Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
Now in the tribunician jurisdiction there emerged a new
power, which on the one hand might interfere against the supreme
magistrate even during his tenure of office, and on the other hand
was wielded against the noble burgesses exclusively by the non-noble,
and which was the more oppressive that neither the crime nor its
punishment was formally defined by law. In reality through the
co-ordinate jurisdiction of the plebs and the community the estates,
limbs, and lives of the burgesses were abandoned to the arbitrary
pleasure of the party assemblies.
In civil jurisdiction the plebeian institutions interfered only so
far, that in the processes affecting freedom, which were so important
for the plebs, the nomination of jurymen was withdrawn from the
consuls, and the decisions in such cases were pronounced by the
"ten-men-judges" destined specially for that purpose (-iudices-,
-decemviri-, afterwards -decemviri litibus iudicandis-).