What is an anterior coxal bone that is connected by fibrocartilage? what exactly is fibrocartilage?

U mean Costal bone?: Its the RIB as it connects to the sternum by way of a Fibrocartilage, which is a thick tissue in the body, in various places, like the Cartilage ( menisci) in knee joint, the Disk in the spine between the Vertebrae, Its a tough tissue to give the Rib cage some elasticity, (called Costal cartilage), which is the dark blue tissue in the middle & lower part of the chest, as seen in the picture here.