A number of adaptations are appeared in the skeleton of birds for flight. Most of the bones are pneumatic and filled with air sacs instead of bone marrow. Bone marrow is a specialized type of soft diffuse connective tissue called myeloid tissue. It takes part in production of blood cells hence, known as aemopoictic tissue. It is composed of adipose tissue, areolar tissue and blood. The red bone marrow produces RBCs, WBCs, platelates, granular leucocyte like basophils, eosinophil and neutrophiles while yellow bone marrow produces blood cells in emergency.