PARAPHYSIS AND PINEAL REGION IN REPTILIA 353 



the cerebellum. In teleosts, the trout, Kupffer and Burckhardt 

 find again a long velum not so extensive as in previous forms, how- 

 ever, and showing no signs of plexus formation. The post velar 

 arch is rather high and narrow. Terry (102) in Opsanus shows 

 a greatly expanded velum taking on the character of a true cho- 

 roid plexus. 



In amphibia, Ichthyophis, Burckhardt (9) Necturus, Kings- 

 bury (55), Warren (97) Diemyctylus, Mrs. Gage (32), the velum 

 is well marked at an early stage and makes a deep angle in the roof. 

 The paraphysis grows as a long narrow tube which takes up all 

 of the cephalic wall of the velum, and causes a deep angle to 

 appear between the prosencephalon and diencephalon the hinder 

 limit of which is made by the caudal wall of the velum, the 

 anterior limit by the remains of the paraphysal arch, Warren (97) 

 figs. 3-8. The caudal wall of the velum soon begins to bulge into 

 the diencephalon to form the diencephalic plexus, and continues 

 until all of the velum and nearly all of the post velar arch are 

 absorbed in the plexus formation. Only a slight extent of the 

 post velar arch persists in front of the superior commissure. In Ich- 

 thyophis, Burckhardt (9), this process is not so extensive, a larger 

 part of the post velar arch remaining intact. See also Kupffer 

 (57), fig. 179-181, Salamandra and Eycleshymer (26), Ambly- 

 stoma. In all these cases the velum is reduced to a mere lip, a 

 very different condition from that in fishes and lower vertebrates 

 where it makes a deep partition in the fore brain. In reptiles 

 the velum is not so well marked as in amphibia. It forms only 

 a relatively low angle in the roof, but is continued laterally into 

 a well marked ridge, figs. 2-7, 17-20. The early stages shown in 

 the models compare with Francotte's figures of about the same 

 stages, Kupffer (57) figs. 239, Lacerta viridis; 240, Anguis fra- 

 gilis; and Herrick (39) Eutaenia. The angle between the caudal 

 wall of the velum behind and the paraphysal arch in front is much 

 less than in Necturus owing to the fact that the velum originally 

 does not grow so far ventrally and the paraphysis by folding back- 

 wards over the post velar arch does not seem to force the para- 

 physal arch so far downwards, figs. 9 and 10. This is certainly 

 the case in the lizard, though in the turtle the condition is nearer 



