This " thumb " is really just a sesamoid , a bit of bone that typically forms inside tendons and ligaments where they cross joints .
这个“拇指”其实只是一个种子骨,通常是在跨关节的肌腱和韧带内形成的一小块骨头。
But in the panda , the sesamoid on the outside base of the true thumb became enlarged , taking on a digit-like identity that helps the animal eat more efficiently .