. On the anatomy of vertebrates [electronic resource] . eriosus passing between the trunk of thepulmonary artery and the descending aortadirects the blood which passes through theright ventricle to the lower regions of the body. In this mannerthe upper regions are supplied with the most arterialised part ofthe blood from the left side of the heart and aorta, while thepurely venous blood is propelled from the right ventricle throughthe pulmonary artery and ductus arteriosus into the descendingaorta, and consequently into the lower part of the body, and bythe allantoic arteries to the placenta.
. On the anatomy of vertebrates [electronic resource] . eriosus passing between the trunk of thepulmonary artery and the descending aortadirects the blood which passes through theright ventricle to the lower regions of the body. In this mannerthe upper regions are supplied with the most arterialised part ofthe blood from the left side of the heart and aorta, while thepurely venous blood is propelled from the right ventricle throughthe pulmonary artery and ductus arteriosus into the descendingaorta, and consequently into the lower part of the body, and bythe allantoic arteries to the placenta. The circulation in thefoetal Mammal thus offers a close and interesting analogy to thatin adult Crocodilian Reptiles (vol. i. p. 512). The foramen ovale in the septum of the auricles, the ductusarteriosus passing from the pulmonary artery to the aorta, theductus venosus leading from the allantoic vein to the post-caval,and the allantoic (umbilical) vein and arteries, are the structuralpeculiarities of the mammalian foetal circulating organs. These 588. Foetal circulation seen frombehind. DEVELOPMENT OF GENERATIVE ORGANS. 757 589 passages are all closed up, and the allantoic vessels obliterated atthe navel, after pulmonic respiration is established at birth. § 411. Definition of Male and Female Organs.—In the Mam-malian as in other vertebrate embryos the urogenital parts, beforeshowing distinction of sex, appear in a seemingly more complexor multiplex condition than when per-fected at a later stage. As in fig. 589,we recognise the basis of the true orpersistent kidneys, a, with their duct,e; the antecedent deciduous kidney,or c Wolffian body, b, is here on thewane, with its excretory duct, f; thebeginning of the essential genitalgland is marked c, the adrenals, d}and the tubes called c ducts of Miii-ler, g. In the male Mammalian embryo theduct,/, becomes connected by a whitegranular process with a similar onefrom the gland, c, on the inner side ofthe Wolffian body : by the un
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