1903.] Gregory, T/ie Shortening of t/ie Elephant's Skull. 3 "9 



widening separation of the inner and outer surfaces of the 

 bones for the sake of lightness and large area for the head 

 muscles, we may ascribe the following morphological con- 

 ditions, which attain the extreme of specialization in the 

 skull of the Mammoth. In the inferior view of the skull the 

 hard palate, contrary to what obtains in most Ungulates, 

 is tilted somewhat upward; the palatines become reduced 

 antero-posteriorly and shoved backward so as to diverge 

 widely posteriorly; the posterior nares, probably pari passu 

 with the anterior nares, have been pushed very far back'; 

 the enormous vertical pterygoid wing of the alisphenoid 

 wraps itself around and functionally replaces the hinder end 

 of the encroaching molar-tooth pouch ; the foramen ovale of 

 the alisphenoid, which in the most primitive Ungulates is 

 anterior to the foramen lacerum medius, has been shifted 

 obliquely backward and outward, and becomes confluent 

 with it externally (Fig. i) ^ ; the presphenoid, basisphenoid, 

 basioccipital thicken in the median plane and at diminishing 

 rates, the lower tabulae of these bones growing downward to 

 a less and less extent as we pass backward, so that in the 

 adult the inferior surface of the basis cranii points sharply 

 downward, and forms, with the plane of the back of the 

 occiput, an angle greater than 90°; the tympanic bullae, rela- 

 tively large and inflated in the young, flatten down and 

 become closely appressed to the skull, pointing obliquely 

 downward, forward, and inward, with the wider end toward 

 the transversely expanded occipital region (Fig. i, Tv-). In 

 brief, the progressive brachycephaly of the skull has appar- 

 ently involved not so much a fore-and-aft shortening of the 

 individual elements as a readjustment and modification of 

 them, and secondly an expansion in the transverse vertical 

 planes. 



The shortening and deepening of the temporal fossae, and 

 perhaps to some extent the above-mentioned expansion of 



' Among the Glyptodonts a similar backward and downward growth of the palate 

 and posterior nares seems to be correlated chiefly with the shortening of the skull, as 

 the anterior nares remain terminal. 



- This change must have taken place at a very early date in the history of the Pro- 

 boscidea, as it is already established in the primitive Mastodon (Trilophodon) productus 

 and also, if Kaup's figures are here rightly interpreted, in Dinotherium. 



