The first sentence I chose was on page 357.
"Gender ought not to be conceived merely as the cultural inscription of meaning on a pregiven sex (a juridical conception); gender must also designate the very apparatus of production whereby the sexes themselves are established."
Someone else has already posted this sentence, but I thought I would post my interpretation since I already analyzed it. With this sentence, I think that Bulter was saying that gender should not be determined by the connection that our culture makes with the gender and sex binary. Gender is not determined by a sex that is given based on genitalia. Gender can also influence and determine sex.
I chose another sentence from page 357 to analyze that I have not yet seen.
"At this juncture it is already clear that one way the internal stability and binary frame for sex is effectively secured is by casting the duality of sex in a prediscursive domain."
In this sentence I think that Butler is saying that our culture casts the binary system of sex and gender (female/male, woman/man) onto a previously unstructured place. For example, we use genitalia to decide if it's a boy or a girl before we even know anything about who that child is as a person. The baby is the prediscursive domain that the boy/girl frame for sex is put on.