Figure 4 — Diagram of the cuirassial breathing system in theropod dinosaurs. When breathing out (expiration), the rectus abdominis muscle pulls the gastralia forwards, swinging the ends of the gastralia inwards and compressing the belly wall. When breathing in, contraction of the pelvic muscles (such as the ischiotruncus) pulls the gastralia to the back, causing them to swing out and expand the body cavity. Diagrams also show the bones of the pelvis (ilium, ischium and pubis) and other musculature (e.g. caudotruncus). From Carrier and Farmer, (2000).