236 . CETACEA 



whalebone blades, and escapes through the lips, leaving the living 

 prey to be swallowed. 1 



Our knowledge of the different structural modifications attained 

 by members of this important group of mammals, though largely 

 increased of late years, is still imperfect. Formerly they were all 

 divided into Right Whales (Balcena) and Rorquals or Fin-Whales 

 (Balcenoptera), the latter distinguished by their smaller heads, 

 elongated and slender form, free cervical vertebrae, tetradactylous 

 maims, and the presence of very conspicuous longitudinal furrows or 

 folds in the skin of the throat and chest, and of a small adipose 

 dorsal fin. Recent discoveries have, however, brought to light 

 several forms holding a somewhat intermediate position, and pre- 

 senting combinations of characters not found in either of the longer 

 known sections. According to our present knowledge the group is 

 naturally divided into five very distinct genera, of which the leading 

 characters are given below. 



Balcena. 2 Skin of throat smooth, not furrowed. No dorsal fin. 

 Cervical vertebras united into a single mass. Pectoral limb short, 

 broad, and pentadactylous. Head very large. Baleen very long 

 and narrow, highly elastic, and black. Scapula high, with a distinct 

 coracoid and acromion process. Tympanic (Fig. 78) deep and angular, 

 its inflation comparatively slight, and the involuted portion not fig- 

 shaped, and frequently without a well-marked depression at the 

 anterior extremity of the superior border of the inner surface for 

 the Eustachian canal. 



FIG. 76. Greenland or Arctic Right Whale (Balcena mysticetus). 



The Greenland, or more properly Arctic, Right Whale (Balcena 

 mysticetus) attains, when full grown, a length of from 45 to 50 

 feet. Its usual vertebral formula is C 7, D 12, L 14, C 22. 

 The external form is shown in Fig. 76 from a careful drawing by 



1 For the structure of whalebone see Hunter, "Observations on the Structure 

 and Economy of Whales," Phil. Trans. 1787 ; Eschricht and Reinhardt, On the 

 Greenland Right Whale, English translation by the Ray Society, 1866, pp. 67-78 ; 

 and Sir W. Turner, in Trans. Roy. Soc. Edin. 1870. 



- Linn. Syst. Nat. 12th ed. vol. i. p. 105 (1766). 



