CASTORID^E— 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: 

 "If 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 of the eyebrows; but in the Euro- 

 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 ami his Works", p. 290. 



