Both the upper and lower limbs are built on the same basic principle. Each limb is made up of two portions: proximal and distal.

The proximal part is called limb girdle and attaches the limb to the trunk. The distal part is free and consists of proximal, middle, and distal segments, which are referred to as arm, forearm, and hand respectively in the upper limb, and thigh, leg, and foot respectively in the lower limb.

Homologous Parts Of The Upper And Lower Limbs

Upper limb 

Lower limb 

Shoulder/pectoral girdle 

Hip girdle/pelvic girdle 

Shoulder joint 

Hip joint 

Arm 

Thigh 

Elbow joint

Knee joint 

Forearm 

Leg 

Wrist joint 

Ankle joint 

Hand 

Foot 

(a) Carpus 

(a) Tarsus 

(b) Metacarpus 

(b) Metatarsus 

(c) Fingers* 

(c) Toes* 

 

A short account of the development of the limbs further makes it easier to understand the differences between the upper and lower limbs.

The development of upper and lower limbs begins in the 4th week of intrauterine life (IUL). A pair of small elevations appears on the ventrolateral aspect of the embryo called limb buds. The anterior pair of the upper limb buds appears opposite the lower cervical segments. The posterior pair of lower limb buds appears 3 or 4 days later at the level of lumbar and upper sacral segments. Thus during an early stage of development all the four limbs appear as paired limb buds. First they are simple flipper-like appendages so that the upper and lower limbs are similar in their appearance. Each has dorsal and ventral surfaces, and preaxial and postaxial borders. The preaxial border faces towards the head. Later in the development, the ends of limb buds become expanded and flattened to form the hand and foot plates in which the digits develop. The digits nearest to the preaxial border are thumb and big toe in the upper and lower limbs, respectively. The limbs then rotate.

The lower limb buds rotate medially through 90° so that their preaxial border faces medially and their extensor surface faces forwards. The upper limb buds on the other hand rotate laterally through 90° so that their preaxial border faces laterally their extensor surface faces backwards.

Summary Table

 

Upper limb 

Lower limb 

Function 

Prehension (i.e., manipulation of objects by grasping) 

Locomotion and transmission of weight 

Bones 

Smaller and weaker 

Larger and stronger 

Joints 

Smaller and less stable 

Larger and more stable 

Muscles 

  • Smaller and attached to smaller bony areas
  • Antigravity muscles less developed
  • Larger and attached to larger bony areas
  • Antigravity muscles more developed

Girdle 

Pectoral girdle

  • Made up of two bones, clavicle and scapula
  • No articulation with vertebral column
  • Articulation with axial skeleton is very small through sternoclavicular joint

Pelvic girdle

  • Made up of single bone, the hip bone*
  • Articulates with vertebral column
  • Articulation with axial skeleton is large, through sacroiliac joint

Preaxial border

Faces laterally 

Faces medially 

 

 

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