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The Origins Limbs – Evolution, Development and Organisation Fins Pectoral Pelvic Axis Borders ANHB 2212 – 2008 Avinash Bharadwaj Preaxial Postaxial D Surfaces Muscles V Dorsal / ventral The Mammalian Limb The Tetrapod Limb Limb girdle (not shown) Dorsal / ventral… ventral… Limb Segments Arm / Thigh (1 bone) Forearm / Leg (2 bones) Carpus / Tarsus 7 – 8 bones Metacarpus / tarsus Digits Girdle Bones Scapula and clavicle Elevation of the trunk Stronger girdle Sling with forelimb Hindlimb girdle fixed Girdle components Limb rotation Nerves and Muscles Dorsal / ventral Coracoid process C Clavicle…?! Single skeletal anchor Scapula Purely diagrammatic! Dorsal ramus Ventral ramus Dorsal Muscles… division Dorsal Hip bone Three parts : Ilium, Ischium, Pubis Sacrum Pubis Ischium musculature Ventral division Coracoid Ventral musculature muscles D / V nerves Divisions of ventral ramus Parts of girdle Coracoid / scapula Ischium + pubis / ilium Muscle Groups Nerves Ventral muscles = flexors + adductors Dorsal muscles = extensors + abductors Notable exceptions Shoulder muscles : Developmentally correct, actionwise variable All but two dorsal Some “problem muscles” elsewhere too! General Plan : Lumbar and sacral Sacral Plexus L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Lumbar : L 2, 3, 4 Anterior and Posterior Divisions Sacral : “Lumbosacral Trunk” + S 1, 2, 3 Anterior and Posterior Divisions All limb muscles hypaxial Nerves are ventral rami of spinal nerves C5 to T1 for upper limb L2 to S3 for lower limb. Branching and reunion : Plexuses UL : brachial plexus LL : Lumbar (L2 – L4), sacral (L4 – S3) Anterior Divisions – White Gluteal Nerves Common peroneal nerve Tibial nerve Muscle groups – Upper limb Brachial Plexus Cords Divisions Trunks Ant Arm Roots L C5 C6 C7 C8 T1 M Post Forearm Muscle acting on : Ant L Wrist, fingers M Post Ventral / dorsal : Flexors / extensors of the elbow Adductors etc…? Ventral / dorsal : Flexors / extensors Pronation and supination More detail : ANHB 2213 ! Nerves : Upper Limb Muscles : Thigh Arm – Ventral : Musculocutaneous Forearm – Ventral : Median + Ulnar Dorsal nerve for arm + forearm : Radial Major nerves for the shoulder : Anterior : Dorsal Flexors of the hip Extensors of the knee Medial : Ventral Adductors of the hip Posterior : Ventral Extensors of the hip Flexors of the knee Axillary and subscapular : dorsal Pectoral (2) : Ventral Lateral : Dorsal Abductor/extensor : hip + Some unusual muscles! Muscles – Back Muscles – Leg Anterior Extensor Ankle , toes Lateral Gluteal Fibular Posterior Flexor Ankle, toes Hamstrings Ankle and toes : “plantarflexion” plantarflexion” / “dorsiflexion” dorsiflexion” Ankle : Eversion and inversion Nerves – Lower Limb Functional Considerations Gluteal nerves : dorsal Thigh In mammals : Anterior (dorsal) : Femoral Medial (ventral) : Obturator Posterior (ventral) : Tibial Leg Anterior + Lateral : Fibular (two parts) Postarior : Tibial Locomotion Mobility The variable clavicle Primates incl. Humans Prehension Mobility and grasping – range Brachiation The Human Hand – power and precision 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
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