. Chordate anatomy. Chordata; Anatomy, Comparative. THE DIGESTIVE SYSTEM 219 pre-oral gut in vertebrate embryos suggests that the alimentary canal formerly extended anterior to the present mouth; and, finally, that in the myxinoids and the embryonic sturgeon the hypophysis actually opens into the pharynx and, like the mouth of urochordate larvae, has a dorsal external opening. (Fig. 208) Whatever view is held of the origin of vertebrates, we must believe that there have been at least two mouths in the course of vertebrate phylogene- sis. The reason for this conclusion is that the original coel
. Chordate anatomy. Chordata; Anatomy, Comparative. THE DIGESTIVE SYSTEM 219 pre-oral gut in vertebrate embryos suggests that the alimentary canal formerly extended anterior to the present mouth; and, finally, that in the myxinoids and the embryonic sturgeon the hypophysis actually opens into the pharynx and, like the mouth of urochordate larvae, has a dorsal external opening. (Fig. 208) Whatever view is held of the origin of vertebrates, we must believe that there have been at least two mouths in the course of vertebrate phylogene- sis. The reason for this conclusion is that the original coelenterate mouth becomes the mouth in no vertebrate, while only in cyclostomes, dipnoans, and possibly some amphibians does it become the anus. The coelenterate HYPOPHYSIAL DUCT. PHARYNX/ ,1 ST GILL APERTURE HYPOBRANCHIAL MUSCLE HYPOPHYSIAL ^ DUCT ^=-^ (RESPIRATORY TUBE. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son & Co.
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