198 MAMMALIA. 



3. Third nerve, proceeding from the inner part of the crus of the brain : it arises 



from the smaller portion of the intermediate layer of the exterior region. 



4. Fourth nerve, arising behind the quadrigeminal bodies at the roof of the 



passage from the third to the fourth ventricle. 



5. Fifth nerve : the figure is placed on the smaller portion which proceeds out- 



wardly from the upper margin of the trapezoid body ; half of the origin of 

 the larger portion is from the ventricular cord, forming the surface of the 

 fourth ventricle, the other half is from the involuntary centre and reaches near 

 the termination of the oblong medulla, forming a conical prominence on this ; 

 the smaller portion is on the inner side, and arises from the tract of the 

 larger portion of the intermediate layer of the exterior region after it has 

 been joined by the tract of the first convolution of the intercedent region : 

 the larger portion undergoes a change in the arrangement of its fibrils in 

 the Gasserian ganglion, and is then divided into three trunks. 



6. Sixth nerve, arising from the trapezoid body in the groove on the outer side 



of the pyramidal body. 



7. Auditory nerve, arising from the side of the fourth ventricle, and the exterior 



layer of the restiform body. 



8. Hard portion of the seventh, connected externally with the trapezoid body : it 



arises from the tract of the larger portion of the intermediate layer of the 

 exterior region, after it has been joined by the tract of the first convolution of 

 the intercedent region. 



9. Glosso-pharyngeal nerve and par vagum, arising from the involuntary tract, 



and having their egress at the side of the restiform body. 



10. Ninth nerve, proceeding from the outer side of the pyramidal body : it arises 



from the continuation of the tract of the larger portion of the intermediate 

 layer of the exterior region, after it has given origin to the smaller portion of 

 the fifth, the sixth, and the hard portion of the seventh. 



11. Accessory nerve. 



12. Inferior part of the hippocampus. 



13. Trapezoid body : it is formed of transverse fibres externally. Internally it is 



