This image shows the skeleton and anatomy of a barbeled dragonfish with a true functional head joint (A) in contrast to the relatively inflexible connection usually found in fishes (e.g., a young Mediterranean sea bass (B)). The bone is stained red and cartilage is stained blue. Some barbeled dragonfishes have reduced the size or completely lost several of the vertebrae just behind the head, while five groups exhibit a true functional head joint like the one pictured above (A). Both adaptations allow a considerable degree of head motion that is significantly expanded in the groups that have a functional head joint.
Nalani Schnell, Muséum national d’Histoire naturelle