The second Mishna in this perek appears on our daf, and it discusses the second daily lottery, which determined which of the kohanim would slaughter the morning tamid sacrifice, who would sprinkle the blood, who would clean out the interior altar, who would clean out the menorah and who would place the various pieces of the butchered animal on the altar. In all 13 different kohanim received their assignments for the day as a result of this lottery.
The korban tamid was a korban olah, which was completely burned on the altar. As with all korbanot olah, after its slaughtering, the animal was divided up into large pieces, which were brought to the altar to be sacrificed. The details of how the animal was divided, which pieces were paired together, how they were carried to the mizbe’ah, etc. are not explained here, as that is the focus of Massekhet Tamid.
The Mishna does teach that the first parts of the animal that were brought to the altar were ha-rosh ve-ha-regel – the head and the legs. Rashi explains that the head is mainly bones, while the legs are mainly meat, so they complement each other while being sacrificed. The Meiri, on the other hand, suggests that they are both mainly bones, and as such they are put together because of their similar nature. The Jerusalem Talmud explains that these two parts of the korban were brought to the altar together as the first parts to be sacrificed because as the animal walks it stretches its neck forward and lifts its legs to move. Thus it is sacrificed in the same manner in which it walked.
The description here in Massekhet Yoma of the active participation of the kohanim in the daily procedure in the Temple acts as a contrast to the avodah of the kohen gadol on Yom Kippur, where he is the sole individual carrying out all of the avodah of that special day.