CASTOROLOGIA. l8l 



with the use of the cutting teeth, located here, but also those which 

 give the lateral or grinding motion necessary for the mastication of 

 the tough bark and vegetable substances. The muscles of the whole 

 system are powerfully developed and their attachment to the skin is 

 so firm that only an experienced hand can remove the skin without 

 leaving great layers of muscle adhering to it. The neck, the tail, 

 and the limbs are each provided with muscles, strong in proportion 

 to the unusual amount of work to be accomplished by these 

 members. 



Of the internal organs so many are peculiar to the beaver, that 

 naturalists are continually disagreeing as to the strict classification of 

 the genus. The cavity of the mouth and the cheeks shows a pecu- 

 har provision for the work the creature is destined to do. The ar- 

 rangement is such that when the incisors only are being used, the 

 tender mucous membrane of the mouth is completely protected from 

 the rough splinters of wood, etc., which might otherwise injure 

 these delicate parts. The space between the incisors and the molar 

 teeth is very narrow and is covered with a hard, dark-colored skin, 

 while the cheeks are furnished with a lining of coarse hairs, suflS- 

 ciently long to prevent any particle of the chip passing, which would 

 injure the tender palate, tongue or cheeks. 



The stomach of the beaver is similar in most respects to those of 

 the other members of the order Rodentia, yet has some minor pecu- 

 liarities. The coecum (corresponding to the vermiform appendage 

 in man) is, in the beaver, larger than its stomach, for while the lat- 

 ter holds but little over three pints, the capacity of the former is 

 nearly six pints. 



In the beaver, as in all diving mammals and birds, a provision 

 exists for suspended respiration. It is an enlargement of the 

 inferior vena cava as it passes through the fissure of the liver, 

 and constitutes a sinus in which a considerable quantity of blood 

 may be temporarily arrested. This discovery was communicated 

 to the Wernerian Society of Edinburgh, by Mr. R. Knox, in the 

 year 1823. 



