DR. W. W. ELY S NOTES ON CHAPTER II. 



501 



and the forms of the sacs which it covers are recognized'. The 

 surface of this muscle next to the sacs is smooth and but slightly 

 attached to them : with the underlying muscles it forms an en- 

 velope capable of compressing these sacs so as to expel their con- 

 tents. The name given to these organs, in view of their supposed 

 analogies, is preputial glands, though by Cuvier and others this 

 term is applied to the lower sacs. I shall call the upper, the cas- 

 toreum sacs, and the lower, oil sacs. By the trappers they are 

 called the bark stone, and the oil stone. 



Fig. 1. 



Drawn by W. W. Ely. 

 Note to Figure 1. 



1. Muscle covering pubis. 5. Oil sacs. 



2. Testicles. 



3. Penis. 



4. Castoreum sacs. 



6. Upper half of cloacal orifice. 



7. Endofrectum within the cloacal 

 orifice. 



Figs. 1 and 2 exhibit these organs in a male and a female beaver, 

 the latter being a small-sized animal, weighing 29^ lbs. The cas- 

 toreum sacs, nearest the pubis, are oval, flattened, of a light color 

 like parchment, and communicate freely with each other by their 

 transverse portion. Linear marks and depressions on their sur- 

 faces correspond with membranous duplicatures within, which 

 add largely to the internal surface, forming septa and cells cov- 

 ered and filled with castoreum. The larger folds have a general 

 direction towards the outlet of the sacs. The sacs arc formed Oi 



