Reference for Chullin 151:15

לבתר דנפק אמר מ"ט לא אמרי ליה

But when he [Ulla] had left, Rab Judah said to himself, 'Why did I not answer him thus: BELOW means below the joint, but ABOVE means above the juncture of the tendons? '<span class="x" onmousemove="('comment',' And so it was also necessary for the Mishnah to teach the law if the leg was cut at the juncture of the tendons.');">¹⁰</span>

Jastrow

Jastrow