488 ARKIV FÖR ZOOLOGI. BAND 1. 



reaping their food, together with the compensating basal 

 growth of the infralabials. By means of the latter the 

 mentale is gradually pushed or nioved forward, wedged in 

 between the infralabials as it is, and then gradually worn 

 away so that finally, as reported above, the median suture of 

 the infralabials extend to the extreme tip of the lower rham- 

 photheca. The submandibulars reach far back and are espe- 

 cially posteriorly well developed. 



The differences in the development of the bilis of these 

 representatives of Tinamidce are in accordance with the diffe- 

 rent diet of the species. It seems also probable that the 

 y oungs of Rhynchotus rufescens shall exhibit a structure of 

 the bill, before it is worn, which is similar to that of the 

 other species which merely use the bill for picking insects, 

 seeds etc. and thus do not exhibit their bilis to such wearing 

 work as Rhynchotus rufescens. 



The portion termed internasal appears in the Tinamous 

 to have a consistency intermediate between a cere and a nor- 

 mal horny shield. It is also in a state of reduction and, as 

 will be shown below, a reduced horny plate is often substi- 

 tuted by a cere of more or less typical appearance. 



The rhamphotheca of the Sphenisciformes is termed »pri- 

 mitive» by GrADOW 1 and it certainly is, so far that a good 

 deal of the reptilian inheritance may be traced although the 

 bill otherwise has become a good deal specialised. For the 

 genera Aptenodytes, Pygoscelis, Catarrhactes and Megadyptes 

 it is indicated that the »culminicorn» by a more or less deep 

 groove is divided from the »latericorn». I have stated this 

 on Aptenodytes pennanti and regard the former as a rostrale, 

 the latter as labiale. The lower jaw of the same bird has 

 a terminal unpaired piece, covering the whole symphyseal 

 tract, and a lateral shield on either side. In Eudyptula 

 minor I have found that a strong rostrale forms a hook at 

 the end of the upper jaw and extends backwards in the me- 

 dian line to the feathered tract. On either side, sharply de- 

 fined from this unpaired median piece by a deep suture-like 

 groove, the jaw is covered by a labial shield. The nostril is 

 situated in the groove formed by the suture mentioned, and 

 above the same is seen a narrow, but well defined, piece 

 which is quite distinct as well from the median as from the 



1 1. c p. 126. 



