MOTOR NUCLEI IN PHYLOGENY 67 



order to which they belong. Thus it will be seen that the distance 

 between the exit level of the caudal border of the VII motor 

 root and the rostral end of the motor vagus nucleus is practically 

 identical in the reconstruction charts (fig. 11, C and D; fig. 12, 

 A, B, andC). 



Furthermore, in contrast to amphibians, a wide interval 

 exists in reptiles between the rostral end of the vagus motor 

 column and the exit level of the motor IX root (fig. 11, A, B, 

 C, andD). 



In all the reptiles examined, with the exception of Boa, a 

 condition obtains in the caudal part of the motor vagus column 

 essentially similar to that described in Damonia. Thus, in 

 Testudo (Lubosch), Chelone, AUigator, and Varanus (Kappers) 

 the motor vagus nucleus extends well into the cervical region 

 and the distribution of cells toward the termination of the column 

 tends to be irregular. 



Nerves VII and IX 



In Damonia the motor root of nerve IX takes its origin in the 

 caudal portion of a nucleus common to it and the motor VII 

 root. This nucleus is situated in the ventrolateral reticular 

 substance of the medulla, and its chief bulk lies caudad of the 

 exit level of the motor IX root (figs. 3, 4 and 11, C). The 



Fig. 3 Damonia subtrijuga. Transverse section through the medulla at the 

 exit level of the motor glossopharyngeal root. Abbreviations: F. s., visceral 

 sensory area in which the descending fibers of the fasciculus solitarius are evi- 

 dent; Nu. VII-IX. m., frontal end of the combined facial and glossopharyngeal 

 motor nucleus; R. VII. m. asc, facial motor root fibers passing dorsomedially 

 from their nucleus of origin to the position in relation to the posterior longitu- 

 dinal bundle Avhich they occupy in their ascending course; R. desc. VIII., descend- 

 ing vestibular root fibers; R. IX. vi., emergent motor glossopharyngeal fibers. 

 Other abbreviations as before. 



Fig. 4 Damonia subtrijuga. Transverse section through the medulla at the 

 exit level of the last abducens rootlet. Abbreviations: Ch., cerebellum; F. s., 

 upper end of visceral sensory column; Fib. arc. dors., dorsal arcuate fibers of the 

 octavomotor sj'stem passing to the abducens nucleus and posterior longitudinal 

 bundle; Nu. ac. d., dorsal acustic nucleus; Nu. VI., scattered large cells of ab- 

 ducens nucleus; Nu. VII-IX. m., frontal tip of combined facial and glossopharyn- 

 geal motor nuclear area; A''. VI., abducens nerve rootlets; 0. s., area in which the 

 scattered cells of the poorly differential superior olive are situated; R. desc. VIII., 

 descending VIII fibers. 



