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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    below, so that where the skin of the forehead meets that of the top of the face there is a very evident selvedge; whilst the farrow between the raphe is of a paler colour, and is but little differentiated from the gelatinous blastema which separates the membranous cranium from the oral mucous membrane*. The li])S, which are so highly developed afterwards, are at present merely represented by the somewhat inturned edges of the oral opening (w.), the upper being formed by the emarginate lower edge of the fronto-nasal process, and the lower on each side by the bevelled supero-internal angle of the descending facial plate. These facial plates are greatly inturned at the mid line, where they form an obliquely descending raphe which is but imperfectly finished above; the oral opening being continuous with a slit which descends for some distance, the right and left facial walls being imperfectly soldered together above. If a vertical section of the head of an embryo at this stage be made, we have the appearance seen in fig. 4. The thick dermal layer [d.) is seen to follow the inflections of the membranous cranium {m.c), which has already a considerable consistence, and the inflections of which relate to the form of the enclosed cerebral vesicles (fig. 4, CI, C 2, C 3) and the rudimentary pituitary body {py-). The flexure of the brain upon itself (mesocephalic flexure) is shown in this figure, although its straightness is in some degree recovered. Underlying the medulla oblongata (m.ob.) and medulla spinalis (m.s.) there is a thick rod of gela- tinous tissue enclosed in its own sheath; it is blunt-pointed and decurved, and it termi- nates a little distance behind the pituitary vesicle (^y.); this is the notochord (n.c). The tissue forming this rod is very similar to that which everywhere fills up the spaces between the rudimentary organs in the embryo at this stage; it is a very watery kind of ' blastema, interspersed in all directions with delicate membranous bands, a structure well displayed in Muller's figure of a transverse section of the notochord of the Hag-fish [Myxine glutinosa) (see ' Myxinoids,' pi. 9, fig. 1). Already, patches of cartilage have appeared in the outer part of the notochordal tube (sheath); the foremost of these become the postpituitary part of the basis cranii, and the following patches form vertebral arches. In this section the yelk-mass [y.) is seen to persist up to nearly the fore end of the notochord above, but lower down it is deficient further back; this is caused by the bulging behind of the mouth-chasm or stomo-pha- ryngeal cavity. Still further down the substance of the yelk itself has undergone transformation, being applied to the formation of the rudimentary heart and its sac (better seen in next stage, fig. \2,p.c.d.). Beneath the sac the cutaneous system has joined from the right and left side and has produced the thick claspers {cp.). In this section the oral mucous membrane is shown lining the cheek, except ante- * Professor Httxlet, at first sight of this figure, pointed out to me that the middle part of this raphe occupies the place of the azygous nasal opening of the young Lamprey (see Muileb's ' Myxinoids,' pi. 4, figs. 9,io,y).