The development of the human body; a manual of human embryology . adually deepen until they finally meet and dividethe bulb into two separate vessels, one of which is thepulmonary aorta and the other the systemic aorta. In the early stages of the hearts development the mus-cle bundles which compose the wall of the ventricle arevery loosely arranged, so that the ventricle is a somewhatspongy mass of muscular tissue with a relatively smallcavity. As development proceeds the bundles nearestthe outer surface come closer together and form a compactlayer, those on the inner surface, however, retaini
The development of the human body; a manual of human embryology . adually deepen until they finally meet and dividethe bulb into two separate vessels, one of which is thepulmonary aorta and the other the systemic aorta. In the early stages of the hearts development the mus-cle bundles which compose the wall of the ventricle arevery loosely arranged, so that the ventricle is a somewhatspongy mass of muscular tissue with a relatively smallcavity. As development proceeds the bundles nearestthe outer surface come closer together and form a compactlayer, those on the inner surface, however, retaining theirloose arrangement for a longer time (Fig. 132). The loweredge of the auricular canal becomes prolonged on the leftside into one, and on the right side into two, flaps whichproject downward into the ventricular cavity, and an ad-ditional flap arises on each side from the lower edge of thepartition of the auricular canal, so that three flaps occurin the right auriculo-ventricular opening and two in theleft. To the under surfaces of these flaps the loosely. Fig. 133.—Diagrams ok Sections through the Heart of EmbryoRabbits to show the Mode of Division of the Ventricles andof the Auriculo-ventricular Orifice. Ao, Aorta; , pulmonary artery; B, aortic bulb; Bw2, one of theridges which divide the bulb; Eo and Eu, upper and lower thicken-ings of the margins of the auriculo-ventricular orifice; , theoriginal auriculo-ventricular orifice; and , right andleft auriculo-ventricular orifices; Oi, interventricular communica-tion; , ventricular septum; Vd and Vs, right and left 257 2^8 THE DEVELOPMENT OF THE HUMAN BODY. arranged muscular trabecular of the ventricle are attached,and muscular tissue also occurs in the flaps. This condi-tion is transitory, however; the muscular tissue of theflaps degenerates to form a dense layer of connective tis-sue, and at the same time the muscular trabecular undergoa condensation. Some of them sep
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
