  In 2004 Oort studied the foliation on the space of $p$-divisible groups. In
his theory, special leaves called central streams play an important role. It is
still meaningful to investigate central streams, for example, there remain a
lot of unknown things on the boundaries of central streams. In this paper, we
classify the boundary components of the central stream for a Newton polygon
consisting of two segments, where one slope is less than $1/2$ and the other
slope is greater than $1/2$. Moreover we determine the generic Newton polygon
of each boundary component using this classification.
