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!)  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

Human Limbs - Comparison  Stabililty and movement – a compromise  Lower limbs  Support  Locomotion  Upper limbs  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 Clavicle…? Complex history Membrane bone Variable Scapula – dorsal Coracoid – ventral (Fused to scapula) Most shoulder muscles are dorsal

Girdles – Lower Limb Ilium Pubis Dorsal and ventral elements…?

The Mammalian Upper Limb  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  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 : Ventral rami, C 5 to T 1  Trunks: Three - Upper, Middle, Lower  Divisions : Two from each trunk  Cords: Three

The Scheme   C5   C6   C7   C8   T1 RootsTrunksDivisions Cords

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  Ilium, Ischium, Pubis  Sacrum  Hip joint  Deep acetabulum  More stable  Scapula (+ coracoid), clavicle  No vertebral anchor  Shoulder joint  Shallow glenoid  Highly movable Upper Lower

Flexor compartments anterior Forearm movements Pronation and supination Preaxial bone (radius) lateral Postaxial bone (ulna) medial (Also true for digits) Versatile hand The Limbs Compared – 2 Upper Lower Flexor compartments posterior Fixed leg bones Socket for ankle Preaxial bone (tibia) medial Postaxial bone (fibula) lateral Stable, supporting foot

Core Concepts  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.