. Text-book of embryology. Embryology. VI HEART OF ELASMOBRANCHS 375 such simple mechanical explanations of developmental phenomena with suspicion. Similarly the atrioventricular cushions become excavated on their ventricular side and form the two atrioventricular valves of the adult. A pair of laterally placed valves also develop. Fig. 179.—Views of the heart of Lepidosiren as seen from the morphologically ventral side. (B and C after J. Robertson, 1913.) A stage 32 ; B, stage 31; C, stage 35. at, atrium ; C, conus arteriosus ; La, left auricle ; , right auricle; V, ventricle. at the openi
. Text-book of embryology. Embryology. VI HEART OF ELASMOBRANCHS 375 such simple mechanical explanations of developmental phenomena with suspicion. Similarly the atrioventricular cushions become excavated on their ventricular side and form the two atrioventricular valves of the adult. A pair of laterally placed valves also develop. Fig. 179.—Views of the heart of Lepidosiren as seen from the morphologically ventral side. (B and C after J. Robertson, 1913.) A stage 32 ; B, stage 31; C, stage 35. at, atrium ; C, conus arteriosus ; La, left auricle ; , right auricle; V, ventricle. at the opening of sinus into atrium but according to extant descrip- tions (Rose, 1890) arise merely as infoldings of the heart wall. DIPNOi. The development of the dipnoan heart has formed the subject of a careful and exhaustive study by Robertson (1913) and her account of the development of the heart in Lepidosiren forms the basis of the following 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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