mrsjorgenson224

external fish skeletal system elbow shoulder ligaments neurotransmitter acetylcholine cleft synaptic plate end synapse neuron motor contraction fiber muscle muscles fertilization amphibians frogs tree salamanders toads tadpoles frog life cycle circulatory three chambers atria ventricle anatomy internal bichir gar breathing lungs walk walking shark tiger ray sting skate hagfish lampreys sharks gills bony jawless cartilaginous joints flexion movement joint abduction extension adduction inversion plantar eversion dorsiflexion hyperextension hip knee