Reference for Chullin 256:29

וכי ימות מן הבהמה מה מיתה שאינה עושה חליפין אף כל שאינו עושה חליפין דברי ר' יוסי

Wherein is there a difference between Rabbi and R'Akiba? - In the case of the nethermost joint [of the leg].<span class="x" onmousemove="('comment',' Sc., the metatarsus or the metacarpus; these consist entirely of bones and veins without flesh. According to R. Akiba, these are limbs and if severed from the living beast render unclean, and so too according to R. Jose; but according to Rabbi these are not limbs.');">¹³</span>

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