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Show 636 MR. W. G. RIPEWOOP ON THE [Nov. 6, Huxley (5) was therefore unduly confident in assuming that this tubercle was the hyomandibular cartilage which he had discovered, and in writing (p. 34) that "this is neither a process of the suspensorium, nor does it articulate with, nor take the principal share in, suspending Hy, which is Dr. Giinther's ' hyoid arch.'" The hyomandibular is still present in this specimen, and lies dorsally to the " tubercle," to which a portion of the ligament still remains attached. The lower end of the hyomandibular cartilage, which Huxley calls the symplectic, is not embedded in the hyosuspensorial ligament, but, as a careful dissection will show, is articulated to the dorsal surface of the suspensorial tubercle, whereas the hyosuspensorial ligament is attached to its posterior surface at a slightly lower level. Gadow's replacement of Huxley's accurate term " hyosuspensorial ligament" by "ligamentum hyomandibulo-hyoideum" is thus singularly unfortunate. The hyomandibular is not connected directly with the ceratohyal, but indirectly by means of a process of the palato-quadrate cartilage, so that, by a slight stretch of the imagination, the skull of Ceratodus might be regarded as partially hyostylie ; the bulk of the evidence, however, is distinctly opposed to this view. Briihl (2) (Taf. lxiii. Fig. 6), in a figure said to be copied from Huxley, shows a ligament running from the ceratohyal to the mandible and to the opercular, but not to the suspensorium nor to the hyomandibular, and in his original figures he is hardly more fortunate. Assuming the determination of the ceratohyal and hyomandibular correct, it is worthy of note that the region of union of these elements, in the Sharks just behind the mandibular articulation, is here, in Ceratodus, raised considerably above the level of the quadrate condyle of the upper jaw (see fig. 2). The shape of the hyomandibular is by no means constant, but is subject to great individual variation, and this even on the right and left sides of the same skull. • By far the commonest form is that shown in fig. 3, a (p. 637). The cartilage is rhombic in shape and applied by its anterior edge to the cranial cartilage, while a ventral process, separated from the skull by a space for the passage of the hyoidean branch of the seventh nerve, is attached to the upper surface of the suspensorial tubercle. In one case examined (fig. 3, o) there is in addition a nodule of cartilage in the hyosuspensorial ligament which may possibly have the value of an interhyal. A similar nodule is mentioned by Pollard (10), but not figured. The two sketches, fig. 3, c and d, show what variation may occur in the relative lengths of the vertical and horizontal diameters of the cartilage, and also that when the longer diameter is horizontal the extent of the attachment to the cranium is reduced to a minimum, |