PROF. OWEN ON THE SKTJLL OP MEGALOSAURTJS. 341 



slender continuation of the jaw, answering to part of that in the 

 subject of the present paper (Plate XI. fig. 1, 21'), which is so pro- 

 longed, appears at c in plate xii. torn. cit. 



Concomitantly with the superior development of the circulating 

 and respiratory organs and their vigorous action in the Avian 

 class, the obliteration of the boundaries of bones takes x>lace earlier, 

 and, among Vertebrates, is most complete in birds. But one result 

 of my researches in the osteogeny of the class was, that in no 

 species was the premaxillary produced backward to beneath the 

 orbit, but that such portion of the upper jaw is contributed by the 

 maxillary bone *. In Dinornis inrjens the maxillo-premaxillary 

 suture is retained f • so likewise in Aptornis : in these great wing- 

 less birds, with somewhat lower locomotive, circulating, and respi- 

 ratory activities, the ossific process is retarded. 



So the experienced ornithotomist Dr. Schufeldt writes : — " The 

 malar is the mid style of the infraorbital bar, the maxillary com- 

 pleting the connexion anteriorly with the intermaxillary." " It 

 simply requires ordinary maceration in the adult of any of the Grouse 

 or Quails to have the three styles separate from each other " %. 



Pterodactyles show a larger proportional size of the premaxillary 

 than do either Iguanodon or Megalosaurus ; but neither in Dimor- 

 phoclon nor any other of its order, in which the maxillo-premaxillary 

 suture can be unequivocally traced, does the premaxillary extend 

 backwards beneath the orbit. 



In this respect birds agree with Pterodactyles ; but as regards 

 the affinity which is held to amalgamate the two groups, the 

 question has always presented itself to my mind in the following 

 condition : — It is true that Pterodactyles new, and birds fly ; but 

 their organs of flight are not only different, but the differences throw 

 light on those of other organs of much greater, indeed of real, im- 

 portance in forming a judgment as to their ciass-affinities. 



In birds the main mechanical part of the wing is due to cuticular 

 developments, in reptiles to cutaneous ones ; in the one 'Appendages 

 of the Integument,' in the other 'Extensions of the Integument' 

 itself, are pressed into the formation of the organs of flight. In 

 birds the ' remiges,' or feathers of flight, are supported and wielded 

 by short and thick bones ; in Pterodactyles the dermal webs are 

 sustained by long and slender bones. 



The main condition of these modifications of wings is the tempera- 

 ture of the body which the two kinds of flyers are, or were, capable 

 of maintaining : in one kind it is fixed ; in the other it varied to a 

 certain extent with that of the atmosphere. In no class of Verte- 



* See ' Archetype and Homologies of the Vertebrate Skeleton,' 8to, 1848, 

 p. 128, fig. 23, 21, 22; 'Anatomy of Vertebrates,' vol. ii. p. 51, figs. 26, 28 

 (young Ostrich), fig. 31 (young Emu), fig. 30 (Parrot). 



t ' Extinct Wingless Birds of New Zealand,' 4to, 1878, vol. ii. pi. lxxxii. 

 fig. 1, 21, 22. 



I See his plate v. fig. 51, showing the remoteness of the premaxillary from 

 the suborbital region, in his 'Contributions to the Anatomy of Birds,' 8vo, 

 1882. 



Q.J.G.S. No. 155. 2 c 



