254 C. JUDSON HERRICK 



tegmentum farther caudad, and still others appear to enter the 

 fasciculus longitudinalis medialis by means of which they may 

 effect connection with the motor nuclei of the medulla oblongata. 



A separate slip of this system arises from the nucleus posterior 

 tecti, passes ventralward in the region of the isthmus, and then 

 turns forward. This is shown in figures 51 to 55 {tr.t.ped. 

 post.), and maybe designated tractus tecto-peduncularis posterior. 

 It probably provides a pathway from the nucleus posterior tecti 

 to the nuclei of the III and IV nerves. 



At the contact between the stratum album and the stratum 

 gl-iseum of the midbrain there is a thin sheet of fibers, chiefly 

 unmyelinated, which are directed chiefly downward and for- 

 ward to the vicinity of the III and IV nuclei. The fibers of 

 the brachium conjunctivum parallel this system immediately 

 caudad. The fibers of this system arise from all parts of the 

 tectum and may be called tractus tecto-peduncularis profundus 

 (figs. 9 to 14, 21, 31, 32, 33, tr.t.ped.p.). Some end in the teg- 

 mentum of the same side and others fij:"st decussate in the ven- 

 tral cormnissure. 



There is a third system of tecto-peduncular fibers which may 

 be termed the tractus tecto-peduncularis intermedius. These 

 fibers, most of which are unmyelinated, arise from the neuropil 

 of the caudal part of the tectum and descend into the under- 

 lying tegmentum at intermediate depths of the stratum album. 

 They form thin sheets of fibers separatmg the longitudinal 

 tracts of the tegmentum, where some ascend and some descend. 

 So far as observed they are all uncrossed (fig. 13, tr.t.ped.i.). 

 The unmyehnated elements of this system are not clearly im- 

 pregnated in our preparations. Most of them are probably 

 dendrites of neurons of the motor tegmentum, reaching upward 

 to receive nervous impulses directly from the sensory tracts in 

 the tectum, and some are known to be dendrites of neurons of 

 the tectum reaching downward to arborize among the dorsal 

 tegmental fascicles. 



In addition to the tecto-peduncular systems already de- 

 scribed (i.e., fibers passing from the tectum to the motor teg- 

 mentum of the same or the opposite side), fibers connected 



