MEDULLA OBLONGATA OF AMBLYSTOMA 357 



buccalis. It follows that in the larva, as m the adult, the ''dorsal 

 island," or lobus lineae lateralis, receives fibers from each of the 

 three peripheral rami of the lateral line VII system. 



The middle lateralis VII root enters the oblongata ventrally of 

 Kingsbury's tract a. The ascending branches of its fibers pass 

 forward parallel with and deeper than those of the dorsal lateralis 

 X root and some of them reach the extreme rostral end of the 

 auricular lobe. The descending branches also occupy a deep posi- 

 tion adjacent to the central gray for most of their course, being 

 readily followed in horizontal sections back to the caudal end of the 

 area acustico-lateralis in the mid- vagal region. Peripherally the 

 fibers of this root can clearly be seen to enter both the anterior and 

 the posterior divisions of the lateralis VII root complex. 



The ventral lateralis VII root in these larvae is larger than the 

 other two roots and its ascending and descending branches form 

 big tracts, each composed of several fascicles, lying between the 

 dorsal and ventral lateralis X roots. The ascending fibers reach 

 the rostral end of the auricular lobe and the descending fibers pass 

 backward to the caudal end of the area acustico-lateralis. This 

 root is also distributed peripherally to both the anterior and the 

 posterior divisions of the lateralis VII root complex. In the case 

 of the anterior divisions of the middle and ventral lateralis VII 

 roots, it is not clear whether their fibers distribute to both the 

 ramus ophthalmicus superficialis VII and the ramus buccalis. 

 Apparently this is the case. The evidence, therefore, strongly 

 suggests that each of the three lateralis VII roots receives fibers 

 from each of the three great lateral line rami of the facialis. 



The anterior lateralis VII ganglion (giving rise to the ramus 

 buccalis and the ramus ophthalmicus superficialis VII) in these 

 larvae is closely applied to the dorsal surface of the trigeminal 

 ganglion, and along the plane of contact there is some mingling 

 of the cells of these two ganglia. The cells of the lateralis gang- 

 lion are of large and medium size. Most of them are typical 

 unipolar T-form neurones (fig. 46, u.p.) of very simple form, the 

 single process very soon dividing into centrally and peripherally 

 directed branches. Amongst these unipolar neurones, however, 

 are found much less numerous bipolar neurones (b.p.), the central 



