358 



U. 8. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



acute angle between the second molars, (first true molars.) The palatal foramina are situated 

 on either side the point of the palatines, their posterior extremity reaching to between the 

 second and third molars. These foramina are situated each in a narrow groove, separated by a 

 ridge which traverses the entire bony palate from the incisive foramen to its posterior acute 

 azygos process. The palate between the molars is considerably cribriform. 



The ante-orbital foramen is not visible at all from the side. It is hidden from view by a broad 

 plate projecting forward from the anterior edge of the maxillary ; it is quite small and verti 

 cally elongated, and gives passage to no muscle. It is entirely separated from the zygomatic 

 arch, being far forward of it. 



The lines of the upper molars are decidedly convergent, and aie nearly tangent with the 

 side of the incisors. The palate is much hollowed out between the incisors and the molars, in 

 this respect differing more from the Sdurinae than in other points. The inner side of the upper 

 molars exhibits one groove, the outer three ; this being reversed in the lower jaw, except in the 

 anterior molar, which shows four grooves on the inner side. The anterior molars, in both 

 jaws, are largest, the rest diminishing backwards very gradually ; the anterior lower molar is, 

 however, longer, proportionally, than the corresponding upper one, and the lower line of 

 molars exceeds considerably the upper. 



The following table will illustrate the absolute dimensions of the skull of the American 

 beaver : 



Measurements of skulls. 



The European and American beaver, though apparently very similar, may (as stated by 

 Cuvier in Ossemens Fossiles, VIII, 112, and by Owen, British Fossil Mammals and Birds, 196; 

 Catal. Osteol. Series R. Coll. Surgeons, 1853, II, No. 2162) be always distinguished by the 

 position of the posterior extremities of the nasal bone. In the Old World species the transverse 

 line touching the point of the nasal bones intersects the orbits behind their middle part, while in 



