The development of the human body; a manual of human embryology . tricle, and as the enlargement ofthe pouches continues their openings into the canal en-large, until finally thepouches become contin-uous with one another,forming a single largesac, and the auricularcanal becomes reducedto a short tube which isslightly invaginated intothe ventricle (Fig. 130). In the mean time thesinus venosus, which wasoriginally an oval sacand opened into the au-ricular canal, has elon-gated transversely untilit has assumed the form of a crescent whose convexity isin contact with the walls of the auricles, an
The development of the human body; a manual of human embryology . tricle, and as the enlargement ofthe pouches continues their openings into the canal en-large, until finally thepouches become contin-uous with one another,forming a single largesac, and the auricularcanal becomes reducedto a short tube which isslightly invaginated intothe ventricle (Fig. 130). In the mean time thesinus venosus, which wasoriginally an oval sacand opened into the au-ricular canal, has elon-gated transversely untilit has assumed the form of a crescent whose convexity isin contact with the walls of the auricles, and its openinginto the heart has verged toward the right, until it issituated entirely within the area of the right auricle. Asthe enlargement of the auricles continues, the right hornand median portion of the crescent are gradually takenup into their walls, so that the various veins which origi-nally opened into the sinus now open directly into theright auricle by a single opening, guarded by a projectingfold which is continued upon the roof of the auricle as a. Fig. 129.—Heart of Embryo of 5mm., Seen from in Front andSlightly from Above.—(His.) ?5- THE DEVELOPMENT OF THE HUMAN BODY. muscular ridge known as the septum spurium (Fig. 130,sp). The left horn of the crescent is not taken up intothe auricular wall, but remains upon its posterior surfaceas an elongated sac forming the coronary sinus. The division of the now practically single auricular cav-ity into the permanent right and left auricles begins withthe formation of a falciform ridge running dorso-ventrally
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
