The results of a histological study of intersegmental joints of the spine are presented for the juvenile silver chimaera Chimaera phantasma. Its occipital-synarcual joint and the joints of the articular processes have a large cavity. The fibrous tissue surrounding the latter connects the articular surfaces, which are thus not totally separated by a cavity. We interpret both joints as hemidiarthroses. There are layers of dense fibrous connective tissue (synarthroses) between the elements of the vertebral arches. The boundaries between the segments in the synarcual are determined only by the spinal nerves. Mineralized cartilage is found only in the synarcual. Our data clearly indicate specialization of the occipital-synarcual joint, since this is the only diarthrosis in the chimaeras spine. Further studies are needed to understand the mechanisms of joint development; however, the cavity itself may indicate adaptation to an extended range of motion in the joint. Early mineralization of the synarcual may testify on the joint load during compression. Clarification of the biological role of this articulation requires observations of the animal in nature. Taking into account both literary sources and the data of present study, we assume that the mobility of the chimaera head is important for tearing off food objects attached to the substrate.
A. V. Romanov (Wed,) studied this question.