Ti characters originally had two common characters, one of which was "from the body and from the origin"
That is, the character for "the body itself", and the other one was "from the person and from the origin". This is our current word "Ti". In ancient times, it belonged to the category of vulgar characters. The picture below is a screenshot of the Chinese characters in the work "My Friend's Post" by Mi Fu, a calligrapher from the Song Dynasty.