[272] “Anterior brain-mass with Sharks and Skates,” American Journal of Science and Arts, Vol. XII. 1876.
[273] Entwicklungsgeschichte d. Unke.
[274] The engraver has not been very successful in rendering these membranes.
[275] “Embryologie d. Coloboms,” Sitz. d. k. Akad. Wien, Bd. LXXI. 1875.
[276] Quarterly Journal of Microscopic Science, Oct. 1874.
[277] Entwicklungsgeschichte der Unke. Götte was the first to draw attention to this fact. His observations were then shewn to hold true for Elasmobranchii by myself, and subsequently for Birds by Mihalkowics.
[278] Arch. f. micr. Anat. Vol. XI.
[279] W. Müller, “Ueber Entwicklung and Bau d. Hypophysis u. d. Processus infundibuli cerebri,” Jenaische Zeitschrift, Bd. VI.
[280] In the presence of this continuous outgrowth of the brain from which spring the separate nerve stems of the vagus, may perhaps be found a reconciliation of the apparently conflicting statements of Götte and myself with reference to the vagus nerve. Götte regards the vagus as a single nerve, from its originating as an undivided rudiment; but it is clear from my researches that, for Elasmobranchii at least, this method of arguing will not hold good, since it would lead to the conclusion that all the spinal nerves were branches of one single nerve, since they too spring as processes from a continuous outgrowth from the brain!
[281] The conclusion here arrived at with reference to the anterior roots, is opposed to the observations of both Gegenbaur on Hexanchus, Jenaische Zeitschrift, Vol. VI., and of Jackson and Clarke on Echinorhinus, Journal of Anatomy and Physiology, Vol. X. These morphologists identify certain roots springing from the medulla below and behind the main roots of the vagus as true anterior roots of this nerve. The existence of these roots is not open to question, but without asserting that it is impossible for me to have failed to detect such roots had they been present in the embryo, I think I may maintain if these anterior roots are not present in the embryo, their identification as vagus roots must be abandoned; and they must be regarded as belonging to spinal nerves. This point is more fully spoken of at p. [428].