. Comparative anatomy. Anatomy, Comparative. POSTERIOR •-"^^ ANTERIOR LOBE- INFUNDIBULUM. POSTERIOR LOBE 0. RANA E. REPTILE F. HOMO Fig. 384.—A series of diagrams showing conditions in six different vertebrates, which are beUeved to represent stages in the evolution of the pituitary gland. The complexity of origin of this gland is correlated with the complexity of its endocrinal functions. The posterior lobe is cross-hatched, intermediate lobe stippled, anterior (hypophysial) lobe piebald, and the pars tuberalis solid black. (Redrawn from Oppel, after Stendell.) the intermediate lobe of t
. Comparative anatomy. Anatomy, Comparative. POSTERIOR •-"^^ ANTERIOR LOBE- INFUNDIBULUM. POSTERIOR LOBE 0. RANA E. REPTILE F. HOMO Fig. 384.—A series of diagrams showing conditions in six different vertebrates, which are beUeved to represent stages in the evolution of the pituitary gland. The complexity of origin of this gland is correlated with the complexity of its endocrinal functions. The posterior lobe is cross-hatched, intermediate lobe stippled, anterior (hypophysial) lobe piebald, and the pars tuberalis solid black. (Redrawn from Oppel, after Stendell.) the intermediate lobe of the pituitary in cyclostomes makes it seem likely that, if it has an endocrinal function in this group, its secretions are poured into the infundibulum. Since the epithelium of the infundibulum and of the hypophysial duct is not thickened but remains single-layered in myxinoids, there is no evidence that these elements in this group have an endocrinal function. Stendell, therefore, seems justified in the conclusion that the intermediate lobe is the first part of the vertebrate pituitary which is differentiated as an endocrinal organ. (Fig. 384) An advance in the evolution of the pituitary is found in Petromyzon. In this animal, as in all higher vertebrates, connexion of the hypophysial duct with the pharynx is lost and the organ ends blindly at its posterior end. From it, however, are proliferated cells into the region between the duct and the infundibulum. The cells which take a position next. 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
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