Sternohyoid muscle
The sternohyoid muscle is a bilaterally paired, long, thin, narrow strap muscle of the anterior neck. It is one of the infrahyoid muscles. It is innervated by the ansa cervicalis. It acts to depress the hyoid bone. Structure 
The sternohyoid muscle is one of the paired strap muscles of the infrahyoid muscles. The muscle is directed superomedially from its origin to its insertion. The two muscles are separated by a considerable interval inferiorly, but usually converge by their mid-point and remain proximal until their superior insertion. Origin 
It arises from the posterior aspect of the medial end (sternal extremity of the clavicle, the posterior sternoclavicular ligament, and (the superoposterior portion of) the manubrium of sternum. It inserts onto the inferior border of the body of hyoid bone. Nerve supply 
The sternohyoid muscle receives motor innervation from branches of the ansa cervicalis (which are ultimately derived from cervical spinal nerves C1-C3). Relations 
The muscle is situated lateral to the trachea. Variations
The muscle may be absent, doubled, exhibit a clavicular slip (the cleidohyoideus), or interrupted by a tendinous intersection; it sometimes presents a transverse tendinous inscription just distal to its origin. Actions/movements 
The muscle depresses the hyoid bone when the bone is in an elevated position. Function 
The sternohyoid muscle performs a number of functions:

 aids in speech (it is primarily involved in modulation with speech volume rather than intonation). contributes to movements of the head and neck. Additional images

References

External links
  - "Nerves and Vessels of the Carotid triangle"
 PTCentral

Muscles of the head and neck