Licence: Public Domain Mark
Credit: On the chorda dorsalis / by Martin Barry. 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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![shows a “growing from” the sheath, as it is called, of the chorda,—“at the expense of its inclosed nucleus,”—or as the chorda is “found to decline,” even in these the last stages of this structure. But if we examine it at periods anterior to these, I think we shall find still stronger grounds for believing, that the chorda dorsalis of authors, in an early state, corresponds to the pin-like object in the mammiferous ovum which I have been comparing with it. Reichert seems to have been led to form the opinion above-mentioned, that the chorda serves as a “support and stay” for parts developed in two halves, by the fol- lowing observations ; namely, that the chorda becomes visible as a single structure at the same time as the foundations, in two halves, of the central nervous system ; and that the central nervous system on the one hand, and his membrana intermedia on the other, are so intimately connected by means of the chorda, that it is not possible to separate them. He even states, that the chorda passes into the foundation of the embryo. Farther, Reichert says, “There are developed on the chorda dorsalis the original halves of the central nervous system, with the higher organs of sense, separating as these do from the central nervous system'f'.” He states that, with a union of the two halves of the central nervous system—such union taking place first at the fore- end—there is observed a decline in the corresponding part of the chorda. On the subject of the membrana intermedia, the same author remarks, that it is found be- tween the central nervous system and the mucous membrane; and that it (the mem- brana intermedia) “is the common original foundation of all structures, systems, and organs, which are the means of operation for the two central organs of animal life. Hence from it [the membrana intermedia] there are developed the vertebral system, the dermal system, the circulating system, and finally, all the structures which support the mucous membrane, and which,” says he, “ I comprehend under the name of system of the intestinal membrane;};.” It would thus seem, according to Reichert, that there is little in the embryo which is not developed out of either the central nervous system, or the membrana inter- media. But these are the very parts which the same observer found so intimately connected by means of the chorda, that it was not possible to separate them. And it appears to be these same parts called by Reichert “ the foundation of the embryo,” into which he says “ the chorda passes.” Taking then the observations of Baer, Rathke, and Reichert, in connection with my own, I venture to believe, that it is not enough to say, with Baer, that the chorda dorsalis is the axis around which the first parts of the foetus form; nor, with Rei- f L. c., pp. 58, 59. + L. c., p. 107. “Da die femeren Doppel-gebilde,” says Reichekt, “sammtlich von der membrana inter- media ausgehen, so tritt die Wirbelsaite [chorda dorsalis] in die innigste Beziehung zu der Letzteren.”](https://iiif.wellcomecollection.org/image/b22296803_0008.jp2/full/800%2C/0/default.jpg)
