490 



PRO!'. G. ELLIOT SMITH ON THE MOKPHOLOGY OF THE 



c.p 



c.d. I y 



f.M. 

 Semi-schematic representation of the roof of the forehrain of Echidna viewed in sagittal section. 



The relations of that portion of the roof which intervenes 

 between the commissura superior and the line x-y (iig. 23) conform 

 to the usual plan, being attached on each side to the taenia thalami. 

 The accompanying crude scheme indicates this usxxal mode of 

 attachment (fig. 2i). 



Behind the cominlssura dorsalis a large complex fold of the 

 epithelial roof extends on each side through the foramen of Monro 

 to form the choroid plexus of the lateral ventricle. If a coronal 

 section 1)e made through the situation of the foramen of Monro, 

 the exact arrangement of this fold will lie intelligible (fig. 25) *. 



Fis. 24. 



dors. 



v.jn. 



vM 



Coronal section of the brain of a foetal Eclddnu, x '20, passing through the foramen of ilouro. 



In the mesial j)lane it is thrown into a complicated series of folds, which form the walls 

 of the paraphysis, and on each side the epithelial fold, forming the roof of the foramen 

 of Monro, projects into the lateral ventricle, and is complexly plicated to form the 



* 1 have represented a section of a foetal brain, because it is ■well-nigh impossible to keep these delicate epithelial 

 folds intact in the adult. 



