42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



In the European and American Hoplocetus {Balcenodon, Physodon, 

 " Scaldicetus," etc.) the teeth are covered with enamel. 



The European Physcterula has lost the enamel, it appears. 



In the genera of the group Physeteres the influence of the facial 

 cushion on the skull has led to fantastic results. The dentition also 

 is modified in a strange manner. In the lower jaw the teeth continue 

 to be well developed ; but in the upper jaw they atrophy and dis- 

 appear either wholly or essentially so. It is not clear what the reason 

 can be for this difference between the upper and lower jaws. Per- 

 haps the difiference is connected with the great lateral broadening 

 out of the maxillary whereby the upper toothrows are so pushed 

 outward that they lose their interaction with the lower toothrows 

 which retain their ancestral position in the closely appressed mandi- 

 bular rami. There has been no hard work for the upper teeth which 

 might have maintained them in spite of all ; the lower teeth together 

 with the palate must have proved sufficient, as the task is indeed 

 scarcely anything else than to grasp the cuttlefish which appear to be 

 the favorite food for this whole family as well as for various other 

 cetaceans, especially for those with more or less degenerate dentition. 



" Cogia " is in some respects the most primitive of the genera. In 

 the upper jaw there is still found, or may be found, a tolerably well- 

 developed tooth. In the skull there remains a rather considerable, 

 curved remnant (although very narrow and compressed) of the 

 heightened osseous ridge which elsewhere in the toothed whales lies 

 between the nares and the occipital wall ; the adipose cushion has not 

 yet wholly destroyed it. Neither has the cushion so grown around 

 the outer nasal passage that it has pushed the orifice away from its 

 accustomed place, nor has it to any noticeable degree pressed the roof 

 of the braincase down. The anterior part of the face has become 

 broader than usual, but it is still rather short, or, more strictly 

 speaking, has been further shortened. On the other hand the lateral 

 margin of the facial depression, over the braincase, is pushed unus- 

 ually far out to the side and raised conspicuously high upward ; it 

 has also acquired a vmique thickness. 



In Physeter nothing has remained of the upper teeth except small 

 vestiges hidden in the skin. The fat-cushion, which has grown 

 gigantically, has caused the bones of the rostrum to grow far forward 

 and to broaden themselves strongly at the side. The posterior margin 

 of the facial depression is more abruptly elevated than in any other 

 whale and is pushed further back. The fat-cushion has completely 

 overgrown and leveled oflf the bony wall which elsewhere lies be- 



