Bechoros, Chapter 6, Mishnah 9. In the previous mishnah, we learned that a significantly protruding upper jaw in a cow, goat, or sheep - a structure somewhat resembling a pig's jaw and protruding snout - is considered a blemish. Now we will discuss the question: What is the law regarding a significantly protruding lower jaw?
The Lower Jaw:
The mishnah brings an incident that happened with a firstborn animal whose lower jaw protruded beyond its upper jaw, like an underbite. This does not refer only to the teeth, but to the entire jaw protruding outward. Rabban Shimon ben Gamliel sent the question of what to do with such an animal to the Sanhedrin, and the Sages replied that it is indeed a blemish - meaning it is permissible to slaughter this animal and eat it outside the Beis Hamikdash.
A Double Ear:
If an animal grows two ears on one side of its head, like two sets of cartilage - is this considered a blemish? In this regard, we must distinguish between two situations:
One continuous cartilage: The additional inner ear is connected at its top to the outer ear, in the shape of an upside-down U, and the entire thing is one long, strange piece of cartilage - this is a blemish.
Two separate ears: It is not a single unit but rather two separate pieces of cartilage, one inside the other (and we must remember that cartilage is hard, but not as hard as bone) - this is not a blemish.
The Bartenura notes that the reason for this law is unexplained: he does not know why an animal that has two ears, one inside the other, when they are not connected and are not a single piece of cartilage - is not considered blemished.
The Tail:
The mishnah rules that the tail of a kid goat "shehu domeh leshel chazir, veshein bah shalosh chulyos" - that is similar to that of a pig, and which does not have three vertebrae - is a blemish. The simple understanding of this seems to refer to the length of the tail. A pig's tail is noticeably longer than the tail of a goat or sheep, and it curls and twists upon itself until it forms a kind of loop.
Goat tails: Very similar to pig tails, except they are shorter.
Sheep tails: Noticeably flatter and fatter than pig tails.
According to this, we have two extremes of a blemish before us: if the tail of the goat or sheep is so long that it twists like a pig's tail - it is blemished; and if it is too short, lacking even three vertebrae (tailbones), having only two - this is also a blemish.
The Bartenura explains based on the Gemara that we must distinguish between goat tails and sheep tails:
"Davka zanav shel taleh" - specifically a lamb's tail. Even though the Mishnah uses the word "gedi" (kid), it is actually referring to a small sheep, for which "d'ba'inan shalosh chulyos" - three tail vertebrae are required.
"Aval zanav shel gedi" - but the tail of a kid. Regarding an actual goat: "chulya achas bilvad mum" - only one vertebra is a blemish. If it has three or two vertebrae, it is valid; and only if it has nothing but a single vertebra is it too short and considered a blemish.
Thus, one must feel the tail and determine the number of its vertebrae in order to decide whether or not it is blemished.