Book - Manual of Human Embryology 17-3

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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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The Development Of The Oesophagus

Frederick Thomas Lewis
Frederick Thomas Lewis (1875-1951)

By Frederic T. Lewis.

Early Development

The oesophagus in the 4.0 mm Bremer embryo (Fig. 266) is an epithelial tube which is greatly flattened laterally. Its lumen is a well-defined dorso-ventral cleft. In most places the epithelium shows two rows of somewhat elongated nuclei, and the row next the lumen exhibits numerous mitotic figures. In the upper part of the oesophagus, at the place where its lateral walls meet dorsally, the epithelium has only one row of nuclei, but the ventral border is expanded and has three or four rows. This thickened portion, however, belongs with the respiratory tract, which has not yet been separated from the oesophagus. The mesenchyma around the oesophagus is an undifferentiated layer with crowded nuclei and many mitotic figures. Below the lung-bud, on either side, the mesenchyma is closely connected with the adjacent ccelomic epithelium, from which it is being produced. There is no histological demarcation between the oesophagus and pharynx above or the oesophagus and stomach below.

Keibel Mall 2 266.jpg

Fig. 266. — Wax model from Bremer's 4 mm. embryo, showing tbe "lung-bud," Pul., and the adjacent part of the oesophagus. Sept., tracheo-cesophageal septum; Sul., lateral oesophageal groove.

The Epithelial Tube

In older embryos, as Forssner recorded (1907), the oesophagus becomes "not only relatively but absolutely smaller in cross section, and the lumen is reduced to a fraction of its former size. " In an embryo of 7.5 mm. the most slender portion of the oesophagus has a cross section about one-third as large as in the 4 mm. embryo, and a lumen one-twentieth as large, yet the length of the oesophagus has increased from less than 0.5 mm. to 1.5 mm. The lower portion of the oesophagus remains flattened laterally, but the upper part has become a round tube which is entirely separate from the trachea. It tapers from the larynx downward, and the lumen becomes minute. The epithelium has 3-4 rows of nuclei above, and is quite like the lining of the pharynx. In the narrowest part of the oesophagus there are but two rows. Mitotic figures are seen almost exclusively in the layer of cells bordering upon the lumen.

In four embryos measuring from 8.4 to 16 mm. the epithelial tube of the oesophagus is shaped as follows : At its laryngeal end it is crescentic, with the concavity of the crescent directed toward the trachea. On its way to the stomach it first becomes round and then transversely elliptical. Near the level of the bifurcation of the trachea it is again round and finally it becomes dorso-ventrally elliptical. In this shape it merges with the stomach. In all of these specimens the lumen is pervious throughout, but it contains a reticular coagulum. The epithelium shows from two to four rows of nuclei. Schridde (1907 and 1908) states that in embryos measuring from 4 to 35 nmi. the oesophageal epithelium has only two layers, although in thick sections (7-10 /*) the number may appear greater. In a 13 mm. embryo he finds that "in a striking manner, the nuclei of both layers are in the upper ends of the cells, toward the lumen," and this condition was figured by Schaffer in 1904. Jahrmaerker (1906) has described two 8 mm. embryos in which the oesophageal epithelium is composed of two layers of tall cells, with a narrow zone free from nuclei along both the basal and free borders. He finds similar conditions in embryos of 14 and 16 mm. A basal zone free from nuclei is shown in Fig. 267, A, but in this section the nuclei are crowded toward the free surface, forming a darkly staining band. Jahrmaerker, in describing embryos of 17 and 18 mm., states that the superficial layer of the epithelium is more deeply stained than the basal layer, but he does not attribute this to a crowding of the nuclei. At 10 mm., as in the smaller embryos, mitotic figures were frequent in the inner layer. In the older specimens no figures were preserved.

Vacuoles in the Epithelium

In human embryos of about 20 mm., large vacuoles occur in the oesophageal epithelium, so that in cross section the oesophagus may appear to have two or three lumina. This was noted by O. Schultze in 1897. Kreuter (1905) studied the vacuoles, and concluded that they were associated with an epithelial proliferation which led to a temporary occlusion of the oesophagus. He had previously studied the solid oesophagus of various vertebrates, following Balfour and others. Forssner (1907) showed by means of a model that the main lumen of the human oesophagus is not obliterated.

In an embryo of 22.7 mm. Forssner found " an uninterrupted open central lumen with a mass of cavities on either side of it, some of which communicate with the mam lumen and others do not; some of them are much smaller and others considerably larger than the lumen itself. These formations may be found scattered along the entire oesophagus (22.7 mm.) ; sometimes only below (20 mm.), sometimes only above (30.5 mm.). In the 31 mm. embryo the wall of the oesophagus, as compared with the main lumen, is considerably thinner than before. The epithelium is several layered; it shows none of the cavity formations just described and the lumen is everywhere undivided. That this process in the esophagus has the result of enlarging the lumen appears probable." Schridde (1908) likewise failed to find an occlusion at any stage.

He denies the presence of vacuoles in the following conclusion : " All these facts go to show that vacuoles never occur in the oesophagus. On the contrary, epithelial bridges are clearly present, having arisen by epithelial proliferation in circumscribed places." The structures in cmestion arc shown in Fig. 2(57, B. Here the central lumen of the oesophagus is bounded by a compact dark zone of nuclei, thus differing from the accessory cavities. C and D in Fig. 267 represent successive sections from a 22.8 mm embryo. In C there are two accessory cavities with compact linings, and the one on the left communicates with the general lumen in D. The oesophagus of these embryos has been modelled by F. P. Johnson in a study of the development of the intestinal mucous membrane.[1] His work affords an independent confirmation of Forssner's conclusions, and shows that Schridde was in error in denying the presence of vacuoles.

Keibel Mall 2 267.jpg

Fig. 267. — Transverse sections of the epithelial tube of the oesophagus. X 160 diam. A, embryo of 16 mm. (Harvard Collection, Series 1322). B, 19 mm. (Harvard Collection, Series 819). C and D, successive sections from an embryo of 22.8 mm. (Harvard Collection, Series 871).

Vacuoles have been found in embryos of 14.5 mm. (Keibel and Elze), but they are sometimes absent in those of 18.5 mm. (Forssner). They acquire a maximum development in specimens of about 20 mm. In a 30 mm. embryo there are occasional vacuoles in the upper part of the oesophagus. In a 42 mm. specimen some small intercellular cavities are found, but there are no characteristic vacuoles.

In discussing the origin of the vacuoles, Kreuter has said correctly that "we have no ground for believing that there is a degeneration of cells, but must conclude that it involves throughout only vital processes. ... A degeneration of cells followed by resorption is nowhere demonstrable." Forssner suggests that there are two sorts of vacuoles, those due to the accumulation of intercellular fluid and those due to an active moving apart of the cells. The cavities in the oesophagus seem to belong to the latter class. It is possible that their formation is associated with the transfer of mitotic activity from the inner to the outer row of cells. A centre of mitosis in the outer layer would account for the local bulging of the epithelium. It is clear that a transfer of mitotic activity from the inner to the outer layer must take place in the embryo, but at what stage this happens is not known. It is generally agreed that the result of the vacuole formation is the enlargement of the lumen.

Keibel Mall 2 268.jpg

Fig. 268. — Models showing the epithelial tube of the oesophagus cut longitudinally. X 120 diam . (After F. P. Johnson.) A, embryo of 19 mm. (Harvard Collection, Series 819). B, 22.8 mm. (Harvard Collection, Series 871).


In cross sections of the oesophagus in embryos of about 10 mm., the lumen presents a clear-cut, round or elliptical outline. In older embryos, owing to the formation of broad folds, in which the mesenchymal layer takes part, the lumen becomes irregularly crescentic, tri-radiate, or shaped like a "Greek cross" (Fig. 269). The fusion of the vacuoles with the central lumen contributes to the irregularity of the shapes presented. Notwithstanding the secondary folds, however, the early form of the oesophageal tube may be recognized even in 30 mm. specimens. The long axis, which is transverse above, becomes dorso-ventral below. This arrangement suggested to Kreuter that the lower part of the oesophagus shared in the rotation of the stomach, but he concluded that "mechanical considerations are against this idea." Johnson has described a dorsal and a ventral fold in the middle part of the oesophagus of a 42 mm. embryo, which become left and right respectively as the stomach is neared. The main trunks of the vagus nerves, which are lateral in the upper part of the oesophagus, become dorsal and ventral below, where, however, they are involved in a coarse plexus. This relation lends support to the idea that the epithelial tube may rotate, but to demonstrate this a more critical study is required. The primary folds in the oesophagus appear to be definitely situated, but those which come later vary in different embryos.

Keibel Mall 2 269.jpg

Fig. 269. — Models showing the development of the epithelial folds in the middle portion of the oesophagus. X 90 diam. (After F. P. Johnson.) A, embryo of 37 mm. (Harvard Collection, Series Template:HEC820). B, 42 mm. (Harvard Collection, Series 838). C, 120 mm.

Ciliated Cells

In 1876 Neumann recorded that in embryos of from 18 to 32 weeks the oesophagus is lined with stratified ciliated epithelium, which, however, is interrupted in many places by nonciliated areas. He states that by isolating the cells through maceration in Miiller's fluid, he obtained all sorts of transition forms between ciliated columnar epithelium and flat epithelium. In a later publication (1897) he has figured the isolated cells, and has shown that the cilia are associated with distinct basal bodies. The smallest embryo in which the cilia have been found measures 44 mm., and its age is estimated at "about 69-70 days" by Jahrmaerker, and at "10-11 weeks" by Schridde, both of whom described this specimen. Schaffer failed to find cilia in a twelve weeks' embryo. They are apparently absent in a specimen of 42 mm. in the Harvard Collection, but are abundant at 55 mm. Cilia are still present at birth according to several observers, but in the specimens examined by Jahrmaerker and Schridde none were found. Fig. 270 is from the oesophagus of a negro child at birth, in which ciliated cells are abundant.

Keibel Mall 2 270.jpg

Fig. 270. — Section of the oesophageal epithelium at birth. X 600 diam.

The ciliated cells arise simultaneously in various parts of the oesophagus at a time when the epithelium is two-layered. They appear to belong with the superficial layer, but Schaffer (1904) has found that some of them may be traced through the entire epithelium to the basement membrane. Jahrmaerker nevertheless considers that the ciliated cells belong with the outer layer, in which some cells become ciliated and others do not. He finds that both forms of cells have finely granular, darkly stained protoplasm.

In the 44 mm embryo, according to Jahrmaerker, the free surface of many non-ciliated columnar cells, generally in small groups or bordering upon the ciliated areas, shows a distinct dark border, which seems to indicate a transition to the ciliated form.

Schridde (1907), by using Unna's Wasserblau-Orcein, found that the ciliated cells have a dark-blue, finely granular protoplasm, and stand out distinctly from the clear columnar cells. He wi-ites : "The discovery of ciliated cells extending to the basement membrane seems to me to be of special significance. In my opinion it is therefore certain that the ciliated cells are not derivatives of the upper layer. . . . We must rather consider that these elements are formed from the basal cells." However, Schridde has neither figured nor described any darkly stained cell which has not reached the free surface, such as would be expected if certain basal cells were pushing outward.

For a time the number of ciliated cells increases. Thus the ciliated areas in a 99 mm. embryo are more extensive than at 55 mm., as shown in models made by Johnson. The epithelium becomes 3-5 layered, but even in five-layered epithelium, according to Schridde, ciliated cells may sometimes be traced to the basement membrane. Ultimately their basal processes are lost and the ciliated cells appear crowded between adjacent vesicular cells. They are more deeply stained than before, which has been attributed both to compression and to degeneration. It is agreed by Schaffer, Jahrmaerker, and Schridde that the ciliated cells are desquamated, together with the outer non-ciliated cells, and in wellpreserved specimens they may be found free in the lumen of the oesophagus. It appears improbable that they lose their cilia and become vesicular cells, as Neumann originally maintained. He seems to have observed various shapes of ciliated cells, rather than transition forms.

Non-ciliated Cells

Schridde has described the differentiation of the non-ciliated cells as follows: In a 100 mm. specimen (16 weeks) the epithelium appears 4-5 layered, and is composed of clear, polyhedral cells. The lowest layer likewise consists of clear cells, which almost throughout are cuboidal or low columnar in form. In a slightly older specimen, under low magnification, the basal layer appears darkly stained. With an immersion lens, the protoplasm of the dark cells is seen to contain interlacing fibrils. The "fibre-cells" are pushed outward, gradually displacing the clear cells. In embryos between 195 and 240 mm. they are found in all of the layers, but some of the earlier generation of clear cells are retained at birth, and they were seen in a child of three days. Intercellular spaces bridged by fibrils were first found in a child at birth. Keratohyalin granules do not appear in the superficial cells until some time after birth.

Schridde finds the number of layers in the epithelium to be 8-10 in a thirty six weeks' embryo, 9-10 at birth, and 12-15 three days after birth. In the specimen from which Fig. 270 was drawn, the number of layers is from 3 to 7, and this accords with Riickert's statement (1904) that the flat epithelial covering of the oesophagus at birth is very thin, sometimes consisting of only two layers. The outermost cells, moreover, are not greatly flattened.

In the lower part of the oesophagus at birth, Strecker (1908 1) found numerous irregular clefts in the epithelium, so disposed that sometimes the intervening cells appeared as pointed epithelial papilla?. In the oesophagus of a child of 13 months he reports true epithelial papillae with connective-tissue cores. " These are occasionally pointed, but generally they are conical, suggesting in their shape the papillce fungiformes of the tongue." The portion of the oesophagus in which they occur, he regards as belonging with the cardiac antrum or " Vormagen." Glands. — Small groups of secreting cells, which represent the earliest gland formations in the oesophagus, may be found in embryos of about 78 mm. (3 months). An imperfect series of such a specimen in the Harvard Collection, is sufficient to show that these areas are present both at the upper and lower ends of the oesophagus.

Schaffer (1904) described such cells in a 4 months' embryo as follows: " With low magnification a well-defined, small, lighter group of cells was seen in the epithelium of the lateral pocket of the oesophagus, at the level of the thira or fourth tracheal cartilage. With higher magnification I found the typical, several-rowed ciliated epithelium . . . interrupted by a group of clear, remark ably tall columnar cells, arranged in a single layer which bulged slightly ab.-> V e the epithelial surface. The number of these cells, in the cross section, was about ten. Their nuclei, placed well toward the base, formed a row which bulged somewhat toward the underlying tissue. In their finer structure the cells accorded fully with the account which d'Hardivillier (1897) has given of the prismatic gland-cells in a 7 months' embryo. The cells appeared as if empty; only their walls stood out clearly. Their uppe~ ends lacked not only the cilia but the border of basal bodies." Schridde (1907) found a similar group of five very tall columnar cells in the lateral pocket of an embryo of 105-110 mm. (16-17 weeks). They were at the level of the cricoid cartilage. In regard to their structure he states: "The upper end of these cells was filled with an elongated oval plug, distinctly red-stained, and presenting a well-defined honey-comb structure. That these plugs were of mucus was shown by Unna's stain, which I am convinced offers a good reaction for mucus, and also by staining with mucicarmin."

Keibel Mall 2 271.jpg

Fig. 271. — Section through a group of mucous cells near the cardiac end of the oesophagus of an embryo of 240 mm. X 600 diam.

At the lower end of the oesophagus, as seen in older erubryos (120 mm. and 240 mm.), such cells are very abundant. Some of them occur in small groups, such as Schaffer and Schridde described (Fig. 271). The secretion, as indicated by the vacuolated protoplasm, nearly fills the cells, so that the nuclei at the basal ends appear compressed. Terminal bars, or intercellular cement lines, are seen at the free surface. These groups of cells are usually, but not invariably, bounded by ciliated epithelium. In the 240 mm. specimen the secreting cells often cover considerable areas which have been evaginated so as to form branching glands (Fig. 272). Usually several short tubules open into a broad cavity, whi;^ in turn connects with the central lumen of the oesophagus. The cavities are lined in part with stratified epithelium, and in part with the simple glandular epithelium which may form a portion of the lining of the oesophagus around the outlet of the gland.

A longitudinal section through the junction of the oesophagus and stomach at 120 mm. shows that the irregular clumps of secreting tubules gradually give place to a succession of quite uniform pits. As the distance from the oesophageal epithelium increases, the tubules become less and less branched (Bensley, 1902). The irregular forms, which occur both in the oesophagus and the cardiac end of the stomach, are the cardiac glands. The simple tubes, occurring further within the stomach, are gastric pits.

At birth the upper group of cardiac glands in the oesophagus may have the simple character which has been described, but as found in the adult they have undergone further development.

in f They were present in 70 per cent, of the cases examined by Schaffer, being found in the lateral folds of the oesophagus between the cricoid and fifth tracheal cartilages, frequently on both sides. They may appear macroscopically as erosions a b-mt 1 mm. in diameter. (The largest area which Sehridde obseiwed was ?3.5 x 9 mm.) The glands discharge through a dilated duct lined with simple columnar epithelium, which is said to open at the top of a connective-tissue papilla.

Tubules of a new soil have grown out from the gland; they consist of cells with round nuclei, and may produce a serous secretion. Certain of the tubules are provided with parietal cells and chief or zymogenic cells, so that the glands resemble those of the stomach. Schridde in 1904 described such areas as " islands of gastric mucosa," and considered that they were remnants of entoderm isolated by the downgrowth of the ectodermal layer (stratified epithelium) from the mouth, — an error which led to prolonged discussion. E. Schwalbe (1905) has found resemblances between the epithelium of the cardiac glands and that of the intestine, even in the production of cells resembling Paneth's cells.

Keibel Mall 2 272.jpg

Fig. 272. — Model of a superficial gland from the cardiac end of the oesophagus at 240 mm. X120 diam. (After F. P. Johnson.) The extent of the glandular epithelium is indicated by the ruled surface; the unruled area is occupied by squamous epithelium.

The lower group of cardiac glands of the oesophagus is usually limited to a /one from 1 to 4 mm. wide, situated at the entrance to the stomach. The glands vary in their development. Those which Strecker fig-ured from a twelve weeks' child are simpler in form than the one shown in Fig. 272, from an embryo of 240 mm. They consist of tall glandular cells forming a simple epithelium. Later, as in the upper group, new tubules develop which may contain chief and parietal cells. The ducts are usually distended and cystic. Between the upper and lower groups cardiac glands are rarely found, but Eberth (1897) has recorded a small area in the beginning of the lower half of the oesophagus in a man 25 years old.

The cardiac glands of the oesophagus have been named by Hewlett (1901) the superficial glands (glandulse oesophageal superficiales). They do not extend through the muscnlaris mucosae. The deep glands, which have their secreting portion in the submucosa, arise later.

They are apparently indicated in the 240 mm. embryo by short rounded downgrowths of stratified epithelium. At this stage there is no evidence of secretory activity. At birth, as shown in Johnson's model (Fig. 273), these glands are somewhat tortuous tubes. Some of them show expanded terminal portions and others have begun to branch. Occasionally, as on the right of Fig. 273, a gland is found in which the terminal secretory portion has not yet developed. The lower portion of the ducts is lined generally with low two-layered epithelium, but in some places only a single layer is found. As the duct approaches the surface, its outer cells become somewhat elongated and they are seen to be continuous with the basal layer of the stratified surface epithelium. The secreting portion consist? typical mucous cells. They are not as slender as those in the cardiac glands, the part occupied by secretion is more homogeneous. They yield the sti reactions for mucus more readily than the cells of the cardiac glands, the diffei being so great that the mucous nature of the latter has been questioned. In the adult the deep glands are said to open between connective-tissue papillae, whereas the cardiac glands open at their summits. This distinction s» ems arbitrary, especially since the papilla 3 arise after the glands are present.

Keibel Mall 2 273.jpg

Fig. 273. — Model showing three deep oesophageal glands at birth. X 90 diam. (After F. P. Johnson.)

The Outer Layers

In the oesophagus, as elsewhere in the digestive tube, it is well known that the circular muscle layer is the first of the outer coats to be differentiated.

At 10 mm. it is represented by a concentric layer of myoblasts, separated from the epithelium by a broad band of undifferentiated mesenchyma. The circular muscle is so far outside of the epithelium that it is undisturbed by the epithelial folds and pockets which arise in later stages. In the 10 mm. embryo there are numerous branches of the vagus nerves, some of them associated with groups of cells with crowded nuclei, found just outside of the circular muscle. These represent the myenteric plexus. Occasionally at this stage similar groups of cells appear along the inner border of the musculaiis, and these give rise to the plexus submucosus.

At 12.5 mm. Keibel and Elze note that the oesophagus shows a circular, but no longitudinal, muscle layer. At 17 mm. they find a strong circular layer, with the longitudinal layer only indicated. Kreuter finds that the circular muscle is already differentiated in the fifth week (9 mm.), but the longitudinal muscle first appears in the eighth week. Happich states that, although the circular muscle in a four months' embryo has attained a considerable strength, the longitudinal muscle is indicated only by very' weak fibres. Schridde, on the contrary, finds that both layers are clearly marked at 12.4 mm., and at 21 mm. the longitudinal musculature is everywhere well developed. It is possible that Schridde mistook the conspicuous layer of nerves, found just outside of the circular muscle at 12 mm., for the longitudinal muscle. These nerves, with the undifferentiated ganglioncells, form a nearly continuous layer.

The longitudinal muscle is perhaps indicated at 30 mm., but at 42 mm. it is thinner and less conspicuous than the layer of nerves which separates it from the circular muscle. At 55 mm. it is present as a definite layer.

The muscularis mucosas is not found in the 55 mm. embryo.

78 mm. it is not distinct at the upper end of the oesophagus, but it SB very definite below. At 91 mm. it is a well-developed layer of longitudinal fibres equalling the tunica propria in breadth, and thrown into folds corresponding with those of the epithelium.

The development of the striated muscle of the human oesophagus has not been satisfactorily studied. The oesophageal smooth muscle layers at first extend to the larynx, where they contrast sharply with the striated fibres of the inferior pharyngeal constrictor. There is no evidence of a downgrowth of these fibres upon the oesophagus.

In pig embryos, according to McGill (1910), the smooth and striated musclefibres of the oesophagus have a common origin in the mesenchymal syncytium. " Until the cross striations appear in the fibrillar of the striated muscle, both developing tissues look precisely alike." Cross striations were first observed in pigs of 13 mm., but " only a few fibrillse become striated before the embryo reaches a length of 30 mm." In cross sections of the upper part of the human oesophagus at 7 8 mm. the longitudinal fibres are triangular or polygonal, with peripheral nuclei, and they show coarse myofibrils, but the circular fibres do not appear to be striated. Striated circular fibres are distinct at 120 mm. It is probable that these are "a further differentiation of smooth muscle" (McGill).

The musculature of the upper half of the oesophagus in the adult consists chiefly of striated fibres, but Klein (1868) has concluded that smooth muscle in the longitudinal layer begins in the upper quarter. Once in an adult he found that the circular layer, 1 cm. below the upper end of the oesophagus, consisted chiefly of smooth muscle. In another case he found that the ventral part of the longitudinal layer at the upper end of the second quarter consisted chiefly of smooth fibres, but that further down the striated fibres increased so that the relation was reversed. He found no striated fibres in the lower half of the oesophagus. Coakley, however (1892), has described striated fibres intermingled with the non-striated in both coats of the diaphragmatic portion of the oesophagus. The majority were in the inner circular layer. He considers that the pillars of the diaphragm are the source of these fibres.

The layer of mesenchyma between the circular muscle and the epithelium in the 10 mm. embryo is quite free from bloodvessels. Vessels have entered it at 14.5 mm., and at 16 mm. they form a distinct plexus. Beginning at about 30 mm. the inner portion of the mesenchymal layer becomes gradually denser, due ( to an abundance of nuclei. Thus the tunica propria, consisting of s reticular tissue, is slowly differentiated from the fibrous conneca tive tissue of the submucosa. At birth the propria contains "" abundant blood-vessels, and apparently lymphatic vessels are present also. No lymph nodules were seen in the sections examined. In the oesophagus of a child Klein (1868) found that the reticulum contained "more or less numerous round cells similar to lymphocytes," but he speaks of nodules only in the adult. The nodules of the oesophagus apparently develop later than those of the stomach and intestine.

As already noted, papillae of the tunica propria are absent at birth, but in cross sections the basal border of the epithelium presents a slightly wavy outline. Since Strecker finds that in longitudinal sections the basal line is usually straight, he considers that the elevations are ridges and not papillae. He finds that the oesophagus passes through three stages of development: 1, in which the tunica propria has a smooth contour ; 2, in which it has formed ridges; 3, in which there are conical papillae upon the ridges. At birth the human oesophagus is in the second stage. In a child of 12 months all the later characteristics are present.

Anomalies of the Oesophagus

In a previous section the anomaly of the oesophagus in which the upper segment ends blindly below and the lower segment arises from the trachea has been discussed (p. 312). It was stated that it must originate in embryos of about 4 mm. This has been confirmed by finding the anomaly well developed in an embryo of 18.1 mm. in the Harvard Collection. In this specimen there is no trace of epithelial connection between the two parts of the oesophagus. Ribbert (1902) has interpreted traction diverticula as a modification, or partial development, of this anomaly. In these cases the ventral wall of the oesophagus, near the level of the bifurcation of the trachea, presents a funnelshaped diverticulum with its apex directed obliquely upward toward the trachea. The epithelial pocket may penetrate the muscle coat, and from its apex a strand of vascular connective tissue generally extends toward the wall of the trachea. The inflammatory conditions which are often found associated with the pocket are regarded by Ribbert as secondary. Although he states that traction diverticula occur chiefly in older people, he believes that in the great majority of cases they have an embryological origin. He considers that there is a defective development of the oesophageal wall at the place where in more radical cases the tracheooesophageal fistula occurs.

An examination of the embryos in the Harvard Collection fails to show such a defect. However, Happich (1905) has recorded that in embryos from 8 or 9 mm. to 3 or 4 months, the entire musculature on the ventral side of the oesophagus is thinner than on the dorsal side, as far down as the bifurcation of the trachea. Below the trachea this distinction is wholly lacking. At birth the ventral musculature is slightly weaker than the dorsal, but the difference is almost imperceptible. It is clear, however, that such a thinning cannot account for the anomaly in question, since it extends the whole length of the trachea and disappears at birth. In addition to the general thinning, Happich has found that the circular muscle, in embryos of 3 or 4 months, is completely interrupted in small areas extending through one or two sections. " These places can readily be distinguished from those through which a vessel penetrates the wall." Schridde (1908) found a larger defect, extending through five sections, in that part of the longitudinal muscle layer which is toward the trachea. This, however, was in a 13 mm. embryo, which is a stage when the longitudinal muscle is not ordinarily recognizable.

Riebold (1903 and 1908) believes that the embryological interpretation of traction diverticula is not justified, and he adheres to the older idea that they are pathological. He cites the literature to show that Ribbert's theory has not met with general acceptance, and states that " up to the present time not a single case of traction diverticulum has been found at birth." Lymphadenitis, with adhesions of the gland to the trachea and a spread of the inflammation along vessels to the oesophagus, is believed to produce a dense scar which draws upon the oesophageal tube, and, as a result, of the motions in swallowing, the diverticulum is drawn out. Diverticula may occur wherever a vessel penetrates the muscle, and therefore below the trachea. They may be multiple, and they are not always ventral.

Embryologically it is probable that if the trachea and oesophagus have separated normally at 4.5 mm., the muscle layers which arise at 9-12 mm. will show no local defect at the place of the former separation. Unless the diverticula are primarily epithelial, they are presumably not congenital.

Pulsion diverticula occur on the dorsal wall of the oesophagus, at its junction with the pharynx, where the tube is narrowest and the muscle coat thinnest (Riebold). They apparently have no embryological significance. Diverticula occur also in other parts of the oesophagus. Some of these are evidently of inflammatory origin. D'Hardivillier has asked whether the islands of simple epithelium do not offer places of lesser resistance which would lead to diverticula, and it has been pointed out that pulsion diverticula and these thin areas both occur at the upper end of the oesophagus. Apparently, however, there is no relation between them.

The irregularities in the oesophageal epithelium in embryos of 18-22 mm. have been supposed to give rise to the cases of atresia and stenosis, and possibly to diverticula, but direct evidence is lacking. Atresia of the oesophagus is abnormal in embryos of all stages. Many records of oesophageal anomalies have been gathered by Happich, Kreuter, and Forssner, who have discussed them embryolosrically.

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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
  1. The work of Mr. Johnson, which was undertaken in connection with this chapter, has recently heen published in the Amer. Journ. of Anat., vol. 10, p. 521561, 1910.