[ 195 ] 
XV. On the Chorda Dorsalis. By Martin Barry, M.D., F.R.SS. L. and E. 
Received January 3, — Read January 7, 1841. 
FOR the discovery of the remarkable structure in the embryo of some of the Ver- 
tebrata denominated the chorda dorsalis, we are indebted to Professor Baer. This 
naturalist considered it “the axis around which the first parts of the foetus form,” 
and “the true virga mensoria for the whole body and all the chief systems-f-.” Rei- 
chert supposes it to be that embryonic structure which serves as a “support and 
stay” for parts developed in two halves^:. 
In the course of my researches on the mammiferous ovum, an object was noticed 
which seems to correspond in appearance to the incipient chorda now referred to. 
I am desirous of drawing attention to this similarity in appearance, but more parti- 
cularly to point out some important differences between my own observations and 
those of others, as to the mode of origin of the objects in question, and their relation 
to surrounding parts. For, should it be found that these objects are the same, my 
belief is that even the most recent views on the incipient growth of the embryo must 
undergo a change. 
Before entering upon the comparison, I must ask the reader to place before him 
my Second Series of Researches in Embryology §, Plates VI. VII. and VIII.; to 
certain of the figures in which I will now briefly refer. 
The object bb, figs. 113 to 116 , is the rudimental embryo of the Rabbit in its 
earliest stage. It is a finely granular, hollow sphere — the nucleus of a cell. Its 
centre, the nucleolus, is brilliantly pellucid. 
The changes which this nucleus undergoes are two-fold. The one consists in the 
formation of a pointed process, as in fig. 121 D, which is sometimes, and perhaps 
generally, curved ; its concave side being directed towards the centre of the ovum. 
In this state the rudimental embryo appears to correspond to what has been sup- 
posed to be the “ primitive trace” in the ovum of the Bird. The other change which 
this nucleus undergoes consists in the origin of fresh substance in its pellucid centre, 
and the expansion of its peripheral portion into cells. Some of these cells occupy 
the area pellucida : others, coalescing, form a little sac (fig. 117 - hh 2 '.), which, ex- 
panding and receiving the yelk into its cavity, assumes the form of a network (fig. 
132 .), and lines the remainder of the ovum (fig. 119 . bb 2 '.). 
f Ueber Entwickelungsgeschichte der Thiere. Beobachtung und Reflexion, 1828. Taf. I. fig. II. III. a. p. 15. 
X Das Entwickelungsleben, 1840, p. 108. — The chorda dorsalis has received other names; viz. Chorda ver- 
tebralis, Riickensaite, Spinalsaite, Wirbelsaite. 
§ Philosophical Transactions, 1839, Part II. p. 307. 
2 D 
MDCCCXLI. 
