الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
This study was carried out on 40 chick embryos collected from incubated eggs of Dandarawi chickens (Gallus gallusdomesticus )at embryonic days 5, 7, 9, 11, 13, 15, 17 and 19 in addition to 15 chicks at day of hatching, one week and two weeks post-hatching(five for each age) collected from farm of Faculty of Agriculture, Assiut University, Egypt for the anatomical, histological, histochemical, SEM, semithin sections and TEM investigations to explain the developmental changes of chicken’s esophagus, crop and proventriculus during their pre- and post-hatching periods.
The first appearance of both parts of the esophagus was at 5thday of incubation. The cervical part was related dorsally to aorta and ventrally to trachea and at and from 9thday it became subcutaneouslly located. At 7thday of incubation the cervical part expanded to form the crop.
The thoracic part of esophagus was related ventrally to trachea at its cranial part and caudally became related to tracheal bifurcation and heart. The proventriculus appeared at 5thday of incubation and it was related dorsally to aorta and ventrally to liver. At 11thday of incubation the proventriculus reached the adult position in the left side related dorsally to left lung and left abdominal air sac, ventrally to left lobe of liver, laterally to left abdominal wall and medially to right lobe of liver.
We found that the length of the cervical part of the esophagus was double the length of the thoracic part. We observed that the morpho metrical measurements which included the height of the epithelium, the height of the mucosal folds, the number of the mucosal folds, the diameter of both esophageal and proventricular glands and the thickness of the muscular layer increased with the advancement of the age.
Histologically the cervical and thoracic parts of the esophagus were lined by pseudo stratified columnar epithelium at 5th and 7th days chick embryo, two layers of cuboidal cells at 9th- 13th days chick embryo and stratified squamous epithelium from 17th day chick embryo till post-hatching. The esophageal glands appeared for the first time at 13th day chick embryo and become functional from 19th day chick embryo. These glands reacted positively to PAS and AB from age 15th day chick embryo and to bromophenol blue from age of 17th day chick embryo. The muscular layer differentiated into inner circular and outer longitudinally at 11th day chick embryo in the thoracic part earlier than the cervical part.
The results of SEM at 9th day chick embryo showed that the surface was covered with short ridge-like mucosal folds which were arranged in very close association to each other with solitary cilium protruded from the surface. At 13th and 19th day chick embryo the surface was covered with polyhedral cells with numerous short irregular microvilli and patches of long cilia.
The crop appeared at 7th day of incubation. It was lined by pseudo stratified columnar from 7th to 13th day chick embryo and become stratified squamous from 15th day chick embryo till post-hatching. The crop not contained any gland. The lamina muscularis mucosa appeared firstly at 13th day of incubation and also at this age, the muscular layer is differentiated into two layers. Its epithelium reacted positively with AB from age of 13th day of incubation, positively to PAS from age of 17th day of incubation and to bromophenol blue from age of 11th day.
The results of SEM showed that the surface epithelium at 9th day chick embryo was covered by ciliated cells with the occurance of single cilium and non-ciliated cells. At 13th and 19th days chick embryo, the cilia increased in number and the non-ciliated cells were covered by microvilli and become most abundant.
The proventriculus appeared as narrow tube at 5th day chick embryo. It was lined by pseudo stratified columnar epithelium from 5th to 13th day chick embryo and from 17th day chick embryo till post-hatching it become simple columnar. The lamina muscularis mucosa begin to appear as isolated bundles at 17th day chick embryo. The proventricular glands appeared firstly at 7th day chick embryo and begin its branching from 9th day chick embryo till post-hatching. These glands were lined by pseudo stratified columnar type from 7th to 11th day chick embryo and become lined by simple columnar at 13th day chick embryo. The muscular layer begin to differentiate into three layers of smooth muscle fibers at age of 11th day chick embryo. The periventricular epithelium and the periventricular glands were reacted positively to PAS, AB and bromophenol blue.
The results of SEM of the proventriculus showed that the surface was covered with short ridge-like mucosal folds at 9th day chick embryo and at 13th day chick embryo, the surface was covered with polyhedral cells which covered with numerous short microvilli and two periventricular glands with large central cavity were embedded in the sub mucosa. At 19th day chick embryo, the epithelial sheet of the proventriculus damaged and the individual columnar cells were observed and these cells were uniformly covered with few and short microvilli. The proventricular glands were arranged in a concentric mannar with large central excretory cavity and the size of the proventricular glands was larger in this age more than the previous ones.
The results of TEM showed that the proventricular glands were lined by pseudo stratified columnar at 9th and 13th day chick embryos and lined by simple columnar at 19th day chick embryo. Adjacent cells were joined by desmosomes. The nucleus was round to oval euchromatic and the cytoplasm contained abundant mitochondria, rough endoplasmic reticulum, ribosomes and lipid droplets. The interstitial tissue contained fibroblasts and telocytes. The fibroblast had irregular cell body with cell processes and the cytoplasm was poor in organelles. The telocytes were composed of cell body and two long cell processes that composed of dilated part called podoms and thin long part called podomeres.