576 MANUAL OF ZOOLOGY. 



The only common British Seal is the Phoca vituUna, which 

 occurs not uncommonly on the northern shores of Scotland. 

 It is yellowish-grey in colour, and measures from three to five 

 feet in length. Other Seals attain a much greater length— the 

 Great Seal measuring from eight to ten feet, and the Bottle- 

 nosed Seal reaching a length of from twenty to twenty-five feet. 

 The only Seals which possess external ears constitute the genus 

 Otaria, and are almost exclusively confined to the seas of the 

 southern hemisphere. 



The second family of the Pinnigrade Carnivores is that of 

 the Trkheddm, comprising only the Walrus or Morse {Trkk- 

 ecus rosmarus). The chief peculiarity by which the Walrus is 



Fig. aas. — Skull of the Walrus tj'richecia rosmarus (after Owen): 

 i TiUsMike upper incisors. 



distinguished from the true Seals is found in the dentition. 

 According to Owen, there are six incisors in the upper jaw 

 and four in the lower; but these are only present in the young 

 animal, and soon disappear, with the exception of the outer-' 

 most pair of upper incisors. The upper canines are enor- 

 mously developed, growing from persistent pulps, and consti- 

 tuting two large pointed tusks, which attain a length of over 

 fifteen inches (fig. 225). The direction of the tusks is down- 

 wards and slightly outwards, and they project considerably 

 below the chin. The adult animal has usually three simple 



