56 THE AMERICAN BEAVER. 



THE SKULL.^ 



The skull of the beaver exceeds that of other ro- 

 dents in solidity and strength. It is much elongated, 

 its length being more than twice and a half its height. 

 Its upper line is nearly plane; a parallel line below 

 touches the condyle, the palatal bone, and the point of 

 the incisive septum. The principal surface of the 

 occipital bone is vertical to this line. The molars 

 occupy the middle of the skull, being separated by an 

 arched space from the incisors. Viewed from above, 

 the skull presents quite a different outline, the width 

 being about two- fifths of the length. These propor- 

 tions are shown in the lateral and the top views of the 

 skull (Plate IV.). 



The nasal bones occupy one-third of the length of 

 the skull; are broadest anteriorly, and at their junc- 

 tion in front form an obt>use point. Their outer 

 margin is a convex curve, where they are joined to 

 the intermaxillaries. Their posterior extremities and 

 those of the intermaxillaries join the frontal on a line 

 with the anterior orbital tubercles of that bone. The 

 intermaxillaries are very strong. A nearly vertical 

 suture connects them with the superior maxillary; a 

 little more than half of the sheath of the incisors is 

 formed by them. The lateral and lower part of the 

 nasal opening in front, which has the form of the 



1 References to figures of the skull, Plates IT. and Y. : 



1. Nasal bone. 6. Occipital. 11. Lachrymal. 



2. Intermaxillary. 7. Temporal. 12. Palatal. 



3. Frontal. 8. Malar. 13. Pre-sphenoid. 



4. Parietal. 9. Tympanic. 14. Post-sphenoid. 



5. Interparietal. 10. Superior maxillary. 15. Ethmoid. 



