344 FOUR-FINGERED WHALES chap. 



The pectoral fin of Whales exists in two forms. In the 

 Toothed Whales it is shorter and rounder ; in the Whalebone 

 ^\^hales longer and narrower. Structural differences accompany 

 these outward dissimilarities. In the first -named group the 

 humerus and the beginning of the radius and ulna are within the 

 body, and do not form a part of the fin. In the Whalebone 

 Whales, on the other hand, the fin contains all the bones of the 

 fore -limb. Another remarkable contrast between the hand in 

 the two groups of Whales is that while the Toothed Wliales have 

 five fingers, thus justifying the prevailing opinion that they are 

 the more primitive of the two groups, the ^Vhaleboue Whales have 

 only four fingers. Actually the Eight Whale, Balaena, seems to 

 have five fingers ; and, indeed, the fact that it has, is often used to 

 distinguish it from the Humpback, which has undoidDtedly only four. 

 But a careful consideration of the state of affairs which prevails in 

 the foetus of Balaenoptera dispels this idea. Between what are 

 apparently the second and third fingers, a rudimentary finger, 

 consisting of four phalanges, appears. This is not produced, as is 

 an additional finger found in the White Whale or Beluga, by a 

 splitting of a finger. Accordingly the four-fingered condition of 

 the A^^ialebone Whales is produced by the dropping out of a finger 

 in the middle of the series, — a very remarkable fact. When 

 fingers disappear, as, for intsance, in the Horse, etc., it is at the 

 two ends of the series that the digits vanish. If this view of 

 Professor Kiikenthal's ^ be accepted, it follows that the pre- 

 sumed thumb of the Eight AVhale is what has been termed the 

 prepollex. 



The hand of the Whales, like those of some other aquatic 

 creatures, e.g. the reptile Ichthyosaurus, has a larger number of 

 phalanges than have terrestrial animals. The result of this is, 

 of course, to increase the length of the fin and its utility as a 

 paddle. It is commonly not all the fingers that have developed 

 this great number of accessory phalanges. Eudimentary nails 

 have been found upon the Cetacean hand ; but in no case are 

 they functionally developed. In the Manatees we have the 

 disappearance of the nails still imperfectly accomplished. In 

 M. latirostris there are nails ; these have vanished, apart from 

 possible traces to be seen with a microscope, in M. immguis. 



A very characteristic feature of certain A^'hales are the furrows 



' Vergleichend-anatniiiische Untersuchungen an Wallhierc, Jena, 1889-93. 



