الفهرس 
Acknowledgements
Microscopic studiesOnly 14 pages are availabe for public view
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Abstract
The present work studied the prenatal development of the rabbit stomach. It was carried out on 87 embryos. The collected material which covered most of the prenatal developmental stages ranged from 10 to 30 day. The main results which were obtained from this study could be summarized as follows:
Concerning the stomach primordium
- The primordium of the rabbit stomach appeared at the 10th day of gestation as an enlargement of the foregut. At this age, the dorsal border was thick and formed the greater curvature, while the ventral border was thin and formed the lesser curvature.
Concerning the wall of the stomach
- The stomach of rabbit was characterized by thin wall whose layers were well organized on the 27th day of gestation.
- The mucosal folds were firstly observed at the medial aspect of the fundus on the 20th day of gestation. On the 23th day, the mucosal folds were observed in all regions of the stomach. They showed varying height, width and number and had a core of lamina propria. On the 27th day, large branched mucosal folds could be observed within the fundus. These folds had a core of lamina propria, muscularis mucosa and submucosa.
- The lining epithelium of the stomach was stratified at 10 day old embryo. By day 27, it transformed to the simple columnar type in all parts of the stomach except near the cardia, where it transformed into stratified squamous epithelium. The reorganization of the surface epithelium from stratified type to simple columnar epithelium occurred by degeneration and not by cellular desquamation as revealed by scanning electron microscopy. - The formation of the gastric pits began on the 20th day at the fundus. On the 23th day, these pits could be observed at all regions of the stomach. The gastric glands started to appear from the 23th day of gestation as evaginations of the epithelium.
- In the embryonic stage, the stomach of the rabbit was of compound monolocular type, where it was lined by both glandular and non glandular mucosa. The non glandular part was confined to a narrow area near the cardia and was lined by stratified squamous epithelium, while the glandular part was arranged in three regions; cardiac, fundic and pyloric gland region which was lined by simple columnar epithelium.
- The muscularis mucosa was firstly observed at the cranial aspect of the fundus on the 23th day as a thin discontinuous layer of circular smooth muscle fibers. It became thick and continuous in all regions of the stomach on the 30th day.
- The tunica muscularis appeared late; nearly at the middle of gestation period (15-16 day old embryo). The development of tunica muscularis of the rabbit stomach was completed on 27th day of gestation. It was thicker at the pyloric part than the other regions of the stomach at all stages of development. The cardiac sphincter was formed mainly by the inner circular muscle layer in addition to the cardiac loop of oblique muscle fiber, while the formation of the pyloric sphincter was only by the oblique muscle layer.
- Telocytes could be observed on the 23th day; between the muscle fibers, around the blood vessels and the myenteric plexus as well as it was abundant in the tunica serosa. On the 30th day, it formed a network within the tunica submucosa as observed by scanning electron microscopy.
Concerning the functional development of the stomach
- The histochemical studies showed varying degrees of positive reaction to PAS and alcian blue in the stomach regions at the various stages of prenatal development. On the 30th day of gestation, the epithelial cells of the mucosal surface and gastric pits in the three regions of the stomach gave positive reactions with PAS and alcian blue. In addition, only the fundic glands showed positive reaction with PAS.
- The endocrine cells were seen initially on the 23th day of gestation. It increased in number with the advancement of the fetal age. By the end of gestation period, most the cells were observed at the gastric pits as well as inbetween the glands and within the glandular epithelium. Some cells were located within the lamina propria at a distance from the epithelium.
- On the 23th day, the fundic glands consisted of three types of cells; undifferentiated cells, future mucous neck cells and pre-oxyntic cells as revealed by transmission electron microscope. On the 30th day, the pre-oxyntic cells differentiated into primitive parietal cells (oxyntic cells) which characterized by presence of intracellular canaliculi. In addition, the primitive chief cells whose cytoplasm was characterized by abundant rough endoplasmic reticulum and zymogenic granules could be observed at this age.
Concerning the rotation of the stomach
- On the 11th day, the stomach rotated about 90º on the left side. On the 12th day, another rotation of the stomach took place about 45º also on the left, resulting in the greater curvature became on the left side and ventral, while the lesser curvature became on the right side and dorsal.
Concerning the gross morphology of the stomach
- In the full term embryo, the rabbit stomach was G- shaped with an oblique long axis and located mainly on the left side. It was positioned in the intrathoracic part of abdominal cavity and extended caudally into the abdominal cavity proper till the level of the 4th lumber vertebra.