"Sometimes a great wound or concussion of the head, especially which happens by falling headlong from an high place, brings a prejudice and weakness to the animal faculty, dulling the understanding"

This quote by Thomas Willis is describing the results of a terrible head injury. He recommends that a fantastic wound or concussion of the head, particularly when triggered by a fall from an excellent height, can have a negative influence on the psychological professors of an individual. This can result in a dulling of the understanding, indicating that the individual might have trouble understanding and processing details. This can also result in a prejudice, implying that the individual might be most likely to make choices based upon their own biases instead of on facts or logic. In short, Willis is recommending that a distressing head injury can have a significant effect on an individual's mental professors, leading to a dulling of the understanding and a bias in choice making.