102 



PERCIVAL UAILEY 



I)anii)hysal arcli. . . ." "Tlie plexuses of the hemispheres 

 arise on either side from the origin of the telencephalic plexus 

 and pass into the lateral ventricles. . . ." 



If we turn now to the human embryo and examine, say, the 

 19 mm. embryo, H 173, we find that it is easy to trace the tela 

 chorioidea telencephali medii over the paraphysal arch and 

 velum transversum to the tela chorioidea diencephali. If, 

 however, we attempt to follow backward the taenia fornicis, it 

 will not be found to be continuous with the taenia thalami at 



Fig. 15 Median view of a model of the forebrain in His' 6.9 mm. embryo, 

 Br. .3. 



the lateral end of the velum transversum, but is separated from 

 the taenia thalami by the fissura chorioidea. In order to ex- 

 plain the difference between the condition in the frog and in 

 the human embryo it is necessary to analyze more closely some 

 younger human embryos. 



Figure 15 shows a medial view of the forebrain of His' embryo 

 Br 3, 6.9 mm. in length. On it is indicated by a row of crosses 

 a line homologous with the taenia fornicis et taenia thalami in 

 the tadpole. The anterior limb of the di-telencephalic groove 

 is marked by small circles and labeled area chorioidea posterior 

 for reasons which will appear later. On the opposite side of 



