الفهرس 
INTRODUCTION
Material and MethodsOnly 14 pages are availabe for public view
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Abstract
The camel has economic importance especially the immune system so the present study was conducted to investigate the development of the thymus gland and spleen in camels during prenatal and postnatal period. For the prenatal period, 69 camel fetuses were utilized. Whereas, 3 samples used for post natal phase. Thymus: The first sign of the thymic primordia appeared at 4 cm CVRL as a mass of epithelial cells surrounded by condensation of mesenchymal cells. During the same period at 4cm CVRL the first lymphocytes (lymphogensis) were also seen. At 6 cm CVRL, the thymus consisted of two lobes and the thymic lobulation was clear with highly vascular connective tissue septa.
The thymuses extended form the neck till the thoracic inlet.
At 10 cm CVRL the thymic connective tissue capsule was revealed, and it was formed mainly of collagen fibers as was demonstrated by Masson’s trichrome stain.
The thymic cortex and medulla was observed.
The outer thymus tissue was densely populated by lymphoid cells( lymphoblast, medium and small lymphocytes and reticuloepithelial cells), while the inner thymic tissue was less cellular and more vascular, being populated by large numbers of reticuloepithelial cells and few lymphoid cells.
The thymus was differentiated into cortex and medulla at 20 cm CVRL, and it was infiltrated by lymphocytes, macrophages and mast cells.
The first sign of Hassall’s corpuscle development was observed at 10 cm CVRL within the medulla.
They appeared as eosinophilic mass surrounded by epithelioreticular cells. At 35 cm CVRL, they showed sing of degeneration, PAS positive material and basophilic patches that represent calcification.
The thymus of one year old showed complete lobulation with clear demarcation of cortex and medulla.
This demarcation became invisible by the second year where the thymus began to loss its lobular architure, and the medulla enlarge on the expense of the cortex.
The amount of reticular fibers and the Hassall’s corpuscles occupies most of the medullary tissue.
At the same time, the connective tissue capsule leading to thymic involution. Spleen The present study revealed that the splenic primordium was observed at 4 cm CVRL as condensed mass of mesenchymal cells of the dorsal mesogastrium beside hepatic, gonadal and mesonephros primordia.
At 4 cm CVRL, the spleen was enclosed by two or three layers of the mesenchyme which give rise to connective tissue capsule later. Lymphopoitic differentiation and vascularization were also recognized at this stage. At 6 cm CVRL, the lymphoid cells aggregate to form lymphopoietic focci.
The amount of lymphocytes becomes aggregated around the blood space, forming the primitive lymphoid follicles that were not organized into nodules.
At 10 cm CVRL, the charactrestic organ structure became established as the splenic vascular lobules begin to be formed. The splenic lobules consisted of central arteriole surrounded by a sheath of lightly stained cells.
At the periphery of these lobules, the red pulp was observed. The appearance of arterial blood vessels is accompanied with appearance of venous blood vessels.
As revealed by the appearance of the subcapsular sinus under the connective tissue capsule.
At 14 to 20 cm CVRL, the capsule consisted of collagen and reticular fibers from which septae of the same structure were extended inward. Lymphoiesis and erythropoiesis were evident and mitotic cells, mast cells, plasma cells and macrophages were observed.
At 22 to 30 cm CVRL, the outer capsule is divided into outer collagenous and inner muscular (smooth muscle) layers. The parenchyma consisted of red and white pulp.
The red pulp composed of venous sinusoids and splenic cords. The white pulp was composed of lymphoid follicle and central arteriole.
At 25 cm CVRL, the splenic cords showed invasion by macrophages, mast cell and plasma cell with different types of lymphocytes. At 32 cm CVRL, the red pulp showed various forms of ellipsoiode, with various cells of granulopoietic that indicate lymphopoiesis.
At 14 cm CVRL, the reticular fibers were observed in the capsule and elsewhere.
With advancing age, they became especially prominent especially around blood vessels.
At 75 cm CVRL, the lymphatic nodules became involuted and at 112 cm CVRL, the plasma cells appeared to be increased in number.
The mature spleen had well developed red and white pulp.
The capsule had well demarcated outer fibrous and inner muscular layers.
The lymphatic nodules had clearly defined germinal centers indicating the progression of antigenic stimulation.