488 DAVIDSON BLACK 
Nucleus paramedianus (Nu. paramed.). The nucleus para- 
medianus, or paraseptalis, is well developed in Selache maxima. 
The sagittal relations of the right nucleus are indicated in the 
reconstruction chart, figure 17 C. This nucleus is bilaterally 
symmetrical, consisting of circumscribed collections of grey mat- 
ter, on each side of the raphé near the ventral periphery of the 
medulla in the neighborhood of the emergent roots of the 
spino-occipital nerves (fig. 10). The connections which this 
nucleus establishes with other centers are not fully understood, 
but Johnston has shown that the neurites of this nucleus in 
Acipenser cross the raphé and end among the tract cells of the 
lateral column (52) and Goronowitsch considered this nucleus 
to the homologue of the inferior olive of higher forms (30). In 
general among vertebrates the size and compactness of the 
nucleus in question varies directly with the relative develop- 
ment of the cerebellum. This has been pointed out by Kappers, 
who has shown that a well circumscribed nucleus paramedianus 
is present only in those forms which possess a relatively large 
cerebellum (64). 
Motor facial, glossopharyngeal and vagal nuclei (Nu. et. rad. 
mot. Nn. VII-IX—-X). The arrangement of the caudal viscero- 
motor column in Selache presents a marked contrast to that 
obtaining in cyclostomes (figs. 7 and 17). In Selache the motor 
nucleus of the facial nerve is situated a considerable distance 
caudad of the level of its root exit and forms the rostral portion 
of a continuous dorsally placed cell column composed of the 
motor VII-IX--X nuclei. This arrangement of the caudal 
viscero-motor column is characteristic of all selachians and the 
situation of the VII motor nucleus far behind the level of its 
own root exit has necessitated the formation of a long ascend- . 
ing. VII motor root in these forms, as already fully set forth by 
Kappers (61, 64, 66 and 72). 
The relations of this ascending root of the facial nerve in 
Selache to its nucleus of origin and to the fasciculus longitu- 
dinalis medialis are illustrated in figures 11 and 12. 
The motor root of the glossopharyngeus in Selache passes 
dorso-mesially from its superficial attachment and _ courses 
