Bechoros Chapter 6, Mishnah 8. The Mishnah continues discussing blemishes on the legs.
"Nishbar etzem yado ve'etzem raglo, af al pi she'eino nikar" - if a bone is broken in the animal's front leg or its hind leg, even though the break is not visible when looking at the animal, but when it walks a limp is noticeable - the very walking in an unusual manner is enough to consider it blemished.
"Mumin elu manah Ila beYavneh":
These two blemishes - a broken front leg bone and a broken hind leg bone - were listed by Ila in Yavneh. "Vehodu lo chachamim" - the Sages agreed with him and established that these are indeed blemishes, and an animal that limps due to a broken leg is considered blemished. However, "od sheloshah hosif, amru lo: lo shamanu es elu" - regarding the three additional blemishes that he listed, the Sages replied to him that they had no tradition for them.
In other words, the Sages of that generation did not accept the continuation of Ila's list, which includes three relatively minor blemishes. However, at the end of the Mishnah it will be explained that afterward they were indeed accepted, and according to halachah they are included in the list of blemishes.
The three blemishes that Ila added:
"Es shegalgal eino agul keshel adam" - according to the Bartenura, this refers to the eye socket: the eye socket of the cow, goat, or sheep is round like that of a human. It is worth noting that a comparison between skulls and pictures of animal eyes to a human eye does not show complete identity, but this is the simple understanding according to the Bartenura. Tosafos cite an opinion based on a textual variant in Rashi, according to which this does not refer to the eyeball or its socket, but to the pupil: the pupil of ruminants - cows, goats, and sheep - is long and thin, like a horizontal line, and is not round like a human pupil. According to this explanation, a pupil that is round like a human's, and not like a long, thin strip as is typical for them, is considered a blemish.
"Ufiv domeh leshel chazir" - in a pig, due to the snout, the upper jaw protrudes beyond the lower jaw, creating the impression of an overbite. In a cow, goat, and sheep, the jaws are aligned with each other, and in sheep and goats this is clearly noticeable. An animal that displays a significant overbite like a pig - it is considered blemished.
"Veshenital rov hamedaber shel leshono" - the tongue is made up of two parts: the part attached underneath, and the front part which is loose and not attached. The front part is what moves and produces sounds in human speech, and is therefore called "the speaking part." Even though an animal does not speak, if most of the front part of its tongue is removed - this is a blemish. Although its mouth is closed most of the time and the matter is not prominent, when it opens its mouth it is noticeable, as was explained regarding the teeth.
The ruling of the subsequent Beis Din:
Even though the Beis Din in Yavneh did not have a tradition regarding these three blemishes, the Mishnah concludes: "Uveis din shel achareihem amru: harei elu mumin" - a later Beis Din confirmed Ila's words and established that even these minor blemishes - a tongue with most of it removed, an animal whose upper jaw protrudes, and an eye that is round like a human's and not in the manner of animals - are absolute blemishes, which permit one to slaughter the cow, goat, or sheep outside the Beis Hamikdash, and if it is a bechor - to be eaten there.