Reference for Chullin 178:5

ר' יהודה אומר

IT APPLIES TO CATTLE AND TO WILD ANIMALS, TO THE RIGHT AND LEFT HIP, BUT IT DOES NOT APPLY TO BIRDS BECAUSE THEY HAVE NO SPOON-SHAPED HIP.<span class="x" onmousemove="('comment',' The muscles upon the hip bone (or femur) of a bird lie flat and are not raised and convex like those of cattle. In cattle the entire hip is very lrhv ;f much like the back of a spoon or like a club. This feature is expressly specified in the prohibition, , the spoon of the thigh, i.e., 'the convex prominence of the thigh'. Gen. ibid.');">⁴</span>

Jastrow

Jastrow