NO. 5 TELESCOPING OF THE CETACEAN SKULL 35 



BEHAVIOR OF THE MODERN CETACEAN SKULL 



Having now reviewed the details of the results accomplished by the 

 process of telescoping it becomes possible to conjecture something as 

 to the probable behavior of the skull while undergoing its modifica- 

 tions. Telescoping of the braincase and basining of the forehead ap- 

 pear to have been mechanical necessities in the development of the 

 modern cetacean skull. These processes have followed two courses, 

 which may be most readily understood by examining the structure of 

 the proximal portion of the maxillary bone (pp. 9-10, pis. 3-4). In 

 the baleen whales the maxillary is seen to have retained the orbital 

 portion of its body, while the ascending process has interlocked with 

 the body of the frontal. Basining appears thus to have been inter- 

 fered with, and telescoping appears to have been made less feasible 

 from before than from behind. In the toothed cetacea the maxillary 

 has lost the orbital portion of its body, while the ascending process 

 has slipped freely over almost the entire frontal. Basining seems 

 thus to have been favo"ed, and telescoping from the front seems to 

 have been rendered more feasible than telescoping from the rear. 

 The opposite interpretation should be considered, namely, that the 

 orbital portion of the maxillary might have been destroyed in the 

 toothed cetacea by an especially strong tendency to basining in the 

 members of this group, arising, perhaps, in connection with the de- 

 velopment of the facial fat mass, and that in the baleen whales the 

 orbital portion might have been permitted to remain, partly because 

 the facial fat mass did not develop, and partly because the tendency 

 toward telescoping from behind was for some unknown reason more 

 pronounced than that toward modification from in front. While 

 it is probably true that the mechanical forces to which the skull has 

 been subjected have not been exactly alike in the members of the two 

 groups, such dififerences as can be discovered do not appear to be 

 sufficient, either in degree or in kind, to have been solely responsible 

 for marking out and maintaining two entirely distinct courses of 

 modification. Furthermore we find that the orbital portion of the 

 maxillary is as completely absent in those toothed cetaceans whose 

 skulls are practically not basined at all {Stcnodclphis, for instance, 

 pi. 7, fig. 2) as it is in those which show the basining process highly 

 developed {Mesoplodon, pi. 5, fig. 5 ; Physeter, pi. 6, fig. i ; Kogia, 

 pi. 7, fig. 3 ; Hyperoodon, pi. 7, fig. 4) . 



Whatever the true history may prove to have been, when revealed 

 by the discovery of fossils now unknown, it is safe to say that 

 .throughout the course of remodeling the skull seems to have behaved, 



