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The appendicular skeleton forms during development from cartilage, by the process of endochondral ossification. The appendicular skeleton is divided into six major regions: Shoulder girdle (4 bones) - Left and right clavicle (2) and scapula (2). Arms and forearms (6 bones) - Left and right humerus (2) (arm), ulna (2) and radius (2) (forearm).
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The pectoral girdles are to the upper limbs as the pelvic girdle is to the lower limbs; the girdles are the part of the appendicular skeleton that anchor the appendages to the axial skeleton. In humans, the only true anatomical joints between the shoulder girdle and the axial skeleton are the sternoclavicular joints on each side.
The body plan of tetrapod limbs are so similar (especially the pentadactyly) that they are given shared terminologies for each component of the appendicular skeleton. [ 3 ] The proximal half of the limb proper has one long bone , the stylopodium (plural: stylopodia ), which may be the humerus of the upper arm (proximal forelimbs), or the femur ...
The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs. The human skeleton performs six major functions: support, movement, protection, production of blood cells , storage of minerals, and endocrine regulation.
Only skeletal and smooth muscles are part of the musculoskeletal system and only the muscles can move the body. Cardiac muscles are found in the heart and are used only to circulate blood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups around joints. [8]
Bones are commonly described with the terms head, neck, shaft, body and base. The head of a bone usually refers to the distal end of the bone. The shaft refers to the elongated sections of long bone, and the neck the segment between the head and shaft (or body). The end of the long bone opposite to the head is known as the base.
The bone or other structure the muscle is attached to that remains immobile during the action. The term "bone" is omitted from bone names. Insertion The attachment point of the muscle, on a bone or otherwise, that moves during the action. Artery The artery which supplies the muscle with blood. The term "artery" is included to avoid confusing ...