NO. 5 TELESCOPING OF THE CETACEAN SKULL 3I 



upper margin lay at a level slightly if at all superior to that of the 

 upper margin of the occipital condyle, much as in Plataiiista (pi. 6, 

 fig. 2). Such a depression of the rostrum at a period when the 

 backward advance of the maxillary was beginning might conceivably 

 place the telescoping elements in such a position as to initiate an 

 upward slope from the anterior orbital rim, the eye acting as a pivot. 

 Depression of the rostrum after an extensive backward movement of 

 the maxillary had taken place would be expected to result in the ter- 

 raced condition of the maxillary seen in Xenorophus (pi. 5, fig. 6) and 

 less conspicuously in Stcnodclphis. 



One form of this kind of telescoping occurs in Platanista (pi. 6, 

 fig. 2). The maxillary rises from the front of the orbit at an angle 

 of about 50 degrees ; the occipital extends far forward in the median 

 region, but at the side it is held back by the rather large parietal. 

 Associated with these peculiarities there occurs a remarkable com- 

 bination of special characters. The edge of the maxillary above the 

 orbital region is developed into a high thin plate apparently homo- 

 logous with the maxillary ridge present in Physetcr, Kogia, Hy- 

 pcroodon and elsewhere (compare especially pi. 6, fig. 2, with pi. 7, 

 fig. 4), but so unusually large and of such peculiar form that, with its 

 fellow of the opposite side, it completely arches over the front of the 

 face and incloses the space occupied by the oily facial cushion ^ ; the 

 squamosal portion of the zygoma is extremely large and the jugal is 

 correspondingly short ; the pterygoid is spread laterally so as to cover 

 the alisphenoid, and its outer plate is so developed as to be an almost 

 exact duplication of the inner plate, the two plates everywhere closely 

 approximated, the space between them occupied by a loose network 

 of bony filaments ; palatines widely separated from each other by the 

 vomer, each entirely covered by the two plates of the pterygoid except 

 where it appears on the surface in the anterior wall of the essentially 

 vertical narial passage ; infraorbital foramen situated at a level con- 

 spicuously behind the much reduced orbit. The teeth, though unusual 

 in form, are normal in structure ; the relationship of the ribs to the 

 vertebras is the same as in the Delphinidce, that is, all tJie ribs are sup- 

 ported by serially homologous transverse processes. 



Another form occurs in the sperm whale (pi. 6, fig. i). Here the 

 frontal and maxillary are essentially like those of Platanista, but the 

 occipital and the squamous portion of the squamosal have advanced 

 laterally to a level not far behind the orbit, thus reducing the parietal 



^ Hinton and Pycraft (.\nn. and 'Slag. Xat. Hist., ser. 9, Vol. 10, p. 234, 

 August, 1922), have suggested that these plates originated as 1)ony stoppers 

 to the blow hole. 



