Struct sk_buff_head

Hello!
I read code from file include/linux/skbuff.h and I have question about sk_buff_head structure. This structure is pointing to next and prev sk_buff structure on list. But I found the same pointers in first field structure sk_buff- it is union, which has pointers to next and prev sk_buff structures on list. Is this union replace sk_buff_head structure? I didn`t found any field in sk_buff, which may use sk_buff_head, but I found some functions which uses this structure.