| OCR Text |
Show 1876.] PROF. T. H. HUXLEY ON CERATODUS FORSTERI. 35 it is itself the dorsal element of the hyoidean arch, attached in normal position, as its relations to the seventh nerve show. The hyoidean cornua are very strong, and consist of a cartilaginous axis almost completely ensheathed by bone. The dorsal end of each is Fig. 6. Ceratodus forsteri. Inner view of the right hyoidean arch (Hy), with the opercular apparatus and part of the suspensorium and of the mandible. H.M, hyomandibular cartilage; Sy, its symplectic process; Op, operculum ; Lop, interoperculum ; B, B\ cartilaginous rays attached to the inner face of the operculum and interoperculum ; VII, exit of the posterior division of the seventh nerve; h.s, hyosuspensorial ligament (immediately beneath it is the mandibulo-hyoid ligament). attached by the strong hyo-suspensorial ligament aforesaid to the suspensorium; but another very strong round ligament (answering to the mandibulo-hyoid ligament of Menobranchus*) connects the dorsal end of the hyoidean cornu with the angle of the inaudible (figs. 4 and 6). Thus the hyoidean arch of Ceratodus strikingly resembles that of a Plagiostome on the one hand, and that of an Amphibian on the other. And the small hyomandibular presents a form and connexions which are strikingly similar to those of the suprastapedial cartilage in the Sauropsidaf, which, on a former occasion, I showed to be the summit of the hyoidean arch and the homologue of the mammalian incus. In describing the operculum Dr. Gunther says (I. c. p. 525), " A small movable piece of cartilage is found inside of the articulary groove of the opercle (pl. xxxiv. figs. 2 and 3, k) : it is a rudiment of the praeoperculum." Neither the figures referred to nor the account given enable me to be certain that they apply to the cartilaginous structures I am about * P. Z. S. 1874, ibid. t " O n the representatives of the Malleus and Incus of the Mammalia in other Vertebrata," P. Z. S. 1869. 3* |
