  We describe all complex geodesics in the tetrablock passing through the
origin thus obtaining the form of all extremals in the Schwarz Lemma for the
tetrablock. Some other extremals for the Lempert function and geodesics are
also given. The paper may be seen as a continuation of the results Abouhajar,
White and Young. The proofs rely on a necessary form of complex geodesics in
general domains which is also proven in the paper.
