66 



BULLETIN 171, UNITED STATES NATIONAL MUSEUM 



columnar portion anterior to the fifth reentrant, counting forward 

 along the inner side of the tooth, is not so well developed in 0. annec- 

 tens as in 0. zibethica. Advanced wear in Mi of 0. zibethica may show 

 this column or loop to be without reentrants although well developed. 



In the description of 0. annedens Brown called attention to the 

 markedly reduced condition of the anteroexternal column of M3. 

 This column is not more reduced in the Cumberland Cave specimen 

 than in certain specimens of 0. zibethica. In Neqfiber this column is 

 greatly reduced. 



In both the Cumberland Cave and Conard Fissure jaws the surfaces 

 for the attachment of the masseter muscles are nearly alike but differ 

 slightly from those of the living species of Neqfiber and Ondatra. 



Figure Z6.— Ondatra cf. annedens (Brown): Left ramus of mandible (U.S.N.M. no. 12044), lateral and 

 occlusal views. X 2. Cumberland Cave Pleistocene, Maryland. 



The masseteric crest in general is bulging and sharply keeled, and there 

 is a well-defined groove marking the posterior margin of the area for 

 attachment of the anterior masseter medialis. The distinguishing 

 feature, however, lies in the position of this sulcus, Vvdiich in 0. annec- 

 tens has its origin much farther back from the anterior end of the mas- 

 seteric ridge from where it curves sharply upward, leaving a definitely 

 wider margin between it and the anterior border of the ascending 

 ramus. It is further noted in the Conard Fissure jaw that the shaft 

 leading to the condyle carries a fairly well developed sulcus on its 

 anterior face nearly as in Ondatra zibethica. Tliis sulcus is incipient 

 or absent in Neofiber. 



Table 21. — Measurements {in millimeters) of inferior dentition of Ondatra cf. 



annectens 



' Approximate. 



