E. LÖNNBERG, ON THE RHAMPHOTHECA OF BIRDS. 481 



nules, the development of scales such as they occur in the 

 Squaniata being a secondary specialisation of comparatively 

 late origin. The first thing to consider is now whether it 

 is possible or not to find in the now living Diapsida any 

 features in the arrangement of the structnral nnits of the 

 horny covering of the preocular head-region that are common 

 to all members of the group. If snch is the case we might 

 venture to regard this as an inheritance from the ancestors 

 and at the same time also ascribe a similar arrangement to 

 the reptilian ancestors of the birds. 



In all now living terrestrial reptiles there is to be found 

 at the end of the snont a more or less strongly developed 

 nnpaired shield, rostrale, and along either margin of the 

 upper jaw a series of supralabials or shortly labials. In 

 the same way the terminal or distal end of the lower jaw is 

 provided with an nnpaired shield, the symphyseal or mentale, 

 and the margins of the jaw are covered in the same way as 

 those of the npper one by a series of infralabials. Even in 

 primitive Sphenodon this structnral arrangement is very well 

 pronounced, and so it is in all Squamata, even in such lizards 

 as the members of GecTconidce, in which no other or very few 

 and small plates are developed on the head which otherwise 

 is covered with granules, and in such as many Fachyglossa, 

 in which the head otherwise is scaly or only covered with a 

 great number of small irregular plates, and in Varanidce 

 with a headcovering of small polygonal scales, and so on. 

 In the Crocodilia the aquatic habits have somewhat influenced 

 the horny structures, but in Crocodilus the above mentioned 

 structures may be discerned on both jaws and tolerably well 

 on the upper jaw of Alli gator, less so or hardly at all on 

 the lower jaw of the latter. From these facts may neverthe- 

 less the conclusion be drawn that the possession of an un- 

 paired rostrale and a series of labials on the upper jaw and 

 of an unpaired mentale and series of infralabials on the lower 

 jaw is a common characteristic to all now living Diapsida 

 and it might well be supposed that the extinct members of 

 this group have been equally provided with the corresponding 

 plates or shields. 



In the now living Squamata there is, as a rule, in con- 

 nection with the nostril a single nasal pierced by the same 

 or two nasals surrounding it, although exceptions from this 



