Johnston, Forehrain Vesicle in Vertebrates. 503 



the plexus and their identity is lost. If the paraphysis is to be found 

 in adult mammals it should be looked for in the chorioid plexus in 

 the middle line between the interventricular foramina. The mem- 

 braneous roof extending forward from the paraphysal arch to meet 

 the lamina terminalis is relatively long in the embryo, spanning the 

 wide opening into the lateral ventricles. In later development these 

 interventricular foramina grow much less rapidly than the hemi- 

 spheres and the roof in question becomes of insignificant length. 

 This is due in part also to the expansion of the lamina terminalis by 

 the commissures which develop in it. 



The neuroporic recess can be located with certainty in the pig 

 embryos. In young stages there appears a slight ridge in each 

 lateral wall just rostral to the preoptic recess. This is the beginning 

 of the corpus striatum. As the two ridges converge toward the mid- 

 dle line they cause a thickening of the lamina terminalis above the 

 preoptic recess (Figs. 38 and 39, between r. p. and r. n.). This is 

 the location of the anterior commissure in later stages. Above this 

 thickening is another pit which in 15 mm. embryos is a smooth 

 rounded concavity in the middle line, not a transverse groove (Fig. 

 38). That this is the recessus neuroporicus seems clear from the 

 fact that it is above the corpus striatum and below the interventricular 

 foramina. As the striatum and lateral vesicles grow this pit becomes 

 deeper and more pointed. 



Three of the young human embryos described in recent years 

 seem to the writer to give clear evidence that the relations in the 

 optic region are the same in man as in fishes, amphibians and other 

 mammals. The embryo described by Low (1908) shows optic pits 

 on the open neural plate. These are apparently connected with one 

 another by a groove running across the middle line parallel with the 

 terminal ridge. The embryo described by Broman (1896) is 3 mm. 

 long and has the neuropore closed. It shows the terminal ridge 

 essentially like that of Squalus or of Amblystoma. The optic 

 vesicles are connected Math the primitive optic groove caudal to the 

 terminal ridge. Broman noticed the terminal ridge and gave to its 

 ectal, concave surface the name ''Fossa interocularis," but did not 

 speak of its significance. The embryo described by Mrs. Gage 



