Infrahyoid muscles

The infrahyoid muscles are a group of four pairs of muscles in the anterior part of the neck. (The term infrahyoid refers to the region below (inferior) to the hyoid bone in the neck. )

Collectively, they are referred to as the strap muscles, because the muscles are long and flat much like a strap.

Individual muscles
Namely, the muscles are:

Innervation
All of the infrahyoid muscles are innervated by the ansa cervicalis from the cervical plexus(C1-3) EXCEPT for the thyrohyoid muscle, which is innervated by only C1.

The stylopharyngeus muscle is considered by many to be one of the strap muscles, but it is innervated by CN9 rather than the ansa cervicalis.

Action
These four muscles also known as the "strap" muscles function is to depress the hyoid bone and larynx during swallowing and speaking