Bechoros Chapter 7, Mishnah 4. The Mishnah continues to list blemishes where the kohen's appearance is not like that of other kohanim, and therefore he is not permitted to serve in the first instance. If he served after the fact - he has nullified a positive commandment, but his service is valid.
"Einav gedolos keshel egel o ketanos keshel avaz" - his eyes are as large as a calf's or as small as a goose's:
In the previous chapter we learned that an animal that has one eye as large as a calf's and one eye as small as a goose's - this is an absolute blemish, and a kohen who has such eyes, his service is disqualified even after the fact. Here, however, we are discussing a kohen whose eyes are both extremely large or extremely small. Since his appearance is abnormal and not like other kohanim, he does not serve in the first instance; and if he served - he has nullified a positive commandment, and after the fact his service is valid.
"Gufo gadol me'eivarav o katan me'eivarav" - his body is larger than his limbs or smaller than his limbs:
This refers to a kohen whose limbs are disproportionate to his body: a regular-sized body with extremely short arms and legs, or extremely long arms and legs. He too is considered a kohen who is not similar to other kohanim.
"Chotmo gadol me'eivarav o katan me'eivarav" - his nose is larger than his limbs or smaller than his limbs:
An abnormally large or small nose is also included in these disqualifications. The Gemara explains the comparative measure of "than his limbs": the length of a person's nose is approximately the length of his pinky, the small finger on his hand, and this is the standard of measurement. If the nose is much larger or smaller than this measure, it is an abnormal appearance.
"Hatzimem vehatzimea" - the tzimem and the tzimea:
The Mishnah itself defines both terms. "Eizehu tzimea? She'oznav ketanos" - what is a tzimea? One whose ears are small - his ears are extremely small. We are not discussing one large ear and one small ear, which we already saw in the previous chapter as an absolute blemish that disqualifies him even after the fact, but rather merely small ears: in the first instance he does not serve, and after the fact his service is valid.
"Vehatzimem - she'oznav domos lisfog" - and a tzimem is one whose ears resemble a sponge. The Rishonim debate the explanation of this comparison:
The Bartenura, following the view of Rashi: This refers to a shriveled and dried sponge. Sponges during the time of the Mishnah were sea creatures - very simple animals, which look like a sponge after they have dried. It is possible that this refers to what is known today as 'cauliflower ear', which is often found among wrestlers.
The Rambam: This does not refer to a dry sponge, but to an ear that is swollen like a sponge. According to this as well, it is possible that the reference is to that same 'cauliflower ear'.
In summary: In all the cases in the Mishnah - eyes as large as a calf's or as small as a goose's, a body that is disproportionate to the limbs, a nose larger or smaller than the measure of his pinky, and ears that are small or resemble a sponge - the appearance of the limbs is abnormal to the point that the kohen is not similar to other kohanim, and therefore he does not perform the Temple service in the first instance, but after the fact his service is valid.