MOTOR NUCLEI IN PHYLOGENY 535 
The oculomotor nucleus and root are both relatively and 
absolutely smaller in Ameiurus than in Solea. It is possible, 
however, to distinguish dorsal and ventral parts in the oculo- 
motor nucleus of,the former animal, though there is but little 
difference in the rostro-caudal extent of these subsidiary cell 
groups, such as was so obvious in Solea. No definite decussation 
of the fibers of the oculomotor nerves at their origin could be 
made out in Ameiurus, and the whole nucleus lies on a more dor- 
sal plane than in Solea. The emergent roots of the oculomotor 
nerve pierce the commissura ansulata on their -way to the 
ventral periphery of the midbrain (fig. 39). 
The trochlear nucleus in Ameiurus is almost directly contin- 
uous with that of the oculomotor nerve but lies on a somewhat 
more dorsal plane. The emergent trochlear fibers pass dorsally 
in the Sylvian gray (Franz, |. c.) to decussate and emerge through 
the valvula on the same level as their nucleus (fig. 38). Though 
the trochlear roots in Ameiurus have not been divided into two 
parts as in Solea, yet they make their exit from the brain stem 
at an unusually rostral level. A similar condition has been - 
recorded by Van der Sprenkel in Silurus glanis, though in this 
form on account of the very slight functional development of 
the eyes, both oculomotor and trochlear nuclei were much 
reduced (fig. 42 A). It would appear that the unusually rostral 
place of exit of the trochlear roots in both Ameiurus and Silurus, 
like the splitting of the rootlets in Solea has also been due in a 
large measure to the mechanical action of the valvula and 
cerebellum during the development of these parts. 
Discussion 
Occipito-spinal-complex. In teleosts no pre-hyal hypobranchial 
spinal muscles are present and according to Furbringer the most 
rostral spino-occipital nerves represented in these animals are 
the occipito-spinal roots b and c. In Siluridae according to this 
investigator both dorsal and ventral roots are represented in the 
occipito-spinal nerve b, the nerve ¢ is missing, while caudal to 
and including the first cervical nerve (Furbringer’s nerve 4) 
