. The elements of embryology. Chickens -- Embryos. 172 THE FOURTH DAY. [CHAP. their appearance unite close to the allantois into a single trunk, the umbilical vein, which, running along the splanch- nopleure, falls into the omphalo-mesaraic vein (Fig. 53, U). 23. Meanwhile the heart is undergoing considerable changes. Though the whole organ still exhibits a marked curvature to the right, the ventricular portion becomes directed more distinctly downwards, forming a blunted cone whose apex will eventually become the apex of the adult heart. The concave (or dorsal) walls of the ventricles become
. The elements of embryology. Chickens -- Embryos. 172 THE FOURTH DAY. [CHAP. their appearance unite close to the allantois into a single trunk, the umbilical vein, which, running along the splanch- nopleure, falls into the omphalo-mesaraic vein (Fig. 53, U). 23. Meanwhile the heart is undergoing considerable changes. Though the whole organ still exhibits a marked curvature to the right, the ventricular portion becomes directed more distinctly downwards, forming a blunted cone whose apex will eventually become the apex of the adult heart. The concave (or dorsal) walls of the ventricles become much thicker, as did the convex or ventral walls on the third day. "Well-marked constrictions now separate the ventricles from the bulbus arteriosus on the one hand, and from the auricles on the other. The latter constriction is very distinct, and receives the name of canalis auricularis (Fig. 54, ); the former, sometimes called the /return Halleri, is far less conspicuous. The most important event is perhaps the formation of the ventricular septum. This, which commenced on the third day as a crescentic ridge or fold springing from the convex or ventral side of the rounded ventricular portion of the heart, now grows rapidly across the ventricular cavity towards the concave or dorsal side. It thus forms an in- complete longitudinal partition extending from the canalis auricularis to the commencement of the bulbus arteriosus, and dividing the twisted ventricular tube into two somewhat Fig. Heart of a Chick on the Fourth Day of Incubation viewed from the Ventral Surface. 1. a. left auricular appendage. C. A. canalis auricularis. V. ventricle, b. bulbus 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), 1851-188
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
