CASTORIDZ—CASTOR—CASTOR FIBER. 439 
differences, some of which are quite striking; and that the structure of the 
castor-sacs and the properties of their secretion also differ notably in the two 
forms. Some of the differences in the structure of the skull pointed out 
have less value than Dr. Brandt assigned to them, being variations of an 
inconstant and individual character, while those he relies upon as of more im- 
portance Dr. Ely shows are not so constant as Brandt, from the study of his 
small number of specimens, supposed them to be. There are few, if any, dif- 
ferences mentioned by Brandt as distinctively characterizing the European 
Beaver that cannot be found occasionally in the American. On this point, 
Dr. Ely remarks, that, through his large series of American skulls, he finds 
“that many more resemblances may be traced between the European and 
the American Beaver than he [Brandt] has observed, thus reducing the 
amount of constant differences between the two varieties”.* 
In respect to the superior aspect of the skull, Brandt says: 
“Tf we examine the skull of the European and of the American Beaver 
[from above], we notice the following special differences : 
“(1) The portion of the frontal bone lying between the arches of the 
eyebrows, in all the European skulls is shorter and broader, much broader 
than long; but in the American narrower and somewhat longer (quite as 
broad as long); so that the middle transverse diameter of the anterior portion 
of the frontal bone—that part lying between the eyes—is in the American 
skulls nearly or quite as long as the arch off the eyebrows; but in the Kuro- 
“pean it appears longer than this.” 
Dr. Ely says this is generally true of the American skulls, but he finds 
exceptions, in which the interorbital portion of the frontals is broader than 
long, a statement my own series of American skulls confirms. In six speci- 
mens, Dr. Ely found the average breadth to be 0.27 of an inch greater than 
the length. 
(2) In the European skulls,” says Brandt, ‘‘the arches of the eyebrows 
are shorter, and their posterior tubercles, opposite the highest point of the 
malar bone, are strongly developed. In the American, on the contrary, the 
posterior eyebrow processes (only indicated, sometimes scarcely indicated at 
all; or at least but slightly developed) can be seen back of the highest point 
of the malar. The anterior eyebrow process is in all the European skulls 
likewise stronger than in the American.” 
* Morgan’s “Beaver and his Works”, p. 290. 
