4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



Mandible 



(Plates 4, 5, g and lo) 



Lipotes Ittia 



Anterior edge of dental foramen Anterior edge of dental foramen 



about 45 mm. behind last tooth. about 20 mm. behind last tooth. 



Distance from symphysis to last Distance from symphysis to last 



tooth much greater than distance tooth equal to distance between last 



between last tooth of opposite rows. tooth of opposite rows. 



Height through coronoid equal to Height through coronoid equal to 



about one-third length of free por- about half length of free portion of 



tion of mandible. mandible. 



Coronoid abruptly rounded. Coronoid broadly rounded. 



Angular process with broadly Angular process with sharp, narrow 



rounded projection. projection. 



A conspicuous median groove be- No median longitudinal groove be- 

 tween toothrows. tween toothrows. 



The pterygoids have probably been injured in the narial region. 

 It is therefore impossible to be certain whether their entire structure 

 is exactly the same as in Inia. At base it is undoubtedly similar to 

 that in the South American animal. The backward-turned portion 

 which fits against the vomer in Inia is not present, though traces of 

 the ridge against which it probably was applied can be distinctly seen. 

 The structure actually present in the Chinese animal could be made 

 from that of Inia by breaking away the bones to the level of the edge 

 of the internarial septum. This is clearly seen on comparing plate 6 

 with Abel's figure of a skull of Inia in which such mutilation has 

 actually taken place (Mem. Mus. roy. Hist. Nat. Belg., Vol. i, pi. 3, 

 fig. 3, 1901). The outer plate associated with the pterygoid in the 

 narial region appears to be nearly perfect. It is like that of Inia 

 except that it is shorter and without fenestration. Posteriorly the 

 pterygoids are much narrowed by the development of a broad notch 

 in the margin of the basal wing. The presence of this notch together 

 with a widening of the expanded posterior portion of the vomer 

 nearly or quite excludes the pterygoids from contact with the basi- 

 sphenoids. 



A very noticeable feature of the skull is the position of the nares. 

 (Compare pis. 2 and 3.) The anterior margin of the aperture is at 

 about the middle of the cranium in Lipotes, decidedly in front of the 

 middle in Inia. Yet when the anterior margin of the nares is com- 

 pared with the temporal fossa these conditions appear to be reversed. 

 Probably the backward bulge to the occipital region in Inia accounts 

 for the first peculiarity, and a difference in the form of the frontal 

 explains the second. 



