to the hindmost jaw bones by only two contact points; this contrasts to the robust-looking skull. Cerroni and colleagues instead found multiple but loose connections between the dentary and the hindmost jaw bones. This articulation, therefore, was very flexible but not necessarily weak. The bottom margin of the dentary was convex, while it was straight in Majungasaurus. The lower jaw was found with ossified hyoid bones, in the position they would be in if the animal was alive. These slender bones, supporting the tongue musculature and several other muscles, are rarely found in dinosaurs because they are often cartilaginous and not connected to other bones and therefore get lost easily. In Carnotaurus, three hyoid bones are preserved: a pair of curved, rod-like ceratobranchials that articulate with a single, trapezoidal element, the basihyal. Carnotaurus is the only known non-avian theropod from which a basihyal is known. The back of the skull had well-developed, air-filled chambers surrounding the braincase, as in other abelisaurids. Two separate chamber systems were present, the paratympanic system, which was connected to the middle ear cavity, as well as chambers resulting from outgrowths of the air sacs of the neck. A number of autapomorphies (distinguishing features) can be found in the skull, including the pair of horns and the very short and deep skull. The maxilla had excavations above the promaxillary fenestra, which would have been excavated by the antorbital air sinus (air passages in the snout). The nasolacrimal duct, which transported eye fluid, exited on the medial (inner) surface of the lacrimal through a canal of uncertain function. Other proposed autapomorphies include a deep and long, air-filled excavation in the and an elongated depression on the of the . Vertebrae The vertebral column consisted of ten cervical (neck), twelve dorsal, six fused sacral and an unknown number of caudal (tail) vertebrae. The neck was nearly straight, rather than having the S-curve seen in other theropods, and also unusually wide, especially towards its base. The top of the neck's spinal column featured a double row of enlarged, upwardly directed bony processes called epipophyses, creating a smooth trough on the top of the neck vertebrae. These processes were the highest points of the spine, towering above the unusually low spinous processes. The epipophyses probably provided attachment areas for a markedly strong neck musculature. A similar double row was also present in the tail, formed there by highly modified caudal