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Show 34 PROF. T. H. HUXLEY ON CER/VTODUS FORSTERI. [Jan. 4, side of the symphysial end of Meckel's cartilage, and unites with a corresponding surface furnished by the expanded symphysial end of the bone, termed "dentary" by Dr. Gunther. I cannot doubt that this bone is the representative of the true " dentary " element; nor is there any question in m y mind that Dr. Giinther's " dentary" is the true "splenial" element, while his articular answers to the "angular" piece of the vertebrate mandible. In the attachment of the tooth to the splenial, and not to the dentary, element, Ceratodus presents an interesting and important feature of resemblance to Siren and to. larval Salamanders on the one hand, and, on the other, to Polypterus. The splenial element in this Ganoid resembles that of Ceratodus, not only in bearing teeth, but in form, position, and relative size. In a young specimen oi Polypterus I find that the splenial does not extend continuously to the symphysis, but that, between its anterior termination and the latter, there are two short and broad bony plates developed in the fibrous tissue which overlies Meckel's cartilage; these bear teeth, and correspond with the expanded symphysial end of the splenial in Ceratodus. Polypterus has a true articulare, from which Meckel's cartilage is continued. The angulare is much shorter, and the dentale much longer than in Ceratodus. The hyoidean and opercular apparatus present characters of singular interest. Dr. Gunther says that " on the hinder side of the tympanic pedicle*, near its base, there is a small round tubercle, for the suspension and articulation of the hyoid arch (pl. xxxiv. fig. 3, z*)." I presume that this " small round tubercle " of the suspensorial expansion of the cranium is the small cartilage marked H.31In figs. 4 and 6. But 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." In fact it is, as fig. 6 shows, a distinct, though small, four-sided, flattened cartilage, the anterior and ventral angle of which is produced into a short conical process (Sy). Its anterior edge is firmly united with the skull, just where the cranium proper passes into the suspensorium, At this point there is a triangular vacuity filled with fibrous tissue, through which the posterior division of the seventh nerve passes (figs. 1 and 6, VII). The outer face of the cartilage is loosely connected with the operculum (Op); and the conical process (Sy) is imbedded in the dorsal and posterior part of the powerful ligament (h.s) (corresponding with the hyosuspensorial ligament in Menobranchus^) by which Hy is mainly kept in place. It is obvious that this little cartilage is the homologue of the hyo-mandibular element of the hyoidean arch of other fishes, the small conical process being the rudimentary sympleciic, and, therefore, that * It is surely to be regretted that any writer of authority should retain the misleading name of " tympanic pedicle" for a part the total distinctness of which from the "tympanic bone" of the higher Vertebrata has now been so copiously demonstrated. t P. Z. S. 1874, pl. xxix. figs. 1 and 2. |
