No. 406.] DINOSAUR-AVIAN STEM. 797 
difficulty which suggested itself to Marsh, is explainable as a 
secondary character, like the secondarily free quadrate of cer- 
tain Lacertilia and Ophidia, due to degeneration of one of the 
cranial arches. 
The passage from a quadrupedal to a bipedal type would 
also mark the transition from the Proganosauria to the Dino- 
sauria, and all that our present knowledge and evidence justify 
us in saying is that zz this bipedal transition, with its tendency 
to form the tibiotarsus, the avian phylum may have been given 
off from the dinosaurian. 
This form of the Huxleyan hypothesis seems more probable 
than that the avian phylum should have originated quite inde- 
pendently from a quadrupedal proganosaur, because the numer- 
ous parallels and resemblances in dinosaur and bird structure, 
while quite independently evolved, could thus be traced back 
to a potentially similar inheritance. 
Upon the whole, therefore, the dinosaur-avian stem hypoth- 
esis deserves not to be discarded but to be very seriously 
reconsidered in connection with future research and discoveries 
among birds and dinosaurs. 
BIBLIOGRAPHY. 
83 Baur, G. Der Tarsus der Vögel und Dinosaurier. Morph. Jahrb. 
Bd. viii, pp. 417 f. Leipzig. 
Note on the Pelvis in Birds and Dinosaurs. Amer. Nat. Vol. 
'84 
xviii, pp. 1273 f. Philadelphia. 
85 (1) Zur Végel-Dinosaurier Frage. Zool, Anz. Bad. viii, pp. 441 f. 
Leipzig. 
85 (2) Dinosaurier und Végel. Eine Erwiederung an Herrn Prof. 
W. Dames in Berlin. Morph. Jahrb. Bd. x, p.446. Leipzig. 
BS (3) Bemerkungen über das Becken der Vögel und Dinosaurier. 
Morph. Jahrb. Bd. x, pp. 613 f. Leipzig. . 
87 CLELAND. “Culminating Sauropsida.” Mature. Vol. xxxv, pp. 391 f£. 
'66 Corr. Proc. Acad. Nat. Sci., Philadelphia. p.317. 
'67 —— Proc. Acad. Nat. Sci., Philadelphia. pp. 234, 235- 
'69 —_ Proc. Acad. Nat. Sci., Philadelphia. p. 123. 
