Makkos, Chapter Two, Mishnah 5. The Mishnah continues to discuss the nature of the six cities of refuge and the roads leading to them.
"U'mechuvanos lahem derachim mizo lazo":
Straight roads were maintained and made ready, and they led to the cities of refuge. The source for this is the verse, "shene'emar: tachin lecha haderech v'shilashta v'gomer" - "tachin lecha haderech", that a person must prepare the road for himself; "v'shilashta", that he must divide it into three parts, and we will yet address what this means. The verse continues: "and you shall divide into three parts the border of your land which Hashem your God gives you as an inheritance, and it shall be that every murderer will flee there" - to divide up the borders of the land that Hashem gives as an inheritance, so that every murderer will be able to flee to the cities of refuge.
The Gemara cites a beraisa that at the crossroads they would write the word "miklat" and post it on a sign, to indicate which of the two directions at the crossroads one should take in order to reach the city of refuge.
In Israel today the protected spaces in buildings are called a 'miklat', and in apartment buildings signs are posted directing people to them - something that recalls this halachah, though there is no way to know whether this is purely a practical measure or an allusion and a connection to this halachah.
"U'mosrin lahen shnei talmidei chachamim":
The court of the city in which the killing took place would send two Torah scholars to accompany the killer on his way to the city of refuge, "shema yahargenu baderech" - lest the blood redeemer, the relative of the victim, seek to kill him along the way. "Vi'dabru eilav" - the two Torah scholars would speak to the relative's heart and persuade him not to take revenge against the killer.
The view of Rabbi Meir:
Rabbi Meir says: "Af hu medaber al yedei atzmo" - the killer himself can and should speak on his own behalf. Two versions of the text affect how we understand his words:
"Af hu medaber al yedei atzmo": According to this version, Rabbi Meir does not disagree with the first Tanna about sending two Torah scholars; he simply adds that the killer himself may also speak.
"Hu medaber al yedei atzmo": According to this version it appears that Rabbi Meir does disagree, and in his view, instead of two Torah scholars, the killer himself is the one who must speak.
Either way, Rabbi Meir derives this idea from the wording of the verse: "V'zeh dvar harotze'ach" - the speech of the killer.
The Gemara cites a beraisa in which the Sages respond to Rabbi Meir with a most interesting idea: "Harbeh shelichus osah" - great is the power of an agent. At times a person speaking on his own behalf does not succeed in obtaining what he wants, whereas someone speaking in his name can accomplish more.