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
Milky spots Milky spots Milky spots are very small white-coloured areas of lymphoid tissue, found in the peritoneal, pleural and pericardial cavities. These are the three coelomic cavities that form as separate compartments from the intraembryonic coelom. More milky spots are found on the greater omentum in the peritoneal cavity than anywhere else. The milky spots are made up of mesenchymal cells and are covered in a layer of mesothelium. These structures surround the small blood vessels. The enclosing mesothelium contains macrophages, lymphocytes and mast cells. They are also known as secondary lymphoid organs. Most milky spots contain extremely thin-walled lymphatic capillaries.