76 DAVIDSON BLACK 



the trochlear root fibers pass laterodorsad and descend in the 

 peripheral portion of the Sylvian gray. At the level of their 

 exit the two roots converge abruptly and after decussating in 

 the medullary velum, emerge upon the dorsal periphery (fig. 7). 



The oculomotor nucleus in Damonia is situated in the gray 

 matter of the midbrain floor. In transverse section it lies dorso- 

 mediad of the faciculus longitudinalis medialis in the angle formed 

 by this structure and the narrow midsagittal fissure of the iter 

 which here extends to within a very short distance of the ventral 

 periphery (fig. 9). The nucleus is composed of large multipolar 

 cells resembling closely those of the trochlear nucleus and forming 

 a fairly compact mass which is not divisible into subsidiary cell 

 groups. The nucleus begins a few sections behind the level of 

 the rostral border of the oculomotor root and extends for some 

 distance below the level of the most caudal emergent fibers of 

 this nerve. A considerable interval, however, separates the 

 oculomotor cell group from the caudally situated trochlear 

 nucleus (fig. 11, C). 



The oculomotor root fibers pass ventrolaterad through the 

 medial part of the faciculus longitudinalis medialis and between 

 the bundles of the tractus tectobulbaris dorsalis cruciatus to 

 reach the periphery on either side of the ganglion interpedunculare. 

 No oculomotor fibers arising in the contralateral nucleus could 

 be distinguished. 



By the degree of their cellular differentiation and in their 

 relations to the exit level of the oculomotor root, the III and IV 

 nuclei and the trochlear roots are strikingly similar in Damonia 

 and Chelone. It is significant also that Boa resembles both 

 Damonia and Chelone in these relations, though in other respects 

 presenting so marked a contrast to these forms. 



In Alligator and Varanus, on the other hand, Kappers has 

 shown that the oculomotor nucleus exhibits a relatively high 

 degree of cellular differentiation, so that in these forms a dorso- 

 lateral and ventromedian oculomotor cell group may be dis- 

 tinguished. A similar condition obtains in Chamaeleon (Kappers, 

 32, p. 63; de Lange, 12, p. 136). ' 



