Let's get into the specialization of the mesoderm. As a reminder, the mesoderm is the middle germ layer. If you look at the image here, we're looking at a cross-section of an embryonic disc, zoomed in, and this entire middle portion in red is the mesoderm. One of the first events of embryonic development is that mesodermal cells at the midline of the embryo will form a structure called the notochord. The notochord helps organize the embryo along a central axis. Eventually, during development, the spinal cord will develop along the notochord, which will in turn become the vertebrae along the spinal cord. You can see this clearly in our image, this central structure is a literal cord that extends down through the embryo along the central axis; that is our notochord. We'll label that there.

What will happen next is that the mesoderm, on either side of the notochord, will differentiate into something called somites. Somites are paired, almost cube-like structures. You can see them developing along the notochord. These somites will develop into the skeleton, the dermis of the skin, and also skeletal muscle. Thus, somites transform into the musculoskeletal system as well as the dermis of the skin. Yet, the mesoderm is not done yet. It will also go on to form the cardiovascular system, the kidneys, the gonads, the membrane of most body cavities, as well as the connective tissue of limbs. In this image, you can see that the mesoderm is much larger and bulkier than the other two blue and yellow layers, because the mesoderm forms the majority of your body, hence more cells and more tissue.

We will have a review video coming up soon to help you remember which structures each of these layers will form, as I know this is a lot to remember. Ok, see you guys in our next video. Bye-bye.