780 THE AMERICAN NATURALIST. (VoL. XXXIV. 
those of birds in their general structure, and, therefore, that 
these extinct reptiles were more closely allied to birds than 
any which now lived.” He did not commit himself to the 
theory of direct ancestry, however, as shown in the follow- 
ing passage: “It may be regarded as certain that we have no 
knowledge of the animals which linked reptiles and birds 
genetically, and that the Dinosauria, with Compsognathus, 
Archzopteryx, and the struthious birds only help us to form a 
reasonable conception of what these intermediate forms may 
have been." In one important anatomical point Huxley was 
in error, since he believed that the pubis of dinosaurs, like that 
of birds, was directed backwards; whereas we now know that 
in all dinosaurs the pubis is directed forwards, like that of 
other reptiles. Huxley’s ideas culminated in his proposal of the 
group Ornithoscelida, or * bird-limbed " reptiles, to embrace two 
suborders, Dinosauria and Compsognatha. The latest expres- 
sion of Huxley's opinion is found in his paper on the “ Respira- 
tory Organs of Apteryx” ('82, p. 569): ** Thus, notwithstanding 
all the points of difference, there is a fundamental resemblance 
between the respiratory organs of birds and those of crocodiles 
pointing to some common form (doubtless exemplified by some of 
the extinct Dinosauria), of which both are modifications.” (The 
italics are our own.) Huxley’s final view, therefore, was that 
birds sprang from some primitive and unknown type of 
dinosaur. 
The conception of direct descent of birds from dinosaurs 
gained ground until it reached the force of positive theory in 
the writings of Hoernes, and especially of Marsh, as seen in 
the following paragraph (77, p. 228): “It is now generally ad- 
mitted by biologists who have made a study of the vertebrates 
that birds have come down to us through the dinosaurs, and 
the close affinity of the latter with recent struthious birds 
will hardly be questioned." Subsequently, however, Marsh 
(80, p. 188) pointed out that the absence of feathers in dino- 
saurs and pterosaurs and the presence of a free quadrate 
in birds rendered it probable that birds descended not from 
dinosaurs but from a more ancient sauropsid form. 
