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 peduncles near their median margins. 
The medulla is coffin-shaped in outline, its sides consisting of a 
short anterior oblique, 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-posterior 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 superficially dorsad under the cerebellum to a prominent 
eminencia acustica. 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. 
