236 CETACEA 
whalebone blades, and escapes through the lips, leaving the living 
prey to be swallowed.? 
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 (Balena) and Rorquals or Fin-Whales 
(Balenoptera), the latter distinguished by their smaller heads, 
elongated and slender form, free cervical vertebre, tetradactylous 
manus, 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. 
Balena.2—Skin of throat smooth, not furrowed. No dorsal fin. 
Cervical vertebra 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. 
Fic. 76.—Greenland or Arctic Right Whale (Balcena mysticetus). 
The Greenland, or more properly Arctic, Right Whale (Balena 
mysticetus) attains, when full grown, a length of from 45 to 50 
feet. Its usual vertebral formula is C 7, D 12, L 14, © 29. 
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. 
2 Linn. Syst. Nat. 12th ed. vol. i. p. 105 (1766). 
