282 THE BRAIN OF THE TIGER SALAMANDER 



figures 9-16; in sagittal sections, '36, figures 3, 18-21. The thalamo- 

 and pedunculo-tegmental fibers of this group are similar in many 

 respects to the crossed and uncrossed fibers of tr. thalamo-tegmen- 

 talis ventralis of groups (4), (6), and (8). Those of group (5) arise 

 chiefly from the peduncle, the others from the thalamus. In the ag- 

 gregate these thick descending paths comprise the chief final com- 

 mon paths from the cerebrum to the peripheral neuromotor appara- 

 tus of the primary activities of the skeletal musculature, notably 

 those of locomotion and feeding. In early larval development these 

 long fibers from the peduncle and ventral thalamus are among the 

 first to appear in the cerebrum. Their adult distribution in the sev- 

 eral tegmental fascicles seems to be determined primarily not by the 

 arrangement in space of the groups of cells from which they arise but 

 by the lower motor fields into which they discharge their nervous 

 impulses. Those in groups (4), (5), and (6) descend more medially 

 and ventrally, the longest in the f. longitudinalis medialis. These 

 longer fibers evidently activate the trunk and limbs. Collaterals of 

 these fibers and accompanying shorter fibers end throughout the 

 isthmic and bulbar tegmentum ('396, figs. 84, 93), thus insuring co- 

 ordination of head movements with those of the trunk and limbs. 

 These more ventromedial fibers, accordingly, comprise the final com- 

 mon paths of fundamental mass movements, total patterns of be- 

 havior. 



The more dorsal fibers of group (8), accompanied by the strio- 

 tegmental fibers of group (9), descend along the outer border of the 

 isthmic gray (figs. 29, 30) to end far laterally in the white substance 

 of the isthmic and trigeminal tegmentum. Here the fundamental 

 reflexes of the musculature of the head, concerned primarily with 

 feeding, are organized. These more dorsal fibers, crossed and un- 

 crossed, have innumerable terminals and collaterals in the peduncle, 

 dorsal tegmentum, and lower tegmental fields ('396, figs. 79-82). 



Ventral fascicles (6). — These fascicles, like those of the fourth 

 group, were originally designated as fibers from the postoptic com- 

 missure ('36, figs. 4, 8, 18, po.{6)). They are now known to be com- 

 posed chiefly of two systems of thick myelinated and unmyelinated 

 fibers which decussate in the postoptic commissure, derived, respec- 

 tively, from the tectum and the ventral thalamus — tr. tecto-thalami- 

 cus et hypothalamicus cruciatus posterior ('42, p. 221 and fig. 5) and 

 tr, thalamo-tegmentalis ventralis cruciatus ('42, p. 225 and fig. 4). 

 The coarsest fibers of these fascicles, probably including some of both 



