Abstract
This paper, which is based on investigation of Acipenser, Polypterus, Amia and Lepidosteus, is written partly to supplement, partly to amend, some scanty notes which I published on the subject in 1911. Observations on Plagiostomi, Teleostei and Amphibia, which have a bearing on the problems discussed, are incorporated in the paper. The Ocular Muscles . The study of the development of the ocular muscles was begun by Balfour (1878), who stated that it is probable that the walls of the 1st head-cavity of Selachian embryos develop into the external ocular muscles. Marshall (1881) stated that the Recti superior, internus and inferior, and probably the Obliquus inferior, are derived from the walls of the 1st head-cavity. He did not find the origins of the Obliquus superior and Rectus externus, but in regard to the latter said that it is probable that it is developed from the walls of the dorsal ends of the 2nd and 3rd head-cavities.

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