|Evolution history of 牵|
Seal Script represented the idea clearer: a hand () use a rope () to lead a buffalo ().
That is the original meaning of 牵 | 牽 - "lead along a buffalo".
Getting back to Tradition character 牽, which is 玄, and 牛. now we can guess that could be ox yoke.
Since 牵 | 牽 contains the representation of connecting with a buffalo using a rope. thus 牵 | 牽 is also extended to mean "connected to / connected with". For example 牵连.
That is all, let us enjoy a Chinese calligraphy with 牵 | 牽 inside: