24 A BOOK OP WHALES 



HIND LIMB 



Traces of a hind limb have been found in many 

 whales ; it is possibly represented in all ; but it has 

 not been discovered in a good many. Of all whales, 

 whose structure is known best, the hind limb is less 

 reduced in Balcena mysticetiis. This is rather a 

 curious fact in view of the usual opinion that the 

 Right whale, and indeed the whalebone whales 

 generally, are the most modified of existing Cetacea. 

 Nevertheless in that whale there is a single bone 

 representing the pelvis, and there are in addition 

 small pieces of a bone or cartilage, which correspond 

 respectively to the femur and to the tibia. The 

 femur is ossified is some 4 to 9 inches in length. 

 The tibia is only cartilaginous. In the rorquals 

 there is an instructive series of stages in the reduc- 

 tion of the hind limb. In Bal&noptera musculus the 

 femur is represented by a spherical bony nodule, first 

 discovered by Sir William Flower ; in B. borealis and 

 B. rostrata no traces of a femur appear to exist. 

 The actual limb itself does not appear to be repre- 

 sented in the toothed whales. 



It is the general view that the curved bone, which 

 is all that is left of the actual pelvis, is the homologue 

 of only one of the three bones, out of which each 

 half of the pelvis is formed in terrestrial mammals. 

 It is considered to be the equivalent of the ischium, 

 mainly on account of certain muscles which are 

 attached to it. Added to this, stress has been laid 

 on the fact that it ossifies from one centre only and 



