On the structure and development of the skull of the common frog (Rana temporaria, L.) / by William Kitchen Parker.

  • Parker, William Kitchen, 1823-1890.
Date:
[1871]
Catalogue details

Licence: Public Domain Mark

Credit: On the structure and development of the skull of the common frog (Rana temporaria, L.) / by William Kitchen Parker. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    but by metamorphosis into fibrous tissue do yield some of the matrix in which the parosteal prsemaxillse are formed. The first possible slice that can be taken from the fore part of the Tadpole's face (Plate V. fig. 6, u.d.g.) when seen from its posterior or cut surface, shows that the upper horny dentigerous (Chimceroicl) plate is formed be- tween the upper labials and the outer skin. The lower labials (Plate V. figs. 1-5, and Plate VI. figs. 1-3, U.) are drumstick- shaped rods of cartilage, having the lower end the stoutest; the upper end is attached to the anterior face of Meckel's cartilage near the symphysis. Their direction is almost vertical; they nearly meet below; and the lower dentigerous plate (l.d.g) is rather below than behind these rods (Plate VI. fig. 2, 11, l.d.g). The creases of the lips (Plate VI. figs. 1 & 2, l.p.) are covered with small hooked teeth, in addition to the two principal plates. The angle at which the lower labial is attached to the Meckelian rod {m.k.) is suggestive of a very difierent origin for the two cartilages thus unconformably related. It would appear, from the imbedded condition of the Meckelian rods at this stage, that the lower labials are really the efiective lower jaws of the Tadpole; we have in the Ver- tebrata a procession of three orders of mandibles—namely, the lower labials, the Mecke- lian rods, and the ' dentary' parostoses. The trabecular horns (Plate V. fig. 1, tr.c.)^ which sprang from the outer angle of the commissure, have grown into long, gently diverging bands, which are strongly de- curved where they articulate with the upper labials [u.l.]. These thickish bands are rounded at the edge; their breadth is best seen in the hori- zontal views (Plate V. figs. 3-6). They are at present distinct up to the commissure [eth., t.c.) (the rudimentary ethmoid), which now rises in front of the cranium as a low, rounded, transverse Avail. This wall lies immicdiately above the pterygo-palatine bar (fig. 1, 'j)g.); in this view the rest of the trabecula is largely hidden by the eyeball (<?); that part, however, which has coalesced with the next bar is seen behind. The sectional view (fig. 2) best shows the manner in which the ethmoidal wall has been formed, and how the rhinencephalon (C 1) lies behind its concave face. The subcranial part of the trabeculae has nearly the same thickness as the free horns (see edge view of right bar in Plate V. fig. 2); nor is their breadth altered in any degree (figs, 3 & 4); and in this stage it seems difficult to suppose that they do not with these horns form one continuous bar with the investing mass; nothing but a study of their development could prevent such a view being taken of them. The trabeculse help to form the skull in the same manner as the investing mass; both lie beneath the membranous cranium, and both, by upward continuous growth of cartilaginous laminas, enclose the fibrous sac. In the postpituitary region this is a very exact repetition of the manner in which the neural laminae of the vertebral moieties enclose the tlieca vertebralis; and the notochordal pith is enveloped by cartilage in the same way as in a vertebra. MDCCCLXXI. T