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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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Online Editor See also: Lewis FT. The form of the stomach in human embryos with notes upon the nomenclature of the stomach. (1912) Amer. J Anat. 13(4): 477-503.
Modern Notes: Stomach Development

Frederick Thomas Lewis
Frederick Thomas Lewis (1875-1951)

The Development of the Stomach

By Frederic T. Lewis.

Early Development

Remak (1855) described the intestinal wall of vertebrates as composed primarily of two layers, — the gland-layer (Darmdrusenblatt) and the fibre-layer (Darmfaserplatte). The former gives rise to the epithelium and glands, and the latter produces the remaining layers. Schenk (1868), from a study of chick embryos, concluded that Remak had overlooked a third layer, which develops downward from the mesodermic somites and extends between the gland-layer and the fibre-layer. He found that this third layer was clearly connected with the somites, but was separate from the adjacent layers. Therefore he concluded that Remak's fibre-layer produced only the lining of the peritoneal cavity. Schenk's interpretation was rejected by Kolliker (1879, p. 850) and by Maurer (1906). Maurer finds that in all vertebrates the embryonic intestinal wall (including that of the stomach) consists at first of two layers, — the entodermal epithelium and the mesodermal epithelium. ' The latter, in the Amniota, becomes stratified, and for some time it may exceed the delicate entoderm in thickness. It produces mesenchymal cells, which form a third layer situated between the two primary epithelia.

The mesodermal epithelium covering the digestive tube is called the splanchnopleure by Maurer, but, as pointed out by Minot (1901), this usage is incorrect, since the term was introduced by Foster to designate the entire intestinal wall. His (1865) proposed the name endothelium in the following passage (here somewhat abbreviated) : " We are accustomed to designate the layers of cells which cover the serous and vascular cavities as epithelia. But all the layers of cells which line the cavities within the middle germ layer have so much in common, and from the time of their first appearance differ so materially from those derived from the two peripheral germ layers, that it would be well to distinguish them by a special term, — -either to contrast them, as false epithelia, with the true, or to name them endothelia, thus expressing their relation to the inner surfaces of the body." The temi endothelium, as proposed by His. is itself too extensive, since it includes both the epithelium lining the vessels and that which lines the body cavities. These epithelia, although similar in the adult, are very distinct embryologically. Accordingly Minot (1892) uses the term mesothelium for the mesodermal cells bounding the body cavities, and applies endothelium to the vascular system. Thus the nomenclature lias become complex. The layer covering the intestine is perhaps best referred to as the ccelomic or peritoneal epithelium.

The two-layered stage of the stomach is seen in the 4 mm Bremer embryo. Here the fore-gut presents a dorso-ventral cleftlike lumen, both in the oesophageal and gastric regions. The thick ccelomic epithelium is in direct relation with the ventral part of the sides of the fore-gut, as far anteriorly as the lung-bud. Thus laterally the gastric region is in the primary two-layered stage, but dorsally and ventrally, and to some extent on the sides, the entodermal epithelium is bounded by mesenchyma. The mesenchyma appears to be derived chiefly from the ccelomic epithelium, yet it is possible that some has grown down from the somites. In this specimen there is no difference between the oesophageal and gastric epithelium.

In a 10 mm embryo the gastric epithelium is distinctly thicker than that of the oesophagus, and its nuclei are more elongated. In the sections examined, the nuclei form four or five overlapping rows, but the true number of cell layers is probably less. Jahrmaerker finds that at 8 mm the gastric epithelium is 2-3 layered, with tall columnar basal cells, whereas both the oesophageal and intestinal epithelia have only two layers. In the 12 mm embryo he attributes the greater thickness of the gastric epithelium, as compared with that of the 'oesophagus or intestine, to the tall basal cells which are found in the stomach.

Vessels and Nerves

The general relations of the stomach in the 10 mm embryo are shown in Fig. 274. At the oesophageal end, the vagus nerves occupy dorsal and ventral positions. Their bundles of fibres are associated with small clumps of cells with crowded nuclei. The dense layer of mesenchyma, indicating the circular muscle, which is distinct along the oesophagus, gradually disappears at the cardia.

In this region a vessel leaves the stomach and passes through the lesser omentum to enter the ductus venosus (Fig. 274, A). This vein was first described by Broman (1903) as follows: "In human embryos 5-16 mm. long, there are always one, two, or several branches of the ductus venosus passing through the lesser omentum to the mesodermal wall of the stomach, where they form a thick plexus. The branches of the cceliac artery connecting with this plexus appear to be relatively insignificant, at least in the earlier stages. In older embryos I have sought in vain for the branches of the ductus venosus, and may therefore believe that they have degenerated."

The coeliac artery is seen leaving the aorta in Fig. 274, C. Its branch, the left gastric artery, lies at the root of the great omentum, along which it ascends to the cardiac end of the stomach. The hepatic branch of the coeliac artery is seen beside the portal vein. Subsequently branches of the portal vein and hepatic artery extend to the pylorus and along the greater curvature, thus forming the right gastro-epiploic vessels. In the 10 mm. embryo these appear to be indicated by minute twigs. In a 22.8 mm specimen the portal vein communicates with the left suprarenal vein by a vessel which receives branches from the stomach, following the course of the left gastric artery. This communicating vein corresponds with the coronary vein of the adult, by forming an anastomosis between the portal and cardinal systems along the lesser curvature of the stomach.

Keibel Mall 2 274.jpg

Fig. 274. Sections of the stomach of a 10 mm embryo (Harvard Collection, Series 1000). A, through the cardia. B, through the fundus. C, through the pylorus. A.coel., coeliac artery ; A.g.s., left gastric artery ; A. hep., hepatic artery ; Alien., splenic artery ; Ao., aorta ;, omental bursa ; C.W., Wolffian body ;, common bile-duct ; D.v., ductus venosus ; F.ep., foramen epiploicum ; N.sym., sympathetic nerve ;, greater omentum ; O.mi., lesser omentum ; Pul., lung ; Va., vagus nerve ; V.p., portal vein ; V.8., left suprarenal vein.

In the 10 mm embryo the dorsal and ventral trunks of the vagus nerves unite to form a large ganglionated plexus on the right side of the stomach, nearly in the median plane of the body (Fig. 274, B). A similar arrangement was found in embryos of 9.4 and 14 mm. There are no distinct nerves along the greater curvature, and there is no indication of the muscle layer. In older embryos (14.5 mm.) the sympathetic nerves communicate with this ganglionic mass, but in the 10 mm. embryo the connection could not be demonstrated. The sympathetic nerves are seen extending forward on either side of the aorta, ventral to which they form a coeliac plexus. From the latter, in older embryos, bundles of fibres extend to the stomach along the dorsal mesentery, following the path shown in Fig. 274, B. Kuntz (1909) has recently published a similar description of the nerves in pig embryos. In 12 mm. specimens he found a vagus plexus around the oesophagus, and " vagus fibres "which are still accompanied by numerous cells may now be traced along the lesser curvature of the stomach." There are still no fibrous connections between the cceliac plexus and the plexuses in the digestive tube. In 16 mm. embryos fibrous connections have become established.

There is another path by which sympathetic fibres may enter the stomach. They may extend from the cceliac ganglion to the pylorus, following the gastric branches of the hepatic artery (Fig. 274, C). His, jun. (1897), has figured a section of a 9.1 mm. embryo which shows sympathetic nerves passing to the stomach along this course. In describing a 10.2 mm. embryo he speaks of a branch of the cceliac plexus which is lost in the mesoderm of the pylorus, and, as shown in his reconstruction, it does not anastomose with the vagus. In the specimens in the Harvard Collection the pyloric branches of the sympathetic cannot be identified at such an early stage. It appears rather as if the gastric plexus first extends downward to the pylorus and duodenum, and is then joined by such sympathetic branches as His described. These are distinct in a 30 mm. embryo.

Epithelium and Gastric Glands

In the 10 mm embryo the free surface of the epithelium is somewhat wavy, whereas the basal surface is nearly smooth. In 16 and 19 mm. specimens the epithelium exhibits occasional vacuoles and a few scattered pits. The vacuoles are small, and, like the pits, they do not cause the basement membrane to bulge. Sometimes the pits expand laterally within the epithelium so that they are flask- shaped. These structures bear a certain resemblance to the oesophageal vacuoles and the intestinal diverticula to be described later.

Elze (1909) has noted that in the stomach of ape embryos {Nasalis larvatus) there are several epithelial buds and diverticula which have the same appearance as the early stages of those found in the intestine.

At 22.8 mm. a few vacuoles are still present. The intraepithelial pits have become numerous. As seen in Fig. 275, A, they are produced by the varying height and characteristic arrangement of cells in an epithelium which has nearly smooth surfaces. In places the epithelium is clearly simple, but elsewhere it may show several rows of nuclei and is perhaps stratified. In a 42 mm. embryo the epithelium is more definitely simple, and the pits form rounded swellings along its mesenchymal surface.

This characteristic stage has been figured by Toldt (1881) in an embryo of the tenth week. It was not seen by Laskowsky (1868), who considered that the gastric glands were produced by the growth of the mesenchymal layer, rather than by epithelial proliferation. His view was accepted by Schenk (1874, p. 117) and others, but Toldt, who considered the pits to be a part of the glands, correctly concluded that "the first formation of the glands is a process which takes place exclusively in the epithelial layer."

At 55 mm the pits still project but slightly below the general level of the basement membrane. The epithelial cells between adjacent pits, in positions corresponding with x in Fig. 275, A, have become greatly compressed below, so that the basal portions of a group of these cells resemble a clump of connective-tissue fibres. In all later stages the epithelial cells along the free surface and the adjacent portions of the sides of the pits may exhibit slender basal prolongations ; they have been described by Baginsky (1882) in a 7 months' embryo, and by Fischl (1891) at birth. In the 55 mm embryo the outer portions of these cells are clear, suggesting a mucous transformation. This is true of the cells on the sides of the pits, but at the bottom of the pits the protoplasm toward the lumen is coarsely granular.

File:Keibel Mall 2 275.jpg

Fig. 275. — Sections of the gastric epithelium. (Harvard Collection, Series 871). X 330 diam. A, from an embryo of 22.8 mm B, from an embryo of 120 mm.

At 99 mm there are distinct mesenchymal elevations between the pits. At the bottom of the pits there are small, nearly solid buds of granular cells, which represent the beginning of the glands proper.

The conditions at 120 mm. are shown in Fig. 275, B. The glands at the base of the pits already exhibit two sorts of cells, differing from one another in their affinity for eosin. The eosinophilic cells occur chiefly at the blind ends of the glands. Very generally they border upon the lumen. In later stages the eosinophilic cells are peripheral in position and are called parietal cells (delomorphous cells). The non-eosinophilic cells represent the chief or adelomorphous cells of later stages. Between the gland and the pit there may be a constriction, as seen in Fig. 275, B. The surface epithelium and that lining the pits is a simple columnar layer, containing mucous cells in various stages of development, but apparently all covered by distinct top plates. Generally the nuclei are elliptical, but occasionally a cell is seen with its nucleus flattened in the basal protoplasm. The basal protoplasm is sometimes eosinophilic, and groups of cells of the parietal type may be found in direct relation with the surface epithelium (as on the right of Fig. 275, B). These seem to represent new gland buds. There are also non-eosinophilic basal cells — the Ersatzzellen of Ebstein (1870) — which presumably develop into new columnar cells. In young embryos Toldt found these basal cells so abundant that in poorly preserved specimens they may easily give the impression of a stratified epithelium, whereas at birth they are relatively infrequent.

The form of the pits and glands in the 120 mm embryo is shown in a model made by Johnson, the upper and under surfaces of which are shown in Figs. 276 and 277 respectively. The gastric pits are seen to be clefts rather than tubules, and the intervening tissue may be considered to form imperfectly separated villi. The pits are separated from one another below by irregular ridges of mesenchyma.

Brand (1877) states that in embryos of two and three months the stomach contains numerous villi, and Kolliker (1879) regards the mesenchymal projections between the pits as " villi." Of their later development he says : " In the fourth month the formation of glands has begun in the mucosa, while between the mesodermal villi, which have become longer, low inter-villi and ridges have grown up, marking out spaces like a honeycomb, into which the epithelium sends hollow cylindrical processes." Sewall (1879) found that in the sheep "from the first the mesodermal outgrowths are not papilliform, but take place along continuous lines of greater or less extent, giving rise to ridges which intersect in all directions." Toldt (1881 ) likewise found, in cat embryos, ridge-like elevations of mesoderm, but he states that it is not to be questioned that in stomachs of human embryos from the third to the fifth month, especially in the pyloric region, villus-like elevations occur, and even true elongated villi. Baginsky (1882) states that " the surface of the gastric fundus in a 4 months' embryo has an exquisite villous appearance." In later stages he finds that the surface becomes gradually smoother as the villus-like elevations disappear. Strecker (1908 1 ) describes an exceptional stomach at birth (?) showing typical villi in the cardiac region.

A mesodermal origin for certain epithelial and gland cells has been considered possible by several investigators. Thus, Ebstein thought that the basal cells may proceed directly from the blood-vessels, and Toldt recorded certain appearances suggesting

File:Keibel Mall 2 276.jpg

Fig. 276. — Model of the gastric epithelium at 120 mm, showing the free surface. X 120 diam. (After F. P. Johnson.) that in young stages mesodermal cells wander into the epithelium. Sewall (1879) and more recently Strecker (1908 2 ) have described the gastric glands as mesodermal.

Sewall (1879) concluded that in sheep embryos only the early generations of chief and parietal cells are formed from the primitive gland cells, and that the later generations arise in the mesenchyma. The parietal cells appear first in the deep parts of the gland (in embryos of about 140 mm). In later stages he concluded that new parietal cells were produced by the differentiation of the surrounding " mesoblast corpuscles," and that, from the parietal cells so formed, new chief cells developed to replace those broken down in the process of secretion. Physiologically he found that extracts of the stomach of the sheep, " even some time before term, showed a considerable proteolytic power." This function appears to coincide with the specialization of the chief cells. The fluid in the embryonic stomach was found to be neutral, even after the differentiation of the parietal cells. It yielded an abundant precipitate of mucus.

File:Keibel Mall 2 277.jpg

Fig. 277. — Model of the gastric epithelium at 120 mm, showing the basal surface. X 120 diam. (After F. P. Johnson.)

Toldt (1881) rejected Sewall's conclusion concerning the mesodermal origin of parietal cells, and described the development of the human gastric glands as follows : " In the fourth and fifth months and also in the beginning of the sixth, parietal cells and their developmental stages are found only at the blind ends of the glands. Beginning with the middle of the sixth month they increase considerably in number and are found everywhere along the sides of the glands, yet they are still in the row of chief cells and therefore border upon the gland lumen. Not earlier than about the middle of the eighth month could I find regularly a considerable number of parietal cells situated on the outer side of the chief cells. At birth and in the first weeks following, this is almost always the case along the sides of the glands, but near and at the base the lumen is still bounded largely by parietal cells which are not fully developed. In children of four or five years all transitions from chief to parietal cells are constantly present in abundance, but later, when the growth of the glands takes place only very slowly, they are seldom found." According to Toldt the chief cells also develop from those which form the walls of the primitive gland. " These cells, differing from the later characteristic chief cells by their cuboidal or polygonal form, their delicate outline, their affinity for eosin, and the strikingly large size of their nuclei, gradually assume the typical form. ... In man this transformation is completed toward the end of the fifth and in the beginning of the sixth month." Chemical tests showed that pepsin was present in the gastric mucosa in the last half of the sixth month, " long before it passed over into the secretion." Strecker (1908 2 ) examined the stomach at birth, and found conditions which have generally been ascribed to post-mortem disintegration, such as the absence of columnar epithelium on the free surface, the presence of detached gland cells in cavities bounded by the tunica propria, and even a superficial layer of fibrin. All these he regards as normal, and states that " unquestionably the large gland cells appear distributed more or less irregularly in the tissue without any typical arrangement. They seem to be lodged in a well-marked reticular tissue, the meshes of which they fill. . . ." He described the embryonic development of these glands as follows: The primitive glands are purely epithelial, but in embryos of 100 mm. another sort of gland formation is seen taking place in the tunica propria. " The propria at this stage is not a connective-tissue layer, but an epithelioid organ." It contains many free nuclei (Bildungskerne) , which produce protoplasmic bodies and form groups of cells, thus giving rise to glands. " Both the chief and parietal cells arise from the same source, namely the Bildungskerne." The Bildungskerne form autogeneously in the original mesenchymal plate of the intestine, and Strecker names them " mesenchymal-epithelioid corpuscles." Not only are free nuclei found in the propria, but there are also non-nucleated masses of protoplasm. Nuclei wander into these, thus giving rise to giant cells. The multi-nucleate cells are generally found at the base of the glands. Portions of them become split off, so that they produce cell material for the gland tube. Strecker states that a true mitotic division in embryological preparations of the gastric glands has never been found by any investigator, but Salvioli (1891) has recorded abundant mitotic figures in rabbit embryos and has made a special study of their location.

From the fact that Strecker found the non-epithelial origin of glands beginning in 100 mm specimens, it is probable that the purely epithelial glands" are the gastric pits, and those arising in the propria are the glands proper. Although, owing to tangential sections, parietal cells often appear isolated in the tunica propria, the conclusion of Sewall and Strecker concerning their mesodermal origin may be confidently rejected. The glands arise as further downgrowths of the pits. In the stomach, as in both small and large intestine, there are at first irregular coarse depressions (pits and intervillous spaces), from the bottom of which glands extend downward. The cells of the pits and villi are characteristically clear, whereas those at the depths of the glands are granular and deeply staining. The transition between the two is not abrupt, as shown in Fig. 275, B.

File:Keibel Mall 2 278.jpg

Fig. 278. — Models of the gastric pits and glands, A, at 240 mm; B, at birth. X 80 diam. (After F. P. Johnson.)

As compared with the pits, the glands steadily increase in length. In a 240 mm embryo they occupy the basal third of the mucosa ; at birth they form nearly half of this layer, and therefore nearly equal the pits. They have branched repeatedly and have increased greatly in number. Their form is shown in Fig. 278, A and B, from models made by Johnson.

Their multiplication has been described by Toldt. He estimated that the total number of gland outlets in the stomach of an eight months' embryo is 128,912; at birth, 268,770; and at ten years, 2,828,560. In the three stomachs referred to, the number of outlets per square millimeter is nearly constant, averaging 56, 51, and 56 respectively. In studying the way in which the glands multiplied, Toldt failed to find primitive stages of gland development among the differentiated glands, but gastric pits were often observed to be partly divided, and he " sees no objection to regarding these divided pits as forerunners of the complete division of the glands." This method of multiplication would cause a reduction in the number of glands opening into each pit, and some reduction was found to occur. The average number of glands emptying into a pit in the last months of embryonic development is 7; at ten years, 6; at fifteen years, 5; and in the adult, 3. During this period Toldt found, however, that the number of gland tubules in the stomach had increased from 930,000 to 25,179,000, which means that many new tubules have been formed. These arise through lateral sprouts of glands already present. Toldt says that " It may be noted that these hollow sprouts are generally seen to develop at places along the gland wall where one or more parietal cells are situated, and that these pass over into the new gland body." Epithelium and Glands at Birth. — Fischl describes the gastric epithelium at birth as a "moderately high columnar epithelium with basal nuclei, appearing somewhat lower on the ridges than in the pits; moreover the nuclei in these two places differ, since they appear more elliptical and deeply stained on the ridges, but in the pits they are rounded and decidedly paler." Except that the cells on the ridges seem taller than in the pits, these observations have been verified. The cells exhibit distinct terminal bars. Those lining the pits are producing and discharging mucus, which fills the lumen and spreads over the free surface. The cells bordering upon the free surface contain a more granular protoplasm, and according to Toldt they sometimes give no indication of the formation of mucus.

Disse (1905), by the use of a mucin stain, found that "the true surface epithelium contains only here and there an isolated mucous cell, but chiefly consists of cells containing no trace of mucus." He concludes that, although in some places the mucous layer is well developed in embryos at term, there are other places in the same stomach where mucus is wholly lacking or forms an interrupted layer. Reyher (1904) and Von der Leyen (1905) have found that the mucous layer is continuous. It is possible that the surface cells with granular protoplasm are those which have previously discharged mucus (see Fig. 275, B).

Fischl was unable to find mitotic figures among the epithelial cells, but Ascoli (1900) has declared that at birth they may be found in large numbers, in cells containing mucus.

Neumann (1876) repeatedly found well-developed ciliated cells among the epithelial cells of the embryonic stomach. (The age of the embryos is not definitely stated.) Baginsky (1882) described the gastric contents of a 7 months' ernbryo as alkaline and containing, together with epidermal cells which were probably swallowed with the amniotic fluid, small ciliated cells, generally isolated. In the specimens in the Harvard Collection no ciliated cells were found.

The glands at birth appear distinctly broader, shorter, and more widely separated than in the adult, as noted by Fischl. In seven cases, all from the first half of the first year, he found the parietal cells only partially differentiated, and represented by rounded, rather small cells, often situated near the gland lumen, and never pushing out into the tunica propria. At the end of the second year, he states that they show no essential difference in staining, form, and arrangement from those of the adult, although they are less abundant.

Fischl's difficulty in demonstrating the parietal cells at birth has not been shared by others, Kalopothakes (1894) having reported them as " perfect " in a six months' embryo; but it is doubtless true that neither they nor the chief cells are fully differentiated until after birth.

Cardiac and Pyloric Glands

The early writers grouped the cardiac and pyloric glands together and named them the mucous glands of the stomach. Thus, Toldt (1881) states that these glands are " quite alike in form and structure," and Strecker has recently noted the " striking similarity" between them. The cardiac glands have apparently been more thoroughly studied than the pyloric, and the literature concerning them has been reviewed by Bensley (1902) and Strecker (1908 1).

Embryologically the pyloric region very early differs from the remainder of the stomach. In a 42 mm. embryo the pits are deeper and more irregular toward the pylorus, where there is an abrupt transition to the characteristic villi of the duodenum, and this is true of all later stages. At 240 mm. the epithelium of the duodenum is a darkly staining granular layer frequently interrupted by clear globular goblet-cells. The pyloric epithelium is a uniform layer of clear columnar cells filled with secretion, thus resembling the epithelium which lines the gastric pits. In the pyloric region the pits are very deep and they coalesce with one another laterally so that the intervening tissue forms long irregular villi. These have been described by Toldt, Baginsky, and others, but apparently they have not been modelled.

In early stages the entire lining of the pyloric glands is like the surface epithelium. This condition is found in an embryo of 120 mm., and Baginsky has recorded it at 4 months. At 7 months, however, he found, in addition to such glands, others which showed, toward their bases, darker, finely granular cells staining clearly with eosin. In an embryo of 240 mm. there are occasional basal eosinophilic cells which resemble parietal cells. Toldt, however, in twenty stomachs from older embryos and children under five years, failed to find any parietal cells associated with the pyloric glands.

The cardiac glands of the oesophagus have already been described (p. 362). They are groups of short tubules lined with a columnar epithelium resembling that of the pyloric glands.

Passing from the oesophagus into the stomach, the cardiac glands become more elongated and more compactly arranged. Their epithelium gradually blends with that of the gastric pits. In the transition the cells become somewhat shorter and stain less brightly with orange G. At the same time gastric glands appear at the base of the pits, and the number of their parietal cells increases. Toldt considered that there is a sharp distinction between the cardiac and the gastric glands, inasmuch as the cells from which they arise are of very different sorts, but there is undoubtedly a gradual transition between them. In man, however, there is no embryological evidence in favor of Bensley's conclusion that "the cardiac glands are decadent or retrogressive structures derived from the fundus glands by the disappearance of their more highly specialized constituents." On the contrary, the cardiac glands are differentiated very early. They can be recognized in a 91 mm. embryo, in which there are still no chief or parietal cells. 12

The Outer Layers. — In 10 mm. embryos the gastric wall consists of three layers, — entodermal epithelium, mesenchyma, and peritoneal epithelium. At 16 mm. there is a condensed zone of mesenchyma indicating the circular layer of muscle. It is best denned along the lesser curvature, but it can be identified over the greater portion of the stomach. A uniform layer of mesenchyma extends between the muscle layer and the entoderm. It already contains a plexus of blood-vessels. The nerves and ganglia have spread from the lesser to the greater curvature. Thev are chiefly outside of the muscularis. At 22.8 mm. there is a slight condensation of the mesenchyma toward the entodermal epithelium, indicating the beginning of the tunica propria. The circular muscle layer is complete, and shows a slight thickening toward the pylorus. A prolonged gradual thickening of this layer, followed by an abrupt thinning at the duodenum, is distinct at 37 mm. and in all later stages. At 37 mm. large lymphatic vessels are seen in the mesentery along the lesser curvature, but apparently they do not penetrate the muscularis. This is true also at 42 mm. At 55 mm. there is a dense tunica propria ; no muscularis mucosae; a submucosa containing blood-vessels and occasional nerves toward the muscularis; a single layer of circular muscle, 12 The histogenesis of the gastric glands in the pig has recently been studied by Kirk (1910). He finds that the parietal cells arise very early as epithelial cells staining intensely with eosin, situated in the deeper parts of the glands. Kirk confirms Toldt regarding the absence of these parietal cells from the pyloric glands. He finds a very gradual transition between the gastric and cardiac glands, and considers that the latter are retarded or regressive glands, following Bensley. But he states that mucous differentiation occurs slightly earlier in the cardia than in the fundus.

outside of which nerves are numerous; and a relatively wide serosa.

At 91 mm. the muscularis at the cardiac end of the stomach shows a few inner longitudinal bundles. These are seen also at 120 mm. At this stage the outer longitudinal layer of the oesophagus may be followed a short distance over the cardia, external to the circular layer. The greater portion of the stomach has only the circular layer. At 240 mm. an outer longitudinal layer is distinct in the pyloric part of the stomach and it becomes thicker toward the duodenum. Some of its bundles are continuous with the longitudinal layer of the duodenum, but others turn into the thick circular layer near the pylorus, forming the dilator pylori (cf. Cunningham, 1908). At birth the thin outer longitudinal layer, according to Fischl, is entirely absent in places, especially along the greater curvature.

The muscularis mucosae is indicated at 120 mm. At birth Fischl finds it clearly divisible into an inner circular and an outer longitudinal layer.

Lymphatic vessels appear in the submucosa in embryos of 214 and 240 mm. Lymph-nodules were found at birth in a considerable percentage of the cases examined by Fischl. They were observed in all parts of the stomach ; sometimes they were at the base of the glands, and did not extend upward between the tubules.

The longitudinal folds of the stomach, which are often found in preserved specimens, appear to be quite irregular. Toldt has seen them formed by muscular contraction in freshly opened embryonic stomachs of cats, and does not consider them to be "specific formations of the mucosa." Kolliker (1879, p. 854) has recorded the number of such longitudinal folds of the mucosa found in human embryonic stomachs of different ages.

Anomalies of the Stomach

Congenital pyloric stenosis is essentially an excessive development of the circular musculature of the pylorus. The other layers in this region, especially the longitudinal layer, may be more or less hypertrophied, and the folds of the mucous membrane are sometimes so highly developed that they appear to obstruct the lumen.

There has been considerable discussion concerning the nature of this condition, the literature of which has been analyzed by Ibraham (1905) and Torkel (1905). It appears to be established that the stenosis is not due to spastic contraction of a normal pylorus, since the muscle layer is actually thickened. A thickening through excessive physiological activity before birth has been suggested. More probably the unknown conditions which normally induce the formation of the sphincter muscle have, in these cases, led to an excessive development. Thus, as Cunningham has recorded, the extremity of the pyloric canal protrudes into the commencement of the duodenum, presenting a striking resemblance to the portio vaginalis of the cervix uteri. In the full-term fetus the protrusion is more marked than in the adult, and in cases of pyloric stenosis it is in all probability still more pronounced. A similar explanation is advocated by Ibraham as according with the relative frequency and remarkable uniformity of the cases observed and the favorable clinical course which they often follow.

Diverticula of the stomach are rare.

Kiiss (1905) has recorded a case in a man 61 years of age. Along the greater curvature, li or 7 cm. from the pylorus, there was a small cavity lined with normal mucous membrane, which penetrated the muscle layer's, pushing a few strands before it. Kiiss states that we are forced to accept a congenital origin for this diverticulum, *' perhaps at the expense of an aberrant outgrowth comparable with the evaginations'of the duodenum which form biliary and pancreatic ducts." Gardiner (1907) has reported a case of accessory pancreas in relation with gastric diverticula, and he refers to Weichselbaum's similar case in which a gastric diverticulum ended in a nodule of pancreatic tissue. According to Orr (1907), W. F. Hamilton has described a stomach with a diverticulum 2 cm. broad and 3 cm. deep, situated on the posterior wall of the cardiac end, near the oesophagus.

The possible embryonic origin of such diverticula will be discussed under anomalies of the small intestine.

It has long been known that stomachs in the adult are occasionally divided more or less completely into two chambers (hourglass stomach), and it was generally believed that some of these cases were congenital. It is now admitted, however, that the great majority of them are due to local physiological contraction of the gastric musculature. Delamare and Dieulafe (1906) described a stomach at birth, which was bilocular, owing to a constriction in the middle part of its corpus. They found that the circular muscle was abnormally thick at the place of constriction, and they attributed this to hypertrophy and not to contraction. But Cunningham (1908) concludes that the hour-glass stomach never arises as a congenital deformity.

Quite distinct from the cases of physiological contraction are those in which a large pars pylorica is separated by a permanent constriction from the corpus. Gardiner (1907) described such a stomach from a three-months child, in which there was a welldeveloped accessory pancreas at the place of constriction. A very similar condition is seen in a 19 mm. embryo in the Harvard Collection. Such cases of "hour-glass stomach" must be distinguished from those which are phases of functional activity.

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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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   Manual of Human Embryology II 1912: 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