The primitive bone marrow stroma includes bone marrow stromal cells (BMSCs), which are skeletal progenitor cells that originate outside of the marrow cavity (from the primitive periosteum and perichondrium) and invade the cavity forming along blood vessels. BMSCs appear as large cells that have prominent nucleoli and bleb-like projections, which largely differs from the spindle-shaped morphology of typical cultured mesenchymal stem cells MSCs. BMSCs in the postnatal bone marrow reside around sinusoids, and maintain a niche for hematopoietic stem cells (HSCs), which, in turn, support hematopoiesis and replenish the differentiated compartment of osteoblasts and adipocytes during tissue growth and turnover. BMSCs also generate cartilage under specific conditions, such as trauma. They can differentiate into: adipocytes, astrocytes, cardiocyocytes, chondrocytes, hepatocytes, mesangial cells, muscles, neurons, and osteoblasts.