Indo-European bh shifted to Germanic b, dh shifted to d, and gh shifted to g.
Indo-European stop consonants, represented in Germanic, underwent the regular changes that Grimm's Law describes; this law essentially states that Indo-European p shifted to Germanic f, t shifted to th, and k shifted to h. Indo-European b shifted to Germanic p, d shifted to t, and g shifted to k. Indo-European bh shifted to Germanic b, dh shifted to d, and gh shifted to g.