NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 4I 



of the opposite side, leaning inward over the intermaxillary and 

 mesethmoid so as to turn a broad shock-receiving surface forward. 

 The nares and middle part of the occipital wall are forced unusually 

 far backward toward the posterior boundary of the braincase. 



The most primitive genus of the group is " Berardius." The 

 longitudinal crest on the upper surface of the maxillary is well 

 developed and erect, but the face, however, has retained essentially 

 its ordinary form. At the front of the lower jaw are found two 

 rather well-developed teeth. 



In Hypcroodon the face becomes with age wholly abnormal, since 

 the longitudinal crest on the maxillary elevates itself to a height 

 which exceeds even the highest part of the occipital wall. In the 

 lower jaw at the front is found only a single tooth (apart from 

 embryonic conditions). 



The genera of the section Physeterini must have originated among 

 the most primitive Xiphiines, from Xiphiines in which the dentition 

 was still rather well developed, with teeth in the intermaxillary as 

 well as the maxillary ; in which the intermaxillaries were free from 

 each other and from the surrounding bones ; in which the mesethmoid 

 was not ossified, etc. Their peculiarity is that the pressure of the 

 facial cushion on its surroundings acts differently than in the 

 Xiphiines, and even more strongly. The facial cushion, especially 

 that part of it which is formed by the adipose mass, widens out still 

 more, particularly outside of and behind the nasal passages. It 

 pushes the median part of the occipital wall far back behind the 

 nares, while at the same time the margins of the facial depression, at 

 the back and at the sides, grow high upward. The bones which form 

 the bottom of the facial cushion's bed are strongly acted upon by the 

 stimulating mass of the cushion. They widen out. This holds good 

 especially of the bones in the rostrum, and chiefly of the anterior 

 part of the maxillary. The lower jaw on the contrary retains its 

 primitive narrowness. 



The genera of the group Hoploceti are extinct, Tertiary, and are 

 only incompletely known, chiefly from fragments of skulls. It may 

 be concluded that the skull in essential respects is modified in the 

 same manner as in the highest group of Physeterids, the Physeteres, 

 but to a distinctly less noticeable degree. They are also less advanced 

 than the Physeteres in the development of the dentition, there being 

 a long row of well-developed teeth in both upper and lower jaws, 

 while the upper teeth of the Physeteres have atrophied. 



