Human cardiovascular system, organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. Blood is propelled by the heart, with arteries, capillaries, and veins serving as the major vessels of the system. The human body is the physical substance of the human organism. Characteristic of the vertebrate form, the human body has an internal skeleton with a backbone, and, as with the mammalian form, it has hair and mammary glands. The skeletal structure of a human being (left) and of a gorilla (right). Several differences allow the human to walk erect on two legs with a striding gait rather than move in a knuckle-walking fashion like the gorilla. In the pelvis these differences include shorter ischia, a broader sacrum, and broader, curved-in ilia with a lower iliac crest. In the legs the femurs (thighbones) are. Human skeleton - Skull, Bones, Joints: The interior of the cranium shows a multitude of details, reflecting the shapes of the softer structures that are in contact with the bones. The internal surface of the vault is relatively uncomplicated. In the midline front to back, along the sagittal suture, the seam between the two parietal bones, is a shallow depression—the groove for the superior. Human muscle system - Upper Limb Changes: The human upper limb has retained an overall generalized structure, with its details adapted to upright existence. Among the primitive features that persist are the clavicle, or collarbone, which still functions as part of the shoulder; the ability to twist one of the forearm bones (the radius) around the other (the ulna) so that the palm is turned. Human evolution, the process by which human beings developed on Earth from now-extinct primates. The only extant members of the human tribe, Hominini, belong to the species Homo sapiens. The exact nature of the evolutionary relationships between modern humans and their ancestors remains the subject of debate. The human skeleton is the internal framework for the human body. It consists of many individual bones and cartilages, as well as bands of fibrous connective tissue—the ligaments and the tendons—which serve in intimate relationship with the parts of the skeleton. Human skeleton - Axial, Visceral, Bones: The cranium—the part of the skull that encloses the brain—is sometimes called the braincase, but its intimate relation to the sense organs for sight, sound, smell, and taste and to other structures makes such a designation somewhat misleading. The cranium is formed of bones of two different types of developmental origin—the cartilaginous, or. Skeletal muscle controls movement, posture (position of the body), and balance. A person can move skeletal muscle just by thinking about it and then doing it. Cordlike structures called tendons connect skeletal muscle to the skeleton. As skeletal muscle tightens, or contracts, it gets shorter. It pulls on the bones attached to it. Human muscle system, the muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle—like the muscles of all vertebrates—is often divided into striated muscle, smooth muscle, and cardiac muscle.