Examville.com - Human Skeletal System: Appendicular Skeleton

HUMAN SKELETAL SYSTEM APPENDICULAR SKELETON It is a part of skeleton that occurs laterally in the body and is usually attached to axial skeleton at an angle. Appendicular skeleton has 126 bones arranged in two complexes, girdles and limb bones. Girdles The are bony supporting complexes of skeleton which mediate attachment of limb bones to axial skeleton. There are two girdle, pectoral and pelvic. 1. Pectoral Girdle (Shoulder Girdle). It is a supporting bony complex between upper limbs and axial skeleton. Pectoral girdle consists of two halves, right and left. Each half consist 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 contain glenoid cavity for articulation with head humerus. \

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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. Innominates 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, ischimum and pubis jointly form an articular cavity called acetabulum. Head of femur bone is fixed into it. Pelvic girdle is attached at the posterior to sacrum. Sacrum and coccyx form basin shaped pelvis. Ilium possesses two depressions, small lesser sciatic notch and large greater sciatic notch.

Functions : (i) It transfers the entire weight of the body to the hind limbs. (ii) It provides strength to the sacral region. (iii) It is the site for the attachment of hind limb bones. (iv) It is the site for the attachment of leg muscles. (v) It provides protection to soft organs inside the pelvic region.

3. Limb Bones. Are of two types, fore limbs and hind limbs. 1. Bones of Fore-Limbs. There is a pair of fore-limbs or upper limbs. Each fore-limb has 30 bones and three parts – upper arm, lower or forearm and hand. Upper arm has only one bone, fore arm two bones while remaining 27 bones belong to hand. Humerus is the single long bone of upper arm. Its body is called shaft. Upper or proximal end bears a round head. Below it is present a narrow neck and two tuberosities – greater tuberosity and lesser tuberosity. A deltoid tuberosity occurs over the shaft – Distal end of humerus has a pulley-like trochlea (attachment of ulna), convex capitulum (attachment to radius) and outgrowths or epicondyles. The two bones of fore or lower arm are radius and ulna. Both are curved with radius towards thumb side and ulna towards the side of little finger. The two bones may lie parallel to each other or cross each other. The latter happens when palm is kept in backward position. Radius is shorter than ulna. Its lower end is broader with two articular facets for carpals. Proximal end

of ulna is elongated to form olecranon that produces elbow joint. Distal end of ulna has one facet for attachment of carpal.

Hand has 8 bones in wrist region, 5 in palm region and 14 bones in fingers. The eight bones of wrist region are called carpals. Carpals are small and irregular. They occur in two irregular rows. Five bones of palm are called metacarpals. The first metacarpals is short and stout. Metacarpals are expanded distally forming knuckles, Bones of the digits are called phalanges. They are 14 in number. Two phalanges occur in thumb, three each in other fingers. Phalanges have broader ends except for the distal end of last phalanges which are narrow. Carpal bones (wrist bones) are 8 in number i.e., Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate. Phalanges are finger bones. A single bone of the finger is called Phalanx. First digit or first finger is called Pollex or thumb. (Thumb, Index finger, middle finger, ring finger, little finger) Functions (i) Fore limbs have opposable thumb which helps in catching and holding of articles. (ii) They are used in lifting and throwing. (iii) The limbs are used in caring of body. Bones of Hind Limbs (Lower Extremities). Bones of a hind limb are thirty in number – one in thigh, two in shank, one over knee and 26 in the foot region. The single bone of thigh is called femur. Femur is the longest bone. It has a body or shaft. The upper end is swollen into head which fits in acetabulum of pelvic girdle. Head is followed by a narrow neck and two ridges, greater trochanter and lesser trochanter. Shaft is curved. Its concave side has a ridge. The distal end of femur has a central groove and two lateral condyles. A triangular disc-shaped patella or knee cap fits over intercondylar groove. The two bones of shank are tibia and fibula. Tibia is inner and thicker with a sharp crest. Its proximal end has concave facets for fitting over condyles of femur. Distally, it bears a projection on inner side called medial malleolus. Fibula is outer and slender bone of shank which is projected distally to form external malleolus.

Foot has seven bones in ankle region, 5 bones in sole region and 14 bones in toes. Seven bones of ankle region are called tarsals. They have different sizes and shapes. Tarsals are arranged in three rows. 2+1+4. The two tarsals of proximal row are large with calcaneum forming the heel and talus forming the ankle joint. Five bones of sole are called metatarsals. First metatarsal is short and strong. Phalanges have 14 bones, two in great toe and 3 each in other toes. Tarsal bones (Ankle bones) are 7 in number i.e., talus (upper most, it is the only bone of foot which articulates with tibia and tibula, during walking it initially bears entire weight of body), calcaneus (heel bone, it is largest and strongest bone tarsal bone), cuboid (it articulates with metatarsals no. IV and V), Navicular, cuneiforms (3, articulate with metatarsals). Phalanges are bones of toes. First toe is called hallux or great toe or big toe.

Erect Posture of Humans. 1. Head. Head lies vertically at the tip of vertebral column, which is semi mobile. Base of head has a wide passage called foramen of Magnum, by which it communicates with rest of the body. 2. Neck. Semi-long neck with cervical vertebrae provides mobility in all directions. 3. Height. Height is due to presence of longer skeletal system and provides wider range of vision. 4. Fore Limbs. Powerful metacarpals and phalanges have gripping power. Palm of hand is wide providing a large area for balance, gripping etc. Opposable thumb providing better tooling power and multifarious use of hand. 5. Backbone. Two convex and two concave curvatures in the backbone make the centre of gravity between the heels, in order to maintain balance and make walking over the legs much easier. 6. Thorax. It helps to provide equilibrium as the sides are wider than region from front to back. 7. Pelvis. It is a bowel-like structure, provides support to the lower abdominal visceral organs. 8. Hind Limbs. Leg bones are stronger than the arm bones since they have to lift the entire weight of the body. Broad and flat feet provide stability and arches in feet provide spring like ability..