90 THE ZOOLOGIST. 



the most conspicuous differences existing in the skull, which is 

 asymmetrical in the toothed forms. Moreover, considerable diffe- 

 rences exist between the various Odontoceti themselves — for in- 

 stance, between the skull oi Hyper oodon, with its great maxillary 

 crests, and the flattened skulls of Monodon and Delphinaipterus. 

 In the Ziphoid Whales and Platanista (Susu) there are great 

 maxillary crests. The skull in the Toothed Whales is often 

 broad and depressed, but the snout may be much elongated, as 

 in the Dolphins, the Ziphoids, and the Susu. The nasal bones 

 occur as ** nodules or flattened plates applied closely to the 

 frontals " (Flower), and not taking any share in the roof of the 

 nostril.* The lachrymal is either fused with the jugal, " or, 

 when distinct, very large, and covering the greater part of the 

 orbital plate of the frontal " (Flower). The tympanic bone is 

 not fused with the periotic, which is only held in position by 

 ligament. The parietals do not meet above, but the space 

 is occupied by the large supra-occipital. The pterygoids are 

 short, thin, involuted, and form with the palatine process the 

 outer wall of the posterior palatine air-sinus. In Physeteroids 

 these bones are only hollowed on the outer side. In Ziphius 

 the premaxillaries are expanded at the sides of the nares, 

 hollowed, and with elevated margins, while the right is more 

 developed than the left. These bones in the Toothed Whales 

 generally bear no teeth, and are characterized by their great 

 length ; moreover, they are ensheathed laterally by the maxillse. 

 In the Ziphoids also there are distinct malar bones, and the 

 pterygoids are large and meet in the middle line. The meso- 

 ethmoid is densely ossified, and in Mesoplodon it coalesces with the 

 others. t The premaxillaries are convex in front of the nares in 

 the White Whale (Delphinapterus) . The halves of the mandible 

 are almost straight, deep posteriorly, and they form a true 

 symphysis anteriorly. The symphysis is generally short, except 



* Short nasals occur in the Saiga, and the spiracular sinuses of this form 

 and the Tapir are, according to Dr. Murie, homologous with those of the 

 Cetaceans (Trans. Zool, Soc. vol. viii. p. 242, &c., text-fig.). 



f Principal Sir William Turner's able account of the skeleton of this 

 form may specially be referred to. He observes that " the meso-ethmoid 

 septum was prolonged into the upper end of the medio-rostral gutter for 

 8 cm., and was embraced anteriorly by the medio- (meso-) rostral bone " 

 (Proc. Roy. Soc. Edin.vol. xxix. p. 687, with text-figs., 1909), 



