ANATOMY OF THE BEAVER. 63 



condyles opposite their middle. The lateral foramina 

 in the vertical portion of the occipital are closed in 

 the recent subject by membrane. 



Wormian bones are occasionally but not commonly 

 found in the sutures. Sometimes a rounded mass of 

 bone is imbedd-ed in the larger mastoid process.^ 



The lower jaw is very massive (Plate V.) . The two 

 parts are joined in front by a long and broad sym- 

 physis, forming below a pointed process. Its poste- 

 rior angle is flattened into a broad process, hollowed 

 within and tipped with a broad long crest — this part 

 extends farther back than the condyle — at the root 

 of the condyle on the outer side is a depression; 

 above this the coronoid process arises and is pointed 

 backward. The anterior line of the process passes 

 downward and forward, the crest terminating at the 

 extremity of the root of the first molar. The con- 

 dyle is quadrangular, rounded, and is nearer the coro- 

 noid process than the posterior crest. The foramina 

 for the nutrient vessels, etc. is behind the molars and 

 higher than their crown surfaces; the mental foramen 

 is below the anterior face of the first molar. 



THE TEETH. 



The character of the Rodentia as a natural order 

 is made to depend upon a peculiar kind of cutting or 

 incisive teeth, which are separated from the grindino- 

 or molar teeth by an empty space, the canine teeth 

 being wanting. The teeth of animals bear a defin- 

 ite relation to their mode of subsistence, and from 



^ For measurements of the skull, and differences in the European 

 and the American beaver, see Appendix A. 



