Appendicular Skeleton

Appendicular Skeleton • Appendages and supporting girdles

Pectoral Girdle • Function

Pectoral Girdle – Replacement bones • Coracoid • (Epicoracoid) • Scapula • Suprascapula

Pectoral Girdle – Membrane bones • Clavicle • Cleithrum • Supracleithrum • Postcleithrum • Posttemporal • Interclavicle • (Episternum in tetrapods)

Pectoral Girdle • Glenoid fossa on scapula for limb attachment

Key Point • What trend do you see as you look at the overview of pectoral girdles?

Pectoral Girdle - Placoderms • First to have a pectoral girdle

Pectoral Girdle - Chondrichthyes • Cartilage • No dermal elements • Coracoid, scapula, suprascapula (scapulacoracoid) • Not connect to axial skeleton, but fused at midline

Pectoral Girdle – Bony fish • Membrane bones • Clavicle, some have interclavicle • Cleithrum – largest • Supracleithrum, postcleithrum • Posttemporal – anchors to skull

Pectoral girdle – bony fish • Replacement bones • Coracoid • Scapula

Pectoral Girdle - amphibians • Membrane bones • Reduced • Lose posttemporal • Early amphibians gained an interclavicle as a brace

Pectoral Girdle - amphibians • Replacement bones • Coracoid • Scapula and suprascapula

Pectoral Girdle - amphibians • Urodeles have no membrane bones, including clavicle • Anurans have clavicle, no interclavicle and usually no cleithrum

Pectoral girdle - Reptiles • Stem reptiles & synapsids • Many membrane bones present • Most replacement bones present • New posterior coracoid present

Pectoral girdle - Reptiles • Modern reptiles have scapula, coracoid, sometimes clavicle, sometimes interclavicle • Crocodiles have reduced clavicle • Turtles have interclavicle fused with shell • Snakes have no girdle • Lizards have a significant clavicle and interclavicle

Pectoral Girdle - birds • Furcula (2 clavicles plus interclavicle) • Scapula – bladelike • Coracoid (anterior or pro-) which articulates with sternum

Pectoral Girdle - mammals • Monotremes similar to stem reptiles • Clavicle in most • Scapula • Coracoid process from posterior coracoid • Spine is new • Acromion process articulates with clavicle (not new)

Pelvic Girdle • Stability, encloses pelvic cavity organs • In tetrapods, it has three parts called the ilium, pubis and ischium • When these three bones fuse into one, the fused bone is the innominate or coxal bone • Acetabulum is the socket for the thigh • Symphysis in all but birds • Replacement bone

Pelvic Girdle - Fish • Pelvic plate or symphysis

Pelvic Girdle - amphibians • Pubis • Ilium (long & slanted in frog) • Ischium

Pelvic Girdle - Reptile • Sacroiliac joint is stronger and broader for more muscle attachment and stability

Pelvic Girdle - birds • Synsacrum – Ilium is braced against fused vertebrae • No symphysis WHY??

Pelvic girdle - mammals • Epipubic bone in marsupials is unique for pouch support

FINS • Steering, rolling, braking, stabilizers, forward & vertical movement

Fin structure • Skin epidermis covering • Fin rays in dermis • Lepidotrichia (scale-hair) bony dermal scales, segmented • Ceratotrichia (horn-hair) cartilaginous unsegmented rays

Fin Structure • Skeletal base (cartilage or bone) for support • Pterygiophores (bearing fin) • Basals are proximal • Radials are distal

Appendicular Skeleton