Broadway and Amsterdam run parallel heading uptown, but here at 72nd street Broadway begins its trip eastward as it heads down to lower Manhattan, fouling up the otherwise relatively rational grid of New York City (if you disregard the mayhem below Canal Street). As Broadway curves to cross Amsterdam it creates a small triangular patch between 72nd and 73rd streets, and while other parts of town might build a skyscraper on any available land no matter how small and oddly shaped (see the Flatiron Building) here a park was created.      Built in 1887 and named after Italian composer Giuseppe Verdi in 1921, Verdi Square consists of a fenced off area containing bushes, trees, and a statue of its namesake surrounded by four of the characters from his operas. The fence is girded by benches which served as a gathering place for musicians like Caruso and Toscanini at the beginning of this century, while more recently the periphery has been an on and off haven for petty drug dealers. (Police contend that they run 'em in, and they're back the next day.)      Verdi Square was landmarked in 1974 and restored in 1997 with private funds.      Accross from Verdi Square is the 72nd St. Subway Station, a landmarked building which, while recently renovated, is still overcrowded during rush hour. Local residents are unnerved by the effect Donald Trump's recent development in the neighborhood may have on crowds in the station. next: The 79th St. Boat Basin