. Human embryology and morphology. Embryology, Human; Morphology. DEVELOPMENT OF THE CIECULATORY SYSTEM. 235 (2) The tubular heart shows demarcations into four parts (Fig. 194): (a) Sinus venosus; (b) Primitive auricle; (c) Primi- tive ventricle ; (d) Conus or bulbus arteriosus. In this condition (third week) the human heart is exactly like that of a fish, viz., a tubular four-chambered heart which pumps blood into the branchial or aortic arches. (3) The disappearance of the mesocardium allows the heart to become twisted and bent. Two chief bends are formed which materially help to give the he
. Human embryology and morphology. Embryology, Human; Morphology. DEVELOPMENT OF THE CIECULATORY SYSTEM. 235 (2) The tubular heart shows demarcations into four parts (Fig. 194): (a) Sinus venosus; (b) Primitive auricle; (c) Primi- tive ventricle ; (d) Conus or bulbus arteriosus. In this condition (third week) the human heart is exactly like that of a fish, viz., a tubular four-chambered heart which pumps blood into the branchial or aortic arches. (3) The disappearance of the mesocardium allows the heart to become twisted and bent. Two chief bends are formed which materially help to give the heart its adult shape (Fig. 195): 'st arch 2nd arch ventral aorta conus arteriosus prim, ventricle. prim, auricle sinus venosus vit. vein^-^ "^vit. vein Fig. 194.—The Primitive Divisions of the Heart. (a) The Ventricular Bend.—The ventricular part of the tube is bent into a V-shaped piece, the apex of the V-shaped loop being- turned towards the right. (b) The Auriculo-ventricular Bend.—The ventricular part is bent in front of the auricular so that the auricle becomes dorsal to the ventricle (Fig. 195). The Sinus Venosus.—The sinus venosus, the first chamber of the foetal heart, is formed by the union of the vitelline veins; the umbilical veins and ducts of Cuvier come subse- quently to open in it (Fig. 185). The sinus is imbedded in the persistent posterior part of the mesocardium (Fig. 202).. 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 Keith, Arthur, Sir, 1866-1955. London : E. Arnold
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