. Carnegie Institution of Washington publication. DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 115 arteries gives rise to a plexus which is ventral to the posterior cardinal vein, but which connects with it. The Wolffian duct intervenes between this plexus and the posterior cardinal vein. In figure 1 of plate 5, and figure 1 of plate 1, are given very characteristic views of these lateral arteries to the pronephros, and in figure 5, plate 3, is shown a ventral view of the arteries of the pronephros from a specimen of the same litter as that of plate 5, figure 1, but a little farther developed. Figu
. Carnegie Institution of Washington publication. DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 115 arteries gives rise to a plexus which is ventral to the posterior cardinal vein, but which connects with it. The Wolffian duct intervenes between this plexus and the posterior cardinal vein. In figure 1 of plate 5, and figure 1 of plate 1, are given very characteristic views of these lateral arteries to the pronephros, and in figure 5, plate 3, is shown a ventral view of the arteries of the pronephros from a specimen of the same litter as that of plate 5, figure 1, but a little farther developed. Figures 1 of plate 5 and 1 of plate 1 show a series of tiny lateral arteries beginning just below the ninth dorsal segmental artery. These arteries are about four to a somite, corresponding to the number of the nephritic tubules, and are connected by a tiny longi- tudinal artery close to the aorta and by a tiny lateral vein. In text- figure 4 is shown a section from a specimen of the litter of plate 1, figure 1, passing through about the .^^•^^^^^^_ ££K?&^!&\ fourteenth somite, showing an injec- tion of one of these lateral arteries. Its exact position with reference to the developing tubule is, I think, important. This is most clearly recognized from the diagram given by Felix of the development of the nephritic tubules (fig. 561, Keibel and Mall, Manual of Human Em- bryology, page 804). The stage cor- responds with diagram d of Felix's figure, and the artery passes directly across the curved bowl which makes the neck of the future Malpighian corpuscle. This is the earliest stage of the vessels of the nephritic tubules I have injected. As is seen in text-figure 4, the lateral vein, the vena cardinalis lateralis, lies ventral to the Wolffian duct, while the vena cardinalis posterior lies directly dorsal to the duct. The posterior cardinal vein is plainly shown in text-figure 4, but was not injected so far caudal- ward in any of my series. Text-figure 5 gives a very inte
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