THE TRUNK 



precisely the same force is unknown. If there be some inequality in- 

 volved, then this must be compensated for by tilting of the flippers. Be- 

 yond question, however, there is a tendency for perfect equalization, 



Figure 31. Sterna of whales and sirenians: (a) Balaena and (f) young dugong 

 (Halicore) (both redrawn from Flower) ; (b) Sibbaldus and {d) Balaenop- 

 tera borealis (both from specimens in the U. S. National Museum) ; and 

 {e) young narwhal {Monodon) (from a photograph in the American 

 Museum of Natural History). 



which presumably has been accomplished as fully as the muscular con- 

 formation will allow. In respect to the latter point, the hypaxial muscles 

 continue robustly only to the last rib, and thence disappear within two or 



[181] 



