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Show 1897.] SKELETON OF PELODYTES PUNCTATUS. 581 half-grown specimens the cartilage bounding the foramen postero-externally is very thin and readily tears away, giving the impression that there exists here an unenclosed sinus such as is shown bv Duges (4. pl. 3. fig. 18) and Parker (12. pl. 25. fig. 9). Both Duges and Parker fail to depict the hyoid arch correctly. The liberated part of the cornu (li, h", fig. 12) resembles very closely in size and shape that of Pelodytes. It is lamellar in front, and ends behind in a hooked process attached to the skull. Parker errs by representing it as rod-like and not separated from the rest of the arch, while Duges fails to notice it at all in pl. 3. fig. 18, but shows it as a rod-like cartilage in pl. 13. fig. 79. Parker (12. p. 261) says that there are two small centres of ossification on each side in the anterior cornua of Pelobates, but this statement I cannot confirm. Cope's figure (2. pl. 76. fig. 5) of the hyoid of Pelobates is not original, but is admitted to be based on the figures of Duges and Parker. The thyrohyals of Pelobates are massive, more especially in old specimens ; and the epiphysis is produced laterally beyond the outer edge of the shaft, giving to the thyrohyal a hooked appearance. There is no ventral ossification such as occurs in Pelodytes. But whether this fact points to a closer alliance between Pelodytes and Alytes than between Pelodytes and Pelobates is, I take it, very doubtful. The bones, in the first place, are not ossifications of the hyobranchial skeleton, but ossifications applied to the surface of it at a late stage of development. If we compare the adult hyoids of Pelobates, Pelodytes, and Alytes we find that the two former resemble one another and differ from the third in the disjointing of the hyoidean cornua, the presence of lateral foramina, and the partial enclosure of the hyoglossal sinus ; while the two latter resemble one another and differ from the first only in the presence of the ventral splint-bone. Also, if we compare the larval hyobranchial skeleton of the three, we find that in Alytes the basihyal extends so far back as to completely separate the hypobranchial plates from one another, whereas in both Pelodytes and Pelobates the two hypobranchial plates are in contact in the median line for some distance behind the basihyal. And in Alytes there is a well-marked median plate of cartilage (the "erste Copula" of Gaupp, 5. p. 412) situated in front of the opaque fibrous band connecting the ceratohyals ; but I find no trace of this in larvae of Pelobates and Pelodytes. And these latter are fundamental differences appearing early, and of an importance which it would be difficult to exaggerate. Development of the Hyobranchial Skeleton of Pelodytes punctatus. The method employed in the investigation of the larval hyobranchial skeleton was of the simplest character. The tadpoles were dissected under spirit, the mandible and hyoid arch disarticulated from the palatoquadrate cartilage, and the branchial skeleton |
