THE SKULL 



side. Lillie (1910) inferred that the laryngeal asymmetry in the Physe- 

 teridae caused the asymmetry of their skulls, but failed to indicate how. 

 I attempted to discover whether there was not a twisting action of the 

 facial muscles in closing the blowhole so that those of the right side de- 

 veloped more strongly than those upon the left, but the results were 

 entirely negative. Nor has Ernst Huber found any differences in the 

 facial muscles of the two sides that might contribute to the condition. 

 In short we know absolutely nothing regarding the cause of this unique 

 cranial asymmetry and no logical theory for it has yet been advanced. 



In regard to the Physeteridae or sperm whales, Kellogg (1928) says 

 it is confidently believed that "generalized sperm whales had been dif- 

 ferentiated from the main odontocete stock subsequent to the elimination 

 of the postorbital constriction, but at a time long before the beginning 

 of the Miocene". In the cachalot (Physeter) the telescoping has also 

 been mainly from before backward, as in other odontocetes, but there 

 has been a basining of the whole facial region, this extending, for the 

 accommodation of the huge spermaceti organ, well back of the bony 

 nares to the cranial crest, which is vertical to the condyles. The maxil- 

 laries reach this at some points, over-riding the frontals, but while the 

 left nasal passage is huge, the right is but a fraction of its size. In conse- 

 quence, extraordinary osteological peculiarities have resulted. While the 

 right premaxilla almost reaches the cranial crest, the left is much shorter, 

 stopping at the blowhole (fig. 18) . Upon the left, the flattened, ex- 

 panded nasal takes the place, posterior to the nares, of the position oc- 

 cupied upon the right by the backward extension of the premaxillary, 

 and the right nasal bone has been eliminated. 



In the case of the odontocete mandible the condyle is reduced and the 

 articulation peculiar in the spreading of the ligaments, but this is more 

 marked in mysticetes. There is a broad, flaring aperture to the dental 

 canal, opening to the rear and partly filled with fatty tissue. The an- 

 terior mandible is usually relatively weak in accordance with reduction 

 in tooth size, but in ziphioids having well developed tusks it may be 

 larger and of peculiar form. There is a true symphysis mend, which in 

 most forms is small in area and lacks strength, but especially in some 

 of the long-beaked, extinct forms, was large. Thus in Argyrocetes, 

 Kellogg (1928) said that the mandible had a length of about 35 inches, 

 three-fifths of which was symphysis. Why the mandible of such forms 

 as Eurhtnodelphis stopped far short of the rostral tip is unknown. In 

 some ziphioids and mysticetes the mandibular tip projects beyond the 

 rostrum. 



[117] 



