Derivation of the Classical Lagrangian for the Relativistic Spinning Particle

The `classical' model for a massive spinning particle, which was recently proposed, is derived from the isotropic rotator model. Through this derivation, we note that the spin can be understood as the relativistic extension of the isotropic rotator. Furthermore, the variables $t_\m$ corresponding to the $\p^*$ of the `pseudo-classical' model, are necessary for the covariant formulation. The dynamical term for these extra variables is naturally obtained and the meaning of the constraint term $p^\s\L_{\s\n}+mt_\n =0$, which was recently shown to give `quasi-supersymmetry', is clarified.