Marshall brings evidence to shew that the rectus externus (as might be anticipated from its nerve supply) has no connection with the walls of the premandibular head-cavity, and finds that it arises close to the position originally occupied by the second and third cavities. Marshall has not satisfactorily made out the mode of development of the obliquus superior.
The walls of the cavities, whose history has just been recorded, have definite relations with the cranial nerves, an account of which has already been given at p. [461].
Head-cavities, in the main similar to those of Elasmobranchii, have been found in the embryo of Petromyzon ([fig. 45], hc), the Newt (Osborn and Scott), and various Reptilia (Parker).
Bibliography.
(507) G. M. Humphry. “Muscles in Vertebrate Animals.” Journ. of Anat. and Phys., Vol. VI. 1872.
(508) J. Müller. “Vergleichende Anatomie d. Myxinoiden. Part I. Osteologie u. Myologie.” Akad. Wiss., Berlin, 1834.
(509) A. M. Marshall. “On the head cavities and associated nerves of Elasmobranchs.” Quart. J. of Micr. Science, Vol. XXI. 1881.
(510) A. Schneider. “Anat. u. Entwick. d. Muskelsystems d. Wirbelthiere.” Sitz. d. Oberhessischen Gesellschaft, 1873.
(511) A. Schneider. Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere. Berlin, 1879.
Vide also Götte (No. [296]), Kölliker (No. [298]), Balfour (No. [292]), Huxley, etc.
[242] If recent statements of Metschnikoff are to be trusted, the Echinodermata must be added to these groups. The amœboid cells stated in the first volume of this treatise to form the muscles in this group, on the authority of Selenka, give rise, according to Metschnikoff, only to the cutis, while the same naturalist states the epithelial cells of the vaso-peritoneal vesicles are provided with muscular tails.
[243] O. and R. Hertwig, Die Cœlomtheorie. Jena, 1881.
[244] Ehrlich, “Ueber den peripher. Theil d. Urwirbel.” Archiv f. mikr. Anat., Vol. XI.
[245] The brothers Hertwig have recently maintained that only the inner layer of the muscle-plates is converted into muscles. In the Elasmobranchs it is easy to demonstrate the incorrectness of this view, and in Acipenser (vide fig. 57, mp) the two layers of the muscle-plate retain their original relations after the cells of both of them have become converted into muscles.
[246] Vide Vetter, “Die Kiemen und Kiefermusculatur d. Fische.” Jenaische Zeitschrift, Vol. VII.