Ess Meliká vs Sechitá

How was the burnt-offering of a fowl brought? [The priest] would ascend upon the ramp He would turn [right] to the surrounding ledge and approach the southeast corner. There he would sever the head [of the fowl] at the nape of its neck, severing [the head] entirely. If he does not sever it entirely, [the sacrifice] is invalid. He then squeezes out the blood of the head and the blood of the body on the wall of the altar above the [scarlet] band in the middle of the altar.
If he squeezed out the blood of the head, but did not squeeze out the blood of the body, [the sacrifice] is invalid. If he squeezed out the blood of the body, but did not squeeze out the blood of the head, [the sacrifice] is valid.

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If one slaughters above this place - in the area called the entrance to the gullet - or below this place - i.e., the beginning of the digestive system, the slaughter is unacceptable.
The measure of the entrance to the gullet above which is unfit for slaughter in an animal or a beast is so one can grab it with two fingers. With regard to a fowl, it depends on its size. The lower limit extends until the crop.

The slaughterer must slaughter in the center of the neck. If he slaughters to the side, it is acceptable.
What is the measure of slaughter? That one [cut] the two identifying marks, the windpipe and the gullet. Superior slaughter involves cutting both of them, whether for an animal or a fowl and a slaughterer should have this intent. [After the fact,] if one cut the majority of one of them for a fowl and the majority of both of them for an animal or a beast, the slaughter is acceptable.

If he cut half of one and half of the other - even in a fowl - the slaughter is unacceptable. When a windpipe is half slit and one cut a little more on the place of the slit, making the cut a majority, the slaughter is acceptable. [This applies] whether one begins [on a portion of the windpipe] that is intact and reaches the slit or one inserts the knife into the slit and [increases its size until it] reaches the majority.

If he slaughtered the majority of one of the signs for a fowl or the majority of both signs for an animal, the slaughter is permitted even if he waited half the day and then returned and finished cutting the signs. For since the minimum measure for slaughter was met, it is as if he is cutting slaughtered meat.

What is meant by ikur? That the gullet and/or the windpipe were displaced and slid [from their place] before the conclusion of the slaughter. If, however, one slit an entire sign or its majority in a fowl, and then the second sign slipped, the slaughter is acceptable.