What main structures derive from the ectoderm?

The ectoderm is one of the three primary germ layers that form during embryonic development, and it primarily gives rise to structures that make up the outer layer of the body. The most significant derivatives of the ectoderm include the skin and the central nervous system, which consists of the brain and spinal cord.

The skin, specifically, originates from the ectoderm as it forms the epidermis, the outer layer that provides a barrier to the environment and plays roles in protection, sensation, and temperature regulation. Additionally, the ectoderm is responsible for the development of the nervous system, where the brain and spinal cord arise from the neural tube, a structure that emerges from the ectodermal layer.

In contrast, the other answer choices refer to structures that develop from the mesoderm and endoderm. Muscles and bones derive from the mesoderm, which also contributes to the formation of various internal organs and the circulatory system, both of which originate from either the mesoderm or endoderm. This distinction highlights the specific developmental roles of the ectoderm, affirming that the brain and skin are indeed the primary structures derived from it.