THE EXTERNAL FORM OF WHALES 17 



whales, with which we are concerned in the present 

 chapter, with a brief account of the essential like- 

 nesses and the essential unlikenesses between the 

 fins of fishes and the limbs of higher vertebrates. 



The fins of fishes consist of a number of cartila- 

 ginous pieces arranged in rows of which the proximal 

 one to four are larger than the rest, and articulate 

 with the shoulder girdle or the pelvic girdle as the 

 case may be. The cartilaginous, or bony pieces, are 

 continued on at their ends by the horny fin rays 

 which extend to the end of the fin. 



The number and arrangements of these various 

 cartilages or bones is naturally subject to some 

 differences in different fishes. It is not our object, 

 however, here to do more than to call attention to 

 the essential features in which the fins of fishes differ 

 from the limbs of the vertebrates which lie higher in 

 the scale. The fish fin is termed the " Ichthyop- 

 terygium " to distinguish it from the limbs of all 

 vertebrates higher than fishes which possess what 

 is called the " Cheiropterygium." The actual facts 

 of difference are these : 



The cheiropterygium, or hand-like limb, always 

 consists of a proximal bone, the humerus or femur, 

 which alone articulates with the shoulder crirdle or 



o 



pelvic girdle ; this is followed by two bones, the 

 radius and ulna (in the hind limb the tibia and fibula); 

 after this follows the carpus or tarsus, composed of 

 a varying number of small bones or cartilages ; then 

 follow the fingers or toes, composed of a varying 

 number of bones there are never more than five 



