No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORTAIAN. 51 



young stages are examined is seen to develop from at least two 

 centers, if not more. The apparent absence of these elements in 

 the majority of the carnivorous Marsupials may be due either to 

 their gradual crowding out upon the occipital crest as seen in the 

 Bandicoots or their union with the occipital at a very early period; 

 but it may be said that in opossum embryos of very young stages 

 they are not evident. 



According to the researches of Parker no elements corresponding 

 to interparietals are ever found in the Edentates except Orycteropus. 

 I have not found any traces of them in very young embryos of 

 Dasypus, and it is doubtful whether they exist in any of the 

 American Edentates. 



Among the Cheiroptera interparietals can always be distinguished 

 in the young stages, and they arise from at least one and probably 

 two pairs of ossific centers. This is also true of the Rodentia, 

 although I have seen little or no evidence of a second pair of centers 

 in this group. In the Insectivora one pair of centers for the inter- 

 parietal can always be made out in the youngest embryos, and in 

 Eincidus, as figured by Parker, there are two pairs of centers for 

 these bones. In the human skull Thompson states that there are 

 two pairs of centers which early unite to form the squamous part of 

 the supraoccipital; and by inference this is true of the other Pri- 

 mates, although I have not seen sufficient embryological evidence 

 to establish it beyond doubt. In CJieirogaleus and Microcehus 

 among the Lemuroids there is a large and distinct interparietal in 

 the adult skull, but in the adult stages, at least, it is absent in the 

 skulls of other lemurs. Among the Carnivora an interparietal is 

 present in the dogs, cats, seals, bears, raccoons, and probably in all 

 others of this order in the younger stages of development. An 

 interparietal is also found in Procavia, in the Ungulates, and the Cetacea, 

 and lastly a pair of large interparietals are seen in the Monotremes. 



The homology of one pair of these interparietal elements with the 

 corresponding bones in the reptilian skull is apparentl}^ not difficult 

 to discover, and if we can judge from the position and relations as 

 seen in many reptilian types, they must represent what are called 

 supratemporals by many authors. It does not appear certain from 

 the numerous figures of the skulls of the extinct Reptilia whether 

 or not there are any of them that have, in addition to the supra- 

 temporals, a pair of prosquamosals, but if such is the case then this 

 second pair of interparietals would be homologous with them,. 

 There can be no doubt, however, that the extinct Batrachians always 

 show three pairs of bones in this situation; and if the supposed 

 reptilian ancestors of the mammals have only a single pair of these 

 elements it is not easy to understand how they could have given 

 origin to those mammals with two pairs of these bones. 



