490 



ANATOMY OF VERTEBRATES. 



anterior dorsal vertebras have a hypapophysial riclge, which, in 

 the latter, is produced into a tuberosity : the lumbar vertebrae 

 are characterized by a pair of hypapophyses from near the hinder 

 end of the centrum. The eared Seals have the same vertebral 

 formula : the anterior sacral vertebrae are narrow. 



The Walrus ( Trichecus Rosmarus), like the Otter, has 14 

 dorsal and 6 lumbar vertebras. Nine pairs of ribs directly join the 

 sternum, which consists of eight bones. The anterior sacrals 

 have o^reater relative breadth than in Phoca or Otaria : as in 

 true Seals the tail is short, with 9 or 10 vertebrae. 



In the Bear-tribe, as in the Seal-tribe, the number of true 

 vertebrae is 27, as a rule, and 14 of these usually bear movable 



336 



Polar Bear {Ursus maritimus). Lxxiii- 



ribs; but I have seen 15 ^ dorsal ' vertebrae in Ursus maritimus, 

 fig. 333, and in U. lahiatus, the latter having 5 lumbar instead of 

 6, which is the common number. Nine pairs of ribs articulate 

 directly mth the sternum, which consists of eight bones, mth a 

 xiphoid appendage. The manubrium is truncate anteriorly. The 

 number of anchylosed sacral vertebrae may vary from 5 to 7, that 

 of the caudal vertebrae rarely exceeds 10. The met- and an- 

 apophyses are distinct on the twelfth dorsal, diverge and increase 

 on the succeeding dorsals, the metapophyses continuing throughout 

 the lumbar series ; the anapophyses, after underlapping the pro- 

 zygapophyses of the first and second lumbar, rapidly subside. 

 The neural spines are better developed than in the Seal-tribe, 



