Dorsal Mesogastrium Research Articles

Exercises in anatomy: cardiac isomerism.

It is well recognized that the patients with the most complex cardiac malformations are those with so-called visceral heterotaxy. At present, it remains a fact that most investigators segregate these patients on the basis of their splenic anatomy, describing syndromes of so-called asplenia and polysplenia. It has also been known for quite some time, nonetheless, that the morphology of the tracheobronchial tree is usually isomeric in the setting of heterotaxy. And it has been shown that the isomerism found in terms of bronchial arrangement correlates in a better fashion with the cardiac anatomy than does the presence of multiple spleens, or the absence of any splenic tissue. In this exercise in anatomy, we use hearts from the Idriss archive of Lurie Children's Hospital in Chicago to demonstrate the isomeric features found in the hearts obtained from patients known to have had heterotaxy. We first demonstrate the normal arrangements, showing how it is the extent of the pectinate muscles in the atrial appendages relative to the atrioventricular junctions that distinguishes between morphologically right and left atrial chambers. We also show the asymmetry of the normal bronchial tree, and the relationships of the first bronchial branches to the pulmonary arteries supplying the lower lobes of the lungs. We then demonstrate that diagnosis of multiple spleens requires the finding of splenic tissue on either side of the dorsal mesogastrium. Turning to hearts obtained from patients with heterotaxy, we illustrate isomeric right and left atrial appendages. We emphasize that it is only the appendages that are universally isomeric, but point out that other features support the notion of cardiac isomerism. We then show that description also requires a full account of veno-atrial connections, since these can seemingly be mirror-imaged when the arrangement within the heart is one of isomerism of the atrial appendages. We show how failure to recognize the presence of such isomeric appendages can lead to spurious diagnoses of discordant atrioventricular connections. Overall, we show that the finding of isomeric atrial appendages, guided by the finding of bronchial isomerism, is but the prelude to full segmental sequential analysis.

Morphogenesis of the spleen during the human embryonic period.

We aimed to observe morphological changes in the spleen from the emergence of the primordium to the end of the embryonic period using histological serial sections of 228 samples. Between Carnegie stages (CSs) 14 and 17, the spleen was usually recognized as a bulge in the dorsal mesogastrium (DM), and after CS 20, the spleen became apparent. Intrasplenic folds were observed later. A high-density area was first recognized in 6 of the 58 cases at CS 16 and in all cases examined after CS 18. The spleen was recognized neither as a bulge nor as a high-density area at CS 13. The mesothelium was pseudostratified until CS 16 and was replaced with high columnar cells and then with low columnar cells. The basement membrane was obvious after CS 17. The mesenchymal cells differentiated from cells in the DM, and sinus formation started at CS 20. Hematopoietic cells were detected after CS 18. The vessels were observed at CS 14 in the DM. Hilus formation was observed after CS 20. The parallel entries of the arteries and veins were observed at CS 23. The rate of increase in spleen length in relation to that of stomach length along the cranial-caudal direction was 0.51 ± 0.11, which remained constant during CSs 19 and 23, indicating that their growths were similar. These data may help to better understand the development of normal human embryos and to detect abnormal embryos in the early stages of development.

English

Accessory spleen (AS) is a congenital ectopic splenic tissue arising during embryologic period of development, most remaining asymptomatic and discovered incidentally. Being present near the splenic hilum usually, it may occasionally be embedded partly or wholly in the tail of the pancreas, sometimes becoming symptomatic and even mimicking tumor. We report a case of an accessory spleen discovered during cadaveric dissection of a middle-aged man in the Department of Anatomy, RIMS, Imphal. Awareness of the possible presence of AS is important during splenectomy for conditions such as immune thrombocytopenic purpura as failure to remove the AS may result in the failure of the condition to resolve. Additionally, during medical imaging, AS may be confused for enlarged lymph nodes or neoplastic growths. The presented case report might remind us the sort of such congenital anomalies during clinical evaluations like splenomegaly, splenic trauma, lymphadenopathies and intra-abdominal mass and subsequent operative strategies. KEY MESSAGE: A routine search for AS intraoperatively along with preoperative radiological scan is recommended to achieve the highest detection rates and to prevent disease recurrence, especially for autoimmune hematological disorders. INTRODUCTION: The spleen consists of a large encapsulated mass of vascular and lymphoid tissue situated in the upper left quadrant of the abdominal cavity between the fundus of the stomach and the diaphragm. The spleen can display various developmental anomalies, including complete agenesis, multiple spleens or polysplenia, isolated small additional splenunculi and persistent lobulation1. Accessory spleens may be formed during embryonic development as ectopic or separated splenic tissue along the path from where the spleen forms at the midline to the spleen's final location on the left side of the abdomen.1, 2 Accessory spleen, found in 10%-30% of patients at autopsy, is due to the fusion failure of the splenic anlage, which is located in the dorsal mesogastrium. 3- 5 The splenic hilus is the most common site of an accessory spleen followed by pancreatic tail. Because an accessory spleen does not usually require treatment, accurate preoperative diagnosis is important.

Torsion of wandering spleen

A 30-year-old gravida 2 para 2 lady presented with severe lower abdominal pain and vomiting of 2 days duration with a similar episode 1 month back. Clinical examination revealed a large tender intra-abdominal mass in lower abdomen. Pregnancy test was negative. Blood count, liver and kidney function tests were normal. Abdominal ultrasonography revealed the spleen in the hypogastric region. There was no free fluid and the rest of the examination was unremarkable. Multidetector CT showed a “wandering spleen” in the lower abdomen with an abnormal horizontal axis (Fig. 1). The classic “whorl” sign (due to twisting of the vascular pedicle of spleen) was seen [1]. These findings were confirmed during laparotomy when splenectomy was performed. An abnormally mobile spleen (“wandering spleen”) is a rare clinical diagnosis. It accounts for 0.25 % of splenectomies. Failure of the fusion of the dorsal mesogastrium with the posterior abdominal wall during embryogenesis has been implicated in its pathogenesis. Women, especially multiparous, are 13-fold more prone due to weakness of the abdominal wall and laxity of the ligaments [1]. Torsion in the wandering spleen can be acute, chronic or intermittent with varied clinical presentations [2]. Imaging helps in early diagnosis and treatment. The treatment options include splenopexy (viable spleen) or splenectomy (non-viable spleen) [2].

Gastric Cancer: Patterns of Disease Spread via the Perigastric Ligaments Shown by CT

The stomach is suspended in the abdominal cavity by perigastric ligaments, which are derived from the dorsal and ventral mesogastrium. These ligaments provide a direct contiguous pathway for the peritoneal spread of gastric cancer. In this article, we discuss the embryology and anatomy of the stomach and describe the specific ligamentous routes along which gastric cancers may spread by direct invasion. Extragastric disease alters the prognosis and treatment options available to patients with gastric cancer. Familiarity with the stomach's embryology will help the radiologist understand its anatomy and, therefore, the patterns of regional spread of gastric cancer. The location of the primary tumor can predict involvement of specific perigastric ligaments because locoregional spread of gastric cancer occurs along the arteries, veins, nerves, and lymphatic channels within those ligaments. Thus, identifying the location of the primary tumor can potentially improve patient outcomes.

Hand-assisted laparoscopy for wandering spleen

A wandering spleen is a rare condition with an unknown incidence. The lack of short gastric vessels and suspensory ligaments is thought to result from a fusion anomaly of the dorsal mesogastrium of the spleen. The major risk in performing a splenectomy for patients with a wandering spleen is overwhelming postsplenectomy infection (OPSI). The incidence of OPSI is 0.13% to 8.1%, with a mortality rate of 30% to 60%. Laparoscopic splenopexy provides the benefits of minimally invasive surgery while avoiding the complications of splenectomy. The reported case presents a patient with a wandering spleen. The patient, an 18-year-old woman, experienced a malarial infection at the age of 5 years and had a computed tomography (CT) scan documenting her spleen in the normal anatomic position. When she was 18 years old, a CT scan showed her spleen located in the right lower quadrant (RLQ). At laparoscopy, the presence of the spleen in the RLQ was confirmed. The spleen could not be easily manipulated with laparoscopic instruments, so a hand port was used to mobilize the spleen to the left upper quadrant (LUQ). No evidence of attenuated suspensory ligaments was seen. The spleen was secured in the left subdiaphragmatic location by the use of a Vicryl mesh bag. An omental sling was used to support the spleen further. A 1-year follow up CT confirmed that the spleen still was located in the correct anatomic position. This is a unique case in that the patient was known to have a normally located spleen at a young age and then found to have a wandering spleen later in life. This could have resulted from a congenital fusion anomaly or attenuation of the patient's suspensory ligaments caused by her previous malarial infection and splenomegaly.

Hepatobiliary and pancreatic: Torsion of an accessory spleen

A 24-year-old man was investigated because of a 3-day history of epigastric pain that was accompanied by nausea and vomiting. Blood tests revealed an elevated white cell count (13.2 × 109/l) and a mild elevation of erythrocyte sedimentation rate (27 mm/hr) and C-reactive protein (18 mg/dl). An ultrasound (US) study revealed a homogeneous hypoechoic mass in the left upper abdomen with an internal tubular anechoic structure. The tubular structure was thought to be a blood vessel but there was no blood flow on a Doppler study. A contrast-enhanced computed tomography (CT) scan showed an ovoid mass, 8 cm in diameter, in the left upper abdomen that was adjacent to the anterior aspect of the distal transverse colon (Figure 1). The mass was clearly separate from a normal spleen, left kidney and left adrenal gland. The mass did not show contrast-enhancement apart from a small wedge-shaped area in the left lateral portion. There was also a whirled tubular structure adjacent to the mass (arrow). At laparotomy, he had a violet, oval tumor under the omentum. The tumor had a twisted vascular pedicle attached to the splenic pedicle. The resected specimen is shown in Figure 2 and pathologic examination confirmed torsion and hemorrhagic infarction of an accessory spleen. In the developing embryo, the spleen arises from several small mesodermal buds in the dorsal mesogastrium. These normally coalesce to form a single organ. However, failure of coalescence can result in the formation of one or more accessory spleens. These can be identified on an US or CT scan in approximately 3%–4% of patients. However, at postmortem examination, the frequency of accessory spleens ranges from 10%–30%. The most common sites for accessory spleens are the splenic hilum, the gastrosplenic ligament and the tail of the pancreas. Most accessory spleens are asymptomatic. However, torsion may occur as described above and hyperplasia can develop after splenectomy. The latter may be clinically significant if splenectomy is performed for hematological disorders such as hereditary spherocytosis and idiopathic thrombocytopenic purpura. On contrast-enhanced CT, the differential diagnosis of torsion of an accessory spleen can include hemorrhagic complications of cysts such as mesenteric cysts, intestinal duplication and pancreatic pseudocysts.

Diaphragmatic crural eventration

Aim:We evaluated patients with gastric volvulus secondary to diaphragmatic pathology.Materials and Methods:Eight patients (5 males and 3 females) presented to the author in a tertiary care center during 1997-2006 were analyzed in terms of age, sex, symptomatology, diagnosis and predisposing factors.Observations:Six had an acute presentation and rest had chronic symptomatology. The two patients who had total gangrene stomach died postoperatively and one patient died preoperatively due to aspiration. All the cases presented with acute symptoms had diaphragmatic pathology, and out of these, three cases had the specific entity, which is named as diaphragmatic crural eventration.Conclusions:Diaphragmatic crural eventration is characterized by the defective development of the right crus of diaphragm, and this is embryologically significant as the right crus and ligaments of the stomach develop from dorsal mesoesophagus and mesogastrium. The author recommends a closer look for this defect of diaphragm while operating a case of gastric volvulus.

Wandering spleen: 11 cases from Uganda.

Abstract Eleven cases of wandering spleen are described of which 8 were in children. Six patients presented with a chronic abdominal mass and 5 with acute torsion. In the chronic case the diagnosis may be clarified by the use of radioactive 51 Cr, and the plain abdominal X-ray is of value in chronic and acute presentations. Splenectomy is required for all acute cases but a technique for preservation of the spleen is feasible in the chronic case. The condition may arise from association of splenomegaly and maldevelopment of the dorsal mesogastrium.

Relationships between gastric development and anatomic bases of radical surgery for cancer.

The aim of this study was to determine with all possible accuracy the processes of embryologic development of the stomach and its lymphatics in order to confirm their supposed link with the modern anatomic bases of gastric cancer surgery. The knowledge of the anatomic behavior of the peritoneal folds and of the lymphatic drainage of the stomach is, in fact, considered the essential basis for the comprehension of the oncologic dissection of the stomach. The study was based on reconstruction of serial histologic sections of 9 human embryos and 8 human fetuses regarding the mesogastric area, as well as anatomic microdissection of 2 9-month fetuses. The proximal part of the stomach is not involved in the rotation mechanism of the other portions; the lesser sac development follows cranial migration of the spleen; the cardiac (pars cardiaca gastris) area is in continuity with the zone of paraaortic lymph node development; lateral and posterior lymph nodes of the hepatoduodenal ligament do not take origin in the dorsal mesogastrium: they develop together with the common bile duct and the ventral pancreas inside the mesoduodenum; the fusion of the dorsal mesogastrium and the gastric fundus with the posterior abdominal wall appears late in development. The embryologic study of the mesogastric area clarifies the real mechanism of development of the stomach and its lymphatic pathways with some differences from classic reports; these results agree with the more recent modification of the lymph nodes classification used in the radical treatment of gastric cancer.

Hox11 is required to maintain normal Wt1 mRNA levels in the developing spleen.

Mice deficient in Hox11 are asplenic. As Hoxll can function as a transcription factor, we examined the spatial and temporal mRNA expression patterns of Hox11 and a candidate target gene, the Wilm's tumor gene Wt1, in the developing spleen. Hox11 mRNA first appears at approximately dE10.5 in the dorsal mesogastrium while Wt1 mRNA is expressed from dE11.5, approximately 24 hours after Hox11 mRNA first appears. Wt1 mRNA was significantly reduced in the spleen anlage of Hox11-null mice suggesting that Wt1 acts downstream of Hox11 in a transcriptional cascade. Additionally, Hox11 protein is able to transactivate the WT1 promoter in a Hox11-null fibroblast cell line. As Wt1-null embryos have recently been reported to be asplenic, these findings suggest that Wt1 and Hox11 may be components common to a genetic hierarchy that is required for spleen development.

Embryonic origins of spleen asymmetry.

The spleen is a vertebrate organ that has both hematopoietic and immunologic function. The embryonic origins of the spleen are obscure, with most studies describing the earliest rudiment of the spleen as a condensation of mesodermal mesenchyme on the left side of the dorsal mesogastrium. The development of spleen handedness has not been described previously, presumably because of the difficulty in assaying spleen position in the embryo and the lack of early, organ-specific molecular markers. Here we show that expression of the homeobox gene Nkx2-5 serves as a marker for spleen precursor tissue. Pre-splenic tissue is initially located in symmetric domains on both sides of the embryo but, during subsequent development, only the left side goes on to form the mature spleen. Therefore, the final location of the spleen on the left side of the body axis appears to result from preferential development of the spleen precursor cells on the left side of the embryo. Our studies indicate that the spleen and heart become asymmetric via different cellular mechanisms. Nkx2-5 may function locally as part of the laterality cascade, downstream of nodal and Pitx2, or it may direct asymmetric morphogenesis after laterality has been determined.

Embryologic bases of extended radical resection in pancreatic cancer.

To analyze whether an embryologic "rationale" exists to the clinical and anatomicopathological data that suggest the execution of extended resections in patients with pancreatic cancer. Reconstruction of serial histological sections of 18 human embryos and fetuses regarding the pancreatic region; anatomical microdissections of two 9-month fetuses. The ventral and dorsal pancreatic buds can be identified until the eighth week of development. A close developmental relationship between the dorsal pancreas and the lymphatic and nervous structures in the dorsal mesogastrium is observed. Other lymphatic stations are exclusively related to the ventral pancreas. The posterior fusion of the dorsal mesogastrium is a late event in embryologic development. The complete fusion of the 2 pancreatic buds occurs later than previously reported in the literature. The close embryologic relations of these buds with the lymphatic and nervous peripancreatic structures may support the need for extended resections in patients with pancreatic cancer.

Time course of expression of neuropeptide Y, calcitonin gene-related peptide, and NADPH diaphorase activity in neurons of the developing murine bowel and the appearance of 5-hydroxytryptamine in mucosal enterochromaffin cells.

Serotoninergic and cholinergic neurons are known to appear earlier in the ontogeny (day E12) of the murine gut than those containing substance P or vasoactive intestinal peptide (day E14). It has also been demonstrated that proliferating neural precursors coexist with mature neurons in developing enteric ganglia. These observations have led to the hypotheses that peptidergic neurons develop later than those that utilize small molecule neurotransmitters and that the activity of early developing neurons may affect the phenotypic expression of coexisting neuroblasts. As a partial test of these hypotheses we studied the phenotypic expression of neurons recognized by antisera to neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP), and of those visualized by the histochemical demonstration of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity. NADPH diaphorase activity, which is coexpressed with NPY immunoreactivity in all submucosal and many myenteric neurons, was first found on day E11 in clusters of cells in the dorsal mesogastrium. These cells also expressed neurofilament reactivity and thus were developing along a neuronal lineage. Enteric neurons that expressed NADPH diaphorase activity were visualized in the stomach one day later, on day E12. At this time, NADPH diaphorase-containing cells could no longer be demonstrated in the dorsal mesogastrium. NPY immunoreactivity first appeared in the wall of the bowel on day E12, when it was seen in cells in the presumptive stomach. By day E13, the entire length of the bowel contained NPY-immunoreactive neurons. Cells that displayed NADPH diaphorase activity were found at this time at both ends of the alimentary tract, but did not appear in the ileum until day E18. In contrast, CGRP immunoreactivity could not be detected anywhere in the gut until day E17, but by day E18 all regions of the bowel contained CGRP-immunoreactive neurons. Endogenous 5-HT was first detected at day E16 in mucosal epithelial cells in all segments of the gut except the stomach, where it appeared at day E18. The NPY/NADPH diaphorase set of neurons thus develop before the acquisition of a detectable level of endogenous 5-HT or enteric neural 5-HT receptors (which arise in the foregut at day E14). These observations demonstrate that enteric neurons that express small molecule neurotransmitters do not necessarily develop earlier than peptidergic neurons as a class; however, various types of enteric neurons do appear in a sequential order.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation of red pulp and evaluation of hemopoietic role of human prenatal spleen.

Both the development of red pulp and hemopoietic activity in spleen obtained from 62 human embryos and fetuses between 30 days and 20 weeks after ovulation were investigated light and electron microscopically. The spleen develops in the left-posterior portion of the dorsal mesogastrium at 35-40 days after ovulation. At the 8th week after ovulation, reticular cells formed a three-dimensional meshwork. Two types of reticular cells (dark and clear reticular cells) were observed in the splenic cord in the 12-13th week after ovulation. Mature hemopoietic cells, mostly of the erythroblastic series, increased in number in the extravascular spaces with the development of the fetus. However, presumptive hemopoietic stem cells or "undifferentiated mononuclear cells" (Fukuda, 1973a) did not appear in the spleen. Moreover, immature hemopoietic cells such as proerythroblasts, myeloblasts and megakaryoblasts could not be detected. Therefore, despite the occurrence of a well-developed reticular cell network, hemopoiesis was judged to have not taken place in human fetal spleen. Macrophages appeared in the spleen at the 8th week after ovulation and increased in number with the the development of the fetus. Phagocytosis of decrepit blood cells proved to be an essential function of the spleen.

Spleen imaging—Enlargement of the spleen

A 19-year-old man was admitted for the acute onset of abdominal pain. He had experienced right abdominal pain for a month before admission but had no other symptoms. Physical examination revealed a hard, somewhat tender, midabdominal mass. Ultrasound and computed tomography (CT) showed a solid vascular mass in the midabdomen. No spleen was demonstrated. The nature of the mass was not clear and a neoplasm was suspected. On liver-spleen scintigram, uptake of colloid was seen in the large mass (Fig. 1). The spleen was not visualized in the left upper quadrant and the mass was considered to be a markedly enlarged and displaced spleen. At surgery a huge congestive spleen, weighing 1190 g, was found. No adhesions or indications of infarction were noted. The pedicle of the spleen was elongated and twisted. Pathologic examination only showed congestion of the spleen. Ectopic, aberrant, ptotic, floating, and wandering spleen are some of the names attached to a rare condition, in which the spleen is found in locations other than the left upper quadrant. Elongation of the splenic pedicle and malformation of the dorsal mesogastrium with laxity, poor development, or even absence of the lienogastric and lienorenal ligaments cause this condition) '2'3 It often occurs in females in childbearing age, and it must be differentiated from a tumor or an ovarian cyst. 34'5 A sudden torsion of the pedicle may cause acute venous occlusion which sometimes leads to infarctions. When the torsion is gradual the spleen may reach huge dimensions, as shown in the present case. The ability to take up colloid is apparently preserved. Diagnosis may be difficult. When the enlarged spleen is not located in the left upper quadrant it may not be recognized and mistaken for a neoplasm. Plain x-rays, excretory urography, barium enema, upper GI series, ultrasound, and angiography have been suggested, but preoperative diagnosis is rarely made. 3'6 Scintigraphy may help in establishing the nature of the mass. Causes of spleen enlargement follow. COM MON

Embryology of the sheep. 3. The respiratory system, mesenteries and celom in the fourteen to thirty-four day embryo.

AbstractThe day‐by‐day developmental changes which occur in the respiratory system, mesenteries and celom of the sheep embryo from 14 to 34 days coital age are documented chronologically and described. This work provides standards of normal development which can be used as a basis for future work on abnormal development of these structures.The respiratory diverticulum which first appears on the seventeenth day is seen as a primitive lung bud on the nineteenth day and becomes bilobed on day 20. By the twenty‐first day a laryngotracheal tube is present and the larynx develops in the next ten days.The dorsal mesogastrium forms on the eighteenth day and the omental bursa is seen as an invagination by the twenty‐first day. A splenic primordium associated with the omentum is present by the twenty‐seventh day.The dorsal mesentery appears on the eighteenth day and undergoes torsion, herniation and coiling on the twentieth, twenty‐second and twenty‐seventh days. The ventral mesentery is present on the seventeenth day but disappears centrally between the eighteenth and twenty‐first days.An extraembryonic celom is seen on the fourteenth day and the formation of the intraembryonic celom occurs on day 15. Development of the pleuroperitoneal membranes commences on the twenty‐first day. Complete separation of pericardial and pleural cavities is completed by the twenty‐eighth day.

ASPLENIA: REPORT OF A CASE DIAGNOSED ANTEMORTEM ON THE BASIS OF ROENTGENOGRAMS.

Over 100 cases of congenital absence of the spleen in association with cardiac abnormalities, varying degrees of visceral symmetry, and situs inversus have been reported. The first account was made by Martin in 1826, but only recently has this combination of anomalies been recognized as a syndrome. Ivemark (4) designated it “asplenia, a teratologic syndrome of visceral symmetry.” It is the purpose of this communication to report a case diagnosed antemortem on the basis of roentgenograms. A review of the mother's history revealed multiple x-ray exposures to the abdomen during the first trimester of pregnancy. The etiology and pathogenesis of asplenia are unknown; however, the explanation for this combination of abnormalities must lie in the closely related embryologic development of the structures involved. At an ovulation age of from twenty to thirty-six days (2–4, 6) the splenic anlage forms from the dorsal mesogastrium; the atrioventricular cushion develops from the cardiac reticulum; the conotruncus se...

人胎児腸管の発生学的研究

1. The pharyngeal pouches contact widely with the skin ectoderm and remain simple till the Streeter's horizon XV stage.2. During the next horizon XVI stage the contact areas becoming smaller surrounded by the mesenchymal mass form 3 pairs of small cervical vesicles corresponding to the 2nd, 3rd and 4th cervical grooves. The 4th cervical groove is the smallest and disappears during the XVI stage, while the 2nd and 3rd are visible in the next XVII stage passing away the former earlier, the latter the largest a little later.3. During these changes of the external forms the internal pharyngeal pouches begin to form the ductless glands. From the 3rd pouches begin to differentiate the parathyreoids 3 and the thymus, from the 4th the parathyreoids 4 and the lateral thyreoids. When these glands appear in form, these pouches are shut off from the cavity of the primive pharynx.4. This differentiation of these ductless glands indicates that it begins a little later than the Streeter's assertion. After the latter's description begins this differentiation in the XIV stage while our material late in the XVI.5. The oesophagus and trachea are embeded in the back body wall till our latest stage of XVIII, although the differentiation of the tissue is proceeding.6. As the stomach deviates to the left, there appears mesogastrium dorsale enclosing the cavity of the bursa omentalis with the dorso-caudal surface of the stomach. After Streeter the pouch for bursa omentalis appears in the horizon XII stage. In our material of the XIV stage the deviation of the stomach is so much advanced that the mesogastrium dorsale and ventrale are distinct.7. The mesoduodenum dorsale becomes evident as “Pancreaswulst” at the site of the dorsal mesentery continuous with the dorsal and ventral mesogastrium in the XVI stage, in which the site of the dorsal and ventral pancreas becomes definite dorsal to the duodenum. Its tissue is becoming massiv through the XVII to XVIII stage that at the latter stage it encloses the distal part of the duodenum close to the right side of the mesocolon.8. After Streeter a definitive mesentery beginning near the caudal end of the duodenum and extending downward to include the upper half of the colon can be spoken first in the XVI stage, but in our material a thin mesentery is visible already in the XIV stage without formation of a intestinal loop, the swelling of caecum also visible in this stage.9. The formation of a intestinal loop begins in the XV stage, which protrudes straight through XVI, XVII stages till about 3mm long, then appear in the XVIII stage curvatures at the cranial half of the loop. In the XVI stage begins the formation of the appendix.

Implications of Agenesis of the Spleen on the Pathogenesis of Conotruncus Anomalies in Childhood

Six embryos measuring 9–12 mm in greatest length have been shown by the writer to contain early splenic primordia in the left aspect of the dorsal mesogastrium. Their ovulation age is estimated to be 31–36 days. Temporal relations of splenic formation to conotruncus septation and division of the A‐V canal have been discussed. This last is divided before septation of the conotruncus is completed. The author has shown that early splenic primordia exist at the time of fusion of the A‐V canal cushions. At the same time there is initiation of pulmonary lobation, and there is a primitive gut mesentery.