The development of the human body; a manual of human embryology . Fig. 142.—The Development of the Vertebral Artery in a RabbitEmbryo op Twelve Days. to , Branchial arch vessels; Ap, pulmonary artery; and , cephalic and cervical portions of the vertebralartery; , subclavian; and , internal and external carotid;, spinal ganglion.—(Hochsteller.) anterior lateral branch, so as to form a longitudinal chainof anastomoses along each side of the neck. In the earlieststage at present known the chain starts from the lateral 27O THE DEVELOPMENT OF THE HUMAN
The development of the human body; a manual of human embryology . Fig. 142.—The Development of the Vertebral Artery in a RabbitEmbryo op Twelve Days. to , Branchial arch vessels; Ap, pulmonary artery; and , cephalic and cervical portions of the vertebralartery; , subclavian; and , internal and external carotid;, spinal ganglion.—(Hochsteller.) anterior lateral branch, so as to form a longitudinal chainof anastomoses along each side of the neck. In the earlieststage at present known the chain starts from the lateral 27O THE DEVELOPMENT OF THE HUMAN BODY. branch corresponding to the first cervical (suboccipital)segment and extends forward into the skull through theforamen magnum, terminating by anastomosing with theinternal carotid. To this original chain other links areadded from each of the succeeding cervical lateralbranches as far back as the seventh (Figs. 142 and 140).But in the mean time the recession of the heart toward the. Fig. 143.—Embryo of 13 mm. showing the Mode of Developmentop the Internal Mammary and Deep Epigastric Arteries.—(Mall.) thorax has begun, with the result that the common carotidstems are elongated and the aortic arches are apparently-shortened so that the subclavian arises on the left sidealmost opposite the point where the aorta was joined bythe sixth branchial vessel. As this apparent shorteningproceeds, the various lateral branches which give rise tothe chain of anastomoses, with the exception of the THE ARTERIES. 27 I seventh, disappear in their proximal portions and thechain becomes an independent stem, the vertebral artery,arising from the seventh lateral branch, which is the sub-clavian. The recession of the heart is continued until it lies belowthe level of the upper intercostal arteries and the uppertwo of these, together with the last cervical branch oneach side, lose their connection with the dorsal aorta, and,sending off anteriorly and posteriorly anastomosing twigs,de
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
