143 



section coiitinuous with the most frontal part of the basis cerebri 

 (more laterally with the mantle) and covering 6, the meso-striatnm 

 or palaeostriatum angmentatum. in which llie lighter centre (richly 

 provided with fibres) is the primitive palaeostriatum, the basal 

 nucleus. 



If we now look at the figures of a 11 days embryo of the chick, 

 we find that the chief alteration exhibited, is the enlargement of 

 both parts of the hyperstrialum, which not only have increased in 



Fig. 7. Sagittal section of the forebrain of a chickembryo of 6 days. 

 b = palaeostriatum augmentatum (= mesostriatum). 

 c = hyperstriatiim inferius. 

 d = hyperstrialum superius. 



thickness (as appears from the fact that mucli less of the ventricle 

 has remained free), but also has enlarged in medial direction. 



The latter fact is evident from a comparison of figg. 9 and 6, 

 which are taken on approximately corresponding levels (rather medial). 



Whereas in fig. 6 on this level nothing is as yet visible of the 

 hyperstriatum, the latter is vei-y clearly shown in fig. 9, as a result 

 of its growth in medial direction, further extending into the ven- 

 tricle. It also shows the division in hyperstriatuivi superius and inferius. 



In this figure we see moreover that the hyperstriatum superius 

 is continuous only with the brainvvall above the ventriculus, 



