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

  • William Kitchen Parker
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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    from a like deposit in the basisphenoidal, whilst, common to both, is the permanently separate cortical plate, the parasphenoid. The posterior sphenoidal region, like the anterior, is devoid of any distinct bony centre, and must likewise be surveyed by the primordial land-marks, the nerve-passages. Thus the lines that fall unto it are from the fenestra, in which the optic passage lies in its fore pa]t, to the great foraaien ovale behind. Apparently its landmark has been removed; for the prootic stretches forwards over two-thirds of this space (Plate VIII, fig. 9, al.s., pro.). Below, in the basisphenoidal region, and on the sides, as far as they are unaffected by the prootics, the posterior resembles the anterior sphenoid in all that is essential; above, however, Ave note a difference; for we are now behind the great fontanelle, and the ali- sphenoids end above in a roof-plate, a rudiment of the very perfect cartilaginous roof of the Shark, in which type the fontanelle looks forwards at the fore end of the cranium. In Osseous Fishes the thick upper edge of the alisphenoidal cartilage adjoining the roof is separately ossified, and forms their large postfrontal, the cartilaginous basis of which may, or may not, pass across the primary fontanelle. The postsphenoidal roof-plate is feebly ossified by endostosis, the rudiment of a supra- sphenoidal bone. This upper tract is lozenge-shaped, but the posterior and lateral angles pass into the adjacent regions (Plate IX. fig. 6, su.s.). The outstretched auditory region has acquired one large pair of bony centres, the prootics [pro.); but the roof-crest (pterotic), the supero-posterior ( epiotic), and the infero-posterior ( opisthotic ) regions are but little differentiated in this way; yet the auditory masses are largely ossified behind, having a borrowed source of bone, the exoccipitals [e.o.). Seen from the inside (Plate IX. fig. 5), the periotic masses have a smoothly rounded face, which, projecting inwards, takes from the cranial cavity (Plate X. fig. 9); outside, as in the Lacertians, these masses project so as to increase the breadth of the skull threefold, thus throwing out the mandibular pier, and giving the mouth its enormous gane. In a section made through the '• foramen ovale (Plate X. fig. 8, 5), the ampulla of the anterior canal is exposed with part of its arch; here the parietal {p.) is the only roof to the skull in one place, above the posterior fontanelle {p-fo.); externally the fore edge of the prootic region {pro.) is rather flat and largely unossified; this is the part where the metapterygoid root has coalesced with the front face of the auditory capsule. This narrow outer half of the projecting prootic region is strongly clamped by the supratem- poral part of the squamosal [s.t.). Ossification has affected the rest of the cartilage throughout, and it reaches nearly to the posterior fontanelle above, and to the thick part of the parasphenoid (pa.s.) below. The Gasserian ganglion (5) is seen in situ, and above it a projecting spur of bone. In the next section (fig. 9) the crown of the arch of the anterior canal is cut through (a.sc), and the whole width of the labyrinth-cavity is exposed, near the middle of which