. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. -Q-Middle Ear O. 1 Cavity (MB ^~ @"5gS-Thyroid Gland S» y-Giiisii* CP^ <£££)--Gill Septum CUD —^S^-Pharynx no ABC Fig. 318. Diagrams to illustrate the formation of the gill slits. A, early stage showing the outpocketings of the pharynx that form the pharyngeal pouches; b, intermediate stage, showing formation of visceral furrows by inpushings of the ectoderm; c, later stage, in which pouches and furrows have met and formed passage-ways, or gill sli
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. -Q-Middle Ear O. 1 Cavity (MB ^~ @"5gS-Thyroid Gland S» y-Giiisii* CP^ <£££)--Gill Septum CUD —^S^-Pharynx no ABC Fig. 318. Diagrams to illustrate the formation of the gill slits. A, early stage showing the outpocketings of the pharynx that form the pharyngeal pouches; b, intermediate stage, showing formation of visceral furrows by inpushings of the ectoderm; c, later stage, in which pouches and furrows have met and formed passage-ways, or gill slits, from the pharynx to the outside. (After Hyman.) The number of pairs of gill slits varies from fourteen in the cyclostome Bdellostoma polytrema of the Pacific Coast, to only one pair, between the third and fourth gill arches, in certain salamanders. The complicated branchial basketwork of tunicates (Fig. 10) forms a remarkable exception, as well as the sixty or more pairs of gill slits in the elongated pharynx of amphioxus (Fig. 13). Among reptiles, birds, and mammals gill slits do not normally break through, although both pouches and furrows occur in the embryo. When- ever a pharyngeal fistula, as occasionally reported in medical literature, turns up in a human being, the comparative anatomist, if not himself the possessor of the strange anomaly, is delighted with this reminder of past 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 Walter, Herbert Eugene, b. 1867; Sayles, Leonard Perkins, 1902-. New York : Macmillan Co.
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
