What is the middle layer of the embryo that forms connective tissues and muscles?

The middle layer of the embryo that forms connective tissues and muscles is indeed the mesoderm. During embryonic development, the three primary germ layers are formed: ectoderm, mesoderm, and endoderm. The mesoderm plays a crucial role as it differentiates into various structures within the body. It gives rise to the musculoskeletal system, including bones and muscles, the circulatory system, and other connective tissues such as blood and lymph tissues. Furthermore, the mesoderm also contributes to the development of the kidneys, heart, and reproductive system. Understanding the functions of each germ layer provides insight into the fundamental processes of embryonic development and how complex organisms are formed from a single fertilized egg.