468 



BARON FRANCIS NOPCSA ON THE 



arboreal types it is of importance that the grasping surface of 

 the whole hand should be as great as possible. This is attained 

 by the retention of all phalanges, and especially by the retention 

 of the fourth (5). In animals in which the function of the 

 manus is different, a reduction of the ulnar phalanges, recalling 

 somewhat the reduction of the fourth and fifth digits of the 

 human hand, can take place. 



The most reduced manus of this sort attained by a terrestrial 

 animal is the manus of Stritthiominmis, and the resemblance to the 

 manus in Archceopteryx is quite easily made out (18). Simthio- 

 miomis, however, did not live on trees (text-fig. 5). This genus is 

 not only suitable for demonstrating that a hand can be developed 

 on terra firtna, but also that a secondary elongation of the fore 

 limb can be attained without adaptation to flight (18). Com- 

 paring the Triassic Procompsognathus, the Jurassic Ornitholesies, 

 and the Cretaceous StTuthioimwius^ none of which were arboreal, 



Text-figure 4. 



Bones of pes in Dinosaurs. 

 (A) Massospondi/lus ; (B) Antrodesmus ; (C) Compsognathus. 



it may be remarked that the anterior limb is short in Pro- 

 compsognafhus, longer in Ornitholestes, and longest in Struthio- 

 mimus. This shows a steady inci-ease in length. Since a similar 

 elongation occurs also in the Sauropoda (for in this group the 

 long-armed Brachiosauridaj certainly descended from the other 

 but short-armed forms) this elongation may well be compared 

 with the elongation that can be seen in the anterior limb of the 

 most primitive bird {Archceopteryx). It is a sort of rejuvenation 

 that suggests also the rejuvenation of the avian hallux already 

 discussed. This observation proves to a certain extent that 

 Hay's objection to my drawing Proavis with relatively short arms 

 does not weigh as much as it seems to do at first. 



After having discovered in the course of our investigation 

 that the similarity of hands and feet in birds and Dinosaurs, and 

 their fundamental difference from these pai-ts in all arboreal 



