of mitotic cells from the innermost layer. Thus mitotic figures appear to be limited to the inner laj^er and the diverticula, but their distribution requires further study. Elze (1909) has stated that a sharp distinction should be made between the dorsal diverticula of the upper intestine and the ventral diverticula which arise later lower down. He was the first to record the typical aboral growth of the latter. It is probable that the vacuoles of the cesophagus, stomach, duodenum, and intestine are comparable structures.


The Formation of Villi

The development of villi begins in the upper part of the small intestine and extends downward. In the duodenum their formation is complicated by the presence of the epithelial proliferations described in the preceding section. There, as seen in Fig. 279, B and C, the epithelial tube expands by producing irregular outpocketings. Forssner (1907) agrees with Tandler that the epithelium is invaded by mesenchymal papillae, but the apparent invasion is probably due to irregularities in the expansion of the epithelium. Such elevations as are seen in Fig. 279, C, have been described both as folds and as villi.

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Fig. 282. — Model of the intestinal epithelium from an embryo of 134 mm., showing villi, glands,, and, in the centre, a "flask-shaped gland." X 80 diam. (After F. P. Johnson.)


According to Meckel (1817), the first elevations are longitudinal folds which become gradually indented along their crests, and are thus broken apart into villi. This interpretation has been defended by Berry (1900), who found folds, but no villi, in a human embryo of 24 mm. At 28 mm. the folds, as seen in his reconstructions, show indications of transverse furrows, as if they were about to break up into blocks or villi, and in later stages he found that villi had replaced the folds. Forssner (1907) agrees with Meckel and Berry. Kolliker (1861), on the contrary, states that the villi arise in the beginning of the third month as wart-like outgrowths of the mesenchymal layer, which push the epithelium before them and become cylindrical. This was confirmed by Barth (1868). Brand (1877) found scattered villi at one and a half months. Voigt (1899), by means of reconstructions of pig embryos, found that depressions and furrows develop on the free surface of the epithelium, marking out areas of greater diameter than the future villi. These apparent epithelial elevations are due to the downgrowth of the surrounding furrows. They are described by Voigt as the bases of the future villi.


Johnson (1910) states that villi begin to develop in 19 mm. embryos. At 22.8 mm. he describes isolated rounded elevations occurring between the pylorus and the duodenal occlusion, and .also in the upper part of the jejunum. In a model (Fig. 283, A) he has shown the transition from the villous portion of the jejunum to the smooth part, and has found that the villi in this region arise independently and not as subdivided folds. In the corresponding portion of the intestine of a 24 mm. embryo, the villi are more numerous (Fig. 283, B). . Although they are arranged in five more or less definite longitudinal rows they do not appear as subdivided folds. At 30 mm. villi are found throughout the upper half of the intestine, but there are none in the ileum. The latter, in cross section, generally shows a trifoliate or four-lobed lumen, due to longitudinal folds of variable length. As this portion of the intestine expands, these folds seem to be obliterated, but villi arise at that time and it is possible that the villi in the ileum are remnants of the folds. The definite relation between theni described by Meckel and Berry is not shown in Johnson's models. At (footnote 42) 387 mm. there are still a few distal coils of the ileum which are without villi. According to Berry they do not extend to the colon at 80 mm., but are found throughout the small intestine at 130 mm.

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Fig. 283. — Models showing the development of villi in the upper portion of the jejunum. X 110 diam. (After F. P. Johnson.) A. from an embryo of 22.8 mm (Harvard Collection, Series 871). B, from an embryo of 24 mm (Harvard Collection, Series Template:HEC24).


During these and later stages the villi increase greatly in length, but their diameter remains nearly constant. Many new villi develop among the old ones, and the way in which they are formed is shown in Fig. 279, C. At the bottom of an outpocketing a secondary elevation appears, which increases in height with the expansion of the epithelial tube. By relatively rapid growth these elevations attain a length equal to that of the older villi.


Another explanation for the uniform height of the villi is given by Fusari (1904). He finds that the distal ends of the older villi degenerate and are cast off simultaneously, forming, with the mucus, a sort of membrane. This process " is certainly repeated at least twice." These observations, however, have not been confirmed, and the appearances are perhaps due to post-mortem degeneration.


At 55 mm. approximately 12 villi are seen in a cross section of the middle portion of the intestine, and at 99 mm. there are 25. Berry has estimated that in an 80 mm. embryo there are 50,000 villi in the entire intestine, and at 130 mm. the number has increased to 330,000. He finds that fully developed villi and young villi exist in the growing intestine side by side, and this conclusion is well established by the reconstructions of Voigt, Berry, and Johnson.


The epithelium covering the elevations in the 30 mm. embryo is thinner and more definitely simple than that in the depressions. At 55 mm. the epithelial cells of the villi are columnar, with conspicuous cell walls and bulging top plates. The rounded nuclei are somewhat below the middle of the cells, and the protoplasm of the outer part is remarkably clear. In the hollows between the villi the nuclei are more oval and the cells are more crowded. The protoplasm is granular. Altogether the epithelium of the depressions appears much darker than that of the villi. In both regions, however, there are occasional dense triangular or saucershaped nuclei, apparently belonging with goblet-cells. Sometimes nuclei are seen displaced outward, but these do not resemble the wandering cells of later stages. Baginsky (1882) contrasted the clear cells of the villi with the dense cells in the hollows between them, as seen in the jejunum at 4 months, and he described the depressions as the first stage in gland formation.


The Formation of the Intestinal Glands

The intestinal glands (of Lieberkuhn) develop gradually among the deeply staining cells in the hollows between the villi, appearing first in the duodenum. As the villi increase in number, the rounded hollows between them give place to narrow clefts, along the base of which knobs and short tubules extend downward. Glands in the form of short tubules are present, near the pylorus, at 78 mm.


At 91 mm. they occur in the middle part of the duodenum, but below this, in the sections examined, they are still absent. They are found in the middle portion of the small intestine at 120 mm., and their size at 134 mm. is shown in the model, Fig. 282.


Brand (1877) found no trace of the glands at 3 months, and states that they first appear in the upper part of the small intestine in embryos of 3 1-2 months (110 mm.?). He considered that they are epithelial pits due to the partial fusion of the bases of adjacent villi. Barth (1868) had previously stated that they are produced by the upward growth of the surrounding mesenchyma, but Kolliker (1861) had described them as tubular downgrowths of the epithelium. Voigt (1899), Hilton (1902), and Johnson (1910) agree with Kolliker.


New glands arise at first as independent buds at the base of the villi, but the older glands branch dichotomously, as observed by Baginsky in a 7 months ' embryo. Branched glands are frequent at birth, and doubtless the branches subsequently become independent glands. Thus the number of tubules increases through bifurcation, as in the stomach.


Although the epithelium of the glands is darker and in early stages taller than that of the villi, the transition is gradual. The relation between them is similar to that which obtains, in the stomach, between the gastric pits and glands. But in the stomach the epithelium of the glands becomes more sharply differentiated from that of the pits, whereas in the intestine the difference gradually disappears. At 240 mm. it is less marked than at 134 mm. Goblet-cells are then found near the bottom of the glands, but often the fundus is composed of darker, granular cells. This is the condition at birth, when the glands have become approximately one-fifth as long as the villi. It is possible that the dark granular cells represent the cells of Paneth.


The Duodenal Glands

According to Brand, the duodenal glands (of Brunner) develop from the intestinal glands, beginning in embryos of Sy 2 months, but Baginsky failed to find them at 4 months. In a 78 mm. embryo, near the pylorus, some of the intestinal glands appear to be more tortuous than others and occasionally show lateral bulgings near their blind ends. At 120 mm., which is before the appearance of the muscularis mucosae, certain of them have grown almost to the circular muscle layer, where they terminate in tubules composed of clear cells, entirely unlike the dark cells at the fundus of the adjacent intestinal glands. A longitudinal section through the stomach and duodenum at this stage shows that these duodenal glands are quite close together near the pylorus, but further on in the duodenum they occur at considerable intervals. At 240 mm., as shown in Johnson's model (Fig. 284), the older glands have branched repeatedly. Certain of the bifurcating intestinal glands in this model probably represent the young stages of the duodenal glands.


The secretory cells of the duodenal glands stain a bright yellow with orange G, and exhibit a delicate reticular structure. Thus they resemble the cells of the pyloric glands, which develop at about the same time, and of the cardiac glands, which arise somewhat earlier. The duodenal glands have been regarded as an extension downward of the pyloric glands, but the considerable morphological differences between them in early stages are against this opinion. In the adult, parietal cells have been found in relation with both the pyloric and duodenal glands (Kaufmann, 1906), but, as already noted, they have been found in the cardiac glands of the oesophagus. They have not been seen in the duodenum of the embryo.


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Fig. 284. — Model showing developing duodenal glands in an embryo of 240 mm. X 160 diam. (After F. P. Johnson.)

Outer Layers

As elsewhere in the digestive tract, the circular muscle layer is the first product of the surrounding mesenchyma. In a 10 mm. embryo, in which this layer is distinct in the oesophagus, but has not yet appeared in the stomach, it may be identified in the duodenal region. Tandler, however, states that it arises at 12.5 mm. In later stages it spreads down the small intestine, and at 22.8 mm. it is present at the junction with the colon. The mesenchyma within the muscle layer contains numerous branches of the superior mesenteric vessels, but no lymphatics. In the duodenal region ganglia are present, and they are found, almost entirely, just outside of the muscle layer. They appear to connect with sympathetic trunks which pass on the right side of the pancreas and also below it. In these specimens it is impossible to determine the lower limit of the vagus plexus, which, according to Kuntz (1909), may invade the small intestine. The nerves to the lower part of the small intestine appear somewhat later. At 42 mm. the ganglia are conspicuous, especially along the line of mesenteric attachment.


The longitudinal muscle layer becomes distinct at about 75 mm. At 134 mm. no musculo ris mucosa was seen, but it is present at 187 mm. Apparently this layer appears first in the oesophagus, then in the stomach, and later in the small intestine. Mall (1897 and 1898) inferred that peristalsis occurs in 130 mm. embryos, since in several embryos of this stage he found that the meconium had been propelled downward toward the csecum.


The tunica propria becomes gradually differentiated before the muscularis mucosae has appeared. It is a dense layer of mesenchyma at 99 mm. The lymphatic vessels, which in earlier stages were present in the mesentery, are now found in the submucosa, but they cannot be seen in the propria. At 240 mm. both solitary and aggregate nodules of lymphoid tissue have appeared in the tunica propria. Their relation to the lymphatic vessels could not be determined in the specimens studied. According to the early observers, the lymphoid tissue arises from the epithelium, aud Retterer (1895 and 1897) has more recently defended this interpretation. It was rightly rejected by Stohr (1889), who concluded that "the lymph-nodules of the intestine arise in the tunica propria, or in the adjacent parts of the submucosa, through mitotic division of the round cells (leucocytes) which are found there." Similarly Czermack (1893) has maintained that the lymphoid tissue develops as a "condensation of the mesenchyma." Czermack is probably correct in concluding that the lymphocytes arise in genetic connection with the reticular tissue. The presence of aggregate nodules (Peyer's patches) in the human intestine at six months and later has been recorded by Kolliker (1861). At seven months Baginsky (1882) recognized very distinctly the central lymphatic vessels within the villi of the duodenum.


The development of the circular folds (valvules conniventes) requires further study. In the middle portion of the intestine at 8 mm. (3 months?), as seen in longitudinal section, there are frequent slight elevations of the submucosa, in which the muscularis is not involved. These are so small that they displace upward (in longitudinal sections) only five villi. In similar sections at 240 mm. there are about ten villi on either side of a fold.


Meckel (1817) stated that there was no trace of the circular folds until the seventh month, when they appeared as slight elevations readily obliterated on stretching the intestine. At birth he found them still poorly developed. Delamare (1903), on the contrary, states that at birth they are as numreous and relatively as high as in the adult. According to Hilton, these folds are not found in apes, but are peculiar to the human intestine.


Fischl (1903) has studied the elastic tissue of the intestine. He finds that at birth there is no elastic tissue in the walls of the intestine or stomach, except in connection with blood-vessels. It begins to develop in the first weeks after birth.


Anomalies of the Small Intestine

In addition to the imperfect torsion of the intestinal loop and the presence of Meckel's diverticulum ilei, which have been described in a previous section, the congenital anomalies of the small intestine include atresia and stenosis, diverticula, and cysts.


Tandler (1900) concluded that the embryological atresia of the duodenmn may sometimes persist and become congenital. He considered this a rare occurrence, since only two cases of intestinal occlusion were found among 111,541 children in Vienna, and nine cases among 150,000 in St. Petersburg. Altogether more than a hundred cases of stenosis or atresia of the small intestine have been described, and rather more than a third of these were found in the duodenum'. Thus they are far more abundant in the duodenum than in any other equal length of the intestinal tract. Kuliga (1903), who reviewed the literature, could not decide between inflammatory and developmental causes for these conditions, but Kreuter (1905) and Forssner (1907) both advocate the ernbryological origin.


The cases vary greatly in degree, and include perforate iris-like folds or valves, complete membranes, and more or less extensive strictures and obliterations of the epithelial tube. Sometimes the muscularis passes smoothly around the blind ends of the divided intestine without extending from one to the other. Cases like that of Preisich (1903), in which, in a boy 6 days old, two valve-like folds were found in relation with the bile and pancreatic ducts, strikingly suggest the conditions in embryos between 15 and 25 mm., and certain of the congenital atresias and stenoses presumably arise at that stage.[1] In other cases, discussed by Forssner, meconium has been found below a complete atresia. This indicates a late origin, possibly through the adhesion of valve-like folds. Moreover, atresia is found in portions of the small intestine where obliteration of the lumen does not normally occur. Such cases may represent the persistence of an abnormal embryological condition. Forssner thinks it probable that exceptionally an epithelial occlusion may be found in all parts of the embryonic intestine.


Diverticula of the duodenum, especially near the outlets of the pancreatic ducts, are relatively common. According to Jach (1899), who found but one case in 200 bodies, Schiippel found seven instances in 45 bodies. They are generally round sacs, opening into the duodenum by clear-cut, circular orifices. Since they are not covered by the muscularis, but push their way through it, they have been described as hernias of the mucous membrane, and as false diverticula, in distinction from the true Meckel's diverticulum. The latter is covered by the muscular coats. Jach believes that they are generally pulsion diverticula, produced by the distention of the upper part of the duodenum following an obstruction lower down. The obstruction may be a cicatricial contraction, or the pressure from a displaced transverse colon. Their occurrence about the outlets of the bile and pancreatic ducts has been attributed to a deficiency in the muscularis where the ducts penetrate it. But Letulle (1899), who has described two cases, concludes that they are undoubtedly of early embryonic origin. Lewis and Thyng (1908) have stated that the diverticula observed in the embryo may possibly give rise to those in the adult. In Fig. 285 their drawing of a model of a duodenal diverticulum from a 13.6 mm. embiyo is placed beside Jackson's sketch of a large diverticulum, 3.5 cm. deep, found in a man of 50 (Jackson, 1908), and the correspondence in location is striking. It is possible that some of the duodenal diverticula are congenital, although apparently no case has yet been recorded at birth (Fischer, 1901).

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Fig. 285. Diverticula of the duodenum. A, in an embryo of 13.6 mm. (Harvard Collection, Series 839). X 55 diam. (From a model by F. W. Thyng.) B, in an adult. (After C. M. Jackson.) In B the outline of the pancreas is dotted. D. chol., common bile-duct; D. pane, d., duct of the dorsal pancreas; Div., diverticulum ; St., stomach.

Occasionally a single diverticulum has been found in the jejunum or in the ileum, but more often there are multiple diverticula. They occur usually in old people, and differ from those of the embryo in their greater relative size and larger number, in occurring only near the mesenteric attachment, and in their distribution which includes the colon. Like the diverticula of the oesophagus, they have been found in relation with the blood-vessels, and have been attributed both to traction by the vessels and to pulsion along the path of the veins as they cross the musculature to enter the mesentery. Hansemann (1896) has produced them experimentally by distending the intestine with water. It is improbable, as stated by Elze (1909), that there is any genetic connection between such structures and the diverticula of the embryo.


Cysts derived from the intestine may be found at birth. Usually they are correctly ascribed to a detached Meckel's diverticulum, even when found within the mesentery (Hennig, 1880; Roth, 1881; Dittricb, 1885). These cysts are occasionally very large (22 cm. long). Their walls include all the layers of the intestine and may contain aggregate nodules. The epithelium is sometimes smooth and ciliated, but it may exhibit more or less perfect glands and villi. In one of Roth's cases, there were two cysts in the abdomen and one in the thorax, and it is stated that they may have arisen in loco from the duodenum and oesophagus. In a pig embryo of 20 mm., Lewis and Thyng have figured a mesenteric cyst which had become detached from the intestine in the lower duodenal region, and it is possible that certain of the congenital intra-mesenteric cysts have a similar origin. The relation of intestinal diverticula and cysts to an accessory pancreas will be considered with the pancreas.


Several small oval cysts have been found by F. P. Johnson among the duodenal villi of a 7 months' embryo. They appear to be distended with mucus, derived from the small group of glands emptying into their basal portions. The epithelium which lines the cysts is separated from the surface epithelium by a thin layer of connective tissue. These structures resemble the cystic glands which Stohr (1898) has figured in the vermiform process of a 5 months' embryo. The closure of the neck of the flask-shaped gland shown in Fig. 282 would apparently produce a similar structure.



  1. The 19 mm. embryo in the Harvard Collection, which has an abnormally shaped stomach with an accessory pancreas, shows also a distinct local constriction of the duodenal epithelium. There is an actual stenosis of the descending part of the duodenal loop.



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العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Grosser O. Lewis FT. and McMurrich JP. The Development of the Digestive Tract and of the Organs of Respiration. (1912) chapter 17, vol. 2, in Keibel F. and Mall FP. Manual of Human Embryology II. (1912) J. B. Lippincott Company, Philadelphia.

XVII. The Development of the Digestive Tract and of the Organs of Respiration: Introduction | Early Entodermal Tract | Mouth and Its Organs | Oesophagus | Stomach | Small Intestine | Large Intestine | Literature | Liver | Pancreas | Pharynx and its Derivatives | Respiratory Apparatus | Figures | Literature
Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


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العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Keibel F. and Mall FP. Manual of Human Embryology II. (1912) J. B. Lippincott Company, Philadelphia.

Manual of Human Embryology II: Nervous System | Chromaffin Organs and Suprarenal Bodies | Sense-Organs | Digestive Tract and Respiration | Vascular System | Urinogenital Organs | Figures 2 | Manual of Human Embryology 1 | Figures 1 | Manual of Human Embryology 2 | Figures 2 | Franz Keibel | Franklin Mall | Embryology History