( The Skull ( Cranium ( ( Face The Axial skeleton ( ( Cervical region ( ( Dorsal region ( Ribs ( The Vertebral column ( ( Sternum ( Lumbar region ( Sacral region ( Coccygeal region ( Scapula ( Shoulder girdle ( Coracoid ( ( Clavicle ( ( ( Arm ( Humerus ( ( ( Fore limb ( Forearm ( Radius ( ( ( Ulna ( ( ( ( ( Carpus The Appendicular skeleton ( ( Hand ( Metacarpus ( ( Phalanges ( ( Pelvic girdle ( Ilium ( (Hip bone) ( Ischium ( ( Pubis ( ( ( Thigh ( Femur ( Hind limb ( ( Leg ( Tibia ( ( Fibula ( ( Foot ( Metatarsus ( Phalanges The bodies of birds contain many air reservoirs to make them light that flying may be more easy. Many bones have their weight in proportion to size and strength thus greatly reduced. In very young birds the cavities of bones contain, instead of air spaces, loosely arranged red marrow, which is in most bones later absorbed. The air reservoirs in bones are most capacious in the best flyers. In the non-flyers more of the bones retain their red marrow. The bones supplied with air spaces are relatively larger than in mammals, and are provided with small transverse osseous columns which cross in different directions and from side to side. These cross beams give stability to the thin wall of the bone. The membranes lining these cavities are very vascular. THE AXIAL SKELETON THE SKULL