simple question on linked list insert

From: Digital Puer (digital_puer_at_hotjail.comet)
Date: 01/27/04 

Date: Tue, 27 Jan 2004 10:20:24 -0800

Can someone explain why the linked list insertion code (emphasised below)
does not work? It is a function to create a linked list and insert
two elements. The code in question creates the head fine, but
subsequent nodes are not inserted.

/* this function creates a linked list with two integers */
void insert(Node **head, int a, int b)
{

   Node *ptr;
   *head = make_node(a);

   /* this works fine */
   ptr = *head;
   ptr->next = make_node(b);

   /*
   BUT THIS CODE DOESN'T -- WHY?????
   ptr = (*head)->next;
   ptr = make_node(b);
   */

}

/* this function allocates memory for a Node and initialises it */
Node *make_node(int data)
{
   Node *node;
   node = (Node *)malloc(sizeof(Node));
   /* I know, I should check for error here */
   node->data = data;
   node->next = NULL;
   return(node);
}

int main()
{
   Node *head;
   insert(&head, 10, 20);
   print(head);

}