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 
Whales 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 Whales have 
five fingers, thus justifying the prevailing opinion that they are 
the more primitive of the two groups, the Whalebone Whales have 
only four fingers. Actually the Right 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 undoubtedly 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 Whalebone 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, ete., 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 Right Whale is what has been termed the 
prepollex. 
The hand of the Whales, like those of some other aquatic 
creatures, e.g. the reptile Jchthyosaurus, 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. Rudimentary 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 JZ inunguis. 
A very characteristic feature of certain Whales are the furrows 
1 Vergleichend-anatomische Untersuchungen an Walthiere, Jena, 1889-93. 
