and sub-rectangular in shape with a tendency to become more elongated in posterior vertebrae. The centra were large and predominantly amphiplatian (flat on both facets) and circular when seen from the front. Sometimes in old individuals the last dorsal vertebra was somewhat coosified to the first sacral. The were firmly coosified giving form to the sacrum, which was connected to the inner sides of both ilia. Their neural spines were broad, not coosified, and rather consistent in length. The centra were mainly opisthocoelous (concave on the posterior facet and convex on the anterior one) and their size became smaller towards the end. The decreased in size progressively towards the end and had very elongated neural spines in the mid-series, forming a sail-like structure. This elongation started from the first to the fourteenth caudal. The centra were (saddle-shaped at both facets). On the anterior caudals they were broad, however, from the twenty-fifth onwards the centra became elongated alongside the neural spines. On the underside of the caudal vertebrae a series of chevrons were attached, giving form to the lower part of the tail. The first chevron was located at the union of the third and fourth caudals. Chevrons three to nine were the largest and from the tenth onwards they became smaller. All vertebrae of Protoceratops had ribs attached on the lateral sides, except for the series of caudals. The first five cervical ribs (sometimes called chevrons) were some of the shortest ribs, and among them the first two were longer than the rest. The third to the sixth dorsal (thoracic) ribs were the longest ribs in the skeleton of Protoceratops, the following ribs became smaller in size as they progressed toward the end of the vertebral column. The two last dorsal ribs were the smallest, and the last of them was in contact with the internal surfaes of the ilium. Most of the sacral ribs were fused into the sacrum, and had a rather curved shape. The pectoral girdle of Protoceratops was formed by the (fusion of the coracoid and scapula) and clavicle. The (shoulder blades) were relatively large and rounded on their inner sides. At their upper region, the scapulae were wide. At their lower region, the scapulae meet the coracoids. The were relatively elliptical, and sometimes coosified (fused) to the scapulae. The clavicle of Protoceratops was an U to slightly V-shaped element that joined to the upper border