OCR Text |
Show 1894.] HYOID ARCH OF CERATODUS. 633 The hypohyal (figs. 1 and 2, hh) is paired, cartilaginous, and isodiametric, and the two hypohyals are applied to one another in the middle line by flat, vertical, articular surfaces which open out in front to receive the wedge-shaped posterior extremity of the basihyal. Fig. 2. bh hh Ceratodus forsteri.-Hinder portion of the skull with the hyoid arch ; left side. The opercular and interopercular bones are removed, bh, basihyal; hh, hypohyal; ch, ceratohyal; hm, hyomandibular ; hsp, hyosuspensorial ligament; sq, squamosal or pre-opercular; qu, quadrate condyle; oc, eye-capsule. The basihyal (figs. 1 and 2, bh) is a median unpaired cartilage which tapers off to a blunt point in front. In Giinther's (4) original description of Ceratodus the hypohyals are called basihyal, while the figures, and the words (p. 526) " the basihyal is short, thick, cartilaginous, interposed between the ends of the ceratohyals and the acutely conical glossohyal," fail to indicate the paired nature of these cartilages. Seeing, however, that they are paired and that the term basihyal is always applied to a median copula, and seeing that they are, from their relation to the ceratohyal, evidently homologous with the hypohyals of the |