Knitting a baby matinee set - have a questions

I am knitting a matinee set - done by Paton and and I have questions.

The matinee set is started from the top going down.
I am doing the first sleeve and these are the instructions.

Rejoin yarn to rem sts and work Firs. Sleeve as follows:
**Next row: (RS). K39 (43-49). Turn.
Next row: K1. Purl to last st. K1.
Cont on these sts in stocking st, shaping sides [U]by dec 1 st at each end of 9th (3rd-next) [/U]and every following 4th row until 33 sts rem. Work 2 (2-0) rows in stocking st, thus ending with WS facing for next row.

I have underlined what I do not understand. Could somebody help me with this.



The pattern is given for 3 different sizes. Instructions for size small are before the parentheses, siize medium and size large inside the parens. You are following only one of these sizes. The directions
"by dec 1 st at each end of 9th (3rd-next) " follow the same pattern: for size small dec at each end of 9th row, size medium at each end of 3rd row and size large, each end of next row. You only need to follow one set of your undelined directions.

I’m sure the set is really cute. I just can’t get over that word matinee. It strikes me as funny. I keep picturing a baby wearing a sweater eating popcorn at the movie theater while watching a Bugs Bunny cartoon. They used to call the various times the movies were shown ‘matinees’. We would get a double feature and a Bugs Bunny cartoon for 25 cents. I’m old.

They still have matinees in most theaters, the prices are about 2/3 the evening rate too. My exbf and I used to go then when we went out to movies.