Appendicular Skeleton

It is a part of skeleton that occurs laterally in the body and usually attached to axial skeleton at an angle. Appendicular skeleton has 126 bones arranged in two complexes, girdles and limb bones.

Girdles

They are bony supporting complexes of skeleton which mediate attachment of limb bones to axial skeleton. There are two girdles, pectoral and pelvic.

•  Pectoral Girdle (Shoulder Girdle). It is supporting bony complex between upper limbs and axial skeleton. Pectoral girdle consists of two halves, right and left. Each half consists of two bones, clavicle and scapula. Clavicle or collar bone is f-shaped twice curved, thin and elongated bone. At one end it is connected with acromion process of scapula and at the other end it is attached to manubrium of sternum. Scapula is a flat, thin curved triangular bone, popularly called shoulder blade. It extends on the back side of thorax between second and seventh rib. It has a hook- like coracoid process and a diagonally placed sharp protuberance called spine. At one end spine possesses thick acromion process. Scapula contains glenoid cavity for articulation with head of humerus.

Fig. Pectoral girdle (Posterior view)

•  Pelvic Girdle It is an irregular trough-shaped supporting bony complex between hind limbs and axial skeleton. Pelvic or hip girdle consists of two halves called innominates or  coxals. Innoniminates are joined together by little movable pubic symphysis. Each innominate consists of three fused bones—largest superior ilium, anterior inferior pubis and posterior  inferior ischium. A large oval gap called obturator foramen occurs between pubis and ischium. Ilium, ischium and pubis jointly form an articular cavity called acetabulum. Head of femur bone is fixed into it. Pelvic girdle is attached posteriorly to sacrum. Sacrum and coccyx form basin shaped pelvis. Ilium possesses two depressions, small lesser sciatic notch and large greater sciatic notch.

Fig. Anterior view of pelvis (hip girdle + sacrum + coccyx)

Functions :

•  It transfers weight of whole body over the hind limbs.
• It provides strength to the sacral region.
•  It is the site for the attachment of hind limb bones.
• It is the site for the attachment of leg muscles.
•  It provides protection to soft organs inside the pelvic region.

Differences between Ilium and Ileum

• It is component of pelvic girdle.    It is component of small intestine.
• It is a curved plate.                          It is tubular coiled structure.
• Ilium is bony structure.                   Ileum is soft hollow tube.
• It is a supporting structure.            It is part of the digestive system.