The brain of "Sphenodon" fills only half of the volume of its endocranium. It is composed of the endocranium and the lower parts of the skull roof. The endocranium and facial bones of the skull are ultimately derived from crest cells. In comparative anatomy, neurocranium is sometimes used synonymously with endocranium or chondrocranium. In 2001, Hans C. E. Larsson published a description of the endocranium of "Carcharodontosaurus saharicus". The occipital bone is part of the endocranium, the most basal portion of the skull. The holotype, an endocranium, was originally described as that of a phlyctaeniid. Structurally, the endocranium consists of a boxlike shape, open at the top. It is overlaying the endocranium, corresponding to the cartilaginous skull in sharks and rays. The endocranium is several times larger than that of its sympatric relative, "B. guangxiensis".