OF DENISON UNIVERSITY. 
27 
The brains were hardened for 24 hours in weak chrome- acetic 
acid, then passed gradually from 50 per cent, to commercial alcohol, 
as usual. All sections were stained by hand with Grenacher’s haema- 
toxylin. The tracts were brought out better by using the concentrated 
stain, making it quite intense. For the minute histology, however, 
much better results were secured by diluting the stain from four to six 
times its volume and applying it long enough to give only a faint 
color. 
EXTERNAL FORM AND MEASUREMENTS. 
Erethizon dorsatus. This brain differs greatly in general appear- 
ance from the usual rodent type. The narrow anterior extremity, 
passing into the olfactories, the comipression at the Sylvian region, and 
the widely diverging fiocculi, which give to the rodent brain its char- 
acteristic appearance are not obvious here. Judging from Owen’s fig- 
ures,* there is a resemblance in these points to the beaver. The porcu- 
pine brain is much wider in proportion to the length of the hemisphere, 
but both are well filled out in front. The European porcupine, 
Hystrix crista, has these characteristics much more pronounced. If 
Owen’s figurest be correct, the cerebrum is considerably wider in pro- 
portion to its length than that of Erethizon. The common American 
muskrat, Fiber zibethicus, also has a cerebrum which much resembles 
that of Erethizon. 
The Rhinencephalon. The olfactories appear rather smaller than 
in most rodents and project only about three mm. beyond the hemi- 
spheres. This is due in part to the unusual development of the an- 
terior portion of the hemispheres themselves, in part to the fact that 
the olfactory lobes are closely appressed to the hemisplieres. The ol- 
factory crus is flexed dorsad and laterad, so that the two lobes are flat- 
tened against the cephalo-ventral aspect of the hemispheres, which 
latter are also flattened at the same region. The two olfactory crura 
are in close contact, but the lobes diverge dorsally. This appression 
of the olfactory lobes may be due to the enormous development of the 
front part of the skull. The inflation of the skull in the region of the 
nasal cavities and above them could readily crowd so closely upon 
*R. Owen, “ On the Structure of the Brain in Marsupials,’’ Philosophical 
Transactions, MDCCCVII, p. 93, Plate V. 
t“ Comparative Anatomy and Physiology of Verterbrates,” Vol. Ill, p. iio^ 
