166 blGH SCHOOL ZOOLOGY. . 



A considei'able proportion of the lengtli of tlie body in the 

 whalebone-wliales likewise belongs to the lioad. Tlie members 

 of this gi'oup attain the lai'gest size of any whales, some of 

 those with a dorsal fin (Phj/salus) measuring as much as one 

 hundred feet in length, while the right whales, which are the 

 chief objects of the whale fisheries, never measure more than 

 sixty feet. (Fig. 112.) 



Fig. 112.— Outline of Greenland Whale. (Dalcetiamyxticctufs.) ^},„ 



22. A third aberrant order, that of the Sirenia, have a 

 certain superficial resemblance to the Cetacea, which is associ- 

 ated with their aquatic mode of life, but they are not so com- 

 jtletely adapted thereto, being herbivorous forms, and thus 

 necessarily frequenting the shallow waters of the shore-zone for 

 sea-weeds, or ascending the estuaries of the great tropical rivers 

 and browsing upon the vegetation which fringes their banks. 

 The manatees (Mayiatus) of Western Tropical Africa, and of 

 Eastern South America, are, indeed, not completely helpless on 

 land, the fingers in the flippers are marked by short nails, and 

 in all the forms, the presence of a neck, the position of the 

 nostrils at the end of the muzzle,^ and the less rudimentary 

 character of the pelvis indicate less departure from the typical 

 mammalian form than is to be seen in the Cetacea. One of 

 the forms, the northern sea-cow, (Jihi/tina), exterminated little 

 more than a century ago, was previously abundant on the 

 shores of Siberia and Kamschatka. It was toothless, the 

 mouth being provided with four horny-toothed pads, which 

 served in place of the grinders of the living forms. The.se are 

 more numei'ous in the manatee, than in the dugongof the Indian 



