. The elements of Embryology,. 216 THE SIXTH DAT. [chap. Fig. 66. j:.ca f^ZCa. xj:.n \ JlPA // e>^ i DiAGKAM OF THE CONDITION OF THE AkCHES OF THE AOETA TOWAEDS THE Close of Incubation. 1,2, 3,4, 5. The several aortic arches. External carotid. Internal carotid. C.( Common carotid. 'Vertebral'artery. Eight subcla\'ian. Left subclavian. Left innominate. AO. Aorta. Pulmonary arteries. Right arterial root, or division of bulbus arteriosus, or pulmonary artery ; the left root or division, con- stituting the aorta, is seen by its si
. The elements of Embryology,. 216 THE SIXTH DAT. [chap. Fig. 66. j:.ca f^ZCa. xj:.n \ JlPA // e>^ i DiAGKAM OF THE CONDITION OF THE AkCHES OF THE AOETA TOWAEDS THE Close of Incubation. 1,2, 3,4, 5. The several aortic arches. External carotid. Internal carotid. C.( Common carotid. 'Vertebral'artery. Eight subcla\'ian. Left subclavian. Left innominate. AO. Aorta. Pulmonary arteries. Right arterial root, or division of bulbus arteriosus, or pulmonary artery ; the left root or division, con- stituting the aorta, is seen by its side. Communication on the right side between the fourth and fifth arches. Communicating trunk between the filth arch and the dorsal aorta. At the same time the connection between the third and fourth pairs of arches on each side grows weaker; and finally the passage between them becomes obliterated, so that less and less of the blood which flows along the third pair of arches is able to pass backwards to the hind end of the body. On the eighth day (according to Rathke, loc. cit.) from the common root of the external and internal carotids of each side, a branch (Fig. 66, ) is given off which passes forwards along the neck, and ends in front by becoming connected with a branch from the external carotid. This vessel is of much larger calibre at its two extremities, than in the central part of its course. In the adult it terminates anteriorly by anastomosing with the occipital artery (a branch from the external carotid). The smaller calibre of the central part is still more marked in the adult, than at the stage we are. 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, Michael. London : Macmillan
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