52 BULLETIN OF THE LABORATORIES 



chiasm system which is partly distinct, lying partly imbedded in the 

 tuber cinereum and crossing directly. Back of the tuber is a well 

 marked trigonum inter-pedunculare, but the third nerves arise from the 

 strongly divergent j^eduncles near their median margins. 



The medulla is coffin-shaped in outline, its sides consisting of a 

 short anterior oblitiue, a median longitudinal, and a longer posterior ob- 

 lique portion. The third nerve is relatively large as compared with 

 the opossum, being ten times the size of the fourth nerve, and arises 

 from a number of closely united roots. 



The fourth nerve is very small and springs from the very lateral 

 portion of the valve of Vieussen's, thence passing to Gasser's gang- 

 lion. 



The fifth has two distinct roots, the ventral portion being a broad, 

 flat band extending nearly horizontally from the base of the main root, 

 from which it is elsewhere independent until merged in the ganglion 

 of Gasser. 



The main root is ten times as large and is flattened slightly hori- 

 zontally. 



The sixth nerve consists of three nearly equal roots springing 

 obliquely from the posterior margin of the pons and along the lateral 

 margin of the ventral median tract of the medulla, which here is very 

 distinct. 



The seventh nerve lies in the same antero-j)OSterior plane as the 

 sixth and i mm. caudad to the fifth. It is a rather large, flat band 

 passing directly lateral, its fibres entering the medulla nearly parallel 

 to the surface. 



The eighth is partly covered by the seventh when viewed from 

 below, and separates imperfectly at first into its two branches. Its 

 tract passes su})erficially dorsad under the cerebellum to a prominent 

 eminenciaacustica. The ninth and tenth nerves immediately follow, 

 but differ in direction. The eleventh can be traced to at least the 

 third cervical. The twelfth arises by three clusters, increasing in size 

 backward and springing from the margin of the medio-ventral tract. 



As compared with the opossum, the brain is broad and compact, 

 the olfactory lobes are relatively small, the optic chiasm is larger, the 

 pyriform lobes are more distinct and prominent, the rhinalis fissure 

 more distinct, and the pons is much larger, as are the cranial nerves. 

 As compared with the rabbit the brain is more massive and compact, 

 but otherwise exhibits only minor differences. 



