主枝

The two halves of the main branch have grown apart.

主枝的左右两边同的方生长。

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.

而论是何种羽毛，羽枝主枝延伸出来的羽小枝，都羽枝脊表面叫做「羽小枝板」的单层细胞长出来。