AQUATIC MAMMALS 



to presume that the joint had lost at least a part of its original mobility. 

 As the antibrachium is essentially a mechanical part of the paddle the 

 tendency is for an increasing flattening of both bones, and for their 

 simplification, following the disappearance of functional antibrachial 

 musculature. 



The only bony details that might be ascribable to present or past mus- 

 cular stimulus is the olecranon. This was large and somewhat pinniped- 

 like in zeuglodonts, and to a lesser degree in Eurhmodelphis. It is 

 usually present in balaenopterids as a well defined process, which at 

 times is of large extent. Schulte (1916) has shown that in the fetal 

 state of at least one species this is truly of phenomenal size and as a 

 distinct bony arm, stretching somewhat distad, may be half the length 

 of the humerus (fig. 37). In Eubalaena it does not constitute a real 

 process, although there is some projection of the ulnar head as a sub- 

 stitute. Usually in odontocetes there is a slight process at this point, 

 but occasionally (as Platanista) in the sorts in which the antibrachium 

 is most reduced there is no indication whatever of an olecranon. 



The reason why the olecranon is of such enormous size in the fetal 

 balaenopterid is unknown, but it is only natural that at this stage it 

 should be larger than in the adult, in which the muscles of the lower 

 arm are so reduced. The muscles most intimately concerned with the 

 olecranon Schulte found to be a long and a short triceps head. He 

 further found as indubitably present flexores ulnaris, radialis, and com- 

 munis, and an extensor digitorum communis, as well as a ligamentous 

 band which he considered as representing the biceps. This is essentially 

 in accord with the findings of other investigators of balaenopterid mus- 

 culature, except that he failed to encounter a plamaris longus, as re- 

 ported by Carte and MacAlister, or a flexor sublimis as mentioned by 

 Perrin. The details of these muscles do not concern us in the present 

 connection. What is of interest is the fact that although they (except- 

 ing possibly the long triceps) are either entirely or virtually nonfunc- 

 tional, there are a number of them clearly present in the arm of mysti- 

 cetes, and this constitutes one of the chief items of evidence that this 

 group as a whole may be less highly specialized than odontocetes. 



Clearly recognizable fore arm musculature has often been reported in 

 the Odontoceti. For instance Schulte (1918) stated that in Kogza 

 there were triceps, extensor communis, flexores carpi ulnaris, digitorum 

 radialis and digitorum ulnaris, as well as interossei. In my own dis- 

 sections of Monodon and Neomeris, however, I failed to find any of 

 these as clearly recognizable muscle remnants. In the former there 



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