MOUTH AND NOSE 



It will be noted that as with terrestrial mammals with tusks, as well 

 as in the case of the majority of mammals bearing antlers or horns, 

 these develop to a considerably greater size in the male. The claim is 

 usually made that this is for the reason that the males may more effec- 

 tively do battle with one another for the females, but this natural 

 selection resulting is likely only secondary. Rather does it seem that 

 the male sex hormone almost invariably stimulates excessive growth of 

 tusks, horns, or other excrescences of a secondary sexual character to a 

 far greater degree than does that of the female, just as it frequently 

 stimulates growth of body in the male. But this is an uncultivated 

 field and I believe there are those who claim that there is no such 

 stimulus in the male, but rather an inhibitional factor in the female. 



Of a somewhat different sort is the development of the large teeth 

 of the hippopotamus, for these are equally developed in both sexes, 

 but overspecialization is indicated here as well. The size of the teeth 

 has evidently kept pace with size of jaw and the result is that the 

 front teeth are so large and unhandily placed that they can serve but 

 little useful purpose and seem detrimental. 



There is much dental variation among the toothed whales. The 

 teeth are usually simply conical and attenuate, but the crowns may be 

 chisel-shaped (Neomaris, Phocaena) and the tusks of the ziphioid 

 whales are at times curiously flattened and twisted. There may be well 

 over 200 teeth present (Eurhinodelphis, Steno del phis), but two, situ- 

 ated in the mandible (some ziphioids), or a single large tusk (Mono- 

 don). So far as known, however, nonfunctional back teeth are always 

 present in the fetal state at least. The teeth of living odontocetes are 

 always of a single or homodont pattern never heterodont and this, 

 as well as the enormous increase in the number of the teeth of some forms 

 over the normal mammalian complement has given rise to endless dis- 

 cussion. To account for the latter condition there was first advanced 

 the theory of the intercalation of milk teeth into the series, but this 

 was abandoned when Kukenthal discovered indications of tooth suc- 

 cession in embryos; and at any rate this theory could not account for 

 the great number of teeth occurring in some sorts. Abel has argued 

 strongly that the original teeth were split up into numerous simpler 

 units ; but this theory is unsupported by any good evidence and is viewed 

 none too favorably by many. In fine, we know absolutely nothing about 

 the matter. There is not always perfect alternation of upper and lower 

 teeth in the closed jaws, and the smaller teeth near the jaw tips are often 

 crowded and insecurely attached, indicating that if the jaws become 



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