Abaye said "the verse is necessary to exclude a Tumtum whose male genitals are on the outside (but his limb is hidden)" - if his male genitals are on the outside why is this a case of Tumtum? - I thought a Tumtum was undetermined gender and in this case he is a male. Thank you for your help.
Avraham Sacks, Ramat Beit Shemesh, Israel
The testicles are on the outside but the limb is hidden. You are correct that this is not the usual case of Tumtum. In most places in Shas it is not known whether the Tumtum is male or female, while in our Gemara he certainly is male but he is still considered a Tumtum. This is because the actual definition of "Tumtum" is not that there is a doubt about his gender identity, but rather that his gender identity is hidden. The origin of the word "Tutmum" is "Atum," or "blocked" (see Rashbam to Mishnah, Bava Basra 140b, DH v'Tumtum). Because the limb is "blocked" or hidden, he is termed a Tumtum even though he is certainly male. And that is why a verse is needed to exclude him.
Kol Tuv,
Dovid Bloom