482 ARKIV FÖR ZOOLOGI. BAND 1. 



are to be found. The situation of these nasals is usually 

 although not always more or less lateral and in the angle 

 between the rostral and the anterior labial or labials. This 

 situation becomes especially apparent in such cases when the 

 rostrale is more or less enlarged and extending on the upper 

 surface of the snout. The upper surface of the preocular 

 head region is often covered by shields in a double or single 

 series. These have been ternied resp. internas alia, fronto- 

 nasale, pr (Bfr ont alia etc. In Crocodilia there is a median series 

 of enlarged unpaired shields and in lizards very often at 

 least some of the elements are unpaired, especially when the 

 snout is pointed and somewhat elongate. No complete evi- 

 dence can be got from this as to the structure of this re- 

 gion in the ancestral reptiles, but there is at least a possi- 

 bility that they have had a nasal shield on either side and 

 a median series of shields on top of the snout behind the 

 rostral. In lizards and snakes there are also below the infra- 

 labials on either side a series of more or less differentiated 

 and enlarged shields which by different authors have been 

 termed »submaxillaria» or »chinshields», but which I prefer 

 naming submandibulars to avoid confusion. These are not 

 always so strongly developed but the fact that they for in- 

 stance are to be found even in Greckoes with mostly granu- 

 lated integument speaks for that they are of phylogenetic 

 value and they may have occurred in the ancestral reptiles 

 as well. 1 



The question is now to try to decide whether any pieces 

 of the compound or »simple» bill of birds can be homologised 

 with the reptilian structures mentioned above and which may 

 be again repeated for the sake of clearness: on the upper 

 jaw 1) rostrale, 2) labialia, 3) nasalia, and 4) internas alia(e)] 

 on the lower jaw 1) mentale (or symphysiale), 2) infralabialia, 

 and 3) submandibularia. When endeavouring to make such 

 a trial it seems opportune to begin with the lowest and 

 least specialised birds, but I wish to confine myself to re- 

 ferring to some examples of the different groups and hope to 

 treat the matter more fully at another opportunity and then 



1 In the crocodiles these submandibulars are less differentiated, but 

 there may anyway be discerned a series of shields along the upper margin 

 of the lower jaw thus representing the infralabials, as stated above, and below 

 these another series which may be regarded as submandibulars. 



