bulb-
combining form 
or bulbo-
Etymology: Middle French & Latin; Middle French bulb-, from Latin, from bulbus 
1. : bulb 
< bulbar >
< Bulbocodium >
2. : bulbar and  — especially in terms referring to the medulla oblongata or to the bulb of the penis or urethra
< bulbospinal >
< bulborectal >
or bulbo-
1.
< bulbar >
< Bulbocodium >
2.
< bulbospinal >
< bulborectal >