STUDIES IN THE TOPOGRAPHY OF THE RODENT 



BRAIN: ERETHIZON DORSATUS AND 



GEOMYS BURSARIUS. 



By C. Judson Herrick. 



The design of the present paper is to contribute further details in 

 the direction indicated by the article on the Central Nervous System 

 of Rodents in Volume V of this Bulletin. The types chosen for these 

 studies were selected partly because they represent groups very differ- 

 ent from Arctomys monax, the type there discussed, partly because 

 they seem to be aberrant members of the rodent stock and present 

 striking peculiarities both in habits and in general structure. Erethi- 

 zon dorsatus is our only North American representative of the Hystri- 

 cidae. In spite of important structural differences, it is very similar 

 to the European genus Hystrix, in which it was placed by Linnaeus, 

 and it seems to be connected with the European porcupines by geo- 

 logical remains.* Geomys bursarious, the "pocket gopher" of the 

 West, is widely separated from the other Myomorpha by its fossorial 

 and nocturnal habit and the peculiarities of structure resulting from 

 it. Points of more general interest with reference to these eccentric 

 forms are discussed elsewhere in this number. 



No attempt has been made to consult all the literature bearing on 

 this subject. Works which have been especially helpful are noticed 

 in connection with their respective topics. f 



*See J. A. Allen in " Monographs of North American Rodentia," Wash- 

 ington, 1877, P- 397- 



"("The following have been consulted for the general topography : 



Krause, W., " Die Anatomie des Kaninchens," Leipzig, [868. 



Steida, L, " Studien ueber dasCentrale Nervensystem der Voegel and Saeu- 

 gethiere." Zeits. f. wiss. Zoologie, Bd. XIX. 



Steida, L., "Studien ueber das Centrale Nervensystem der Wiebelthiere." 

 Zeits. f. wiss. Zoologie, Bd. XX. 



