Specimens of Tyrannosaurus and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone (a 1.15 m long femur), from a 68-million-year-old "Tyrannosaurus". The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated MOR 1125 (and known informally as B-rex), the dinosaur had been excavated from the Hell Creek Formation. Flexible, bifurcating blood vessels and fibrous but elastic bone matrix tissue were recognized. In addition, microstructures resembling blood cells were found inside the matrix and vessels. The
Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Medical terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the Greek word ("haima") for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and