Humphrey, Brain of the Snapping Turtle. 81 



of seeming greater length than is necessary and are folded upon 

 themselves. This same condition was found in the sea turtle. 



III. Occulo- Motor Nerves. — These originate near the mesal 

 line of the ventral surface ventrad of the central portion of the 

 pregemina (Fig. 2). They run cephalad in a slightly diverg- 

 ing course, within the cranial cavity, until opposite the junction 

 of the cerebrum and olfactory lobes where they pierce the dura 

 and pass farther cephalad until they reach the eye socket into 

 which they pass dorsad of the optic nerves. 



IV. Trochleans Nerves. — This pair is quite small. It 

 takes its origin near the mesal line on the caudo-dorsal margin 

 of the mesencephal ( Fig. 1). Each nerve passes latero-cephalad 

 around the geminum and then is carried forward until about op- 

 posite the cephalic third of the cerebrum where it, like the third 

 pair, pierces tne dura and continues forward in this membrane 

 until it passes into the eye socket. 



V. Trigeminus Nerves. — This pair springs from the meten- 

 cephal ventrad of the central portion about the middle of the 

 dorso ventral diameter ( Fig. 1). Directly after it emerges it 

 forms a ganglion, Gasser's, which is not so prominent as is usu- 

 ally figured in other classes of vertebrates. From this ganglion 

 it passes immediately into the skull. 



VI. Abducens Nerves. — These are very small. They orig- 

 inate near the ventral furrow ventrad of the origin of the 5 th 

 nerve ( Fig. 2). Diverging they pass ventro-cephalad and pierce 

 the base of the skull. 



VII. and VIII. Facial and Auditory Nerves. — These orig- 

 inate as a common trunk a little caudad and slightly dorsad of 

 of the 5th pair (Fig. 1). They pierce the dura and enter the 

 skull as a common trunk, but this trunk quickly divides ; the 

 caudal branch subdividing enters the auditory capsule, while the 

 cephalic portion also divides and its caudal branch passes into 

 the auditory capsule while the cephalic branch extends per- 

 ipherad as the true facialis. In Che lone midas these nerves or- 

 ginate as two roots a small root arising directly ventrad of the 

 main root but joining it at once. 



