Where thread gets it's PC value if we create thread using pthread_create?

Question

My question is regarding the PC register value of which is giving to the created thread.

if I create a new process with fork() the PC value will be copied from parent to child as PC value is the next command in the code.

However if I create a new thread as following

#include <pthread.h>
int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void), void *restrict arg)

with:

err = pthread_create(&thready, NULL, &mythread, NULL);

Now the question is where the created thread gets it's PC value. How does the PC value set to the first line of mythread code?