Final answer:
The mesoderm is the embryonic germ layer responsible for forming a wide range of tissues, including muscle and connective tissues, and is pivotal to the development of various systems and structures during embryogenesis.
Step-by-step explanation:
The germ tissue that forms predominantly muscle tissue and connective tissue, including muscles, bones, cartilage, adipose tissue, circulatory vessels and blood, lymphatic system, dermis, genitourinary tract, serous membranes, and the notochord, is known as the mesoderm. This middle embryonic germ layer is crucial for the development of these systems and structures during embryogenesis. The mesoderm is responsible for the formation of a wide range of tissues including the mesothelium, which is the epithelial portion of serous membranes covering major body cavities, and mucous connective tissue, which is specialized loose connective tissue found in the umbilical cord. The formation of these various tissues and structures from the mesoderm is a part of the process of gastrulation, followed by organogenesis, which leads to the development of the embryo's organs.