Jonathan Richman’s babycakes enthusiasm has subtly but undoubtedly grounded popular music’s excesses over the past 15 years: singers of elephantine pretentiousness, from Emerson, Lake and Palmer to John Cougar Mellencamp, have had to keep an eye looking over their shoulders as Richman has not only filled his albums with songs like “I’m Nature’s Mosquito” and “The UFO Man” but ended up making better albums than theirs to boot. (Back in Your Life, in its own way, is almost as broadly revelatory as This Year’s Model.) Richman remains faintly touching and avowedly childlike–when he’s given cocredit for cover art, you know he did the crayoning. The late 80s have seen him manage a slight return to form on two Rounder albums, Modern Lovers ’88 and a new self-titled work; live he’s just great. He plays Friday and Saturday; opening the first night is the Spanic Boys, from Wisconsin, a reputedly very engaging quasi-rockabilly foursome led by a father-son pair; on Saturday Big Shoulders opens. Tonight and Saturday, Lounge Ax, 2438 N. Lincoln; 525-6620.