The Brain of Diemydylus Viridescens 265 



from the striatum ; its endymal surface is marked by sulci, 

 one of which extends from the porta to the infundibuUmi — 

 another continues caudad as the widest part of the mesocoele, 

 another lies ventrad of the enlargement of the habena (Fig. 

 20-22). 



The roof of the diencephal (Fig. 52) is separated caudad 

 from the mesencephal by the postcommissure. Cephalad of 

 this are, (i) the simple layer of endyma which underlies (2) 

 the epiphysis, (3) the supracommissure connecting the habenae 

 (Fig. 59-60), and (4) a layer of flattened cells passing ceph- 

 alo-ventrad from the supracommissure and reflected over the 

 diaplexus. This order agrees with that now usually accepted 

 and not with that mentioned by Edinger (10, p. 37) in 

 which he places the connection of the epiphysis with the roof 

 cephalad of the supracommissure. 



The epiphysis is insignificant (see p. 285). The supracom- 

 missure (Fig. 52) is traversed by processes of the endymal 

 cells covering it. 



Plexuses. — The supraplexus is seen on the dorsal surface of 

 the brain (Fig. 4). It is a complicated coil of blood vessels 

 connected with the blood supply of most of the cephalic part 

 of the brain. Vessels lying in the intercerebral pia (Fig. 6, 7), 

 and vessels extending between the cerebrum and thalami 

 unite with it (Fig. 21), and from it are supplied the two plex- 

 uses entering the brain at this point. Within its coils lies the 

 paraphysis (Fig. 6, 52, 59), (see p. 286). The opening of 

 the paraphysis indicates the division between two plexuses 

 which are here named from the place at which they enter the 

 cavities the auliplexus and the diaplexus, in preference to the 

 terms of Burckhardt (6). He calls the same things in Ich- 

 thyophis, superior, inferior and medius, making three divis- 

 ions instead of two. 



Figure 6 shows these two plexuses from the meson. The dia- 

 plexus extends sometimes to the cerebellum or even farther, 

 or sometimes is found with its tip pressed close to the po.st- 

 commissure. Its blood supply is from the caudal side of the 

 opening of the paraphysis, while the auliplexus receives its 

 supply from the cephalic side (Fig. 7). The latter at its en- 



