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What Is the Appendicular Skeleton?

The appendicular skeleton is responsible for movement.
The lower limbs attach at the pelvis.
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  • Written By: Jessica Gore
  • Edited By: J.T. Gale
  • Last Modified Date: 26 March 2014
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The appendicular skeleton is the portion of the skeleton that includes the limbs, the pelvis, and the pectoral girdle. For adult humans, this includes approximately 126 of the roughly 206 bones that make up the skeleton. Its counterpart, the axial skeleton, is comprised of the skull, the spinal column, the sternum and the ribs. The primary function of the appendicular skeleton is movement and support, whereas the primary function of the axial skeleton is protection of internal organs. In general, all bones of the human skeleton also assist in mineral storage and blood cell production.

Two girdles, the pectoral girdle and the pelvis, serve as anchors to attach the appendicular portion to the axial skeleton. The pectoral girdle, consisting of the collarbone and shoulder blades, connects the upper limbs to the sternum. Each shoulder blade sits at rest over the ribs of the back, and the collarbone attaches in the front of the body with the sternum. The upper arm bone fits into a cuff of muscles that sits between the shoulder blade and collarbone. As this is the only point of attachment of the upper limbs to the axial skeleton, the shoulder joint is allowed a wide range of motion compared to other joints, but it also holds increased potential for injury, so care must be taken by athletes to avoid dislocation of the shoulder.

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Lower limbs attach at the hips where the femur — the largest bone in the human body — fits into the pelvis. A comparatively sturdy structure, the pelvis is actually comprised of several distinct bones joined by five different cartilaginous joints. The largest and most prominent areas of the pelvis are the hips. Each hip is made up of three fused bones: the pubic bone, the ilium, and the ischium. At the back of the body, the hips come together at the sacrum, which connects the lower appendicular skeleton to the axial skeleton by fusing with the tailbone.

Both the upper and lower limbs attach to the girdles using ball and socket joints, in which the rounded end of a bone fits into a cup-shaped socket of muscles. This arrangement allows for a maximum degree of flexibility, allowing the limbs to move freely in a rotating motion. By comparison, the hinge joints of the knees and elbows allow a relatively restricted motion along a single plane.

Perhaps the most complex structures of the human skeleton, the hands and feet together make up more than half of the bones in the human body, with 27 bones in each hand and 26 in each foot. The wrists and ankles are a particular type of joint known as condyloid. These joints allow movement along two planes but with less freedom of rotation than the ball and socket joints. The delicate structure and flexibility of the hands and feet are remarkable in that they allow humans to do many of the things that are considered to be uniquely human, such as writing, playing music, and walking upright.

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Discuss this Article

anon295713
Post 3

Describe the make-up and role of both the axial and appendicular skeleton, including a list of the major bones?

anon275264
Post 2

Is a pendicular skeleton the same as an apendicular skeleton?

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