358 
U. S. 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 are 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 Sciurinae 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. 
Current numbers. 
Locality. 
Age and sex. 
Length. 
Width. 
Width of muzzle 
at base. 
Length of nasal. 
Collected by— 
2146 
Cheyenne river, Nebraska 
9 
5.80 
4. 16 
1. 54 
2. 00 
Dr. Hayden._ 
2377 
TJpper Missouri 
5. 53 
4. 04 
1. 40 
2. 00 
do . _ _ _ 
2378 
5. 38 
3. 90 
1. 36 
1. 84 
1003 
Rio Grande, Texas_ 
$ 
3. 86 
1. 30 
1. 87 
J. H. Clark. 
1414 
Matamoras._ 
5. 32 
3. 96 
1. 36 
1.80 
Lieut. Couch_ 
1416 
5.30 . 
3. 82 
1. 70 
2031 
Washington Territory_ 
5. 23 
3. 37 
1.12 
1. 81 
Dr. Cooper.__ 
823 
Upper Missouri- _ 
5.17 
3. 70 
1.12 
1.70 
T. Culbertson___ 
2376 
.do. 
4. 82 
3. 48 
1.10 
1.70 
Dr. Hayden ___.... 
2380 
_do_ 
4. 73 
3. 50 
1. 60 
2144 
__do _ _ 
$ 
4. 67 
3. 40 
1.10 
1. 62 
2270 
Lake Superior_*___ 
4. 60 
1. 58 
Dr. Newberry. _.... 
2145 
Upper Missouri _ _ _ ____ 
4. 59 
3. 25 
1. 50 
Dr. Hayden __... 
2143 
do 
4. 50 
3. 29 
1.10 
1. 50 
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 B. 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 
