PARAPHYSIS AND PINEAL REGION IN REPTILIA 327 



ment, //. D., at its dorsal side. It should be noted however that 

 the second diencephalic segment is distinctly wedge shaped. 

 There is a well defined arch in its roof with a cavity just below, 

 but this cavity soon fades away into a thick ridge separating 

 diencephalon from mesencephalon. This segment is not as well 

 marked here as it was in the lizard, but all three segments are de- 

 fined at this stage. Furthermore all the primary arches are pres- 

 ent in the roof of the fore brain; a well marked paraphysal arch 

 in the roof of the telencephalic segment ; a short post velar arch 

 and a rather poorly developed epiphysal arch or thickening in the 

 roof of the first diencephalic; and a low arch, the synencephalic, 

 in the roof of the second diencephalic segment immediately ante- 

 rior to the mid brain. This stage therefore corresponds closely to 

 that in fig. 3, although the parts are not quite so sharply defined 

 as in the lizard of 2,4 mm. The mid brain here seems to be di- 

 vided into two segments, I.M., and II.M. 



Fig. 18 shows a brain of an embryo of 5 mm. Here the velum, 

 the paraphysal and post velar arches are all well marked. A small 

 outgrowth extending upward and backward from the region of the 

 rudimentary epiphysal arch, is the anlage of the epiphysis, E. 

 Behind this is a well marked intercalated arch, S, with very 

 definite boundaries below at the habenular flexure, although its 

 anterior boundary is not very distinct in the lateral wall of the 

 brain. This stage corresponds very closely to that of Lacerta 

 muralis of 3.2 mm., fig. 5. 



Fig. 19 shows the brain of an embryo of 7.6 mm. Imme- 

 diately in front of the velum which forms a well marked angle in 

 the roof is a single small outgrowth, the beginning of the para- 

 physis, P. Among all the specimens at my disposal I was unable 

 to find any case of multiple paraphysal outgrowths which were 

 quite common in the specimens of the lacertilia. A large 

 vein is seen lying close to the paraphysis. The branches of 

 this vessel form a sort of network about the paraphysis 

 shov/ing that at the earliest possible stage the paraphysis enters 

 into a close relation with the veins overlying this part of the brain 

 which later concentrate to form the superior longitudinal sinus. 

 Practically the same relations are seen in lacerta embrvos of a 



