Reference for Eruvin 40:18

אמר רב אחא בר רב הונא אמר רב ששת שאני גמל הואיל וצוארו ארוך

Now what is the ruling? - The other replied: You have learnt it: PROVIDED A COW CAN BE WITHIN [THE ENCLOSURE WITH] ITS HEAD AND THE GREATER PART OF ITS BODY WHEN DRINKING. [This refers,] does it not, to a case where [the keeper] holds the vessel but not the cow? - No, [it may refer to one] who holds both the vessel and the cow.

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