Final answer:
The endoderm is the primary germ layer responsible for forming the tympanic cavity and auditory tube during embryonic development.
Step-by-step explanation:
The primary germ layer that forms the tympanic cavity and auditory tube is the endoderm. During the embryonic development, the formation of the three primary germ layers occurs within the first 2 weeks. The tympanic cavity and auditory tube are essential components of the ear involved in hearing.
Gastrulation is a key process in early development, resulting in the formation of these germ layers. The innermost layer, the endoderm, will eventually give rise to many internal structures, including parts of the ear.
The middle layer, or mesoderm, contributes to forming many organs and systems but not the tympanic cavity. Lastly, the ectoderm forms external structures, like the epidermis and nervous system, but also does not contribute to the tympanic cavity or auditory tube.