524 H. W. NORRIS AND SALLY P. HUGHES 



THE FACIAL NERVE 

 1. Roots and ganglia of the facial nerve 



Three distinct elements are discernible in the root of the 

 facialis: a motor root of deeply meduUated fibers (Vllrm.) which 

 emerges on the ventral lateral border of the auricular lobe of the 

 medulla, a visceral sensory lightly medullated component (Vllrc) 

 which enters the medulla closely associated with fibers of the 

 auditory nerve, and a third distinctly but not heavily medullated 

 element (VIIrlL) that enters the medulla farther dorsallythan 

 the other components (figs. 28, 44). 



In the lateral wall of the medulla in the Urodela, at the origin 

 of the VII-VIII nerves, a region occurs, dorsal to the heavily 

 medullated tractus spinalis trigemini, which may be termed the 

 acusticum. In it are three longitudinal columns of white matter. 

 The roots of the auditory nerve are connected with the ventral 

 of these, and associated with it is a small medullated tract, 

 'tractus b' of Kingsbury ('95) ,which a posterior auditory rootlet 

 enters. Through this ventral column of the acusticum the 

 communis root of the facialis passes transversely to enter the 

 fasciculus communis. With the middle column of the acusticum 

 the second and third lateral line roots of the facialis are con- 

 nected. The dorsal column, 'dorsal island' of Kingsbury, re- 

 ceives the first lateral-line root of the seventh nerve. 



In Herpele there are two longitudinal fiber columns in the 

 acusticum. Into the ventral of these the fibers of the auditory 

 nerve enter, and with it is associated a small medullated tract, 

 into which some posterior root fibers of the same nerve enter. 

 The communis root of the facialis passes through this ventral 

 column, closely associated as in the Urodela, with the anterior 

 root of the auditory nerve (fig. 28). The dorsal of the two col- 

 umns of the acusticum receives the fibers of the dorsal root of 

 the facialis above mentioned. A true lateral line lobe is absent 

 in the caecilians, but this dorsal alba seems to correspond to 

 the column with which the second and third lateral-line roots in 

 the Urodela are associated. That is, in its relation to the other 

 components of the facialis, in its entrance into the medulla. 



