OF DENISON UNIVERSITY. 35 



similar. The mammilare is single, median, and large, occupying the 

 whole caudal part of the cinereum. The hypophysis and epiphysis 

 were not observed. Both the prsegeniculatum and the postgenicula- 

 tum are more prominent than in Erethizon, especially the latter. The 

 caudal membecs of the corpora quadrigemina are covered by the cere- 

 bellum, the cephalic members are nearly covered by the hemispheres. 

 The former are broader laterally, the latter are longer. They are 

 of about equal hight. 



The Epencephalon is compact, like that of Erethizon, but very dif- 

 ferent in shape. The median lobe is produced farther both caudad 

 and cephalad, thus making the cerebellum considerably longer, and 

 giving it a decidedly rhomboidal shape when looked at from above. 

 In the flocculus it resembles Erethizon, thus -differing widely from 

 other myomorphs, whose flocculi are longstalked and encased in spec- 

 ial cavities of the skull. 



The Metencephahn is oblong, about as wide as long. Ventrally 

 the pyramids do not stand out in as bold relief as in Erethizon, 

 neither is the pons as sharply defined. On the dorsal surface, the 

 clava is not so wide as in Erethizon, being crowded mesad by the 

 larger lateral columns. The obex is small, but sharply defined. The 

 eminentia acustica is large and the strise medullares are very conspicu- 

 ous. The fasciculi teretes and other structures of the floor of the 

 fourth ventricle are not so prominent as in Erethizon. With reference 

 to the nerve roots, the most important peculiarity is the unusually 

 small size of the second pair. This is readily accounted for by the 

 small size of the eyes and the nocturnal habits of the animal. The fifth 

 nerves are easily separable into three fasciculi before they enter Gas- 

 ser's ganglia. Of these the middle bundle is the largest. 



Measurements. Total length, tip of olfactories to end of medulla, 

 22.5 mm.; greatest width of the two hemispheres, 16.5 mm.; length 

 of hemisphere, 13.5 mm.; depth of hemisphere, 10 mm.; tip of olfac- 

 tory to cerebellum, 16 mm.; tip of olfactory to pons, 14 5 mm.; tip of 

 olfactory to hypophysis, 12.5 mm.; tip of olfactory to chiasm, 10 mm.; 

 length of cinereum, 5 mm.; width of cinereum, 5.5 mm.; length of 

 cerebellum, 9.5 mm.; width of cerebellum, 13.5 mm.; depth of cere- 

 bellum, 7 mm.; length of flocculis, 4.5 mm.; length of medulla, 7.5 

 mm.; width of medulla, 7 mm.; thickness of medulla at pons, 5 mm.; 

 width of spinal cord, 4.5 mm. 



