10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. "^6 



postero-external angle of the plate to a point distinctly above the 

 antorbital foramen. To develop the baleen whale type from a start- 

 ing point at which the structure resembled that which is now present 

 in the furseal or sea-lion it is merely necessary to suppose that the 

 pressing together of the orbital plate of the maxillary and the ex- 

 panding postorbital process of the frontal may have forced the jugal 

 bone to abandon its connection with all of the " malar process " of 

 the maxillary except the lowest, most posterior portion. The develop- 

 ment of the toothed cetacean type from a starting point resembling 

 the fox structure might equally well be conceived as primarily the 

 result of degeneration of the orbital plate accompanying complete 

 elimination of the large teeth to which, in the fox, this plate is 

 intimately adjusted.' In the fox the heaviest, widest teeth lie behind 

 the level of the antorbital foramen; but in no modern cetacean are 

 any functional teeth whatever known to occur in this region. With 

 the elimination of the posterior teeth and the subsequent degeneration 

 of the orbital plate in a maxillary resembling that of a fox the pos- 

 terior portion of the malar process might be expected gradually to 

 disappear, thus cutting away or shriveling up the area of connection 

 for the jugal bone with the maxillary until this area became restricted 

 to the highest, most anterior part of its original extent. The dif- 

 ferences just described as distinguishing the maxillary of the fox 

 from that of the furseal or sea-lion may be at least partly connected 

 with the relatively very different size of the eye in the two animals. 

 The wide, horizontal orbital plate of the seal and sea-lion acts as a 

 support to the enlarged eye while the narrow oblique plate of the 

 fox meets all the requirements of a normal eye. The orbital plate's 

 persistence in one suborder of modern cetaceans and its absence in 

 the other may therefore point, perhaps, to a difference in the history 

 of the eye in the two groups." 



The foregoing comparison between cetacean structures and the 

 conditions found in living pinnipeds and carnivores must not be 

 misinterpreted as implying an idea of immediate affinity among any 

 of the animals in question ; each group appears to have had its own 

 independent history. I do not know of any reason to suppose that a 



^ In the actual ancestors the plate was almost certainly not developed to 

 the extent that it is in the fox ; this does not lessen the value of the fox as a 

 convenient illustration of the general mechanical course of the process. 



' Putter has recorded various peculiarities of the eye and its accessory 

 structures which appear to have this meaning (Zool. Jahrb., Anat., Vol. 17, 

 pp. 99-402, Nov. 10, 1902). 



