22 SUMMARY OF CURRENT RESEARCHES RELATING TO 



wings occur only in the Pterosauria, the Chiroptera, and in birds, among 

 Vertebrates, and in each case the hand has in different ways been modi- 

 fied in connection with the organ. Nevertheless, the conditions seen 

 in Galeopitliecus, where the hand supports the patagium, shows that 

 the distinction between the latter and a true wing is not absolute, and 

 wings must be supposed to have arisen from patagia. If this be so r 

 all winged vertebrates must have had climbing ancestors. To this 

 statement birds seem to form an exception, but the claws and climbing 

 habit of the hand of the young hoatzin (Opisthocomus), and the claws 

 of Arcliseopteryx, show that birds may be regarded as descendants of 

 climbing animals, who have lost their claws owing to the acquisition of 

 the power of flight. Another important point is that while parachutes 

 may occur as it were sporadically in animals which still display many 

 characters in common with allied forms without parachutes, true flying 

 animals form sharply demarcated independent groups, distinguished by 

 their wealth of species. The last fact is due in part to the fact that, 

 while the deep-seated modifications associated with the development of 

 wings are slow, patagia are such recent modifications that differentia- 

 tion has not bad. time to act, and partly to the fact that the power of 

 true flight gives the possessors such an advantage in the struggle for 

 existence that the formation of new species must be rapid. 



Relation of Dinosaurs to Birds.* — Prof. H. F. Osborn discusses 

 the evidence for a common dinosaur-avian stem in the Permian. We 

 do not summarise the paper, but its ending. If bipedalism subse- 

 quently proves to be a common dinosaur character, it would naturally 

 strengthen the dinosaur-avian stem hypothesis. The presence of a free 

 quadrate in birds may be explainable as a secondary cbaracter, like the 

 secondarily free quadrate of certain Lacertilia and Ophidia, due to 

 degeneration of one of the cranial arches. The passage from a quad- 

 rupedal to a bipedal type would also mark the transition from the Pro- 

 ganosauria to the Dinosauria ; and in this bipedal transition, with its 

 tendency to form the tibio-tarsus, the avian phylum may have been 

 given off from the dinosaurian. Thus, the author submits that the 

 dinosaur-avian stem hypothesis should be very seriously reconsidered 

 in future research among birds and dinosaurs. 



Pneumaticity of Skull in Mammals, j — Dr. Simon Paulli gives 

 details of his results in regard to this point in various orders of Eutheria, 

 and also sums up the general conclusions obtained from his completed 

 research. He finds that tbe degree of pneumaticity depends upon the 

 size of tbe species, and increases with tbe increase in size of the species. 

 Tbe most general significance of the pneumaticity is that it affords a 

 means whereby the characteristic shape of the skull may be attained 

 with the minimum expenditure of osseous tissue ; i.e. it is entirely an 

 adaptive phenomenon. In consequence it is not possible to directly homo- 

 logise the pneumatic cavities of the skull in Mammalia generally, except 

 in regard to their point of origin, that is their position in regard to the 

 wall of the nasal cavity. In other words, there are no pneumatic spaces- 

 of fixed morphological value, and sucb phrases as the " sinus frontalis " 

 or " sinus sphenoidalis " have no significance in comparative anatomy. 



* Amer. Nat., xxxiv. (1900) pp. 777-99 (12 figs.). 



t Morph. Jabrb., xxviii. (1900; pp. 483-564 (3 pis. and 3G figs.). 



