Final answer:
Galen concluded that the brain and nerves control the voice when he observed that a pig stopped squealing after he tied off its laryngeal nerve, which is responsible for controlling the vocal cords.
Step-by-step explanation:
When Galen tied off the laryngeal nerve of a pig and it stopped squealing, he concluded that b. the brain and nerves control the voice. The laryngeal nerve is responsible for innervating the muscles that control the vocal cords, which in turn produce sound. When the nerve was tied off, it could no longer send signals to these muscles, leading to an absence of squealing. This demonstrates the role of the nervous system, specifically how the laryngeal nerve and brain contribute to the control of vocalization. In humans, similar principles apply, where the nervous system, particularly the vagus nerve, and its branches, play critical roles in regulating the functions of the respiratory and vocal systems, including bronchoconstriction and bronchodilation.