Limbs
Evolution, Development
And Organisation
212 – 2004 – Week 13
Avinash Bharadwaj
Origins
 Extensions (appendages) of the body wall
 Hypaxial structures
 Supplied by ventral rami of spinal nerves!
 Two pairs
 Pectoral and pelvic fins
 Forelimbs and hindlimbs (quadrupeds)
 Upper and lower limbs (humans)
General Plan
 Fins
 Pectoral and Pelvic
 The Axis
 Borders
 Preaxial
 Postaxial
 Surfaces & Muscles
 Dorsal and ventral
All limb musculature is hypaxial!
“Dorsal” and “Ventral” refer to arrangements within the limb.
The Tetrapod Limb
 Limb girdles – pectoral and pelvic
 Anchor to the trunk (vertebral column)
 Limb “Segments”
(Not to be confused with developmental segments!)
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Arm / Thigh (1 bone)
Forearm / Leg (2 bones)
Carpus (Wrist) / Tarsus – 8 bones
Metacarpus / Metatarsus – 5 bones
Digits – 2, 3, 3, 3, 3.
 Basic pentadactyl structure
 Modifications
Quadruped and Human Limbs
1
1
1
2
2
2
3
4
3
1
3
4
2
4
3
4
Human Limbs - Comparison
 Stabililty and movement – a compromise
 Lower limbs
 Support
 Locomotion
 Upper limbs
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Reaching out
Grasping
Fine movements
Greater mobility
Terminology of Movements
 Flexion / Extension
 Bending and straightening
 Flexion : approximation of ventral surfaces
 Special terms for ankle and foot
 Abduction / Adduction
 Abduction : Movement away from midline
 Special reference line for fingers and toes
 Rotation : Medial and Lateral
 Other movements
 Pronation / supination (forearm and hand)
 Inversion and eversion (Foot)
All joints do not exhibit all movements.
The Tetrapod Limb
 Dorsal and ventral surfaces
 Limb girdles (not shown here)
Muscles
Groups
In general…
Flexors and adductors are ventral muscles.
Extensors and abductors are dorsal muscles.
There are notable exceptions!
Girdles – Upper Limb
Scapula – dorsal
Coracoid – ventral
(Fused to scapula)
Most shoulder muscles are dorsal
Clavicle…?
Complex history
Membrane bone
Variable
Girdles – Lower Limb
Ilium
Pubis
Dorsal and ventral elements…?
The Mammalian Upper Limb
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Elevation of the trunk
The pectoral muscle sling
Girdle components
Clavicle…
Limb Rotation
 Recognise ventral and dorsal surfaces
 Nature of skin in human limbs
 Arm, forearm and palm – ventral surfaces
 Thigh and leg –
 Dorsal surfaces are anterior!
 Foot – “dorsum” faces up
 Sole faces the ground
 Normal angulation
 Terminology
 “Flexion” – plantarflexion
 “Extension” - dorsiflexion
Limb Axes
 Embryonic positions
 Thumb and great toe face cranially
 Final position
 Thumb lateral, great toe medial!
 Radius – preaxial, ulna postaxial
 Tibia – preaxial, fibula postaxial
Limb – Body Wall Segments
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Upper Limb : C5 to T1
Lower Limb : L2 to S3
Both hypaxial, supplied by ventral rami
Nerve Plexuses
 Upper Limb
 Brachial Plexus : Ventral rami of C5 – T1
 Lower Limb
 Lumbar and sacral plaxuses (Lumbosacral
plexus)
 L 2,3,4 + S 1,2,3
Nerve Plexuses and Muscles
 Ventral rami – ventral and dorsal divisions
 For ventral and dorsal muscles
 Pattern simpler in lower limb
 Brachial plexus : more stages
Muscle Groups - Shoulder
 Deltoid
 Pectoralis major and minor
Pectorals (front) :
The only ventral muscles of shoulder!
Arm
 Ventral and dorsal groups
 Ventral – flexors of elbow
 Dorsal – extensors of elbow
Forearm
 Flexors :
 Wrist and fingers +
 Hand muscles :
Ventral!
 Extensors
 Ext. Wrist + fingers
 Abductors of thumb
Brachial Plexus
 Roots
 Trunks
: Ventral rami, C 5 to T 1
: Three - Upper, Middle, Lower
 Divisions
: Two from each trunk
 Cords
: Three
The Scheme
Cords
Divisions Trunks
Roots
 C5
 C6
 C7
 C8
 T1
Nerves
 Dorsal
 Axillary, Radial (and others)
 Ventral
 Musculocutaneous
 Median
 Ulnar
 Others
Functional Considerations
 In mammals :
 Locomotion
 Mobility
 The variable clavicle
 Primates incl. Humans
 Prehension
 Mobility and grasping – range
 Brachiation
 The Human Hand – power and precision
Lower Limb – Thigh
 Muscle Groups
 Anterior : Flexors of
hip, extensors of knee
 Medial – adductors
 Posterior : Extensors
of hip, flexors of knee
Muscles - Back
 Gluteal
(dorsal)
 Hamstrings
(ventral)
Leg – Muscle Groups
 Anterior
Extensor
 Lateral
Peroneal
 Posterior
Flexor
The Limbs Compared – 1
Upper
 Scapula (+ coracoid),
clavicle
 No vertebral anchor
 Shoulder joint
 Shallow glenoid
 Highly movable
Lower
 Ilium, Ischium, Pubis
 Sacrum
 Hip joint
 Deep acetabulum
 More stable
The Limbs Compared – 2
Upper
Lower
Flexor compartments anterior
Flexor compartments posterior
Forearm movements
Pronation and supination
Fixed leg bones
Socket for ankle
Preaxial bone (radius) lateral
Postaxial bone (ulna) medial
(Also true for digits)
Preaxial bone (tibia) medial
Postaxial bone (fibula) lateral
Versatile hand
Stable, supporting foot
Core Concepts
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Hypaxial structures
Common plan
Identify bones
Preaxial and postaxial structures
Rotation of limbs
Functional considerations
Conducting this unit has been a great pleasure.
Thank you and best wishes.