500 'Journal of Comparative Neurology and Psychology. 



This corresponds in position to the paraphysis of lower forms (cf. 

 Figs. 30 to 33). Since there is no glandular development known 

 in mammals, it may be called the paraphysal arch, a name which 

 Minot (1901) applies to the corresponding structure in birds. In 

 front of the paraphysal arch a membrane continues forward to meet 

 the lamina terminalis. ^Vhen the lateral cerebral vesicles are formed 

 it is seen (Figs, 37, 38, 39) that this membrane lies over the ventricle 

 between the interventricular foramina. 



Fig. 38. Pig embryo, 15 mm. Median sagittal section of the forebrain. 

 The dotted outline of the hemisphere is reconstructed from several sections. 

 X 15. 



As development proceeds the velum transversum becomes a fold 

 with a sharper angle but less deep in proportion to the size of the 

 brain. The paraphysal arch remains a distinct median pouch until 

 the lateral vesicles are well formed. In sagittal sections to one side 

 of the median plane the lateral ventricle appears as a dorsal cavity 

 opening by way of the inten^entricular foramen in front of the 

 paraphysal arch into the median ventricle. (Fig. 38, 39.) These 

 simple relations persist up to the 17 mm. stage or later. By the 



