主枝

The two halves of the main branch have grown apart.

左右两边各向不同方向生长。

In both types of feather, the barbules that extend from the barb ramus grow from a single layer of cells, called the barbule plate, on the periphery of the barb ridge.

而不论是何种羽毛，羽延伸出来羽小，都羽脊表面叫做「羽小」单层细胞长出来。