DEVELOPMENT OF THE CHOROID PLEXUS 83 



morphological feature in the roof of the prosencephalon of 

 vertebrates. 



The tela chorioidea diencephali has been the subject of an 

 extensive anatomical, embryological and comparative study by 

 Lachi ('88). It presents few features of interest. A number 

 of names have been applied to parts of it (Zirbelpolster, dorsal- 

 sac, post-paraphysis, post-velar arch, etc.), but it has generally 

 been recognized as extending from the superior commissure to 

 the velum transversum. 



With regard to the roof of the telencephalon, however, there 

 is no such unanimity of opinion. I shall not attempt to review 

 the observations on the lower vertebrates. Johnston ('13) 

 reviews the literature fully and on the basis of this and his own 

 extensive observations presents the following scheme as covering 

 all the forms of the roof of the telencephalon, beginning with 

 the preoptic recess in wliich the sulcus limitans ends: 



Lamina tenninalis (containing the anterior eoinniissurei 

 Recessus ncuroporicus 



Lamina supraneuroporica (containing tlie pallial commissures^ 

 Recessus superior 

 Tela chorioidea telencephali 

 • Paraphysis 



Vehim transversum (anterior leafi 



Instead of tela chorioidea telencephali, the more definite term, 

 tela chorioidea telencephali medii, will be used in this paper. 

 This plan may be completed for the diencephalon as follows: 



Velum transversum (posterior leaf' 

 Tela chorioidea diencephali 

 Commissura superior 

 Epiphysis 



The posterior commissure belongs to the mesencephalon. 

 The neuropore itself has never been followed through the suc- 

 cessive stages of its development in the human embryo. 



The evidence for transferring the above scheme to the human 

 embryo is not wholly conclusive, and the present work was under- 

 taken primarily to determine in how far the morphology in this 

 region in certain human embryos was compatable with the 

 above scheme. 



