108 PERCIVAL BAILEY 



corpus striatum is not formed by fusion, and there is as yet no 

 fusion here. The intermediate root of the corpus striatum prob- 

 ably extends into the medial hemisphere wall, but the external 

 morphology does not suggest it. 



2. Diencephalon 



a. Tela chorioidea diencephali. It is to be noted that the 

 tela chorioidea diencephali shows no indications of folding 

 except at its anterior extremity. In the 32 mm. embryo, a 

 pouch arises at the anterior end and extends forward over the 

 velum transversum and the paraphysal arch (fig. 25, a.p.). 

 Streeter, in Keibel and Mall's textbook, as was mentioned in the 

 history, makes the statement that ''Orally this choroid roof [of 

 the third ventricle] is continued into the telencephalon where 

 it forms a pointed pouch overlapping the lamina terminalis and 

 the contained commissures. . . . The anterior choroidal 

 pouch has been homologized with the paraphysis of the lower 

 vertebrates." There is not up to this stage any pointed pouch 

 in the telencephalic roof. The pouch noted above lies in the 

 roof of the diencephalon, just back of the velum transversum 

 and hence cannot be the paraphysis. The true paraphysal 

 arch has been pointed out above. In comparing Francotte's 

 figures with this region in embryos of approximately the same 

 age in the Chicago collection, I feel sure that it was this anterior 

 pouch of the tela chorioidea diencephali which he described as 

 the paraphysis. 



I have not followed the thalamic lip fully in later stages, but 

 in an embryo of 60.4 mm. greatest length, H 44 of the Chicago 

 collection, the thalamic lip is fused with the lateral thalamic wall 

 toward the anterior end. 



b. Epiphysis. The epiphysis, in the 19 mm. embryo especially, 

 shows marked indications of a differentiation into epiphyseal 

 stalk and epiphyseal vesicle. Such a condition is very char- 

 acteristic of lower vertebrates, especiallj^ reptiles, but has never 

 before been noticed in the human embryo. The epiphyses of 

 the 28 mm. and 32 mm. embryos show similar indications. 



