Appendicular Skeleton

The bones of the limbs along with their girdles constitute the appendicular skeleton.

Each limb consist of 30 bones.

1.0Forelimbs Bones

The bones of the hand (fore limb) are humerus, radius and ulna, carpals (wrist bones – 8 in number), metacarpals (palm bones – 5 in number) and phalanges (digits – 14 in number).

Forelimb Bones

Humerus

• The humerus is a long bone in the arm that runs from the shoulder to the elbow.
• It articulates proximally with the scapula & distally with two bones, the ulna & the radius, to form the elbow joint.

Radius & Ulna

• The ulna is located on the little finger side of the forearm and is longer than radius. The radius is smaller bone of the forearm and is located on the thumb side of the forearm.
• In contrast to the ulna, the radius is narrow at its proximal end and widens at its distal end. 

Carpals

• Wrist is the proximal region of hand and consists of small bones called carpals.
• Carpals are 8 in number in each fore limb.
• Carpals are arranged in two transverse rows of four bones each.

Meta Carpals

• The palm is the intermediate region of the hand and consists of metacarpals.
• Each fore limb consist of 5 Metacarpals.
• The head of the metacarpals commonly called knuckles are readily visible in a clenched fist.

Phalanges

• Phalanges make up the distal part of hand.
• Each fore limb consists of 14 phalanges.
• Digital formula for phalanges is 2, 3, 3, 3, 3.

2.0Hindlimbs Bones

• Each lower limb has 30 bones.
• Femur (thigh bone – the longest bone), tibia and fibula, tarsals (ankle bones – 7 in number), metatarsals (5 in number) and phalanges (digits – 14 in number) are the bones of the legs (hind limb). 
• A cup shaped bone called patella cover the knee ventrally (knee cap).

Femur

• Thigh bone is the longest, heaviest and strongest bone in the body.
• The proximal end of femur consists of a rounded head that articulates with the hip bone to form hip joint. 

Patella

• A cup shaped bone called patella cover the knee ventrally (knee cap). 

Tibia

• Medial & larger bone of the leg.

Fibula

• Lateral & smaller bone of the leg. It is parallel and lateral to the tibia, but it is considerably smaller.

Tarsals

• The tarsus (ankle) is the proximal region of the foot and consists of tarsal bones.
• Tarsal bones are much larger & stronger than carpal bones because they have to support & distribute body weight.
• Total number of tarsal bones is seven.

Meta Tarsals

• The intermediate zone of foot consists of metatarsal bones.  
• Meta tarsal bones are 5 in number.

Phalanges

• The phalanges comprise the distal components of the foot.
• 14 Phalanges, 2 for great toe & 3 each for other four phalanges. 
• As compared to Phalanges of hand, these are small in size. 
• Digital formula = 2,3,3,3,3

The arrangement and number of bones in the lower limb are similar to those of the upper limb. However, the bones of the lower limb are adapted for weight bearing and locomotion. 

3.0Pectoral Girdle

• Human body has two pectoral girdles that helps in the articulation of the upper limbs with the axial skeleton.
• Each of the two pectoral girdle consists of a clavicle (Collar bone) and a scapula. 

Scapula

• Scapula is a large triangular flat bone situated in the dorsal part of the thorax between the second and the seventh ribs. 

Acromion            

• The dorsal, flat, triangular body of scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion. 
• Clavicle articulates with Acromion process of scapula to form acromioclavicular joint.
• Below the acromion process is a depression called the glenoid cavity.

Shoulder joint

Head of humerus fits in glenoid cavity of scapula and form shoulder joint.

Clavicle

• Each clavicle is a long slender bone with two curvatures. This bone is commonly called the collar bone.
• Lateral curvature of clavicle forms acromioclavicular joint with acromion process of scapula whereas median curvature of clavicle form sternoclavicular joint with sternum.

4.0Pelvic Girdle

• Pelvic girdle consists of two coxal bones (hip bones). 
• Each coxal bone is formed by the fusion of three bones – ilium, ischium and pubis. 
• At the point of fusion of ilium, ischium, pubis is a cavity called acetabulum to which the thigh bone articulates.

Female Pelvic Girdle

• The two halves of the pelvic girdle meet ventrally to form the pubic symphysis containing fibrous cartilage.

Note:

• The complete ring composed of the hip bones, pubic symphysis and sacrum forms a deep basin like structure called bony pelvis (Plural is Pelves or Pelvises).
• Functionally the bony pelvis provides a strong and stable support for the vertebral column and pelvic & lower abdominal organ.
• The pelvis is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region).
• Reproductive organs, urinary bladder and some part of large intestines are located in this region.

Differences between male and female pelvis