model {
  for (i in 1:n) {
    len[i] ~  dnorm(mu[i], tau[1])
    mu[i]  <- beta[1] + beta[2]*dose[i]
  }
  for (i in 1:2) {
    beta[i]  ~  dnorm(0, tau[2])
    tau[i]   ~  dgamma(0.001, 0.001)
    sigma[i] <- sqrt(1/tau[i])
  }
}
