OCR Text |
Show 1897.] SKELETON OF PELODYTES PUNCTATUS. 591 usually to be found in regions where such absorption is proceeding, but at the same time the general proportions of the basal plate suggest that it is quite possible that this process does take place. The newly added cartilages (pa., fig. 7) at the inner edges of the anterior ends of the hyoid arch are now directed towards one another, having lost their forward slope; and the line of junction between them and the original hyoidean cartilage is still apparent. The greater part of the ceratohyal has become diminished in thickness so as now to have the form of a bent rod of approximately uniform diameter. About the level of the bottom of the hyoglossal sinus the ceratohyals exhibit the first indications of the absorption which later results in the dismemberment of the arch (h, fig. 7). A new notch or sinus (/., fig. 7) has developed at the side of the basal plate, mainly by the absorption of the cartilage in that position. But the sinus is rendered more complete by the simultaneous Outgrowth of a process ( pal., fig. 7) which is to be identified with the antero-lateral or alary process of the hyoid apparatus of the Erog (pal., fig. 11). In consequence also of "this outgrowth of cartilage the middle of the three lateral sinuses, that between the antero-lateral and the postero-lateral processes, is beginning to make its appearance. STAGE 8. Distance from snout to cloaca, 17 mm. Length of hind limb, extended, 25 mm. Length of fore limb, extended, 9 mm. (Plate X X X V . fig. 8.)1 The basal plate or body of the hyoid is n o w small in proportion to the size of the outstanding processes. The postero-lateral process (ppl., fig. 8) is longer than before but not appreciably thicker; the sinus of which it forms the posterior boundary is much deeper than in the last stage. The antero-lateral process (pal.) has enlarged and is already somewhat dilated at its extremity. The first of the three lateral sinuses (fi.) has n o w the form of an ellipse, incomplete externally. One of the most noteworthy features about this stage is the separation of the distal part of the hyoidean cornu. The absorption of cartilage leading to such separation occurs antero-externally to the last-mentioned sinus, and the pointed form of the cartilage in this region shows that the dismemberment has only recently occurred. N o w that the outlines of the constituents of the body of the hyoid have completely disappeared, it is very difficult to define the limits of that part of the ceratohyal which is not detached, but I should judge that a line drawn through the bottom of tbe hyoglossal sinus and through the middle of the lateral sinus marked fi. would indicate the proximal limit of the anterior or hyoidean cornu. The recently added anterior processes (pa.) are nov indistinguishably fused with the cartilage of the ceratohyal and are directed backwardly as well as inwardly. It is curious to note how these processes first 1 The above specimen, the hyoid of which is shown in fig. 8, happens to be slightly smaller than that representing Stage 7, but otherwise the two are perfectly indistinguishable externally. 39* |