 So let's talk about how bone forms. Like, where does your bone come from in the first place? And this is relevant because there are actually two different processes by which bone organs form, and they don't come out of nowhere. It's not like a random, a zencomal cell is going to say, oh, gee, I feel like we need a bone here, so let's build some bone. In the process of development, like fetal development, where you are just a little slime inside your mama's belly, you, at a certain point, about eight weeks along, your body says, we now have structures in place to build bone, and there's two ways that that happens. The first one that we're going to talk about is called intramembranous ossification. Brannous ossification. Intramembranous ossification make you think of bone ossification. Yeah, we're making bone, dog pounds. So all bone formation, you have to start with some sort of connective tissue precursor. You can't make bone out of a random cell or out of a muscle cell or out of epithelial tissue. Bone has to come from an existing knowledge, I mean, an existing connective tissue model almost. And in the case of intramembranous ossification, there is a dense irregular connective tissue, for lack of a better word, membrane, where the bone will form. So visualize. Intramembranous ossification happens with flat bones. So your skull bone, like your frontal bone, there is a dense, and this is back in the day, when you're eight weeks in your mama's belly, there is a flat dense irregular connective tissue structure in your forehead. And if you, somebody went in and squished your head, they'd squish it because it's just dense irregular connective tissue, it is not yet bone. So the first thing that happens is that this dense irregular connective tissue membrane has mesenchymal cells in there, right? Makes perfect sense. And the mesenchymal cells are going to differentiate ultimately into osteoblasts. And this happens in like an ossification center. Like there are places in the dense irregular connective tissue membrane where there's going to be a thickening. And the mesenchymal cells there are going to differentiate and become osteoblasts. And the osteoblasts are going to start doing their thing as they produce bone matrix or bone tissue. Of course, they're going to get trapped and become osteocytes, and of course, they're going to build their little lacunas around themselves surrounded by bone matrix. And eventually, they actually are going to make spongy bone. This would be step three. The osteoblasts make spongy bone. And now you have all this spongy bone. And the osteoblasts... Oops, we don't go backwards in our numbers. We go forwards most of the time. The osteoblasts in the spongy bone keep building bone. And eventually, can you visualize how the spongy bone could if we kept building bone tissue all around ourselves before the osteoblasts, we could eventually that bone, the spongy bone, could turn into compact bone. And the end model that you end up with is a layer of compact bone. So this is my compact bone. And then what's in between your compact bone? Spongy bone, little bit of a mess. You get what I'm saying right there. And that's like if you chop a bone in half and you look on the inside, the bone, like the medullary cavity in the middle of a bone, the space where the bone marrow is, it's like kind of, it looks spongy. And that's because there's spongy bone tissue in there. One thing that I did not tell you about bone tissue, and this is also true about cartilage. Let's do it in... Oh, gosh, sure. Bone tissue is surrounded by a dense, irregular connective tissue layer called the periosteum. So the tissue that it's made out of is dense or regular connective tissue. The structure is called the periosteum. The periosteum houses different cells that are going to help maintain and continue building and growing this bone, which originally was formed through the process of intramembranous ossification. That's the work for y'all. Let's talk about the other form of ossification, which is endocondral ossification, and that's how we end up with our long bones.