358 U. & 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 Sciwrinae 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. 
=e ; | 2 = 
z Locality. a A - sa Collected by— 
E 2 =] BS BS) q 
5 4 A EF | E 4 
2146 | Cheyenne river, Nebraska ---- Q 5. 80 4.16 1.54 2.00 Drs Hayden... <> eee 
2377 «| Upper. Missouri-_.-..-=---+--|-----==< BABS wll Ad04, slp Oe gl 200 es dO .u22 00a 
2am Neo aon a eee ae eos Pere 5. 38 3.90 1. 36 Pee aeeaas d0.:.--22cSaeee eee 
1003 | Rio Grande, Texas---.-.------ rol 5. 38 3. 86 1. 30 1. 87 ok A. ‘Clark J 226 2soe ene 
PAG Matamoras= 9-0 esss Seen |e geen = 5. 32 3. 96 1. 36 1. 80 Lieut. Couch.2. -- 22222 ee Seee 
1016 4, 02-2. rat hdd ot Be RM Lies ae Ua Ne iy a Lor pies ee do. 2.6. ee 
2031 | Washington Territory-.-.----|-------- 623°" S58% | 1512 —| se. |" Dm Cooper: 2a 
Bis seo pper Mikconrins. == =e e eee == 5.17 3.70 1.12 1.70 T. Culbertson -22 2-25 soeeeee 
CE eee ieee eee eae 4, 82 3. 48 1.10 1.70 Dr, Hayden. .- 22 <soeeeeee 
{i Eee (PASS Snes SES ae Bea 4.73 ha) a See ss UES Da Hepa d0-- <. -- = se= eee 
YY Ue ee G6 Soiccwsunnoss seesce fof 4, 67 3. 40 1.10 A. G2") |teoenen 0. -- 4 =. 22See eee 
Beno) | bake Siperior 2s 5. so-o6. sa|eancoes- 4:60) |C. S2-—e| eee 1. 58 Dr: Newberty..-s~aeeeeeeeee 
D145) 4) Upper Migsouri->-<=-------=-|-----.- 4.59 Sy2b) We sees 1.50 Dr. Hayden....¢5-555-5-—- ee 
7A 7. Ss TY CORE ae ea ee eee eet 4,50 3. 29 1.10 B00) | Vee ae Cee ee 
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 
