. The elements of Embryology,. VI.] THE AETERIAL ARCHES. 169 pair of arclies we may consider that there are in all four pairs of arches. When the first and second arches are obliterated, it is only the central portion of each arch on either side which absolutely disappears. The ventral portion connected with the bulbus arteriosus, and the dorsal portion which joins the dorsal aorta, both remain, and are both carried straight forward towards the head. The ventral portions of both first and second arches unite on each side to form a branch, the external carotid (Fig. 52, E, GA), which runs strai

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. The elements of Embryology,. VI.] THE AETERIAL ARCHES. 169 pair of arclies we may consider that there are in all four pairs of arches. When the first and second arches are obliterated, it is only the central portion of each arch on either side which absolutely disappears. The ventral portion connected with the bulbus arteriosus, and the dorsal portion which joins the dorsal aorta, both remain, and are both carried straight forward towards the head. The ventral portions of both first and second arches unite on each side to form a branch, the external carotid (Fig. 52, E, GA), which runs strai Stock Photo
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. The elements of Embryology,. VI.] THE AETERIAL ARCHES. 169 pair of arclies we may consider that there are in all four pairs of arches. When the first and second arches are obliterated, it is only the central portion of each arch on either side which absolutely disappears. The ventral portion connected with the bulbus arteriosus, and the dorsal portion which joins the dorsal aorta, both remain, and are both carried straight forward towards the head. The ventral portions of both first and second arches unite on each side to form a branch, the external carotid (Fig. 52, E, GA), which runs strai
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. The elements of Embryology,. VI.] THE AETERIAL ARCHES. 169 pair of arclies we may consider that there are in all four pairs of arches. When the first and second arches are obliterated, it is only the central portion of each arch on either side which absolutely disappears. The ventral portion connected with the bulbus arteriosus, and the dorsal portion which joins the dorsal aorta, both remain, and are both carried straight forward towards the head. The ventral portions of both first and second arches unite on each side to form a branch, the external carotid (Fig. 52, E, GA), which runs straight up from the bulbus arteriosus to the bead. J.CA. State of Arterial Circulation on the Fifth or Sixth Day. E. CA. external carotid. /. CA. internal carotid. AO. dorsal aorta, wf. A. arteries to the Wolffian bodies. Ver. A. arteries given oiF between each of the vertebrae. Of. A. omphalo-mesaraic artery. UA. umbilical artery. I A. iliac artery. In the same way the dorsal portions form a branch, the internal carotid, which takes its origin from the dorsal or far end of the third arch. 22. In the venous system important changes also occur. As the liver in the course of its formation wraps round the common trunk of the omphalo-mesaraic veins, or meatus venosus, it may be said to divide that vessel into two parts :. 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 work.. Foster, Michael. London : Macmillan