THE NERVOUS SYSTEM. 



545 



Luysii, connected by fiber bundles with the corpus striatum and tegmentum. 

 Epithalamic connections are represented by bundles from anterior olfactory 

 regions (stria medullaris, seventh week) , by the commissura habenularis, and by 

 bundles to caudal regions (fasciculus retroflexus of Meynert to the interpedun- 

 cular ganglion, middle of second month), (pp. 474 and 512.) The posterior 

 commissure fibers are formed early in the second month in the fold between 

 mid- and inter-brain (Fig. 467). (Fig. 470). 



Fig. 470. — Construction of the brain of a 19 mm. human embryo (7J weeks), showing the stage of 

 development of some of the principal fiber-systems. His. 



Co., posterior commissure; F.s., tractus solitarius; FA., fasciculus spinalis trigemini (spinal V); 

 K, nuclei of dorsal funiculi of cord; L., medial longitudinal fasciculus; M., fasciculus retro- 

 flexus of Meynert; Ma., mammillarv bundle; n.i, nervus intermedius; O., olive; Ok, olfactory 

 nerve; S., fillet; Si., stria medullaris thalami; T:, thalamic radiation; T. </., tractus opticus; 

 V, Gasserian ganglion; VII, facial nerve and geniculate ganglion; VIII, ganglia of acoustic 

 nerve; IX, N. glossopharyngeus; X, N. vagus. 



The Telencephalon (Rhinencephalon, Corpora Striata and Pallium). 



To understand the development of this part of the brain it is necessary to 

 keep firmly in mind certain relations which are laid down at a comparatively 

 early stage. Some of these relations are shown in the diagram of the inner sur- 

 face of a model of a brain of four weeks. At this stage the pallium is unpaired, 

 i.e., there is no mediae furrow separating the two halves of the pallial expansion. 

 The various boundaries of the pallium in one side are (1) the median line uniting 



