30 
BULLETIN OF THE LABORATORIES 
marked. The lateral columns are greatly enlarged ventrad to the 
clava, forming the area ovalis of Wilder. The relations of the dorsal 
columns and the structures on the floor of the fourth ventricle are 
shown by Plate 1 , Fig. 3. The funiculus gracilis and the funiculus 
cuneatus fuse at the region of the calamus scriptorius to form the 
clava, which is very large. The obex is also large, lying ventrad of 
the preceding. On the floor of the ventricle the fasciculi teretes are 
divaricated caudad by the projecting genua of the seventh nerve. The 
eminentia acustica are large and double, being divided into two por- 
tions by a longitudinal fissure. The strios medullares are hardly visi- 
ble in Erethizon; in Geomys they are very large. The posterior 
peduncle of the cerebellum passes into the restiform iract in the usual 
way. 
The cranial nerves are illustrated by Plate I, Fig. 6. The optic 
nerves are smaller than usual, 1.2 mm. in diameter, i cm. from their 
insertion. 'Fhe third nerves are about the usual size, inserted i cm. 
caudad of the chiasm on the ventral aspect of the crura. The fourth 
nerves are very small, pursuing the usual course The fifth is large, 
3 mm. in diameter at insertion, rapidly flattening out to much wider. 
It lias two roots. The median is ventral and smaller and crosses the 
other at the Gasserian ganglion. The sixth is small, inserted just 
caudad of the pons about 3 mm. from the meson. But one root is ap- 
parent. The seventh is inserted on the caudal margin of the pons 
laterad of the sixth. The eighth is inserted i to 2 mm. caudo laterad 
of the seventh. There are two roots, which lie in very close contact. 
The ninth, tenth and eleventh are closely associated in their exit. The 
ninth is small and more easily separated from the other two. The 
tenth has several large roots which are hard to separate from those of 
the eleventh. The eleventh itself can be followed as a large strand as 
far back as the third spinal, and for at least two-thirds of this distance 
gives off frequent smaller fasciculi into the medulla and cord. The 
twelfth arises on the caudal aspect of the pyramids by about six roots. 
Measurements. Total length, tip of olfactories to end of medulla, 
46.5 mm.; olfactory to cerebellum, 33 mm., to pons, 29 mm., to hy- 
pophysis, 21 mm., to chiasm, 17.5 mm.; width of the two hemi- 
spheres, median, 35 mm., one-fourth distance from caudal end, 33.5 
mm. three-fourths distance from caudal end, 32 mm.; length of crura 
exposed, 8 mm.; length of tuber cinerum, 7 mm.; width of tuber cin- 
erum, 6.5 mm ; length of corpora quadrigemina, 7.5 mm.; width of 
