LIASSIC FORMATIONS. 



65 



separated by a suture, at the slight constrictiou suggesting that structure in Ft. crassi- 

 rosiris,^ without leaving some indication of its original existence, especially on the palate. 



In the anterior confluence of right and left premaxillaries, and the backward produc- 

 tion from their upper part of a bony bar uniting with the nasals and dividing the nostrils, 

 we have a character of the Dicynodonts and of some Lacertians {Varanus) as well as of 

 Birds, and the Saurian affinity is shown to be the truer one by the firmness of the naso-pre- 

 maxillary union and the absence of any power of, or provision for, that hinge-like movement 

 of the upper mandible upon the cranium which is peculiar to, though not constant in, the 

 Avian class. ]\Ioreover, the outer surface of the premaxillary shows none of that s[)ongy 

 porosity and rugosity which relates to the sheath or horny covering of the beak character- 

 istic of the Bird. Such structure has not even been detected in the feeble trace of eden- 

 tulous anterior production of the upper jaw in Ilhamphurlii/ncJius, Von Meyer. I cannot, 

 therefore, sec, with Von Meyer, the beak of the Bird in an animal with a fixed and toothed 

 upper jaw;'- for on every hypothesis of its bony structure it finds a closer resemblance 

 among the toothed Reptiles than in the class of Birds. 



The mandible, or lower jaw, is supported, as in all Vertebrates below Mammals, by the 

 tympanic, viz. the bone (28, Pis. XVIII and XX) which is shown by its osseous connec- 

 tions, its relations to the ' facial nerve,' ^ or its equivalent the * ramus opercularis,' * and 

 by its mode of formation, to answer to that which in Mammals is mainly reduced to the 

 function of supporting the ear-drum. In air-breathing Ovipara it superadds this function 

 to its more constant and essential use in non-mammalian Vertebrates, of supporting the 

 lower jaw. 



In reference to the question of affinity before us, the tympanic gives valuable evidence by 

 reason of the moveable articulation and peculiar connections with the upper mandible 

 essentially correlated to a covering of feathers. In Pterosauria the tympanic at its 

 proximal end resembles that of Lizards by its fixed sutural mode of union with the 

 cranium, and it furthermore resembles that in Crocodiles by the abutment of the zygoma 

 against its distal end, to which it is suturally attached. 



In Birds the tympanic enjoys a synovial moveable articulation by a single or double 

 condyle at its proximal or cranial end, and presents a synovial cavity to a condyloid con- 

 vexity of the hind part of the zygoma. By this test, therefore, the Pterosauria 

 are shown to be not only ' Saurian,' but to be nearest akin to the existing orders 

 which possess double-jointed ribs and the correlated cardiac structure. The difference 

 of shape between the tympanic of the Pterodactyle and that of the Bird is too strongly 

 marked not to have attracted attention ; but I do not find in that of the Chameleon tlie 



' Goldfuss, loc. cit. 



' " \Vir sebcn aho bier die Schnautze der Vogel auf ein Tliier mil unbcwcgliclicr und niit Ziilmeii 

 bewaflfneteu Scbnautze angewendet." — Op. cit., p. 15. 



^ ' .Vnatomy of Vertebrates,' vol. ii, 8vo, 18GG, p. 121, vol. ill, p. 155. 

 * lb., vol. i, p. 303. 

 9 



