PARAPHYSIS AND PINEAL REGION IN REPTILIA 355 



The same author gives a series of sagittal and transverse 

 sections of crocodilus madagascarensis, figs. 1-11, which corre- 

 spond still more closely with the development of this region in the 

 Lacerta. The post velar arch, however, is rather more highly 

 developed at first. The oldest stage is almost identical with 

 fig. 13, though the epiphysis is absent and the paraphysis not so 

 large. The velum is a thin lip, then comes a portion of the post 

 velar arch, flat and unconvoluted. Towards the apex of the dor- 

 sal sack the diencephalic plexus is seen extending almost to the 

 superior commissure, and the dorsal sack itself forms a high narrow 

 slit, the superior commissure being almost in contact with the 

 velum. 



Voeltzkow (96) figs. 21 and 22 of Chelone imbricata show a 

 picture quite similar to my fig. 23. The dorsal sack is spacious and 

 filled by an elaborate diencephalic plexus which extends to the 

 mouth of the paraphysis and obscures the velum. In Chelydra 

 serpentina Humphrey (51) described a well marked post velar 

 arch the greater part of which is occupied by folds of the dience- 

 phalic plexus, fig. 30. The velum is reduced to a mere lip as in 

 my models. He also gives a sagittal view of Chelone midas, 

 where the dorsal sack, however, is more compressed antero-pos- 

 teriorly and the superior commissure is nearer the velum than in 

 Chrysemys. In pi. 2, fig. 7, he shows the brain of Chelone 

 midas. This approaches nearer to the lizards in having a very 

 deep and narrow dorsal sack, as in fig. 12. In ophidians Leydig 

 shows figure of Tropidonotus natrix and Ringelnatter which 

 approach the conditions seen in turtles. The velum is insignifi- 

 cant, the post velar arch fairly high and expanded and the dien- 

 cephalic plexus well developed. In Vivipara urcini the condi- 

 tions resemble rather those seen in Lacerta viridis, fig. 13. In 

 Eutaenia the velum becomes very indistinct being reduced to 

 the narrowest possible lip. The dorsal sack is well arched and 

 completely filled by a large diencephalic plexus extending from 

 the paraphysis to the supra commissure. Ssobolew (91) has 

 described this region in Tropidonotus natrix and Vipera berus, 

 where the velum and dorsal sack are the same as shown by Leydig. 



