主枝

The two halves of the main branch have grown apart.

主枝的左右两边各向不同的方向生。

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，枝主枝延伸出来的小枝，都枝脊表面叫做「小枝板」的单层出来。