366 C. JUDSON HERRICK 



Following the fasciculus solitarius caudad, it is seen to be 

 enlarged by successive additions from the VII, IX and X nerves 

 (figs. 3 and 12 to 18) and in the vagus region there is an ill defined 

 \'entricular eminence formed by the thickening of the stratum 

 griseum adjacent to the fasciculus solitarius (figs. 2, 14 to 17, lob. 

 vis.). The rostral end of this visceral lobe is separated from the 

 overlying area acustico-lateralis by a shallow sulcus, but caudad 

 of the latter area the visceral lobe rises up quite to the dorsal 

 border of the massive wall of the fourth ventricle. In this lower 

 region of the oblongata the fibers of the fasciculus solitarius also 

 rise up within the substance of the visceral lobe and, just below 

 the calamus scriptorius, the remaining fibers decussate in the com- 

 missura infima Halleri, near which they terminate in the com- 

 missural nucleus of Cajal in the same way as in fishes and mammals 

 (figs. 17, 18). There is also a decussation of fibers from the 

 somatic sensory column in the commissura infima (fig. 18, com.i.s.), 

 so that the relations in this region closely resemble those which I 

 have previously described ('08) in teleosts. Wallenberg ('07) 

 in the frog describes fibers of the spinal V root entering the com- 

 missura infima and fibers of the fasiculus solitarius descending to 

 the third spinal segment. 



Summary. The preceding account shows that* most of the 

 sensory root fibers of the cranial nerves which enter the medulla 

 oblongata of larval Amblystoma immediately divide and extend 

 in ascending and descending directions throughout the greater 

 part of the length of the oblongata. These fibers give off frequent 

 collateral branches, thus effecting synaptic relations with den- 

 drites of neurones of the adjacent gray substance throughout 

 their entire extent. In this respect they resemble the root fibers 

 of the spinal nerves, though here there is a well defined grouping 

 of the fibers into separate longitudinal fascicles each of which 

 contains fibers of similar physiological type from a single root 

 which has a definite peripheral distribution. These fascicles 

 retain their individuality and amongst them is a very limited 

 amount of neuropil containing the synapses between the collat- 

 erals and terminals of the root fibers and the dendrites of the 

 neurones of the second order whose cell bodies lie in the underlying 



