Yoreh Deah Siman 24 Seif 4

ד שְׁנַיִם אוֹחֲזִין בַּסַכִּין וְשׁוֹחֲטִין, אֲפִלּוּ זֶה לְמַעְלָה לְצַד הָרֹאשׁ וְזֶה לְמַטָּה לְצַד הֶחָזֶה, שׁאוֹחֲזִין אוֹתוֹ בַּאֲלַכְסוֹן, כְּשֵׁרָה וְלֹא חַיְישִׁינָן שֶׁמֶּא יִדְרְסוּ זֶה עַל זֶה.

Seif 4

 

Two [people] are holding the knife and slaughter, one from above, the side of the head, and one from below, the side of the chest, holding it [the knife] diagonally, it is kosher and there is no concern of “dirasah”. (one struck the neck with a knife as one strikes with a sword)