In old medical texts the urinary bladder is sometimes written 脬.
Tips
history
脬 is barely used in modern Chinese, where the bladder is 膀胱. It joins the flesh radical ⺼ with 孚 for the sound. The same 孚 phonetic family includes 泡 and 孵.
register
Classical and dialectal; in standard modern Chinese the everyday word is 膀胱.