MORPHOGENESIS OF THE CHOROID PLEXUSES 



515 



Observations on the Marsupial brain are remarkably meagre. 

 I have been able to find but two statements bearing on the sub- 

 ject. Broom ('97) says of a 14.8 mm. embryo of Trichosurus 

 vulpecula: "The choroid folds into the lateral ventricles, is partlj^ 

 formed, and the paraphysis well marked." He has no figures of 

 sections. Selenka ('91) has a simple statement that the paraphy- 

 sis is present in Marsupials, presumably in the opossmn. ''Bis 

 jetzt habe ich die Paraphyse bei embrj'onen von Haifischen, 

 Reptihen, und Beuteltieren beobachtet, zweifle jedoch nicht, 

 dass sie alien Wirbeltieren gemeinsam ist." That is all, but I 

 hope soon to fill this gap. 



Fig. 6 Sagittal section of the forcbraiii of a 15 mm. pig. Copied from John- 

 ston. X 10. Labels mine. 



Fig. 7 Sagittal section of the forebrain of a 11 mm. embryo of Erinaceus 

 europaeus. Copied from Gronbcrg. X 10. LabeLs mine. 



Thanks mainly to Gronberg, the brain of the Insectivora is 

 better known. His work was done with Erinaceus euro])aeus. 

 Ziehen ('06) says of Tupaja, "Die Verhilltnisse gleichen den fiir 

 den Igel beschriebenen in hohem Masse." 



Gronberg's figures 25, 26, and 27 show clearly the velum trans- 

 versum and paraphysal arch although he is loath to call them 

 so. A comparison of figures 6 and 7 will make this plain. He 

 describes also plexuses in the diencephalon and fourth ventricle. 

 Of the lateral telencephahc plexus he writes: 



