Stately, plump Buck Mulligan came from the stairhead, bearing a bowl of lather on which a mirror and a razor lay crossed. A yellow dressinggown, ungirdled, was sustained gently behind him on the mild morning air. He held the bowl aloft and intoned:
—Introibo ad altare Dei.
Halted, he peered down the dark winding stairs and called out coarsely:
—Come up, Kinch! Come up, you fearful jesuit!
annotation:
I think the challenge for me here is to make Buck Mulligan look “stately” and “plump” without drawing him fat. I’m basically going to base his physicality on Charles Carson from Downton Abbey (source), 
partially because that’s who I picture when I think of a “Stately, plump” man, and partially because I like to imagine Mr. Carson living this free spirited lifestyle at some point earlier in his history.
“—Introibo ad altare Dei.” means “go to the alter of God” apparently from Catholic mass, and an obvious irreverent joke on the part of Buck. I’m also interested as to why Buck refers to Stephen as “Kinch”. After a little digging I found that person from Joyce’s life on whom he based Buck, a man named Oliver St. John Gogarty, called Joyce that same name which means “knife blade”. (source)