. Text-book of embryology. Embryology. 398 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. a duct of Botallus forming a connexion between the pulmonary artery and the aortic root m IV V VI A just as is shown in Fig. lU 186, B () for the Uro- dele amphibian. In other cases it may persist as a ligamentous vestige, as is the case on the left side in Tropidonotus. As a rule the portion of aortic root lying between arches III and IV disap- pears during development but in most Lizards (not in Chameleons and Moni- tors) it persists in the adult, so that in a dis- section arches III and IV appear to r
. Text-book of embryology. Embryology. 398 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. a duct of Botallus forming a connexion between the pulmonary artery and the aortic root m IV V VI A just as is shown in Fig. lU 186, B () for the Uro- dele amphibian. In other cases it may persist as a ligamentous vestige, as is the case on the left side in Tropidonotus. As a rule the portion of aortic root lying between arches III and IV disap- pears during development but in most Lizards (not in Chameleons and Moni- tors) it persists in the adult, so that in a dis- section arches III and IV appear to run into one another peripherally. In Monitors (Vara- nidae), in correlation with the elongation of the neck, arches III and IV become widely separated from one another and the interven- ing portion of ventral aorta shows a corresponding lengthening both in its paired (common carotid) and its unpaired (primary carotid) portions. In Birds (Fig. 187a, D) arch IV completely dis- appears on the left side and with it the portion of the left aortic root lying posterior to it. Conse- quently in the adult Bird there is only a single sys- temic aortic arch and it passes down the right side of the body. Elasmobeanchii.— In the Ichthyopsida, as we should expect, the depart- ures from the primitive scheme are lesspronounced: Fig. 188.—Illustrating the modification of aortic arches III-VI during ontogeny in Scyllium, according to Dohrn. A, Dorsal aorta; a/, afferent branchial; an, anastomotic vessel; ef, efferent branchial; v. A, ventral aorta; , visceral clefts ; III, IV, V, VI, aortic 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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