THE SYSTEMS OF FIBERS 271 



related with the several parts of the brain, accompanied by dia- 

 grams, and some classified lists, including the lemniscus and visceral- 

 gustatory systems (chap, xi); connections of the interpeduncular 

 nucleus (chap, xiv) ; some tectal connections (chap, xvi) ; stria medul- 

 laris thalami, fasciculus retroflexus, stria terminalis, and fornix (chap, 

 xviii); some olfactory connections (chap, xix); and in the next fol- 

 lowing sections the basal forebrain bundles, tegmental fascicles, f. 

 tegmentalis profundus, and the commissural systems. 



THE BASAL FOREBRAIN BUNDLES 



In a survey of the forebrains of fishes, attention was called to the 

 important part played in morphogenesis by these great systems of 

 longitudinal conduction ('22a, p. 175), and here this theme has re- 

 ceived further consideration in chapter vii. These bundles of Nec- 

 turus were described in comparison with those of other amphibians 

 ('336, p. 166), and their arrangement in Amblystoma has been illus- 

 trated ('27, p. 285; '36, p. 335 and figs. 5, 6; '396, p. 533 and fig. 1). 

 In sections of these brains the basal bundles are the most obvious 

 landmarks, extending from the hemispheres backward through the 

 brain into the medulla oblongata. Some of their fibers, in other 

 species, have been described as extending into the ventral funiculi of 

 the spinal cord, but our material yields no evidence that in Amblys- 

 toma any fibers which descend from the hemispheres in these bun- 

 dles go back without interruption farther than the level of the roots 

 of the VIII nerve. These bundles contain ascending and descending 

 fibers, many of the latter decussating in the anterior commissure. 

 In addition to these main lines of through descending traffic, many 

 other kinds of fibers enter these bundles, and these connections will 

 now be summarized. 



The fibers of these bundles are arranged in three groups of fascicles 

 as indicated in figures 19, 20, 21, 101; but these groups are not 

 sharply separated, for there is much interchange of fibers among 

 them. Their descending fibers are roughly comparable with the sub- 

 cortical components of the mammalian extra-pyramidal systems, and 

 the more dorsal ascending fibers of the thalamo-frontal tract (figs. 19, 

 101, tr.th.f.) correspond with the thalamo-striatal system. The dorsal 

 group of fascicles, the lateral forebrain bundle (i. lateralis telencepha- 

 \\,f.lat.t.), connects with the lateral wall of the hemisphere and has 

 dorsal and ventral components with different connections. The ven- 

 tral group, the medial forebrain bundle (f. medialis telencephali, 



