LIASSIG FORMATIONS. 
65 
separated by a suture, at the slight constriction suggesting that structure in Pt. crassi- 
rostris^ 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. Moreover, the outer surface of the premaxillary shows none of that spongy 
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 Bhamphorhynchus, Von Meyer. I cannot, 
therefore, see, 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 the 
‘ Goldfuss, loc. cit. 
2 “ Wir seben also hier die Schnautze der Vogel auf ein Tbier mil unbeweglicber und mit Ziilineii 
bewaflfneteu Scbnautze angewendet.” — Op. cit., p. 15. 
3 ‘ Anatomy of Vertebrates,’ vol. ii, 8vo, 1866, p. 124, vol. iii, p. 155. 
^ lb., vol. i, p. 303. 
y 
