On the structure and development of the skull in the Batrachia. Part II / by William Kitchen Parker.

  • Parker, William Kitchen, 1823-1890.
Date:
[1876]
Catalogue details

Licence: Public Domain Mark

Credit: On the structure and development of the skull in the Batrachia. Part II / by William Kitchen Parker. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    who had made out much of the 'adult skull, carefully observing the nervous trunks, and who also examined the skull and cranial nerves of one or two small larvae. Help from such a quarter was of the utmost importance to me, and we both felt that we had to deal with a most difficult and enigmatical type. The figures of early larvae given in my former paper (“ Frog’s Skull,” pi. iii.) do not show the whole of the creature; yet, as far as they go, they show how different our typical Batrachian larva is from that of the Cape Toad. Equally important, both to Zoology and to Morphology, are the most patent differences: these are as follows, namely:— a. The mouth is not inferior in position, suctorial, and small, but is very wide, like that of the “Siluroids” and Lophius; has an underhung lower jaw, an immensely long- tentacle from each upper lip, and possesses no trace of the primordial horny jaws of the ordinary kind. h. In conformity with these characters the head is extremely flat or depressed, instead of being high and thick. c. There are no “ claspers ” beneath the chin (“ Frog’s Skull,” pi. iii. figs. 10 & 11, cp.). d. The branchial orifice is not confined to the left side, but exists also on the right (Huxley). e. The tail, like the skull, is remarkably chimceroid; it terminates in a long, thin, pointed lash, and the whole caudal region is narrow and elongated as compared with that of our ordinary Batrachian larvae. f. The fore limbs are not hidden beneath the opercular fold. To the anatomical reader I scarcely need explain the importance of these characters, especially that of the absence of the horny jaws; as it is at once seen that here this aglossal form agrees with most of the “ Urodela,” and that it helps to lessen the reentering angle between the diverging lines of those two amphibian groups, the Batrachia and the Urodela. At present, in this the youngest larvae, whose whole length is an inch and a quarter (three fifths of which is caudal), the fore and hind limbs are nearly equal in size (figs. 1 & 3); afterwards they show a different rate of growth; this is explained when we look at the disproportionate size of the hind limbs in the adult (Gray, op. cit. p. 461). In seeking to decipher a chondrocranium like that of this stage of the Dactylethra’s Tadpole, the earliest condition of such a skull, that is, as soon as this cartilage appears, must be held in mind. Now we have seen that such a simple framework can be made out, and that it differs but little in the Batrachia and Urodela (Plate 55. figs. 1, 2; and Huxley, “ On Menohranchus,,, plate xxxi. figs. 1, 2). The points in which the two types differ are the early appearance of the bony plates in the Urodela; the absence in them, at this time at least, of a pterygo-palatine conjugation; the non-coalescence, at this early stage, of the pedicle of the mandible with the elbow of the trabeculae ; and the membranous condition of the fore part of the trabeculae, namely, the intemasal region