The READY queues just contain pointers to process table entries. Each process table entry contains a pointer that can be used to point to the next READY process on its READY queue when the process is in fact READY.

#define NR_SCHED_QUEUES   16   /* MUST equal minimum priority + 1 */

EXTERN struct proc *rdy_head[NR_SCHED_QUEUES]; /* ptrs to ready list
      headers */
EXTERN struct proc *rdy_tail[NR_SCHED_QUEUES]; /* ptrs to ready list
      tails */