466 



BARON FRANCES NOPOSA ON THE 



As a second feature pointing in the same direction, the 

 great variety of the flexor muscles of the hallux can be 

 brought forward. If the functioning type of hallux were the 

 primitive t3'pe in birds, then the arrangement of the flexor 

 muscles could be everywhere alike, whereas, if the hallux was 

 rejuvenated and secondarily but independently strengthened in 

 diiferent groups of birds, the flexor muscles might vary. As is 

 known, the latter is actually the case, and the variation has been 

 used in the classification of birds (7). These detailed observa- 

 tions show that the functioning hallux in birds is perhaps a 

 secondary adaptation. A feature worth mentioning is that in 

 the apparently tridactyle foot of those bipedal animals that passed 

 through a stage of arboreal specialisation (Kangaroo) the fourth 

 toe is the longest (5), while it is the third that is the longest in 

 Dinosaurs, birds, and Alactaga (14). 



Text-figure 2. 



B A 



Footprints of digitigrade Triassic reptiles. 

 {A) AnomoBftis; (B) Apatichnus ; (C) AncJiisawripus; (D) Gh'allator. 



Turning now from the pes to the manus in primitive birds 

 (Archceopier7/x), it may be remarked that this is a long and 

 slender organ, adapted to some extent for grasping, but this alone 

 is again no sign of arboreal specialisation. 



The partial use of the anterior limb as a grasping organ 

 occurs in different teri'estrial quadrupeds. The fore leg is used 

 as a manus in the Kangaroo when taking up food ; it is similarly 

 used in mice and rabbits and, partly for the same purpose and 

 partly also as a weapon, in cats and bears. Members of each 

 of these groups are, it is true, partly also arboreal ; but neverthe- 

 less the terresti'ial representatives in these groups do not descend 

 from the arboi'eal forms, for, on the contrary, it was the use 

 of the anterior limb as a grasping organ that enabled some of the 

 terrestrial forms to climb trees. 



Steiner has proved in a recent highly valuable contribution (17) 



