8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.63, 



swollen or conspicuously convex internally, and the rostrum is not 

 constricted behind the tooth rows. 



As seen from ventral view, the nasal passages of the Platanista 

 skull are far jDosterior to that which is normal for practically all 

 living porpoises, for their posterior margins lie in the same level 

 as the anterior margins of the squamosals. In skulls of Lipotes 

 and Inia, and in practically all of the Delphinidae, the nasal pas- • 

 sages are situated considerably in advance of the anterior ends of 

 the squamosals. The ventral opening for the infraorbital canal in 

 the skull of Platanista is considerably behind the supraorbital 

 process and entirely within the temporal fossa. In most dolphins, 

 including Lipotes and Inia^ the opening for this canal is situated in 

 advance of or but slightly posterior to the anterior margin of the 

 supraorbital process of the frontal and never within the temporal 

 fossa. The optic canal is floored by the frontal bone in Platanista 

 while in Lipotes the ventral wall of the canal is missing. 



The external and internal pterygoids project forward in front of 

 the nasal passages in the Platanista skull. In skulls of Lipotes and 

 Inia^ the forward projecting external pterygoid is absent and a large 

 expanded alisphenoid fills the space between the squamosal, parietal, 

 frontal, and internal pterygoid. Skulls of Lipotes and Inia thus 

 lack one of the characteristic bones of the Platanista skull. It is not 

 surprising that the external pterygoid should disappear, for it arises 

 from the processus alaris of the basisphenoid and in some cetaceans, 

 including Platanista., prevents the ascending process (alisphenoid) 

 of that bone from appearing in the temporal fossa. The development 

 and pressure of air sacs in this region according to Winge may ac- 

 count for the final disappearance of the external pterygoid. The rela- 

 tions of the internal pterygoid, vomer, and maxilla to one another 

 are described in another part of this paper (pp. 15-16). 



The cavity for the brain in the skull of Platanista is relatively 

 smaller than that of Lipotes. It does not necessarily follow that the 

 brain of Platanista is either a primitive or a secondarily degenerated 

 type. Although more than 40 years have elapsed since the publica- 

 tion of Anderson's notable memoir on Platanista., no additional in- 

 formation regarding the brain of this porpoise has been published. 

 The following quotations* summarize the conclusions reached by 

 Anderson. 



I may sum up this much of the cerebral anatomy by stating that, so far as 

 the convolutions and sulci are concerned, this species of dolphin has a brain of 

 a considerably simpler type than in the porpoise or common dolphin, tending 

 perhaps to some of the Carnivora, though in such a slight degree as still to 

 Impress it with all the attributes of the complex convoluted cerebrum of the 



* Anderson, J., Anatomical and Zoological Researches: Comprising an account of the 

 Zoological Results of the Two Expeditions to Western Yunnan in 1868 and 1875. Lon- 

 don (1878), pp. 465, 466-467, 1879. 



