. The American journal of anatomy . the posterior endocardial cushion a marked band of muscleextends from the wall of the sinus venosus to the interventricularforamen where it spreads over the inner walls of the two ventriclesas shown in fig. 9. This is the sino- or atrio-ventricular bundle(bundle of His). These structures I shall describe in the heart ofembryo No. 353 which is an unusually well preserved specimen,perfect in every respect and of the right stage of developmentfor this purpose. 266 FRANKLIN P. MALL Embryo No. 353 is 11 mm. long with a well formed arm andhand plate. A profile out
. The American journal of anatomy . the posterior endocardial cushion a marked band of muscleextends from the wall of the sinus venosus to the interventricularforamen where it spreads over the inner walls of the two ventriclesas shown in fig. 9. This is the sino- or atrio-ventricular bundle(bundle of His). These structures I shall describe in the heart ofembryo No. 353 which is an unusually well preserved specimen,perfect in every respect and of the right stage of developmentfor this purpose. 266 FRANKLIN P. MALL Embryo No. 353 is 11 mm. long with a well formed arm andhand plate. A profile outline of the embryo may be seen in thefigure by The sections are 10/j, thick in a coronal direc-tion and slightly oblique, that is, they strike the heart heart which has been modeled in wax is mm. wide and long. The apex is cleft as is so often the case in this stage The septum aorto pulmonale is complete and theanterior and posterior cushions are fully united into a single mass. Fig. 11 View from below of a model of the hear! of an embryo 11 (). X 50. The ventricles have been cutoff. The connective tissue septa arecolored yellow. of connective tissue. This mass extends to a point up in the atrialseptum on its dorsal side, to the left valve of the opening intothe sinus venosus. The complete union of the two cushions hasobliterated the foramen ovale I and the foramen ovale II is wellabove the common fibrous process of the united cushions. Aview from below, that is after the apex of the heart is cut off, 13 Evans, Keibel-Mall Handbuch, Bd. 2, fig. 469. 14 Mall, Bifid apex in the human heart. Anat. Rec, vol. G, 1912. DEVELOPMENT OF THE HUMAN HEART 267 shows that the cushions mark the borders of the medial sides ofthe right and left ostia, these being notched to indicate the extentof the anterior and posterior cushions. This is well shown inFig. 11 which was drawn from the model. On the dorsal side,the posterior cus
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
