OCR Text |
Show 1876.] PROF. T. H. HUXLEY ON CERATODUS FORSTERI. '67 ventral line, between the ends of the ventral pieces, lie two cartilages- an anterior elongated and spindle-shaped (M.B1), which is connected by a strong ligament with the median piece of the hyoid arch, and a posterior rounded nodule (M.B2) at some distance from the foregoing. The fifth arch consists of a single piece of cartilage curved forwards and united with the principal branchial of the fourth arch, both above and below ; in front of it, close to the ventral end of the fifth arch, was a small nodule of cartilage, which is probably a rudimentary sixth arch (6). Fig. 7. Ceratodus forsteri. Dorsal aspect of the skull, a, the anterior end of the chondrocranium; b, the antorbital process of the chondrocranium; c, its suprabranchial expansion; d, lateral elevations of the occiput; and e, median ridge, with the surface for the attachment of the anterior fin-ray; /, articular surface for the second fin-ray; A, anterior median bone; B, posterior median bone; C, inner lateral bone; C, distinct ossification on the posterior extremity of this bone; B, outer lateral bone (squamosal); E, a separate ossification on the left side; Op, operculum; Or, orbit; Sb.o, suborbital bones; 2, the posterior upper labial cartilage. As Dr. Gunther has pointed out, the osseous shield which covers the dorsal aspect of the skull consists of two median bones (fig. 7, A, B), one anterior and one posterior, which he terms "ethmoid" and "scleroparietal," and of two pairs of lateral bones, the "frontals" internally (fig. 7, C) and the " tympanic laminae " externally (fig. 7, D). In m y specimens the anterior half of the anterior median bone (A) has a different shape from that given in Dr. Giinther's plate xxxiv. fig. 1, and its margins are very well defined. Moreover, in |