Final answer:
The sternothyroid muscle is responsible for depressing the thyroid cartilage after swallowing, thereby resetting the position of the larynx.
Step-by-step explanation:
The muscle that depresses the thyroid cartilage to return it to its original position after swallowing is the sternothyroid muscle. This muscle works together with other infrahyoid muscles, such as the omohyoid, sternohyoid, and thyrohyoid muscles, which have functions including the depression of the hyoid bone and the control of the larynx's position. Specifically, the sternothyroid depresses the larynx's thyroid cartilage assisting in the creation of different tones of voice and the return of the larynx to its resting state post-swallowing.