52 THE AMERICAN BEAVER. 



vertebrae have large transverse processes. The sa- 

 crum is straight, the first bone being somewhat prom- 

 inent anteriorly. The caudal vertebrae gradually 

 diminish in size and lose their vertebral characters. 

 In the sixth, the posterior lateral articulating surfaces 

 disappear, and the spinal canal in the tenth becomes 

 a mere groove. The spinous processes also disappear 

 in the eighth or ninth. The transverse processes are 

 long, broad, and toward the end of the tail are bifid 

 or double. The lateral foramina, which begin in the 

 sacrum at the posterior edge of the transverse pro- 

 cesses, continue to the sixth caudal. 



The ribs are slender, rounded, in 14 pairs. Seven 

 are articulated by cartilage with the sternum. The 

 cartilages of the 8th and 9th are connected with the 

 costal cartilages. The remaining ribs are tipped with 

 free cartilage. 



The sternum is composed of five narrow slender 

 bones; the first and fourth are the broadest. Theensi- 

 form cartilage expands into a broad flat disk. Length 

 of sternum and ensiform cartilage, 6". The clavicles 

 are strong, 2" 16'" in length. The scapula is 3" 25'" 

 long, and 1" 50'" broad. Its spine is prominent, and 

 the acromion is 1" 18'" in length. 



The humerus is 3" long; its body is triangular and 

 compressed; the tubercle at the head is large; about 

 the middle of the bone anteriorly is a large tubercle 

 for the insertion of the deltoid muscle; the lower end 

 is broad, thin, not perforated; the external condyle 

 spreads out to a thin convex edge which passes up 

 the middle of the posterior surface of the bone. 



The radius is slender, and lies close to the ulna in 

 its whole length. The olecranon is 94'" long, and the 



