EXTENT OF THE FLOOR-PLATE OF HIS 



121 



crescence and joined together by the floor-plate. I shall recur 

 to this later. His figure 8, from his ('93,1) paper on the frontal 

 end of the brain tube, reproduced here as figure 5, illustrates this 

 clearly. Johnston ('09), from a study of the early developmental 

 stages in the shark, the salamander, and the pig, has given valid 



Fig. 4 Copy of figure 1 of Wilhelm His ('92, 2). Schema in explanation of 

 the bent brain tube and its relations to chorda dorsalis (Ch.), to Sessel's pocket 

 (S) and to the pharyngeal membrane (Rht.). d.N., dorsal seam (Naht); f.N., 

 frontal seam; Mb., stomodeum; G., basal plate; F., alar plate; B., basilar fold 

 (Basilarleiste). 



Fig. 5 Copy of figure 8 of Wilhelm His ('93, 1). The attempt is made to pro- 

 ject the individual brain regions upon the medullary plate of a selachian at a 

 stage in which it is still spread out flat. The regions are indicated as follows: 

 Ag., optic vesicle; A.t., angulus terminalis; Cm., corpus mamillare; C.q., corpus 

 quadrigeminum, Hb., tori tegmentales (Haubenwiilste) ; Hs., pallium cerebri; Hth., 

 hypothalamus; L.o., lobus olfactorius; L.t., lamina terminalis; R.i., recessus in- 

 fundibuli; R.o., recessus opticus; T.c, tuber cinereum. The region of the optic 

 ohiasma would be between R.i. and R.o. 



