MORPHOGENESIS OF THE CHOROID PLEXUSES ;V2< 



telencephalic plexus is strongly developed the lateral plexus 

 appears to be an appendage of it (Necturus, Warren); where 

 the velum is involved in an extensi\'e plexus formation, the 

 lateral plexus appears to be an appendage of it (Acanthias. 

 Minot); but always arises from the region of the telencephalic 

 roof plate described above, and medial to the taenia fornicis. 



With the Chelonia comes a change. The lateral plexus arises 

 in the anterior area chorioidea lateralis telencephali as has been 

 previously described but in its later de\elopment crosses the 

 taenia fornicis and invaginates also the i)osterior area chorioidea 

 lateralis telencephali in the medial hemis]ihere wall. Such a 

 condition is found also in the (Jecko brain (Tandler and Kantori. 

 This imohement of the medial hemisphere wall comes more and 

 more to i:)redominate in the development of the lateral plexus as 

 the hemis])heres come more and more to dominate the devol(»))- 

 inent of the telencephalon, but even in the highest Mannnaha 

 the anterior extremity of the lateral choroid ])!exus dev(^loi)s 

 from the loof plate of the telence]ihnlon and th(^ evidence ni:iy 

 briefly be summarized hci'e: 



(a) Elliot Smith ('S)7) in describing the br.-'iii of a foelal Oi ui- 

 Ihorhyncus described the lateral choroidal plexus as arising from 

 the continuation backwards of the horizontal jxirt of the lamina 

 sui)raneui'oporica, which term he used to include all the i-oof 

 plate of the telencej^halon between the velum transversum and 

 the lamina terminalis. Again in 190.'?. he reiteiated his belief 

 that the anterior extiemity of the latei:il chomid;!! j)Iexu< :iii>c^ 

 from the roof plate. 



(6) Th. Ziehen's figures of l^chidii;', do not show l\w anterior 

 extremity of the lateral plexus, but he states that it opens into 

 the Sichelspalte. that is, into the cleft between the hemisi)heies 

 anterior to the diencephalon, as well as the sulcus hemisphaerieus 

 (di-telencephalic groove) . 



(c) Observations on the ]\laisu]iials up to i)resent ie\eal 

 nothing. 



(d) Crronberg states of Erinaceus euro])aeus that the anterior 

 extremity of the lateral plexus is better developed in his earliest 

 stage than the posterior extremity and appai-ently arises fii-st. 



THE JOURXAI. Ol- COMPARATIVE XEUROI.OGV, VOL. 26, NO. 5 



