. The elements of embryology. Embryology; Embryology. IX.] THE ARTERIAL ARCHES. 291 Fig. W\ State of Arterial Circulation on the Fifth or Sixth Day. external carotid. internal carotid. dorsal aorta. vitelline artery. allantoic artery. We have already seen (Chap. vii. p. 225) that of the three aortic arches which make their appearance on the third day, the first two disappear: the first on the fourth, the second on the fifth day; but that their dis- appearance is accompanied by the formation behind them of two new aortic arches, the fourth and the fifth. Thus t
. The elements of embryology. Embryology; Embryology. IX.] THE ARTERIAL ARCHES. 291 Fig. W\ State of Arterial Circulation on the Fifth or Sixth Day. external carotid. internal carotid. dorsal aorta. vitelline artery. allantoic artery. We have already seen (Chap. vii. p. 225) that of the three aortic arches which make their appearance on the third day, the first two disappear: the first on the fourth, the second on the fifth day; but that their dis- appearance is accompanied by the formation behind them of two new aortic arches, the fourth and the fifth. Thus there are generally three, never more than three, pairs of aortic arches present and functional at one time. This statement needs some limitation ; for according to Yon Baer there are four arches present both on the fourth and fifth days. In the case of the fourth day a shght remnant of the first pair of arches still persists when the fourth pair is already formed; and on the fifth day the second pair has not entirely disappeared when the fifth pair is formed. In both of these cases however the first pair of arches of the four is only present for a very short time, and then is so diminished in size as to be of no importance. J 9—2. 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 Foster, M. (Michael), Sir, 1836-1907; Balfour, Francis M. (Francis Maitland), 1851-1882; Sedgwick, Adam, 1854-1913; Heape, Walter, 1855-1929. London : Macmillan and Co.
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Keywords: ., bookcentury1800, bookdecade1, booksubjectembryology, bookyear1883
