This list contains only the mesodermal structures

The correct option is "Heart, blood, bones, notochord".

During embryonic development, triploblastic animals form three primary germ layers: the ectoderm, the mesoderm, and the endoderm. Each layer is responsible for generating specific tissues and organs in the developing organism.
The mesoderm is the middle layer, and it gives rise to most of the internal structural and circulatory systems of the body.

Let us break down why the structures in the correct option are all derived from the mesoderm:
1. Heart: The cardiovascular system, including the heart and blood vessels, is formed from the lateral plate mesoderm.
2. Blood: Blood cells and the circulatory fluid are derived from the mesoderm (specifically, hematopoietic stem cells originate from mesodermal tissues).
3. Bones: The skeletal system (except for some facial bones derived from the neural crest) is derived from the paraxial and lateral plate mesoderm.
4. Notochord: The notochord is a flexible rod-like structure that defines the primitive axis of the embryo. It is formed from chordamesoderm, which is a specialized type of mesoderm.

To understand why the other options are incorrect, we can identify the non-mesodermal structure present in them:
- Liver: The liver is derived from the endoderm, the innermost germ layer. This rules out the options containing "liver" (Option 2, Option 3, and Option 4).

Therefore, the only list containing exclusively mesodermal structures is "Heart, blood, bones, notochord".