The adrenal glands are enclosed in two-layered capsule; an outer fibrous and an inner cellular layers. The cellular layer haselongated spindle shaped connective tissue cells. Originating from the capsule C. T. trabeculae. Clusters of cells resembled the cmedullary cells sometimes were found within the adrenal cortexand trabeculae. Their appearance was definitely related to theadvancing of age. Adrenal cortex is structured in three different layers. The zona glomerulosa; the outer most layer. The zona fasciculata; the middlelayer, and the zona reticularis; close to the adrenal medulla. The zona glomerulosa cells were large cuboidal and arranged ill subcapsular glomeruli. The zona glomerulosa and itsoccurrence of respiratory diseases in chickens.In the present work, 204 specimens (102 lungs and 102 tracheas) of 102chickens with respiratory manifestations collected from EI-sharkia and EI-dakahlia Governorates from different breeds with different ages all over theyear seasons. The specimens were examined phenotypically andgenotypically for the detection of the most important virulence genes ofM.gallisepticum and E. coli accused of CRD occurrence in chickens.Concerning to the prevalence of single and combined infection withM.gallisepticum and E. coli in respiratory organs of respiratory manifestedbroilers, the recorded results revealed that E. coli was highly detected with apercentage of 49% followed by M gallisepticum (13.7%) and lastly combinedM. gallisepticum E. coli infection (8.8%).