Gemara

Beraisa - Beis Shamai: A bald Nazir must pass a razor over his head;

Beis Hillel say, he need not do so.

R. Avina: Beis Shamai say that he must, i.e. he must shave, but he cannot.

R. Avina argues with R. Pedas, who says that Beis Shamai and R. Eliezer said similar laws.

Mishnah: A Metzora lacking a right (ear,) thumb or big toe can never become Tahor;

R. Eliezer says, it suffices to put (the blood and oil) on the place where the limb should be;

R. Shimon says, if he put on the left ear thumb or big toe he was Yotzei.

Sanhedrin 45b - Shmuel: If the witnesses' hands were cut off, the defendant is not stoned, because we cannot fulfill "Yad ha'Edim Tihyeh Bo va'Rishonah".

Question: If so, witnesses without hands should be invalid from the beginning!

Answer: "Yad ha'Edim" teaches that if they had hands from the beginning, those hands must kill him.

Support (Beraisa - R. Yishmael): If a city does not have a street, it cannot become an Ir ha'Nidachas (because the verse says that we gather everything into the street);

R. Akiva says, if it has no street, we build a street.

They argue about whether or not the street must be there from the beginning, but all require a street!

Tana'im (in the above Mishnah of a Metzora without a right thumb) argue about Shmuel's law.

Menachos 5a - Rav Papa: Regarding Taharas Metzora it says "Zos Tihyeh Toras ha'Metzora". This teaches that everything must be in order.

19a - Mishnah: The four species used for Taharas Metzora (Erez, Ezov, Shni Tola'as and birds) are Me'akev each other.

It says "Zos Tihyeh Toras ha'Metzora". This is (Me'akev) as if it said 'Chukah'.

Rishonim

Rambam (Hilchos Mechusarei Kaparah 5:1): A Metzora lacking a right thumb, big toe or ear can never become Tahor.

Rambam (Hilchos Tum'as Tzara'as 11:4): Shaving a Metzora, Tevilah and sprinkling (blood of the slaughtered bird on him) do not Me'akev each other. Everything else is Me'akev.

Objection (Ra'avad): The Toras Kohanim and Tosefta (8:6) say just the opposite! Only actions to his body are Me'akev, but not Tevilah of his clothes or sending the bird...

Answer (Kesef Mishneh): Perhaps the text of the Rambam should be like the Ra'avad. Alternatively, the Rambam teaches that the order in which he does these is not Me'akev.

Rambam (Hilchos Nezirus 8:5): A bald Nazir need not pass a razor over his head. Shaving (and waving) is l'Chatchilah, it is not Me'akev.

Question: The Gemara connotes that whoever holds that a Metzora lacking a thumb cannot become Tahor holds that a bald Nazir cannot become permitted!

Note: The Gemara in Nazir attributes this opinion to R. Eliezer. It also brings two versions of the argument about Nazir which are unlike the version in Yoma.

Answer #1 (Lechem Mishneh): The Rambam rules like R. Eliezer, who explains the verse simply, both regarding Metzora and Nazir. However, he rules like Chachamim that shaving a Nazir is not Me'akev, because of the Gezeirah Shavah "Achar-Achar". There is no Gezeirah Shavah regarding Metzora, so he rules that putting the blood on the Behonos is Me'akev.

Answer #2 (Tosfos Yom Tov Nega'im 14:9 DH v'Ein): The Rambam rules like (Beis Hillel and Chachamim according to) the text in Yoma, because in Nazir the opinions in the Mishnah in Nega'im are switched (or because the text in Yoma is like the text in the Tosefta and the Yerushalmi - Tziyonei Maharan, brought in Likutim in Frankel Rambam).

Answer #3 (Keren Orah Nazir 46a DH u'Mimeila): The Gemara compares Taharas Metzora and Nazir according to the opinion that shaving is Me'akev for a Nazir. Just like passing a razor over a bald head is not considered shaving, putting blood where the ear should be does not help. We hold like Beis Hillel that shaving is not Me'akev a Nazir. It appears that if a Metzora has no hair, passing a razor over his body is not considered shaving, so he cannot become Tahor.

Answer #4 (Radvaz): The correct text of the Rambam should say that a bald Nazir must pass a razor over his head. This is considered shaving, even though he has no hair.

Rambam (Hilchos Sanhedrin 14:8): If someone sentenced to death resisted execution and Beis Din could not restrain him to administer the proper Misah, the witnesses may kill him in any way possible. Others may not kill him first. Therefore, if the witnesses' hands were cut off, he is exempt. If the witnesses had no hands from the beginning, others may kill him.

Bartenura (Nega'im 14:9): The first Tana says that a Metzora missing his right ear (or thumb or toe) can never become Tahor. This is only if he lost it after he became Tamei.

Question #1 (Tosfos Yom Tov ibid.): If he was missing it before becoming Tamei, it is not Me'akev. Even Shmuel requires the verse ("Yad ha'Edim Tihyeh Bo va'Rishonah") as it is written only if the witnesses had hands at the time they testified. The Rambam rules like Shmuel regarding stoning, but regarding Metzora he does not distinguish when the Metzora lost his ear! Regarding Nazir he says that the verse is only l'Chatchilah!

Answer #1 (Boaz 5): "Yad ha'Edim" connotes the hand the witnesses had at the time of (seeing or giving) testimony. Regarding Metzora it does not say 'Yad ha'Metzora', therefore it does not matter when he lost his hand. A Nazir is permitted through Zerikas Dam of his Korbanos. His Heter does not depend on shaving and waving.

Question #2 (Tosfos Sanhedrin 45b DH Ein): The Gemara here says that Shmuel holds like the Tana who says that there is no Taharah for a Metzora without an ear. Perhaps the Tana normally does not require fulfilling the verse literally, only regarding Metzora, because it says "Tihyeh"! In Menachos (5a and 19a), "Tihyeh" teaches that everything about Metzora is Me'akev!

Answer (and Answer #2 to Question #1 - Tosfos Yom Tov ibid.): The Rambam holds that the Sugya in Sanhedrin argues with those in Menachos. He rules like those in Menachos, that "Tihyeh" teaches that everything about Metzora is Me'akev. He has a different source to rule like Shmuel, i.e. the Beraisa of Ir ha'Nidachas.

Poskim

Shulchan Aruch (651:4): Someone without a hand takes the Lulav in his arm, and also the Esrog.

Magen Avraham (10): The Roke'ach learns this from a Metzora with no right thumb; we put Dam ha'Asham in its place (Sanhedrin 45b). But this is like R. Eliezer! The Halachah follows the first Tana, who says that he has no Taharah; the Rambam rules like him. Perhaps the Roke'ach holds like the text in Nazir which switches the opinions. According to the Rambam it is better to take them in his hand one at a time. Alternatively, the Rambam agrees to the Shulchan Aruch, because the Torah never specified that one must take four species in his hand. The Gemara (Yevamos 105a) says similarly regarding Chalitzah.

Mishnah Berurah (21,22): If he has elbows, he takes the Min(im) usually taken in that hand in the elbow. If not, he takes them under the arm. If he does not have arms at all, he is exempt. Taking in the mouth is not 'Lekichah'.

Sha'arei Teshuvah (6): The Torah did not say that Chalitzah must be done with the hand, therefore a handless Yavam may remove the shoe with the foot. Some say that the same applies to taking the four Minim; one should take them without a Berachah. If one cannot take something with his hand (e.g. it is in a cast), it is as if it is missing.

Kaf ha'Chayim (43): Some say that if one is missing only one hand, he takes the Lulav (bundle) in his hand, even if it is the left hand, and the Esrog under the other arm. Others say that he takes both in one hand at once; this is better than taking one after the other. One can do one way, and then the other way, to fulfill both opinions. If he is missing an entire arm, he takes both in his hand or (if he has only an arm) under his arm. If this is impossible, he takes the one after the other. However, some say that one after the other is better than both at the same time in one hand.