PARAPHYSIS AND PINEAL REGION IN REPTILIA 365 



In the turtle the same condition is seen, fig. 20. Here the 

 commissure is confined to the synencephalon and later, figs. 21- 

 22 spreads backward into the mid brain. In the turtle the com- 

 missure is not doubled over on itself as was the case in the lizard. 



Epiphysis and pineal eye 



Of all the structures that develop from the roof of the fore brain 

 the epiphysis and especially the pineal eye have been of the great- 

 est interest to investigators. Consequently the literature on 

 this subject is very voluminous and the region has been very 

 thoroughly studied in all the more important vertebrate forms. 

 It is intended to discuss here a few points only concerning the 

 epiphysis and pineal eye as nothing especially new has been 

 brought out in this paper on these structures. The models how- 

 ever give a good view of the topographical relations of this region. 



The epiphysis always arises from the caudal part of the dien- 

 cephalic roof and appears in every case before the paraphysis. 

 Its anlage is the epiphysal arch, Minot (71), from which it 

 appears first as a simple outgrowth. The superior commissure 

 develops immediately in front of the epiphysis and usually lies 

 close against its stalk, except in certain amphibia, where there 

 is a distinct interval between it and the epiphysis, Cameron 

 (15, 16), Kupffer (57), fig. 228. The epiphysis marks the caudal 

 boundary of the parencephalon and behind is the roof of the 

 synencephalon on pars intercalaris. Here develops first the 

 posterior commissure which later usually takes in all that seg- 

 ment and comes to lie close against the hinder side of the stalk 

 of the epiphysis, Terry (102). In some cases, for example Nectu- 

 rus, the commissure is separated from the epiphysis by a distinct 

 interval. The epiphysis always remains attached to the brain 

 by some sort of stalk which is usually very thin in adult forms. 

 This stalk contains a cavity up to certain stages which communi- 

 cates with the diencephalon, but the cavity is almost always oblit- 

 erated before the final stage in development is reached. The 

 changes in shape and size of the epiphysis in both lizard and turtle 

 can be followed in the models. In both forms the organ is ex- 



