Cross references: Globin Heme Muscle Innervation
Motor Neuron Evolution Motor Nerve Organization
Medial Motor Column Fast vs. Slow Twitch Muscles
protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. Myoglobin is only found in the bloodstream after muscle injury. It is an abnormal finding, and can be diagnostically relevant when found in blood. 
Myoglobin is the primary oxygen-carrying pigment of muscle tissues.
High concentrations of myoglobin in muscle cells allow organisms to
hold their breaths longer. Diving mammals such as whales and seals have
muscles with particularly high myoglobin abundance.
Evolutionary implications: myoglobin-like proteins found in ancient microorganisms - 2000 (Goog)