178 GEORGE L. STREETER 



In embryos between 35 and 50 mm. long (figs. 14-15) we can 

 recognize a main channel of the anterior dural plexus, that is, to 

 become the 'transverse sinus.' If we disregard the sigmoid por- 

 tion of it, it forms a fairly straight line with the internal jugular 

 vein. In the interval between the 50 mm. embryo and the 

 adult, the transverse sinus bends backward until it comes to lie 

 at an angle of 90° with the internal jugular. This marked change 

 in position is accomplished in large part by spontaneous migra- 

 tion, by the repeated shifting back of the main blood current 

 into more caudal loops of the plexus with subsequent dwindling 

 of the discarded anterior loops. As the sinus becomes more 

 definitely established the dural plexus becomes relatively smaller 

 (fig. 16) and the final change in position is completed by passive 

 migration, that is, actual traction on the vein wall by its environ- 

 ment. In this change in position of the transverse sinus the 

 superior sagittal sinus and the straight sinus participate and 

 we find in the adult, at the point where they meet, an anasto- 

 mosis, the 'confluens sinuum,' which is usually plexiform in char- 

 acter and represents the last trace of the anterior dural plexus. 



LITERATURE CITED 



Evans, H. ]\I. 1901) On the development of the aortae, cardinal and umbilical 

 veins and other blood vessels of vertebrate embryos from capillaries. 

 Anat. Rec, vol. 3. 



1912 The development of the vascular system. Keibel-Mall Manual 

 of Human Embryology, vol. 2. 



Grosser, O. 1907 Die Elemente des Kopfvenensystem der Wirbeltierc. \'erh. 

 Anat. Gesell., Wiirzburg. Anat. Anz., Bd. 30, Erganz. Hft. 



Grosser, O. und Brezina, E. 1895 Ueber dieEntwicklungder Venen dos Kopfes 

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Mall, F. P. 1905 On the development of the blood vessels of the brain in the 

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Markoa^ski, J. 1911 Ueber die Entwicklung der Sinus durae matris und der 

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Sarin, F. R. 1915 On the origin of the duct of Cuvier and the cardinal veins. 

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 1915 On the fate of the posterior cardinal veins and their relation to 

 the development of the vena cava and azygos in the embryo pig. 

 Contributions to Embryology, Carnegie Institution of Washington, 

 Pub. No. 223. 



Salzer, H. 1895 I'eber die Entwicklung der Kopfvenen des JMeerschweinchens. 

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