NO. 5 TELESCOPING OF THE CETACEAN SKULL 53 



ribs to form a distinct family. In general they appear to be more 

 specialized than the dolphins ; but the area formed by the palatine 

 in the anterior wall of the narial passage as compared with that 

 formed by the maxillary is narrower than in the dolphins, an ap- 

 parently primitive feature which might indicate that the group origi- 

 nated from dolphin-like animals which were considerably less modi- 

 fied than any now living. 



Platanistidcc. — The genus Plafaiiista alone represents the family 

 Platanistidcc. The type of telescoping shown by its skull is strikingly 

 different from that seen in the recent genera Inia, Lipotes and 

 Stcnodelphis, and the fossil Pontoplanodes (as shown by Abel's 

 photographs, Sitzungsber. k. Akad. Wissensch. Wien., Math. -Nat. 

 Kl., Vol. ii8, pt. I, pi. facing p. 272, 1909), all of which, at one 

 time or another, have been associated with it. In this character as 

 well as in the anterior position of the orbit relatively to the narial 

 passages it agrees wuth Physeter so far as general structure of 

 the cranium is concerned ; merely the lateral portion of the occipital 

 has not advanced so far forward at the expense of the parietal as 

 in the sperm whales. The resemblance of the frontal to that of a young 

 Physeter is particularly noticeable (pi. 6, figs, i, 2). In all other 

 features the skull differs so widely from that of the sperm whale and 

 its allies that the similarities in the type of telescoping cannot be 

 regarded as indications of near relationship. On the contrary, among 

 living odontocetes the total specialization of the skull is least of all in 

 the physeteroids and greatest of all in Platanista, thus indicating the 

 widest possible degree of separation between the two groups. Some 

 of the more important of the special characters of the skull which 

 show extreme departure from ordinary mammalian structures are : 

 the great size of the pterygoid which spreads laterally to cover the 

 alisphenoid and interlock with the squamosal and frontal, and whicb 

 extends so far forward that about half of its area lies in front of the 

 infraorbital foramen, into the formation of whose posterior and 

 superior margins it largely enters ; the development of the outer 

 reduplication of the pterygoid as a heavy plate exceeding the original 

 portion of the bone in both size and in density of structure (this 

 plate is not homologous with the ectopterygoid of other mammals, 

 an outgrowth from the alisphenoid which does not occur in modern 

 cetaceans) ; the greatly reduced condition of the palatine, widely 

 separated from its fellow of the opposite side and completely covered 

 by the pterygoid except where it appears at the surface in the anterior 

 wall of the narial tube ; the backward forcing of the base of the 



