Summary of Skull Characters. It will perhaps have been noted that I have quoted Heilmann rather freely in the above remarks; and it may be thought that I have chosen to do so because his views on the nature of Archæopteryx and Archæornis were possibly biassed in the same direction as mine, viz. that they were reptiles, not birds. Such, however, is not at all the case, for the quotations from his book ‘The Origin of Birds’, of which I have so freely made use, are far from being biassed, inasmuch as in spite of the facts which he has brought to light from actual work on the fossil skull in Berlin, he says, on page 12 that it is “ obviously on the way to become a bird's skull ”. We can therefore take it for granted that the above quotations represent the actual facts as interpreted and set forth by an eminent biologist searching for the truth with an open mind. Such being the case I can only state that my deductions differ from Heilmann's since I can find nothing in the skull which could be definitely labelled avian as opposed to reptilian, and everything reptilian as opposed to avian. I find it difficult, therefore, to understand how, after enumerating the facts he has unearthed, Heilmann could come to the conclusion he has reached. In fact it seems to me that it only requires the discovery of a transverse bone in addition to the pre-frontals to set the reptilian seal upon the skull beyond any question of dispute. Unfortunately, neither the base nor vertex of the skull are as yet available for our inspection, so that if a transverse bone is indeed present no one has ever seen it. Heilmann has, however, reconstructed the vertex in wax and gives us a picture of it in his book. In figure 6 of his book this conception is compared with figures of Euparkeria and a Pigeon. The post-axial border of the frontal is shown to be further back than it is in Ewparkeria and on the contrary further forward than in the Pigeon. It shows in fact that if the conception in wax is true Archseornis had a little more brain-power than Euparkeria; but considering that it had taken to an arboreal life and had got as far as gliding, this is not very improbable nor does it seem to suggest that it was necessarily a bird. Supra-temporal vacuities and distinct post-orbitals and post-frontals arc shown. How then can Heilmann's statements about the actual morphology of the structures in the skull of Archseornis be reconciled with the deduction that “it is obviously on the way to become a bird's skull.”
Before, however, leaving the subject of the skull I should like to call attention to the fact that in Heilmann's drawings of the skull (he. cit. fig. 8), if a perpendicular is dropped from the line of junction between the frontal and parietal, indicated by an actual suture, it falls just within the orbital vacuity, as it does in the case of the Triassic Aëtosaurus and Ewpar-keria. If, on the other hand, we examine Petronievic's drawing of the same (Taf. ii. “Ueber die Berliner Archæornis”, Genf, 1925) it falls a long way behind it, and I venture to say bears no relation to the actual position of the suture just referred to. Heilmann's drawing, on the contrary, provides almost conclusive proof that as compared with a bird the brain of Archseornis was very feebly developed indeed and fell far short of being avian. In his reconstruction of the vertex of the skull I venture however to think that the extension of the frontal backwards has been slightly exaggerated, more so perhaps than his drawing of the lateral view would warrant. But in reality this does very little to detract from the conclusion that the brain of Archseornis might have been that of an “advanced dinosaur”, but fell far short of being avian.